This week: a teardown of Cree's BR30 flood light, a different explanation for LED droop, and revised L Prize requirements for LED PAR lamps.
Again with the droop
Just when you thought the mystery of LED droop had been solved once and for all, another research group comes forward with a different explanation published in yet another prestigious physics journal. Why does the rate of increase in light output fall off when current is increased in LEDs? We covered the news last April when researchers from UC Santa Barbara and the École Polytechnique in France published definitive proof that LED droop occurs in the presence of Auger non-radiative recombination of electrons.
Now, a group of researchers from Rensselaer Polytechnic Institute and Samsung have demonstrated that an electric field develops within the p-type region of the diode, sweeping electrons out of the active region. They published this explanation in Applied Physics Letters. As usual, the actual paper is paywalled, so I can't see whether it references the Auger recombination work published in Physical Review Letters last spring.
DOE revises PAR38 L Prize requirements
The US Department of Energy has relaxed some of the requirements for a PAR38 LED lamp in the L Prize competition (formally called the Bright Tomorrow Lighting Prize). Beam width, previously limited to a range from nine to 12 degrees, now can be 12 to 15 degrees. The requirement for a commitment to manufacture 250,000 of the prize-winning bulbs has been dropped. And perhaps most significantly, the requirement for US manufacture of the LED chips has been dropped. (Details here.)
The L Prize for a 60W-equivalent A19 bulb was won in 2011 by Philips Lighting North America. That competition drew three entrants; but the PAR38 competition has yet to attract any. As the figure indicates, the efficacy requirement is far out ahead of where the market is at present.
LED supply glut to persist through 2016
An LED lighting analyst for IHS has projected the next several years' development of the excess supply of LEDs that began in 2010. Alice Tao expects the oversupply to last through 2016. The factors leading to this conclusion are robust shipments of metal organic chemical vapor-deposition (MOCVD) equipment -- up 17 percent in the second quarter of this year -- and rising rates of factory utilization, especially in Asia.
Tao reports that in Korea, factories were running at 75 percent utilization in the quarter, up from 60 percent in 2012, and that rates for some companies in Taiwan and China have reached 90 percent. Tao expects the supply of LEDs to exceed demand by 69 percent in 2013 and 2014. The glut will decline to 61 percent in 2015 and to 40 percent in 2016.
Cree BR30 teardown
Margery Conner at Designing with LEDs has described her deconstruction of the Cree 65W-equivalent BR30 flood light we discussed a couple of weeks back. Inside, she found ten
Cree XLamp XB-E high-voltage white LEDs, a non-isolated power driver, and an STMicro L6562A power management IC. A nice tear-down article, a process which Conner apparently relishes.
— Keith Dawson , Editor-in-Chief, All LED Lighting