Recent progress of high efficiency white LEDs

Abstract

AbstractWe fabricated three types of white light emitting diodes (LEDs). The first is the white LED, which has a high general color rendering index (Ra) of 97 and CRI‐No. 9 of 96. The CRI‐No. 9 denotes the color reproduction in the red region. These values are higher than those of a tri‐phosphor fluorescent lamp (Ra = 85 and CRI‐No. 9 = 8). The second is the high efficiency white LED fabricated from the small‐size high efficiency blue LED chip. The output power (Po), the external quantum efficiency (ηex) and wall‐plug efficiency (WPE) of the small‐size blue LED were 35.0 mW, 63.3% and 56.3%, respectively, at a forward‐bias current of 20 mA. The luminous flux (Φ), luminous efficiency (ηL) and WPE of the second white LED are 8.6 lm, 138 lm/W and 41.7%, respectively. The luminous efficiency is 1.5 times greater than that of a tri‐phosphor fluorescent lamp (90 lm/W). The third is the high power white LED fabricated from the larger‐size blue LED chip. Po, ηex and W.P.E. are 458 mW, 47.2% and 39.7%, respectively, at 350 mA. Φ, ηL and WPE of the third white LED are 106 lm, 91.7 lm/W and 27.7% at 350 mA, respectively. Moreover, Φ of 247 lm and 402 lm at 1 A and 2 A are obtained, respectively. Φ at 2 A is equivalent to the total flux of a 30 W incandescent lamp. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)