JP2016066572A - Planar light unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a planar light unit which can suppress a bright line generated by a curve part even when a light guide plate includes a curve part on the periphery, as, when there is a curve part on a lateral surface of the light guide plate, a bright line may occur along the curve part.SOLUTION: A light guide plate 22 included in a planar light unit 20 has a disk-like shape, so that a lateral surface 22d becomes a curve part, and the lateral surface 22d of the curve part becomes a diffusion surface. A part of the light entered the light guide plate 22 from light incident surfaces 22a, 22b, 22c is reflected irregularly at the lateral surface 22d instead of condensing, so that a bright line is eliminated.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a planar light unit that illuminates a display body having a curved side surface like a dial of a watch from the back.

  2. Description of the Related Art An illumination device that illuminates a small and circular display body such as a timepiece dial from the upper side around the display body is known. For example, the front light (illuminating device) shown in FIG. 1 of Patent Document 1 includes an annular light guide, and the light guide emits light from the periphery of the dial toward the center to illuminate the dial. ing. Then, FIG. 1 of patent document 1 is re-displayed in FIG. 7, and the structure is demonstrated. FIG. 7 is a perspective view of a front light (illumination device) shown as a conventional example.

  As shown in FIG. 7, the front light 10 includes a light guide member 9 including a light guide 12 and a light source unit 11. The light guide 12 has an incident surface 12a, and the light source unit 11 is attached to the incident surface 12a. The inner peripheral side of the light guide 12 is an emission surface 12 b that emits light introduced into the light guide 12. The outer peripheral side of the light guide 12 is a reflection surface 12c, and the reflection surface 12c includes a reflection groove 14 having a wedge-shaped cross section, and reflects light toward the emission surface 12b. As described above, the front light 10 uniformly illuminates the circular area inside the light guide 12.

  A liquid crystal panel may be used for a dial when it is desired to display a variety of information beyond simple display such as time. As is well known for information equipment and the like, a liquid crystal panel has a better appearance of a backlight (planar light unit) than a front light. On the other hand, an EL panel has been used as a backlight for a liquid crystal panel for a timepiece dial, which is required to be small and thin. However, the EL panel requires a high voltage of about 100 V, and the light emission color and light emission efficiency are not good. Therefore, these problems can be solved by adopting a backlight having an LED as a light source and a thin light guide plate.

  The inventor of the present application manufactured a backlight (planar light unit) including an LED and a light guide for a timepiece having a liquid crystal panel as a dial based on knowledge of a front light, a back lighting device of information equipment, and the like. In this backlight, a part of a disc-shaped light guide plate was linearly cut to form an incident surface, and an LED was attached to the incident surface. A light extraction dot was formed on the side opposite to the light exit surface of the light guide plate. At this time, the side surface of the light guide plate other than the incident surface was made a mirror surface so that the light that propagated through the light guide and reached the side surface was directed to the center of the light guide plate. The mirror surface is a surface flattened so that total reflection occurs, and the outer periphery of the light guide plate is surrounded by a white frame.

JP 2004-134223 (FIG. 1)

  However, when the above-described backlight was turned on, an annular bright line was generated on the exit surface of the light guide plate. Further, it has been found that not only the disc-shaped light guide plate but also the light guide plate having a curved portion around the emission surface, this bright line is generated along the curved portion.

  Therefore, the present invention has been made in view of the above problems, and suppresses the bright lines generated by the curved portion even when the light guide plate has a curved portion when viewed from the exit surface side of the light guide plate. An object of the present invention is to provide a planar light unit that can be used.

The planar light unit of the present invention includes a light source and a light guide plate, and emits light incident on the incident surface of the light guide plate from the light source from the exit surface of the light guide plate orthogonal to the incident surface. In
The light guide plate includes a curved portion when viewed from the light exit surface side, and a side surface of the curved portion is a diffusion surface.

  When the planar light unit of the present invention is viewed from the exit surface side of the light guide plate, a curved portion is formed around it. In this curved portion, the side surface orthogonal to the emission surface is a diffusion surface. A part of the light beam (light) incident on the light guide plate from the incident surface of the light guide plate propagates while being totally reflected in the light guide plate, and is diffusely reflected on the side surface of the curved portion. That is, in the conventional light guide plate, light rays reflected from the side surface of the curved portion are locally concentrated based on the curved shape, and bright lines are generated, whereas in the light guide plate of the present invention, the side surface of the curved portion is formed. Since the reflected light is diffusely reflected and is not concentrated, the bright line is suppressed.

  The light guide plate may have a disc shape, and the incident surface may be formed by cutting a part of the disc.

  The side surface may be a diffusion surface formed by electric discharge machining.

  The side surface may be a diffusion surface formed by a mold.

  The diffusion surface may be a prism surface or an uneven surface.

  The inner side surface of the mold may be subjected to electric discharge machining.

  There are a plurality of the light sources facing the incident surface, and a plurality of prisms whose ridge lines are continuous in the thickness direction of the light guide plate are formed on the incident surface facing at least the light source closest to the side surface. An average value of angles formed by the sides of the prisms on the side opposite to the side surface of the light guide plate in the horizontal cross section and the optical axis of the light source is on the side surface side of the light guide plate. It may be smaller than the average value of the angles formed by the sides of the prism and the optical axis of the light source.

  In the horizontal section, the prism may be an unequal triangle, and the prism whose apex angle is a right angle or an acute angle on the incident surface and the prism whose apex angle is an obtuse angle may be alternately arranged.

  There may be a flat portion between the plurality of prisms.

  As described above, in the planar light unit of the present invention, bright lines generated when the side surface of the curved portion is a mirror surface are suppressed by using the side surface as a diffusion surface.

The disassembled perspective view of the planar light unit shown as 1st Embodiment of this invention. The perspective view of the light-guide plate contained in the planar light unit shown in FIG. The top view of the light-guide plate shown in FIG. It is an enlarged view of the light-guide plate side surface, (a) is a comparative example, (b) is the light-guide plate shown in FIG. The top view of a part of planar light unit shown as 2nd Embodiment of this invention. The top view of a part of planar light unit shown as 3rd Embodiment of this invention. The perspective view of the front light shown as a prior art example. The top view which shows a part of light-guide plate contained in 4th Embodiment of this invention.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to FIGS. In the description of the drawings, the same or equivalent elements will be denoted by the same reference numerals, and redundant description will be omitted.

(First embodiment)
The planar light unit 20 shown as 1st Embodiment of this invention with FIGS. 1-4 is demonstrated. FIG. 1 is an exploded perspective view of the planar light unit 20. FIG. 2 is a perspective view of the light guide plate 22 included in the planar light unit 20. FIG. 3 is a plan view of the light guide plate 22. FIG. 4 is an enlarged view of the side surface of the light guide plate 22, (a) is a comparative example before electric discharge machining, and (b) is the light guide plate 22 of the first embodiment.

  As shown in FIG. 1, in the planar light unit 20, a light guide plate 22, a diffusion sheet 23, and prism sheets 24 and 25 are laminated on a reflection sheet 21. Three LEDs 26 are attached to the light guide plate 22.

  The reflective sheet 21 shown in FIG. 2 has a thickness of 65 μm and directs light leaking from the lower surface of the light guide plate 22 toward the light exit surface 22 e of the light guide plate 22. The light guide plate 22 has a thickness of 400 μm, includes incident surfaces 22a, 22b, and 22c on the side surfaces, and a plurality of dots (not shown) formed on the bottom surface. The light incident from the incident surfaces 22a, 22b, and 22c changes the traveling direction by the dots formed on the bottom surface while propagating through the light guide plate 22, and is emitted from the emission surface 22e. The diffusion sheet 23 has a thickness of 35 μm and is formed by spreading and fixing diffusion particles on a transparent sheet, and spreads light emitted from the light guide plate 22. The prism sheets 24 and 25 have a thickness of 65 μm, and fine prisms are arranged on the upper surface side to adjust the light emission direction. The prism ridge line of the prism sheet 24 is orthogonal to the prism ridge line of the prism sheet 25.

  As shown in FIGS. 2 and 3, the light guide plate 22 has incident surfaces 22a, 22b, and 22c formed at positions where a circular flat plate is cut out. The incident surfaces 22a, 22b, and 22c are divided into three regions by two protrusions. The central incident surface 22b is formed so that the perpendicular bisector passes through the center of the disk (light guide plate 22). The regions 22a and 22c on both sides are inclined so that the central side is deeply cut with respect to the central incident surface 22b. Due to this inclination, the regions adjacent to the left and right of the incident surfaces 22a, 22b, and 22c are sufficiently distributed.

  As shown in FIG. 1, one LED 26 is attached to each region of the incident surfaces 22a, 22b, and 22c. The LED 26 is mounted on an FPC (flexible printed circuit board) (not shown), and the exit slope of the LED 26 faces the incident surfaces 22a, 22b, and 22c. A light-shielding sheet (not shown) is provided on the light guide plate 22 side of the FPC so that the colored light that enters the FPC from the LED 26 and does not enter the light guide plate 22 again. The periphery of the light guide plate 22 is surrounded by a white frame (not shown).

  In the light guide plate 22, the side surface 22d of the curved portion shown by the thick line in FIG. 2 is a diffusion surface. The dots formed on the lower surface of the light guide plate 22 are changed in density or size depending on the location so that the emitted light is uniform.

Next, the state of the side surface 22d of the light guide plate 22 will be described with reference to FIG. As shown in FIG. 4A, the light guide plate 22h of the comparative example (suffix h is added to indicate that it is the light guide plate of the comparative example. The comparative example is only the processed state of the side surface in the curved portion of the light guide plate 22h. The side surface 22g is a flat surface. This flat surface (side surface 22g) is a mirror surface when taken out of the mold. Moreover, the light guide plate 22h of the comparative example shown in FIG. 4A is the one before the electric discharge machining of the light guide plate 22 shown in FIG. On the other hand, in the light guide plate 22 shown in FIG. 4B, the side surface 22d of the curved portion is subjected to electric discharge machining, and a random uneven shape is formed on the side surface 22d.

  In the planar light unit 20 and the comparative example, light rays that have entered the light guide plates 22 and 22a from the entrance surfaces 22a, 22b, and 22c propagate through the light guide plates 22 and 22a while repeating total reflection, and a part of them is a curved portion. The side faces 22d and 22g are reached.

  If the side surface 22g of the curved portion of the light guide plate 22a is made flat as shown in FIG. 4A, light incident on the side surface 22g at a critical angle or more is totally reflected. At this time, since the side surface 22g is curved, the light rays totally reflected by the side surface 22g are concentrated in an annular shape. The light rays concentrated in the ring form an annular bright line. In particular, the annular bright line is conspicuous in the region near the incident surfaces 22a and 22c where the incident angle is larger with respect to the side surface 22g, and is not conspicuous in the region opposite to the center (the region facing the incident surface 22b). The light incident on the side surface 22g at a critical angle or less passes through the side surface 22g, is diffusely reflected by the white frame surrounding the outer periphery of the light guide plate 22a, and is incident on the light guide plate 22a again.

  On the other hand, when the side surface 22d of the light guide plate 22 is an irregular reflection surface (diffusion surface) as shown in FIG. 4B, the direction of the light beam reflected by the side surface 22d is random. As a result, the concentration of light rays due to the reflection of the side surface 22d is eliminated, and the annular bright line generated in the light guide plate 22a in FIG. 4A is generated in the light guide plate 22 in which the side surface 22d in FIG. No longer. The light beam incident on the side surface 22d at a critical angle or less is transmitted through the side surface 22d, diffusely reflected by the white frame surrounding the outer periphery of the light guide plate 22, and incident on the light guide plate 22 again.

(Second and third embodiments)
In the planar light unit 20 shown as the first embodiment, the side surface 22d of the light guide plate 22 is a diffusion surface formed by electric discharge machining. However, in the planar light unit of the present invention, the diffusing surface formed on the side surface of the light guide plate is not limited to the one by electric discharge machining. Accordingly, planar light units 30 and 40 in which the side surfaces of the curved portions are prism surfaces and uneven surfaces will be described with reference to FIGS. 5 and 6 as second and third embodiments of the present invention. 5 and 6 are enlarged plan views of a part of the curved portions of the planar light units 30 and 40, and correspond to a region B surrounded by a broken line in FIG.

  The planar light unit 30 is the same as the planar light unit 20 shown in FIG. As shown in FIG. 5, the side surface of the curved portion of the light guide plate 32 is a prism surface, and the microprisms 31 are arranged. The microprism 31 extends in the thickness direction of the light guide plate 32 and has a triangular cross section. A part of the light reaching the side surface of the curved portion is reflected by the microprism 31. Since the reflecting surface of the microprism 31 cancels the concave mirror-like curved shape of the curved portion, the reflected light is not condensed. The remaining part of the light reaching the side surface is transmitted through the side surface, diffusely reflected by the white frame surrounding the outer periphery of the light guide plate 32, and is incident on the light guide plate 32 again. The cross-sectional shape of the microprism 31 is not limited to a triangle, and may be a cylinder or a rectangle. Since the light guide plate 32 is molded by a mold, the manufacturing process is shorter than that of the light guide plate 22 shown in FIG.

The planar light unit 40 is the same as the planar light unit 20 shown in FIG. 1 except for the light guide plate 42. As shown in FIG. 6, the side surface of the curved portion of the light guide plate 42 is an uneven surface, and the micro dots 41 are arranged. The minute dots 41 are dome-shaped and are also arranged in the thickness direction of the light guide plate 42. A part of the light reaching the side surface of the curved portion is reflected by the minute dots 41. Since the reflective surface of the minute dots 41 cancels the concave mirror-like curved shape of the curved portion, the reflected light is not condensed. The remaining portion of the light reaching the side surface is transmitted through the side surface, diffusely reflected by the white frame surrounding the outer periphery of the light guide plate 42, and is incident on the light guide plate 42 again. The light guide plate 42 can be manufactured by a mold. In order to make it easy to take out the light guide plate 42 from the mold, the side surface is inclined about 5 °. If it does in this way, when taking out the light-guide plate 42 from a metal mold | die, it will become difficult to catch the fine todd 41. FIG. Further, like the light guide plate 32 shown in FIG. 5, the manufacturing process of the light guide plate 42 can be shortened.

  In the planar light unit 40 shown in FIG. 6, the dome-shaped minute dots 41 are formed on the side surface of the curved portion of the light guide plate 42, and the portion is used as the diffusion surface. The uneven shape formed on the side surface of the light guide plate 42 is not limited to the dome shape, and is a random uneven shape like the side surface 22d in the curved portion of the light guide plate 22 included in the planar light unit 20 shown in FIG. Also good. In order to manufacture the light guide plate having the random uneven shape with a mold, the inner side surface of the mold (the portion corresponding to the side surface of the curved portion) may be roughened by electric discharge machining.

  In the planar light units 20, 30, and 40 shown as the first to third embodiments, the shape of the light guide plates 22, 32, and 42 is a disk shape. However, the light guide plate included in the planar light unit of the present invention is not limited to a disk shape. That is, if there is a curved portion that behaves in a concave mirror manner on a part of the side surface of the light guide plate, the side surface of the curved portion can be used as a diffusing surface to suppress bright lines generated due to the curved shape of the curved portion.

(Fourth embodiment)
The light guide plates 22, 32, and 42 included in the planar light units 20, 30, and 40 shown in the first to third embodiments have the side surfaces 22d and the like as irregular reflection surfaces, and the surfaces opposite to the emission surfaces as described above. The uniformity of the emitted light was ensured by adjusting the density and size of the dot pattern to be formed. Furthermore, the uniformity of the emitted light can be improved by adjusting the light distribution of the light incident on the light guide plate. Therefore, as a fourth embodiment with reference to FIG. 8, a planar light unit 80 provided with a prism on the incident surface and adjusting the distribution of incident light by this prism will be described.

  FIG. 8 is a plan view showing a part of the light guide plate 82 included in the planar light unit 80. FIG. 8A is a plan view in the vicinity of the incident surfaces 82a, 82b and 82c, and FIG. 8B is an incident surface 82a. FIG. 8C is a plan view in which a part of the incident surface 82b is enlarged.

  As shown in FIG. 8A, the light guide plate 82 includes incident surfaces 82a, 82b, and 82c and side surfaces 82d and 82e. The light guide plate 82 is the same as the light guide plate 22 shown in FIGS. 2 and 3 except for the prisms 83, 85, 86, and 88 (see FIGS. 8B and 8C) formed on the incident surfaces 82a, 82b, and 82c. Shape and structure are equal. In FIG. 8A, the side surface is divided into a side surface 82d and a side surface 82e for convenience of explanation. An LED (light source) (not shown) is arranged with respect to the incident surfaces 82a, 82b, and 82c so that the light emitting surfaces face each other. The incident surface 82a is an incident surface facing the LED (light source) closest to the side surface 82d. The incident surface 82c is an incident surface that faces the LED (light source) closest to the side surface 82e.

  As shown in FIG. 8B, the incident surface 82 a is formed with a plurality of prisms 83 and 85 whose ridge lines are continuous in the thickness direction of the light guide plate 82. The prism 83 has an unequal triangular shape whose apex angle is a straight obtuse angle in the horizontal section. At this time, the angle θ2 formed by the side 83b of the prism 83 on the side opposite to the side surface 82d of the light guide plate 82 {see FIG. 8A} and the optical axis L1 of the LED is the prism 83 on the side surface 83d side of the light guide plate 82. Is smaller than an angle θ1 formed by the side 83a of the LED and the optical axis L1 of the LED. The optical axis L1 of the LED is a normal direction of the outgoing slope of the LED, and is also a normal direction of the incident surface 82a (hereinafter the same). Since the prism 83 is a triangular prism, it has the same shape in plan view and horizontal section (the same applies hereinafter). Here, the horizontal cross section is a cross section parallel to the exit surface of the light guide plate 82 (the same applies hereinafter).

As shown in FIG. 8B, the prism 85 has an unequal triangular shape whose apex angle is a right angle or an acute angle in the horizontal section. In the horizontal section, the angle θ4 formed by the side 85b of the prism 85 on the opposite side of the side surface 82d of the light guide plate 82 (see FIG. 8A) and the optical axis L1 of the LED is the prism on the side surface 82d side of the light guide plate 82. It is smaller than an angle θ3 formed by the side 85a of 85 and the optical axis of the LED. The height h2 of the prism 85 is higher than the height h1 of the prism 83, and the flat portion 84 is between the prism 85 and the prism 83. The prisms 85 and the prisms 83 are alternately arranged.

  For example, the angles θ1, θ2, θ3, and θ4 are 75 °, 65 °, 50 °, and 40 °, respectively, the heights h1 and h2 are 0.005 mm and 0.010 mm, the pitch between the prisms 83, and the pitch between the prisms 85, respectively. Each pitch is 0.060 mm.

  As shown in FIG. 8C, the incident surface 82 b is formed with a plurality of prisms 86 and 88 whose ridge lines are continuous in the thickness direction of the light guide plate 82. The prism 86 is an isosceles triangle having an obtuse angle in the horizontal section. At this time, the angle θ6 formed between the side 86b of the prism 86 and the optical axis L1 of the LED is equal to the angle θ5 formed between the side 86a of the prism 86 and the optical axis L1 of the LED. Similarly, the prism 88 is an isosceles triangle whose apex angle is an acute angle in the horizontal section. At this time, the angle θ8 formed between the side 88b of the prism 88 and the optical axis L1 of the LED is equal to the angle θ7 formed between the side 88a of the prism 88 and the optical axis L1 of the LED. The height h4 of the prism 88 is higher than the height h3 of the prism 86, and a flat portion 87 is provided between the prism 88 and the prism 86. The prisms 88 and the prisms 86 are alternately arranged.

  For example, the angles θ5, θ6, θ7, and θ8 are 70 °, 70 °, 45 °, and 45 °, respectively, the heights h3 and h4 are 0.005 mm and 0.010 mm, the pitch between the prisms 86, and the distance between the prisms 88, respectively. Each pitch is 0.060 mm.

  On the incident surface 82c, a prism row that is symmetrical to the prism row formed on the incident surface 82a is formed with a straight line (not shown) passing through the center of the incident surface 82b and the center of the light guide plate 82 as an axis. Hereinafter, the incident surface 82c is axisymmetric with respect to the incident surface 82a, and thus the description thereof is omitted.

  First, the light distribution of light incident on the light guide plate 82 from the incident surface 82b will be described with reference to FIG. Light (light beam) emitted from the LED disposed opposite to the incident surface 82b and incident on the side 86b of the prism 86 is refracted to the left side of the drawing. On the other hand, light (light beam) emitted from the LED disposed opposite to the incident surface 82b and incident on the side 86a of the prism 86 is refracted to the right side of the drawing. The same applies to the prism 88, but the refraction angle is larger than that of the prism 86. As described above, the light distribution of the light emitted from the LED disposed opposite to the incident surface 82b and incident on the light guide plate 82 from the incident surface 82b is symmetrically spread in the horizontal direction. The flat portion 87 existing between the prism 88 and the prism 86 and the alternate arrangement of the prism 88 and the prism 86 function to overlap the three types of light distributions, thereby improving the uniformity of the luminance distribution on the exit surface. doing.

  Next, the light distribution of light incident on the light guide plate 82 from the incident surface 82a will be described with reference to FIG. The light that is emitted from the LED disposed opposite to the incident surface 82a and is incident on the side 83b of the prism 83 is refracted to the left in the drawing. On the other hand, the light emitted from the LED disposed opposite to the incident surface 82a and incident on the side 83a of the prism 83 is refracted to the right side in the figure. At this time, the difference between the prism 83 and the prism 86 in FIG. 8C is that the light (light beam) refracted at the side 83b in the prism 83 is refracted to the incident surface 82a side more than the light (light beam) refracted at the side 83a. It is to be. As a result, the light (light ray) that goes around in the corner direction where the incident surface 82a and the side surface 82d intersect increases.

Similarly, light emitted from an LED disposed opposite to the incident surface 82a and incident on the side 85b of the prism 85 is refracted on the left side of the drawing. On the other hand, the light emitted from the LED disposed opposite to the incident surface 82b and incident on the side 85a of the prism 85 is refracted to the right side of the drawing. At this time, the difference between the prism 85 and the prism 88 in FIG. 8C is that the light (light ray) refracted at the side 85b in the prism 85 is refracted to the incident surface 82a side more than the light (light ray) refracted at the side 85a. It is to be. As a result, the light (light ray) that goes around in the corner direction where the incident surface 82a and the side surface 82d intersect increases.

  As a result, the prisms 83 and 85 formed on the incident surface 82a increase the luminance of the corner portion where the incident surface 82a and the side surface 82d intersect. The effect of increasing the luminance similarly occurs in the vicinity of the side surface 82d and becomes weaker as the distance from the incident surface 82a increases.

  When the light guide plate is rectangular, since the incident surface is orthogonal to the side surface, the LED serving as the light source can be disposed close to the side surface. As a result, if the light guide plate is rectangular, it is difficult for a dark portion to occur in a portion extending from the corner portion to the side surface. However, if the light guide plate 80 is circular, there is a portion where the distance between the side surfaces 82d and 82e increases as the distance from the incident surfaces 82a to 82c increases. Therefore, the prisms 86 and 88 shown in FIG. Even if the light is provided on the incident surface 82a, light shortage (dark portion) may occur in the portion where the side surface 82d extends from the above-described corner portion. Therefore, in the planar light unit 80, the prisms 83 and 85 provided on the incident surface 82a of the light guide plate 82 are made unequal, and light distribution from the corner portion to the extended portion of the side surface 82d is secured.

  The flat portion 84 existing between the prism 85 and the prism 83, and the alternate arrangement of the prism 85 and the prism 83 function to overlap the three types of light distributions, thereby improving the uniformity of the luminance distribution on the exit surface. doing. In addition, since the incident surface 82a is inclined, there is an effect that when the circular light guide plate is cut out to form the incident surface, the notched portion can be reduced. It can be said that this effect is supplemented or reinforced by the prisms 83 and 85. Further, the planar light unit 80 has a feature that the prisms 83 and 85 are regularly arranged on the incident surface 82a, so that the LED is resistant to positional deviation of the LEDs in the arrangement direction of the prisms 83 and 85. The prisms 83 and 85 formed on the incident surface 82a reduce the design load of dots formed on the surface opposite to the light emitting surface of the light guide plate 82, and contribute to narrowing the frame.

  In the planar light unit 80, the prisms 83, 85 and the like formed on the incident surfaces 82a, 82c are triangular prisms whose horizontal cross section is an unequal triangle. However, the prism for increasing the light distribution on the curved side surface of the light guide plate is not limited to such a triangular prism. For example, it may be a quadrangular column whose trapezoidal shape has a horizontal cross section with different lengths on the left and right sides, or a columnar object whose horizontal cross section is asymmetric and curved. At this time, the prism has an asymmetric shape in the horizontal section, and the average value of the angle formed by the side of the prism on the side opposite to the side surface of the light guide plate in the horizontal section and the optical axis of the light source is on the side surface side of the light guide plate. It suffices if it is smaller than the average value of the angles formed by the sides of the light source and the optical axis of the light source.

20, 30, 40, 80 ... planar light unit,
21 ... reflective sheet,
22, 32, 42, 82 ... light guide plate,
22a, 22b, 22c, 82a, 82b, 82c ... incident surface,
22e: emitting surface,
22d, 22g, 82d, 82e ... side face,
23 ... diffusion sheet,
24, 25 ... Prism sheet,
26 ... LED,
31 ... micro prism,
41 ... minute dots,
83, 85, 86, 88 ... Prism,
83a, 83b, 85a, 85b, 86a, 86b, 88a, 88b ... sides,
84, 87 ... flat part,
L1: Optical axis.

Claims (9)

In a planar light unit that includes a light source and a light guide plate, and emits light incident on an incident surface of the light guide plate from the light source, from an output surface of the light guide plate orthogonal to the incident surface.
When the light guide plate is viewed from the light exit surface side, the light guide plate includes a curved portion around the light guide plate, and a side surface of the curved portion is a diffusing surface.   The planar light unit according to claim 1, wherein the light guide plate has a disk shape, and the incident surface is formed by cutting a part of the disk.   The planar light unit according to claim 1, wherein the side surface is a diffusion surface formed by electric discharge machining.   The planar light unit according to claim 1 or 2, wherein the side surface is a diffusion surface formed by a mold.   5. The planar light unit according to claim 4, wherein the diffusing surface is a prism surface or an uneven surface.   The planar light unit according to claim 5, wherein an inner side surface of the mold is subjected to electric discharge machining.   There are a plurality of the light sources facing the incident surface, and a plurality of prisms whose ridge lines are continuous in the thickness direction of the light guide plate are formed on the incident surface facing at least the light source closest to the side surface. An average value of angles formed by the sides of the prisms on the side opposite to the side surface of the light guide plate in the horizontal cross section and the optical axis of the light source is on the side surface side of the light guide plate. The planar light unit according to any one of claims 1 to 6, wherein the planar light unit is smaller than an average value of angles formed by a side of the prism and the optical axis of the light source.   In the horizontal section, the prism has an unequal triangular shape, and the prism whose apex angle is a right angle or an acute angle on the incident surface and the prism whose apex angle is an obtuse angle are alternately arranged. The planar light unit according to claim 7.   The planar light unit according to claim 7 or 8, wherein a flat portion is provided between the plurality of prisms.

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