JP2001043714A - Surface light source device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent unevenness of luminance like fireflies from being generated, by converting reflected light pattern formations on a light reflection surface side positioned in a perpendicular direction in relation to spot light sources at a part on an extension of the spot light source and a part other than the extension by using a plurality of spot light sources. SOLUTION: A light guide plate converts light reflection pattern formations on a light reflecting surface 11 side, positioned in the perpendicular direction (a direction of an arrow A) in relation to a spot light source 2. That is, the pattern formations of light reflection pattern 11A parts on the extensions of respective LED chip parts 21, 22 and 23 of the spot light sources 2 and light reflection pattern 11B parts between the LED chips are converted. More specifically, the area ratio of the light reflection pattern of the light reflection pattern 11B part is set larger than that of the light reflection pattern 11A. The area ratio of the light reflection pattern 11B between the LED chips is increased, and therefore, the reflection factor in this range is improved, and unevenness of luminance can be prevented.

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 comprising a group of point light sources including light emitting elements such as light emitting diode (LED) elements and mainly used for a backlight of a liquid crystal display panel.

[0002]

2. Description of the Related Art As a surface light source for a backlight of a liquid crystal display panel, an edge light type using a light-transmitting flat plate as a light guide plate is known. In such a surface light source, light is incident from one of the side end surfaces (edge portions) of a light guide plate made of a transparent parallel flat plate or a wedge-shaped flat plate, and propagates uniformly throughout the light guide plate. Is formed as diffuse reflection light by the light reflection member on the back surface of the light guide plate, and diffused light is emitted from the surface of the light guide plate.

An edge light type light guide plate is widely used because the thickness of the light guide plate can be reduced and the structure can be simplified. A cold cathode tube lamp is used as a light source provided at the edge of the edge light type light guide plate.

In recent years, portable electronic devices have become widespread, and there is a demand for power savings. Therefore, as a light source of a backlight unit of a portable electronic device, a light source using an LED that consumes less power than a conventional cold-cathode tube lamp has attracted attention and has been put to practical use.

[0005]

However, when an LED is used as a light source as compared with a cold-cathode tube lamp, several LED chips are arranged as point light sources. For this reason, unevenness occurs in the luminance in the vertical direction of the point light source (the direction extending on the light extension of the point light source) between the portion where the point light source is arranged and the portion where the point light source is not arranged. In particular, there is a problem that the luminance unevenness increases in a portion close to the LED chip, and firefly-like luminance unevenness occurs.

SUMMARY OF THE INVENTION An object of the present invention is to provide a surface light source which prevents the above-mentioned fire-like luminance unevenness from occurring.

[0007]

According to the present invention, light is incident from a light source disposed on one of the side end surfaces of a light guide plate, reflected by a light reflection surface on the back surface of the light guide plate, and emitted from the surface of the light guide plate. In a surface light source device, a plurality of point light sources are used as the light source, and a light reflection pattern shape on a light reflection surface side positioned in a direction perpendicular to the point light source is formed by extending an extended portion of the point light source and a point light source. It is characterized in that it is changed with parts other than the extension.

Further, the present invention is characterized in that the area ratio of the light reflection pattern in the portion other than the extension of the point light source is larger than the area ratio of the light reflection pattern in the portion on the extension of the point light source.

Further, the present invention is characterized in that the shape of the light reflection pattern on the light reflection surface side is partially changed between a portion extending from the point light source and a portion other than the extension of the point light source.

Further, the present invention is preferably configured so that the area ratio of the light reflection pattern is increased as the distance from the point light source increases.

With the above configuration, the brightness of the portion other than the extension of the point light source can be increased, and the brightness can be made closer to the brightness of the point light source portion to eliminate uneven brightness.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a plan view showing a schematic configuration of a surface light source device utilizing the present invention, and FIG. 2 is a schematic sectional view of the same.

As shown in FIGS. 1 and 2, the surface light source according to the present invention includes a light guide plate 1, a point light source 2 composed of LEDs, various control circuits (not shown), and the like. The control circuit includes, for example, a circuit that detects the total amount of light emitted from the light emission surface 12 of the light guide plate 1 and adjusts and supplies power to the point light source 2 so that the amount of emitted light is optimized. ing.

At the edge of the light guide plate 1, a point light source 2 composed of a white LED chip is arranged. In the present embodiment, three white LED chips 21 and
2 and 23 are implemented. The white LED chip includes, for example, a structure in which three LEDs of R, G, and B are housed in one package to emit white light,
What is necessary is just to use what constituted the monochromatic LED so that the emitted light from LED may be converted into white light using a fluorescent substance.
For example, when a GaN-based blue LED is used as the phosphor, a YAG (yttrium-aluminum-garnet) -based phosphor may be used.

A light reflecting surface 11 is provided on a side of the light guide plate 1 which is located in a direction perpendicular to the point light source 2. The light reflecting surface 11 is formed by dot printing or a cone-shaped depression formed after resin molding to prevent light from leaking and to increase the reflection efficiency, and is further provided with a light reflection pattern by a film or aluminum. Can be As will be described later, the shape of the light reflection pattern is changed between a portion on the LED chip extension of the point light source 2 and another portion (between the LEDs).

A light exit surface 12 is provided on the side of the light guide plate 1 facing the light reflection surface 11. Then, the light from the LEDs 21, 22, and 23 of the point light source 2 is reflected by the light reflecting surface 11 and the three side surfaces 13 of the light guide plate 1, and almost all of the incident light is finally uniform from the light emitting surface 12. It is emitted as combined light having directivity. In addition, a leakage prevention member such as a white tape is attached to the side surface 13 in order to prevent light leakage.

The material of the light guide plate 1 described above is selected from light-transmissive materials, and usually acrylic or polycarbonate resin is used. The shape of the light guide plate 1 is a parallel flat plate or a wedge-shaped flat plate having a cross section of about 1 to 5 mm. The thickness of the light guide plate 1 is further reduced by using LEDs, compared to the case of using a cold cathode tube lamp. It becomes possible.

Other translucent materials include acrylates or methacrylates such as polymethyl methacrylate and polymethyl acrylate, and homo- or copolymers thereof, and polyesters such as polyethylene terephthalate and polybutylene terephthalate. Thermoplastic resins such as polycarbonate, polystyrene and polymethylpentene, or acrylates such as polyfunctional urethane acrylates and polyester acrylates cross-linked by ultraviolet rays or electron beams, transparent resins such as unsaturated polyesters, transparent glass, transparent ceramics, etc. Is used.

The surface light source comprises LED chips 21, 22,
A reflection sheet 5 for reflecting the light of the LED is arranged so as to surround the periphery of the LED 23. As mentioned above,
A light reflection pattern is formed on the light reflection surface 11 side of the light guide plate 1 by printing or integral molding, and a reflection sheet 5 is disposed on the lower surface thereof. Further, a diffusion sheet 3 and a lens sheet 4 are disposed on the upper surface of the light exit surface of the light guide plate 1.

The point light source 2 is fixed at a predetermined position on the light guide plate 1 by fixing a substrate 24 on which each LED is mounted to an outer frame (not shown) located outside the reflection sheet 5 with a screw or an adhesive. Placed in

Each LED light from the point light source 2 enters the inside of the light guide plate 1 and is reflected by the light reflection pattern provided on the light reflection surface 11 and the three side end surfaces 13 to repeatedly converge. The light is emitted from the emission surface 12 to the diffusion plate 3, is uniformly and isotropically diffused within a desired angle range by the lens sheet 4, and is emitted as combined light. A liquid crystal display panel is arranged close to the lens sheet 4.

FIG. 3 is a schematic diagram showing a layout of a light reflection pattern provided on the light reflection surface 11 side of the light guide plate 1. In the light guide plate 1 of the present invention, the shape of the light reflection pattern located in the direction perpendicular to the point light source 2 (the direction of arrow A in the figure) is changed. That is, each LED chip 21 of the point light source 2
(22) Light Reflection Pattern 1 on Extension of Part (23)
The pattern shapes of the portion 1A and the light reflection pattern 11B between the LED chips are changed. Light reflection pattern 1
The area ratio of the light reflection pattern of the portion 1A is determined by the light reflection pattern 11
B is larger than the area ratio. The light reflection pattern may be printed or integrally formed.

As described above, by increasing the area ratio of the light reflection pattern 11B between the LED chips, the reflection efficiency in this region is improved, and luminance unevenness is prevented.

FIG. 4 shows an example of the light reflection pattern. The light reflection pattern is formed in a circular shape, and the area ratio is gradually increased in the direction perpendicular to the point light source 2 (direction A), that is, as the distance from the LED chip increases.
Then, in the horizontal direction (B direction) with respect to the point light source 2,
The area ratio between the LED chips of the light source 2 is larger than that of a certain portion of the LED chips. This is because a portion closer to the LED chip is more likely to cause fire-like luminance unevenness, so that the reflectance at that portion is reduced and the unevenness in luminance is reduced.

The area ratio is evaluated based on the area of the pattern per unit area. When the light reflection pattern is three-dimensional, the evaluation is based on the bottom area on the light reflection surface. For example, in the case of FIG. 4, a circular print pattern or a conical three-dimensional cone pattern may be used.

In the above-described embodiment, a white LED chip is used.
A plurality of ED chips (for example, blue) can be used. In this case, wavelength conversion means for converting the emitted light into white light may be used for the light guide plate 1. For example, the wavelength converting means can be formed of a fluorescent substance added to the inside of the light guide plate 1 or a fluorescent substance layer provided on the light emitting surface 12 and the light reflecting surface 11 of the light guide plate 1. As this fluorescent substance,
When a GaN blue LED is used, a YAG (yttrium aluminum garnet) fluorescent substance may be used.

As the LED chip of the point light source 2, R
Using the three LED chips of the LED chip for G, the LED chip for G, and the LED chip for B, the LED chip is synthesized in the light guide plate 1,
The light guide plate 1 may be configured to emit white light.

[0028]

As described above, when, for example, several LED chips are arranged as a point light source, the luminance in the vertical direction of the point light source becomes uneven at the portion between the point light source and the point light source. Occurs, especially in the area near the LED chip,
According to the present invention, this uneven brightness can be prevented, and the degree of uneven brightness on the light exit surface of the light guide plate can be reduced. Thus, a surface light source device that is uniform in appearance can be provided.

[Brief description of the drawings]

FIG. 1 is a plan view showing a schematic configuration of a surface light source device according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating a schematic configuration of a surface light source device according to an embodiment of the present invention.

FIG. 3 is a schematic diagram showing a layout of a light reflection pattern provided on the light reflection surface side of the light guide plate in the present invention.

FIG. 4 is a schematic view showing an example of a light reflection pattern according to the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 light guide plate 2 point light source 11 light reflecting surface 12 light emitting surface

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Satoshi Kuwahara 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. F-term (reference) 2H091 FA23Z FA45Z FD04 LA18

Claims (4)

[Claims] 1. A surface light source device that receives light from a light source disposed on one of the side end surfaces of a light guide plate, reflects the light on a light reflection surface on the back surface of the light guide plate, and emits light from the surface of the light guide plate. A plurality of point light sources are used as the light source, and the shape of the light reflection pattern on the light reflection surface located in the direction perpendicular to the point light source changes between an extension of the point light source and a portion other than the extension of the point light source A surface light source device, characterized in that: 2. The surface according to claim 1, wherein the area ratio of the light reflection pattern in a portion other than the extension of the point light source is larger than the area ratio of the light reflection pattern in a portion on the extension of the point light source. Light source device. 3. The light reflection pattern on the light reflection surface side is partially changed between a portion on the extension of the point light source and a portion other than on the extension of the point light source. A surface light source device according to claim 1. 4. The surface light source device according to claim 1, wherein the area ratio of the light reflection pattern is increased as the distance from the point light source increases.