JP4899930B2 - LIGHT GUIDE, BACKLIGHT DEVICE, DISPLAY DEVICE, AND ELECTRONIC DEVICE - Google Patents

Description

  The present invention relates to a light guide that emits a surface of light emitted from a light emitting element, an optical element used therefor, a backlight device using these, a display device, and an electronic apparatus.

  As a backlight of a liquid crystal display using a light emitting element such as an LED (Light Emitting Diode) as a light source, there are a so-called edge light type and a direct type. The edge light type is a backlight in which LEDs are arranged on the end surface (side surface) of the light guide plate. In the direct type, the LED is arranged facing the wide main surface which is the light emitting surface of the light guide plate. Depending on the size of the display, a plurality of LEDs are often arranged in either type.

  For example, an edge light type backlight has the following problems. In general, since the light emitting area of the LED is smaller than the area of the light incident surface of the light guide plate, the light emitting state is close to a point light source on a macro basis. Therefore, in contrast to the cold cathode tube type in which light can be uniformly incident on the entire surface of the light incident surface, only the vicinity where the LEDs are arranged is extremely bright and the space between the LEDs becomes dark. Therefore, the surface light emission is not uniform over the entire light guide plate. In addition, due to the demand for a narrow frame accompanying the downsizing of the liquid crystal module, it is desirable to shorten the distance from the light incident surface of the light guide plate to the practical light emitting area (usually referred to as the active area) as a backlight. As a matter of course, luminance unevenness generated on the light emitting surface near the light incident portion is easily exposed to the active area.

  In order to solve the problem of uneven brightness, a light guide plate is disclosed in which a prism or the like is formed on the light incident surface to control the optical path of incident light (see, for example, Patent Document 1). However, the current situation is that it has not been uniformized to a satisfactory level. In addition, in a light guide plate having a prism-shaped light incident surface, the traveling angle of light after incidence is widened. Therefore, in general, a light guide plate designed for light in a certain angle range (mainly in a certain angle range centered on the normal direction of the macroscopic incident surface) uses the light. Will fall.

  On the other hand, there is a backlight using a diffusion sheet or the like having a dot pattern in order to suppress luminance unevenness (see, for example, Patent Document 2).

JP 2002-196151 A (paragraph [0019], FIG. 2) JP 2001-312916 A (FIG. 19)

  However, a diffusion sheet having a dot pattern as in Patent Document 2 has lower light utilization efficiency than a light guide plate having a prism-shaped light incident surface.

  In view of the circumstances as described above, an object of the present invention is to provide a technique capable of suppressing luminance unevenness to achieve uniform light emission and improving light utilization efficiency.

  In order to achieve the above object, a light guide according to the present invention is provided on a light guide plate that guides light emitted from a light source block, an incident surface on which light emitted from the light source block is incident, and the incident surface side. An optical element having a reflecting surface for reflecting the light toward the light guide plate, and between the light guide plate and the optical element, and transmits the first light having an angle smaller than a critical angle to transmit the light. A boundary layer that is incident on the light plate and reflects the second light that is equal to or greater than the critical angle so that the second light is reflected by the reflecting surface and is incident on the light guide plate.

  In the present invention, the first light is transmitted from the optical element to the light guide plate through the boundary layer, and the second light reflected by the reflection surface of the optical element is transmitted to the light guide plate through the boundary layer. By appropriately setting the angle of the reflecting surface and the like, parallel light rays increase in the light guide plate. Therefore, luminance unevenness can be suppressed and light utilization efficiency can be improved.

  A plurality of reflecting surfaces may be provided according to the angle of the light beam included in the second light.

  According to an aspect of the present invention, the boundary layer reflects the second light so that the third light having an angle smaller than a predetermined angle out of the second light is guided to the reflection surface. A first boundary layer that reflects the fourth light of the predetermined angle or more, and a second boundary layer that reflects the fourth light reflected by the first boundary layer so as to guide it to the reflection surface. And a boundary layer.

  In the present invention, since the second boundary layer reflects the fourth light reflected by the first boundary layer so as to guide it to the reflection surface of the optical element, the light utilization efficiency can be improved.

  According to an aspect of the present invention, the first boundary layer is formed in a convex shape toward the incident surface.

  According to one form of this invention, the said 2nd boundary layer is arrange | positioned in parallel with the said entrance plane.

  According to an aspect of the present invention, the optical element has a reflective film on the reflective surface. Thereby, the reflectance at the reflecting surface is increased, and the light utilization efficiency is improved. For example, the reflection surface has a prism shape.

According to one aspect of the present invention, the light source block has a plurality of light emitting elements arranged,
The length of the first boundary layer in the direction in which the light emitting elements are arranged is longer than the length of the light source block in the direction. Thereby, many parallel lights can be made compared with the case where the length of a light source block is longer than the length of the 1st boundary layer.

  According to an aspect of the present invention, a plurality of the light source blocks are provided, and a plurality of the first boundary layers are provided so as to correspond to the light source blocks. In this invention, each light emitted from the several light source block is made into parallel light in a light-guide plate.

  A light guide according to another aspect of the present invention is provided on an incident surface on which light emitted from a light source block is incident, on the incident surface side, and disposed at a predetermined angle with respect to the incident surface, An optical element having a reflective surface for reflecting light; a light guide plate for taking in and guiding the light emitted from the optical element; and a portion formed in a convex shape toward the incident surface; And a boundary layer that transmits the light reflected by the reflecting surface of the light and enters the light guide plate.

  In the present invention, since the boundary layer has a portion formed in a convex shape, many parallel light beams are produced from light transmitted from the optical element to the light guide plate in this portion. Further, by setting the angle of the reflecting surface as appropriate, a lot of parallel light can be produced from the light reflected by the convex portion. Therefore, luminance unevenness can be suppressed and light utilization efficiency can be improved.

  As described above, according to the present invention, luminance unevenness can be suppressed and light emission can be made uniform, and light utilization efficiency can be improved.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a plan view showing a light guide (and a light source block 4 attached to the light guide 10) according to an embodiment of the present invention. FIG. 2 is a side view of the light guide 10 shown in FIG.

  The light guide 10 is assembled with a collimator 2 as an optical element to which the light source block 4 is attached and which makes light emitted from the light source block 4 as close to parallel light as possible, and a light guide plate 3 for guiding the light emitted from the collimator 2. Prepare as.

  The light source block 4 includes at least three light emitting elements 9 of red, green, and blue (RGB). For example, an LED is used as the light source block 4 or the light emitting element 9, and it may be either inorganic or organic. The light source block 4 of the present embodiment has, for example, five light emitting elements 9. The combination of the five colors can be set as appropriate, and the light source block 4 emits white light or light of a color close to white by the combination of the five colors. The number of light emitting elements 9 included in the light source block 4 is not limited to five, and may be six or more, or two or less. A white LED may be used. Alternatively, the light source block 4 is not necessarily limited to a form that emits white light, and may be a form that emits other colors by one or a plurality of light emitting elements 9.

  The collimator 2 has a function of emitting the light emitted from the light source block 4 as parallel light as much as possible and entering the light guide plate. The collimator 2 faces the light emitting surface 4a of the light source block 4 and has an incident surface 2b on which light emitted from the light source block 4 is incident. The light source block 4 has a light reflecting surface 2a provided on the incident surface 2b side. As will be described later, the reflecting surface 2a reflects light traveling in the collimator 2 so as to be directed toward the light guide plate 3. A plurality of reflecting surfaces 2a are provided, and the plurality of reflecting surfaces 2a are realized by forming a plurality of triangular prisms on the collimator 2. However, the reflecting surfaces 2a are not limited to the triangular shape, and may be trapezoidal or other shapes. . The reflection surface 2a is set to an angle at which as much light as possible is totally reflected. Or the metal film for improving a reflectance may be formed in the reflective surface 2a. The metal film can be formed by vapor deposition of, for example, silver or aluminum.

  FIG. 3 is a plan view of the light guide 10 in which the vicinity of the light source block 4 is enlarged. A cutout surface 2 c is formed on a part of the light exit surface 6 provided on the light guide plate 3 side of the collimator 2. As will be described later, a part of the light emitted from the light source block 4 is emitted from the notch surface 2 c by the notch surface 2 c and is incident on the light guide plate 3. The notch surface 2c is formed in, for example, a triangular shape as viewed in FIG. On a part of the light incident surface 7 provided on the collimator side of the light guide plate 3, a triangular projection surface 3c is formed along the notch surface 2c. In other words, the light guide 10 is substantially parallel to the incident surface 2b and the first boundary layer 11 convex between the collimator 2 and the light guide plate 3 on the light source block 4 side (incident surface 2b side). A second boundary layer 12. Hereinafter, this is referred to as a “boundary layer” 15 in a sense including the first boundary layer 11 and the second boundary layer 12.

  The light exit surface 6 of the collimator 2 and the light entrance surface 7 of the light guide plate 3 may be joined with, for example, an adhesive. However, in principle (or microscopic), the boundary layer 15 has air, and the boundary layer 15 becomes an air layer. Note that the collimator 2 and the light guide plate 3 may be fixed with an appropriate fixing tool by intentionally providing a gap between the collimator 2 and the light guide plate 3 without using an adhesive.

  The apex 3d of the projection surface 3c and the apex 2d of the notch surface 2c are typically designed so as to be located at the center in the width direction (X direction) of the light source block 4. However, the vertices 3d and 2d do not necessarily have to be located in the central portion, and may be offset in the X direction. In the present embodiment, the collimator 2 has a symmetrical structure with the normal direction (Y direction) of the light emitting surface of the light source block 4 passing through the center of the light source block 4 as an axis. In particular, the notch surface 2c, the projection surface 3c of the light guide plate, and the reflection surface 2a are arranged at symmetrical positions.

  With reference to FIG. 3, the apex angle θ of the projection surface 3 c (which is also the apex angle of the notch surface 2 c) is set to about 100 °, for example. For example, θ can be set to about 70 to 140 °. The distance d1 from the incident surface 2b of the collimator 2 to the vertex 2d of the notch surface 2c and the width d2 of the notch surface 2c in the X direction can be set as appropriate. d2 is typically set larger than the width d3 of the light source block 4. The optimum θ (not limited to the above 70 to 140 °), the distance d1, and the like for generating more parallel light beams in the collimator 2 are determined by the type of the light source block 4, its light distribution characteristics, the light emission area, and the like. It is done. Further, the amount of light emitted from the light guide plate 3 can be controlled by θ, d1, or the like.

  FIG. 4 is a cross-sectional view schematically showing the structure of the display device 50 including the light guide 10 configured as described above. The display device 50 includes a backlight 16 including the light guide plate 3 and the downward prism sheet 5, and a liquid crystal panel (modulation element) 8 for partially selectively modulating the light intensity of the backlight 16.

  For example, a diffusion sheet (not shown) is typically disposed between the light guide plate 3 and the downward prism sheet 5 in the backlight 16. A reflection sheet (not shown) may be disposed on the lower surface 3 e side of the light guide plate 3. The lower surface 3e of the light guide plate 3 has a prism shape, but may be a plane parallel to the upper surface 3f. Alternatively, the lower surface 3e of the light guide plate 3 may be a tapered surface (or a slope) that approaches the upper surface 3f as the distance from the light source block 4 increases. Further, although the downward prism sheet 5 is used as the prism sheet, an upward prism sheet may be used. In addition, a plurality of prism sheets having different cutting directions may be used. Various modifications can be made to the optical sheets constituting the portion other than the light guide 10 of the display device 50 as described above.

  Next, the operation of the light guide 10 will be described.

  As shown in FIG. 1, the light emitted from each light emitting element 9 of the light source block 4 is diffused light having a certain angle. As shown in FIG. 3, light (first light) p <b> 1 smaller than the critical angle α with respect to the notch surface 2 c of the collimator 2 is included in the notch surface 2 c, the first boundary layer 11, and the incident light. The light passes through the projection surface 3 c and enters the light guide plate 3. Since the projecting surface 3 c and the cutout surface 2 c are substantially parallel, the angle of the first light p <b> 1 in the collimator 2 is also maintained in the light guide plate 3. The collimator 2 is designed so that the angle of the first light p1 is as close to parallel light as possible (that is, light parallel to the Y direction). For example, when the refractive index of the collimator 2 is 1.59, the critical angle α can be set to 39 °, but α can be changed as appropriate.

  On the other hand, of the light from the light source block 4 incident on the collimator 2, the light (second light) p <b> 2 having the critical angle α or more with respect to the cutout surface 2 c is reflected (total reflection) by the first boundary layer 11. ) Of the second light p2 reflected by the first boundary layer 11, the third light p3 having an angle smaller than a predetermined angle with respect to the first boundary layer 11 is directly reflected by the reflecting surface 2a of the collimator 2. . The predetermined angle is a value appropriately determined by the design of the collimator 2. Of the second light p <b> 2 totally reflected by the first boundary layer 11, the fourth light p <b> 4 having a predetermined angle or more is incident on the second boundary layer 12 at a critical angle or more. The fourth light p <b> 4 is reflected by the second boundary layer 12 and then reflected by the reflecting surface 2 a of the collimator 2. That is, the third light p3 and the fourth light p4 are finally reflected by the reflecting surface 2a and transmitted through the light exit surface 6 of the collimator 2, the second boundary layer 12, and the light incident surface 7 of the light guide plate 3. And parallel light.

  As shown in FIG. 4, the light guided in the light guide plate 3 is repeatedly reflected several times, rises below a predetermined critical angle by the prism on the lower surface 3e, and exits from the upper surface 3f. The light is controlled by the downward prism sheet 5 so as to approach the vertical direction (Z direction) and is emitted from the upper surface of the downward prism sheet 5. Thereby, the backlight 16 emits surface light.

  Here, FIG. 5 is a diagram for explaining a demerit when the parallel light is small in the light guide plate 103. 5A is a plan view of the backlight 200, and FIG. 5B is a front view of the backlight 200 viewed in the direction of arrow A in FIG. 5A. When the incident angle from the light source block 104 to the light guide plate 103 is large, that is, when the number of parallel rays is small, as shown in FIG. 5B, the viewing angle direction (Z More light is emitted out of the direction. This reduces the light use efficiency (luminance in the viewing angle direction). In order to increase the light utilization efficiency, as shown in FIGS. 6A and 6B, when there are many parallel rays on the light guide plate 3 as in this embodiment, the viewing angle direction as shown in FIG. There are few rays that come off. Therefore, the luminance in the viewing angle direction is improved and luminance unevenness is also suppressed.

  As described above, according to the light guide 10 according to the present embodiment, the first light p1 is transmitted from the collimator 2 to the light guide plate 3 through the first boundary layer 11, and the reflecting surface 2a of the collimator 2 is obtained. The second light p2 reflected by the light is transmitted to the light guide plate 3 side through the second boundary layer 12. Here, parallel light rays increase in the light guide plate 3 by appropriately setting the position and angle of the reflecting surface 2a. If the number of parallel rays increases, luminance unevenness can be suppressed and light utilization efficiency can be improved.

  In particular, when viewed microscopically, each light emitting element (LED) 9 of the light source block 4 is a surface light emitter, and light emitted from each light emitting element 9 becomes divergent light having an angle that can be visually confirmed. If the light-emitting element 9 is a point light source, it is possible to use a small lens or the like to spread the light beam and make it parallel light at a certain width. However, even in the case of a point light source, an arrangement space for the lens system is required. However, in reality, since each light emitting element 9 is a surface light emitter as described above, the size of the lens system is further increased, and a larger arrangement space is required. It is not practical to incorporate such a lens system into a backlight device. According to the present embodiment, it is possible to suppress luminance unevenness and improve light utilization efficiency without using such a lens system.

  Further, in the present embodiment, the light source block 4 has a plurality of light emitting elements and, as shown in FIG. 3, d2> d3, so that more parallel light is efficiently used than in the case of d2 <d3. I can make it well.

  FIG. 7 is a diagram simulating the light rays of the light guide according to the present embodiment. From this figure, it can be seen that many rays are parallel to each other. In the light guide shown in FIG. 7, the number of the reflecting surfaces of the collimator is larger than the number of the reflecting surfaces 2a of the collimator shown in FIG.

  FIG. 8 is a photograph showing a state in which a light emission test was performed using a prototype. FIG. 8A shows an example in which one light source block and one collimator are provided. There is one light guide plate.

  FIG. 8B shows an example in which two light source blocks and two collimators are provided. There is one light guide plate, and two light-projecting surfaces are provided on the light incident surface of the light guide plate. Thus, an example in which a plurality of light source blocks and a plurality of collimators are provided is also conceivable. The plurality of collimators can be configured as a single unit rather than as separate units.

  FIGS. 9A and 9B show design diagrams of the collimator used in the prototypes of FIGS. 8A and 8B, respectively (unit: mm). Of course, these collimators are just examples.

  FIG. 10 is a diagram showing a boundary layer of a collimator and a light guide plate according to another embodiment of the present invention. In these drawings, the vicinity of the boundary layer, particularly the vicinity of the first boundary layer is shown, and the other parts are omitted because they are the same as those in the above embodiment.

  The shape of the boundary layer shown in FIG. 10 is all included in the concept of “convex shape toward the incident surface”. Members indicated by reference numerals 23, 33, and 43 are light guide plates, and members indicated by reference numerals 22, 32, and 42 are collimators.

  Part of the first boundary layer according to the example shown in FIG. 10A is provided with a portion 17 substantially parallel to the incident surface of the collimator. A curved portion 18 is provided in a part of the first boundary layer according to the example shown in FIG. The first boundary layer according to the example shown in FIG. The curve 19 is, for example, an arc, but may be an ellipse, a parabola, or a hyperbola.

  FIG. 11 shows an example in which θ and d1 in the form shown in FIG. 3 are modified, and is a diagram in which light rays are simulated for each of FIGS. 11 (A) to 11 (C). D1-1 shown in FIG. 11A is set longer than d1-2 shown in FIGS. 11B and 11C. In FIG. 11A and FIG. 11B, θ1 is about 110 °. In FIG. 11C, θ2 is about 80 °. Among them, the example shown in FIG. 11B produces the most parallel rays.

  FIG. 12 is a plan view showing a light guide provided with a plurality of light source blocks, for example. In this light guide 20, as described in the description of FIG. 8B, a plurality of light source blocks 4 and a plurality of collimators 2 are attached to one light guide plate 53. In this case, each light emitted from the plurality of light source blocks 4 is converted into substantially parallel light in the light guide plate 53.

  FIG. 13 is a perspective view showing a laptop PC (Personal Computer) as an electronic apparatus equipped with a display including the light guide 20 shown in FIG. In this PC 100, the light source block 4 and the collimator 2 are disposed at the lower part of the display 24, but may be disposed at at least one of the left and right end portions of the display 24. When the light guide 20 is incorporated in a device about the size of the PC 100, the number of the light source blocks 4 and the collimators 2 will be further increased than that shown in FIG.

  In FIG. 13, a PC is taken as an example of an electronic device. However, not only a PC but also a PDA (Personal Digital Assistance), an electronic dictionary, a camera, an audio / visual device, a mobile phone, a game device, a car navigation device, and other electrical appliances.

It is a top view which shows the light guide which concerns on one embodiment of this invention (and the light source block attached to this light guide). It is a side view of the light guide shown in FIG. It is a top view of the light guide which expanded the vicinity of the light source block. It is sectional drawing which shows typically the structure of the display apparatus containing the light guide which concerns on one Embodiment. It is a figure for demonstrating the demerit in case there are few parallel lights in a light-guide plate. It is a figure for demonstrating the case where there are many parallel lights in the backlight which concerns on one Embodiment. It is the figure which simulated the light ray of the light guide which concerns on one Embodiment. It is the photograph which shows a mode that the light emission test was done by the prototype. FIG. 9 is a design diagram of a collimator used in each of the prototypes of FIGS. 8 (A) and 8 (B). It is a figure which shows the boundary layer of the collimator and light guide plate which concern on other embodiment of this invention. The example which changed (theta) and d1 in the form shown in FIG. 3 is shown. It is a light guide which concerns on another embodiment of this invention, Comprising: It is a top view which shows the light guide provided with multiple light source blocks. It is a perspective view which shows laptop PC as an electronic device carrying the display containing the light guide shown in FIG.

Explanation of symbols

p1 ... first light p2 ... second light p3 ... third light p4 ... fourth light 2, 22, 32, 42 ... collimator 2b ... incident surface 2a ... reflecting surface 2c ... notched surface 3,23, 33, 43, 53 ... Light guide plate 3c ... Projection surface 4 ... Light source block 4a ... Light emitting surface 8 ... Liquid crystal panel 9 ... Light emitting element 10, 20 ... Light guide 11 ... First boundary layer 12 ... Second boundary layer 24, 50 ... Display device 100 ... PC (electronic equipment)

Claims (9)

A light guide plate for guiding the light emitted from the light source block;
An optical element having an incident surface on which light emitted from the light source block is incident, and a reflective surface that is provided on the incident surface side and reflects the light toward the light guide plate;
Provided between the light guide plate and the optical element, transmits the first light having an angle smaller than the critical angle, enters the light guide plate, and reflects the second light having the critical angle or more. And a boundary layer that reflects the second light on the reflecting surface and enters the light guide plate .
The boundary layer is
Of the second light, third light having an angle smaller than a predetermined angle is reflected so as to be guided to the reflecting surface, and among the second light, fourth light having the predetermined angle or more is reflected. A first boundary layer to be
A second boundary layer that reflects the fourth light reflected by the first boundary layer so as to guide the fourth light to the reflecting surface;
With light guide. The light guide according to claim 1 ,
The light guide, wherein the first boundary layer is formed in a convex shape toward the incident surface. The light guide according to claim 1 ,
The light guide, wherein the second boundary layer is disposed in parallel to the incident surface. The light guide according to claim 1,
The optical element is a light guide having a reflective film on the reflective surface. The light guide according to claim 1 ,
The light source block has a plurality of light emitting elements arranged,
The length of the first boundary layer in the direction in which the plurality of light emitting elements are arranged is a light guide longer than the length of the light source block in the direction. The light guide according to claim 1 ,
A plurality of the light source blocks are provided,
A plurality of the first boundary layers are provided so as to correspond to the light source block. A light source block;
A light guide plate for guiding light emitted from the light source block;
An optical element having an incident surface on which light emitted from the light source block is incident, and a reflective surface that is provided on the incident surface side and reflects the light toward the light guide plate;
Provided between the light guide plate and the optical element, transmits the first light having an angle smaller than the critical angle, enters the light guide plate, and reflects the second light having the critical angle or more. And a boundary layer that reflects the second light on the reflecting surface and enters the light guide plate .
The boundary layer is
Of the second light, third light having an angle smaller than a predetermined angle is reflected so as to be guided to the reflecting surface, and among the second light, fourth light having the predetermined angle or more is reflected. A first boundary layer to be
A second boundary layer that reflects the fourth light reflected by the first boundary layer so as to guide the fourth light to the reflecting surface;
Backlight device having A light source block;
A light guide plate for guiding light emitted from the light source block;
An optical element having an incident surface on which light emitted from the light source block is incident, and a reflective surface that is provided on the incident surface side and reflects the light toward the light guide plate;
Provided between the light guide plate and the optical element, transmits the first light having an angle smaller than the critical angle, enters the light guide plate, and reflects the second light having the critical angle or more. A boundary layer that reflects the second light on the reflecting surface and enters the light guide plate;
A modulation element that modulates the intensity of light emitted by the light guide plate ,
The boundary layer is
Of the second light, third light having an angle smaller than a predetermined angle is reflected so as to be guided to the reflecting surface, and among the second light, fourth light having the predetermined angle or more is reflected. A first boundary layer to be
A second boundary layer that reflects the fourth light reflected by the first boundary layer so as to guide the fourth light to the reflecting surface;
A display device. A light source block;
A light guide plate that guides light emitted from the light source block, an incident surface on which light emitted from the light source block is incident, and a reflective surface that is provided on the incident surface side and reflects the light toward the light guide plate. A first light having an angle smaller than a critical angle is transmitted and incident on the light guide plate, and a second greater than or equal to the critical angle is provided between the optical element and the light guide plate and the optical element. A light guide having a boundary layer that reflects the second light and reflects the second light on the reflection surface to be incident on the light guide plate;
A modulation element for modulating the intensity of light emitted by the light guide;
A control unit that controls the modulation element in response to an operation input ,
The boundary layer is
Of the second light, third light having an angle smaller than a predetermined angle is reflected so as to be guided to the reflecting surface, and among the second light, fourth light having the predetermined angle or more is reflected. A first boundary layer to be
A second boundary layer that reflects the fourth light reflected by the first boundary layer so as to guide the fourth light to the reflecting surface;
Electronic equipment having