JPH0627420A - Back light device - Google Patents

Abstract

PURPOSE:To provide a back light device which projects the light from a light source on a liquid crystal panel by almost 100% and to increase the brightness of an image displayed on the liquid crystal panel. CONSTITUTION:The light source light from a parabolic mirror 14 is spectrally split to the P polarized light and the S polarized light by a polarized light beam splitter 15. Besides, the split S polarized light is changed to the P polarized light by a 1/2 wavelength plate 19. Then, the P polarized light transmitted through the plate 19 and the P polarized light transmitted through the splitter 15 are respectively condensed at an identical position by condenser lenses 20 and 22. Besides, the P polarized light condensed by the lenses 20 and 22 is reflected on the reflecting surface 24 of a concave mirror 23 and made incident on the liquid crystal panel 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight device used in, for example, a liquid crystal projector or a liquid crystal display device.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 2, a backlight device of this type conventionally includes a light source 1 such as a metal halide lamp and a parabolic mirror 2, and the source light generated by the light source 1 is a parabolic mirror. 2 reflects the light toward the light incident surface of the liquid crystal display panel 3.

[0003]

In the backlight device having such a configuration, the light source light generated by the light source 1 includes both P-polarized light and S-polarized light with respect to the light incident surface of the liquid crystal display panel 3. Therefore, it is necessary to dispose a polarizing plate on the light incident side of the liquid crystal display panel 3 and absorb either the P polarized light or the S polarized light by the polarizing plate. However, if either the P-polarized light or the S-polarized light is absorbed by the polarizing plate, the light amount of the light source light incident on the liquid crystal display panel 3 will be halved, and the amount absorbed by the polarizing plate will be wasted. There is a problem that the brightness of the liquid crystal display panel 3 is also halved.

The present invention has been made in view of the above problems, and an object thereof is to allow almost 100% of light from a light source to enter a liquid crystal display panel and to increase the brightness of the liquid crystal display panel. It is intended to provide a backlight device that can be operated.

[0005]

In order to solve the above-mentioned problems, the present invention provides a light source, a parabolic mirror which reflects the light of the light source generated by the light source in a forward direction, and a parabolic mirror. The light source light reflected by the light source is split into two linearly polarized lights having polarization directions different from each other by 90 degrees, and one of the two linearly polarized lights split by this spectrally polarized light is the same as the other linearly polarized light. And a first condensing means for condensing the linearly polarized light from the polarizing means, and the other linearly polarized light of the two linearly polarized light dispersed by the spectroscopic means. Second condensing means for condensing at the same position as the means, and a first condensing means and a second condensing means having a focal point at the same position as the first condensing means and the second condensing means.
A concave mirror having a reflecting surface having a radius of curvature smaller than the focal length of the light collecting means and reflecting the linearly polarized light collected by the first light collecting means and the second light collecting means toward the liquid crystal display panel. It is equipped with.

[0006]

In the present invention having such a structure, the first and second
When the linearly polarized light collected by the light collecting means is applied to the liquid crystal display panel by applying it to the reflecting surface of the concave mirror, the amount of light entering the liquid crystal display panel increases, so that the brightness of the image displayed on the liquid crystal display panel is increased. The height can be increased.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to FIG. FIG. 1 is a diagram showing a schematic configuration of a liquid crystal display device. The liquid crystal display device includes a liquid crystal display panel 11 and a backlight device 1 for illuminating the liquid crystal display panel 11 from the back side.
2 and.

The backlight unit 12 includes a light source 13 such as a metal halide lamp, and a parabolic mirror 14 that reflects the light source light generated by the light source 13 in parallel to the front side. A polarization beam splitter 15 is arranged in front of 14 to face it.

The polarization beam splitter 15 has a spectral plane 16 for splitting the incident light from the parabolic mirror 14 into P-polarized light and S-polarized light. Is emitted from the side surface 17 of the polarization beam splitter 15, is incident on the half-wave plate 19 via the mirror 18.

The half-wave plate 19 has a polarization effect of changing the polarization direction of incident light by 90 degrees.
The S-polarized light that has entered the wave plate 19 becomes P-polarized light that is emitted from the half-wave plate 19 and enters the condenser lens 20. The condenser lens 20 has a condensing function of condensing the incident light at the point A, and the incident light (P
After being condensed at point A, the polarized light becomes diffused light and strikes the reflecting surface of the concave mirror 23 described later.

On the other hand, the P-polarized light split into the S-polarized light on the spectral surface 16 is emitted from the rear surface 21 of the polarization beam splitter 15 and is incident on the condenser lens 22. The condenser lens 22 has a condensing function of condensing the incident light at the point A, and the incident light (P-polarized light) incident on the condenser lens 22 from the polarization beam splitter 15 is condensed at the point A. It becomes diffused light and strikes the reflecting surface 24 of the concave mirror 23.

The concave mirror 23 is arranged with the reflecting surface 24 facing the light incident surface of the liquid crystal display panel 11, and has a focal point at the same position as the condenser lenses 20 and 22. Further, assuming that the focal lengths of the condenser lenses 20 and 22 are F1 and F2, the concave mirror 23 has radiuses of curvature R1 and R2 of about 1 of the focal lengths F1 and F2.
/ 2.

In this embodiment having such a configuration, the light source light from the parabolic mirror 14 is split into P-polarized light and S-polarized light by the polarization beam splitter 15, and the split S-polarized light is divided into half wavelength plates 19 Liquid crystal display panel 11
Since only P-polarized light can be made incident on the liquid crystal display panel 11 and either the P-polarized light or the S-polarized light is not absorbed by the polarizing plate arranged on the light incident side of the liquid crystal display panel 11, Almost 1 light is transmitted to the liquid crystal display panel 11.
It can be made incident at 00%.

Further, in this embodiment, the P-polarized light transmitted through the half-wave plate 19 and the P-polarized light transmitted through the polarization beam splitter 15 are condensed at the same positions by the condenser lenses 20 and 22, respectively. 22 has a focal point at the focal point and has radiuses of curvature R1 and R2 of approximately 1 with respect to focal lengths F1 and F2 of the condenser lenses 20 and 22
By reflecting the P-polarized light from the condenser lenses 20 and 22 toward the light incident surface of the liquid crystal display panel 11 by the / 2 concave mirror 23, the light amount of the light source light incident on the liquid crystal display panel 11 is almost doubled. The brightness of the image displayed on the liquid crystal display panel 11 can be doubled.

In the above embodiment, the polarization beam splitter 15 is used as a means for splitting the light source light from the parabolic mirror 14 into two linearly polarized lights (P-polarized light and S-polarized light) whose polarization directions are different from each other by 90 degrees. Alternatively, a polarizing prism or the like may be used. Further, in the above-described embodiment, the S-polarized light of the P-polarized light and the S-polarized light split by the polarization beam splitter 15 is changed to the P-polarized light by the ½ wavelength plate 19.
The two-wave plate 19 may be changed to S-polarized light.

Further, in the above embodiment, the half-wave plate 19 is used.
Although the condenser lenses 20 and 22 are used as means for condensing the P-polarized light that has passed through and the P-polarized light that has passed through the polarization beam splitter 15, a concave mirror or the like may be used.

Further, in the above embodiment, the case where the backlight device according to the present invention is applied to the liquid crystal display device has been described, but it goes without saying that it can also be applied to a liquid crystal projector or the like.

[0018]

As described above, according to the present invention, almost 100% of the light from the light source can be incident on the liquid crystal display panel, and the brightness of the image displayed on the liquid crystal display panel can be increased. It is possible to provide a back light device that can do so.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of a backlight device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a schematic configuration of a conventional backlight device.

[Explanation of symbols]

11 ... Liquid crystal display panel, 12 ... Backlight device, 13
... light source, 14 ... parabolic mirror, 15 ... polarization beam splitter, 18 ... mirror, 19 ... 1/2 wave plate, 20, 22 ...
Condenser lens, 23 ... concave mirror.

Claims (1)

[Claims] 1. A light source, a parabolic mirror that reflects the light source light generated by the light source toward the front in parallel, and a light source light reflected by the parabolic mirror whose polarization directions differ from each other by 90 degrees. A linearly polarized light from the linearly polarized light from the linearly polarized light from the linearly polarized light from the linearly polarized light from the linearly polarized light First condensing means for condensing, and second condensing means for condensing the other linearly polarized light of the two linearly polarized light separated by the spectroscopic means at the same position as the first condensing means. Has a focal point at the same position as the first light converging means and the second light converging means, and has a reflecting surface having a radius of curvature smaller than the focal lengths of the first light converging means and the second light converging means. The linearly polarized light collected by the first light collecting means and the second light collecting means is And a concave mirror that reflects toward the crystal display panel.