JPH05313163A - Plane light source device - Google Patents

Abstract

PURPOSE:To provide a plane light source device which can utilize light incident on the top surface of a light guide plate in the direction other than that perpendicular to the plate, is superior in light utilization efficiency and is improved in brightness. CONSTITUTION:This plane light source device is equipped with a flat plate type transparent light guide plate 1 which transmits the light, a light source 2 which is provided closely on at least one of four sides of the light guide plate 1, and a reflecting mirror 3 which covers the light source 2, and a tooth- shaped pattern 12 is partially formed on the projection-side surface of the light guide plate 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flat light source device suitable for use in, for example, a liquid crystal display device.

[0002]

2. Description of the Related Art In recent years, transmissive or semi-transmissive liquid crystal display devices have been widely used for display devices such as word processors and personal computers. As a lighting method in such a liquid crystal display device, generally, a light source is arranged directly below the back surface of the liquid crystal display plate, or a light source is arranged substantially on the side surface of the liquid crystal display plate without arranging the light source directly below the back surface of the liquid crystal display plate. It is known that a planar light emitting illumination is created by using a light guide plate made of acrylic or the like. The latter method is a known method, for example, in JP-A-61-99187 and JP-A-63-62104.

This latter flat light source device is conventionally constructed as shown in FIG. 3, and reference numeral 1 in the drawing is a flat transparent light guide plate for transmitting light. A light source 2 is provided near at least one of the four sides of the light guide plate 1, and a reflecting mirror 3 is provided so as to cover the light source 2. Further, a diffusion plate 4 is arranged on the exit side surface of the light guide plate 1 at a predetermined interval, a plurality of reflective dots 5 are provided on the surface opposite to the exit side, and reflection is performed at a predetermined interval. A plate 6 is arranged.

[0004]

In operation, as shown in FIG. 4, the light beam 7 emitted from the light source 2 is reflected by the reflective dots 5.
Thus, only the light 8 scattered in the vertical direction on the upper surface 1a of the light guide plate 1 contributes to the illumination light 9 and the efficiency is poor. Furthermore,
If the upper and lower surfaces of the light guide plate 1 or one surface is smooth or has a diffusing surface, most of the light rays 7 cannot be emitted from the inside of the light guide plate 1. That is, as shown in FIG. 5, light entering at an incident angle C ° larger than the critical angle A ° is totally reflected by the upper surface 1 a of the light guide plate 1 and does not go out of the light guide plate 1. When the incident angle B ° is smaller than the critical angle A °, the reflected light 10 and the emitted light 11 have a certain degree.
Cause

The present invention has been made in view of the above circumstances, and it is possible to contribute to the illumination light incident in directions other than the direction perpendicular to the upper surface of the light guide plate, the light utilization efficiency is excellent, and the brightness is improved. An object is to provide a flat light source device.

[0006]

SUMMARY OF THE INVENTION According to the present invention, a plate-like transparent light guide plate for transmitting light, a light source provided in proximity to at least one of the four sides of the light guide plate, and the light source are covered. A planar light source device including a reflecting mirror and having a sawtooth pattern partially formed on a surface of the light guide plate on the exit side.

[0007]

According to the present invention, since the sawtooth pattern is partially formed on the exit side surface of the light guide plate, the light utilization efficiency is remarkably excellent and the brightness is improved as compared with the conventional case.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings.

The flat light source device according to the present invention is constructed as shown in FIGS. 1 and 2, and FIG. 2 is an enlarged view of a main part of FIG. When the same parts as those in the conventional example (FIG. 3) are designated by the same reference numerals, reference numeral 1 in the drawing is a flat transparent light guide plate that transmits light. A light source 2 is provided near at least one of the four sides of the light guide plate 1.
A reflecting mirror 3 is provided so as to cover the. Further, a sawtooth pattern 12 is partially formed on the exit side surface of the light guide plate 1. Further, a diffusion plate (not shown) is arranged on the exit side surface of the light guide plate 1 at a predetermined interval as in the conventional example, and a plurality of reflection dots (see FIG. (Not shown), and a reflector (not shown) is arranged at a predetermined interval. The reflective dots and the reflective plate may be omitted in some cases, but it is more effective to use them.

In the above case, if the sawtooth pattern 12 is provided on the entire exit side of the light guide plate 1, all the light rays inside the light guide plate 1 are emitted on the exit side surface of the light guide plate 1 close to the light source 2. Therefore, the sawtooth pattern 12 is partially distributed so as to eliminate uneven brightness. As a result, the light beam 7 emitted from the light source 2 also contributes to the illumination light 9 by the sawtooth pattern 12 even when the light beam is incident on the upper surface 1a of the light guide plate 1 in a direction other than the vertical direction.

[0011]

According to the present invention, since the sawtooth pattern is partially formed on the exit side surface of the light guide plate, the utilization efficiency of light is remarkably excellent and the brightness is improved as compared with the conventional case. .

[Brief description of drawings]

FIG. 1 is a sectional view showing a flat light source device according to an embodiment of the present invention.

FIG. 2 is an enlarged cross-sectional view showing a main part of FIG.

FIG. 3 is a cross-sectional view showing a conventional flat light source device.

FIG. 4 is a sectional view showing a defect in the conventional flat light source device.

FIG. 5 is a sectional view showing a defect in the conventional flat light source device.

[Explanation of symbols]

1 ... Light guide plate, 2 ... Light source, 3 ... Reflector, 9 ... Illumination light, 12
… Sawtooth pattern.

Claims (1)

[Claims] 1. A flat transparent light guide plate for transmitting light,
In a flat light source device comprising a light source provided near at least one of four sides of the light guide plate, a sawtooth pattern is partially formed on a surface of the light guide plate on an illumination light emission side. A flat light source device characterized by the following.