Backlighting system with faceted light pipes

摘要

A light pipe used for backlighting liquid crystal displays has a planar front surface and a stair-stepped or faceted back surface. Light is injected from the ends of the light pipe from cold- or hot-cathode, apertured, fluorescent lamps. The cold-cathode lamps are preferably insulated to raise their operating temperature. The back surface has a series of planar portions parallel to the front surface connected by facets, which are angled so that the injected light reflects off the facets and through the front surface. A reflector having a planar, highly reflective, highly scattering surface or a sawtoothed or grooved upper surface in located adjacent to and parallel with the light pipe back surface to reflect light escaping from the back surface back through the light pipe to exit the front surface. The axis of grooves is preferably slightly skewed from the facet axis to reduce moire pattern development. A low-scattering or low-loss diffuser is located adjacent to and parallel with the light pipe front surface to reduce moire pattern development. The liquid crystal display is located over the low scattering diffuser. A separate injector may be located between the lamp and the light pipe to better couple the light into the light pipe. Light pipes may be stacked to provide a backlight system having increased brightness and/or greater viewing angle.