|The Optoelectronics Packaging & Materials Labs at the University of California, Irvine, has developed neutral-white and warm-white multichip emitters that are claimed to have record performance in terms of lumen efficiency. Both were made from blue LED chips available on the open market.
The performance of the two emitters was confirmed in reports issued in December 2008 by the National Institute of Standards and Technology (NIST).
Both measurements were conducted after a thermal equilibrium was reached between the emitter and its heat sink with a steady-state temperature of 37 deg.C.
Frank Shi, professor of Optoelectronics Packaging & Materials Labs at UCal, said that a combination of innovations in package design, packaging process development, white LED phosphors, and packaging materials processing optimization was used to achieve this result.
Also, the results were achieved without using special prototype blue LED chips.
Warm-white 18W emitter
A multi-chip integrated warm-white LED compact single emitter with an input power of 18.62W, producing a total of 1444 lm at a CRI of 91.3 and a CCT of 3928K, reached a lumen efficiency of 77.4 lm/W, according to the NIST report.
The measurement was conducted after a thermal equilibrium was reached between the emitter and its heat sink with a steady-state temperature of 37 deg.C. Thus, the lumen efficiency is estimated as high as 82 lm/W if the LED junction temperature is kept at 25 deg.C, which is the normal industrial standard LED junction temperature in reporting the lumen measurement.
The optical power for each bare die of the blue LED chips was at ~260 mW (@350 mA). However, the optical output of a bare blue chip is now as high as 571 mW (@350 mA), according to a major LED chip producer. Thus, if the present packaging technology and white LED technologies are applied to those 571 mW blue chips, the lumen output could be as high as 170 lm/W.
Neutral-white 72W emitter
A multi-chip integrated compact white LED single emitter with an import power of 72.84 W, producing a total of 6543 lm at a CCT of 4455K, has also reached a record lumen efficiency of 89.8 lm/W, according to NIST’s report.
The measurement was again performed after a thermal equilibrium was reached at 37 deg.C. Thus, the efficiency was estimated to be high as 95 lm/W if the LED junction temperature is kept at 25 deg.C.
The optical power for each bare die is about 260 mW. However, if 571 mW blue chips are used for the present emitter, the lumen output could be as high as 197 lm/W.