Recent progress of high efficiency white LEDs

We fabricated three types of white light emitting diodes (LEDs). The first is the white LED, which has a high general color rendering index (R-a) 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 (R-a = 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 (P-o), the external quantum efficiency (eta(ex)) 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 (Phi), luminous efficiency (eta(L)) 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, eta(ex) and W.P.E. are 458 mW, 47.2% and 39.7%, respectively, at 350 mA. Phi, eta(L) and WPE of the third white LED are 106 lm, 91.7 lm/W and 27.7% at 350 mA, respectively. Moreover, Phi of 247 lm and 402 lm at 1 A and 2 A are obtained, respectively. Phi at 2 A is equivalent to the total flux of a 30 W incandescent lamp. (C) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.