Sheng-Han TU, Jui-Wen PAN, Chih-Ming WANG¹, Yeeu-Chang LEE², and Jenq-Yang CHANG

Department of Optics and Photonics, National Central University, Jhongli, Taiwan 32001, R.O.C.
¹Institute of Opto-Electronic Engineering, National Dong Hwa University, Hualien, Taiwan 97401, R.O.C.
²Department of Mechanical Engineering, Chung Yuan Christian University, Jhongli, Taiwan 32023, R.O.C.

(Received July 15, 2008; Accepted February 18, 2009)

Light emitting diodes (LEDs) have numerous advantages as light sources in projectors. LEDs are more compact, exhibit a larger color gamut, have a longer lifetime, and need a lower supply voltage. However, there is still one important disadvantage: the optical power per unit of étendue (luminance) of an LED is significantly low. As a result of the étendue limitations of LEDs, the projected flux on the screen will not be high. Despite this shortcoming, LED's are still of great interest for low power applications because of their other superior properties. Thus we collect the available light flux optimally and combine multiple high luminance LEDs within the system. In this study we discuss three collection systems designed to collect the LED flux with high optical efficiency while retaining small device size. The best collection efficiency attained with our collection systems is 96%. The fabrication tolerance and cost of our collection systems are also analyzed.

Key words: pocket size projector, collection system, light emitting diode (LED) light source, light engine, collection system