White light emitting diodes with super-high luminous efficacy

Abstract

We fabricated three types of high luminous efficacy white light emitting diodes (LEDs). The first was a white LED with a high luminous efficacy (η L ) of 249 lm W −1 and a high luminous flux (ϕ v ) of 14.4 lm at a forward-bias current of 20 mA. This η L was approximately triple that of a tri-phosphor fluorescent lamp (90 lm W −1 ). The blue LED used as the excitation source in this white LED had a high output power (ϕ e ) of 47.1 mW and a high external quantum efficiency (η ex ) of 84.3%. The second was a high-power white LED, fabricated from the above high-power blue LED, and had a high ϕ e of 756 mW at 350 mA. ϕ v and η L of the high-power white LED were 203 lm and 183 lm W −1 at 350 mA, respectively. The third was a high-power white LED fabricated from four high-power blue LED dies. ϕ v and η L of the high-power white LED were 1913 lm and 135 lm W −1 at 1 A, respectively. The white LED had a higher flux than a 20 W-class fluorescent lamp and 1.5 times the luminous efficacy of a tri-phosphor fluorescent lamp (90 lm W −1 ).