In a paper in the Japanese Journal of Applied Physics (*), first author Yukio Narukawa and colleagues have reported ultra-high performance white LEDs built from blue chips coated with YAG phosphors. The chips use patterned sapphire substrates and an indium–tin oxide (ITO) contact as the p-type electrode.
Ultra-high efficacy in small LEDs
Nichia has developed small-size (240 ×420 micron) blue LED chips with quantum efficiency of 63.3% at a forward-bias current of 20 mA.
White LEDs produced with these chips had a luminous flux of 8.6 lm and a luminous efficacy of 138 lm/W. This exceeds the value of 131 lm/W reported by Cree recently for a standard-sized LED, and is 1.5 times greater than that of a tri-phosphor fluorescent lamp (90 lm/W).
The forward-bias voltage was 3.11 V and the wall-plug efficiency (WPE) was 41.7%, respectively. The white LED had a correlated color temperature of 5450 K.
High power LEDs
Nichia has also fabricated high-power white LEDs using large-size (1 ×1 mm) blue LED chips with an output power of 458 mW at 350 mA.
White LEDs demonstrated a luminous flux of 106 lm at 350 mA, and a luminous efficacy of 91.7 lm/W. The forward voltage was 3.29 V and the WPE value of 27.7% is greater than that of a fluorescent lamp (25%) in the visible region. The correlated color temperature of the high-power white LED was 5450 K.
Moreover, the luminous flux of the high power white LED reaches to 402 lm at 2 A, which is equivalent to the total flux of a 30 W incandescent lamp.
*Japanese Journal of Applied Physics Vol. 45, No. 41, 2006, pp. L1084-L1086 – see JJAP website.
"Ultra-High Efficiency White Light Emitting Diodes" by Yukio Narukawa, Junya Narita, Takahiko Sakamoto, Kouichiro Deguchi, Takao Yamada and Takashi Mukai of Nitride Semiconductor Research Laboratory, Nichia Corporation and LED Front-End Engineering Department, Nichia Corporation. Received September 14, 2006, published online October 13, 2006.