This 2009 "Scientific American" article reports on growing use of more energy-efficient light-emitting diodes, or LEDs and organic, or OLEDs, as an alternative to incandescent bulbs for lighting, which accounts for about 22 percent of electricity use in the U.S. Source: Scientific American, March 18, 2009.
LED There Be Light
More energy-efficient light-emitting diodes are rapidly becoming the preferred lighting solution worldwide
By David Biello March 18, 2009
Torraca is a small village of 1,200 people in Italy. It is also the first place in the world to be totally illuminated by light-emitting diodes (LEDs). Representing a sea change, much like when electric lamps first graced London's Holborn Viaduct back in 1878, some 700 streetlights (each containing 54 LEDS) now line Torraca's arteries—and locales around the world, from Beijing's Bird's Nest Olympic Stadium to the Raleigh Convention Center's Shimmer Wall in North Carolina, have begun to use LEDs to light up the night.
"There are more than 30 installations like Torraca around the world," says Mark McClear, director of business development at Durham, N.C.-based LED-maker Cree, Inc., which made the LEDs in Torraca's streetlamps. "It's growing weekly."
The lightbulb of the future may just be a small piece of semiconductor. Rather than heating tungsten to at least 3,100 degrees Fahrenheit (1,700 degrees Celsius) or exciting fluorescent gases, LEDs can produce lumens with less electricity. Diodes are composed of two conductive materials, such as silicon or germanium; the light-emitting variety uses materials such as gallium arsenide, which releases photons when electricity flows through it.
Such LED technology has been in electronics like calculators for decades, but remains too expensive to replace cheap incandescents. An LED version of a 100-watt incandescent lightbulb, for instance, still costs roughly $80 compared with around $3 for a traditional incandescent.
Cost has been the major obstacle for LEDs, which last up to as 50,000 hours (10 years if used 12 hours a day)—gradually dimming over time—compared with about 800 hours for a typical 100-watt incandescent. "The average bulb is on two hours a day. At that rate, an LED would last 136 years," McClear says. "If you bought a fixture and only used it two hours a day, it would last longer than your house. It would last longer than you."
Potential energy savings, however, appear to hold more sway with cities and building owners than cost. After all, some 22 percent of all electricity use in the U.S. is devoted to lighting, according to the U.S. Department of Energy—and switching to LEDs could save $280 billion by 2028. In fact, researchers at the Rensselaer Polytechnic Institute in Troy, N.Y., estimate that replacing incandescents with LEDs could save $1.83 trillion in energy costs globally over the next decade and eliminate the need for 280 1,000-megawatt power plants.
"Forcing electricity though a filament and heating it up to the point where it emits light, [is] horribly inefficient, on the order of 95 percent inefficient," McClear says. "The best LEDs are on the order of 35 percent more efficient."
Among those dazzled by LEDs: North Carolina State University in Raleigh, which last year installed 730 Cree LED lights in a dormitory building and saved 44 percent of the energy consumed by the fluorescent predecessors per day, according to the university. Discount chain Wal-Mart has replaced fluorescent light fixtures in its freezer sections with LEDs. And the City of Los Angeles plans to replace some 140,000 street lamps with LED fixtures by 2014 at a cost of $57 million, tapping some of its funding from the Clinton Climate Initiative and the Los Angeles Department of Water & Power.
New LED lights can put out the equivalent light of 100-watt incandescent while only consuming 13 watts of power. They also outlast equivalent compact fluorescent lightbulbs but use 50 percent less energy and skip the toxic mercury required as ballast. The U.S. Environmental Protection Agency (EPA) estimates that 670 million such fluorescent lights end up in the trash yearly and release some two to four tons of mercury per annum into the environment.
Advances in the underlying technology have allowed Cree, for one, to boost output from a single one-square-millimeter diode to 161 lumens per watt. Partially as a result, the Federal Reserve is using LEDs for its overhead recessed lights and the Pentagon has installed some 4,200 LED fixtures to reduce energy costs and improve light quality, according to the U.S. Department of Defense.
Potential downsides: individual LEDs must be kept cool, and it may end up that the tiny fans in the multiple LED fixtures used to cool the lights will wear out long before the diodes. But manufacturers, including Brite Components, Cree, General Electric, Lighting Science Group, Osram and Philips say they are working to offset that problem.
Nevertheless, LEDs will not replace all lightbulbs, because they produce light in only one direction, like a laser, rather than illuminating an area. To fill that lighting need, some companies are creating organic LEDs, or OLEDs, that emit light in all directions and are already used in advanced televisions and other screens.
Such OLEDs—diodes made from organic material such as polyacetylene rather than semiconducting metals—may prove an even more intriguing future solution, because they can be crafted into ceiling panels or even windows (they are often translucent) and are potentially even more efficient at producing light (though not yet). BASF and Osram, for example, have achieved a white OLED capable of 60 lumens per watt. Others have achieved 100 lumens per watt in the laboratory, according to Barry Young, managing director of the OLED Association.
Unfortunately, such an OLED light panel at this point would cost at least $75 per square foot ($800 per square meter) and is not commercially available yet, Young says. But he believes the price tag can be significantly reduced by using plastic polymers and other cheap substances in lieu of glass. OLED lights are likely to become available as soon as 2011, according to a report from display consultants at the firm DisplaySearch in Austin, Tex. "It's likely to last longer [than LED fixtures] because it doesn't have anything to fail and it also doesn't have a lot of heat," Young says. "It won't generate the kind of heat that you would in an LED from the standpoint of air-conditioning."
But even Young believes that LEDs and OLEDs will likely coexist, serving different functions: LEDs will likely replace incandescents whereas OLEDs might light the offices of the future in the form of glowing ceiling panels or windows that light up as the sun sets. "It's happening faster than anybody thought it would or could," Cree's McClear says. "It doesn't make a lot of sense to do anything that's not green."
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