Improvement of Luminous Efficiency in White Light Emitting Diodes by Reducing a Forward-bias Voltage

We fabricated three types of high luminous efficiency white light emitting diodes (LEDs). The first is the white LED, which had a high luminous efficiency (η L ) of 161 lm/W with the high luminous flux (φ v ) of 9.89 lm at a forward-bias current of 20 mA. The blue LED had a high output power (φ e ) of 42.2 mW and a high external quantum efficiency (η ex ) of 75.5%. The second is the high luminous efficiency white LED with a low forward-bias voltage ( V f ) of 2.80 V, which was almost equal to the theoretical limit. η L and wall-plug efficiency (WPE) were 169 lm/W and 50.8%, respectively, at 20 mA. They were approximately twice higher than those of a tri-phosphor fluorescent lamp (90 lm/W and 25%). The third is the high power white LED fabricated from the high power blue LED with high φ e of 651 mW at 350 mA. φ v , η L , and WPE of the high power white LED were 145 lm, 134 lm/W, and 39.6% at 350 mA, respectively.