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A Rising Star: Solid-State Lighting

June 16, 2009 - 5:00am


Just when consumers started getting familiar with the spiral ice-cream cone-shaped and prong-shaped compact fluorescents (CFLs), along comes LED lighting, a solid-state lighting (SSL) solution. Some experts are predicting that solid-state lighting is set to turn the current lighting industry on its head, and perhaps in the not-too-distant future make the century-old incandescent light bulb go the way of the dinosaur.

Many consumers have been saving money and helping the environment for years by using LED lights during the holidays. These light strings use 75% less energy than conventional (i.e., incandescent) light strings. ENERGY STAR decorative light strings are independently tested to meet strict lifetime and electrical requirements and come with a three-year warranty. The ENERGY STAR decorative light strings site provides both a list of qualified brands and a list of manufacturers of these energy-stingy lights.

LEDs flashlights are also popular because LEDs provide a bright light and draw little power, keeping batteries charged longer. LED nightlights, including those with light and motion sensors, are popping up on shelves of many retailers.

The ultimate target of LED manufacturers is the general illumination market. Before consumers start replacing incandescent light bulbs (and even fluorescent tubes and CFLs) with LEDs in large numbers, they will need to understand how LED lighting differs from these other lighting technologies.

Even more so than compact fluorescent lighting, many more color variations exist for "white" LED lighting, so product selection requires more thought than when buying incandescent bulbs. As I mentioned in an earlier blog on compact fluorescents, the color temperature and Color Rendition Index (CRI) differ a lot more than for incandescents. The range is even larger in available LED products than among compact fluorescents. To make matters more confusing, LEDs, by the very nature of the light they produce, cannot easily be compared using standard CRI measurements. Different metrics are under development. Many people—including my wife—prefer warm white bulbs (which confusingly have lower color temperatures: 2700–3000 K), while I think cool white bulbs (with higher color temperatures of at least 3600 K) are "cool."

LEDs are uni-directional, i.e., they shine in a single direction, unlike your standard incandescents and fluorescents, which shine all around in 360°. This makes them ideal candidates for certain types of lighting, such as accent lighting, spot lighting, and downlighting. Conversely, it's more challenging for manufacturers to develop LED light sources intended to illuminate all around. But there's another side to this coin. Incandescents and fluorescents lose a lot of their light within the fixture before the light even reaches you. Fixtures specifically designed to use LED light sources—i.e., they are designed to maximize energy efficiency and minimize light loss—could be ultra-efficient compared to conventional fixtures equipped with conventional light sources.

To learn more about LED lighting, visit DOE's solid-state lighting Web site.

Informed consumers will need access to reliable, unbiased LED product performance information. In that vein, the DOE Commercially Available LED Product Evaluation and Reporting (CALiPER) program supports unbiased testing of a wide array of LED products available for general illumination. DOE buys LED products on the open market through normal channels (retail, distribution, or online sales) and sends them to laboratories for testing. DOE does not accept submissions or requests to be included in the testing program from manufacturers, distributors, or retailers. Thus, CALiPER tests what you and I might buy in stores or online. CALiPER testing began in Oct 2006. Its latest round of testing, Round 7, was completed in January 2009.

"It was the best of times, it was the worst of times…it was the Season of Light, it was the Season of Darkness…"—Charles Dickens

Over 120 products have been tested through the CALiPER program to date. The CALiPER results are very illuminating, if you'll excuse the pun. The testing has shown that there are some very good LED products on the market, and many that are not. Many test results reveal low light output, poor or inconsistent color quality, and exaggerated performance and lifetime claims. The good news is that improvements are occurring at a staggering pace and problem areas are improving. The bad news is that many inaccurate or misleading claims regarding LED product performance were still found in all product categories in Round 7, most frequently for replacement lamps. Overall, roughly half of the LED products tested in Round 7 were found to have inaccurate or misleading literature. More good news, however, is that new measurement protocols and test procedures are currently being developed for LEDs that will make it easier for consumers to compare products.

LED downlights are one lighting application that looks very promising. At equal output levels, tested LED downlights surpass their incandescent and halogen counterparts in efficacy, and some outperform CFL downlights. Yes, they are still expensive, but product costs are dropping as product performance steadily improves.

To date, CALiPER has tested more than a dozen low-cost LED replacement bulbs available at retail. These LED lights are designed to replace standard screw-in, typically incandescent, bulbs. None met light output levels comparable to the bulbs they purport to replace, most had very poor color quality and many failed within the test period (<200 hours of operation). Overall, CALiPER testing of LED replacement bulbs has yielded decidedly mixed results, with a wide range in product quality that encompasses both the good and the bad. The average consumer or retailer currently has no way to distinguish between them.

So what's a consumer to do? When shopping for LED lighting products, I highly recommend selecting only those products with the ENERGY STAR label.

The ENERGY STAR program began covering LED lighting products for general illumination on September 30, 2008. The program currently includes only a limited number of lighting applications. The rapid pace of solid-state lighting technology advances led DOE to select a unique two-phase approach. The first phase allows for early participation of a limited range of market-ready products while the second phase sets out more rigorous performance targets for future products. The criteria are continually updated to keep pace with solid-state lighting technology advances.

The coverage of general illumination LED lighting is fairly new, so few products have received the ENERGY STAR label. There are no LED screw-in bulbs, designed to replace regular screw-base incandescent bulbs. LED bulbs will be included as soon as the products can meet the stringent requirements of the program. What if you don't see the LED lighting products you want with an ENERGY STAR label?

  • Check out the products that CALiPER has already tested. You can sign up for free online access to the CALiPER report results after agreeing to abide by DOE's No Commercial Use policy. You'll not only see the laboratory testing results, but you'll see how much they differ from the claims made by the manufacturer.
  • Check out also the winners of the Next Generation Luminaires contests that the U.S. Department of Energy (DOE) supports. Stringent competition requirements and rigorous evaluation by a panel of impartial judges ensure that the winning products have been thoroughly assessed and tested, removing some of the risk involved in selecting new LED products.
  • DOE GATEWAY demonstrations showcase high-performance LED products for general illumination in a variety of commercial and residential applications. View the GATEWAY demonstration results. Available reports include detailed analysis of data collected, projected energy savings, payback analysis, and user feedback.
  • The Lighting for Tomorrow competition selects exemplary residential lighting products. Check out the 2008 winners.