JPH11260130A - Surface lighting system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To arbitrarily control the light guide efficiency/outgoing efficiency by varying the refraction factor of a light guide plate in the thickness direction. SOLUTION: The refraction factor (n) of a light guide plate 2 is varied in the thickness direction. That is, the refraction factor (n) is changed so that the refraction factor (n) at a front side is higher than that of a rear side. The light emitted from a light source 1 is introduced into the light guide plate 2 from a side edge 3 thereof directly or after reflected by a reflector 11, the incident light is bent to the surface side without straightly advanced, and the light is controlled to prevent the outgoing of light from the rear side outer face 4b of the light guide plate 2. As a result, the light is efficiently emitted from the surface side outer face 4a of the light guide plate 2 at an angle not over the total reflection angle, and a surface side of a display sign is illuminated by the outgoing light advanced while repeating the above process. Accordingly the light guide efficiency/outgoing efficiency can be controlled on the arbitrary position by adjusting the pattern and degree of the change of the refraction factor (n), and a surface lighting system can easily cope with various types.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for emitting light from a light source from a side end of a light guide plate to emit light on the outer surface of the light guide plate. The present invention relates to a surface lighting device applied to a light or the like.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 15 (a), there is known a surface illuminating device which causes light from a light source 1 to enter from a side end 3 of a light guide plate 2 and causes an outer surface 4 of the light guide plate 2 to emit light. Have been. The surface illuminating device is used as a thin guide light. In this case, a reflection sheet 9 having a high reflectance is provided along the back outer surface 4b of the light guide plate 2, and the light guide plate 2 is provided together with the reflection sheet 9. A box-shaped display sign 10 covering the front outer surface 4a and the back outer surface 4b is provided, and a light source 1 made of a cold cathode tube is provided at a side opening of the display sign 10, and a curved reflection covering the outside of the light source 1 is provided. A plate 11 is provided. In addition, the back outer surface 4b of the light guide plate 2 is formed as an uneven back surface reflection surface 5 in which a number of V-shaped grooves 12 parallel to the light source 1 are arranged, and the light guide plate 2 is formed as shown in FIG. As shown in b), the refractive index n in the thickness direction is uniform.

Accordingly, in this case, the light emitted from the light source 1 is directly or reflected by the reflection plate 11 and enters the light guide plate 2 from the side end 3 thereof. The refractive index n of the light guide plate 2 is uniform, and the incident light travels inside the light guide plate 2 by repeating total reflection, and when the light hits the back surface reflection surface 5 on the back side, the traveling direction is changed by diffusion, regular reflection and refraction. The light reaching the front outer surface 4a of the light guide plate 2 at an angle not exceeding the total reflection angle is transmitted to illuminate the front side of the display sign 10. However, in this case,
Since the front outer surface 4a of the light guide plate 2 is flat, the light from the light source 1 is totally reflected and hardly transmitted through the front outer surface 4a, and the light from the light source 1 does not efficiently reach the front side of the display sign 10. There was a problem.

In order to solve this problem, a technique disclosed in Japanese Patent Application Laid-Open No. 5-150237 is also known. This is one in which the front outer surface 4a of the light guide plate 2 in the above-mentioned surface illumination device is formed in an uneven shape so that most of the light reflected from the back reflection surface 5 can be transmitted. Most of the light passes through the front outer surface 4a of the light guide plate 2 and exits to efficiently reach the front side of the display sign 10.

[0005]

However, in any of the above-mentioned prior arts, in any case, the front outer surface 4a or the rear outer surface 4b of the light guide plate 2 is formed in an uneven shape or the shape of the uneven shape is variously changed. Although the output efficiency can be controlled to some extent, the control of the output efficiency by the light guide plate 2 itself is limited because the refractive index n of the light guide plate 2 itself is uniform. There is a problem that it is not possible to cope with various types of surface illumination devices in which the light emission rate around the character is increased or the outer surface 4 emits light in various ways.

SUMMARY OF THE INVENTION The present invention has been made to solve all the problems in the prior art described above, and an object of the present invention is to control light guide efficiency / output efficiency arbitrarily and to cope with various types. Is to provide a simple surface lighting device.

[0007]

According to a first aspect of the present invention, there is provided a surface illuminating apparatus for emitting light from a light source through a side end of a light guide plate and emitting light from the outer surface of the light guide plate. Thus, the refractive index of the light guide plate is changed in the thickness direction. Therefore, in this case, since the refractive index of the light guide plate itself is changed in the thickness direction, the light guide efficiency / emission efficiency can be arbitrarily controlled by adjusting the pattern and degree of the change in the refractive index. It is easy to handle various types.

According to a second aspect of the present invention, in the surface illuminating device according to the first aspect, the refractive index is changed so that the refractive index on the front side is larger than that on the back side. . Therefore, in this case, in particular, the light incident on the light guide plate is controlled not to go straight but to be bent to the front side, so that the light is prevented from being emitted from the back outer surface of the light guide plate, and the efficiency is reduced from the front side outer surface of the light guide plate. It is emitted well.

According to a third aspect of the present invention, in the surface illuminating device according to the first aspect, the refractive index is changed so that the refractive indexes on both the front and back sides are larger than the middle. And Therefore, in this case, in particular, the light incident on the light guide plate is controlled not to go straight but to be bent to the front and back sides, and to be efficiently emitted from both front and back outer surfaces of the light guide plate.

According to a fourth aspect of the present invention, in the surface illuminating device according to the first aspect, the refractive index is changed so that a middle refractive index is larger than both front and back sides. And Therefore, in this case, in particular, the light incident on the light guide plate is repeatedly bent to the middle side without going straight, and is controlled such that emission from both sides of the front outer surface and the back outer surface of the light guide plate is prevented, The light travels long so that it does not exit the light guide plate.

According to a fifth aspect of the present invention, there is provided the surface illuminating device according to the first aspect, wherein the refractive index is changed so that the refractive index on the back side is larger than that on the front side, and the back side of the light guide plate. The outer surface is formed as an uneven back reflection surface. Therefore, especially in this case,
The light incident on the light guide plate is bent to the back side without going straight, and travels long while being prevented from being emitted from the front outer surface of the light guide plate, and is reflected and refracted by hitting the back outer surface formed as the back surface reflection surface of the light guide plate. , So that the light is efficiently emitted from the front outer surface of the light guide plate at an angle not exceeding the total reflection angle.

According to a sixth aspect of the present invention, in the surface illuminating device according to the first aspect, the front outer surface of the light guide plate is formed as an uneven transmission light emitting surface on which a plurality of prism shapes are arranged. It is characterized by having done. Therefore, particularly in this case, most of the light reaching the front outer surface of the light guide plate is
The light guide plate is controlled so as to transmit without being reflected on the front side outer surface formed as the uneven transmission / emission surface, and to efficiently emit the light from the front side outer surface of the light guide plate.

According to a seventh aspect of the present invention, there is provided the surface illuminating device according to the first aspect, wherein the refractive index is changed in the thickness direction and the refractive index is made uniform in the thickness direction. And a light guide plate. Therefore, in this case, in particular, in a uniform portion where the refractive index is uniform in the thickness direction, light goes straight in the light guide plate, and in a refractive portion in which the refractive index is changed in the thickness direction, the light bends in the light guide plate. The light is controlled so that it travels and is bent at an arbitrary position where the refraction unit is arranged.

According to an eighth aspect of the present invention, in the surface illuminating device according to the seventh aspect, a refracting portion is located near a side end of the light guide plate on which light is incident. It is characterized in that the refractive index is changed such that the refractive index is larger than both sides. Therefore, in this case, in particular, the light incident on the light guide plate is bent to the middle side by the refraction portion, and the light is controlled so as not to be emitted from both sides of the front outer surface and the back outer surface near the side end of the light guide plate. Thus, high brightness near the incident side end in the light guide plate is prevented.

According to a ninth aspect of the present invention, in the surface illuminating device according to the first aspect, the refractive index of the light guide plate is changed by changing the material density of the same material. . Therefore, in this case, in particular, even if the light guide plate is integrally formed of the same material, the light guide plate having a changed refractive index by varying the material processing density by changing the molding processing conditions in the thickness direction or the like. It can be easily obtained by integral molding.

According to a tenth aspect of the present invention, there is provided a surface illuminating device,
The surface illumination device according to claim 1, wherein the layers of different materials are laminated to change the refractive index of the light guide plate. Therefore, in this case, particularly, a light guide plate having a refractive index changed in the thickness direction is formed by laminating layers of different materials, and the same light guide plate having a changed refractive index is injection-molded from a plurality of materials. And can be easily obtained by laminating or the like.

[0017]

1 to 3 show the first embodiment of the present invention.
2 shows an embodiment corresponding to FIG. 2, and the surface lighting device of this embodiment is a surface lighting device in which light from a light source 1 is made incident from a side end 3 of a light guide plate 2 and an outer surface 4 of the light guide plate 2 emits surface light. The refractive index n of the light guide plate 2 is changed in the thickness direction. In the surface illumination device of the embodiment, in particular, FIG.
As shown in (b), the refractive index n is changed so that the refractive index n on the front side is larger than that on the back side.

The surface illumination device is used as a thin guide light. In this case, as shown in FIGS. 2 and 3, a reflection sheet 9 having a high reflectance is provided along the back outer surface 4b of the light guide plate 2. , Together with the reflection sheet 9, the front outer surface 4a of the light guide plate 2
And a box-shaped display sign 10 covering the back outer surface 4b is provided,
A light source 1 made of a cold cathode tube is provided at a side opening of the display sign 10, and a curved reflecting plate 11 that covers the outside of the light source 1 is provided.

Therefore, in the surface illumination device of this embodiment, since the refractive index n of the light guide plate 2 itself is changed in the thickness direction, the light guide is adjusted by adjusting the pattern and degree of change of the refractive index n. Efficiency / emission efficiency can be controlled at any position, making it easy to handle various types.

That is, in the surface illumination device of this embodiment, the refractive index n is changed so that the refractive index n on the front side is larger than that on the back side. In this case, as shown in Table 1 below, the refractive index depends on the material. Since the rate n is different, for example,
No. 18 to No. 18 are arranged on the front side, and No.
By adopting a structure in which any of the materials of No. 5 is arranged, it can be easily controlled.

[0021]

[Table 1]

Therefore, in the surface illumination device of this embodiment, the refractive index n is changed so that the refractive index n on the front side is larger than that on the back side, and therefore, as shown in FIG. The light emitted from the light guide plate 1 is directly or reflected by the reflection plate 11 and is incident on the light guide plate 2 from the side end 3 thereof. The incident light is bent straight to the front side without going straight, and the back outer surface of the light guide plate 2 The light is controlled so as to prevent the light from being emitted from the light guide plate 4b, and is efficiently emitted from the front outer surface 4a of the light guide plate 2 at an angle not exceeding the total reflection angle. 10 fronts are illuminated.

FIG. 4 shows another embodiment corresponding to claims 1 and 3 of the present invention. In the surface illumination device of this embodiment, as shown in FIG. Is changed to be larger than the middle value. In this case, for example, it is easy to control by arranging any material of No. 11 to No. 18 on the front and back sides in Table 1 above and arranging any material of No. 1 to No. 5 in the middle. be able to.

Therefore, in this case, in particular, FIG.
As shown in the figure, the light incident on the light guide plate 2 from the side end 3 is bent straight to both the front and back sides without going straight, and the front outer surface of the light guide plate 2 is formed.
Control is performed so that light is efficiently emitted from both outer surfaces 4 of the back surface 4a and the back outer surface 4b.

Therefore, it is optimal when the display sign 10 has a small width in the light traveling direction.
Both sides are effectively illuminated. Except for this, the configuration is the same as that of the embodiment shown in FIGS. 1 to 3, and the operation and effect other than those according to claim 2 are exerted in the same manner as in the embodiment shown in FIGS. You.

FIG. 5 shows another embodiment corresponding to claims 1 and 4 of the present invention. In the surface illumination device of this embodiment, as shown in FIG. Is changed so that the refractive index n becomes larger than both sides. In this case, for example, in the above Table 1, any of the materials No. 11 to No. 18 is arranged in the middle, and any of the materials No. 1 to No. 5 is arranged on both the front and back sides to easily control. be able to.

Therefore, in this case, in particular, FIG.
As shown in FIG. 5, light incident on the light guide plate 2 from the side end 3 is not straightly traveled but is repeatedly bent to the middle side, so that emission from both sides of the front outer surface 4a and the back outer surface 4b of the light guide plate 2 is prevented. And the light travels long so that the light does not exit the light guide plate 2.

Therefore, it is optimal when the display sign 10 has a large width in the light traveling direction.
The front and back sides of 10 may be evenly illuminated over a long distance, or the portion of the display sign 10 opposite to the light source 1 may be illuminated. Except for this, the configuration is the same as that of the embodiment shown in FIG. 4, and the operation and effect other than those according to claim 3 are exerted as in the embodiment shown in FIG.

FIG. 6 shows another embodiment corresponding to the first, fifth and sixth aspects of the present invention. In the surface illumination device of this embodiment, as shown in FIG. While changing the refractive index n so that n becomes larger than the front side,
The back outer surface 4b of the light guide plate 2 is formed as an uneven back reflection surface 5. In this case, a number of V-shaped grooves 12 parallel to the light source 1 are juxtaposed on the back outer surface 4b of the light guide plate 2, and the uneven back surface 5 is formed. Moreover, in this case, the front outer surface 4a of the light guide plate 2 may be formed as an uneven transmission / emission surface 6 having a large number of prisms. In addition, for example, in the above Table 1, any material of No. 11 to No. 18 is arranged on the back side, and any of No. 1 to No. 5 is arranged on the front side, so that it can be easily controlled. .

Therefore, in this case, in particular, FIG.
As shown in FIG. 3, the light incident on the light guide plate 2 from the side end 3 is bent straight to the back side without going straight, and the light guide plate 2 travels long while being prevented from being emitted from the front outer surface 4a. When the light strikes the rear outer surface 4b formed as the rear reflective surface 5,
The direction of travel is changed by refraction, and the light is controlled to be efficiently emitted from the front outer surface 4a of the light guide plate 2 at an angle not exceeding the total reflection angle.

Further, at this time, most of the light reaching the front outer surface 4a of the light guide plate 2 is transmitted through the prism-shaped uneven transmission light-emitting surface 6a.
Transmitted through the outer surface 4a of the same side formed without being reflected,
The light guide plate 2 is controlled so as to be efficiently emitted from the front outer surface 4a. In addition, the front side of the display sign 10 is uniformly and effectively illuminated over a long distance by the light emitted while traveling while repeating this. Except for this, the configuration is the same as that of the embodiment shown in FIGS. 1 to 3, and the operation and effect other than those according to claim 2 are exerted in the same manner as in the embodiment shown in FIGS. You.

FIG. 7 shows another embodiment corresponding to claims 1 and 7 of the present invention. In the surface illumination device of this embodiment, as shown in FIG. The light guide plate 2 is provided with a refraction portion 7 changed in step (1) and a uniform portion 8 having a uniform refractive index n in the thickness direction. Therefore, in this case, in particular, as shown in FIG. 7A, in the uniform portion 8 where the refractive index n becomes uniform in the thickness direction, the light travels straight through the light guide plate 2 and the refractive index n is changed in the thickness direction. In the refracting portion 7, the light is controlled to bend in the light guide plate 2 and to be bent at an arbitrary position where the refracting portion 7 is arranged. In this case, in the refraction portion 7, the refractive index n is changed so that the refractive index n on both the front and back sides is larger than the middle. For example, any one of the materials No. 11 to No. 18 in Table 1 above is used. The structure can be easily controlled by arranging it on both sides and arranging any one of materials No. 1 to No. 5 in the middle.

In this case, the plurality of refracting portions 7 and the uniform portions 8
Are alternately arranged, the light is bent to the front side at a plurality of positions, and the bent light is emitted from a plurality of predetermined portions of the front side outer surface 4a of the light guide plate 2, and the light on the front side of the display sign 10 Are illuminated by the same emitted light. In addition,
Otherwise, the configuration is the same as that of the embodiment shown in FIGS. 1 to 3, and the operation and effect other than those according to claim 2 are exerted as in the embodiment shown in FIGS. 1 to 3.

FIG. 8 shows another embodiment corresponding to the first, seventh and eighth aspects of the present invention. In the surface illumination device of this embodiment, as shown in FIG. The refractive portion 7 in the embodiment shown in FIG. 7 is located near the side end 3 of the light guide plate 2, and the refractive index n in the refractive portion 7 is such that the middle refractive index n is larger than both the front and back sides. Is changing. In this case, for example, one of the materials No. 11 to No. 18 in Table 1 above is arranged in the middle, and No. 1 to No.
By employing a structure in which any of the above materials is arranged, it can be easily controlled.

Therefore, in this case, in particular, FIG.
As shown in the figure, the light incident on the light guide plate 2 is bent to the middle side by the refraction portion 7, and the light does not exit from both sides of the front outer surface 4a and the back outer surface 4b near the side end 3 of the light guide plate 2. Thus, the display sign 10 located near the incident side end 3 in the light guide plate 2 is prevented from increasing in brightness. Otherwise, the configuration is the same as that of the embodiment shown in FIG. 7, and the same operation and effect as in the embodiment shown in FIG.

FIG. 9 shows another embodiment corresponding to the first, second, and ninth aspects of the present invention. In the surface illumination device of this embodiment, as shown in FIG. Although the refractive index n is changed so that n becomes larger than the back side,
In this case, the refractive index n of the light guide plate 2 is changed by changing the material density of the same material. Therefore, in this case, in particular, even when the light guide plate 2 is integrally formed of the same material, the material density is varied by changing the molding processing conditions in the thickness direction, and the refractive index n is changed. The light plate 2 can be easily obtained by integral molding.

That is, in this case, when the light guide plate 2 is integrally formed of the same material by injection molding or the like, after being taken out of the mold, the front outer surface 4a of the light guide plate 2 is rapidly cooled to obtain a structure shown in FIG. ), The density near the front side outer surface 4a is made higher than that of the other parts to increase the refractive index side part 13a having a large refractive index n.
Is formed. For example, when the material is PMMA (polymethyl methacrylate), the relationship between the density and the refractive index n is as shown in FIG. 10, and the higher the rapid cooling speed, the higher the density. By changing the quenching speed, the refractive index n can be easily adjusted by changing the material density. Except for this, the configuration is the same as that of the embodiment shown in FIGS. 1 to 3, and the same operation and effect as those in the embodiment shown in FIGS.

FIG. 11 shows another embodiment corresponding to the first, sixth and ninth aspects of the present invention. In the surface illumination device of this embodiment, as shown in FIG. The refractive index n is changed so that n becomes larger than the front side. In this case, as in the embodiment shown in FIG. Contrary to the embodiment shown, by rapidly cooling the back outer surface 4b of the light guide plate 2, as shown in FIG. 11A, the density near the back outer surface 4b is made higher than that of the other portions, and the refractive index n Is formed.

Here, for example, when the material is PMMA (polymethyl methacrylate), the relationship between the density and the refractive index n is as shown in FIG. 10, and if the rapid cooling speed is high, Since the density also increases, the refractive index n can be easily adjusted by changing the quenching speed to change the material density. Also, as in the embodiment shown in FIG. 6, the front outer surface 4a of the light guide plate 2 is formed as an uneven transmission / emission surface 6 having a large number of prisms.

Therefore, in this case, as shown in FIG. 11 (a), the light incident on the light guide plate 2 from the side end 3 is bent straight without going straight, and is reflected along the back side of the light guide plate 2. The light is reflected by the sheet 9 and is exposed to the front side outer surface 4a of the light guide plate 2.
In this case, most of the light reaching the front side outer surface 4a of the light guide plate 2 is reflected by the front side outer surface 4a formed as the prism-shaped uneven transmission / emission surface 6. The light guide plate 2 is controlled so as to be transmitted efficiently and to be efficiently emitted from the front outer surface 4a of the light guide plate 2. Except for the above, the configuration is the same as that of the embodiment shown in FIG. 6, and the operation and effect other than those related to the back reflection surface 5 are exerted as in the embodiment shown in FIG.

In the surface illumination device of the present invention, FIG.
As shown in 2 to 14, layers a, b, and c of different materials can be formed in a laminated shape to change the refractive index n of the light guide plate 2. In this case, the embodiment corresponds to the first and tenth aspects. In particular, the laminated light guide plate 2 having the changed refractive index n can be easily obtained by injection molding or lamination molding of a plurality of materials. The effect comes to play.

That is, in the case shown in FIG. 12, a plurality of types of resin materials having different refractive indexes n are integrally injection-molded by an injection molding machine 14 used for a multicolor molding method, and a layer a of a different material is formed. , B and c are formed. In this case, for example, any of the materials No. 1 to No. 18 having different refractive indices n shown in Table 1 above can be selected and the layers a, b, and c of different materials can be easily controlled. . In the case shown in FIG. 13, a plurality of types of resin materials having different refractive indices n are laminated and integrated by lamination molding to form a laminated light guide plate 2 composed of layers a, b, and c of different materials. ing. In the case shown in FIG. 14, a plurality of types of base monomer materials having different refractive indices n are kneaded in a mold 15 and manufactured by an interfacial gel polymerization method or the like, so that layers a, b, and c to form a laminated light guide plate 2. In this case, the layers a and c are the same kind of material, and the layers a and b are different kinds of materials. Further, in the surface illumination device of the present invention, as shown in FIGS.
With the configuration of 0, the light guide plate 2 can be manufactured at low cost.

[0043]

As described above, in the surface illumination device according to the first aspect of the present invention, the light guide efficiency / emission efficiency can be arbitrarily adjusted by adjusting the pattern and degree of change in the refractive index of the light guide plate itself. It can be controlled, and it is easy to correspond to various types.

In the surface illuminating device according to the second aspect of the present invention, in particular, the light incident on the light guide plate is controlled so as to be prevented from exiting from the back side, and the efficiency is improved from the front outer surface of the light guide plate. It is emitted well.

In the surface illumination device according to the third aspect of the present invention, in particular, the light incident on the light guide plate is controlled so as to be efficiently emitted from the outer surfaces on both the front and back surfaces.

In the surface illuminating device according to the fourth aspect of the present invention, in particular, the light incident on the light guide plate is controlled so as to be prevented from being emitted from both the front and back sides, and travels long in the light guide plate. Is done.

In the surface illumination device according to the fifth aspect of the present invention, in particular, the light incident on the light guide plate travels long while being prevented from being emitted from the front side, and hits the rear surface reflection surface of the light guide plate. The light guide plate is controlled so as to be efficiently emitted from the front outer surface.

In the surface illumination device according to the sixth aspect of the present invention, in particular, most of the incident light is reflected by the back reflection surface or the reflection sheet without being disturbed by the front outer surface of the light guide plate. Only the front surface is controlled so as to be efficiently emitted from the front side outer surface, and the function of the front side outer surface formed as the light distribution transmitting / emitting surface is improved.

In the surface illuminating device according to claim 7 of the present invention, in particular, in the uniform portion, the light goes straight in the light guide plate, and in the refraction portion, the light travels in the light guide plate in a curved manner. The light is controlled so as to be bent at an arbitrary position where the portion is arranged.

In the surface illuminating device according to the eighth aspect of the present invention, in particular, the light incident on the refracting portion near the side end of the light guide plate is controlled so as not to be emitted from both the front and back sides, and the light inside the light guide plate is controlled. High brightness near the incident side end is prevented.

In the surface illumination device according to the ninth aspect of the present invention, in particular, by changing the material density in the thickness direction, a light guide plate having a changed refractive index can be easily obtained by integrally molding. .

In the surface illumination device according to the tenth aspect of the present invention, the light guide plate having a refractive index changed in the thickness direction can be easily formed by forming the layers of different kinds of materials into a laminated shape. Obtainable.

[Brief description of the drawings]

FIG. 1A is a side view of a main part showing a surface illumination device according to an embodiment of the present invention, and FIG. 1B is a line graph showing a refractive index of a light guide plate in the surface illumination device.

FIG. 2 is a side view showing the same-side lighting device.

FIG. 3 is an exploded perspective view showing the same-side lighting device.

FIG. 4A is a side view of a main part showing a surface illumination device according to another embodiment, and FIG. 4B is a line graph showing a refractive index of a light guide plate in the surface illumination device.

5A is a side view of a main part of a surface illumination device according to still another embodiment, and FIG. 5B is a line graph showing a refractive index of a light guide plate in the surface illumination device.

6A is a side view of a main part of a surface illumination device according to still another embodiment, and FIG. 6B is a line graph showing a refractive index of a light guide plate in the surface illumination device.

FIG. 7A is a side view of a main part showing a surface illumination device according to still another embodiment, and FIG. 7B is a line graph showing a refractive index of a light guide plate in the surface illumination device.

8A is a side view of a main part showing a surface illumination device according to still another embodiment, and FIG. 8B is a line graph showing a refractive index of a light guide plate in the surface illumination device.

9A is a side view of a main part of a surface illumination device according to still another embodiment, and FIG. 9B is a line graph showing a refractive index of a light guide plate in the surface illumination device.

FIG. 10 is a line graph showing the relationship between the density and the refractive index of PMMA.

11A is a side view of a main part showing a surface illumination device according to still another embodiment, and FIG. 11B is a line graph showing a refractive index of a light guide plate in the surface illumination device.

FIG. 12 is a cross-sectional view illustrating a method for manufacturing a light guide plate in the surface illumination device of the present invention.

FIG. 13 is a cross-sectional view illustrating another method for manufacturing a light guide plate in the surface illumination device of the present invention.

FIG. 14 is a cross-sectional view illustrating still another manufacturing method of the light guide plate in the surface illumination device of the present invention.

15A is a side view showing a conventional surface illumination device, and FIG. 15B is a line graph showing a refractive index of a light guide plate in the same surface illumination device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Light source 2 Light guide plate 3 Side end 4 Outer surface 5 Back reflection surface 6 Transmissive light emission surface 7 Refraction part 8 Uniform part

Claims (10)

[Claims] 1. A surface lighting device for emitting light from a light source from a side end of a light guide plate to emit light from the outer surface of the light guide plate, wherein the refractive index of the light guide plate is changed in a thickness direction. apparatus. 2. The surface illumination device according to claim 1, wherein the refractive index is changed so that the refractive index on the front side is larger than that on the rear side. 3. The apparatus according to claim 1, wherein the refractive indices are changed so that the refractive indices on both the front and back sides are larger than the middle.
A surface lighting device according to claim 1. 4. The apparatus according to claim 1, wherein the refractive index is changed so that the middle refractive index is larger than both sides.
A surface lighting device according to claim 1. 5. The surface according to claim 1, wherein the refractive index is changed so that the refractive index on the back side is larger than that on the front side, and the outer surface on the back side of the light guide plate is formed as an uneven back reflecting surface. Lighting equipment. 6. The surface illuminating device according to claim 1, wherein the outer surface on the front side of the light guide plate is formed as an uneven transmission / emission surface having a plurality of prism shapes. 7. The surface illumination device according to claim 1, wherein a refraction portion having a refractive index changed in the thickness direction and a uniform portion having a uniform refractive index in the thickness direction are provided on the light guide plate. . 8. A refracting portion is positioned near a side end of a light guide plate on which light is incident, and the refractive index is changed so that the refractive index at the middle of the refracting portion is larger than on both sides. The surface lighting device according to claim 7, wherein 9. The surface illumination device according to claim 1, wherein the refractive index of the light guide plate is changed by changing the material density of the same material. 10. The surface lighting device according to claim 1, wherein layers of different materials are laminated to change the refractive index of the light guide plate.