Lighting theory and luminous characteristics of white light-emitting diodes

A near-ultraviolet (UV)-based white light-emitting diode (LED) lighting system linked with a semiconductor $InGaN$ LED and compound phosphors for general lighting applications is proposed. We have developed for the first time a novel type of high-color rendering index $(Ra)$ white LED light source, which is composed of near-UV LED and multiphosphor materials showing orange (O), yellow (Y), green (G), and blue (B) emissions. The white LED shows the superior characteristics of luminous efficacy and high $Ra$ to be about $40lm∕W$ and 93, respectively. Luminous and chromaticity characteristics, and their spectral distribution of the present white LED can be evaluated using the multipoint LED light source theory. It is revealed that the OYGB white LED can provide better irradiance properties than that of conventional white LEDs. Near-UV white LED technologies, in conjunction with phosphor blends, can offer superior color uniformity, high $Ra$, and excellent light quality. Consequently we are carrying out a “white LEDs for medical applications” program in the second phase of this national project from 2004 to 2009.