2013-04-27

Monday Roundup: Droopy LEDs

This week: Bridgelux & Toshiba a'sittin' in a tree, the Klauf Light Bar on Kickstarter, and a bid to reduce light pollution using LEDs.

Mystery of LED "droop" solved
Why does LED efficiency drop at high drive currents? Researchers at UC Santa Barbara and CNRS-École Polytechnique in France have definitively identified the cause: it's Auger non-radiative recombination. In this process, electrons in the diode lose energy to collisions with other electrons. The researchers mounted a complex experiment, involving an LED with a specially prepared surface, and unambiguously measured the energetic signature of electrons that had undergone the Auger process.

These results were published in the prestigious journal Physical Review Letters last week. In a few days we'll take a deeper look at this research and the promise it holds out for brighter and more efficient LEDs.

Bridgelux & Toshiba, sittin' in a tree
We have mentioned in conversations in this community the year-old partnership between Bridgelux and Toshiba, for further developing and scaling up the former's GaN-on-Si process. This partnership deepened and morphed in the week of Lightfair.

The Wall Street Journal's Don Clark explains the deal's structure: Toshiba is buying Bridgelux's GaN-on-Si intellectual property and taking on board Bridgelux's staff of 40 researchers, easing the cash burn for the Livermore, California startup. (Those folks will continue to work in place at Livermore.) The two companies will cooperate to build out a factory in Japan, where Toshiba will manufacture GaN-on-Si LEDs. Bridgelux will buy these for its products. The WSJ's Clark nods to the obvious analogy with the solar industry in the US, which trod a path similar to the one on which Bridgelux is embarking.

Reducing light pollution with LEDs
Here's another thing you can do with LEDs that you can't do with traditional light sources: put light exactly where you want it, in a shape like (say) a rectangle. This would be both more energy-efficient, and far less polluting of the darkness of the night sky, which is under threat everywhere.

In a study lead by the National Central University of Taiwan, researchers envisioned a streetlight that loses only 2 percent of its light horizontally. This compares to 10 percent for the best LED streetlights currently available, and 20 percent for mercury vapor or high-pressure sodium lights. The researchers haven't actually built a prototype so far. They hope to do so in 3 to 6 months and to mount a demonstration project early next year. Their paper is available at the open access journal Optics Express.

The Klauf Light Bar on Kickstarter
This remote-phosphor lighting strip produces even, 2700K light, 435 lumens per linear foot. It's dimmable down to zero using "virtually any inexpensive dimmer of your choice." It runs on 120-volt AC. Segments 6 and 12 inches long can be plugged together up to 15 feet. Efficacy is 50 lm/W.

The CRI is 80. The designer, Joseph Lee, replied to a query I left via Kickstarter with this elaboration: "We're considering doing a 90 CRI, as that phosphor is available, we just didn't have as much room in the first batch's profitability to make it worthwhile. Typical consumers cannot tell the difference between 80 and 90 CRI." This is probablly true.

I confidently predict that this 4-day-old Kickstarter is going to get funded; in fact it's going to blow out its goal of $36,000. In the time I watched it on Friday, support went from 23 percent of the goal to over 34 percent. More than 230 backers have put up anywhere from $35 to $140 for early and discounted access to the Klauf Light Bar.

While the Kickstarter is running, you can get a 6" Light Bar for $45 and a 12" one for $55. Assuming it gets funded and goes into wide production, the retail price will be some 40 percent higher than that. Shipping is free to addresses in the US only.

Full disclosure: I'm backing this project. Come August, a 12" and a 6" Klauf Light Bar, with connectors, should arrive at my door, soon to see service in my kitchen.

— Keith Dawson , Editor-in-Chief, All LED Lighting