JPS6310102A - Illumination device for transmissive image display device - Google Patents

Abstract

PURPOSE:To prevent a drop of the luminance of both end parts of a diffusion plate by radiating a light beams radiated to the lower part of a light source, to a part where the luminance drops by a reflecting surface of a crest-shaped plane which has been provided on a reflecting member. CONSTITUTION:A reflecting member 8 having a reflecting surface consisting of a crest-shaped plane and a paraboloid is provided on the lower part of a light source 5. In this state, by the reflecting surface of the crest-shaped plane which has been provided in the vicinity of the reflecting member 8, a light beam from the light source is radiated to a part which is separated from the light source of a diffusion plate 6, and also, radiated to the whole diffusion plate 6 by the reflecting surface of the paraboloid. Accordingly, that which has added a direct projection light beam to these radiated light beams is radiated to the diffusion plate 6. As for the diffusion plate 6, its sectional shape is trapezoidal, and it consists of such a structure as plate thickness of the center part is thick and that of the peripheral part is thin. In this way, the diffusion plate 6 to which the direct projection light beam from the light source 5 and the reflected light beam beams from the reflecting member have been radiated in a well-balanced state can realize a uniform luminance distribution.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an illumination device that is disposed on the back side of a transmissive image display device and illuminates the image display element uniformly from the back side.

Conventional Technology Transmissive image display devices using image display elements such as liquid crystals use an illumination device as shown in FIG. 5, for example, in order to brightly and uniformly illuminate the image display element from the back side. .

That is, a parabolic reflector 2 is provided below the linear light source 1 to efficiently condense the light emitted from the light source 1, and the direct light from the light source 1 and the reflected light from the reflector 2 are separated. By irradiating the diffuser plate 3 provided above the light source 1, the back surface of the image display element 4 placed parallel to the diffuser plate 3 is illuminated.

Problems to be Solved by the Invention In such a conventional lighting device, since the reflecting surface of the reflecting plate 2 is a paraboloid, a part of the light from the light source 1 reflected by the reflecting plate 2 is reflected by the diffuser plate. It is irradiated almost perpendicularly to 3. If only the reflected light from the reflector 2 is irradiated onto the diffuser plate 3, the luminance distribution of the diffuser plate 3 will be nearly uniform. However, since the diffuser plate 3 is also irradiated with direct light from the light source 1 in addition to the reflected light, the 11 degree distribution is a combination of the direct light and the reflected light as shown in FIG. The brightness is high, and the edge of the diffuser plate 3, that is, the light source 1
Since the brightness decreases as the distance increases, the brightness of the image display element 4 becomes non-uniform.

As a method to make the brightness distribution of the diffuser plate 3 uniform, it is possible to block direct light from the light source 1, or to make the diffuser plate 3 made of a material with high diffusion properties (as close as possible to perfect diffuse transmission properties: for example, opal glass). ), but both are undesirable because they reduce the light utilization efficiency of the light source 1.

In addition, various types of flat lighting devices such as EL (electroluminescence), LED (light emitting diodes), and flat fluorescent tubes have been proposed as flat lighting devices with improved uniformity of brightness distribution, but they have low luminous efficiency and poor luminescent color. There are problems such as limited availability.

Therefore, the present invention provides a planar illumination device that uses white light with a uniform luminance distribution without reducing the efficiency of using light from a light source.

Means for solving the problems and technical means of the present invention for solving the above problems are as follows:
The part of the diffuser plate where the brightness decreases, that is, the part away from the light source, is irradiated with the light that is irradiated directly below the light source using the chevron-shaped flat reflective surface of the reflective member, and this is combined with the direct light from the light source. This is intended to make the luminance distribution of the diffuser plate uniform.

action The effect of this technical means is as follows.

That is, a reflecting member having a reflecting surface consisting of a chevron-shaped plane and a paraboloid is provided below the light source. The light from the light source is irradiated onto a portion of the diffuser plate away from the light source by the reflective surface in the shape of a chevron provided near the reflective member, and the light from the light source is irradiated onto the entire diffuser plate by the reflective surface of the radiation surface. The diffuser plate is irradiated with the direct light from the light source added to these irradiated lights. The diffuser plate has a trapezoidal cross-sectional shape, and is thick at the center and thin at the periphery. Therefore, a diffuser plate that is irradiated with direct light from the light source and reflected light from the reflecting member in a well-balanced manner can realize a uniform brightness distribution.

Embodiments Hereinafter, embodiments of the present invention will be described based on the accompanying drawings.

In FIG. 1, reference numeral 5 denotes a linear light source (for example, a fluorescent lamp), and a diffusion plate 6 is provided above the light source 5 in parallel with the tube axis direction of the light source 5.

Furthermore, there is an image display element 7 placed above the diffuser plate 6 in parallel with the diffuser plate 6, and the diffuser plate 6 and the image display element 7 are arranged as follows.
They are arranged close to each other with an interval of several mm. On the other hand, at the bottom of the light source 5, there is provided a reflecting member 8 consisting of two types of reflecting surfaces, a chevron-shaped plane and a paraboloid as shown in FIG. 5 is placed.

The material of the reflective member 8 is acrylic resin, and the light source 5 on the surface
The part facing the mirror (reflecting surface) is coated with a metal-deposited aluminum film and functions as a reflecting mirror.

Further, as shown in FIG. 3, the cross-sectional shape of the diffuser plate 6 is thick in the vicinity of the light source 5, and becomes thinner as it moves away from the light source 5. Accordingly, the transmittance changes (the thinner the transmittance, the more the transmittance increases). (becomes high).

By configuring the illumination device as described above and setting the width (A) of the chevron-shaped plane part of the reflecting member 8 and the width (B) of the paraboloid to appropriate values as shown in FIG. Of the light irradiated from the light source 5, 6 indicates directly irradiated light [direct light (a
)], the light reflected by the parabolic reflecting surface provided on the surface of the reflecting member 8 [reflected light (b)], and the light reflected by the flat reflecting surface of the reflecting member 8 [reflected light (C)]; )
], and the combined light is irradiated. Here, especially the reflected light (
For this purpose, in C), the angle of the chevron-shaped flat reflecting surface is set so that the end portion of the diffuser plate 6, that is, the portion away from the light source 5, is irradiated intensively. From the above, the luminance distribution on the diffuser plate 6 is as shown in FIG.

In FIG. 4, (a) shows the brightness distribution due to direct light (a) from the light source 5, where the brightness near the light source 5 is high. (b) shows the brightness distribution due to the reflected light (b) from the paraboloid of the reflecting member 8, and the brightness outside the vicinity of the light source 5 is almost uniform. Furthermore, (c) is the brightness distribution due to the reflected light (c) from the flat surface of the reflecting member 8, and the brightness is high in the portion away from the light source 5. By combining these brightness distributions (a), (b), and (c), the target brightness distribution (d) can be obtained.

Although acrylic resin is used as the material for the reflective member 6 in the present invention, the same effect can be achieved even if an aluminum plate with high specularity is used instead of acrylic resin.

In addition, although a straight tube fluorescent lamp was used as the light source 5 in this embodiment, linear light sources such as a cold cathode discharge lamp and a segmented halogen bulb may also be used, as well as a tungsten lamp and an L lamp.
A plurality of EDs connected in a linear manner may also be used.

In the present invention, the light source is placed in the center of the reflective member and the diffuser plate, and the light emitting surface is made symmetrical with respect to the light source. Even if a lighting device is constructed using the above, the functions and effects are the same as those of the above embodiments.

Effects of the Invention The present invention is able to irradiate the light irradiated to the lower part of the light source to the part where the brightness decreases, that is, the part away from the light source, by means of the mountain-shaped flat reflection surface provided on the reflection member. It is possible to prevent a decrease in brightness at both ends of the diffuser plate, which was a problem in the prior art, and achieve a uniform brightness distribution.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a lighting device according to an embodiment of the present invention, FIG. 2 is a configuration diagram of a reflecting member in the lighting device, FIG. 3 is a configuration diagram of a diffuser plate in the lighting device, and FIG. 4 is a configuration diagram of the lighting device. FIG. 5 is a sectional view of a conventional illumination device, and FIG. 6 is a characteristic diagram of the brightness distribution of a diffusion plate in the same illumination device. 5. Light source, 6. Diffusion plate, 7. Image display element, 8.
・Reflective member agent's name: Patent attorney Toshio Tsuchinakao (1 person) Figure 2: 8 Measuring part: Amanesha; shape of the material Figure 3: 6 Hole: 1. ) Expansion of the light source (Expansion) of the 4 major vr surface shapes Figure 4 I1 [ Figure 5 I of the light source I Figure 4J! Image display element l light source figure 6 jin 1 wide 1 sentence 4 tan

Claims (1)

[Claims] A linear light source, a reflecting member provided at the bottom of the light source to reflect a part of the irradiated light from the light source onto a diffuser plate, and a reflecting member provided at the top of the light source to reflect the direct light from the light source and the reflecting member. a diffuser plate that is irradiated with reflected light from the reflecting member, the shape of the reflecting surface of the reflecting member is a chevron-shaped plane near the light source, and the shape of the other reflecting surface is a paraboloid; An illumination device for a transmissive image display device in which the thickness of the diffuser plate becomes thinner as the distance from the light source increases.