Shedding some light

At their introduction, white LEDs were at once revolutionary and the obvious next-logical evolutionary step for visible-light devices that began a half century ago. Nick Holonyak, Jr invented the first practical visible-spectrum LED in 1962 with a GaAsP process at General Electric (http://bit.ly/J9i14g). As you may note with some sense of irony as you read this month's special report on lighting products and systems, Holonyak is also the inventor of the household dimmer switch. Since Holonyak's first red LED, decades of process and device engineering dramatically improved LED's yield, operating lifetime, robustness, brightness, and cost and gave rise to devices of shorter wavelength. Shuji Nakamura demonstrated the first high-brightness blue LED in 1993. The addition of a yellow down-converting phosphor lens coating, resulted in the first white LED almost immediately. The market ramifications of white LEDs were clear, yet it took many more years of engineering to develop practical devices for general illumination, particularly with regard to color quality, efficacy, and cost. This is not, however, to peer into rear-view mirror: Of greater interest is the current state of SSL (solid-state lighting) technology and its applications. Toward this end, in addition to this month's special report, I recommend to your attention three resources from the US DOE (Department of Energy). The CALiPER summary reports detail tests of commercially-available LED-lighting products, including comparisons to conventional lighting devices (http://1.usa.gov/IF6pt7). Between the initial December 2006 pilot round and the October 2011 Round 13 Report, the CALiPER summaries covered a variety of lighting products. Starting in March 2012, DOE renamed the series Application summary reports, which focus on a single product type or application. A forward-looking report, Energy savings potential of solid-state lighting in general-illumination applications 2010 to 2030, provides insight into current trends and expectations for lighting demand and technology improvements in both conventional and solid-state lighting. With much current industry focus going to efficacy, one exhibit caught my eye—the LED efficacy prediction for commercialized SSL devices—that predicts a near-constant rate of improvement over the next decade or so (Figure 1). The segment of the curve SSLs are already on indicates roughly an octave improvement in six or seven years. SSL lighting is already benefitting from reductions in device cost as commercial products continue to make inroads in interior commercial and residential applications. Apropos of this trend, DOE started a new report series, Retail replacement-lamp testing, which include test results and analysis for SSL replacement lamps available at retail (http://bit.ly/IzbcIL). A great deal of engineering effort continues to pour into SSL technology to address ongoing cost, color quality, efficacy, and control challenges. Enjoy this month's special report on lighting products and systems, which sheds more light on this important topic. www.powersystemsdesign.com