JP2007027144A - Light guide plate and flat lighting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light guide plate capable of emitting high luminance light in a uniform distribution with less loss. <P>SOLUTION: The light guide plate 12 includes a surface part 15 emitting light, a rear face part 21 placed on the opposite side of the surface part 15, and an incident end face part 13 placed on one end side of the surface part 15 and the rear face part 21 connecting to the surface part 15 and the rear face part 21, and also introducing light from a light source lamp 14, the light guide plate 12 is to emit the incident light entered from the incident end face part 13, from the surface part 15. A concave face 24 and a convex face 25 to deflect light emitted from the surface part 15 onto a predetermined direction are formed in a wave shape on the surface part 15, a plurality of convex parts 23 having inclined planes 22 to reflect all the light entered from the incident end face part 13 to the surface part 15 side are formed on the rear face part 21. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  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.

  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.

  For this purpose, the conventional flat illumination device is provided with a prism sheet in which a light reflecting sheet is provided on the back side of the light guide plate and isosceles triangular prism surfaces are arranged in parallel on the front side of the light guide plate. A structure in which two sheets are overlapped so that the longitudinal directions of the surfaces are orthogonal to each other is adopted. 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-luminance illumination light can be obtained. Consideration.

  In addition, there are also known innumerable dots having a size of about several hundreds μm printed with white ink or the like on the back surface of the light guide plate for the purpose of uniform dispersion of light incident on the light guide plate. In this case, a light diffusing sheet 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 sheet.

  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.

  Therefore, printing with dots of white ink on the back surface of the light guide plate to diffuse the light propagating through the light guide plate has a disadvantage that light absorption loss occurs. Moreover, since it is necessary to use a light diffusing sheet so that these dots are not conspicuous, most of the light passing through this light diffusing sheet becomes diffused light, resulting in a significant reduction in luminance, resulting in a large amount of light. Must use a large bright light source. In addition, control of the direction of light travel becomes impossible.

  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.

  In addition, the conventional flat illumination device uses two prism sheets in addition to the diffusion sheet so as to overlap each other on the light guide plate, so that the number of parts is large and the thickness cannot be reduced as a whole. . In addition, the loss of light due to interface reflection between the diffusion sheet and the two prism sheets is large, and it is necessary to use a bright light source with a large amount of light, which hinders compactness and low power consumption of the entire apparatus. .

  A first object of the present invention is to provide a light guide plate that has little loss and can emit high-luminance light with a uniform distribution.

  A second object of the present invention is to provide a flat illumination device that has a small number of parts as well as light loss, and is compact and capable of reducing power consumption.

The first aspect of the present invention includes a front surface portion from which light is emitted, a flat back surface portion located on the opposite side of the front surface portion, and the front surface portion and the back surface located on one end side of the front surface portion and the back surface portion. An incident end face part for connecting light to the light source and introducing light from the light source, and a reflection end face part located on the opposite side of the incident end face part. Light incident from the incident end face part is transmitted from the surface part. A light guide plate for emitting light, wherein a plurality of convex portions protruding from the back surface portion are randomly formed on the back surface portion, and the convex portions are on the incident end surface portion side with respect to the reflection end surface portion side. In the case where the surface of the light guide plate has an inclined surface whose interval is wider, the refractive index of the material constituting the light guide plate is expressed as n ₁ , α = sin ⁻¹ (1 / n ₁ ), and the circumferential ratio is expressed as π. , The angle θ between the inclined surface and the surface portion ranges from {(2π / 9) − (α / 2)} to {(11π / 36) − (α / 2)}. It is characterized by being in a box.

Further, the second embodiment of the present invention includes a surface portion from which light is emitted, a flat back surface portion located on the opposite side of the surface portion, and the surface portion positioned on one end side of the surface portion and the back surface portion. And a light guide plate connected to the back surface portion and for introducing light from the light source and for emitting light incident from the light input end surface portion from the front surface portion, the back surface portion A plurality of convex portions projecting from the back surface portion are randomly formed, the convex portions are formed by a part of a spherical surface having a predetermined curvature, and the refractive index of the material constituting the light guide plate is n ₁ , ^{α = sin -1 (1 / n} 1), the circular constant [pi, the radius of the convex portion when expressed as r, the projecting amount h of the sphere from the radius of curvature R and the rear surface portion of the spherical The relationship is h = R (1-cos θ ₂ ) and R = r / sin θ ₂ , and θ ₂ changes from {(2π / 9) − (α / 2)} to {(11π / 36) − (α / 2 )}.

  In the first and second embodiments of the present invention, when the light from the light source that has entered the light guide plate from the incident end face reaches the convex portion protruding from the back surface of the light guide plate, the total reflection condition changes. Part of the light is emitted to the outside of the light guide plate.

  In the light guide plate according to the first and second embodiments of the present invention, light deflecting means for deflecting light emitted from the surface portion in a predetermined direction can be formed on the surface portion.

  It is desirable that the convex portion is set so that the proportion of the rear surface portion per unit area increases as the distance from the incident end surface portion increases, and the size of the convex portion is effectively in the range of 10 μm to 150 μm. is there.

  The light deflecting means may have a concavo-convex surface with a predetermined curvature radius that extends in a direction orthogonal to the incident end surface portion and is alternately arranged along the width direction of the light guide plate, or a direction orthogonal to the incident end surface portion. And having a prismatic prism surface arranged along the width direction of the light guide plate.

  On the other hand, the 3rd form of this invention is the light source plate by the 1st or 2nd form of this invention, the light source which projects light toward the incident-end surface part of this light guide plate, and the surface part of the said light guide plate. A plane portion that is smooth along the surface, a prismatic prism surface that extends in a direction parallel to the incident end surface portion of the light guide plate and is arranged in a direction orthogonal to the incident end surface portion, and the surface portion of the light guide plate And a light reflecting sheet that covers a portion other than the surface portion and the incident end face portion of the light guide plate.

  In the third embodiment of the present invention, when the light from the light source that has entered the light guide plate from the incident end face reaches the convex portion protruding from the back surface of the light guide plate, the total reflection condition changes and partly Is emitted to the outside of the light guide plate, and then guided again from the back surface of the light guide plate into the light guide plate by the light reflecting sheet. A part of the light propagating in the light guide plate is emitted from the surface portion of the light guide plate and deflected in a predetermined direction by the light deflecting plate. In this way, the light emitted from the portion other than the surface portion of the light guide plate and the incident end surface portion to the outside of the light guide plate is again introduced into the light guide plate by the light reflecting sheet, and finally all from the surface portion of the light guide plate. Exit.

  In the flat illumination device according to the third aspect of the present invention, light deflecting means for deflecting light emitted from the surface portion in a predetermined direction can be formed on the surface portion of the light guide plate. In addition, the prism surface of the light deflector plate alternately has first inclined surfaces whose distance from the flat surface portion increases toward the incident end surface portion side, and second inclined surfaces that follow the first inclined surface, It is effective that the angle formed between the portion and the first inclined surface is smaller than the angle formed between the flat portion and the second inclined surface.

  According to the light guide plate and the flat illumination device of the present invention, since the plurality of convex portions each having an inclined surface whose distance from the front surface portion increases toward the incident end surface portion side with respect to the reflection end surface portion side is randomly projected from the back surface portion. The light that has entered the light guide plate from the incident end face can be efficiently emitted to the outside of the light guide plate.

  Further, when the light deflecting means is formed on the surface portion of the light guide plate, the light emitted from the surface portion of the light guide plate to the outside of the light guide plate can be deflected in a predetermined direction.

  In the flat illumination device according to the present invention, when the angle formed by the flat portion of the light guide plate and the first inclined surface of the light deflecting plate is set smaller than the angle formed by the flat portion and the second inclined surface, the second The light refracting action of the first inclined surface is larger than that of the inclined surface, and the light can be deflected more strongly in the direction in which the distance from the flat portion of the first inclined surface is increased as a whole.

  On the other hand, when the convex portion protruding from the back 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 is 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 conspicuous, and it is not necessary to use a light diffusion sheet in combination.

  Further, when the light deflecting means is integrally formed on the surface portion of the light guide plate, it is possible to further omit the prism sheet that has been used in the past, and there is less light loss and power consumption, and it is thinner. A flat illumination device can be obtained.

  An embodiment of a flat illumination device according to the present invention will be described in detail with reference to FIGS.

  As shown in FIG. 1 showing the cross-sectional structure of the flat illumination device according to the present embodiment and FIG. 2 showing the appearance of the disassembled state, the flat illumination device 11 in the present embodiment includes a light guide plate 12 having a rectangular plate shape. The linear light source lamp 14 disposed along the incident end face portion 13 of the light guide plate 12, the light deflection plate 16 superimposed on the surface portion 15 of the light guide plate 12, the incident end face portion 13 of the light guide plate 12, and A light reflecting sheet 17 covering a portion other than the surface portion 15. The light source lamp 14 composed of a cold cathode tube or a plurality of LEDs is surrounded by a reflector 18 having a parabolic cross section, and the reflected light from the reflector 18 is substantially parallel to the surface portion 15. The light is incident on the light guide plate 12 from the incident end face portion 13.

  The light guide plate 12 in this embodiment is formed of a transparent acrylic resin (PMMA) having a refractive index of 1.49, and an incident end face part 13 for introducing light from the light source lamp 14 and the incident end face part 13. A reflection end face portion 19 located on the opposite side of the light source, a pair of side end face portions 20 connected to both ends of the incident end face portion 13 and the reflection end face portion 19, and the incident end face portion 13, the reflection end face portion 19 and the side end face portion. 20 has a front surface portion 15 and a back surface portion 21 for emitting light incident from the incident end surface portion 13. The back surface portion 21 located on the opposite side of the front surface portion 15 has a distance from the front surface portion 15 such that the distance between the front surface portion 15 and the back surface portion 21 is narrower toward the reflection end surface portion 19 side than the incident end surface portion 13 side. The taper is inclined at about 0.5 to 1 degree.

  FIG. 3 schematically showing the back surface portion 21 of the light guide plate 12, FIG. 4 showing the extracted enlarged shape along the IV-IV arrow section, and FIG. 5 showing the extracted enlarged shape along the VV arrow section. As shown in FIG. 6 which is an enlarged view of the arrow VI, the back surface portion 21 of the light guide plate 12 has a triangular prism shape having an inclined surface 22 whose distance from the surface portion 15 increases toward the incident end surface portion 13 side. The convex portions 23 are arranged at random, and consideration is given so that moire fringes and the like do not occur between the convex portions 23 and the uneven surface 24 formed on the surface portion 15 and the light deflection plate 16 described later. The convex portion 23 is for efficiently reflecting the light that is incident from the incident end surface portion 13 and propagates through the light guide plate 12 and guides the light to the surface portion 15 side. Each side is set to a size of 150 μm or less so that it cannot be identified, but it is preferably 10 μm or more in consideration of the problem of light diffusion due to being too small and ease of manufacturing.

  Thus, by setting the size of the convex portion 23 in the range of 10 to 150 μm, it is not necessary to use a conventional light diffusion sheet, and the traveling direction of light can be controlled relatively easily. It becomes.

By the way, the light beam incident on the light guide plate 12 is 0 ≦ | α | ≦ sin ⁻¹ (1 / n) according to the refractive index n of the light guide plate 12.
It proceeds in the range of the incident angle α that satisfies the above. The incident light beam L _I propagating through the light guide plate 12 at an incident angle α with respect to the direction parallel to the surface portion 15 is relative to the inclined surface 22 having an inclination angle θ with respect to the direction parallel to the surface portion 15. In order to cause total reflection, when the refractive index of the light guide plate 12 is n (= 1.49), the critical angle is φ, and the circumferential ratio is π,
θ ≦ (π / 2) −α−φ
Need to be. However, sinφ = 1 / n, and in the case of the light guide plate 12 using the acrylic resin as in the present embodiment, the critical angle φ is about 42 °.

In addition, in order for the reflected light beam LO totally reflected by the back surface portion 21 to be emitted from the surface portion 15 of the light guide plate 12 to the outside,
θ ≧ {(π / 2) −α−φ} / 2
It is necessary to satisfy. That is, in order to effectively extract the light propagating through the light guide plate 12 to the outside, the inclination angle θ of the inclined surface 22 of the convex portion 23 is −π / 36 ≦ θ− (π / 4) + (α / 2). ≦ π / 18
Need to be satisfied.

  It should be noted that the energy of the reflected light beam emitted to the outside of the light guide plate 12 becomes maximum when the incident angle α is 0 degrees as shown in FIG. 7 when the light reflecting sheet 17 is not present, and gradually increases as the incident angle α increases. Although it becomes small and becomes almost zero at about 42 degrees or more, although there is a loss due to interface reflection or absorption of the inclined surface 22 or the like, the presence of the light reflecting sheet 17 finally causes the outer surface of the light guide plate 12 to be outside the surface portion 15. All are emitted.

Thus, totally reflected by the inclined surface 22 of the incident light L _I convex portion 23, and the reflected light L _O is for emitting from the surface portion 15 without being totally reflected by the surface portion 15 to the outside of the light guide plate 12 In this case, the incident angle α and the inclination angle θ need to exist in the hatched area shown in FIG. The inclination angle θ satisfying such a condition in this embodiment using an acrylic resin having a refractive index n of 1.49 is in the range of about 24 degrees to about 48 degrees. In this case, the incident angle α is 0. From about 24 degrees.

That is, incident light with an incident angle α of 24 degrees or less is totally reflected by the inclined surface 22 of the convex portion 23 and propagates toward the surface portion 15 side. Further, most of the incident light beam L _I having an incident angle α exceeding 24 degrees is emitted from the convex portion 23 to the outside of the light guide plate 12, but is incident on the light guide plate 12 again by the light reflecting sheet 17. The light is emitted from the surface portion 15 to the outside of the light guide plate 12. Further, a part of the incident light having an incident angle α exceeding 24 degrees causes interface reflection on the inclined surface 22 of the convex portion 23, propagates to the surface portion 15 side, and exits to the outside of the light guide plate 12.

  Since the light incident on the light guide plate 12 decreases in energy as it travels through the light guide plate 12, it is necessary to gradually change the occupancy ratio of the convex portions 23 protruding from the back surface portion 21 of the light guide plate 12. There is. Specifically, the area ratio of the convex portion 23 occupying per unit area of the back surface portion 21 (hereinafter referred to as this) so that the reflected light beam emitted from the front surface portion 15 has uniform brightness over the entire surface portion 15. FIG. 8 shows the relationship between the position of the back surface portion 21 along the traveling direction of light from the light source lamp 14 (the right direction in FIG. 1) and the occupancy rate of the convex portion 23. In addition, the occupancy ratio is set to be larger toward the reflection end face portion 19 side.

  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 convex portion 23 is set 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 convex portion 23 is set to be smaller than the subsequent portion.

  In the present embodiment, the maximum value of the occupation ratio of the convex portions 23 is set to about 70%, but it is naturally possible to set this to almost 100%.

  The surface portion 15 of the light guide plate 12 has an irregular surface with a predetermined radius of curvature that extends in a direction orthogonal to the incident end face portion 13 (left and right direction in FIG. 1) and is arranged along the width direction of the light guide plate 12 to form a waveform. 24, 25 are formed. The concave surface 24 diffuses the light emitted from the surface portion 15, while the convex surface 25 focuses the light emitted from the surface portion 15 so that a more uniform luminance distribution can be obtained. The interval between the adjacent concave surface 24 and the convex surface 25 is preferably set to about 30 to 100 μm, and the height difference between the concave surface 24 and the convex surface 25 is preferably about 10 to 45 μm.

As shown in FIG. 9 showing the shape of the side surface of the light deflection plate 16, the light deflection plate 16 in the present embodiment is formed of a transparent acrylic resin and is a smooth flat portion facing the surface portion 15 of the light guide plate 12. 26 and a triangular prism-like prism surface 27 extending in a direction parallel to the incident end surface portion 13 of the light guide plate 12 and arranged in a direction orthogonal to the incident end surface 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.

  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. It is for emitting from the surface portion 15, and the inner surface side is mirror-finished by aluminum vapor deposition.

  In the embodiment described above, the concave and convex surfaces 24 and 25 having a predetermined radius of curvature are formed on the surface portion 15 of the light guide plate 12 in a corrugated shape, but an isosceles triangular prism surface having an apex angle of about 95 to 105 degrees is continuously formed. You may make it form. Moreover, although the triangular prism-shaped thing was employ | adopted as the convex part 23, it is also possible to employ | adopt the shape formed in a part of spherical surface of a predetermined curvature radius.

  FIG. 10 showing the schematic structure of another embodiment of the light guide plate 12 according to the present invention is shown in FIG. Shall be omitted. That is, convex portions 31 formed by a part of the spherical surface 30 having a predetermined radius of curvature are randomly arranged on the back surface portion 21 of the light guide plate 12, and the uneven surface 24 formed on the convex portions 31 and the surface portion 15. In addition, consideration is given so that moire fringes and the like are not generated between the optical deflector 16 and the light deflector 16. The convex portion 31 is for efficiently reflecting the light incident from the incident end face portion 13 and propagating through the light guide plate 12 to the surface portion 15 side. The individual convex portions 31 are visually observed. The diameters are set to 150 μm or less so that they cannot be identified, but it is desirable that the diameter is 10 μm or more in consideration of the problem of light diffusion due to being too small and the ease of manufacturing.

  Thus, by setting the size of the convex portion 23 in the range of 10 to 150 μm, it is not necessary to use a conventional light diffusion sheet, and the traveling direction of light can be controlled relatively easily. It becomes.

Here, when the refractive index of the material constituting the light guide plate 12 is n, α = sin ⁻¹ (1 / n), the circumference is π, and the radius of the convex portion 31 is r, the radius of curvature of the spherical surface 30 is expressed. The relationship between R and the protrusion amount h of the spherical surface 30 from the back surface portion 21 is h = R (1-cos θ ₂ ) and R = r / sin θ ₂ , and θ ₂ is {(2π / 9) − (α / 2)} to {(11π / 36) − (α / 2)}, the efficiency using total reflection due to the same effect as the convex portion 23 having the inclined surface 22 is achieved. A good light guide plate 12 can be obtained.

It is sectional drawing showing the schematic structure of one Embodiment of the planar illuminating device by this invention. It is a disassembled perspective view of embodiment shown in FIG. It is a bottom view showing the external appearance of the back surface part of the light-guide plate in embodiment shown in FIG. It is an expanded sectional view along the IV-IV arrow in FIG. It is a VV arrow sectional view in FIG. It is an extraction enlarged view of the arrow VI part in FIG. It is a graph showing the relationship between the incident angle α of incident light incident on the convex part, the inclination angle θ of the inclined surface of the convex part, and the light energy. It is a graph showing the relationship between the back surface part of the light-guide plate from an incident end surface part to a reflective end surface part, and the occupation rate of the convex part per unit area. It is an extraction enlarged view showing the side shape of the light deflection plate in the embodiment shown in FIG. It is sectional drawing of the principal part in other embodiment of the light-guide plate by this invention.

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 deflector plate 17 Light reflection sheet 18 Reflector 19 Reflective end surface part 20 Side end surface part 21 Back surface part 22 Inclined surface 23 Convex part 24 Concave surface 25 Convex surface 26 Plane Part 27 Prism surface 28 First inclined surface 29 Second inclined surface 30 Spherical surface 31 Convex portion L _I incident light L _O reflected light α incident angle of incident light θ inclination angle of inclined surface

Claims (10)

A surface part from which light is emitted, a flat back part located on the opposite side of the front part, and a light from a light source connected to the front part and the back part located on one end side of the front part and the back part A light guide plate for emitting light incident from the incident end surface portion from the surface portion, and an incident end surface portion for introducing the light, and a reflection end surface portion located on the opposite side of the incident end surface portion. ,
A plurality of convex portions projecting from the back surface portion are randomly formed on the back surface portion, and these convex portions are inclined such that the distance from the surface surface portion increases toward the incident end surface portion side with respect to the reflective end surface portion side. Has a surface,
When the refractive index of the material constituting the light guide plate is n1, α = sin ⁻¹ (1 / n ₁ ), and the circumferential ratio is π, the angle θ formed by the inclined surface and the surface portion is {( 2π / 9) − (α / 2)} to {(11π / 36) − (α / 2)}. A surface part from which light is emitted, a flat back part located on the opposite side of the front part, and a light from a light source connected to the front part and the back part located on one end side of the front part and the back part And a light guide plate for emitting light incident from the incident end surface portion from the surface portion,
A plurality of convex portions protruding from the back surface portion are randomly formed on the back surface portion, and these convex portions are formed by a part of a spherical surface having a predetermined curvature,
When the refractive index of the material constituting the light guide plate is n1, α = sin ⁻¹ (1 / n ₁ ), the circumference is π, and the radius of the convex portion is r, the radius of curvature R of the spherical surface is The relationship between the protrusion amount h of the spherical surface from the back surface portion is h = R (1-cos θ ₂ ) and R = r / sin θ ₂ , and θ ₂ is {(2π / 9) − (α / 2)}. To {(11π / 36) − (α / 2)}.   The light guide plate according to claim 1, wherein light deflecting means for deflecting light emitted from the surface portion in a predetermined direction is formed on the surface portion.   The guide according to any one of claims 1 to 3, wherein the convex portion is set so that a proportion of the back surface portion per unit area increases as the distance from the incident end surface portion increases. Light board.   5. The light guide plate according to claim 1, wherein a size of the convex portion is in a range of 10 μm to 150 μm.   The said light deflection | deviation means has an uneven | corrugated surface of the predetermined curvature radius which extends in the direction orthogonal to the said incident end surface part, and is alternately arranged along the width direction of the said light-guide plate. The light guide plate according to any one of the above.   6. The light deflecting unit according to claim 1, further comprising a triangular prism-shaped prism surface that extends in a direction orthogonal to the incident end surface portion and is arranged along the width direction of the light guide plate. The light guide plate described in 1. A light guide plate according to any one of claims 1 to 7,
A light source that projects light toward the incident end face of the light guide plate;
A smooth flat surface 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, And an optical deflection plate superimposed on the surface portion of the light guide plate,
A flat illumination device comprising: a light reflecting sheet covering a portion other than the surface portion and the incident end face portion of the light guide plate.   9. The flat illumination device according to claim 8, wherein light deflecting means for deflecting light emitted from the surface portion in a predetermined direction is formed on the surface portion of the light guide plate.   The prism surface of the light deflector plate has alternately a first inclined surface whose distance from the flat surface portion increases toward the incident end surface portion side, and a second inclined surface following the first inclined surface. 10. The plane according to claim 8, wherein an angle formed between the flat portion and the first inclined surface is smaller than an angle formed between the flat portion and the second inclined surface. Lighting device.

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