JPH0642028B2 - Flat light source - Google Patents

Description

The present invention relates to a thin flat light source.

More specifically, the present invention relates to a flat light source in which a first light flux generated by focusing, guiding, and diverging a light flux of an artificial light source and a second light flux passing through a light guide system are light source light fluxes.

Conventionally, what has been used as a flat light source is EL
(Electroluminescence), a flat fluorescent tube, an electric bulb as shown in FIG. 1, or a system using a discharge tube and a light diffusion plate. When using high power consumption equipment and these planar light sources, the power consumption of the light source is not a problem. However, when used in combination with a low power consumption device such as a liquid crystal display device, the flat light source must obtain sufficient brightness with low power consumption. The conventional planar light source emits light by itself, and when the ambient light is strong, a large amount of power is always required to obtain a light amount comparable to the ambient light. This is a fatal drawback for low power consumption devices.

The present invention has been devised in view of the drawbacks of the conventional flat light source. When the ambient light is strong, it is used positively, and the light of the internal artificial light source is used only when the ambient light is weak. The purpose is to reduce the power consumption of the system.

Hereinafter, the present invention will be described in detail based on examples.

Example 1 FIG. 2 shows a light guide system including a wedge-shaped light guide body and an internal artificial light source with a generally cross section. A fluorescent tube was used as the artificial light source, but various discharge tubes, incandescent lamps, EL,
Of course, a light emitting diode or the like can also be used. The light guide is
As shown in the cross-sectional views of FIGS. 3 (a) and 3 (b), one surface of which has a sawtooth (Fresnel) shape (a) and a scattering surface (b) is processed to have at least a refractive index of the surrounding medium. It is a larger transparent body. Although acrylic resin is used here in terms of workability, the material is not particularly limited. In the type of the saw-like cross section shown in FIG. 3 (a), each surface is mirror-finished so as to facilitate total reflection. In order to change the light distribution characteristic of the emitted light, it is possible to deal with it by changing the inclination of the sawtooth shape and the like to optimize the surface roughness pitch. FIG. 3 (b) is a scatter processed product. As shown in Figs. 3 (a) and 3 (b), the luminous flux of the internal artificial light source (solid arrow) that is incident from the wide end face.
Is totally reflected, refracted and then totally reflected, and is emitted from the emission surface (upper surface in FIG. 3) of the light guide. This is the first light flux. Since the light source of FIG. 3 shows a part of the luminous flux, there are, of course, luminous fluxes that are not effectively used.

Next, the ambient light, which is the second light flux, enters from the molding surface of the light guide as shown by the broken line arrow in FIG. 3, is refracted and transmitted by the light guide, and is emitted to the side opposite to the molding surface. . When the ambient light is strong, the ambient light is used in this way. It is also possible to use the internal artificial light source that is the first light flux and the ambient light that is the second light flux at the same time.

This principle is that, as shown in FIG. 3, two luminous fluxes having different incident directions are totally reflected at the interface, and the other is refracted and transmitted and emitted in the same direction. Furthermore, the fact that the light beam propagating through the high-refractive medium enters the molding surface from a specific direction is used.

Although various artificial light sources can be adopted, they can be turned on arbitrarily,
It must be able to be turned off or dimmed. This is because, as described above, the amount of luminous flux of the artificial light source is adjusted depending on the intensity of ambient light. In this way, it is possible to reduce power consumption averaged over time by dimming or turning off the artificial light source.

In order to make the ambient light effectively enter the light guide, the fourth
It is advisable to employ the reflector, light guide, etc. shown in FIGS. FIG. 4 shows the case where a reflector is used.
A large amount of ambient light can be incident on the light guide body by the reflection plate. This is because the ambient light generally has many components that are incident from above.
Also, in order to reduce the fluctuation due to the direction of ambient light,
A light diffusion plate may be installed. The installation position of the light diffusion plate is
Although there are the exit surface side of the light guide, the molding surface side, immediately before the reflector, etc., the location where the brightness distribution of the flat light source is made small is selected. FIG. 5 shows the case where a light guide in which optical fibers are focused is used. This is also one method of effectively guiding the ambient light to the light guide.

Further, if a light converging unit is used to effectively guide the light flux of the artificial light source to the light guide, a brighter flat light source can be obtained.

Example 2. FIG. 6 shows a case where particles having a refractive index different from that of the transparent body are dispersed in a plate-shaped transparent body having a refractive index larger than that of the surrounding medium as a light guide (a), and reflective particles are dispersed. It is a figure which shows the cross section of the light guide of (b). The artificial light source light flux (solid arrow), which is the first light flux, enters from the end face of the light guide and is reflected by the refraction index particles or the reflective fine particles, or after refraction is reflected or scattered, and a part thereof is generated. It is taken out from the emitting surface. This is the first light flux.

The ambient light enters the second light flux (broken line arrow) from the incident surface, is reflected, refracted, and then reflected and scattered like the first light flux, and a part thereof is extracted from the emission surface. The first light flux and the second light flux are thus mixed by the light guide body, and both become the light flux of the planar light source.

A method for effectively taking in ambient light similar to that of the first embodiment,
It is of course possible to adopt a method of homogenizing the brightness distribution of the flat light source.

Since the luminous flux of the artificial light source can be changed depending on the intensity of the ambient light, the power consumption of the system can be reduced as in the first embodiment.

In the above description, the first light flux is the light flux from the artificial light source and the second light flux is the light flux from the ambient light. However, conversely,
It is of course possible to use the first light flux as ambient light and the second light flux as an artificial light source.

As described above, the present invention has the following effects.

The first effect is that the first light flux and the second light flux pass through the two brightness distribution homogenizing means, that is, the sawtooth shape or the dispersion shape formed on the second surface, and the light diffusing plate. , It is possible to realize a homogenized luminance distribution in a wide area, and further, the first light flux incident from the first surface is reflected on the slope and then reaches the second surface, and directly to the second surface. Since there is a luminous flux that reaches, the incident angle distribution of the first luminous flux incident on the second surface becomes large, and the luminance distribution of the first luminous flux is further homogenized. That is, the synergistic effect of homogenization can significantly improve the homogenization of the luminance distribution.

The second effect is that the sawtooth shape or the dispersion shape formed on the second surface of the light guide system and the light diffusing plate are arranged so as to be separated from each other by the thickness of the light guide system. Can be realized.

Using the flat light source of the present invention as a basic configuration, the first light flux is a light flux of an artificial light source, the second light flux is a light flux of ambient environment light, and the ambient light is increased by using a light guide focusing a reflector or an optical fiber. By efficiently incorporating the light into the light guide system, high brightness can be obtained, and the light amount of the artificial light source can be reduced, so that the power consumption of the artificial light source can be reduced. That is,
It is possible to realize a flat light source that is thin, has uniform brightness, high brightness, and low power consumption.

INDUSTRIAL APPLICABILITY The present invention is effective as a flat light source used in low power consumption devices, and is particularly effective as a back light source of a liquid crystal display device having a large display area.

[Brief description of drawings]

FIG. 1 shows an example of a conventional flat light source. FIG. 2 is a cross-sectional view of a system using the wedge-shaped light guide according to the present invention. FIG. 3 is a sectional view of the light guide. (a) shows the case of Fresnel (sawtooth) shape. (b) shows the case of the scattering shape. FIG. 4 is a cross-sectional view when the ambient light is effectively used by using a reflector. FIG. 5 is a cross-sectional view when the ambient light is effectively used by using the light guide. FIG. 6 is a sectional view of the light guide. (a) shows the case where the modified refractive index particles are dispersed. (b) shows the case where the reflective particles are dispersed.

Claims (2)

[Claims] 1. A planar light source in which two light beams are incident on a substantially wedge-shaped light guide system and the two light beams are emitted from the same surface of the light guide system, wherein the light beams are emitted from the light guide system. It has an inclined surface, a first surface and a second surface on which a light beam is incident, and the cross section of the second surface has a sawtooth shape or a scattering shape, and a light diffusion plate sandwiches the inclined surface. The first light flux is incident on the light guide system from the first surface, and the second light flux is transmitted from the second surface to the light guide system. Incident, the first light flux and the second light flux exits from the slope,
A flat light source, characterized in that the flat light source transmits the light through the light diffusion plate. 2. The flat light source according to claim 1, wherein the first light flux is a light flux generated by an artificial light source and the second light flux is a light flux generated by ambient light.