A new backlighting system using a polarizing light pipe

Abstract

A new backlight with a polarizing light pipe that has great potential for improving the light yield of a liquid crystal display (LCD) is being developed. The aim is to eliminate the three major absorption losses of a TN LCD, which occur in the dichroic polarizer attached to the thin-film-transistor (TFT) glass, the black matrix on the TFT glass, and the color-filter array. The loss in the dichroic polarizer is reduced by the use of a backlight with a polarizing light pipe which produces linearly polarized light output. Both by theory and by experiment we have shown that the polarizing light pipe produces highly polarized light output under optimum conditions, i.e., a 17:1 polarization ratio in the viewing range from -10° to 10°. The brightness gain by polarization is calculated to be 1.44. The losses in the black matrix on the TFT glass and the absorbing color filter are reduced by making these components reflective, so that the light which was previously absorbed is now reflected back into the backlight for recycling. The backlight with a polarizing light pipe is effective in reusing the reflected light. When a reflective color filter is used, the brightness gain of a backlight with a polarizing light pipe over a conventional backlight is 11.3%. The total potential brightness gain by this method 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.