|Cree has reported R&D results of 129 lumens per watt for a cool-white LED and 99 lumens per watt for a warm-white LED. The drive current was 350 mA, and the output was measured after five minutes of operation to ensure thermal stabilization.
The results were verified by the National Institute of Standards and Technology (NIST). NIST’s tests confirmed that the cool-white (5,813 K) LED produced 135.7 lumens of light output and achieved 129 lumens per watt efficacy.
This means that the input power was 1.05 W and the forward voltage was very low at 3.0 V.
The warm-white (2,950 K) LED produced 104.2 lumens of light output and achieved 99 lumens per watt efficacy.
The chips used in these demonstrations are significantly different from Cree's current production chips. The R&D chips are larger and in fact are the same chips used to demonstrate an output in excess of 1000 lumens from a cool-white LED driven at 4 A (see Cree R&D achieves 1,000 lm from single-chip LED).
Cree describes the results as "the best reported for packaged, high-power LEDs", and certainly these numbers have not been surpassed in public announcements. In January 2007, Lumileds reported a figure of 115 lm/W for a device driven at 350 mA (see Philips Lumileds reports 115 lm/W power LED at 350 mA). Again, this was an R&D result.
The important point about these numbers, as far as the industry is concerned, is not which company has the lead but that ongoing improvements will lead to even higher performance devices in production in the future.
Commenting on the latest results, John Edmond, Cree co-founder and director of advanced optoelectronics, said “To replace traditional light sources, LEDs need to provide both high light output and high efficacy. Cree continues to push the limits of LED performance in order to realize the potential of the LED lighting revolution – energy-efficient, long-lasting LED light.”