JPH0575737U - Surface light source - Google Patents

Abstract

(57) [Summary] [Object] An object of the present invention is to provide a surface light source device using a light guide body which is bright and has a uniform luminance distribution. According to the surface light source device of the present invention, the light sources are arranged along the four sides of the light guide, and the back surface of the light guide has a large area in one direction in the center and becomes smaller as the light source approaches. It is provided with a pattern that is constant in the perpendicular direction.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a surface light source device using a light guide.

A conventional surface light source device using a light guide is generally configured as shown in FIG. That is, a linear light source 2 such as a cold cathode tube is arranged on both end faces or one end face of a plate-shaped light guide 1 having a constant thickness of transparent material, and a diffusion plate 3 is provided on the surface of the light guide 1. Is arranged and a reflective surface is provided on the back surface. In such a surface light source device, the light from the light source 2 is made incident on the inside of the light guide body 1, is emitted from the surface while the light is transmitted through the inside of the light guide body 1, and is made to be diffused light through the diffusion plate 3. To do.

[0003]

[Problems to be solved by the device]

 In the above-mentioned surface light source device, there is a demand for higher brightness, and various measures have been taken for that. As one of them, in addition to the one-lamp type or the two-lamp type as shown in FIG. 8, the one in which the light source 1 is arranged on all the end faces along all the sides of the light guide 1 as shown in FIG. 10 is known. , It is possible to increase the brightness. 8 shows the structure as seen from the side and FIG. 10 shows the structure as seen from above.

Further, as another requirement of the surface light source device, there is a problem of uniform brightness distribution. In order to solve this problem, the conventional surface light source device controls the distribution of a pattern formed of dot-shaped patterns, that is, minute diffusing portions having a diffusing action, formed on the back surface of the light guide 1, particularly the density in the area. Brightness distribution is made uniform. For example, when the pattern having the above-mentioned diffusing action is uniformly distributed, a portion near the light source 1 becomes bright and becomes darker as the distance from the light source 1 increases. In order to remove this, the pattern of the above-mentioned minute diffusion part is used with a specific distribution.

For example, in a surface light source device in which the light source 2 is arranged only on one end face 1 a side of the light guide 1, the end face 1 a side is bright and the opposite end face 1 b is dark. Therefore, a light diffusion pattern as shown in FIG. 9 is formed on the back surface of the light guide 1 by printing or molding. In this pattern, the minute diffusion portion 5a on the end face 1a side is small, and the minute diffusion portion 5b on the other end face 1b side is large. As described above, on the incident side (end face 1a side), the area (density in the area) of the minute diffusion portion occupying a certain area is small and the opposite side is large. In this way, the luminance distribution on the diffusion plate 3 is made uniform.

However, some of the one-lamp type and two-lamp type surface light source devices have a fairly uniform luminance distribution, but in the four-lamp type surface light source device, light is emitted from all sides (four sides). Since it is incident, it is difficult to control the brightness, and no one is currently known that the overall brightness distribution is uniform.

As described above, conventionally, no surface light source device that sufficiently satisfies the above two requirements has been known.

An object of the present invention is to provide a surface light source device in which the brightness distribution is bright and uniform over the entire light emitting surface.

[0009]

[Means for Solving the Problems]

 The surface light source device of the present invention comprises a plate-shaped light guide body made of a transparent material and having a constant thickness, in which light sources are arranged so as to be incident from all end faces along the four sides. A diffuser is placed on the front side and an anti-slope is provided on the back side of the light guide, and a pattern consisting of minute diffusion parts is formed on the back side of the light guide by means such as printing or molding. , The density of the area where the minute diffusion portions are provided in the central portion of the pattern is high, and the area density gradually decreases from the central portion in two directions parallel to the opposite sides of the pair of light guides, It has a distribution of minute diffusion parts whose area density is constant in the direction perpendicular to it.

In the surface light source device of the present invention, the amount of light incident on the light guide is significantly increased by allowing light to enter from all the end faces of the light guide by the above-described method, and the light is emitted from the surface. By increasing the amount of light to be emitted to make the diffuser plate surface brighter and the pattern formed on the back surface of the light guide as described above, the luminance distribution on the diffuser plate surface is made uniform. This makes it possible to completely satisfy the two requirements of the surface light source device.

Further, in the light source used in the present invention, it is necessary to arrange the light source so as to surround the light guide in order to allow light to enter from all the end faces of the light guide. Therefore, as the light source, one quadrangular shape extending along four sides, a combination of two L-shaped light sources, or four linear light sources is used.

Further, when the four linear light sources are arranged close to the respective sides, the length of each light source should not exceed either the plus or minus 15 mm of the corresponding side of the light emitting surface. Preferably. If the length is longer than the above length, it is not preferable for downsizing the surface light source device and effectively utilizing light. When shortened, the corners naturally become dark.

[0013]

【Example】

 Next, each embodiment of the surface light source device of the present invention will be described.

1 and 2 are a vertical cross-sectional view and a plan view of a first embodiment of the present invention, in which 1 is a light guide, 2 is a light source disposed near the light guide 1 so as to surround it, Reference numeral 3 denotes a diffusion plate provided on the front surface side of the light guide body 1, and 4 denotes a reflection surface provided on the back surface side of the light guide body 1. The back surface of the light guide 1 has a pattern as shown in FIG. 3, for example. In other words, the longitudinal direction (X direction in FIG. 2) of the surface of the light guide 1 has a uniform distribution, and the direction orthogonal thereto (Y direction in FIG. 2) has a high density at the center and a low density at both ends. Is becoming

In the surface light source device according to the first embodiment, since the light sources 2 are provided along all four sides of the light guide body 1, light enters the light guide body 1 from all end surfaces. The amount of light incident on the light guide 1 is very large, and therefore the amount of emitted light is also large. Also, since the pattern as shown in FIG. 3 is formed on the back surface of the light guide 1 by printing, molding or any other method, the amount of light emitted from the surface of the light guide 1 is related to the place of emission. However, the brightness distribution on the surface of the diffusion plate 3 is uniform. This has been confirmed experimentally, but is considered to be due to the following reasons.

FIG. 4 shows a two-lamp type surface light source device, in which light sources are provided on opposite sides, and the brightness distribution thereof is represented by isoluminance lines as shown in FIG. The brightest part is the darkest part D. Further, in the surface light source device of FIG. 4, when a pattern used in the present invention (the pattern shown in FIG. 3) is provided on the back surface of the light guide, as shown in (C) of FIG. The difference in brightness at the center of the image becomes smaller.

Further, when the light sources are provided on opposite sides different from the case of FIG. 4, and the pattern shown in FIG. 3 is further provided on the back surface of the light guide, it becomes as shown in FIG. 5C.

When considering the luminance distribution, the surface light source device of the first embodiment of the present invention is a combination of the luminance distribution of FIG. 4C and the luminance distribution of the surface light source device of FIG. 5C. it is conceivable that. That is, the luminance distribution shown in (C) of FIG. 4 and the luminance distribution shown in (B) of FIG. 5 are combined, and one bright portion and the other dark portion, one dark portion and the other bright portion, and an intermediate portion. The part and the middle part are superposed, and the entire surface has a uniform brightness distribution. In the case of this embodiment, the length of each light source is preferably within the dimension of the light emitting surface plus 15 mm. Within this range, the external dimensions of the device can be reduced and the light can be effectively used.

FIG. 6 shows a second embodiment of the present invention. In the first embodiment, as the light source 1, two cold cathode tubes surrounding the light guide 1 are used. In the above, two L-shaped light sources are used in combination.

FIG. 7 shows a third embodiment, in which one light source causes light to enter from four sides of the light guide.

[0021]

[Effect of the device]

 The surface light source device of the present invention is extremely bright and has a uniform brightness distribution.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a first embodiment of the present invention.

FIG. 2 is a plan view of the surface light source device.

FIG. 3 is a diagram showing a pattern formed on the back surface of the surface light source device.

FIG. 4 is a diagram showing the principle of the present invention, showing isoluminance lines when light sources are arranged on the left and right sides of the diagram.

FIG. 5 is a diagram showing the principle of the present invention, showing isoluminance lines when light sources are arranged above and below the diagram.

FIG. 6 is a plan view of a second embodiment of the present invention.

FIG. 7 is a plan view of a third embodiment of the present invention.

FIG. 8 is a sectional view of a conventional surface light source device.

FIG. 9 is a diagram showing a pattern used in a conventional surface light source device.

FIG. 10 is a plan view of a conventional four-lamp type surface light source device.

[Explanation of symbols]

 1 Light guide 2 Light source 3 Diffuser

Claims (5)

[Scope of utility model registration request] 1. A light guide body made of a plate-shaped transparent body having an arbitrary constant thickness, a light source arranged so that light can enter from any of the four end faces of the light guide body, and A diffusion plate arranged on the front surface side of the light guide body, a pattern made up of minute diffusion parts for brightness adjustment formed on the back surface of the light guide body, and a reflection surface arranged on the back surface side of the light guide body, 2. A surface light source device, wherein the pattern has a constant density from the center toward both opposite sides of one side in the area of the minute diffusion portion and decreases toward the other opposite sides. 2. The surface light source device according to claim 1, wherein the light source comprises one light source surrounding a light guide. 3. The surface light source device according to claim 1, wherein the light source is composed of two L-shaped light sources and is arranged so as to substantially surround the light guide body as a whole. 4. The surface light source device according to claim 1, wherein the light source is composed of four linear light sources, and is arranged near an end face along each side of the light guide. 5. The surface light source device according to claim 4, wherein the length of each light source does not exceed either the plus or minus 15 mm of the side length of the light emitting surface on the side where each light source is arranged.