JPH07114021A - Surface light source device - Google Patents

Abstract

PURPOSE:To make thickness smaller and to obtain high and uniform luminance by arranging a reflection layer on the base of a transparent substrate of a valley shape in cross section having light transmissivity, a milky white plate atop the substrate, linear-shaped light sources on its flanks and a light diffusion plate on the upper part. CONSTITUTION:A planar light transmission plate is constituted by disposing the reflection layer 3 on the base of the transparent substrate 2 having the valley shape in sectional plane shape and the light transmissivity and disposing the milky white plate 1 having a light diffusion function atop the layer. The linear-shaped light sources 4 are arranged on the flanks of the light transmission plate and the light diffusion plate 5 is arranged in the upper part, by which the light source device is constituted. For example, a transparent acrylic plate, etc., are used for the transparent substrate 2. For example, a milky white acrylic resin plate, etc., are used for the milky opaque plate 1. For example, a light transmission plate deposited with metal, such as aluminum, by evaporation on the base of the plate is used for the light reflection layer 3. The shape at the boundary between the milky white plate 1 and the transparent substrate 2 is formed as a shape symmetrical with the central part between the light sources. The light reflection plate is so mounted as to cover the linear-shaped light sources 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface light source device used for a display device or the like.

[0002]

2. Description of the Related Art Conventionally, as a surface light source device for a liquid crystal display device such as a personal computer or a television, there are a type in which a light source is directly arranged on the back surface of a light guide plate, a type in which a linear light source is arranged on the side surface of the light guide plate, and the like. Are known. The type in which the light source is arranged on the back surface of the light guide plate requires a considerable distance between the light source and the light diffusion plate in order to obtain uniform brightness, and the shape of the reflection plate becomes complicated. There is a problem that it is difficult to reduce the thickness of the device because of its thickness. As the type in which the linear light source is arranged on the side surface of the light guide plate, for example, the linear light source is arranged on the side surface of the light guide plate composed of a mountain-shaped reflecting surface and a lens or a prism (JP-A-2-32320). ), It is difficult to make the brightness of the surface light source uniform, and in order to obtain a surface light source with uniform brightness, it is necessary to give various shapes to the light guide plate, and there is a problem that the device becomes complicated. It was In order to solve the above-mentioned problems, the present inventors have already proposed a surface light source device in which a linear light source is arranged on the side surface of a light guide plate which is a combination of a light diffusion plate having a chevron cross section and a transparent plate (Japanese Patent Laid-Open No. Hei 4).
However, there is a demand for a planar light source in which the brightness of the planar light source is further improved.

[0003]

Therefore, the present inventors have found that
As a result of further diligent study, it was possible to obtain high brightness and even brightness for a surface light source device of a type in which the device was thinned by disposing a linear light source on the side surface of the light guide plate. The present invention has been completed.

[0004]

That is, according to the present invention, a reflective layer (3) is disposed on the bottom surface of a transparent substrate (2) having a light-transmitting cross section and having a valley-shaped cross section, and a light diffusion function is provided on the upper surface. It is characterized in that a milky white plate (1) is arranged to form a planar light guide plate, a linear light source (4) is arranged on the side surface of the light guide plate, and a light diffusion plate (5) is arranged on the upper side. A surface light source device is provided.

The surface light source device of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic perspective view of a surface light source device. The material of the transparent substrate (2) is not particularly limited, but it is preferable that the transparent substrate (2) is excellent in transparency because it serves as a light guide portion, and it is desired to be easy to handle, easy to mold, and lightweight. A transparent acrylic plate or the like is preferably used.

The material of the milky white plate (1) is not particularly limited, but an incident light can be diffused uniformly and the molding is easy. For example, a milky white acrylic resin plate is preferably used. .

Further, the transparent substrate (2) and the milky white plate (1) may contain additives which are generally used. Examples of the method of processing the light guide plate including the transparent substrate (2) and the milky white plate (1) include processing and bonding plate-shaped molded products, two-color molding by injection molding, and the like. The processing method is not limited.

Light reflection layer (3) arranged on the bottom surface of the light guide plate
The material thereof is not particularly limited, but it is possible to prevent incident light from leaking to the outside, and to reflect and diffuse the light more efficiently to obtain high brightness, for example, a metal such as aluminum on the bottom surface of the light guide plate. Those obtained by vapor-depositing, or those obtained by simply laminating a mirror surface plate and the like are preferably used.

There are no particular restrictions on (4) as long as it is a linear light source, and examples thereof include fluorescent lamps and cold cathode tubes.

Reference numeral (5) is a light diffusing plate, and the material thereof is not particularly limited, but one capable of making the brightness uniform is preferably used. Although the light diffuser plate (5) is used here as shown in the figure, it may be omitted if uniform brightness can be obtained without using the light diffuser plate (5).

FIG. 2 is a sectional view of the surface light source device. In this figure, the shape of the interface between the milky white plate (1) and the transparent substrate (2) is expressed by the following equation. y = −ax + b (0 ≦ x ≦ L / 2) y = ax + b−aL (L / 2 ≦ x ≦ L) a and b are constants 0 <a ≦ 2h / L 0 <b ≦ h b−aL / 2 ≧ 0 L is the distance from the light incident end surface of the light guide plate to the other end surface h is the distance from the bottom surface of the light guide plate to the exit surface x is the distance from the end surface of the light guide plate in the L direction y is the light guide plate The distance from the bottom surface to the emitting surface direction The shape of the interface between the milky white plate (1) and the transparent substrate (2) is not particularly limited, but as shown in the above equation, it is symmetrical at the central portion between the light sources. It is preferable that it has a different shape. Further, the bottom surface and the top surface of the light guide plate are preferably parallel to each other, but are not particularly limited.

The light reflecting plate (6) is provided, if necessary, in order to prevent a decrease in the brightness near the incident surface and to efficiently introduce the incident light into the light guide plate to increase the brightness as a whole. It may be attached so as to cover the linear light source (4) as shown in FIG. 3, and the light reflection plate (6) may be extended to the light incident end face of the light guide.

[0013]

The reflective layer (3) is arranged on the bottom surface of the transparent substrate (2) having a valley-shaped cross section having a light transmitting property, and the milky white plate (1) having a light diffusing function is arranged on the upper surface. By constructing a planar light guide plate, and arranging the linear light source (4) on the side surface of the light guide plate and arranging the light diffusion plate (5) on the upper side, it is possible to make the device thin, and also with high brightness and uniformity. It has become possible to obtain a surface light source device which gives a high brightness.

[0014]

EXAMPLES The present invention will be described below with reference to examples, but it goes without saying that the present invention is not limited to the examples.

Example 1 L = 225 mm, h = 15 mm, a = 0.11, b = 1
Using a light guide plate of No. 5, a surface light source device as shown in FIG. 2 in which two 8 watt fluorescent lamps were used as linear light sources was used to measure the luminance distribution on the light emitting surface. A luminance meter LS-100 manufactured by Minolta was used for measuring the luminance. The light emitting surface was evenly divided into 16 parts, and the brightness in the vicinity of the center of each divided section was measured. The results are shown in Table 1. In Table 1, the positions of the linear light sources are the upper part and the lower part of the table.

[0016]

[Table 1]

Example 2 In Example 1, the light reflecting plate (6) as shown in FIG. 3 was used.
Using the same surface light source device as in Example 1 except that a light guide plate covering the linear light source (4) from the periphery to the light incident surface is used.
Luminance was measured in accordance with Example 1. The light emitting surface was evenly divided into 16 parts, and the brightness in the vicinity of the center of each divided section was measured. The results are shown in Table 2. In Table 2, the positions of the linear light sources are the upper part and the lower part of the table.

[0018]

[Table 2]

Comparative Example 1 A surface light source device similar to that of Example 1 is used except that the light guide plate shown in FIG. 2 is used as the light guide plate formed by dot printing on the bottom surface of a transparent plate having a simple plate shape. Luminance was measured in accordance with Example 1. The light emitting surface was evenly divided into 16 parts, and the brightness in the vicinity of the center of each divided section was measured. The results are shown in Table 3. In Table 3, the positions of the linear light sources are the upper part and the lower part of the table.

[0020]

[Table 3]

Comparative Example 2 L = 225 mm, h = 15 mm, a = 0.11, b = 1
Using a light guide plate of No. 5 and a surface light source device as shown in FIG. 5 in which two 8-watt fluorescent lamps were used as linear light sources, the distribution of luminance on the light emitting surface was measured. A luminance meter LS-100 manufactured by Minolta was used for measuring the luminance. The light emitting surface was evenly divided into 16 parts, and the brightness in the vicinity of the center of each divided section was measured. The results are shown in Table 4. In Table 4, the positions of the linear light sources are the upper part and the lower part of the table.

[0022]

[Table 4]

[Brief description of drawings]

FIG. 1 is a schematic perspective view of a surface light source device.

2 is a cross-sectional view of the surface light source device shown in FIG.

FIG. 3 is a cross-sectional view of the surface light source device shown in FIG. 1 when a light reflection plate is provided so as to cover the linear light source.

FIG. 4 is a schematic perspective view of a surface light source device.

5 is a cross-sectional view of the surface light source device shown in FIG.

[Explanation of symbols]

 (1): Milky white plate (2): Transparent substrate (3): Light reflection layer (4): Linear light source (5): Light diffusion plate (6): Light reflection plate h: Light emission from bottom surface of light guide Distance to surface L: Distance between both end surfaces of light guide

Claims (3)

[Claims] 1. A transparent substrate (2) having a light-transmitting cross section with a valley-shaped cross section has a reflective layer (3) on the bottom surface and a milky white plate (1) having a light diffusing function on the upper surface. A surface light source device comprising a planar light guide plate, a linear light source (4) disposed on a side surface of the light guide plate, and a light diffusion plate (5) disposed on an upper portion thereof. 2. The surface light source device according to claim 1, wherein in the cross section of the light guide plate according to claim 1, the interface between the milky white plate (1) and the transparent substrate (2) is represented by the following equation. . y = −ax + b (0 ≦ x ≦ L / 2) y = ax + b−aL (L / 2 ≦ x ≦ L) a and b are constants 0 <a ≦ 2h / L 0 <b ≦ h b−aL / 2 ≧ 0 L is the distance from the light incident end surface of the light guide plate to the other end surface h is the distance from the bottom surface of the light guide plate to the exit surface x is the distance from the end surface of the light guide plate in the L direction y is the light guide plate Distance from bottom to exit surface 3. The surface light source device according to claim 1, wherein a light reflection plate (6) is provided so as to cover the linear light source (4) arranged on the side surface of the light guide plate according to claim 1.