Oct 13 2007
Researchers at Cree have posted another breakthrough in high-brightness LED performance - marking the best efficacy yet seen from white chips operating at 350 mA.
The GaN semiconductor structures have been tested by the US National Institute of Standards and Technology (NIST), showing an efficacy of 129 lm/W for a cool-white emitter (5813 K).
Meanwhile, the warm-white version (2950 K) delivered 99 lm/W. NIST tested the LEDs after they had been switched on for five minutes, to ensure that any thermal effects had stabilized.
The total light output for each LED was 135.7 lm for the cool-white device, and 104.2 lm for the warm-white equivalent. Just last week, Cree announced that its laboratory team had made a single-chip LED capable of emitting over 1000 lm.
While the latest milestone must be treated as a laboratory phenomenon for the time being, Cree has a track record of turning its research results into production-worthy technology suitable for volume manufacture within two years.
As Cree's John Edmond notes, the key aspect of this latest result is that it has been achieved with very bright chips that operate at 350 mA - just the kind of chips that will ultimately be required for general lighting applications.
While higher LED efficacies have certainly been seen previously, these have tended to be with smaller, low-current devices operating at 20 mA. Nichia is currently ramping up its production of such LEDs, for example.
The key challenges for Cree's technologists now will be to come up with a way to deal with the heat generated by the large, high-current chips, and to fabricate them with a high-yielding process at its semiconductor wafer fab.
If they can do that, these devices could be a key element of the trend to low-cost, high-efficiency solid-state lighting in the future.