GB2308202A

GB2308202A - Subtractive colour liquid crystal device

Info

Publication number: GB2308202A
Application number: GB9625829A
Authority: GB
Inventors: Eung-Sang Lee
Original assignee: Samsung Display Devices Co Ltd
Current assignee: Samsung SDI Co Ltd
Priority date: 1995-12-15
Filing date: 1996-12-12
Publication date: 1997-06-18
Also published as: JPH09179115A; DE19652045A1; JP3011893B2; KR970058021A; GB9625829D0; KR0176426B1

Description

2308202 LIQUID CRYSTAL LIGHT VALVE AND PROJECTION SYSTEM USING THE SAME

Background of the Invention

The present invention relates to a projection system, and more particularly, to a liquid crystal light valve and a projection system using the same.

Currently, with the development of image reproducing apparatuses and image softwares of higher screen quality, research has been conducted on image reproducing apparatuses having a large screen for obtaining higher screen quality such as a 26-inch or larger direct-view televisions or So-inch or larger projection systems using a cathode ray tube. Also, development of a liquid crystal projection system using a liquid crystal panel of a TFT method as a light valve has been vigorous. The projection system using the liquid crystal display device has low consumption power, and is small in size Is and lightweight, which has made it more popular than other kinds of apparatuses. For the liquid crystal projection system, methods employing a color filter and a dichroic mirror are used.

FIG. 1 shows a projection system using the color filter employing method.

As shown in FIG. 1, the system is comprised of a light source 12 disposed in front of a reflector 11, a liquid crystal display device 13 disposed in front of the light source 12, a color filter 14 adjacent to the liquid crystal display device 13, a projection lens 15 for projecting an 1 is image of the liquid crystal display device 13 on a screen 16.

Here, light radiated from the light source 13 passes through the liquid crystal display device 13 to form an image, and the image is colored by passing through the color filter 14, and then passes through the projection lens 15 to be projected on the screen 16.

However, in forming the color image through the color filter, efficiency in the use of light isvery low thereby limiting the luminance of the image.

FIG. 2 shows a projection system using the dichroic mirror method. As shown in FIG. 2, white light radiated from a light source 21 is divided into red, blue and green light by reflecting mirrors 22a and 22b and dichroic mirrors 23a and 23b having spectral properties. Light of each color is irradiated to three liquid crystal display devices 24a, 24b and 24c to form images, and then the images are combined using a reflecting mirror 25 and dichroic mirrors 26a and 26b. The light combined while reflecting off the reflecting mirror 25 and passing through the dichroic mirrors 26a and 26b is projected on a screen (not shown) through a projection lens 27.

The above-described projection system using the dichroic mirror, in which light radiated from the light source 21 is separated by the dichroic mirrors 23a and 23b, passed through the liquid crystal display devices, and recombined by dichroic mirrors 26a and 26b, requires a large structure and a relatively long optical path, thereby deteriorating the 2 efficiency of light use.

Summary of the Invention

Accordingly, it is an object of the present invention to provide a thin and lightweight liquid crystal light valve using a subtractive color mixture capable of enhancing the efficiency of light use and a projection system using the same.

To accomplish the above object of the present invention, there is provided a liquid crystal light valve for forming a color image by passing light radiated from a light source therethrough, the liquid crystal light valve comprising: at least three liquid crystal display devices; a plurality of color polarizing plates arranged such that the liquid crystal display devices are alternately disposed between the color is polarizing plates, the color polarizing plates arranged using a subtractive color mixture method.

Preferably, the color polarizing plates include a cyan polarizing plate, a green polarizing plate, a red polarizing plate and a magenta polarizing plate.

To accomplish the above object of the present invention, there is provided a projection system comprising: a light source; a liquid crystal light valve including at least three liquid crystal display devices disposed in front of the light source and a plurality of color polarizing plates arranged alternately with the liquid crystal display devices and using a subtractive color mixture method, and for forming a color 3 image by passing light radiated from the light source therethrough; a group of projection lenses located in front of the liquid crystal light valve; and a screen on which the light passed through the projection lenses is projected to form a color image.

Brief Description of the Drawincrs

The above objects and advantages of the present invention will become more apparent by describing in detail a preferred embodiment thereof with reference to the attached drawings in which:

FIG. 1 is a schematic diagram illustrating an example of a conventional projection system using a color filter method; FIG. 2 is a schematic diagram illustrating another example of a conventional projection system using a dichroic mirror method; FIG. 3 is a schematic diagram illustrating a projection system using a light valve according to the present invention; FIG. 4 is a diagram showing the principle of subtractive color mixture; and FIG. 5 is a t.able illustrating the on/off states of liquid crystal display devices for forming various color pixels according to the projection system of the present invention.

Detailed Description of the Invention

As shown in FIG. 3, the projection system according to 4 the present invention is comprised of a light source 41, a reflector 42 disposed behind the light source 41, a light valve 30 disposed in front of the light source 41 and for forming a color image by a subtractive color mixture method, a group of projection lenses 43 disposed in front of the light valve 30, and a screen 44 on which light passing through the group of projection lenses 43 is projected to form an image.

The light valve 30 includes at ledst three liquid crystal display devices 31, 32 and 33 and a plurality of color polarizing plates 35 to form a color image using the subtractive color mixture method, by which each color of outgoing light is obtained by subtracting each wavelength of incident light.

The color polarizing plates 35 include a cyan polarizing plate 35a, a green polarizing plate 35b, a red polarizing plate 35c and a magenta polarizing plate 35d. The liquid crystal display devices 31, 32 and 33 are arranged between the polarizing plates 35a, 35b, 35c and 35d, respectively. The polarization axis of each of the polarizing plates 35a, 35b, 35c and 35d, each forming color images, are parallel. Here, a yellow polarizing plate instead of the green or red polarizing plate 35b or 35c can be used.

The operation of the above-mentioned liquid crystal light valve according to the present invention and the projection system using the same will be described as follows.

Light radiated from the light source 41 passes through the first, second and third liquid crystal display devices 31, 32 and 33 which is selectively driven and the color polarizing plates 35 to form an image, and the image is projected on the screen 44 through the group of projection lenses 43 to form a color image.

A process of forming the color image by the subtractive color mixture method in the light valve 30 will be described with reference to FIG. 4. By the subtractive color mixture method, in case that the color filters, fbr example, a magenta polarizing plate, a cyan polarizing plate, a yellow polarizing plate, are arranged in series as shown in FIG. 4, the final output of light is obtained by subtracting (AND-operating) wavelengths of light corresponding to the respective polarizing plates.

Accordingly, when the first, second and.third liquid crystal display devices 31, 32 and 33 are selectively driven, as shown in FIG. 5, a pixel having a desired color can be obtained. For example, in the case that the first, second and third liquid crystal display devices 31, 32 and 33 are turnedoff, light cannot pass. Thus, a black pixel is obtained. In the case that the first liquid crystal display device 31 is turned-on and the second and third liquid crystal display devices 32 and 33 are turned-off, a red pixel is obtained. Similarly, when voltage applied to the liquid crystal display device in the same manner is controlled, images having the colors shown in FIG. 5 are obtained.

As described above, according to the liquid crystal light valve of the present invention and a projection system using 6 the subtractive color mixture method, an image having a luminance which is at least three times as bright as that of a projection system using a conventional color filter can be obtained. Also, the liquid crystal light valve formed by accumulating the liquid crystal display device and the polarizing plate, is thin, small and lightweight. Accordingly, the optical path in the projection system is shortened, to thereby enhance the efficiency of light use.

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Claims

CLAIMS:

1. A liquid crystal light valve for forming a color image by passing light radiated from a light source therethrough, said liquid crystal light valve comprising: at least three liquid crystal display devices; a plurality of color polarizing plates arranged such that said liquid crystal display devices are alternately disposed between said color polarizing plates, said color polarizing plates arranged using a subtractive colof mixture method.

2. A liquid crystal light valve according to claim 1, wherein said color polarizing plates include a cyan polarizing plate, a green polarizing plate, a red polarizing plate and a magenta polarizing plate.

3. A projection system comprising: a light source; a liquid crystal light valve including at least three liquid crystal display devices disposed in front of said light source and a plurality of color polarizing plates arranged alternately with said liquid crystal display devices and using a subtractive color mixture method, and for forming a color image by passing light radiated from said light source therethrough; a group of projection lenses located in front of said liquid crystal light valve; and a screen on which the light passed through said projection lenses is projected to form a color image.

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4. A projection system according to claim 3, wherein said color polarizing plates include a cyan polarizing plate, a green polarizing plate, a red polarizing plate and a magenta polarizing plate.

5. A liquid crystal light valve according to claim 1, substantially as herein described with reference to the accompanying drawings.

6. A projection system according to claim 3, substantially as herein described with reference to the accompanying drawings.

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