By James Van Howe
Data points from Osram Opto Semiconductor of Germany. Lower black square at 142 lm/W demonstrating record white-light LED efficiency; second black square at 160 lm/W shows projected efficiency after further optimization
This post originally appeared on Jim’s Cleo Blog and is reproduced with permission from its author.
You may not think that LED lighting would be a controversial topic, but as the New York Times reports, it may be indirectly responsible for new anger among conservative lawmakers in the United States. A U.S. federal law passed in 2007 by the Bush administration will, among other energy-saving measures, make the sale of the incandescent 100-watt light bulbs illegal in 2012. Republican representatives Joe Barton of Texas and Michelle Bachmann of Minnesota, and Republican Senator Rand Paul of Kentucky have recently become vocal about the rights of Americans to purchase lighting of their choice (energy-efficient or not).
The alternatives to the more-than-a-century-old technology spurning this debate are a new make-over of halogens (not much more efficient than incandescent bulbs at about 20 lumens/W), compact fluorescent bulbs (about70 lumens/W), and LED lighting (Osram Opto Semiconductors of Germany just recently claimed to have set a record for warm-white LED chips at 142 lumens/W). CLEO attendees beware: might tea-party members be planning protests of sessions within CLEO Science and Innovation 15: LEDs, Photovoltaics and Energy-efficient (“green”) Photonics?
The “controversial” talks related to LED lighting can be found specifically in sessions “Nano-structured LEDs” on Monday, May 2, 1:30-3:15 pm and “Toward More Efficient Visible LEDs” on Wednesday, May 4, 1:30-3:10 pm. Many of these talks will address specific problems in the overarching goal of fabricating highly-efficient LEDs that can simultaneously mimic the white-light spectrum of an incandescent light bulb. White-light LEDs could reach luminous efficiencies of greater than 300 lumens/W once certain device and fabrication challenges are overcome.1
One of the greater challenges is overcoming the emission gap in the green-yellow region of the visible spectrum (515-600 nm).1,2 Whether multiple LEDs of different color are combined to produce white-light, or one or two different colored LEDs are used to pump phosphors to produce white light, current designs lack efficient production of yellow-green photons for true white-light color (a stinging irony for a technology slated as “green” photonics). Invited talk, CMU5, “Nitride-based Nano-columns and Applications” and contributed paper CMU6, “Diffraction-Coupled Plasmon-Enhanced Light Emission from InGaN/GaN Quantum Wells” in session “Nano-structured LEDs”will show different approaches to generating green light using nano-structures on InGaN. Lowering the dimensionality by using nano-structures allows one to play with defect, strain, and polarization properties of the material and hence light generating capability and extraction.2
Another challenge being addressed in session “Toward More Efficient Visible LEDs” is “efficiency droop” particular to InGaN…for the full post click here.
Posted: 20 March 2011 by
James Van Howe
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