JP7510624B1 - Optical member, surface light source device, and display device - Google Patents

Abstract

[Problem] To efficiently expand the viewing angle in a display device using a surface light source device. [Solution] An optical member includes a light guide plate including a light output surface and a back surface facing the light output surface, and an optical sheet including a prism surface facing the light output surface. The back surface includes a plurality of inclined surfaces arranged alternately in a first direction D1 and a plurality of connecting surfaces not parallel to the inclined surfaces. The inclined surfaces are inclined with respect to the first direction so as to approach the light output surface on a first side in the first direction. The optical sheet includes a plurality of unit prisms arranged in the first direction. Each unit prism includes a first prism surface located on a first side in the first direction, and a second prism surface facing the first prism surface from the first direction. The prism surface includes a first prism surface and a second prism surface. The first prism surface includes a first element surface, a second element surface, and a third element surface. The second element surface is located between the first element surface and the third element surface. The inclination angle difference between the first element surface and the third element surface is 5° or more. [Selected figure] Figure 3

Description

This disclosure relates to optical members, surface light source devices, and display devices.

As disclosed in Patent Document 1, a surface light source device including a light-emitting surface is known. The conventional surface light source device disclosed in Patent Document 1 is an edge-light type and includes a reflection sheet, a light guide plate, and an optical sheet. In the surface light source device of Patent Document 1, the light guide plate includes a light output surface and a back surface facing the light output surface. The conventional back surface includes an inclined surface inclined with respect to the light output surface. The angle of incidence of light traveling through the light guide plate on the light output surface becomes smaller by twice the angle of the inclined surface each time the light is reflected on the inclined surface. By repeating reflection on the inclined surface, the angle of incidence of the light on the light output surface becomes less than the total reflection critical angle, and the light can be output from the light guide plate. In this surface light source device, the direction of light output from the light output surface of the light guide plate is biased within a very narrow angle range that is greatly inclined with respect to the stacking direction of the light guide plate and the optical sheet.

In the surface light source device of Patent Document 1, the optical sheet includes a prism surface facing the light output surface of the light guide plate. The prism surface includes a first prism surface and a second prism surface in an alternating manner. The second prism surface is the light input surface for light from the light guide plate. The first prism surface reflects the light that has passed through the second prism surface. Reflection by the second prism reduces the angle between the stacking direction of the light guide plate and the optical sheet and the traveling direction of the light. In a surface light source device using such a light guide plate and optical sheet, it is possible to increase the brightness in a specific direction, such as the front direction.

Light traveling in a direction greatly inclined with respect to the stacking direction may be incident on the tip side of the first prism surface, which is close to the light guide plate. Light traveling in a direction that forms a relatively small angle with respect to the stacking direction is incident on the base side of the first prism surface, which is away from the light guide plate. In the surface light source device disclosed in Patent Document 1, the first prism surface is a bent surface. At the tip side, close to the light guide plate, the angle of the first prism surface with respect to the stacking direction is relatively large. At the base side, away from the light guide plate, the angle of the first prism surface with respect to the stacking direction is relatively small. By making the first prism surface a bent surface, it is possible to further increase the brightness in a specific direction, such as the forward direction.

JP 2016-95347 A

As described above, in conventional surface light source devices, optical components including a light guide plate and an optical sheet exhibit excellent light-collecting capabilities. This allows for high brightness in a specific direction, such as the front direction. On the other hand, the amount of light in directions other than the specific direction is low, resulting in a narrow viewing angle. The present disclosure aims to efficiently expand the viewing angle in a display device that uses a surface light source device.

The optical member of the first surface light source device according to the embodiment of the present disclosure includes:
a light guide plate including a light output surface and a back surface facing the light output surface;
an optical sheet including a prism surface facing the light output surface,
the rear surface includes a plurality of inclined surfaces alternately arranged in a first direction and a plurality of connecting surfaces non-parallel to the inclined surfaces;
the inclined surface is inclined with respect to the first direction so as to approach the light output surface on a first side in the first direction,
the optical sheet includes a plurality of unit prisms arranged in the first direction,
Each unit prism includes a first prism surface located on a first side in the first direction and a second prism surface facing the first prism surface in the first direction,
the prism surface includes the first prism surface and the second prism surface,
the first prism surface includes a first element surface, a second element surface, and a third element surface;
the second element surface is located between the first element surface and the third element surface;
The difference in inclination angle between the first element surface and the third element surface is 5° or more.

The optical member of the second surface light source device according to the embodiment of the present disclosure includes:
a light guide plate including a light output surface and a back surface facing the light output surface;
an optical sheet including a prism surface facing the light output surface,
the rear surface includes a plurality of inclined surfaces alternately arranged in a first direction and a plurality of connecting surfaces non-parallel to the inclined surfaces;
the inclined surface is inclined with respect to the first direction so as to approach the light output surface on a first side in the first direction,
the optical sheet includes a plurality of unit prisms arranged in the first direction,
Each unit prism includes a first prism surface located on a first side in the first direction and a second prism surface facing the first prism surface in the first direction,
the prism surface includes the first prism surface and the second prism surface,
the first prism surface includes a first element surface, a second element surface, and a third element surface;
the second element surface is located between the first element surface and the third element surface;
The difference in inclination angle between the first element surface and the third element surface is greater than twice the inclined surface angle with respect to the first direction.

A surface light source device according to an embodiment of the present disclosure includes:
a light guide plate including a light output surface, a back surface facing the light output surface, and a light input surface located between the light output surface and the back surface;
an optical sheet including a prism surface facing the light output surface;
A reflective sheet facing the back surface;
A light source that emits light incident on the light guide plate,
the rear surface includes a plurality of inclined surfaces alternately arranged in a first direction and a plurality of connecting surfaces non-parallel to the inclined surfaces;
the inclined surface is inclined with respect to the first direction so as to approach the light output surface on a first side in the first direction,
the optical sheet includes a plurality of unit prisms arranged in the first direction,
Each unit prism includes a first prism surface located on a first side in the first direction and a second prism surface facing the first prism surface in the first direction,
the prism surface includes the first prism surface and the second prism surface,
the first prism surface includes a first element surface, a second element surface, and a third element surface;
the second element surface is located between the first element surface and the third element surface;
The difference (°) in the inclination angles of the first and third element surfaces is equal to or greater than the half-width at half maximum (°) in the angular distribution of luminance on the light output surface.

The optical member of the third surface light source device according to the embodiment of the present disclosure includes:
An optical member used in a surface light source device disposed opposite a display panel,
a light guide plate including a light output surface and a back surface facing the light output surface;
an optical sheet including a prism surface facing the light output surface,
the rear surface includes a plurality of inclined surfaces alternately arranged in a first direction and a plurality of connecting surfaces non-parallel to the inclined surfaces;
the inclined surface is inclined with respect to the first direction so as to approach the light output surface on a first side in the first direction,
an arrangement pitch of the connection surfaces in the first direction being greater than an arrangement pitch of pixels of the display panel in the first direction;

The optical member of the fourth surface light source device according to the embodiment of the present disclosure includes:
a light guide plate including a light output surface and a back surface facing the light output surface;
an optical sheet including a prism surface facing the light output surface,
the rear surface includes a plurality of inclined surfaces alternately arranged in a first direction and a plurality of connecting surfaces non-parallel to the inclined surfaces;
the inclined surface is inclined with respect to the first direction so as to approach the light output surface on a first side in the first direction,
The arrangement pitch of the connection surfaces in the first direction is 0.060 mm or more.

A first surface light source device according to an embodiment of the present disclosure includes:
Any optical member according to an embodiment of the present disclosure;
A light source that emits light that is incident on the light guide plate.

A second surface light source device according to an embodiment of the present disclosure includes:
a light guide plate including a light output surface, a back surface facing the light output surface, and a light input surface located between the light output surface and the back surface;
an optical sheet including a prism surface facing the light output surface;
A reflective sheet facing the back surface;
A light source that emits light incident on the light guide plate,
the rear surface includes a plurality of inclined surfaces alternately arranged in a first direction and a plurality of connecting surfaces non-parallel to the inclined surfaces;
the inclined surface is inclined with respect to the first direction so as to approach the light output surface on a first side in the first direction,
the optical sheet includes a plurality of unit prisms arranged in the first direction,
Each unit prism includes a first prism surface located on a first side in the first direction and a second prism surface facing the first prism surface in the first direction,
the prism surface includes the first prism surface and the second prism surface,
the first prism surface includes a first element surface, a second element surface, and a third element surface;
the second element surface is located between the first element surface and the third element surface;
The difference (°) in the inclination angles of the first and third element surfaces is equal to or greater than the half-width at half maximum (°) in the angular distribution of luminance on the light output surface.

A display device according to an embodiment of the present disclosure includes:
A surface light source device according to any one of the embodiments of the present disclosure;
and a display panel facing the surface light source device.

According to the present disclosure, it is possible to efficiently expand the viewing angle in a display device that uses a surface light source device.

FIG. 1 is a diagram for explaining an embodiment of the present disclosure, and is a vertical cross-sectional view showing a schematic configuration of an example of a display device, a surface light source device, and an optical member. FIG. 2 is a plan view showing an example of a pixel arrangement in the display device shown in FIG. Fig. 3 is a vertical cross-sectional view of the surface light source device and the optical member shown in Fig. 1. It is a diagram for explaining the operation. FIG. 4 is a plan view of the surface light source device and the optical member shown in FIG. FIG. 5 is a perspective view showing an example of a light guide plate that can be included in the surface light source device and the optical member shown in FIG. FIG. 6 is a partially enlarged cross-sectional view showing the light guide plate shown in FIG. FIG. 7 is a perspective view showing an example of an optical sheet that can be included in the surface light source device and the optical member shown in FIG. FIG. 8 is a partially enlarged cross-sectional view showing the optical sheet shown in FIG. FIG. 9 is a vertical cross-sectional view showing an example of a reflecting sheet that can be included in the surface light source device and the optical member shown in FIG. FIG. 10 is a graph showing the luminance angular distribution on the light exit surface of the light guide plate. FIG. 11 is a cross-sectional view corresponding to FIG. 3, showing a modified example of the light guide plate.

One embodiment of the present disclosure relates to the following <1> to <28>.

<1>
a light guide plate including a light output surface and a back surface facing the light output surface;
an optical sheet including a prism surface facing the light output surface,
the rear surface includes a plurality of inclined surfaces alternately arranged in a first direction and a plurality of connecting surfaces non-parallel to the inclined surfaces;
the inclined surface is inclined with respect to the first direction so as to approach the light output surface on a first side in the first direction,
the optical sheet includes a plurality of unit prisms arranged in the first direction,
Each unit prism includes a first prism surface located on a first side in the first direction and a second prism surface facing the first prism surface in the first direction,
the prism surface includes the first prism surface and the second prism surface,
the first prism surface includes a first element surface, a second element surface, and a third element surface;
the second element surface is located between the first element surface and the third element surface;
An optical member for a surface light source device, wherein a difference in inclination angle between the first element surface and the third element surface is 5° or more.

＜2＞
The optical member of the surface light source device according to <1>, wherein a difference in inclination angle between the first element surface and the third element surface is greater than twice the inclination angle of the inclined surface with respect to the first direction.

＜3＞
a light guide plate including a light output surface and a back surface facing the light output surface;
an optical sheet including a prism surface facing the light output surface,
the rear surface includes a plurality of inclined surfaces alternately arranged in a first direction and a plurality of connecting surfaces non-parallel to the inclined surfaces;
the inclined surface is inclined with respect to the first direction so as to approach the light output surface on a first side in the first direction,
the optical sheet includes a plurality of unit prisms arranged in the first direction,
Each unit prism includes a first prism surface located on a first side in the first direction and a second prism surface facing the first prism surface in the first direction,
the prism surface includes the first prism surface and the second prism surface,
the first prism surface includes a first element surface, a second element surface, and a third element surface;
the second element surface is located between the first element surface and the third element surface;
an inclination angle difference between the first element surface and the third element surface is greater than twice the inclination angle of the inclined surface with respect to the first direction;

＜4＞
The optical member of the surface light source device according to any one of <1> to <3>, wherein an arrangement pitch of the connection surfaces in the first direction is 0.060 mm or more.

＜5＞
The optical member according to any one of <1> to <4>, wherein an arrangement pitch of the connection surfaces in the first direction is larger than an arrangement pitch of pixels along the first direction of a display panel arranged opposite the surface light source device.

＜6＞
The optical member according to any one of <1> to <5>, wherein a ratio of an arrangement pitch of the connection surface in the first direction to an arrangement pitch of pixels in the first direction of a display panel arranged opposite the surface light source device is 1.0 or more and 2.2 or less.

＜７＞
The optical member according to any one of <1> to <6>, further comprising a reflective sheet facing the back surface.

＜8＞
the reflective sheet includes, in this order from the light guide plate, a surface layer, an internal diffusion layer, and a metal layer;
The optical member according to <7>, wherein the internal diffusion layer includes a base layer and a light diffusing component held in the base layer.

＜9＞
The specular gloss of the reflective sheet at an incident angle of 20° is 200 or less,
The optical member according to <7> or <8>, wherein the reflecting sheet has a specular gloss of 75 or more at an incident angle of 85°.

＜10＞
The optical member according to any one of <7> to <9>, wherein the specular glossiness G(20) of the reflecting sheet at an incident angle of 20°, the specular glossiness G(60) of the reflecting sheet at an incident angle of 60°, and the specular glossiness G(85) of the reflecting sheet at an incident angle of 85° satisfy the following relationship:
|G(60)-G(85)|＜|G(20)-G(60)|

<11>
The optical member according to any one of <7> to <10>, wherein the specular glossiness G(20) of the reflecting sheet at an incident angle of 20°, the specular glossiness G(60) of the reflecting sheet at an incident angle of 60°, and the specular glossiness G(85) of the reflecting sheet at an incident angle of 85° satisfy the following relationship:
|G(60)-G(85)|/((G(60)+G(85))/2)＜|G(20)-G(60)|/((G(20)+G(60))/2)

＜12＞
The optical member according to any one of <7> to <11>, wherein the diffuse reflectance of the reflective sheet is 65% or more and 90% or less.

＜13＞
The optical member according to any one of <7> to <12>, wherein the reflecting sheet has a specular gloss of 75 or more at an incident angle of 85°.

＜14＞
The optical member according to any one of <7> to <13>, wherein a ratio of the specular gloss of the reflecting sheet at an incident angle of 85° to the specular gloss of the reflecting sheet at an incident angle of 20° is 0.85 or more.

＜15＞
The optical member according to any one of <7> to <14>, wherein the specular glossiness G(20) of the reflecting sheet at an incident angle of 20° and the specular glossiness G(85) of the reflecting sheet at an incident angle of 85° satisfy the following relationship.
G(20)-G(85)≦0

＜16＞
The optical member according to any one of <7> to <15>, wherein a ratio of the specular gloss of the reflecting sheet at an incident angle of 85° to the specular gloss of the reflecting sheet at an incident angle of 60° is 0.55 or more and 2.0 or less.

＜１７＞
The optical member according to any one of <7> to <16>, wherein a specular glossiness G(60) of the reflecting sheet at an incident angle of 60° and a specular glossiness G(85) of the reflecting sheet at an incident angle of 85° satisfy the following relationship:
15≦G(60)-G(85)≦22

＜18＞
<1> to <17>, and
The surface light source device further comprises a light source that emits light incident on the light guide plate.

＜19＞
The surface light source device according to <18>, wherein a difference (°) in inclination angle between the first element surface and the third element surface is equal to or greater than a half-width at half maximum (°) in an angular distribution of luminance on the light exit surface.

＜20＞
<18> or <19>, and
a display panel facing the surface light source device.

＜21＞
a light guide plate including a light output surface, a back surface facing the light output surface, and a light input surface located between the light output surface and the back surface;
an optical sheet including a prism surface facing the light output surface;
A reflective sheet facing the back surface;
A light source that emits light incident on the light guide plate,
the rear surface includes a plurality of inclined surfaces alternately arranged in a first direction and a plurality of connecting surfaces non-parallel to the inclined surfaces;
the inclined surface is inclined with respect to the first direction so as to approach the light output surface on a first side in the first direction,
the optical sheet includes a plurality of unit prisms arranged in the first direction,
Each unit prism includes a first prism surface located on a first side in the first direction and a second prism surface facing the first prism surface in the first direction,
the prism surface includes the first prism surface and the second prism surface,
the first prism surface includes a first element surface, a second element surface, and a third element surface;
the second element surface is located between the first element surface and the third element surface;
a difference (°) in inclination angle between the first element surface and the third element surface is equal to or greater than a half-width at half maximum (°) in an angular distribution of luminance on the light exit surface.

＜22＞
The surface light source device according to <21>, wherein an arrangement pitch of the connection surfaces in the first direction is larger than an arrangement pitch of pixels in the first direction of a display panel disposed opposite the surface light source device.

＜23＞
The surface light source device according to <16>, <21>, or <22>, wherein an arrangement pitch of the connection surfaces in the first direction is 0.060 mm or more.

＜24＞
<18> to <23>, and a surface light source device according to any one of <18> to <23>.
a display panel facing the surface light source device.

＜25＞
An optical member used in a surface light source device disposed opposite a display panel,
a light guide plate including a light output surface and a back surface facing the light output surface;
an optical sheet including a prism surface facing the light output surface,
the rear surface includes a plurality of inclined surfaces alternately arranged in a first direction and a plurality of connecting surfaces non-parallel to the inclined surfaces;
the inclined surface is inclined with respect to the first direction so as to approach the light output surface on a first side in the first direction,
an arrangement pitch of the connection surfaces in the first direction being greater than an arrangement pitch of pixels of the display panel in the first direction;

＜26＞
a light guide plate including a light output surface and a back surface facing the light output surface;
an optical sheet including a prism surface facing the light output surface,
the rear surface includes a plurality of inclined surfaces alternately arranged in a first direction and a plurality of connecting surfaces non-parallel to the inclined surfaces;
the inclined surface is inclined with respect to the first direction so as to approach the light output surface on a first side in the first direction,
An optical member for a surface light source device, wherein the arrangement pitch of the connection surfaces in the first direction is 0.060 mm or more.

＜27＞
The optical member according to any one of <25> and <26>,
The surface light source device further comprises a light source that emits light incident on the light guide plate.

＜28＞
The surface light source device according to <27>,
a display panel facing the surface light source device.

An embodiment of the present invention will now be described with reference to the drawings. In the drawings accompanying this specification, the scale and aspect ratios have been appropriately altered and exaggerated from those of the actual objects for the sake of ease of illustration and understanding. Configurations shown in some drawings may be omitted in other drawings.

In this specification, terms that specify shapes and geometric conditions and their degrees, such as "parallel," "orthogonal," and "same," as well as values of lengths and angles, are not limited to their strict meanings, but are interpreted to include the range in which similar functions can be expected.

In this specification, terms such as "sheet," "film," and "plate" are not distinguished from one another solely on the basis of differences in name. For example, an "optical sheet" cannot be distinguished solely from a component called an optical film or optical plate. A "reflective sheet" cannot be distinguished solely from a component called a reflective film or reflector plate. A "light guide plate" cannot be distinguished solely from a component called a light guide sheet or light guide film.

In this specification, the normal direction of a sheet-like (sheet-like, plate-like) member refers to a direction parallel to the normal or perpendicular line to the sheet surface of the target sheet-like (film-like, plate-like) member. The "sheet surface (film surface, plate surface)" refers to the surface that coincides with the planar direction of the target sheet-like (film-like, plate-like) member when the target sheet-like (film-like, plate-like) member is viewed overall and globally.

In this specification, when multiple upper limit candidates and multiple lower limit candidates are given for a certain parameter, the numerical range of the parameter may be constructed by combining any one of the upper limit candidates and any one of the lower limit candidates. As an example, consider the description: "Parameter B may be A1 or more, A2 or more, or A3 or more. Parameter B may be A4 or less, A5 or less, or A6 or less." In this example, the numerical range of parameter B may be A1 or more and A4 or less, A1 or more and A5 or less, A1 or more and A6 or less, A2 or more and A4 or less, A2 or more and A5 or less, A2 or more and A6 or less, A3 or more and A4 or less, A3 or more and A5 or less, or A3 or more and A6 or less.

To clarify the directional relationships between the drawings, several drawings show the first direction D1, the second direction D2, and the third direction D3 as common directions using arrows with common symbols. The tip of the arrow is the first side of each direction. The side opposite the tip of the arrow is the second side of each direction. For example, as shown in Figure 1, a symbol with a dot in a circle indicates an arrow pointing away from the paper in a direction perpendicular to the paper surface of the drawing.

"Restrain" means to hold back the realization or occurrence of something, or to hinder the realization or occurrence of something. "Restrain" does not only mean to completely prevent the realization or occurrence of something, but also to reduce the possibility of the realization or occurrence of something, or to make the realization or occurrence of something less likely to occur.

FIGS. 1 to 11 are diagrams for explaining one embodiment. The surface light source device 20 may include an optical member 28 and a light source 24. The optical member 28 adjusts the optical path of the light emitted from the light source 24. The surface light source device 20 includes a light-emitting surface 21. Light is emitted from the light-emitting surface 21. FIG. 1 shows a schematic diagram of a display device 10 as an application example of the surface light source device 20 and the optical member 28.

The present embodiment will be described below using an example in which the surface light source device 20 and the optical member 28 are applied to the display device 10. In this embodiment, a device is devised to efficiently expand the viewing angle in the display device 10 using the surface light source device 20 and the optical member 28. However, the surface light source device 20 and the optical member 28 are not limited to application to the display device 10. The surface light source device 20 and the optical member 28 can be applied to various applications such as a lighting device.

As shown in FIG. 1, the display device 10 may include a display panel 15 and a surface light source device 20. In the illustrated example, the display panel 15 and the surface light source device 20 may be stacked in a third direction D3. The display panel 15 and the surface light source device 20 may extend in a direction perpendicular to the third direction D3, which is the stacking direction.

In the illustrated example, the liquid crystal display panel 15 and the surface light source device 20 extend in the first direction D1 and the second direction D2. The illustrated liquid crystal display panel 15 and the surface light source device 20 are flat. The first direction D1 and the second direction D2 are orthogonal. The third direction D3 is orthogonal to the first direction D1. The third direction D3 is orthogonal to the second direction D2. The illustrated liquid crystal display panel 15 and the surface light source device 20 have a rectangular shape when observed from the third direction D3. The illustrated liquid crystal display panel 15 and the surface light source device 20 have a pair of edges extending in the first direction D1 and the second direction D2, respectively, when observed from the third direction D3.

In the illustrated example, the first direction D1 may be a vertical direction. In the illustrated example, the first side in the first direction D1 may be the upper side in the vertical direction. In the illustrated example, the second direction D2 and the third direction D3 may each be along a horizontal direction. In the illustrated example, the normal direction of the display panel 15 is parallel to the third direction D3, and the normal direction of the surface light source device 20 is parallel to the third direction D3. In the illustrated example, the display surface 11 is perpendicular to the third direction D3, and the light-emitting surface 21 of the surface light source device 20, which will be described later, is perpendicular to the third direction D3. In the illustrated example, the reflective sheet 70, the light guide plate 30, and the optical sheet 50 included in the surface light source device 20 and the optical member 28 are perpendicular to the third direction D3.

The display panel 15 may constitute the display surface 11. The normal direction of the display surface 11 may be parallel to the third direction D3. An image may be displayed on the display surface 11. In the example shown in FIG. 1, the surface light source device 20 serves as a backlight and illuminates the display panel 15 from behind. The display panel 15 may be a transmissive display panel. The display panel 15 may be a liquid crystal display panel. The type of the liquid crystal display panel is not particularly limited. The display panel 15 may be a TN type liquid crystal display panel, a VA type liquid crystal display panel, or an IPS type liquid crystal display panel. The display panel 15 may include a plurality of pixels 16. The display panel 15 functions as a shutter that controls the transmission or blocking of light from the surface light source device 20 for each pixel. A pixel is the smallest unit that constitutes an image.

Figure 2 shows a specific example of a pixel arrangement in a display panel 15. The illustrated display panel 15 includes a first pixel 16A, a second pixel 16B, and a third pixel 16C.

2, the first pixel 16A, the second pixel 16B, and the third pixel 16C are arranged in the second direction D2 in a repeating order. In the example shown in FIG. 2, the first pixels 16A are continuously arranged in the first direction D1. In the example shown in FIG. 2, the second pixels 16B are continuously arranged in the first direction D1. In the example shown in FIG. 2, the third pixels 16C are continuously arranged in the first direction D1. In the example shown in FIG. 2, the pixels 16A, 16B, and 16C are arranged at a first pixel pitch PP1 in the first direction D1. The pixels 16A, 16B, and 16C are arranged at a second pixel pitch PP2 in the second direction D2.

The first pixel 16A, the second pixel 16B, and the third pixel 16C may emit image light of different colors. The first pixel 16A may emit blue image light. The second pixel 16B may emit green image light. The third pixel 16C may emit red image light. A unit pixel may be formed by one first pixel 16A, one second pixel 16B, and one third pixel 16C arranged continuously in the second direction D2. FIG. 2 illustrates one unit pixel by enclosing it in a dotted line.

As shown in FIG. 3, the surface light source device 20 includes a light source 24 and an optical member 28. The optical member 28 adjusts the optical path of the light emitted from the light source 24. The optical member 28 may form the light-emitting surface 21. In this embodiment, the surface light source device 20 may be configured as an edge-light type. The light emitted from the light source 24, i.e., the light source light, may be incident on the optical member 28 from the side. That is, the light may be incident on the optical member 28 from a direction non-parallel to the third direction D3, for example, from a direction perpendicular to the third direction D3.

As shown in FIG. 3, the optical member 28 may include a reflective sheet 70, a light guide plate 30, and an optical sheet 50. The reflective sheet 70, the light guide plate 30, and the optical sheet 50 may be stacked in this order in the third direction D3. That is, the light guide plate 30 may be positioned between the reflective sheet 70 and the optical sheet 50 in the third direction D3.

In the illustrated example, the reflective sheet 70, the light guide plate 30, and the optical sheet 50 extend in the first direction D1 and the second direction D2. The illustrated reflective sheet 70, the light guide plate 30, and the optical sheet 50 are flat. The reflective sheet 70, the light guide plate 30, and the optical sheet 50 shown in FIG. 4 have a rectangular shape when observed from the third direction D3. The reflective sheet 70, the light guide plate 30, and the optical sheet 50 have a pair of edges extending in the first direction D1 and the second direction D2, respectively, when observed from the third direction D3. In the example shown in FIG. 4, the light source light emitted from the light source 24 enters the optical member 28 from the second side in the first direction D1.

The light source 24 is not particularly limited. The light source 24 may include, for example, a fluorescent lamp such as a linear cold cathode fluorescent tube, or a light emitter such as a point-shaped LED (light emitting diode) or an incandescent light bulb. As shown in FIG. 4, the light source 24 may include a plurality of point light emitters 25 arranged in the second direction D2. The light emitters 25 may be light emitting diodes (LEDs). The light emitters 25 may face the optical member 28 from the side. The light emitters 25 may be disposed facing the light guide plate 30. Alternatively, the light emitted from the light emitters 25 may be guided to the optical member 28 by a reflecting member or the like.

As shown in FIG. 5, the light guide plate 30 is plate-shaped. The light guide plate 30 may include a pair of main surfaces, a light output surface 31 and a back surface 32. The light output surface 31 may face a first side in the first direction D1. The light output surface 31 may face the optical sheet 50. The back surface 32 may face a second side in the first direction D1. The back surface 32 may face the reflective sheet 70. The light guide plate 30 may include a side surface located between the light output surface 31 and the back surface 32. The side surface of the light guide plate 30 may face a direction perpendicular to the third direction D3.

The light guide plate 30 may include a light entrance surface 33 facing the second side in the first direction D1 as a side surface. The light source light may enter the light guide plate 30 through the light entrance surface 33. The light emitter 25 may be disposed facing the light entrance surface 33. The light entrance surface 33 shown in FIG. 5 shows a position facing the light emitter 25 forming the light source 24. The light source light entering the light guide plate 30 from the light entrance surface 33 advances through the light guide plate 30 toward the opposite surface 34 facing the light entrance surface 33 in the first direction D1, which is the light guide direction. In the illustrated example, the light guide plate 30 further includes a first side surface 35a and a second side surface 35b extending between the light entrance surface 33 and the opposite surface 34 as side surfaces located between the light exit surface 31 and the back surface 32.

The light guide plate 30 mainly guides the light source light incident from the light entrance surface 33 in the first direction D1. The material constituting the light guide plate 30 may be a transparent material, for example a transparent resin material. "Transparent" means that the total light transmittance is 50% or more, and may be 80% or more, or 90% or more. The total light transmittance is a value measured according to JIS K 7361-1:1997. The angle of incidence when measuring the total light transmittance is 0°. The angle of incidence means the angle (°) that the direction of travel of the incident light makes with respect to the normal direction of a sheet-like member or the like into which the light is incident. The angle of incidence is an angle of 0° or more and 90° or less. The measurement environment when measuring the total light transmittance is a temperature of 23°C ± 2°C and a relative humidity of 50% ± 5%. The sample to be measured is placed in the measurement environment for 16 hours before the start of the test. Before measuring the total light transmittance, turn on the light source of the measuring device for 15 minutes to stabilize the light source output.

As shown in Figs. 5 and 6, the rear surface 32 may be configured as an uneven surface. The rear surface 32 may include a plurality of inclined surfaces 37 and a plurality of connecting surfaces 39. As shown in Figs. 5 and 6, the inclined surfaces 37 and the connecting surfaces 39 may be arranged alternately in the first direction D1.

In the illustrated example, the inclined surface 37 is inclined with respect to the first direction D1 so as to approach the light output surface 31 on the first side in the first direction D1. That is, the distance along the third direction D3 between the light output surface 31 and one of the inclined surfaces 37 gradually becomes shorter toward the first side in the first direction D1. The light is guided in the light guide plate 30 by total reflection at the light output surface 31 and the back surface 32, which are a pair of main surfaces of the light guide plate 30. However, the reflection at the inclined surface 37 reduces the angle of incidence when the light is incident on the pair of main surfaces 31 and 32. When the reflection at the inclined surface 37 makes the angle of incidence on the pair of main surfaces 31 and 32 less than the total reflection critical angle, the light can be emitted from the light guide plate 30. The inclined surface 37 functions as a light extraction element for extracting light from the light guide plate 30.

The connection surface 39 may be inclined toward the opposite side to the inclined surface 37 with respect to the third direction D3 as the center, or may extend along the third direction D3. By arranging the connection surface 39 between two adjacent inclined surfaces 37, the thickness variation of the light guide plate 30 at each position in the first direction D1 can be reduced.

The rear surface 32 may further include a flat surface 38 in addition to the inclined surface 37 and the connecting surface 39. The angle between the first direction D1 and the flat surface 38 may be smaller than the angle between the first direction D1 and the inclined surface 37. The angle between the first direction D1 and the flat surface 38 may be smaller than the angle between the first direction D1 and the connecting surface 39. As shown in Figures 3 and 6, the flat surface 38 may be parallel to the first direction D1. By providing the flat surface 38, the distribution of the inclined surface 37 along the first direction D1, which is the light guide direction, can be adjusted. By adjusting the distribution of the inclined surface 37, the distribution of the amount of light emitted from the light guide plate 30 along the first direction D1 can be adjusted.

The angle between the first direction D1 and the inclined surface 37 means the angle between the first direction D1 and the inclined surface 37 in a cross section along the first direction and the third direction D3. The angle between the first direction D1 and the flat surface 38 means the angle between the first direction D1 and the flat surface 38 in a cross section along the first direction and the third direction D3. The angle between the first direction D1 and the connecting surface 39 means the angle between the first direction D1 and the connecting surface 39 in a cross section along the first direction and the third direction D3. These angles are between 0° and 90°. Figure 6 shows the angle θy between the first direction D1 and the inclined surface 37.

The angle θy between the first direction D1 and the inclined surface 37, i.e., the inclined surface angle θy of the inclined surface 37 with respect to the first direction D1, may be 0.10° or more, 1.0° or more, or 1.5° or more. By setting a lower limit to the inclined surface angle θy, the light extraction efficiency from the light guide plate 30 can be improved. The inclined surface angle θy of the inclined surface 37 with respect to the first direction D1 may be 5.0° or less, 3.0° or less, or 2.0° or less. By setting an upper limit to the inclined surface angle θy, the traveling direction of the light emitted from the light output surface 31 of the light guide plate 30 can be limited to a narrow angle range. The inclined surface 37 may be a flat surface. The inclined surface angle θy of each inclined surface 37 may be constant within the inclined surface 37. The inclined surface 37 may include a curved surface. The inclined surface 37 may include a folded surface. The inclined surface angle θy of the inclined surface 37, which includes curved and folded surfaces, is the inclined surface angle measured at the center position in the first direction D1.

In the example shown in FIG. 3, the proportion of the inclined surface 37 on the back surface 32 increases from the light entrance surface 33 toward the opposite surface 34 along the light guide direction D1, that is, from the second side toward the first side in the first direction D1. This configuration can promote the emission of light from the light guide plate 30 in an area away from the light entrance surface 33 along the light guide direction. This can prevent the amount of emitted light from decreasing with increasing distance from the light entrance surface 33. The illuminance distribution along the first direction D1 on the light exit surface 31 can be made uniform.

As shown in FIG. 5, the inclined surface 37 may extend in the second direction D2. The angle θy between the inclined surface 37 and the first direction D1 may be constant at each position in the second direction D2. The connecting surface 39 may extend in the second direction D2. The angle between the connecting surface 39 and the first direction D1 may be constant at each position in the second direction D2. The flat surface 38 may extend in the second direction D2. The angle θy between the flat surface 38 and the first direction D1 may be constant at each position in the second direction D2.

The flat surface 38 is adjacent to the inclined surface 37. As shown in FIG. 3 and FIG. 6, the flat surface 38 may be connected to the inclined surface 37 from the second side in the first direction D1. The flat surface 38 may be connected to the inclined surface 37 from the first side in the first direction D1. The flat surface 38 may be connected to the inclined surface 37 from both sides in the first direction D1. The flat surface 38 may be connected to the inclined surface 37 from a certain side in the first direction D1, or the flat surface 38 may not be connected to the inclined surface 37 from a certain side in the first direction D1. As shown in FIG. 3 and FIG. 6, the end of the first side of the inclined surface 37 in the first direction D1 may appear at a certain period in the first direction D1. As shown in FIG. 3 and FIG. 6, the end of the first side of the connection surface 39 in the first direction D1 may appear at a certain period in the first direction D1.

The arrangement pitch PC of the connection surfaces 39 in the first direction D1 may be longer than conventional. By setting a lower limit for the arrangement pitch PC of the connection surfaces 39 in the first direction D1, the generation of stray light and the like can be suppressed, and the efficiency of use of the light from the light source can be improved. The arrangement pitch PC of the connection surfaces 39 in the first direction D1 may be 0.060 mm or more, 0.070 mm or more, 0.080 mm or more, or 0.20 mm or more. The arrangement pitch PC of the connection surfaces 39 in the first direction D1 may be 0.37 mm or less, 0.32 mm or less, or 0.28 mm or less. By setting an upper limit for the arrangement pitch PC of the connection surfaces 39 in the first direction D1, the unevenness of the back surface 32 can be suppressed from being observed.

The arrangement pitch PC (mm) of the connection surfaces 39 in the first direction D1 may be greater than the arrangement pitch PP1 (mm) of the pixels 16 in the first direction D1. By lengthening the arrangement pitch PC of the connection surfaces 39 in the first direction D1 in this manner, the occurrence of stray light, etc. can be suppressed, and the efficiency of use of the light from the light source can be improved.

The ratio of the arrangement pitch PC (mm) of the connection surface 39 in the first direction D1 to the arrangement pitch PP1 (mm) of the pixels 16 in the first direction D1 may be 0.60 or more, 1.0 or more, 1.2 or more, or 1.4 or more. By setting a lower limit to this ratio, the occurrence of stray light and the like can be suppressed, and the efficiency of use of the light from the light source can be improved. The ratio of the arrangement pitch PC (mm) of the connection surface 39 in the first direction D1 to the arrangement pitch PP1 (mm) of the pixels 16 in the first direction D1 may be 2.2 or less, 2.0 or less, 1.9 or less, or 1.8 or less. By setting an upper limit to this ratio, it is possible to suppress the observation of unevenness on the back surface 32. By setting an upper limit to this ratio, it is possible to make moire caused by interference between the regularity of the configuration on the back surface 32 and the regularity of the pixels less noticeable.

Other dimensions of the light guide plate 30 may be set as follows, for example. The length of the light guide plate 30 in the third direction D3, i.e., the thickness of the light guide plate 30, may be 0.10 mm or more, 0.20 mm or more, or 0.30 mm or more. The length of the light guide plate 30 in the third direction D3 may be 1.0 mm or less, 0.9 mm or more, or 0.7 mm or less. The length of the light guide plate 30 in the first direction D1 and the length of the light guide plate 30 in the second direction D2 are not particularly limited. The length of the light guide plate 30 in the first direction D1 and the length of the light guide plate 30 in the second direction D2 may be determined depending on, for example, the size of the display device.

The light guide plate 30 may be manufactured using extrusion molding, UV molding, injection molding, etc. Various materials may be used as the material of the light guide plate 30. The material of the light guide plate 30 may be a transparent resin mainly composed of one or more of acrylic resin, polystyrene resin, polycarbonate resin, polyethylene terephthalate resin, polyacrylonitrile resin, etc. The light guide plate 30 may include a base material portion of a resin material and a light diffusing component dispersed in the base material portion. The light diffusing component may be inorganic particles such as silica (silicon dioxide) and alumina (aluminum oxide). The light diffusing component may be organic particles such as acrylic resin, polycarbonate resin, silicone resin, etc.

As shown in FIG. 7, the optical sheet 50 is plate-shaped. The optical sheet 50 may include a pair of main surfaces, a first surface 51 and a second surface 52. The first surface 51 may face a first side in the third direction D3. The second surface 52 may face a second side in the third direction D3. The second surface 52 may face the light guide plate 30. The second surface 52 is configured as a prism surface 53.

The optical sheet 50 may include a body portion 55 and unit prisms 60. The body portion 55 may be sheet-like. The body portion 55 may include a light exiting side surface 55a and a light entering side surface 55b. As in the illustrated example, the light exiting side surface 55a of the body portion 55 may constitute a first surface 51 of the optical sheet 50. The first surface 51 may be a surface perpendicular to the third direction D3.

The first surface 51 may be a flat surface. The first surface 51 may be a matte surface. The first surface 51 may be an uneven surface. For the purpose of adjusting the amount of light or brightness in the second direction, the first surface 51 may be configured with linear convex portions or linear concave portions extending in the first direction. The linear convex portions or linear concave portions extending in the first direction may be arranged in the second direction D2.

A plurality of unit prisms 60 may be provided on the light-entering side surface 55b of the main body portion 55. A plurality of unit prisms 60 may be provided without gaps on the light-entering side surface 55b of the main body portion 55. The plurality of unit prisms 60 may form the second surface 52 of the optical sheet 50. The prism surface 53 may be formed by the plurality of unit prisms 60.

A "unit prism" is an element that has the function of exerting optical effects such as refraction and reflection on light, thereby changing the direction in which the light travels. A "unit prism" is not distinguished from a "unit shape element," a "unit optical element," or a "unit lens" solely on the basis of the difference in name.

The multiple unit prisms 60 may be arranged in a first direction D1. Each unit prism 60 may extend linearly. As in the example shown in FIG. 7, each unit prism 60 may extend linearly. As in the example shown in FIG. 7, each unit prism 60 may extend linearly in a second direction D2 perpendicular to the first direction D1, which is the arrangement direction. As in the example shown in FIG. 7, the multiple unit prisms 60 may form a linear array prism. Each unit prism 60 may be columnar.

The arrangement of the multiple unit prisms 60 is not limited to the example shown in FIG. 7. The multiple unit prisms 60 may be arranged in two or more directions including the first direction D1 and a direction non-parallel to the first direction D1. The multiple unit prisms 60 may form a two-dimensionally arranged microlens array.

Each unit prism 60 may include a first prism surface 61 and a second prism surface 62. The first prism surface 61 and the second prism surface 62 may face the first direction D1. The first prism surface 61 may be located on a first side in the first direction D1. The second prism surface 62 may be located on a second side in the first direction D1. The prism surface 53 may include the first prism surface 61 and the second prism surface 62. The prism surface 53 may be composed of only the first prism surface 61 and the second prism surface 62. As described later, the second prism surface 62 may function as an entrance surface onto which light emitted from the light guide plate 30 is incident. The first prism surface 61 may function as a reflecting surface that reflects light that passes through the second prism surface 62 and travels through the unit prism 60.

As in the example shown in FIG. 8, the first prism surface 61 and the second prism surface 62 may each extend from the main body portion 55. The first prism surface 61 and the second prism surface 62 may be connected to the main body portion 55 at one end. As in the example shown in FIG. 8, the first prism surface 61 and the second prism surface 62 may be connected to each other at the other end. At the other end, the first prism surface 61 and the second prism surface 62 may form the apex 63 of the unit prism 60 that is furthest from the main body portion 55 in the third direction D3.

In the illustrated example, in the main cut surface of the optical sheet 50 parallel to both the first direction D1 and the third direction D3, the first prism surface 61 and the second prism surface 62 approach each other as they move away from the main body portion 55. In the main cut surface of the optical sheet 50 shown in FIG. 8, the unit prism 60 has a tapered cross-sectional shape. In the example shown in FIG. 7, the cross-sectional shape in the main cut surface of the optical sheet 50 is constant at each position in the second direction D2. The illustrated unit prism 60 extends in the second direction D2 with a constant cross-sectional shape. In the illustrated optical sheet 50, the multiple unit prisms 60 have the same configuration. Not limited to the illustrated example, the multiple unit prisms 60 may have different configurations. Not limited to the illustrated example, the cross-sectional shape of each unit prism 60 may be different at each position in the second direction D2.

8, the first prism surface 61 may be a folded surface. The first prism surface 61 may include a first element surface 66, a second element surface 67, and a third element surface 68. The first prism surface 61 may include a first element surface 66, a second element surface 67, and a third element surface 68. The first element surface 66, the second element surface 67, and the third element surface 68 may be connected in order. The first element surface 66, the second element surface 67, and the third element surface 68 may be arranged in this order from the apex 63 of the unit prism 60 toward the base end. The second element surface 67 may be located between the first element surface 66 and the third element surface 68. The first element surface 66 may constitute the apex 63 at one end. The first element surface 66 may be connected to one end of the second element surface 67 at the other end. The second element surface 67 may be connected at the other end to one end of the third element surface 68. The third element surface 68 may be connected at the other end to the main body portion 55. The first prism surface 61 may include four or more element surfaces, without being limited to the example shown in FIG. 8.

The angle between the prism surface or element surface and the third direction D3, which is the stacking direction of the components of the optical member 28, is the inclination angle θx (°). The inclination angle θx (°) is an angle between 0° and 90°. The inclination angle of the prism surface including a curved surface or the element surface including a curved surface is an angle measured at the center position of the prism surface or the element surface in the first direction D1. The inclination angle of the element surface included in the first prism surface 61 may become smaller as the position of the element surface approaches the main body 55 from the apex 63. In the illustrated example, the first element surface inclination angle θxe1 of the first element surface 66 may be larger than the second element surface inclination angle θxe2 of the second element surface 67. The second element surface inclination angle θxe2 of the second element surface 67 may be larger than the third element surface inclination angle θxe3 of the third element surface 68. According to this configuration, the entire area of the first prism surface 61 can be effectively utilized to perform the optical path adjustment.

A lower limit may be set for the inclination angle difference (°) between the first element surface 66 and the third element surface 68. That is, a lower limit may be set for the inclination angle difference (°) between the first element surface inclination angle θxe1 and the third element surface inclination angle θxe3. By setting a lower limit for the inclination angle difference (°), the light incident on the optical sheet 50 from the light guide plate 30 can be diffused by reflection on the first prism surface 61. This allows the viewing angle of the display device 10 to be effectively widened. An upper limit may be set for the inclination angle difference (°) between the first element surface 66 and the third element surface 68. By setting an upper limit for the inclination angle difference (°), excessive diffusion can be suppressed. This allows the light source light to be used with high efficiency for image formation in the display device 10. The inclination angle difference (°) between the first element surface 66 and the third element surface 68 may be 5° or more, 8° or more, 10° or more, or 12° or more. The difference in inclination angle (°) between the first element surface 66 and the third element surface 68 may be 20° or less, 18° or less, or 15° or less.

The inclination angle difference (°) between the first element surface 66 and the third element surface 68 may be greater than twice, greater than 2.5 times, greater than 3 times, greater than 4 times, or greater than 6 times the inclination angle θy of the inclined surface 37 with respect to the first direction D1. According to this example, the inclination angle difference (°) can be made sufficiently large to cope with variations in the direction of travel of the light emitted from the light guide plate 30. Therefore, the light incident on the optical sheet 50 from the light guide plate 30 can be diffused by reflection at the first prism surface 61. This makes it possible to effectively widen the viewing angle of the display device 10.

The difference in inclination angle (°) between the first element surface 66 and the third element surface 68 may be equal to or greater than the half-width at half maximum (°) in the angular distribution of luminance at the light output surface 31 of the light guide plate 30. According to this example, the difference in inclination angle (°) is sufficiently large relative to the variation in the direction of travel of the light exiting the light guide plate 30. Therefore, the light incident on the optical sheet 50 from the light guide plate 30 can be diffused by reflection at the first prism surface 61. This makes it possible to effectively widen the viewing angle of the display device 10.

Here, the angular distribution of luminance is a distribution of luminance (cd/m ² ) in each direction in a plane including the third direction D3, which is the lamination direction of the light guide plate 30 and the optical sheet 50, and the first direction D1. As an example, as shown in FIG. 10, the relationship between luminance and the angle (°) between the direction in which the luminance is obtained and the third direction D3 is shown. When the direction in which the luminance is obtained is inclined toward the first side in the first direction D1 with respect to the third direction D3, the angle (°) between the direction and the third direction D3 is a positive value. That is, the luminance in the direction inclined from the third direction D3 to the first side in the first direction D1 from the light output surface 31 takes a positive value as the angle on the horizontal axis. The luminance angular distribution on the light output surface 31 is a measured value in a state in which the components on the light emitting surface 21 side of the surface light source device 20 are removed. In the surface light source device 20 shown in FIG. 3, the measured value is a device including the light source 24, the light guide plate 30, and the reflective sheet 70. The half-width at half maximum HW (°) means the angle (°) between the direction in which the maximum brightness value BMAX is obtained and the third direction D3, in which a brightness BF that is half the maximum brightness value BMAX is obtained, and the direction in which the maximum brightness value BMAX is obtained.

The luminance (cd/m ² ) in the luminance angular distribution is measured using EZ Contrast XL80 manufactured by ELDIM Co., Ltd. The luminance angular distribution shown in FIG. 10 was measured using EZ Contrast XL80 manufactured by ELDIM Co., Ltd.

The first element surface inclination angle θxe1 may be 25° or more, 30° or more, or 35° or more. The first element surface inclination angle θxe1 may be 55° or less, 50° or less, or 45° or less. The second element surface inclination angle θxe2 may be 19° or more, 24° or more, or 29° or more. The second element surface inclination angle θxe2 may be 49° or less, 44° or less, or 39° or less. The third element surface inclination angle θxe3 may be 12° or more, 17° or more, or 22° or more. The third element surface inclination angle θxe3 may be 42° or less, 37° or less, or 32° or less. The inclination angle θx2 of the second prism surface 62 may be 20° or more, 25° or more, or 30° or more. The inclination angle θx2 of the second prism surface 62 may be 50° or less, 45° or less, or 40° or less.

The length Wx of the unit prism 60 in the first direction D1, i.e., the width Wx of the unit prism 60, may be 12 μm or more, 14 μm or more, or 16 μm or more. The length Wx of the unit prism 60 in the first direction D1 may be 32 μm or less, 30 μm or less, or 28 μm or less. The value of the ratio (Wx1/Wx) of the length Wx1 of the first prism surface 61 in the first direction D1 to the length Wx of the unit prism 60 in the first direction D1 may be 0.32 or more, 0.37 or more, or 0.42 or more. The value of the ratio (Wx1/Wx) of the length Wx1 of the first prism surface 61 in the first direction D1 to the length Wx of the unit prism 60 in the first direction D1 may be 0.62 or less, 0.57 or less, or 0.52 or less.

The value of the ratio (Wxe1/Wx) of the length Wxe1 of the first element surface 66 in the first direction D1 to the length Wx of the unit prism 60 in the first direction D1 may be 0.050 or more, 0.070 or more, or 0.090 or more. The value of the ratio (Wxe1/Wx) of the length Wxe1 of the first element surface 66 in the first direction D1 to the length Wx of the unit prism 60 in the first direction D1 may be 0.17 or less, 0.15 or less, or 0.13 or less. The value of the ratio (Wxe2/Wx) of the length Wxe2 of the second element surface 67 in the first direction D1 to the length Wx of the unit prism 60 in the first direction D1 may be 0.080 or more, 0.10 or more, or 0.12 or more. The value of the ratio (Wxe2/Wx) of the length Wxe2 of the second element surface 67 in the first direction D1 to the length Wx of the unit prism 60 in the first direction D1 may be 0.20 or less, 0.18 or less, or 0.16 or less. The value of the ratio (Wxe3/Wx) of the length Wxe3 of the third element surface 68 in the first direction D1 to the length Wx of the unit prism 60 in the first direction D1 may be 0.16 or more, 0.18 or more, or 0.20 or more. The value of the ratio (Wxe3/Wx) of the length Wxe3 of the third element surface 68 in the first direction D1 to the length Wx of the unit prism 60 in the first direction D1 may be 0.28 or less, 0.26 or less, or 0.24 or less.

The length Hx of the unit prism 60 in the third direction D3, i.e., the height Hx of the unit prism 60, may be 8.0 μm or more, 10 μm or more, or 12 μm or more. The length Hx of the unit prism 60 in the third direction D3 may be 20 μm or less, 18 μm or less, or 16 μm or less. The length of the optical sheet 50 in the third direction D3, i.e., the thickness of the optical sheet 50, may be 115 μm or more, 125 μm or more, or 135 μm or more. The length of the optical sheet 50 in the third direction D3 may be 175 μm or less, 165 μm or less, or 155 μm or less.

The optical sheet 50 can be manufactured using extrusion molding, UV molding, injection molding, etc. Various materials can be used as the material of the optical sheet 50. The material of the optical sheet 50 may include a transparent resin containing one or more of acrylic resin, polystyrene resin, polycarbonate resin, polyethylene terephthalate resin, polyacrylonitrile resin, etc. as a main component. The material of the optical sheet 50 may include a reactive resin (such as an ionizing radiation curable resin) such as an epoxy acrylate resin or a urethane acrylate resin.

As shown in Figs. 3 and 4, the reflective sheet 70 is in the form of a sheet. The reflective sheet 70 reflects the light emitted from the rear surface 32 of the light guide plate 30 and returns it to the light guide plate 30. The reflection by the reflective sheet 70 may be regular reflection (specular reflection), diffuse reflection, or anisotropic diffuse reflection. The reflective sheet 70 having the regular reflection function may include a surface layer of a thin metal film. The reflective sheet 70 having the diffuse reflection function may be a sheet containing inorganic particles such as titanium oxide or silicon oxide. The reflective sheet 70 having the anisotropic diffuse reflection function may be a sheet containing a light diffusing component having a longitudinal direction in an oriented state, or a sheet containing convex portions or concave portions having a longitudinal direction in an oriented state.

The total light reflectance of the reflective sheet 70 may be 75% or more, 80% or more, or 85% or more. By setting a lower limit on the total light reflectance, the efficiency of using the light from the light source can be improved. No upper limit is set for the total light reflectance of the reflective sheet 70. The total light reflectance of the reflective sheet 70 may be 100% or less, or may be less than 100%.

The reflective sheet 70 having a diffuse reflection function can efficiently expand the viewing angle in the display device 10 using the surface light source device 20. A lower limit may be set for the diffuse reflectance of the reflective sheet 70. By setting a lower limit for the diffuse reflectance of the reflective sheet 70, the viewing angle can be efficiently expanded. The diffuse reflectance of the reflective sheet 70 may be 65% or more, 70% or more, or 75% or more.

An upper limit may be set for the diffuse reflectance of the reflective sheet 70. By setting an upper limit for the diffuse reflectance of the reflective sheet 70, the decrease in maximum brightness can be suppressed. The diffuse reflectance of the reflective sheet 70 may be 90% or less, 87% or less, or 85% or less. The diffuse reflectance (%) is the omnidirectional diffuse reflectance obtained by excluding the light reflectance of specularly reflected light from the total light reflectance.

The total light reflectance (%) is determined using the measured value of the spectral total light reflectance. The measured value of the spectral total light reflectance for each wavelength in 1 nm increments in the visible light wavelength range from 380 nm to 780 nm is used to determine the total light reflectance. A D65 light source is used to measure the spectral total light reflectance. The angle of incidence to the sample surface is 8°. The measurement environment for measuring the spectral total light reflectance is a temperature of 23°C ± 2°C and a relative humidity of 50% ± 5%. The sample to be measured is placed in the measurement environment for 16 hours before the start of the test. Before measuring the spectral total light reflectance, the light source of the measuring device is turned on for 15 minutes to stabilize the light source output.

When measuring the total spectral reflectance, a black plate is attached to the back side of the sample to be measured, opposite the incident surface, via an optically transparent adhesive sheet. The optically transparent adhesive sheet is Panac's "Panaclean PD-S1". The black plate is Kuraray's "Comoglass DFA2CG 502K (black) series".

To measure the total spectral reflectance, a UV-Vis-NIR spectrophotometer UH4150 manufactured by Hitachi High-Tech Science Corporation may be used. A standard integrating sphere with a diameter of 60 mm (four holes) may be used as a reflectance detector.

The total light reflectance is specified using the following formula (X), which is equivalent to the visible light reflectance specified in formula (18) in the "7.2 Basic Formulas" column of JIS R 3106:2019. According to formula (X), the total light reflectance is calculated taking into account the CIE daylight D65 spectral distribution of the light source and the CIE photopic standard relative luminous efficiency. The total light reflectance is specified as the weighted average of the spectral total light reflectance using the CIE daylight D65 spectral distribution of the light source and the CIE photopic standard relative luminous efficiency as weighting coefficients. "A(λ)" in formula (X) is the spectral distribution of the D65 light source. "B(λ)" in formula (X) is the CIE photopic standard relative luminous efficiency. "C(λ)" in formula (X) is the spectral total light reflectance (%).

The total light diffuse reflectance is determined as the difference between the total light reflectance and the specular reflectance. The specular reflectance is determined using the measured value of the spectral specular reflectance. The specular reflectance is determined using the measured value of the spectral specular reflectance for each wavelength in 1 nm increments in the visible light wavelength range from 380 nm to 780 nm. The D65 light source is used to measure the spectral specular reflectance. The angle of incidence with respect to the surface of the sample is 8°. The measurement environment for measuring the spectral specular reflectance is a temperature of 23°C ± 2°C and a relative humidity of 50% ± 5%. The sample to be measured is placed in the measurement environment for 16 hours before the start of the test. Before measuring the spectral specular reflectance, the light source of the measurement device is turned on for 15 minutes to stabilize the output of the light source. The spectral specular reflectance may be measured using the measurement device used to measure the spectral total light reflectance.

When measuring the spectral specular reflectance, a black plate is attached to the back side of the sample to be measured, opposite the incident surface, via an optically transparent adhesive sheet. The optically transparent adhesive sheet is Panac's "Panaclean PD-S1". The black plate is Kuraray's "Comoglass DFA2CG 502K (black) series".

Specular reflectance is specified using the following formula (Y), which is equivalent to the visible light reflectance specified in formula (18) in the "7.2 Basic Formulas" column of JIS R 3106:2019. According to formula (Y), the specular reflectance is calculated taking into account the CIE daylight D65 spectral distribution of the light source and the CIE photopic standard relative luminous efficiency. The specular reflectance is specified as a weighted average of the spectral specular reflectance using the CIE daylight D65 spectral distribution of the light source and the CIE photopic standard relative luminous efficiency as weighting coefficients. "A(λ)" in formula (Y) is the spectral distribution of the D65 light source. "B(λ)" in formula (Y) is the CIE photopic standard relative luminous efficiency. "D(λ)" in formula (Y) is the spectral specular reflectance (%).

An upper limit may be set for the specular glossiness G(20) of the reflective sheet 70 at an incidence angle of 20°. The specular glossiness G(20) of the reflective sheet 70 at an incidence angle of 20° may be 200 or less, 150 or less, or 100 or less, to two significant digits. By setting an upper limit for the specular glossiness G(20) of the reflective sheet 70 at an incidence angle of 20°, the reflective sheet 70 can be given a diffuse reflection function. In particular, light that is incident on the reflective sheet 70 at a small incidence angle can be diffused. This makes it possible to efficiently expand the viewing angle in the display device 10 using the surface light source device 20.

A lower limit may be set for the specular glossiness G(20) of the reflective sheet 70 at an incidence angle of 20°. By setting a lower limit for the specular glossiness G(20) of the reflective sheet 70 at an incidence angle of 20°, a decrease in the maximum brightness can be suppressed. The specular glossiness G(20) of the reflective sheet 70 at an incidence angle of 20° may be 65 or more, 75 or more, or 85 or more.

A lower limit may be set for the specular glossiness G(85) of the reflective sheet 70 at an incidence angle of 85°. The specular glossiness G(85) of the reflective sheet 70 at an incidence angle of 85° may be 75 or more, 85 or more, or 90 or more. By setting a lower limit for the specular glossiness G(85) of the reflective sheet 70 at an incidence angle of 85°, it is possible to suppress the diffusion of light that is incident on the reflective sheet 70 at a large incidence angle. This makes it possible to suppress a decrease in the maximum brightness.

An upper limit may be set for the specular glossiness G(85) of the reflective sheet 70 at an incidence angle of 85°. By setting an upper limit for the specular glossiness G(85) of the reflective sheet 70 at an incidence angle of 85°, the viewing angle can be expanded. The specular glossiness G(85) of the reflective sheet 70 at an incidence angle of 85° may be, to two significant digits, 110 or less, 105 or less, or 100 or less.

The specular glossiness G(20) of the reflective sheet 70 at an incidence angle of 20° may be set to the upper limit as described above, and the specular glossiness G(85) of the reflective sheet 70 at an incidence angle of 85° may be set to the lower limit as described above. The specular glossiness of the reflective sheet 70 at an incidence angle of 20° may be 200 or less, and the specular glossiness of the reflective sheet 70 at an incidence angle of 85° may be 75 or more. According to this example, the viewing angle can be efficiently expanded while sufficiently suppressing the decrease in the maximum luminance.

The ratio value (G(85)/G(20)) of the specular glossiness G(20) of the reflective sheet 70 at an incidence angle of 20° to the specular glossiness G(85) of the reflective sheet 70 at an incidence angle of 85° may be 0.85 or more, 0.90 or more, or 0.95 or more. By setting a lower limit for the ratio value (G(85)/G(20)), it is possible to diffuse light incident at a small incidence angle while suppressing the diffusion of light incident at a large incidence angle. This makes it possible to efficiently expand the viewing angle in the display device 10 using the surface light source device 20 while suppressing the decrease in the maximum brightness. The upper limit of the ratio value (G(85)/G(20)) is not particularly set. The ratio value (G(85)/G(20)) may be 2.2 or less, 1.6 or less, or 1.2 or less.

The difference (G(20)-G(85)) between the specular glossiness G(20) at an incidence angle of 20° of the reflecting sheet 70 and the specular glossiness G(85) at an incidence angle of 85° of the reflecting sheet 70 may be 0 or less, -2 or less, -4.5 or less, or -5 or less, to two significant digits. By setting an upper limit on the specular glossiness difference (G(20)-G(85)), it is possible to diffuse light incident at a small incidence angle while suppressing the diffusion of light incident at a large incidence angle. This makes it possible to efficiently expand the viewing angle in the display device 10 using the surface light source device 20 while suppressing the decrease in the maximum brightness. The lower limit of the specular glossiness difference (G(20)-G(85)) is not particularly set. The specular glossiness difference (G(20)-G(85)) may be -75 or more, -45 or more, or -15 or more.

The angle θMAX at which the maximum brightness value BMAX in the brightness distribution on the light exit surface 31 of the light guide plate 30 is obtained does not deviate significantly from 60°. Therefore, the light emitted from the light exit surface 31 or rear surface 32 of the light guide plate 30 at an emission angle θk of approximately 60° can be effectively used in the surface light source device 20 with high efficiency. For this reason, the specular glossiness G(60) at an incidence angle of 60° of the reflecting sheet 70 may be closer to the specular glossiness G(85) at an incidence angle of 85° of the reflecting sheet 70 than the specular glossiness G(20) at an incidence angle of 20° of the reflecting sheet 70.

From this point of view, the specular gloss G(20) of the reflective sheet 70 at an incidence angle of 20°, the specular gloss G(60) of the reflective sheet 70 at an incidence angle of 60°, and the specular gloss G(85) of the reflective sheet 70 at an incidence angle of 85° may satisfy the following relationship.
|G(60)-G(85)|＜|G(20)-G(60)|
According to this example, it is possible to diffuse light incident at a small angle of incidence while suppressing diffusion of light incident at a large angle of incidence, thereby efficiently expanding the viewing angle in display device 10 using surface light source device 20 while suppressing a decrease in the maximum luminance.

Similarly, the specular gloss G(20) of the reflective sheet 70 at an incident angle of 20°, the specular gloss G(60) of the reflective sheet 70 at an incident angle of 60°, and the specular gloss G(85) of the reflective sheet 70 at an incident angle of 85° may satisfy the following relationship.
|G(60)-G(85)|/((G(60)+G(85))/2)＜|G(20)-G(60)|/((G(20)+G(60))/2)
According to this example, it is possible to diffuse light incident at a small angle of incidence while suppressing diffusion of light incident at a large angle of incidence, thereby efficiently expanding the viewing angle in display device 10 using surface light source device 20 while suppressing a decrease in the maximum luminance.

"|G(60)-G(85)|" means the absolute value of the difference between the specular gloss G(60) of the reflective sheet 70 at an incident angle of 60° and the specular gloss G(85) of the reflective sheet 70 at an incident angle of 85°.
"|G(20)-G(60)|" means the absolute value of the difference between the specular gloss G(20) of the reflective sheet 70 at an incident angle of 20° and the specular gloss G(60) of the reflective sheet 70 at an incident angle of 60°.

A lower limit may be set for the specular glossiness G(60) of the reflective sheet 70 at an incidence angle of 60°. The specular glossiness G(60) of the reflective sheet 70 at an incidence angle of 60° may be 85 or more, 95 or more, or 105 or more, to two significant digits. By setting a lower limit for the specular glossiness G(85) of the reflective sheet 70 at an incidence angle of 60°, it is possible to suppress the diffusion of light that is incident on the reflective sheet 70 at a large incidence angle. This makes it possible to suppress a decrease in the maximum brightness.

An upper limit may be set for the specular glossiness G(60) of the reflective sheet 70 at an incidence angle of 60°. By setting an upper limit for the specular glossiness G(60) of the reflective sheet 70 at an incidence angle of 60°, the viewing angle can be expanded. The specular glossiness G(60) of the reflective sheet 70 at an incidence angle of 60° may be, to two significant digits, 140 or less, 130 or less, or 120 or less.

The ratio value (G(85)/G(60)) of the specular glossiness G(60) of the reflective sheet 70 at an incidence angle of 60° to the specular glossiness G(85) of the reflective sheet 70 at an incidence angle of 85° may be 0.55 or more, 0.65 or more, or 0.75 or more. The ratio value (G(85)/G(60)) may be 2.0 or less, 1.5 or less, or 1.0 or less. By setting an upper and lower limit for the ratio value (G(85)/G(60)), it is possible to diffuse light incident at a small incidence angle while suppressing the diffusion of light incident at a large incidence angle. This makes it possible to efficiently expand the viewing angle in the display device 10 using the surface light source device 20 while suppressing the decrease in the maximum luminance.

The difference (G(60)-G(85)) between the specular glossiness G(60) at an incidence angle of 60° of the reflective sheet 70 and the specular glossiness G(85) at an incidence angle of 85° of the reflective sheet 70 may be 22 or less, 21 or less, or 20 or less to two significant digits. The difference in specular glossiness (G(60)-G(85)) may be 10 or more, 15 or more, or 18 or more to two significant digits. By setting an upper and lower limit for the difference in specular glossiness (G(60)-G(85)), it is possible to diffuse light incident at a small incidence angle while suppressing the diffusion of light incident at a large incidence angle. This makes it possible to efficiently expand the viewing angle in the display device 10 using the surface light source device 20 while suppressing the decrease in the maximum luminance.

Specular gloss is measured in accordance with JIS Z 8741:1997, except that the angles of incidence are set to 20°, 60°, and 85°. The measurement environment for measuring specular gloss is a temperature of 23°C ± 2°C and a relative humidity of 50% ± 5%. The sample to be measured is placed in the measurement environment for 16 hours before starting the measurement. Before measuring specular gloss, the light source of the measuring device is turned on for 15 minutes to stabilize the light source output.

When measuring specular gloss, a black plate is attached to the back side of the sample to be measured, opposite the incident surface, via an optically transparent adhesive sheet. The optically transparent adhesive sheet is Panac's "Panaclean PD-S1". The black plate is Kuraray's "Comoglass DFA2CG 502K (black) series".

9, the reflective sheet 70 may include a plurality of layers. As shown in Fig. 9, the reflective sheet 70 may include, in this order from the light guide plate 30, a surface layer 75, an internal diffusion layer 74, and a metal layer 72. According to the reflective sheet 70 having such a configuration, it is possible to realize one or more of the above-mentioned characteristics of the reflective sheet, specifically, the following optical characteristics.
The total light reflectance of the reflective sheet is 75% or more and 100% or less. The diffuse reflectance of the reflective sheet is 65% or more and 90% or less. G(20)≦200 and 75≦G(85)
・|G(60)-G(85)|＜|G(20)-G(60)|
・ G(60)-G(85)|/((G(60)+G(85))/2)＜|G(20)-G(60)|/((G(20)+G(60))/2)
75≦G(85)≦110
0.85≦G(85)/G(20)
・ G(20)-G(85)≦0
Here, G(20) is the specular gloss of the reflective sheet 70 at an incidence angle of 20°. G(60) is the specular gloss of the reflective sheet 70 at an incidence angle of 60°. G(85) is the specular gloss of the reflective sheet 70 at an incidence angle of 85°. For example, by strengthening the internal diffusivity in the internal diffusion layer 74, G(20) can be effectively increased while suppressing increases in G(60) and G(85). For example, by strengthening the surface diffusivity in the surface layer 75, G(60) and G(85) can be effectively increased while suppressing increases in G(20).

The surface layer 75 functions as an adhesion prevention layer. The surface layer 75 prevents the reflection sheet 70 from coming into surface contact with the light guide plate 30, and prevents the reflection sheet 70 from sticking to the light guide plate 30. The surface layer 75 may be a layer having an uneven surface. The surface layer 75 may be formed by embossing and have unevenness. The surface layer 75 contains particles and a binder resin, and may have unevenness caused by the particles.

The internal diffusion layer 74 diffuses incident light. By providing the internal diffusion layer 74, the diffuse reflectance of the reflective sheet 70 can be increased. With the combination of the surface layer 75 and the internal diffusion layer 74, the surface layer 75 reflects light with a large angle of incidence. The internal diffusion layer 74 diffuses light with a small angle of incidence that passes through the surface layer 75. By reducing the diffuse reflectance at the surface layer 75, the diffuse reflectance of the reflective sheet 70 having the internal diffusion layer 74 and the surface layer 75 changes depending on the angle of incidence.

As shown in FIG. 9, the internal diffusion layer 74 may include a base layer 74a and a light diffusion component 74b held in the base layer 74a. The internal diffusion layer 74 may include, as the light diffusion component 74b, one or more of a metal compound, a porous substance containing a gas, resin beads holding a metal compound around it, white fine particles, and simple air bubbles. The base layer 74a may be a transparent resin. The material of the base layer 74a may be a transparent resin mainly composed of one or more of acrylic resin, polystyrene resin, polycarbonate resin, polyethylene terephthalate resin, polyacrylonitrile resin, etc.

The metal layer 72 reflects light that has passed through the surface layer 75 and the internal diffusion layer 74. By providing the metal layer 72, the total light reflectance of the reflective sheet 70 can be increased. The metal layer 72 may be a metal film having a high reflectance. The metal layer 72 may be a vapor-deposited film of silver.

As shown in FIG. 9, the reflective sheet 70 may further include a support 71 and an anchor layer 73. As in the illustrated example, the reflective sheet 70 may include, in order from the light guide plate 30, a surface layer 75, an internal diffusion layer 74, an anchor layer 73, a metal layer 72, and a support 71. The support 71 supports the other layers included in the reflective sheet 70. The support 71 may be a plate made of resin, metal, paper, or the like. The anchor layer 73 may be a layer that improves adhesion between the metal layer 72 and the internal diffusion layer 74.

Table 1 shows the reflection characteristics of the reflective sheets according to Samples 1-3. The reflective sheet 70 according to Sample 1 had the configuration shown in FIG. 9. That is, the reflective sheet according to Sample 1 included a support 71, a metal layer 72 as a silver vapor deposition layer, an anchor layer 73, an internal diffusion layer 74, and a surface layer 75. The reflective sheet according to Sample 2 included a support 71, a metal layer 72 as a silver vapor deposition layer, an anchor layer 73, and an internal diffusion layer 74. In Samples 1 and 2, the internal diffusion layer 74 was a polyethylene terephthalate sheet containing silica particles. The reflective sheet according to Sample 3 included a support 71 and a metal layer 72 as a silver vapor deposition layer. In the reflective sheets according to Samples 1 to 3, the same layers were used for the common layers 71, 72, 73, and 74. The total light reflectance, regular reflectance (specular reflectance), diffuse reflectance, and specular gloss were measured for the reflective sheets according to Samples 1 to 3. The total light reflectance, regular reflectance (specular reflectance), and diffuse reflectance were measured using a UV-Vis-Near-Infrared Spectrophotometer UH4150 manufactured by Hitachi High-Tech Science Corporation. The specular gloss was measured using a glossmeter (Model 14563) manufactured by BYK Gardner, with the specular gloss at an incidence angle of 20° G(20), the specular gloss at an incidence angle of 60° G(60), and the specular gloss at an incidence angle of 85° G(85).

From the results in Table 1, the reflection characteristics of Sample 1 are similar to those of Sample 2, which has diffuse reflection characteristics, for light with an incident angle of 20°. On the other hand, the reflection characteristics of Sample 1 are similar to those of Sample 3, which has specular reflection characteristics, for light with an incident angle of 85°.

Next, the functions of the illustrated display device 10, surface light source device 20, and optical member 28 will be described.

As shown in FIG. 3, light is emitted from the light emitter 25. Light L31 and L32 pass through the light entrance surface 33 and enter the light guide plate 30. As shown in FIG. 3, light L31 and L32 are reflected at the light exit surface 31 and the back surface 32 within the light guide plate 30. The reflection at the light exit surface 31 and the back surface 32 is total reflection due to the difference in refractive index between the material constituting the light guide plate 30 and air. Light L31 and L32 are repeatedly reflected at the light exit surface 31 and the back surface 32, and travel in the first direction (light guide direction) D1 within the light guide plate 30.

In the illustrated example, the back surface 32 includes an inclined surface 37. The inclined surface 37 is inclined so as to approach the light exit surface 31 as it moves from the light entrance surface 33 toward the opposite surface 34. The inclined surface 37 forms the back surface 32 together with the connection surface 39 and the flat surface 38. In the illustrated example, the connection surface 39 extends in the third direction D3. Therefore, most of the light L31, L32 traveling through the light guide plate 30 to the first side in the first direction D1 enters the inclined surface 37 or the flat surface 38 of the back surface 32 without entering the connection surface 39. As shown in FIG. 6, the incident angle θa2 when the light L61 enters the inclined surface 37 is smaller than the incident angle θa1 when the light L61 immediately before enters the light exit surface 31 by the inclined surface angle θy of the inclined surface 37. Next, the angle of incidence θa3 when the light L61 re-enters the light output surface 31 is smaller than the angle of incidence θa2 when the light L61 immediately before enters the inclined surface 37 by the inclined surface angle θy of the inclined surface 37. That is, by being reflected by the inclined surface 37, the angle of incidence of the light is reduced by the inclined surface angle θy of the inclined surface 37 each time the light is reflected by the light output surface 31 and the back surface 32. As a result, the angle of incidence of the light L31, L32, and L61 traveling through the light guide plate 30 on the light output surface 31 is reduced by twice the angle of the inclined surface θy each time the light is reflected by the inclined surface 37.

In this way, the angle of incidence of light on the light output surface 31 and the back surface 32 gradually decreases due to reflection at the inclined surface 37, and becomes less than the critical angle of total reflection. Light that is incident on the light output surface 31 or the back surface 32 at an angle of incidence less than the critical angle of total reflection can be emitted from the light guide plate 30. The light L31, L32 emitted from the light output surface 31 travels toward the optical sheet 50 arranged on the light output side of the light guide plate 30. On the other hand, the light L32 emitted from the back surface 32 is reflected by the reflective sheet 70 arranged on the back surface of the light guide plate 30, enters the light guide plate 30, and travels inside the light guide plate 30.

In the illustrated example, the proportion of the inclined surface 37 on the rear surface 32 increases as one approaches the opposite surface 34 from the light entrance surface 33 along the light guide direction. This configuration makes it possible to prevent the amount of light emitted from the light exit surface 31 of the light guide plate 30 from becoming too large in areas close to the light entrance surface 33 of the light guide plate 30, where the amount of emitted light tends to be large. It is possible to ensure a sufficient amount of light emitted from the light exit surface 31 of the light guide plate 30 in areas away from the light entrance surface 33 of the light guide plate 30, where the amount of emitted light tends to be small. This makes it possible to uniformize the amount of emitted light along the first direction D1, which is the light guide direction.

The emission angle θk of the light emitted from the light guide plate 30 becomes large as shown in FIG. 6 because the light had previously traveled mainly in the first direction D1 within the light guide plate 30. The emission angle means the angle (°) that the traveling direction of the emitted light makes with respect to the normal direction of the sheet-like member from which the light is emitted. The emission angle is an angle between 0° and 90°. The emission angle θk is biased within a narrow angle range that is a relatively large angle. The light emitted from the light guide plate 30 is in a direction within a narrow angle range that is significantly inclined with respect to the third direction D3.

Figure 10 shows an example of the angular distribution of luminance measured on the light output surface 31 of the light guide plate 30. This angular distribution of luminance is measured for a surface light source device 20 from which the configuration closer to the light emitting surface 21 than the light guide plate 30 has been removed. The luminance distribution shown in Figure 10 is the result of an actual investigation of the luminance on the light output surface 31 in each direction in a plane parallel to both the first direction D1 and the third direction D3. In the graph shown in Figure 10, the angle of the direction in which the luminance was measured, which is written on the horizontal axis, is a positive value for the angle inclined from the third direction D3 to the first side in the first direction D1.

The luminance angle distribution shown in FIG. 10 was investigated for the surface light source device 20 adopting the above-mentioned shape and size range. The luminance angle distribution is the distribution of luminance on the light output surface 31 of the light guide plate 30 in each direction in a plane parallel to both the third direction D3 and the first direction D1 of the light guide plate 30. The angle θMAX in the luminance angle distribution can satisfy the formula (1). By adjusting the shape and size of each component, the angle θMAX in the luminance angle distribution may further satisfy the formula (2). The angle θMAX is the angle at which the direction at which the maximum luminance value BMAX in the luminance angle distribution is obtained is tilted from the third direction D3 of the light guide plate 30 to the first side in the first direction D1.
60°≦θMAX≦85° (1)
70°≦θMAX≦80° (2)

The half-width at half maximum HW in the luminance angular distribution can satisfy formula (3). By adjusting the shape and dimensions of each component, formula (4) may be satisfied. The half-width at half maximum HW is the magnitude of the angle at which a direction in which a luminance BF that is half the maximum luminance value, located between the third direction D3 of the light guide plate 30 and the direction in which the maximum luminance value BMAX is obtained, is tilted toward the other side in the first direction D1 from the direction in which the maximum luminance value is obtained.
5°≦HW≦25° (3)
5°≦HW≦15° ... (4)

The light emitted from the light guide plate 30 then enters the optical sheet 50. As described above, the optical sheet 50 includes unit prisms 60 whose apexes 63 protrude toward the light guide plate 30. The longitudinal direction of the unit prisms 60 intersects with the light guide direction D1 of the light guide plate 30. In the example shown in FIG. 3, the longitudinal direction of the unit prisms 60 is perpendicular to the light guide direction D1.

As shown in Figures 3 and 6, light L31, L32, and L61 traveling toward the optical sheet 50 passes through the second prism surface 62 of the unit prism 60 and enters the unit prism 60. As shown in Figures 3 and 6, light L31, L32, and L61 is reflected by the second prism surface 62 and the first prism surface 61 facing the first direction D1, changing its traveling direction. The reflection at the first prism surface 61 may be total reflection.

In a cross section parallel to both the third direction D3 and the first direction D1 shown in FIG. 3 and FIG. 6, i.e., in the main cross section of the optical sheet, the light L31, L32, and L61 traveling in a direction within a narrow angle range greatly inclined from the third direction D3 is bent by total reflection at the first prism surface 61 so that the angle of the traveling direction with respect to the third direction D3 becomes small. The optical sheet 50 raises the traveling direction of the light traveling in a direction greatly inclined to the third direction D3 to follow the third direction D3 by reflection at the unit prisms 60. In combination with the light guide plate 30 satisfying the above-mentioned conditions (1) and (3), the optical sheet 50 can exhibit an excellent light path adjustment function. Furthermore, in combination with the light guide plate 30 satisfying the above-mentioned conditions (2) and (4), the optical sheet 50 can exhibit an even better light path adjustment function.

The light whose optical path has been adjusted by the unit prisms 60 travels toward the first surface 51 of the optical sheet 50. The first surface 51 constitutes the light-emitting surface 21 of the surface light source device 20. The light passes through the light-emitting surface 21 and is emitted from the optical member 28 and the optical sheet 50. The light emitted from the light-emitting surface 21 illuminates the display panel 15 from behind. The display panel 15 forms an image on the display surface 11 by selectively transmitting the light from the surface light source device 20 for each pixel. The viewer can observe the image on the display surface 11.

However, conventional optical members and conventional optical sheets that include a light guide plate that includes an inclined surface and an optical sheet that includes a prism surface facing the light guide plate exhibit a strong light-collecting function. As a result, conventional optical members and conventional optical sheets can increase the luminance in a specific direction, such as the front direction. However, the amount of light in directions other than the specific direction is small. In a display device that uses a surface light source device, the viewing angle is narrow. In contrast, according to the present embodiment, as described below, the viewing angle in a display device that uses a surface light source device can be efficiently expanded.

According to this embodiment, the angle of incidence of the light traveling through the light guide plate 30 on the light output surface 31 is reduced by twice the angle of the inclined surface angle θy of the inclined surface 37 each time the light travels through the light guide plate 30 and is reflected by the inclined surface 37. The light L31 and L32 traveling through the light guide plate 30 can be emitted from the light output surface 31 when the angle of incidence on the light output surface 31 becomes less than the total reflection critical angle. By setting the inclined surface angle θy to a small value within the above-mentioned range, the light emitted from the light guide plate 30 travels in a direction within a narrow angle range that is greatly inclined with respect to the third direction D3. In other words, the light guide plate can limit the emission direction of the light from the light output surface 31 to a narrow angle range that is greatly inclined with respect to the third direction D3. The light emitted from the light guide plate 30 passes through the second prism surface 62 and enters the optical sheet 50. The light that passes through the second prism surface 62 is reflected by the first prism surface 61. Reflection from the first prism surface 61 can significantly change the direction in which light travels. Even after reflection from the first prism surface 61, the light reflected from the first prism surface 61 can travel in a direction within a narrow angle range.

As described above, the inclination angle difference (dθ = first element surface inclination angle θxe1 - third element surface inclination angle θxe3) between the first element surface 66 and the third element surface 68 of the first prism surface 61 may be 5° or more. The inclination angle difference dθ between the first element surface 66 and the third element surface 68 may be greater than twice the inclination surface angle of the inclined surface 37 with respect to the first direction D1. The inclination angle difference dθ (°) between the first element surface 66 and the third element surface 68 may be greater than the half-width at half maximum HW (°) in the angular distribution of luminance at the light output surface 31. Such an inclination angle difference dθ of the first prism surface 61 is usually greater than the variation angle of the traveling direction of light that passes through the second prism surface 62 and enters the optical sheet 50. Therefore, by setting the inclination angle difference dθ of the first prism surface 61 in this manner, light that travels in a direction within a narrow angle range and enters the first prism surface 61 can be effectively diffused. This allows the viewing angle of the display device 10 using this surface light source device 20 to be expanded.

In particular, in this embodiment, the light incident on the first prism surface 61 of the optical sheet 50 travels in a direction within a narrow angle range due to the optical path adjustment function of the light guide plate 30. The concentrated light is diffused to a desired degree using the first prism surface 61. Therefore, excessive light diffusion at the first prism surface 61 can be avoided. By suppressing the generation of stray light and light loss, the light source light can be used with high efficiency. As a result, in the display device 10 using the surface light source device 20, the viewing angle can be efficiently expanded while sufficiently suppressing the decrease in the maximum brightness.

In addition, Patent Document 1 (JP Patent Publication No. 2016-95347), which was described as the conventional technology, also proposes providing a folded surface to the unit prism. In this conventional technology, the inclined surface angle of the element surface included in the unit prism with respect to the third direction D3 becomes smaller from the tip to the base end of the unit prism. Patent Document 1 proposes ensuring an excellent light-collecting function by arranging an element surface with a large angle with respect to the third direction D3 on the tip side where relatively inclined light is likely to enter, and an element surface with a small angle with respect to the third direction D3 on the base end side where relatively upright light is likely to enter. In this conventional technology, the inclination angle difference of the element surfaces included in the first prism surface is not considered, and a lower limit of the inclination angle difference is not set, so that the prism surface exerts a light-collecting function opposite to the diffusion function. From this perspective, it can be said that the effect of imparting a diffusion function to the first prism surface 61 by setting a lower limit to the inclination angle difference dθ between the first element surface 66 and the third element surface 68 of the first prism surface 61 is remarkable and exceeds the range predicted from the state of the art.

As described above, the light emitted from the light output surface of the light guide plate travels in a direction within a narrow angle range that is greatly inclined with respect to the front direction. In combination with such a light guide plate, the reflection at the reflective sheet has traditionally been specular reflection. Specular reflection can prevent the direction of light travelling within the light guide plate before it is emitted from the back surface from differing greatly from the direction of light travelling after being reflected by the reflective sheet and re-entering the light guide plate. This allows the light path adjustment function of the light guide plate and reflective sheet to effectively function even with respect to the re-entering light. In other words, by making the reflection of the reflective sheet specular reflection, the direction of travel of the light emitted from the light output surface of the light guide plate can be within a narrow angle range that is greatly inclined with respect to the front direction.

In contrast, in this embodiment, the diffuse reflectance of the reflective sheet 70 may be 65% or more. In other words, the reflection from the reflective sheet may be mainly diffuse reflection.

The light guide plate 30 having the connection surface 39 and the inclined surface 37 can be manufactured by extrusion molding, UV molding, injection molding, etc., as described above. However, it is assumed that the end of the inclined surface 37 and the part adjacent to the connection surface 39 of the back surface 32, such as the end of the inclined surface 37 and the end of the flat surface 38, may not be given a predetermined shape with sufficient precision. The light emitted from the back surface 32 also includes light diffused in the non-effective area of the back surface 32 that has not been processed with sufficient precision. In addition, there is also light that is reflected by the reflective sheet and then enters the connection surface and is diffused. In other words, the light emitted from the back surface includes light emitted from the light guide plate as diffused light.

By making the reflection by the reflective sheet 70 diffuse reflection, only the light emitted from the rear surface 32 can be appropriately diffused by the reflective sheet 70. The light that does not exit from the rear surface 32 and exits from the light exit surface 31 is subjected to the optical path adjustment function of the light guide plate 30 with high precision, and is not diffused by the reflective sheet 70. Therefore, while maintaining a strong directivity in the direction of emission from the light exit surface 31 of the light guide plate 30, other light can be diffused uniformly. This makes it possible to efficiently expand the viewing angle while sufficiently suppressing the decrease in maximum luminance in the display device 10 using the surface light source device 20.

The diffuse reflectance of the reflective sheet 70 may be 90% or less. By setting an upper limit on the diffuse reflectance, it is possible to ensure a specular reflection component. This makes it possible to suppress a decrease in the maximum brightness.

In addition, the specular glossiness G(85) of the reflective sheet 70 at an incidence angle of 85° may be set to 75 or more, and the specular glossiness G(20) of the reflective sheet 70 at an incidence angle of 20° may be set to 200 or less. The specular glossiness G(85) of the reflective sheet 70 at an incidence angle of 85° may be set to 75 or more and 110 or less. The ratio (G(85)/G(20)) of the specular glossiness G(85) of the reflective sheet 70 at an incidence angle of 85° to the specular glossiness G(20) of the reflective sheet 70 at an incidence angle of 20° may be set to 0.85 or more. The difference (G(20)-G(85)) between the specular glossiness G(20) of the reflective sheet 70 at an incidence angle of 20° and the specular glossiness G(85) of the reflective sheet 70 at an incidence angle of 85° may be set to 0 or less. That is, the reflection of light incident on the reflecting sheet 70 at an angle of incidence of 85° may contain a large regular reflection component (i.e., specular reflection component). According to one or more of these configurations, it is possible to increase the specular reflectance of light incident on the reflecting sheet 70 at large angles of incidence, including 85°, while increasing the diffuse reflectance of light incident on the reflecting sheet 70 at small angles of incidence, including 20°.

The angle of incidence is large for light that is emitted from the rear surface 32 by the light guide plate 30 after the light path adjustment function is appropriately applied, that is, light that travels from the rear surface 32 of the light guide plate 30 in a direction that is greatly inclined with respect to the third direction D3. Such light is incident on the reflection sheet 70 at a large angle of incidence, and is likely to be specularly reflected by the reflection sheet 70 whose specular gloss has been adjusted as described above. Therefore, the light that is emitted from the rear surface 32 by the light guide plate 30 after the light path adjustment function is appropriately applied can be selectively specularly reflected by the reflection sheet 70 and returned to the light guide plate 30 while maintaining its traveling direction. Such light can then be emitted from the light exit surface 31 of the light guide plate 30 in a direction that is greatly inclined with respect to the third direction D3. The light that is emitted from the light exit surface 31 of the light guide plate 30 in a direction that is greatly inclined with respect to the third direction D3 can travel in a direction in which the maximum brightness is obtained. Therefore, the reflection sheet 70 whose specular gloss has been adjusted as described above can maintain the traveling direction of light that is likely to contribute to the maximum brightness.

Some of the light emitted from the rear surface 32 of the light guide plate 30 is not subject to the optical path adjustment function caused by the inclined surface 37 of the light guide plate 30. This light is not emitted in a direction in which maximum brightness is obtained. The emission angle of such light from the light guide plate 30 is smaller than the emission angle of light that has been subject to the optical path adjustment function caused by the inclined surface 37 of the light guide plate 30. The reflective sheet 70 diffusely reflects light that is incident on the reflective sheet 70 at a small angle of incidence with a high diffuse reflectance. Therefore, the reflective sheet 70 can selectively diffusely reflect light that does not contribute to maximum brightness.

As a result, other light can be diffused uniformly while maintaining strong directivity in the direction of emission from the light output surface 31 of the light guide plate 30. This makes it possible to efficiently expand the viewing angle in a display device 10 using the surface light source device 20 while sufficiently suppressing a decrease in the maximum luminance.

As shown in FIG. 9, the reflective sheet 70 may include, in order from the light guide plate 30, a surface layer 75, an internal diffusion layer 74, and a metal layer 72. With such a reflective sheet 70, the light L91 traveling in a direction greatly inclined with respect to the third direction D3 can be reflected with high reflectance by the surface layer 75. That is, the light L91 having a large incident angle can be mainly reflected by the surface layer 75. The light L92, L93 traveling in a direction not greatly inclined with respect to the third direction D3 can be reflected by the internal diffusion layer 74 and the metal layer 72. That is, the light L92, L93 having a small incident angle can be mainly reflected by the internal diffusion layer 74 and the metal layer 72. With this reflective sheet 70, the diffuse reflectance can be adjusted according to the incident angle to the reflective sheet 70. For example, by reducing the surface roughness Ra, Rz of the surface layer 75 and strengthening the internal diffusion of the internal diffusion layer 74, the light L91 traveling in a direction greatly inclined to the third direction D3 can be mainly specularly reflected on the surface of the surface layer 75. The light L92, L93 traveling in a direction not greatly inclined to the third direction D3 can be mainly diffusely reflected inside the internal diffusion layer 74. According to this example, the reflection sheet 70 maintains the traveling direction of the light L91 that easily contributes to the maximum brightness, and selectively diffusely reflects the light L92, L93 that does not easily contribute to the maximum brightness. That is, while maintaining a strong directivity in the emission direction from the light output surface 31 of the light guide plate 30, other light can be diffused uniformly. As a result, in the display device 10 using the surface light source device 20, the viewing angle can be efficiently expanded while sufficiently suppressing the decrease in the maximum brightness.

Furthermore, the specular glossiness G(60) of the reflective sheet 70 at an incident angle of 60° and the specular glossiness G(85) of the reflective sheet 70 at an incident angle of 85° may satisfy any one of the following relationships.
・0.55≦G(85)/G(60)≦2.0
・15≦G(60)-G(85)≦22
Light emitted from the light exit surface 31 or the back surface 32 of the light guide plate 30 at an emission angle θk of 60° can also be effectively utilized with high efficiency in the surface light source device 20. Therefore, according to the reflecting sheet 70 in which these relationships are satisfied, the maximum luminance can be efficiently improved. Alternatively, the luminance can be improved in a direction that is not greatly inclined with respect to the direction in which the maximum luminance is obtained.

In addition, the specular gloss G(20) of the reflective sheet 70 at an incident angle of 20°, the specular gloss G(60) of the reflective sheet 70 at an incident angle of 60°, and the specular gloss G(85) of the reflective sheet 70 at an incident angle of 85° may satisfy any of the following relationships.
・|G(60)-G(85)|＜|G(20)-G(60)|
・|G(60)-G(85)|/((G(60)+G(85))/2)＜|G(20)-G(60)|/((G(20)+G(60))/2)
The reflective sheet 70 that satisfies these relationships can specularly reflect light emitted in a direction in which the maximum brightness is obtained and in a direction with a small inclination angle with respect to the direction with a high reflectance. Therefore, it is possible to diffuse light incident at a small incidence angle while suppressing the diffusion of light incident at a large incidence angle. This makes it possible to efficiently expand the viewing angle in the display device 10 that uses the surface light source device 20 while suppressing the decrease in the maximum brightness.

As described above, the arrangement pitch PC of the connection surface 39 in the first direction D1 may be larger than the arrangement pitch PP1 of the pixels 16 in the first direction D1 of the display panel 15. The arrangement pitch PC of the connection surface 39 in the first direction D1 may be 0.060 mm or more. By lengthening the arrangement pitch PC of the connection surface 39 in this way, the number of connection surfaces 39 and the number of inclined surfaces 37 can be reduced. As described above, the light guide plate 30 having the connection surface 39 and the inclined surface 37 can be manufactured by extrusion molding, UV molding, injection molding, etc. However, it is also assumed that the end of the inclined surface 37 and the part adjacent to the connection surface 39 of the back surface 32, such as the end of the inclined surface 37 and the end of the flat surface 38, cannot be given a predetermined shape with sufficient accuracy. Light that enters the non-effective area of the back surface 32 that has not been processed with sufficient accuracy does not proceed in the expected direction. These lights can become stray light. Even if these lights are emitted from the light-emitting surface 31, they can become light that cannot form an image on the display panel 15. That is, light that enters the non-effective area of the back surface 32 may not be used effectively. In contrast, when the arrangement pitch PC of the connection surfaces 39 is increased, the number of connection surfaces 39 and the number of inclined surfaces 37 are reduced, and the proportion of the non-effective area on the back surface 32 can be reduced. Therefore, the light path adjustment function of the light guide plate 30 works more effectively. This improves the efficiency of use of the light from the light source, and both an increase in the viewing angle and an increase in brightness can be achieved. For example, in a display device 10 using a surface light source device 20, the viewing angle can be efficiently increased while sufficiently suppressing a decrease in the maximum brightness.

If the arrangement pitch of the connection surface in the first direction is made longer than the arrangement pitch of the pixels in the first direction of the display panel, moire is more likely to occur. For this reason, in conventional surface light source devices, the arrangement pitch of the connection surface in the first direction is shorter than the arrangement pitch of the pixels in the first direction of the display panel.

After examining this point, it was found that there exists an arrangement pitch PC of the connection surface 39 in the first direction D1 that can make the moire less noticeable even if it is longer than the arrangement pitch PP1 of the pixels 16 along the first direction D1 of the display panel 15. Furthermore, by adjusting the processing conditions within the range that has been conventionally selected, it is possible to reduce the variation in the arrangement pitch PC of the connection surface 39 in the first direction D1. As a result, it was confirmed that the problem of moire occurrence can be addressed even if the arrangement pitch PC of the connection surface in the first direction is made longer than the conventional length.

In addition, if the arrangement pitch of the connection surfaces in the first direction is increased, uneven brightness may occur due to the arrangement of the connection surfaces and inclined surfaces. For this reason, in conventional surface light source devices, the arrangement pitch of the connection surfaces in the first direction is set short and is shorter than the arrangement pitch of the pixels along the first direction of the display panel.

After considering this point, it was found that by setting the arrangement pitch PC of the connection surfaces 39 in the first direction D1 to 0.37 mm or less, or by setting the ratio of the arrangement pitch PC of the connection surfaces 39 in the first direction D1 to the arrangement pitch PP1 of the pixels 16 of the display panel 15 in the first direction D1 to 2.2 or less, it was possible to make the unevenness in brightness caused by the arrangement of the connection surfaces 39 and the inclined surfaces 37 less noticeable.

In addition, by imparting a diffuse reflection function to the reflective sheet 70, it is possible to effectively make the unevenness in brightness caused by the arrangement of the connection surface 39 and the inclined surface 37 less noticeable. It is believed that the unevenness in brightness caused by the arrangement of the connection surface 39 and the inclined surface 37 was also caused by the light emitted from the rear surface 32 of the light guide plate 30. By directly diffusing the light that causes the unevenness in brightness with the reflective sheet 70, excessive diffusion can be avoided and the unevenness in brightness can be made less noticeable efficiently.

As described above, in this embodiment, the optical member 28 includes a light guide plate 30 including a light output surface 31 and a back surface 32 facing the light output surface 31, and an optical sheet 50 including a prism surface 53 facing the light output surface 31. The back surface 32 includes a plurality of inclined surfaces 37 and a connection surface 39 arranged alternately in the first direction D1. The inclined surface 37 is inclined with respect to the first direction D1 so as to approach the light output surface 31 on the first side in the first direction D1. The optical sheet 50 includes a plurality of unit prisms 60 arranged in the first direction D1. Each unit prism 60 includes a first prism surface 61 located on the first side in the first direction D1 and a second prism surface 62 facing the first prism surface 61 from the first direction D1. The prism surface 53 includes the first prism surface 61 and the second prism surface 62. The first prism surface 61 includes a first element surface 66, a second element surface 67, and a third element surface 68. The second element surface 67 is located between the first element surface 66 and the third element surface 68. The inclination angle difference dθ between the first element surface 66 and the third element surface 68 of the first prism surface 61 may be 5° or more. The inclination angle difference dθ between the first element surface 66 and the third element surface 68 may be greater than twice the inclination surface angle of the inclined surface 37 with respect to the first direction D1. The inclination angle difference dθ (°) between the first element surface 66 and the third element surface 68 may be greater than the half-width at half maximum HW (°) in the angular distribution of luminance on the light output surface 31. According to this embodiment, the inclination angle difference dθ of the first prism surface 61 can be greater than the variation angle in the traveling direction of light that passes through the second prism surface 62 and enters the optical sheet 50. Therefore, the viewing angle in the display device 10 using the surface light source device 20 can be efficiently expanded.

In this embodiment, the optical member 28 includes a light guide plate 30 including a light output surface 31 and a back surface 32 facing the light output surface 31, and a reflection sheet 70 facing the back surface 32. The back surface 32 includes a plurality of inclined surfaces 37 and a connection surface 39 arranged alternately in the first direction D1. The inclined surface 37 is inclined with respect to the first direction D1 so as to approach the light output surface 31 on the first side in the first direction D1. The diffuse reflectance of the reflection sheet 70 may be 50% or more. The light emitted from the back surface 32 includes the light emitted from the light guide plate 30 as diffuse light. By making the 9 reflections at the reflection sheet 70 diffuse reflections, the light emitted from the back surface 32 is appropriately diffused by the reflection sheet 70, thereby maintaining a strong directivity in the direction of emission from the light output surface 31 of the light guide plate 30, and other light can be diffused uniformly. This allows the display device 10 using the surface light source device 20 to efficiently expand the viewing angle while adequately suppressing the decrease in maximum luminance.

In this embodiment, the optical member 28 includes a light guide plate 30 including a light output surface 31 and a back surface 32 facing the light output surface 31, and a reflecting sheet 70 facing the back surface 32. The back surface 32 includes a plurality of inclined surfaces 37 and a connecting surface 39 arranged alternately in a first direction D1. The inclined surfaces 37 are inclined with respect to the first direction D1 so as to approach the light output surface 31 on the first side in the first direction D1. The reflecting sheet 70 may be configured to satisfy any one or more of the following. Note that G(20) is the specular gloss of the reflecting sheet 70 at an incident angle of 20°. G(60) is the specular gloss of the reflecting sheet 70 at an incident angle of 60°. G(85) is the specular gloss of the reflecting sheet 70 at an incident angle of 85°.

The reflective sheet 70 includes, in this order from the light guide plate 30, a surface layer 75, an internal diffusion layer 74, and a metal layer 72, and the internal diffusion layer 74 includes a base layer 74a and a light diffusion component 74b held within the base layer 74a. G(20)≦200 and 75≦G(85).
・|G(60)-G(85)|＜|G(20)-G(60)|
・ G(60)-G(85)|/((G(60)+G(85))/2)＜|G(20)-G(60)|/((G(20)+G(60))/2)
The diffuse reflectance of the reflective sheet 70 is 65% or more and 90% or less. 75≦G(85)≦110
0.85≦G(85)/G(20)
・ G(20)-G(85)≦0

A reflective sheet 70 that satisfies any one of the conditions can maintain the direction of travel of light that is likely to contribute to the maximum brightness, and selectively diffuse and reflect light that is unlikely to contribute to the maximum brightness. In other words, it can uniformly diffuse other light while maintaining strong directivity in the direction of emission from the light output surface 31 of the light guide plate 30. This makes it possible to efficiently expand the viewing angle in a display device 10 that uses a surface light source device 20, while sufficiently suppressing a decrease in the maximum brightness.

In this embodiment, the optical member 28 includes a light guide plate 30 including a light output surface 31 and a back surface 32 facing the light output surface 31, and an optical sheet 50 including a prism surface 53 facing the light output surface 31. The back surface 32 includes a plurality of inclined surfaces 37 arranged alternately in the first direction D1 and a plurality of connecting surfaces 39 that are not parallel to the inclined surfaces 37. The inclined surfaces 37 are inclined with respect to the first direction D1 so as to approach the light output surface 31 on the first side in the first direction D1. The arrangement pitch PC of the connecting surfaces 39 in the first direction D1 may be larger than the arrangement pitch PP1 of the pixels 16 in the first direction D1 of the display panel 15. The arrangement pitch PC of the connecting surfaces 39 in the first direction D1 may be 0.060 mm or more. By increasing the arrangement pitch PC of the connecting surfaces 39, the number of connecting surfaces 39 and the number of inclined surfaces 37 are reduced, and the proportion of the non-effective area on the back surface 32 that is not processed with sufficient precision can be reduced. Therefore, the light path adjustment function of the light guide plate 30 works more effectively. This improves the efficiency of use of the light from the light source, and both an increase in the viewing angle and an increase in brightness can be achieved. For example, in a display device 10 using a surface light source device 20, the viewing angle can be efficiently increased while adequately suppressing a decrease in the maximum brightness.

One embodiment has been described with reference to specific examples, but the above-mentioned specific examples do not limit the embodiment. The above-mentioned one embodiment can be implemented with various other specific examples, and various omissions, substitutions, changes, additions, etc. can be made within the scope of the gist of the embodiment.

Below, an example of a modification will be described with reference to the drawings. In the following description and the drawings used in the following description, parts that can be configured similarly to the above-mentioned specific example will be designated by the same reference numerals as those used for the corresponding parts in the above-mentioned specific example, and duplicated descriptions will be omitted.

In addition, various modifications are possible to the light guide plate 30, optical sheet 50, and reflective sheet 70 described above. For example, the second prism surface 62 of the optical sheet 50 may be a folded surface including a plurality of element surfaces. The second prism surface 62 may be symmetrical to the first prism surface 61 about an axis parallel to the third direction D3 in a cross section along both the third direction D3 and the first direction D1. In addition, the reflective sheet 70 may not include the internal diffusion layer 74, but may include a surface layer 75 and a metal layer 72.

As shown in FIG. 11, a reflective layer 46 may be superimposed on the opposite surface 34 of the light guide plate 30. The reflective layer 46 can reflect light emitted from the opposite surface 34 of the light guide plate 30. This can improve the efficiency of use of the light from the light source.

Furthermore, the overall configuration of the above-mentioned surface light source device 20 and display device 10 can be modified in various ways. For example, the surface light source device 20 may further include a reflective polarizing separation sheet.

10: display device, 11: display surface, 15: display panel, 16: pixel, 16A: first pixel, 16B: second pixel, 16C: third pixel, 20: surface light source device, 21: light emitting surface, 24: light source, 25: light emitting body, 28: optical member, 30: light guide plate, 31: light exit surface, 32: back surface, 33: light entrance surface, 34: opposite surface, 35a: first side surface, 35b: second side surface, 37: inclined surface, 38: flat surface, 39: connection surface, 46: reflective layer, 50: optical sheet, 51: first surface, 52: second surface, 53: prism surface, 55: main body, 55a: light exit side surface, 55b: light-entering side surface, 60: unit prism, 61: first prism surface, 62: second prism surface, 63: top, 66: first element surface, 67: second element surface, 68: third element surface, 70: reflective sheet, 71: support, 72: metal layer, 73: anchor layer, 74: internal diffusion layer, 74a: base layer, 74b: light diffusion component, 75: surface layer, D1: first direction, D2: second direction, D3: third direction, θxe1: first element surface inclination angle, θxe2: second element surface inclination angle, θxe3: third element surface inclination angle, θy: inclined surface angle

Claims (19)

a light guide plate including a light output surface and a back surface facing the light output surface;
an optical sheet including a prism surface facing the light output surface,
the rear surface includes a plurality of inclined surfaces alternately arranged in a first direction and a plurality of connecting surfaces non-parallel to the inclined surfaces;
the inclined surface is inclined with respect to the first direction so as to approach the light output surface on a first side in the first direction,
the optical sheet includes a plurality of unit prisms arranged in the first direction,
Each unit prism includes a first prism surface located on a first side in the first direction and a second prism surface facing the first prism surface in the first direction,
the prism surface includes the first prism surface and the second prism surface,
the first prism surface includes a first element surface, a second element surface, and a third element surface;
the second element surface is located between the first element surface and the third element surface;
a difference in inclination angle between the first element surface and the third element surface is 5° or more;
an inclination angle difference between the first element surface and the third element surface is greater than twice the inclination angle of the inclined surface with respect to the first direction ; a light guide plate including a light output surface and a back surface facing the light output surface;
an optical sheet including a prism surface facing the light output surface,
the rear surface includes a plurality of inclined surfaces alternately arranged in a first direction and a plurality of connecting surfaces non-parallel to the inclined surfaces;
the inclined surface is inclined with respect to the first direction so as to approach the light output surface on a first side in the first direction,
the optical sheet includes a plurality of unit prisms arranged in the first direction,
Each unit prism includes a first prism surface located on a first side in the first direction and a second prism surface facing the first prism surface in the first direction,
the prism surface includes the first prism surface and the second prism surface,
the first prism surface includes a first element surface, a second element surface, and a third element surface;
the second element surface is located between the first element surface and the third element surface;
an inclination angle difference between the first element surface and the third element surface is greater than twice the inclination angle of the inclined surface with respect to the first direction; The optical member of claim 1 , wherein the connecting surfaces are arranged at an arrangement pitch in the first direction of the optical member is equal to or greater than 0.060 mm. 3 . The optical member according to claim 1 , wherein an arrangement pitch of the connection surfaces in the first direction is larger than an arrangement pitch of pixels in the first direction of a display panel disposed opposite the surface light source device. 3. The optical element according to claim 1, wherein a ratio of the arrangement pitch of the connection surface in the first direction to the arrangement pitch of pixels in the first direction of a display panel arranged opposite the surface light source device is greater than or equal to 1.0 and less than or equal to 2.2 . The optical member according to claim 1 , further comprising a reflective sheet facing the rear surface. the reflective sheet includes, in this order from the light guide plate, a surface layer, an internal diffusion layer, and a metal layer;
The optical member according to claim 6 , wherein the internal diffusion layer includes a base layer and a light diffusing component carried by the base layer. The specular gloss of the reflective sheet at an incident angle of 20° is 200 or less,
7. The optical member according to claim 6 , wherein the reflecting sheet has a specular gloss of 75 or more at an incident angle of 85°. The optical element of claim 6, wherein the specular gloss G(20) of the reflecting sheet at an incident angle of 20°, the specular gloss G(60) of the reflecting sheet at an incident angle of 60°, and the specular gloss G(85) of the reflecting sheet at an incident angle of 85 ° satisfy the following relationship.
|G(60)-G(85)|＜|G(20)-G(60)| The optical element of claim 6, wherein the specular gloss G(20) of the reflecting sheet at an incident angle of 20°, the specular gloss G(60) of the reflecting sheet at an incident angle of 60°, and the specular gloss G(85) of the reflecting sheet at an incident angle of 85 ° satisfy the following relationship.
|G(60)-G(85)|/((G(60)+G(85))/2)＜|G(20)-G(60)|/((G(20)+G(60))/2) The optical member according to claim 6 , wherein the diffuse reflectance of the reflecting sheet is 65% or more and 90% or less. 7. The optical member according to claim 6 , wherein the reflecting sheet has a specular gloss of 75 or more at an incident angle of 85°. 7. The optical member according to claim 6 , wherein a ratio of the specular gloss of the reflecting sheet at an incident angle of 85° to the specular gloss of the reflecting sheet at an incident angle of 20° is 0.85 or more. 7. The optical member according to claim 6 , wherein the specular gloss G(20) of the reflecting sheet at an incident angle of 20° and the specular gloss G(85) of the reflecting sheet at an incident angle of 85° satisfy the following relationship:
G(20)-G(85)≦0 7. The optical member according to claim 6 , wherein a ratio of the specular gloss of the reflecting sheet at an incident angle of 85° to the specular gloss of the reflecting sheet at an incident angle of 60° is 0.55 or more and 2.0 or less. 7. The optical member according to claim 6 , wherein the specular gloss G(60) of the reflecting sheet at an incident angle of 60° and the specular gloss G(85) of the reflecting sheet at an incident angle of 85° satisfy the following relationship:
15≦G(60)-G(85)≦22 The optical member according to claim 1 or 2 ;
The surface light source device further comprises a light source that emits light incident on the light guide plate. 18. The surface light source device according to claim 17 , wherein a difference (°) in inclination angle between the first element surface and the third element surface is equal to or greater than a half-width at half maximum (°) in an angular distribution of luminance on the light exit surface. The surface light source device according to claim 17 ,
a display panel facing the surface light source device.