JPH0617154Y2 - Liquid crystal display - Google Patents

Description

[Detailed description of the device]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device in which light is emitted from the back surface of a liquid crystal display plate.

[0002]

2. Description of the Related Art A liquid crystal display device used in a vehicle instrument panel, a liquid crystal television, or the like is designed to emit light from the back surface of a liquid crystal display plate. A structure is adopted in which a lamp to be used is housed, the light emitted from the lamp is diffused by a light diffusing plate provided in the opening of the casing, and then the back surface of the liquid crystal display plate is illuminated.

As the above-mentioned lamp, a small baseless electric bulb, a rare gas discharge lamp, a cold cathode fluorescent lamp or the like is used. However, the brightness distribution of each of these lamps greatly decreases with the distance from the lamp. When illuminating a liquid crystal display panel having an area of a predetermined size, there is a problem that brightness varies depending on the location. In order to prevent this, the light emitted from the lamp is once diffused by the light diffusing plate made of heat-resistant acrylic or the like, and the illumination is made uniform by the diffused light.

[0004]

However, in the conventional liquid crystal display device, since the light source is directly above the light diffusing plate, the illuminance distribution in front of the light diffusing plate is high near the lamp and It gets lower with distance. Therefore, due to such an illuminance distribution, the illuminance distribution of diffused light transmitted through the light diffusion plate is not uniform over the entire surface, and there is a problem that uneven brightness occurs. In order to solve such a problem, the present applicant has proposed a liquid crystal display device in which a thick portion is formed on the inner surface of a light diffusion plate. This is one in which the thickness of the inner surface side of the light diffusion plate just above the lamp is maximized, and the thickness is gradually reduced as the distance from the lamp increases.

In this way, since the thickness of the light diffusion plate is right above the lamp, the light transmittance is reduced, and there is an advantage that the light distribution can be approximated to a substantially uniform brightness as a whole.

However, recently, there is a demand for downsizing of this type of liquid crystal display device, and there is a demand for thinning of the casing. When the casing is thin,
When the lamp and the light diffusion plate are close to each other and a thick portion is formed on the inner surface of the light diffusion plate, the lamp and the light diffusion plate are too close to each other and the incident angle of light to the thick portion is appropriate. However, there is a drawback that the light diffusivity is deteriorated and a uniform illuminance distribution cannot be obtained.

Further, if the lamp and the light diffusion plate are too close to each other, there is a concern that the portion protruding inside the light diffusion plate will be heated and thermally deformed due to heat radiation from the entire lamp or from the electrodes.

An object of the present invention is to provide a liquid crystal display device in which the illuminance distribution is substantially equalized, the casing can be made thin, and the light diffusing plate is not easily thermally deformed.

[0009]

The present invention is characterized in that a light diffusing convex portion protruding toward the liquid crystal display plate side is formed at a position of the light diffusing plate facing the light source.

[0010]

According to the present invention, since the convex portion protruding outward is formed at the portion right above the light source of the light diffusing plate, the convex portion diffuses the light to be transmitted therethrough to the side. The brightness of the portion directly above the light source can be reduced to make the overall brightness even. Further, since the inner surface of the light diffusion plate is separated from the lamp with a predetermined size, the influence of heat from the lamp during lighting is reduced, and the light diffusion plate is not partially thermally deformed. As a result, it is possible to illuminate a large area substantially uniformly over the entire area and realize a thin casing.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on an embodiment shown in the drawings.

FIG. 1 is an exploded perspective view of a liquid crystal display device. In FIG. 1, reference numeral 1 is a casing which also serves as a reflector. The casing 1 is made of a metal plate and has a tub-like cross section with a quadratic curve. A white coating or a reflecting surface 2 is formed on the inner surface of the casing 1, and a flange portion 3 is formed on the peripheral edge of the opening. Further, lamp holding recesses 4 and 4 are formed at both ends in the longitudinal direction of the casing 1.

Reference numeral 5 is a lamp as a light source, for example, a cold cathode discharge lamp is used. The lamp 5 is in the form of a straight tube, and has electrodes formed of cold cathodes (not shown) sealed at both ends thereof, and these ends are attached to the holding recesses 4 and 4 of the casing 1 through fixtures not shown.

A light diffusion plate 6 is formed of, for example, a heat resistant acrylic resin. The light diffusing plate 6 is provided with a light diffusing convex portion 7 protruding outwardly at a position facing the cold cathode fluorescent lamp 5.

The convex portion 7 extends along the tube axis direction of the lamp 5, has a circular cross section in the direction orthogonal to the lamp axis direction of the lamp 5, and gradually lowers as the distance from the lamp 5 increases. It has a smooth curved surface.

The peripheral portion of the light diffusing plate 6 is overlapped with the flange portion 3 of the casing 1. In this case, it is desirable that the peripheral portion of the light diffusion plate 6 be held by an elastic holder (not shown), and this elastic holder be superposed on the flange portion 3 of the casing 1. A liquid crystal display plate 8 is provided in front of the light diffusion plate 6. Since the liquid crystal display panel 8 may be a known one, detailed description thereof will be omitted.

In the liquid crystal display device having such a structure, a part of the light emitted from the lamp 5 is in the casing 1.
The light is reflected by the reflecting surface 2 of the above to go to the light diffusing plate 6, and the rest goes directly to the light diffusing plate 6. The light diffusing plate 6 diffuses the light by refraction or reflection while transmitting the light, and thus irradiates the back surface of the liquid crystal display plate 8 with the diffused light. The liquid crystal display panel 8 receiving such back light displays an image based on the liquid crystal display.

According to the above embodiment, the light diffusing plate 6 includes:
A convex portion 7 is formed so as to face the cold cathode fluorescent lamp 5 toward the liquid crystal display panel 8 side. The convex portion 7 has a maximum protrusion directly above the cathode fluorescent lamp 5 and gradually lowers toward both sides. Therefore, the lamp 5 in this light diffusion plate 6
Of the light that is going to be transmitted right above is bent laterally, so that the light that is going to be transmitted just above the lamp 5 is reduced, and the amount of light going to both sides of the convex portion 7 is relatively gradually increased. Therefore, the diffused light transmitted through the light diffusion plate 6 has a uniform illuminance distribution over almost the entire surface and a uniform brightness.

In the above construction, since the convex portion 7 projects outside the light diffusing plate 6, it does not project to the inner surface, so that the lamp 5 and the light diffusing plate are separated from each other, and the light emitted from the lamp diffuses the light. There is no concern that the plate 6 will be thermally deformed. On the contrary, in the case where the same spacing dimension as the conventional one is ensured, the lamp 5 can be arranged close to the light diffusing plate 6, and the casing 1 can be thinned accordingly. The present invention is not limited to the above embodiments, and the lamp 5 may be, for example, a small baseless bulb, a rare gas discharge lamp, a hot cathode fluorescent lamp, or the like. Also, the casing 1 may have a light diffusing surface instead of the reflecting surface 2.

[0020]

As described above, according to the present invention, the convex portion protruding outward is formed on the outer surface of the light diffusing plate so as to face the light source. The brightness can be reduced to the top, and the overall brightness can be made closer to equalization. Further, since the inner surface of the light diffusion plate can be separated from the lamp by a predetermined dimension, the influence of heat from the lamp during lighting is reduced, and the light diffusion plate is not partially thermally deformed. From this,
It is possible to illuminate a large area substantially uniformly over the whole area and to make the casing thinner.

[Brief description of drawings]

FIG. 1 is an exploded perspective view of a liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is a sectional view of the same embodiment in an assembled state.

[Explanation of symbols]

1 ... Casing, 2 ... Reflective surface, 5 ... Lamp, 6 ... Light diffusing plate, 7 ... Convex part, 8 ... Liquid crystal display plate.

Claims (1)

[Scope of utility model registration request] 1. A light source is housed in a casing having an opening on one side, a light diffusing plate is provided in the opening of the casing, and a liquid crystal display plate is installed in front of the light diffusing plate to emit light from the light source. In a liquid crystal display device in which light is diffused by the light diffusing plate to irradiate the back surface of the liquid crystal display plate, the light diffusing plate has a light diffusing plate that projects toward the liquid crystal display plate at a position facing the light source. A liquid crystal display device, characterized in that a convex portion for forming is formed.