JPH03144486A - Plane light source device - Google Patents

Abstract

PURPOSE:To minimize useless light by forming plural recessed parts having saw-tooth cross-sections in a range from around one-tenth of full length to an incident end surface on the reflecting side of a light transmission body. CONSTITUTION:The recessed part 5 with a triangular (saw tooth) cross-section is formed over prescribed length in the vicinity of the incident end surface on the side of the reflecting surface 4 of the light transmission body 2. The range of forming the recessed parts 5 is from the end surface of the light transmission body to a length of around one-tenth of the full length L of the light transmission body. Since the plural recessed parts 5 are formed in the vicinity of the end of the light transmission body, the light that is reflected on the opposite end surface of the incident end and returns after it is made incident on the light transmission body is again returned. Thus, the loss of light quantity from light leakage can be minimized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a surface light source device using a light guide, which is used as a backlat of a liquid crystal display device or the like.

[Prior Art] A conventional surface light source device using a light guide has a configuration as shown in FIG. That is, a diffuser plate 3 is provided on the front side of the light guide 2 whose incident end face 2a is placed close to the light source 1, and a reflective surface 4 is formed on the back side of the light guide 2, which is the opposite side to the diffuser plate 3. . This conventional surface light source device using a light guide allows light from a light source 1 to enter the light guide 2 from the surface 2a, and this incident light is reflected by the front and back surfaces of the light guide. In the process of traveling to the side opposite to the incident end surface, some of the light passes through the diffusing surface 3 and is emitted as diffused light, resulting in a surface light source that emits diffused light uniformly from the entire surface of the light guide 2. .

[Problems to be Solved by the Invention] In the conventional surface light source device as shown in FIG. , return inside the light guide 2. This returning light also passes through the diffusion surface 3 and goes out as diffused light, but some of it is
As shown by reference numeral 6 in the drawing, the light exits from the incident end face 2a and becomes wasted light that is not used as illumination light.

An object of the present invention is to provide an efficient surface light source device in which wasted light exiting from the incident end surface 2a is reduced as much as possible.

[Means for Solving the Problems] A surface light source device of the present invention includes a light source, a light guide whose incident end face is arranged close to the light source, a diffusion surface provided on the surface of the light guide, and a back surface of the light guide. A recess with a triangular (serrated) cross section is formed over a certain length near the incident end face on the reflective surface side of the light guide. Light that travels through the interior, is reflected at the end surface opposite to the incident end surface, and returns toward the diffusing surface near the incident end surface, thereby eliminating wasted light and making effective use of the light.

[Example] Next, an example of the surface light source device of the present invention will be described based on the drawings.

1 to 3 are diagrams showing an embodiment of the surface light source device of the present invention, in which FIG. 1 is a plan view, FIG. 2 is a sectional view, and FIG. 3 is an enlarged sectional view of the main part. . In these figures, l is the light source,
Reference numeral 2 denotes a light guide, 3 a diffusion surface, and 4 a reflection surface, which have substantially the same structure as the conventional example shown in FIG. 5 is light guide 2
A recess formed on the reflective surface 4 side near the incident end surface 2a of the light guide 2.
This is to prevent the light reflected and returned from going out from the incident end face 2a like the light 6 shown in FIG.

The recesses 5 have a triangular shape as shown in an enlarged view in FIG. 3, and when a large number of recesses are provided, they form a sawtooth shape. The area in which this recess 5 is formed is about 17t, which is the total length of the light guide from the end face of the light guide.

The appropriate length is up to .

Optical glass, synthetic resin, etc. can be considered as materials generally used for the light guide. Among these, synthetic resin materials are often used because of their light weight and low cost, and among them, acrylic resin, methacrylic resin (PMMA), etc. are common. In the case of light guides made of these materials, experimental results have revealed that most of the light incident from the light guide end face 2a has an incident angle of 70° to 89°. Therefore, the light incident on the light guide 2 passes through the diffuser plate 3 as diffused light and does not go out of the light guide, but is repeatedly reflected, reflected at the end surface opposite to the incident end surface, and then returned from the incident end surface. Most of the incident light is at the incident angle of 70° to 89°. Therefore, the light that returns at this angle of incidence may be returned in the exact opposite direction near the incident end face.

For light with an incident angle of 70°, as shown in FIG. 3, the angle α of the recess 2a is 20°, the thickness of the light guide 2 is 4 mm, and ffT
It was found that the optical loss can be minimized when the h major length is 20 flnm and y = 45°.

The shape of this recess varies depending on the material (refractive index), size, thickness, etc. of the light guide.

[Effects of the Invention] As described above, in the present invention, by forming a plurality of recesses near the entrance of the light guide, the light that enters the light guide is reflected at the end surface opposite to the incident end. By returning the returning light again, a bright lighting device can be obtained by minimizing the loss of light amount due to light leakage.

[Brief explanation of the drawing]

1 and 2 are respectively a plan view and a sectional view of an embodiment of the present invention, FIG. 3 is an enlarged sectional view of a recess formed in the light guide of the above embodiment, and FIG. 4 is a conventional surface light source. FIG. 2 is a cross-sectional view of the device. l... Light source, 2... Light guide, 3... Diffusion surface, 4...
... Reflective surface, 5... Concave part

Claims (1)

[Claims] In a surface light source device comprising a light source, a light guide whose incident end surface is disposed close to the light source, a diffusing surface provided on the surface of the light guide, and a reflective surface provided on the back surface of the light guide, the light guide 1. A surface light source device comprising: a plurality of recesses each having a sawtooth cross-section extending from an incident end face to about 1/10 of the total length on a reflective surface side of the device.