A NEW BACKLIGHTING SYSTEM USING A POLARIZING LIGHT PIPE

A new backlight with a polarizing light pipe that has great potential for improving the light yield of a liquid crystal display (LCD) is bei ng developed. The aim is to eliminate the three major absorption losse s of a TN LCD, which occur in the dichroic polarizer attached to the t hin-film-transistor (TFT) glass, the black matrix on the TFT glass, an d the color-filter array. The loss in the dichroic polarizer is reduce d by the use of a backlight with a polarizing light pipe which produce s linearly polarized light output. Both by theory and by experiment we have shown that the polarizing light pipe produces highly polarized l ight output under optimum conditions, i,e,, a 17:1 polarization ratio in the viewing range from -10 degrees to 10 degrees, The brightness ga in by polarization is calculated to be 1,44, The losses in the black m atrix on the TFT glass and the absorbing color filter are reduced by m aking these components reflective, so that the light which was previou sly absorbed is now reflected back into the backlight for recycling, T he backlight with a polarizing light pipe is effective in reusing the reflected light. When a reflective color filter is used, the brightnes s gain of a backlight with a polarizing light pipe over a conventional backlight is 11,3%, The total potential brightness gain by this metho d of light recycling is theoretically estimated to be 3,16, Therefore, the total gain of an LCD using a polarizing light pipe and reflective components over a conventional LCD is 4,55, This large gain suggests great potential for the polarizing light pipe.