WO1995006889A1

WO1995006889A1 - Surface light emitting device

Info

Publication number: WO1995006889A1
Application number: PCT/JP1993/001238
Authority: WO
Inventors: Yukio Yoshikawa; Shigekazu Nakamura
Original assignee: Copal Company Limited
Priority date: 1993-09-01
Filing date: 1993-09-01
Publication date: 1995-03-09

Abstract

A surface light emitting device emits light from a light emitting surface, the light being from a light source arranged on one side of the light emitting surface. On the bottom which faces the light emitting surface, a transparent light-guiding board is arranged. The board has small reflecting projections thereon. The density of the reflecting projections increases gradually from the light source. The light from the light source is reflected by the reflecting projections and emitted from the light emitting surface. Since the light from the light source is reflected toward the light emitting surface side in accordance with the density of the reflecting projections, the light is uniformly emitted from over the entire emitting surface. The reflecting projections are staggered in the direction where light is emitted from the light source, making it easy for the light to strike the staggered reflecting projections. The surface of each projection, extending from the top to the board, is preferably a curved one, or the shape of each one is preferably a cone.

Description

Specification

Surface emitting device Technical field

The present invention relates to a surface emitting device used to illuminate a liquid crystal display panel or the like, which is an illuminated body in a liquid crystal television, a portable personal computer or a word processor, from the back. Background art

Conventionally, in a surface light emitting device, in order to guide light emitted from a light source to a light emitting surface, light from the light source is incident on a light guide plate and then emitted toward the light emitting surface. As this light guide plate:-A surface facing the light-emitting surface is subjected to hairline processing to diffuse the light impinging on the surface, thereby efficiently guiding the light from the light source to the light-emitting surface. For example, Japanese Patent Publication No. 58-17995 Techniques such as No. 7 Public Bulletin (Japan) are known.

However, in recent years, liquid crystal display panels and the like have been increased in size, and the area of the light-emitting surface of the surface-emitting device serving as the backlight has also increased. On the other hand, the demand for smaller and lighter devices incorporating liquid crystal panels and the like has led to a demand for thinner surface emitting devices. As described above, when the surface light emitting device is enlarged and thinned, in the conventional surface light emitting device using the light guide plate, a portion near the light source is bright, and a portion far from the light source is dark because light is hard to reach. As described above, the brightness of the light emitting surface was uneven, and it was difficult to emit light with uniform brightness as a whole.

As an improvement over such a surface light emitting device, for example, as described in Japanese Patent Application Laid-Open No. 2-125601 (Japan), a light source is provided on a surface facing a light emitting surface of a light guide plate. A technique is known in which the dot pattern of an ink is printed so that the density gradually increases as the distance from the light source increases, so that the brightness of the light emitting surface is made uniform.

However, when the ink or the like is printed in this manner, it is difficult to completely eliminate the light absorbing effect of the ink itself, and there is a disadvantage that the emission efficiency is reduced. In addition, there is a disadvantage that the process of printing ink is required, which complicates the manufacturing process and leads to cost up. The present invention has been made in view of the above conventional example, and has as its object to provide a surface light emitting device capable of uniformly emitting light from a light source to the entire light emitting surface to emit light without unevenness. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a sectional view of a surface light emitting device according to an embodiment of the present invention.

FIG. 2 is a top view of the surface light emitting device.

FIG. 3 is an enlarged view of the bottom surface of the light guide plate.

FIG. 4 is a cross-sectional view showing a projection formed on the bottom surface of the light guide plate shown in FIG. FIG. 5 is a sectional view showing a light guide plate according to another embodiment of the present invention.

FIGS. 6 (A) and (B) are cross-sectional views showing another embodiment of the convex portion formed on the bottom surface of the light guide plate. Disclosure of the invention

In order to achieve the above object, a surface light emitting device according to the present invention is a surface light emitting device that emits light from a light source disposed on a side of a light emitting surface from the light emitting surface, and a bottom surface portion facing the light emitting surface. In addition, there is provided a transparent light guide plate in which a reflection-shaped portion formed by minute projections is arranged so that its density gradually increases in accordance with the distance from the light source. Light incident from the light source is reflected by the reflection shape part and emitted from the light emitting surface. With this configuration, the light from the light source is reflected toward the light emitting surface in accordance with the density of the reflective shape portion, so that light can be uniformly emitted on the entire light emitting surface.

Preferably, the reflection-shaped portions are arranged in a staggered pattern in a direction away from the light source. With such a configuration, light emitted from the light source is likely to directly enter many convex portions.

Also preferably, the reflection-shaped portion is a minute projection formed by forming a continuous portion from the top portion to the bottom portion with a curved surface. Alternatively, the reflecting shape portion is a minute convex portion formed by forming a continuous portion from the top portion to the bottom portion in a conical shape, preferably, the apex angle satisfies a range of 90 degrees to 140 degrees. It has a conical shape. Regardless of the shape, the convex part of the reflective shape part can be integrally formed during processing, and post processing is required And not. BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a sectional view of a surface light emitting device according to an embodiment of the present invention. In the figure, the light source

Reference numeral 4 is attached to a substrate 5, and a light guide plate 1 made of a transparent material such as acryl is provided near the light source 5 so that light from the light source enters from an end face 1f. The light guide plate 1 is covered with a reflective frame 3 on a surface other than the upper surface 1a on the light emitting surface side, and has a smooth surface finish except for a bottom surface 1b opposite to the upper surface 1a. On the bottom surface 1 b of the light guide plate 1, minute projections 31 having a circular cross section parallel to the bottom surface are formed integrally with the light guide plate 1, and the top surface is finished flat. ing. As shown in FIG. 3, the convex portion 31 has a rising portion and a falling portion continuous from the top to the bottom portion and has a curved surface with a diameter R, and is arranged as shown in FIG. I have.

The diffusion plate 2 is mounted on the upper surface 1 a of the light guide plate 1. The diffusion plate 2 is made of frosted glass or the like, and diffuses light emitted from the upper surface 1a of the light guide plate 1 to illuminate an illuminated body (not shown) by the light emission surface 2a.

FIG. 3 is a perspective view in which the bottom surface 1b of the light guide plate 1 is enlarged and partially cut out. Each of the minute projections 31 is a reflection-shaped portion for reflecting light from the light source, has a circular cross-section, and has a funnel shape having a curved surface with a radius R with an outer periphery of a continuous portion with respect to the light guide 扳 1. It is formed (hereinafter, this round part is called an edge).

FIG. 4 shows an enlarged cross-sectional view of the projection 31. The size of the projections 31 is such that the thickness H of the light guide plate 1 is about 1 mm, while the height h of each projection is about 0.03 to 0.07 mm, d is about 0.05 to 0.2 mm, and all have the same shape.

FIG. 2 is a view of the surface light emitting device of the present example as viewed from above, in a state where the diffusion plate 2 is removed. Each of the small circles in the figure is a minute protrusion 31, and is arranged in a staggered lattice shape in a direction away from the light source 4. Further, the density at which the protrusions 31 are formed on the light guide plate 1 also gradually increases as the distance from the light source increases.

Light emitted from the light source enters the light guide 扳 1 from the end face 1 f of the light source 4. Light guide plate In the case of krill, the refractive index of acryl is n = 1.49, and the critical angle at which incident light is totally reflected at the light guide plate interface is 42.16 degrees. The light incident and refracted from the end face 1 f is totally reflected and leaks to the outside when it hits the flat surface 1 a, ld, 1 e and the bottom 1 b of the light guide plate 1 at an angle greater than the critical angle. Never. When the light strikes the end face 1 c, the light is reflected by the reflection frame 3.

Thus, the light that has entered the light guide plate 1 directly or repeatedly undergoes total reflection as described above, and strikes the edge of the convex portion 31 of the bottom surface lb. As described above, the 緣 portion is formed with a curved surface, and the light hitting it is reflected and emitted from the upper surface 1a, diffused by the diffusion plate 2 and emitted by the light emitting surface 2a.

As described above, since the light emitted from the light guide plate 1 is reflected by the edge of the projection 31, if the density of the projection 31 is high, the amount of light emitted from the upper surface 1 a in the vicinity increases. Become. Therefore, by gradually increasing the density of the projections 31 as the distance from the light source 4 increases, the amount of light emitted near the light source with a large amount of incident light decreases, and the incident light decreases. The opposite is true in the portion where the amount of light is small, and the amount of light emitted from the upper surface 1a of the light guide plate 1 is made uniform.

By arranging a small funnel-shaped convex part with rising and falling parts forming a curved surface on the bottom surface of the light guide 1 so that its density decreases as the distance from the light source increases, the following effects can be obtained. Is obtained.

(1) By arranging circular projections, light can be reflected at the same reflectance no matter from which direction the light hits, and the uniformity of light can be obtained without the directionality due to the shape of the projections.

(2) By making the projections the same shape, the reflectance can be controlled by their density, and the light amount of the surface light source can be made uniform.

(3) By arranging the protrusions in a staggered lattice pattern, the light emitted from the light source can easily enter the many protrusions directly, and uniformity of light can be obtained without brightening specific parts.

④Such a light guide plate can be manufactured at low cost without the need for a post-process such as hairline processing by integrally forming the projections during processing.

FIG. 5 shows another embodiment of the present invention. FIG. 5 is a cross-sectional view showing a light guide plate of a surface emitting device according to another embodiment, in which the shape of the projection is different from that of the above-described embodiment. Since the other structure is the same as that of the above-described embodiment, detailed description thereof will be omitted using the same reference numerals.

As shown in FIG. 5, the protrusion 33 has a conical shape whose cross section parallel to the bottom surface is circular. As is clear from the figure, the shape of the rising portion and the falling portion continuous from the top to the bottom portion of the convex portion 32, that is, the shape of the edge portion is a linear cross section having a fixed angle of 0 at the vertex angle.

The optical path of the light that has entered the light guide plate 1 from the light source 4 when the projections 33 have a conical shape will be described.

As described above, when the light guide plate 1 is acryl, the critical angle is 42.16 degrees.c The incident angle in the light guide plate of light that enters the light guide plate 1 from the light source 4 through the end face 1 f a is in the range of 0 degrees to 42.16 degrees. Therefore, the angle b of the light from the light source to the projection 33 directly through the end face 1 f without being reflected on the other surface of the light guide plate is 47.84 degrees (= 90−42. 1 6) ~ 90 degrees.

Here, if the vertex angle 0 of the convex portion 33 is set so that the light reflected at the edge of the convex portion 33 is perpendicularly reflected in the direction of the light emitting surface 1 a of the light guide plate 1, The angle S ranges from 90 degrees to 132.16 degrees (= (90—47.84Z2) Z2).

Further, the angle b of the light that passes through the end face 1 f from the light source 4, is reflected once by another surface of the light guide plate 1 (for example, the inner surface of the light emitting surface 1 a), and reaches the 緣 portion of the convex portion 33 is Since the critical angle of is 42.16 degrees, it becomes 42.16 degrees to 90 degrees. Therefore, if the vertex angle 0 of the convex portion 33 is set so that the light reflected at the edge of the convex portion 33 is perpendicularly reflected to the light emitting surface 1a of the light guide plate 1, the vertex angle 0 of the convex portion 33 becomes The range is 90 degrees to 137.85 degrees (= (90-42.16 / 2) no 2).

From the above, it is preferable that the vertex angle 0 of the convex portion 33 be set in a range of 90 degrees to 140 degrees. Preferably, when the average angle of light reaching the convex portion 33 is calculated as 68.92 degrees (= (90 + 48.7.4) Z2), the apex angle Θ becomes 11.08 degrees. Therefore, the apex angle of the projection 33 is preferably about 110 degrees.

In addition, as shown in FIG. 6 (A), the convex portion 34 may have a flat top portion of the conical shape, and as shown in FIG. 6 (B), the convex portion 35 The top of the conical shape may be curved. As described above, by arranging a small funnel-shaped convex portion having a conical rising portion and a falling portion forming a straight line in cross-section such that the density decreases as the distance from the light source increases, the lower the light-guiding plate 1 is, the lower the density becomes. The same effects (1) to (5) as in the first embodiment described above can be obtained, and the rate of directing the light reflected from the convex portion toward the light emitting surface in the vertical direction can be increased, and the brightness in front of the light emitting surface can be improved. Can be increased.

In the first embodiment and the other embodiments described above, the light guide plate 1 of the light source 4 is arranged so that light is incident on one end face of the light guide plate 1.However, when a large light guide plate 1 is used, However, light sources can be arranged at both ends. In this case, the convex portions on the bottom surface of the light guide plate 1 are arranged so as to have a high density near the center farthest from the two light sources, and are arranged with a gradient of density so as to have a low density near the light sources. In this way, a uniform surface emitting device can be realized.

Further, in each of the embodiments, the convex portion is formed as a convex portion whose top is directed to the light emitting surface 1a side by forming a depression in the light guide 扳 1, but is opposite to the light emitting surface 1a. The crest may be made to protrude, and in this case, substantially the same effect as in the above-described embodiment can be obtained. Industrial applicability

As described above, the surface light-emitting device according to the present invention has an effect that light from a light source can be uniformly emitted to the entire light-emitting surface to emit light uniformly without having a complicated structure. is there.

Claims

The scope of the claims

1. A surface light emitting device that emits light from a light source disposed on a side of a light emitting surface from the light emitting surface,

A transparent light guide plate is provided on a bottom surface portion facing the light emitting surface, wherein a reflection shape portion formed by minute projections is arranged so that its density gradually increases according to the distance from the light source. The light emitted from the light emitting surface is reflected by the reflecting shape part and emitted from the light emitting surface.

2. The surface emitting device according to claim 1, wherein the reflection-shaped portions are arranged in a zigzag pattern in a direction away from the light source.

3. The surface light emitting device according to claim 1, wherein the reflection-shaped portion is a minute convex portion formed by forming a continuous portion from a top portion to a bottom portion with a curved surface.

4. The surface-emitting device according to claim 1, wherein the reflection-shaped portion is a minute projection having a conical portion formed from a top portion to a bottom portion.

5. The surface emitting device according to claim 4, wherein the continuous portion of the reflection shape portion has a conical shape satisfying an apex angle of 90 degrees to 140 degrees.