JP2013206595A - Light guide plate and lighting device as well as display device using light guide plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light guide plate realizing uniform luminance distribution and of superb appearance.SOLUTION: A light guide plate made of a platy transparent material is provided with side end faces as incident faces for taking in light from light sources, an emission face for emitting light, and a bottom face facing the emission face. At least the bottom face has a plurality of concave elements concave in a plat thickness direction, and a depth of the concave element increases as it gets away from the incident face in a first direction as a normal direction of the incident face in a first cross section vertical to the incident face and parallel with the plate thickness direction, while, in a second cross section parallel with the incident face, a depth of the concave element increases as it gets away from a center part of the second cross section in a first direction and a second direction orthogonal the plate thickness direction.

Description

  The present invention relates to a light guide plate, an illumination device using the light guide plate, and a display device.

  A display device such as a general liquid crystal display has an illumination device (backlight unit) on the back surface of a transmissive liquid crystal panel. This backlight unit is divided into two systems: a light guide (so-called edge light) system that multi-reflects light from a light source lamp within a flat light guide plate excellent in light transmission and a direct type system that directly illuminates with a light source lamp. Broadly divided.

  In an illuminating device in which a light source is arranged in the vicinity of a side end portion of this type of light guide plate, light incident on the light guide plate from one side end surface of the light guide plate is totally reflected on the plane portion of the light guide plate and is reflected in the light guide plate. Continue on. In addition, the shape of this light source is not limited, For example, a linear form and a dot form may be sufficient.

  When the surface of the light guide plate facing the display device (hereinafter referred to as the exit surface) and the opposite surface (hereinafter referred to as the bottom surface) are flat throughout, most of the incident light is the boundary between these and the outside air. The light is totally reflected on the surface, and the light emission efficiency from the light guide plate, that is, the irradiation efficiency to the display device is lowered. For this reason, many light guide plates have a large number of fine irregularities on the emission surface or bottom surface thereof, thereby preventing the repetition of only total reflection, thereby improving the light emission efficiency.

  In a display device using this type of lighting device, for example, a lighting device described in Patent Document 1 has been proposed as a method for reducing unevenness in luminance and uniformly brightening the entire screen. In Patent Document 1, light control elements that reflect / diffuse incident light are arranged at the same interval on the bottom surface of the light guide plate, and the size of the light control elements is increased as they move away from the light source, or equal in size. A configuration is shown in which the density is increased by changing the arrangement interval of the light control elements in a two-dimensional direction to be small.

  However, in the conventional light guide plate as described above, the luminance in the vicinity of the end surface facing the incident surface, particularly in the corners thereof, is insufficient, the luminance uniformity in the surface is poor, and the light control element in the vicinity of the light source In particular, since it is sparse, there is a problem that it is easily visible as a bright spot.

Japanese Patent Laid-Open No. 3-6525

  The present invention has been made in view of the above problems, and a main object of the present invention is to provide a light guide plate that realizes a uniform luminance distribution and has a good appearance.

  The present invention employs the following configuration in order to solve the above-described problems.

  The light guide plate of the first aspect is a plate-like light guide plate made of a transparent material, and is a side end surface that is an entrance surface for taking in light from a light source, an exit surface that emits light, and faces the exit surface. A bottom surface, and at least the bottom surface includes a plurality of concave elements that are concave in the plate thickness direction, and the depth of the concave elements is incident on the first cross section perpendicular to the plane of incidence and parallel to the plate thickness direction. In the second cross section parallel to the incident surface, the depth of the concave element increases from the center of the second cross section to the first direction and the first direction that is the normal direction of the incident surface. The distance increases in the second direction perpendicular to the plate thickness direction.

  The second aspect is that, in the first aspect, in the second cross section, the difference between the depth of one of the concave elements at both ends spaced in the second direction and the depth of the concave element at the center is the second The cross section increases as the distance from the incident surface increases in the first direction.

  A third aspect is characterized in that, in the first or second aspect, the occupied area per unit area with respect to the bottom surface of the concave element increases as the distance from the incident surface increases in the first direction.

  In a fourth aspect according to any one of the first to third aspects, in the second cross section of the point where the incident surface is one side end surface and the distance in the first direction from the incident surface is α mm, The ratio ΔH of the difference between the depth of one of the concave elements at both ends spaced in two directions and the depth of the concave element at the central portion to the depth of the concave element at the central portion is such that every time α increases by 5 mm, It is characterized by an increase of 0.07 to 0.09%.

  According to a fifth aspect, in any one of the first to third aspects, the incident surface is two opposing side end surfaces, and the distance in the first direction from the closer of the two incident surfaces is α mm. In the second cross section of the point, the ratio ΔH of the difference between the depth of the concave element at either end spaced in the second direction and the depth of the concave element at the central part to the depth of the concave element at the central part is When α increases by 5 mm, it increases by 0.07 to 0.09%.

  The illumination device according to a sixth aspect includes the light guide plate according to any one of the first to fifth aspects and a light source unit.

  A display device according to a seventh aspect includes the illumination device according to the sixth aspect and an image display element that defines a display image.

  According to the above configuration, a large number of minute concave elements are formed on the bottom surface of the light guide plate, and the concave elements are in a direction perpendicular to the incident surface and a direction parallel to the incident surface. Its depth changes. As a result, a uniform luminance distribution can be realized on the exit surface of the light guide plate. In addition, in the region close to the incident surface, the concave element with low light emission ability can be arranged with a large occupied area, preventing the concave element from being visually recognized as a bright spot in the region, and improving the appearance. be able to.

  According to the present invention, it is possible to provide a light guide plate that realizes a uniform luminance distribution and has a good appearance.

1 is an exploded sectional view of a display device 1 according to an embodiment of the present invention. A front view, a plan view, and a side view showing an arrangement example of the concave elements 9 when the light source 4 is disposed only on one end face side of the light guide plate 6. The front view and top view which show the example of arrangement | positioning of the concave element 9 when the light source 4 is distribute | arranged to the both-sides end surface side which the light-guide plate 6 opposes Schematic diagram showing the path of light incident on the light guide plate 6 Schematic showing an example of the shape of the concave element 9 Schematic diagram showing an example of the division of the bottom surface 8 Schematic diagram showing an example of the division of the bottom surface 8 Schematic diagram showing the measurement points on the exit surface 10 in the evaluation of the deviation of the surface brightness

  Hereinafter, a display device 1 according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is an exploded perspective view showing an example of the configuration of the display device 1 using the light guide plate 6 according to the present embodiment. As shown in FIG. 1, the display device 1 includes an illumination device 2 and an image display panel 3.

  The illumination device 2 includes an optical sheet 11, a light guide plate 6, a reflection sheet 5, and a light source 4 and is configured in a rectangular plate shape or a wedge shape.

  The light source 4 includes light emitting elements such as CCFL (Cold Cathode Fluorescent Lamp), HCFL (Hot Cathode Fluorescent Lamp), EL (Electro Luminescence), and LED (Light Emitting Diode). More preferably, the light source 4 is provided with a housing that reflects the light and efficiently enters the light guide plate 6 so as to cover the light of the light source 4. The light source 4 may be disposed only on one side end face side of the light guide plate 6 (see FIG. 2 described later), but may be disposed on both end face sides (see FIG. 3 described later).

  The reflection sheet 5 is provided in order to prevent light loss due to light incident on the light guide plate 6 coming out of the bottom surface. As the reflection sheet 5, for example, a resin sheet in which a void is formed by kneading and stretching a filler in PET, PP or the like to increase the reflectivity, or a transparent or white resin having a mirror surface formed by vapor deposition of aluminum on the surface. A sheet, a metal foil such as aluminum, a resin sheet carrying the metal foil, or a metal thin plate having sufficient reflectivity on the surface can be used.

  The light guide plate 6 has a function of guiding light from the light source 4 to the entire surface of the image display panel 3. The light guide plate 6 is a plate-like object made of a transparent material, and has an emission surface 10 that emits light in a direction in which the image display panel 3 is positioned, and a bottom surface 8 that faces the emission surface 10. A large number of fine concave elements 9 are formed on the bottom surface 8. Light incident from one end face (incident surface 7) of the light guide plate 6 travels inside the light guide plate 6 while totally reflecting the flat portion of the light guide plate 6. At this time, since the concave element 9 is formed on the bottom surface 8 of the light guide plate 6, the path of incident light is changed at the interface of the concave element 9 as shown in FIG.

  The light guide plate 6 is made of a material having high light transmittance and low birefringence. For example, UV or radiation curable resin is used on a substrate such as glass, or a thermoplastic resin material such as polymethyl methacrylate (PMMA), polycarbonate (PC), or cyclic olefin copolymer (COC) is used. Then, it is molded by a known extrusion molding method or injection molding method.

  Although the thickness of the light-guide plate 6 is not specifically limited, About 0.5-5 mm is preferable. If it is thinner than 0.5 mm, it is easy to break, and the handleability is deteriorated. If it is thicker than 5 mm, the entire backlight unit becomes large and its application is limited. For example, it is not suitable for a thin display.

  The optical sheet 11 is disposed between the light guide plate 6 and the image display panel 3. In FIG. 1, two optical sheets are used, but the number of sheets is not limited. The optical sheet 11 is, for example, a prism sheet that is a resin film having a prism structure, a micro lens sheet having a micro lens structure, a diffusion sheet in which fine particles having different refractive indexes are mixed, and the like, and exhibits a light diffusing or condensing effect. . The former means that the deviation of the light source incident from the light source due to the direction of the arrangement of the light sources, the occurrence of local light and darkness due to scratches or dirt on the light guide plate 6, and the concave element 9 on the bottom surface 8 can be easily recognized. prevent. The latter improves the brightness by narrowing the distribution of the angles of light emitted from the light guide plate 6.

  The image display panel 3 includes two polarizing plates (polarization films) 12 and 13 and an image display element 14 sandwiched therebetween. The image display panel 3 is constituted by a liquid crystal panel, for example, and the image display element 14 is constituted by filling a liquid crystal layer between two glass substrates. The liquid crystal display element selected as the image display element 14 is a typical element that transmits and blocks light in pixel units and displays an image, and can improve image quality compared to other display elements. .

  Next, the shape of the concave element 9 will be described with reference to the drawings. FIG. 2 shows a front view, a plan view, and a cross-sectional side view of the concave element 9 formed on the bottom surface 8 of the light guide plate 6. In FIG. 2, the light source 4 is disposed only on one end face side of the light guide plate 6 (left side of the light guide plate 6 shown in the front view of FIG. 2), and the light guide plate 6 has one incident surface 7 (FIG. 2). Only the left end portion of the light guide plate 6 shown in the front view of FIG. In FIG. 2, the normal direction of the incident surface 7 is set as the x direction, the thickness direction of the light guide plate 6 is set as the h direction, and the x direction and the direction orthogonal to the h direction are set as the y direction.

  As shown in FIG. 2, the light guide plate 6 has a concave element 9 on the bottom surface 8 that is concave in the thickness direction (h direction). The size of the concave element 9 is preferably such that it is not clearly visible, and preferably fits in a 300 um square. The concave element 9 may be formed not only on the bottom surface 8 but also on a plurality of surfaces including the bottom surface 8.

  The shape of the bottom surface 8 of the concave element 9 is not particularly limited. For example, it may be a perfect circle or a star shape, but a substantially rectangular shape or a substantially oval shape is preferable. In the case of a substantially rectangular shape or a substantially elliptical shape, the long side direction of each figure is preferably parallel to the incident surface 7 (y direction shown in FIG. 2). Incident light from the light source 4 travels in the light guide plate 6 in a direction that is mainly perpendicular to the incident surface (the x direction shown in FIG. 2), and is reflected on the inclined surface extending in the y direction of the concave element 9 to be emitted. Is done. Therefore, in order to efficiently launch light with a small number of concave elements 9, it is preferable to arrange the substantially rectangular or substantially elliptical concave elements 9 so that the long side direction thereof is in the y direction.

  As shown in the front view of FIG. 2, the concave element 9 has a depth or height that increases as the distance from the incident surface increases in the direction perpendicular to the incident surface 7 (the x direction shown in FIG. 2). It is formed to increase. In the x direction, the height of the concave element 9 increases monotonously as the distance from the incident surface 7 increases, but the change may be continuous or intermittent.

  Further, as shown in the sectional side view of FIG. 2, the concave element 9 has a section parallel to the incident surface 7 (y-direction section shown in the sectional side view of FIG. 2), and its distance from the center increases. It is formed to increase its height. Specifically, in the y-direction cross section of the light guide plate 6, the height (he) of the concave element 9 at both ends is higher than the height (hc) of the concave element 9 at the center of the cross section, and the difference Δh is This increases as the distance in the x direction from the light source 4 in the cross section in the y direction increases. In the conventional light guide plate 6, in the cross section in the y direction at a certain point, both end portions are darker than the central portion, and the difference between the two becomes larger as the distance in the x direction from the light source 4 at that point increases. This non-uniformity can be eliminated by increasing Δh in the cross section in the y direction of the light guide plate 6 as the distance in the x direction from the light source 4 increases.

  As described above, in the x direction of the light guide plate 6, by disposing the concave elements 9 that emit light more efficiently in the regions farther from the incident surface 7 and the both end regions of the y-direction cross section, these regions are Darkening can be prevented and surface luminance uniformity can be improved. Further, in order to obtain uniform luminance, the conventional light guide plate 6 arranged so that the size of the concave elements 9 and / or the arrangement density of the concave elements 9 increases as the distance from the incident surface 7 increases. The concave element 9 is so sparse that it tends to stand out as a bright spot, but by reducing the height of the concave element 9 in that region, that is, by arranging the concave element 9 having a lower light emission ability, Since the area occupied by the concave element 9 in the region can be increased and the light / dark ratio can be decreased, the concave element 9 can be hardly seen.

  Here, when the distance from the incident surface 7 where the height of the concave element 9 is the largest in the x direction is x1, as shown in FIG. 2, when the light guide plate 6 has the incident surface 7 having only one side end surface, x1 is equal to the length of the light guide plate 6 in the x direction. At this time, the ratio Δh% of the height difference Δh between he and hc to the height of hc at a point where the distance from the incident surface 7 is α mm in the x direction is approximately 0 every time α increases by 5 mm. 0.08% increase is preferred.

  In a general light guide plate in which the heights of the concave or convex light control elements are uniform, the difference in luminance between the both end portions and the central portion of the light guide plate in the y direction increases as the distance from the incident surface 7 increases. However, as described above, by increasing ΔH as described above as α increases, it is possible to eliminate the uneven luminance in the y direction. Note that if the amount of change in ΔH with respect to increase / decrease in α is too small, the brightness at both ends is insufficient in the y direction, and if the amount of change in ΔH with respect to increase / decrease in α is too large, both ends in the y direction become bright. In any case, the luminance distribution of the exit surface 10 of the light guide plate 6 is biased.

  It is even better if the concave elements 9 increase in density, ie the area occupied by the concave elements 9 per unit area on the bottom surface 8, as the distance from the entrance surface 7 in the x direction increases. The change in the occupied area ratio on the bottom surface 8 may be due to a change in the area per concave element 9, a change in the number of concave elements 9, or both. Further, the change in the occupation area ratio may be continuous or discontinuous. However, since the former requires complicated arrangement data and high molding accuracy, the latter is easier to manufacture. Examples of the latter include dividing the bottom surface 8 into a plurality of blocks and changing them in stages.

  In the above description, it is assumed that the light source 4 is disposed only on one end face side of the light guide plate 6 (left side of the light guide plate 6 shown in the front view of FIG. 2). However, as shown in FIG. 3, the light source 4 is disposed on both side end surfaces of the light guide plate 6 (left and right sides of the light guide plate 6 shown in the front view of FIG. 3). It is good also as what has the entrance plane 7 (right-and-left both ends of the light-guide plate 6 shown to the front view of FIG. 3). In this case, the change in the height of the concave element 9 is the same as that described with reference to FIG. 2 in the y direction, but is different from that in FIG. 2 in the x direction. Specifically, the height of the concave element 9 is formed so as to increase as the distance from the closest incident surface 7 out of the two incident surfaces 7 increases. Therefore, the height of the concave element 9 is maximized at the center of the light guide plate 6 in the x direction. That is, when the distance from the left incident surface 7 where the height of the concave element 9 is the largest in the x direction is x2, x2 is equal to half the length of the light guide plate 6 in the x direction. At this time, in the x direction, the ratio Δh% of the height difference Δh between he and hc to the height of hc at the point where the distance from the closest incident surface 7 of the two incident surfaces 7 is α mm. Is preferably increased by approximately 0.08% for each 5 mm increase in α.

  In the above embodiment, ΔH is preferably increased by approximately 0.08% every time α is increased by 5 mm, based on the following simulation result. First, the light guide plate 6 is a rectangular plate made of PMMA, has an x-direction length of 300 mm, a y-direction length of 500 mm, and a thickness of 3 mm. A fine concave element 9 is arranged on the bottom surface 8 of the light guide plate 6. The height H is assumed to be uniform over the entire surface. Then, using a plurality of light guide plates 6 having different heights H, the relationship between the height H and the center luminance was examined by simulation using lighting design analysis software LightTools manufactured by Optical Research Associates. As a result, the luminance was increased by about 2%.

  Next, the light guide plate 6 is a rectangular flat plate made of PMMA, has an x-direction length of 300 mm, a y-direction length of 500 mm, and a thickness of 3 mm, and a fine concave element 9 is disposed on the bottom surface 8 of the light guide plate 6. Using the light guide plate 6 having a uniform height H of 20 μm, the distance αmm in the x direction from the incident surface 7 at a certain point and the ratio of the luminance difference between the central portion and both ends to the luminance of the central portion in the y-direction As a result of examining the relationship of Δb, it was found that Δb increased by about 0.16% as the distance from the incident surface 7 increased by 5 mm in the x direction. The luminance was measured using a spatial luminance meter ProMetric (PM-1200) manufactured by Cybernet. From the above results, the ratio Δh% of the height difference Δh between he and hc to the height of hc at the point where the distance in the x direction from the incident surface 7 is α mm is approximately every time α increases by 5 mm. An increase of 0.08% was preferred.

  As described above, the light guide plate 6, the illumination device 2 including the light guide plate 6, and the display device 1 including the illumination device 2 according to the embodiment have been described. However, the illumination device 2 is not applied only to the display device 1. Absent. The technical scope of the present invention is not limited to the above-described embodiment, and various modifications such as a shape change can be made without departing from the spirit of the present invention. Examples of the present invention will be described in detail below, but the present invention is not limited to the following examples.

  The light guide plate 6 used in this example is a rectangular plate made of PMMA, the length in the x direction is 300 mm, the length in the y direction is 500 mm, and the length (thickness) in the h direction is 3 mm. The concave elements 9 arranged on the bottom surface 8 of the light guide plate 6 are each a concave lens having a substantially semi-ellipsoidal shape shown in FIG. 5, a microlens shape having a length WL = 200 μm, a width WS = 100 μm, and a height H = 10 μm. It was. Further, the light source 4 is disposed only on one side end face side (left end face side shown in FIG. 6) of the light guide plate 6, the bottom face 8 is divided into six regions shown in FIG. 6, and the incident face 7 (shown in FIG. 6). As the distance from the left end surface increases, the area occupied by the bottom surface 8 of the concave element 9 is intermittently increased at the boundary between the regions.

  A white LED was used as the light source 4, the reflective sheet 5 was disposed on the bottom surface 8 side of the light guide plate 6, and the optical sheet 11 was disposed on the light exit surface 10 side of the light guide plate 6 to produce the lighting device 2.

  Hereinafter, a change in which the height of the concave element 9 on the bottom surface 8 becomes higher as the distance from the incident surface 7 in the x direction increases is referred to as an accompanying x change. On the other hand, a change in which the height of the concave element 9 on the bottom surface 8 increases as the height of the concave element 9 increases from the center of the light guide plate 6 in the y direction is referred to as an accompanying y change.

  In Examples 1 to 8, the height of the concave element 9 on the bottom surface 8 increases as the distance from the incident surface 7 increases in the x direction and increases as the distance from the center of the light guide plate 6 increases in the y direction. A light plate 6 was used. In other words, the light guide plates 6 of Examples 1 to 8 have a change in accompanying x and a change in accompanying y.

  In the light guide plate 6 of Example 1, both the accompanying x change and accompanying y change were continuously changed over the entire bottom surface 8. In the light guide plate 6 of Example 2, the accompanying x change was continuous, but the accompanying y change was intermittently changed at the boundary of the five regions shown in FIG. In the light guide plate 6 of Example 3, the accompanying x change was changed intermittently at the boundary of the six regions shown in FIG. 6, and the accompanying y change was changed continuously. In the light guide plates 6 of Examples 4 to 8, the accompanying x change was intermittently changed at the boundary of the six regions shown in FIG. 6, and the accompanying y change was changed intermittently at the boundary of the five regions shown in FIG. In Examples 4 to 8, the amount of change in accompanying y change was changed.

  About the said Examples 1-4, the brightness | luminance in 25 points | pieces of the injection surface 10 shown in FIG. 8 was measured. Each numerical value shown in FIG. 8 indicates the ratio of the distance in each direction when the length of the light guide plate 6 in the x direction is 1 and the length in the y direction is 1. And the ratio (M / m) of the maximum value (M) with respect to the minimum value (m) among the brightness | luminances of 25 points | pieces was calculated. The surface brightness uniformity was evaluated as NG when the M / m value exceeded 1.25. The luminance at each point was measured with a spectral radiance meter SR-UL2 manufactured by Topcon. Further, the visibility of the concave element 9 was visually evaluated. The evaluation results of Examples 1 to 4 are shown in Table 1, and the evaluation results of Examples 4 to 8 are shown in Table 2.

  In Examples 1 to 4, the accompanying x change and accompanying y change were prepared as continuous and discontinuous, but in any of these, the surface luminance uniformity and the visibility of the concave element 9 were Both were good results. This indicates that the accompanying x change and accompanying y change, whether continuous or discontinuous, have no significant difference in the effect on the surface luminance uniformity and visibility.

  In each of Examples 5 to 8, the surface luminance uniformity and the visibility of the concave element 9 were both good, but the M / m values of Examples 1 to 4, 6 and 7 were 1.20. The M / m values of Examples 5 and 8 were more than 1.20 and slightly inferior, while being particularly excellent. From this, it was shown that the amount of change in the accompanying y is good in the surface luminance uniformity such that ΔH increases or decreases by 0.07 to 0.09% with respect to the increase or decrease of α by 5 mm.

  As Comparative Example 1, a light guide plate 6 having an accompanying x change but no accompanying y change was prepared. In Comparative Example 2, the light guide plate 6 having no accompanying x change and having accompanying y change was used. In Comparative Example 3, the light guide plate 6 having no accompanying x change and no accompanying y change was used. These accompanying x changes and accompanying y changes were assumed to be discontinuous.

  About these comparative examples 1-3, the brightness | luminance in 25 points | pieces of the output surface 10 shown in FIG. 8 was measured, and the ratio (M / m) of the maximum value (M) with respect to the minimum value (m) was computed. The surface brightness uniformity was evaluated as NG when the M / m value exceeded 1.25. The luminance at each point was measured with a spectral radiance meter SR-UL2 manufactured by Topcon. Further, the visibility of the concave element 9 was visually evaluated. Table 3 shows the evaluation results of Example 4 and Comparative Examples 1 to 3.

  The surface luminance uniformity was good only in Example 4 and not in Comparative Examples 1 to 3. Although the M / m value of Comparative Example 2 was less than 1.3, the M / m values of Comparative Examples 1 and 3 exceeded 1.3, and the uniformity of surface luminance was particularly poor.

  As for visibility, Example 4 and Comparative Example 1 were good, and Comparative Examples 2 and 3 were poor. From this test, it was shown that the concave element 9 formed in the light guide plate 6 needs to have both an accompanying x change and an accompanying y change.

DESCRIPTION OF SYMBOLS 1 Display apparatus 2 Illumination apparatus 3 Image display panel 4 Light source 5 Reflective sheet 6 Light guide plate 7 Incident surface 8 Bottom surface 9 Concave element 10 Output surface 11 Optical sheets 12, 13 Polarizing plate 14 Image display element

Claims (7)

A light guide plate of a plate-like material made of a transparent material,
A side end surface that is an incident surface that takes in light from the light source, an emission surface that emits the light, and a bottom surface that faces the emission surface,
At least the bottom surface includes a plurality of concave elements that are concave in the thickness direction,
In the first cross section perpendicular to the incident surface and parallel to the plate thickness direction, the depth of the concave element increases as the distance from the incident surface increases in the first direction that is the normal direction of the incident surface. ,
In the second cross section parallel to the incident surface, the depth of the concave element increases as the distance from the central portion of the second cross section increases in the second direction perpendicular to the first direction and the plate thickness direction. Characteristic light guide plate.   In the second cross section, the difference between the depth of the concave element at either end portion spaced apart in the second direction and the depth of the concave element at the central portion is that the second cross section is The light guide plate according to claim 1, wherein the light guide plate increases as the distance from the first direction increases.   3. The light guide plate according to claim 1, wherein an occupation area per unit area of the concave element with respect to the bottom surface increases as the distance from the incident surface increases in the first direction. 4. The incident surface is one of the side end surfaces,
In the second cross section at a point where the distance in the first direction from the incident surface is α mm, the depth of the concave element at either end portion spaced in the second direction and the concave element in the central portion The ratio ΔH of the difference from the depth to the depth of the concave element in the central portion increases by 0.07 to 0.09% every time α increases by 5 mm. The light guide plate according to any one of the above. The incident surface is two opposite side end surfaces,
In the second cross section at a point where the distance in the first direction from the closer of the two incident surfaces is α mm, the depth of the concave element at either end portion spaced in the second direction, The ratio ΔH of the difference from the depth of the concave element in the central portion to the depth of the concave element in the central portion increases by 0.07 to 0.09% every time α increases by 5 mm. The light guide plate according to any one of claims 1 to 3.   An illumination device comprising: the light guide plate according to claim 1; and a light source unit.   A display device comprising the illumination device according to claim 6 and an image display element for defining a display image.

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