JP3875362B2 - Light guide plate and flat illumination device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a light guide plate that radiates light introduced from a side end surface from the surface and a flat illumination device using the light guide plate, and is particularly suitable for use in illumination of a liquid crystal display surface.
[0002]
[Prior art]
A flat illumination device used as a so-called backlight source of a liquid crystal display guides light from a light source lamp from the side end surface of a transparent light guide plate into the light guide plate, and uses light reflection in the light guide plate to guide the light. This light is uniformly emitted from the entire surface of the optical plate. In consideration of the characteristics of the liquid crystal display in which the flat illumination device is used, the functions required for this flat illumination device are that it is a thin plate as a whole and that the power consumption of the light source lamp is minimized. In addition, it is particularly important to emit uniform light throughout.
[0003]
For this purpose, the conventional flat illumination device is provided with a light reflecting sheet on the back side of the light guide plate and arranged in parallel with isosceles triangular prism surfaces having an apex angle of approximately 90 degrees on the front side of the light guide plate. A structure is adopted in which two prism sheets are overlapped so that the longitudinal directions of these prism surfaces are orthogonal to each other. That is, the light emitted from the back side of the light guide plate is again incident on the light guide plate by the light reflecting sheet, and the light emitted from the surface of the light guide plate is converged by the pair of prism sheets so that high-intensity illumination light can be obtained. Consideration.
[0004]
In addition, in order to uniformly disperse light incident on the light guide plate, an infinite number of dots having a size of about several hundreds μm are printed on the back surface of the light guide plate with white ink or the like. In this case, a light diffusing plate is interposed between the light guide plate and the prism sheet so that the dots are not obstructed, and the light emitted from the surface of the light guide plate is dispersed by the light diffusing plate.
[0005]
[Problems to be solved by the invention]
The light emitted from the surface of the light guide plate usually has uncontrollable directivity depending on the structure of the light guide plate, and the direction in which the maximum luminance is obtained may not match the desired viewing direction. Is almost. For this reason, when the prism sheet is simply overlapped on the surface of the light guide plate, the light from the light guide plate is emitted only from one slope side of the prism surface, and the light intensity with a uniform distribution cannot be obtained.
[0006]
Printing with white ink dots on the back surface of the light guide plate to diffuse the light propagating through the light guide plate has the disadvantage of causing light absorption loss. Moreover, since it is necessary to use a light diffusing plate so that these dots are not conspicuous, most of the light passing through this light diffusing plate becomes diffused light, resulting in a significant reduction in brightness, resulting in a large amount of light. Large power consumption because it is necessary to use a large bright light source. In addition, control of the direction of light travel becomes impossible.
[0007]
Moreover, although the conventional prism sheet can converge the diffused light from the light guide plate, the light emitted from the light guide plate is not perpendicular to the surface of the light guide plate, but is generally inclined in a direction away from the light source. There are many ingredients. For this reason, the conventional prism sheet cannot deflect light emitted from the surface of the light guide plate in a desired direction, that is, a direction perpendicular to the surface of the light guide plate.
[0008]
Furthermore, the conventional flat illumination device uses two prism sheets in addition to the light diffusing plate superimposed on the light guide plate, so that the number of parts is large and the thickness cannot be reduced as a whole. It was. In addition, it is necessary to use a bright light source with a large amount of light due to a large loss of light due to interface reflection between the light diffusing plate and the two prism sheets. Become.
[0009]
OBJECT OF THE INVENTION
A first object of the present invention is to provide a light guide plate that can emit light with a desired distribution with little loss and high brightness.
[0010]
A second object of the present invention is to provide a flat illumination device that has not only light loss but also a small number of parts, is thin and compact, and can reduce power consumption.
[0011]
[Means for Solving the Problems]
The first aspect of the present invention introduces light from a light source located on one side of the front surface portion and the back surface portion, a front surface portion from which light is emitted, a back surface portion located on the opposite side of the front surface portion. And a light guide plate for emitting light incident from the incident end surface portion from the surface portion, and the surface portion has light collecting properties and direction controllability. In addition, a plurality of forward projections for emitting light reflected from the back surface portion from the front surface portion are randomly formed, and the forward projections are projected perpendicularly to the front surface portion. The contoured shape forms a triangle having one side substantially parallel to the incident end face part, and the one side is located on the incident end face part side with respect to the vertex that does not include the one side of the triangle. A pair of vertical surfaces that are substantially vertical and do not include the one side It is characterized in.
[0012]
According to the present invention, a part of the light from the light source that has entered the light guide plate from the incident end face part is totally reflected toward the surface part side at the back surface part of the light guide plate, and a part thereof is a forward convex part. The light enters and exits from the light guide plate in a state of being more perpendicular to the surface while being condensed.
[0013]
According to a second aspect of the present invention, the light guide plate according to the first aspect of the present invention, a light source that projects light toward the incident end surface portion of the light guide plate, and the surface portion of the light guide plate. And a prismatic prism surface extending in a direction parallel to the incident end surface portion of the light guide plate and arranged in a direction orthogonal to the incident end surface portion, and is superimposed on the surface portion of the light guide plate. it has been in flat illumination device, characterized in that it comprises a light deflector for deflecting the light emitted in a predetermined direction from the surface portion of the light guide plate.
[0014]
According to the present invention, a part of the light from the light source that has entered the light guide plate from the incident end face part is totally reflected toward the front surface side by the back surface part of the light guide plate, and a part of the light enters the convex part and is collected. Light is emitted to the outside of the light guide plate in a state of being more perpendicular to the surface portion. The light emitted from the surface portion of the light guide plate in this way is deflected in a predetermined direction by the light deflection plate.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
In the light guide plate or the flat illumination device according to the present invention, a triangular prism-like prism surface may be formed on the back surface portion of the light guide plate in a direction parallel to the incident end surface portion and extending in a direction orthogonal to the incident end surface portion. . Further, the contour shape projected perpendicularly to the surface portion forms a triangle having one side substantially parallel to the incident end surface portion, and the apex not including the one side of the triangle is located closer to the incident end surface portion than the previous one side. A plurality of convex portions in the reverse direction are randomly formed on the surface portion, and the convex portions in the reverse direction have a pair of vertical surfaces that are substantially perpendicular to the surface portion and do not include the one side. Good.
[0016]
In this case, the triangles of the convex portions in the forward direction and the reverse direction are preferably isosceles triangles, and are triangular pyramids that are inclined with respect to the surface portion and include a conical surface including one side and a pair of vertical surfaces. There may be, and a triangular prism shape may be sufficient. These forward and reverse convex portions may be formed integrally by sharing one side, and in this case, the convex portions may form a quadrangular prism as a whole. Furthermore, the angle formed by the two hypotenuses including the apex of the triangle is tan ⁻¹ when the refractive index of the material constituting the convex portion is n and the angle between the light ray incident on the convex portion and the flat portion is β. It is desirable that it is not less than [cosβ · tan {π-2sin ⁻¹ (1 / n)}]. In addition, the ratio of the forward projections per unit area of the surface portion is set to increase as the distance from the incident end face portion increases, or the ratio of the forward and reverse projections per unit area of the surface portion is set to the incident end face. It is desirable to set a relatively large value at both end portions in the width direction of the surface portion along the longitudinal direction of the portion. The size of the forward and reverse convex portions is preferably 150 μm or less. Furthermore, the lengths of the two hypotenuses of the convex portions in the forward direction may be different from the lengths of the two hypotenuses of the convex portions in the reverse direction .
[0017]
On the other hand, in the flat illumination device according to the present invention, a light reflection sheet may be further provided to cover portions other than the surface portion and the incident end surface portion of the light guide plate. In addition, light diffusing fine irregularities may be formed on at least one of the prism surface and the plane portion of the light deflection plate. Further, an angle formed between the flat surface portion of the light deflector plate and the inclined surface in which the distance between the flat surface portion increases toward the incident end surface portion side of the light guide plate, You may make it make it smaller than the angle | corner made.
[0018]
【Example】
An embodiment of the flat illumination device according to the present invention incorporating the light guide plate according to the present invention will be described in detail with reference to FIGS. 1 to 10, but the present invention is not limited to such an embodiment, and these are further combined. Or can be applied to technologies in other fields including similar problems.
[0019]
FIG. 1 shows a cross-sectional structure of the flat illumination device according to the first embodiment of the present invention, and FIG. That is, the flat illumination device 11 in the present embodiment includes a light guide plate 12 having a rectangular plate shape, a linear light source lamp 14 disposed along the incident end surface portion 13 of the light guide plate 12, and the light guide plate 12. The light deflector 16 is superimposed on the surface portion 15, and the light reflecting sheet 17 covers the light guide plate 12 other than the incident end surface portion 13 and the surface portion 15. The light source lamp 14 composed of a cold cathode tube and a plurality of LEDs is surrounded by a reflector 18 having a concave curved reflecting surface, and the reflected light from the reflector 18 is substantially parallel to the surface portion 15. The light enters the light guide plate 12 from the incident end face portion 13 of the light guide plate 12.
[0020]
The light guide plate 12 in this embodiment is formed of a transparent acrylic resin (PMMA), and an incident end face part 13 for introducing light from the light source lamp 14 and a reflection located on the opposite side of the incident end face part 13. An end face 19 surrounded by the end face 19, a pair of side end faces 20 connected to both ends of the incident end face 13 and the reflection end face 19, and the incident end face 13, the reflection end face 19 and the side end face 20. It has the surface part 15 for emitting the light which injected from the part 13, and the back surface part 21 located in the other side. Further, the back surface portion 21 is about 0.5 to 1 degree with respect to the front surface portion 15 so that the distance between the front surface portion 15 and the back surface portion 21 becomes narrower toward the reflecting end surface portion 19 side than the incident end surface portion 13 side. The taper is inclined.
[0021]
The light reflection sheet 17 described above covers the reflection end surface portion 19, the pair of side end surface portions 20, and the back surface portion 21 of the light guide plate 12, and reflects the light emitted from these into the light guide plate 12 again. The light is emitted from the surface portion 15 and is formed by bending white paper or the like.
[0022]
The surface portion 15 of the light guide plate 12 is schematically shown in FIG. 3, and the extracted and enlarged shape of the convex portion in the forward direction (hereinafter referred to as “ first” ) in this embodiment is shown in FIG. That is, on the surface portion 15 of the light guide plate 12, the contour shape projected perpendicularly to the surface portion 15 forms a triangle, and an isosceles triangular pyramid having a pair of symmetrical vertical conical surfaces 22 and inclined conical surfaces 23. Liquid crystal in the case where first convex portions 24 having a shape are randomly arranged, between the first convex portions 24 and a light deflecting plate 16 described later, and when this flat illumination device is used as a backlight light source of a liquid crystal display. Consideration is given so that moire fringes and the like do not occur between the panel cell and the first convex portion 24, respectively. In this case, it is preferable to set an arbitrary one side of each first convex portion 24 to a size of 150 μm or less so that the individual first convex portions 24 cannot be identified with the naked eye. Is preferably 10 μm or more, and by setting the size of the first convex portion 24 in the range of 10 to 150 μm, it is not necessary to use a conventional light diffusing plate, and the light progresses. The direction can be controlled relatively easily.
[0023]
Further, although it is preferable that the vertical conical surface 22 of the first convex portion 24 is perpendicular to the surface portion 15, it is necessary to set an appropriate draft for the mold at the time of manufacturing the light guide plate 12. The angle formed by the surface portion 15 may be set to exceed 90 degrees. Further, the base 25 of the inclined cone surface 23 of the protrusion 24 is set to be substantially parallel to the incident end surface portion 13.
[0024]
By the way, the light incident on the incident end face portion 13 of the light guide plate 12 with an incident angle, that is, the angle between the surface portion 15 and the light beam, is γ. The refractive index n of the material constituting the light guide plate 12 (the acrylic resin of this embodiment) In the case of n = 1.49), 0 ≦ | γ | ≦ sin ⁻¹ (l / n)
The light guide plate 12 travels within the range of the incident angle γ that satisfies the above. Then, a part of the light beam propagating to the surface portion 15 side enters the first convex portion 24, the other part is emitted from the surface portion 15 as it is to the outside of the light guide plate 12, and the rest is the surface portion 15. It is totally reflected and propagates to the back surface 21 side.
[0025]
The side surface shape of the surface portion 15 and the light deflection plate 16 is enlarged and shown in FIG. 5, and the planar shape of the first convex portion 24 is shown in FIG. That is, in order for the light beam L that has entered the first convex portion 24 to exit from the pair of vertical conical surfaces 22 without being totally reflected, consider the light beam L that travels in a plane parallel to the surface portion 15. When the incident angle of the light ray L with respect to the vertical conical surface 22 is θ,
θ ≦ sin ⁻¹ (l / n)
Need to be satisfied. Here, when the circumference is π, the angle α ₁ formed by the pair of vertical conical surfaces 22 is α ₁ = 2 · {(π / 2) −θ}.
α ₁ ≧ π-2sin ^-1 (l / n)
However, as a practical matter, the plane including the optical path of the light beam L is inclined with respect to the surface portion 15, and the angle α formed by the pair of vertical conical surfaces 22 in this plane is the light beam L and the surface portion 15. Tan α = cos β · tan α _1, where β is the angle between
α ≧ tan ⁻¹ [cosβ · tan {π-2sin ⁻¹ (1 / n)}]
It can be seen that it should be satisfied.
[0026]
Specifically, in the present embodiment in which an acrylic resin having a refractive index n of 1.49 is adopted as the light guide plate 12, it is desirable that α is in the range of 85 to 135 degrees in order to improve the light collecting property. As a practical matter, the plane including the optical path of the light beam L is inclined with respect to the surface portion 15, and when the angle formed by the light beam L and the surface portion 15 is β, this is totally reflected by the vertical conical surface 22. To exit from here without
β ≦ (3/2) · sin ⁻¹ (l / n)
Need to be satisfied. Here, when β = (3/2) · sin ⁻¹ (l / n), the above-mentioned α in the present embodiment is about 135 degrees, so that α falls within the range of 95 degrees to 135 degrees. The first convex portion 24 is preferably formed.
[0027]
That is, the first convex portion 24 described above functions to deflect the direction of light emitted from the surface portion 15 more vertically.
[0028]
The light beam that has entered the light guide plate 12 from the light source lamp 14 has its energy reduced as it travels through the light guide plate 12, so that the first convex portion 24 that protrudes from the surface portion 15 of the light guide plate 12. It is necessary to gradually change the occupation ratio. Specifically, the area ratio of the first protrusions 24 per unit area of the surface portion 15 (hereinafter referred to as the following) so that the light emitted from the surface portion 15 has a uniform brightness over the entire surface portion 15. This is described as an occupation ratio) represents the relationship between the position of the surface portion 15 along the traveling direction of light from the light source lamp 14 (right direction in FIG. 1) and the occupation ratio of the first convex portion 24. As shown in FIG. 7, it is set at random so as to have a larger occupation ratio toward the reflection end face portion 19 side.
[0029]
In this case, the surface portion 15 close to the incident end surface portion 13 of the light guide plate 12 has a tendency that the light from the light source lamp 14 is directly transmitted to increase the luminance, and therefore the back surface portion 21 close to the incident end surface portion 13 is. The occupation ratio of the first convex portion 24 is set to be smaller than the subsequent portion. Similarly, the front surface portion 15 close to the reflection end surface portion 19 of the light guide plate 12 has a tendency that the reflected light from the reflection end surface portion 19 is transmitted to increase the brightness, and therefore the back surface portion 21 close to the reflection end surface portion 19. The occupancy ratio of the first convex portion 24 is set to be smaller than the subsequent portion.
[0030]
When the light emitting area of the light source lamp 14 is shorter than the width dimension of the incident end face portion 13 of the light guide plate 12, the amount of light incident on the both end portions in the width direction of the light guide plate 12 tends to be insufficient. For this reason, it is desirable to set the occupation ratio of the first convex portions 24 at both end portions in the width direction of the surface portion 15 of the light guide plate 12 to be relatively larger than that of other portions. In any case, in the present embodiment, the maximum value of the occupation ratio of the first convex portion 24 is set to about 70%, but it is naturally possible to set it to a value higher than that.
[0031]
FIG. 5 shows a side shape of the light deflection plate 16. That is, the light deflecting plate 16 in the present embodiment is formed of a transparent acrylic resin, and is in a direction parallel to the smooth flat portion 26 facing the surface portion 15 of the light guide plate 12 and the incident end face portion 13 of the light guide plate 12. And a prism surface 27 having a triangular prism shape arranged in a direction orthogonal to the incident end face portion 13. The prism surface 27 alternates between a first inclined surface 28 whose distance from the flat surface portion 26 increases toward the incident end surface portion 13 side of the light guide plate 12 and a second inclined surface 29 that follows the first inclined surface 28. The angle δ ₁ formed by the flat surface portion 26 and the first inclined surface 28 is smaller than the angle δ ₂ formed by the flat surface portion 26 and the second inclined surface 29. For example, δ ₁ is (28 ± 3). ) Degrees and δ ₂ is set to (62 ± 3) degrees.
[0032]
The prism surface 27 in this embodiment has minute irregularities having an appropriate surface roughness for diffusing the light emitted from the prism surface 27 to some extent, but the minute irregularities are formed on the flat portion 26. You may make it do. Moreover, although the 1st convex part 24 was set to the triangular pyramid shape, it is also possible to make it a triangular prism shape, and also in this case, the efficient light guide plate similar to the previous Example can be obtained.
[0033]
Next, a second embodiment according to the present invention will be described in detail with reference to FIGS. 8 to 10. However, the same reference numerals are given to the members having the same functions as those of the previous embodiments, and they are duplicated. The description will be omitted.
[0034]
That is, as shown in FIG. 8 showing the cross-sectional structure of the flat illumination device according to the embodiment, FIG. 9 showing the extracted and enlarged projections, and FIG. 10 showing the cross-sectional structure taken along the line XX in FIG. On the surface portion 15 of the optical plate 30, a convex portion 31 is formed in a reverse direction (hereinafter referred to as second ) in which the contour shape projected perpendicularly to the surface portion 15 forms a rhombus. The second convex portion 31 in the present embodiment is combined so as to be in contact with and facing the base 25 of the first convex portion 24 of the previous embodiment, and the vertex with respect to the base 25 that is set substantially parallel to the incident end face portion 13. Is an isosceles triangular pyramid having a pair of symmetric vertical conical surfaces 32 and inclined conical surfaces 33, which are located closer to the incident end face 13 than the base 25. In this embodiment, the first convex portion 24 and the second convex portion 31 are set in a mirror image relationship with the base 25 as the axis of symmetry. In this case, the length of the hypotenuse of one vertical conical surface 22 is set. On the other hand, the length of the hypotenuse of the other vertical conical surface 32 may be different, and it is desirable that it be symmetric with respect to the diagonal C orthogonal to the base 25.
[0035]
The second convex part 31 mainly functions to guide the light returning from the light guide plate 30 from the reflection end face part 19 side to the incident end face part 13 side out of the surface part 15. For this reason, it is not necessary to incline the back surface portion 21 with respect to the front surface portion 15 as in the previous embodiment, and both the incident end surface portion 13 side and the reflection end surface portion 19 side can be set to a uniform plate thickness. Is possible.
[0036]
Further, on the back surface portion 21 of the light guide plate 30, a triangular prism-shaped prism surface which is arranged in a direction parallel to the incident end surface portion 13 and extends in a direction orthogonal to the incident end surface portion 13 and has a known light reflecting function. The first and second convex portions 24 and 31 and the prism surface 34 control the direction of emitted light from the surface portion 15 of the light guide plate 30 in a substantially vertical direction.
[0037]
In addition, the prism surface 36 of the light deflection plate 35 in the present embodiment forms an acute isosceles triangular prism whose apex angle is smaller than 90 degrees, and the surface portion 15 of the light guide plate 30 faces the surface portion 15 of the light guide plate 30. It is arranged in a state of being superimposed on.
[0038]
As described above, in this embodiment, light returning from the light guide plate 30 from the reflection end face portion 19 side to the incident end face portion 13 side is also actively led out from the surface portion 15. Strongly radiated light is emitted in the direction facing directly.
[0039]
In the embodiment described above, the first convex portion 24 and the second convex portion 31 are set in a combined shape. However, by setting the inclined conical surfaces 23 and 33 in parallel with the surface portion 15, a quadrangular prism shape is formed. In this case as well, an efficient light guide plate similar to the previous embodiment can be obtained. In addition, the second convex portion 31 is arranged separately from the first convex portion 24, and the distribution state is different from the distribution state of the first convex portion 24, for example, increases toward the incident end face portion 13 side. The light returning from the reflection end face portion 19 side can be more uniformly guided from the surface portion 15 of the light guide plate 30.
[0040]
【The invention's effect】
According to the light guide plate and the flat illumination device of the present invention, the light guide plate has a plurality of convex portions that have light collecting properties and direction controllability, and allow light incident from the incident end surface portion of the light guide plate to be emitted from the surface portion. Therefore, a part of the light from the light source that has entered the light guide plate from the incident end face part is totally reflected on the back surface part of the light guide plate, and from the surface part of the light guide plate to the outside of the light guide plate without loss. Can be emitted. For this reason, there is little loss of light and power consumption, and a thinner flat illumination device can be obtained.
[0041]
In addition, since the convex portion protruding from the front surface portion of the light guide plate is set so that the proportion of the back surface portion per unit area increases as the distance from the incident end surface portion increases, the luminance distribution of the emitted light can be made uniform. In addition, by setting the size of the convex portion to 10 to 150 μm, it is possible to obtain a good light guide plate in which the convex portion is not noticeable, and it is not necessary to use a light diffusing plate in combination.
[0042]
Furthermore, a light guide plate having a desired luminance distribution can be obtained by controlling the occupation ratio of the convex portions.
[Brief description of the drawings]
FIG. 1 is a sectional view showing a schematic structure of a first embodiment of a flat illumination device according to the present invention.
FIG. 2 is an exploded perspective view of the embodiment shown in FIG.
3 is a plan view showing the appearance of the surface portion of the light guide plate in the embodiment shown in FIG. 1. FIG.
4 is an enlarged perspective view showing the appearance of convex portions in the embodiment shown in FIG.
5 is an enlarged side view showing the surface portion and the side surface shape of the light deflection plate in the embodiment shown in FIG.
6 is a plan view of a convex portion in the embodiment shown in FIG.
FIG. 7 is a graph showing the relationship between the surface portion of the light guide plate from the incident end surface portion to the reflective end surface portion and the occupancy rate of the convex portion per unit area.
FIG. 8 is a sectional view showing a schematic structure of a second embodiment of the flat illumination device according to the present invention.
FIG. 9 is an enlarged perspective view showing the appearance of a convex portion in the embodiment shown in FIG.
10 is a cross-sectional view taken along the line XX in FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 Planar illuminating device 12 Light-guide plate 13 Incident end surface part 14 Light source lamp 15 Surface part 16 Light deflection plate 17 Light reflection sheet 18 Reflector 19 Reflective end surface part 20 Side end surface part 21 Back surface part 22 Vertical conical surface 23 Inclined conical surface 24 1st Convex portion 25 Base 26 of inclined cone surface Flat portion 27 Prism surface 28 First inclined surface 29 Second inclined surface 30 Light guide plate 31 Second convex portion 32 Vertical cone surface 33 Inclined cone surface 34 Prism surface 35 Optical deflecting plate 36 Prism surface α Angle formed between a pair of vertical conical surfaces β Angle formed between the plane portion and the light beam δ Angle formed between the ₁ plane portion and the first inclined surface δ ₂ Angle formed between the 2 plane portion and the second inclined surface Ray C Diagonal

Claims (9)

A front surface portion from which light is emitted, a back surface portion located on the opposite side of the front surface portion, and an incident end surface portion for introducing light from a light source located on one end side of the front surface portion and the back surface portion , A light guide plate for emitting light incident from the incident end face part from the surface part,
The front surface portion has light condensing properties and direction controllability, and a plurality of forward convex portions for emitting light reflected from the back surface portion from the front surface portion are randomly formed,
These forward convex portions are formed by a triangle having one side whose outline shape projected perpendicularly to the surface portion is substantially parallel to the incident end face portion, and the one side does not include the one side of the triangle. Further, the light guide plate has a pair of vertical surfaces which are located on the incident end surface portion side and are substantially perpendicular to the surface portion and do not include the one side. The contour shape projected perpendicularly to the surface portion forms a triangle having one side substantially parallel to the incident end surface portion, and a vertex not including the one side of the triangle is located closer to the incident end surface portion than the one side. A plurality of reverse convex portions are randomly formed on the surface portion, and the reverse convex portions have a pair of vertical surfaces that are substantially perpendicular to the surface portion and do not include the one side. The light guide plate according to claim 1. The convex portion of the front Symbol forward, claim 1 or claim, wherein the inclined with respect to the surface portion, and a conical surface comprising said one side, a triangular pyramid consisting of the pair of vertical surfaces 2. The light guide plate according to 2. Protrusion of the front Symbol reverse direction, inclined with respect to said surface portion, and a conical surface comprising said one side, according to claim 2, characterized in that a triangular pyramid consisting of the pair of vertical surfaces Light guide plate. The light guide plate according to claim 1 or claim 2 protrusions before Symbol forward, characterized in that the form a triangular prism. The light guide plate according to claim 2, wherein the convex portion in the reverse direction has a triangular prism shape. The forward convex portion and the reverse convex portion are formed integrally so as to share the one side. Light guide plate.   The triangular prism-shaped prism surface extending in a direction orthogonal to the incident end surface portion and arranged in a direction parallel to the incident end surface portion is formed on the rear surface portion of the light guide plate. The light guide plate according to claim 7. The light guide plate according to any one of claims 1 to 8,
A light source that projects light toward the incident end face of the light guide plate;
A planar portion along the surface portion of the light guide plate, and a prismatic prism surface extending in a direction parallel to the incident end surface portion of the light guide plate and arranged in a direction orthogonal to the incident end surface portion, A flat illumination device comprising: a light deflecting plate that is superimposed on the surface portion of the light guide plate and deflects light emitted from the surface portion of the light guide plate in a predetermined direction.

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