This week: light pollution and the rainforest, powering LEDs with triboelectric generation, and higher efficiency with GaN transistor drivers.
GaN transistors in LED drivers
Transistors don't have to be made of silicon or gallium arsenide; gallium nitride works, too. GaN transistors can operate at much higher temperatures and higher voltages than GaAs. They excel in high-frequency switching applications such as RF. GaN transistors are available from Cree, Macom, Nitronix, TriQuint, and other suppliers. Now researchers at the Fraunhofer Institute for Applied Solid State Physics IAF in Germany are claiming that GaN transistors convey significant advantages when used in LED drivers.
A driver thus designed can operate at a frequency 10 times higher than one built on silicon transistors; thus the size of energy-storing coils and capacitors can be reduced. Heat tolerance is no bad thing in an LED driver (though I'm not aware that heat-induced failure of silicon transistors is common in this application).
Fraunhofer claims to have boosted the overall efficiency of the GaN driver to 86%, an improvement of between 1 and 4 percent over a silicon-based driver. Seems like a small victory to me, yet this announcement is being covered widely. Is 1 to 4 percent really that big a deal in lamp and luminaire design?
Looking ahead to recycling LEDs
The EU is ahead of the US in its foresight on the problems of recycling electronic waste: Most EU countries have implemented Waste Electrical and Electronic Equipment (WEEE) legislation. LEDs Magazine is featuring an article by Nigel Harvey, CEO of Recolight, a WEEE-compliant recycling service provider in the UK. The subject is the practicalities involved in recycling LED-based products.
Harvey is of the opinion that LED lighting now has such low penetration in the lighting waste stream, around 0.1 percent, that it is not worth separating it out from waste fluorescents, with which it is now co-collected in many EU countries. As for the rare-earths present in LEDs at picogram levels, "the quantities are so small that there is currently no economic incentive to separate them out -- and also no technology available to recover them." Harvey believes that the stage is set to require collecting waste LED lighting separately once its level has risen to significance, and methods have been devised to recover value from it, some years from now.
Light pollution slows rainforest regeneration
The Journal of Applied Ecology has published research from a group at the German Leibniz Institute, which studied the behavior of fruit bats in the presence of artificial lighting at night. Such bats are instrumental in the recovery of harvested rain forests, because they disperse seeds in flight over deforested land, and few other species do anything similar. The researchers found that the bats entered dark areas twice as frequently as those lit with sodium street lights, and harvested fruit 28 percent more often in the dark. The group proposes that "the impact of light pollution could be reduced by changes in lighting design and by setting up dark refuges connected by dark corridors for light-sensitive species like bats."
Stomp a foot, light 1,000 LED bulbs
This item from last December describes on ongoing research program led by a Georgia Tech professor named Zhong Lin Wang. His group generates electricity from the friction of dissimilar materials, a process called "triboelectrification." They have used this technique to power portable electronic devices and small sensors for such purposes as detecting motion, vibration, water leaks, explosions, or falling rain. Two dissimilar nanostructured polymer sheets are typically involved, though cloth and even paper have been pressed into service for generating small amounts of electricity. Triboelectric generators have been incorporated into clothing, shoes, floor mats, backpacks, and floats moving with ocean waves.
The researchers have improved the amount of electricity they can produce by a factor of 100,000 since the beginnings of triboelectricity in 2011. Now "volume power density reaches more than 400 kilowatts per cubic meter at an efficiency of more than 50 percent," according to the Georgia Tech press release. That would power a lot of LED lights.
— Keith Dawson , Editor-in-Chief, All LED Lighting