Gradually tapered light pipes for illumination of LED projectors

LEDs are totally different from classical light sources: they have a different shape, radiation pattern, driving requirements, etc. Therefore, the illumination engine, which determines the brightness and uniformity of the system, has to be redesigned for LED-based projectors. A compact illumination system based on gradually tapered light pipes (GTLP) will be presented. The GTLP collects, reshapes, and uniformizes the light flux from the LED to illuminate the light-valve uniformly. The design and the simulations have been completed. The result is a uniformly illuminated rectangular beam at the end of the pipe with an efficiency of 81.1%. Afterwards, the light pipe was fabricated, and the experimentally measured efficiency is 76.9%, which demonstrates a successful manufacturing process. Finally, two recycling techniques to enhance the brightness have been applied and these enhancements were experimentally observed.