[Technology Report]
LEDs Lighten The Energy Load
Move over, fluorescent bulb. See ya later, halogen lamp. Solid-state lighting's longer life and greater efficiency are making it the lighting option of choice.
Forgive the pun, but the future looks bright for solid-state lighting. Light-emitting diodes (LEDs) lead the way, while organic LEDs (OLEDs) promise even greater lighting efficiency and more energy savings in the years ahead. In fact, we'll soon see more LEDs in indoor and outdoor lighting applications than traditional light bulbs, incandescents, fluorescents, and halogen lamps.
LEDs offer longer life and greater efficency than those other technologies, which is why they're seeing rapid adoption in buildings, parking lots, plants, streets, stadiums, airports, and other large facilities. The U.S. Department of Energy (DoE) is putting some muscle (read: funding) into this growth with its Solid State Lighting (SSL) plan, which spans the years 2000 to 2020. The program consists of core technology research, product development, and commercialization support activities.
Increases in solid-state lighting luminous efficiencies are quite dramatic when compared to other conventional light sources, which have reached roughly even plateaus with no significant additional growth expected (Fig. 1). Huge electrical energy savings are expected from solid-state lighting, too. According to the DoE, 22% of the electricity produced in the U.S. goes to power light sources.
Progress on the white-light LED front is moving faster than originally anticipated. According to the DoE, researchers have already improved the efficacy of white LEDs available on the market to about 50 to 60 lm/W. That's almost four times more efficient than incandescent sources, furthering energy savings nationwide.
Based on the U.S. government's Energy Star ratings, the use of efficient solid-state lighting all over the U.S. (where it has been shown to be profitable) would cut the nation's demand for electricity by more than 10%. This translates into a $17 billion savings in energy costs and pollution reduction of 202 million metric tons of carbon dioxide—the equivalent of taking 15 million cars off the road.
Though light source costs are still high, we're seeing significant drops from approximately $250/klm in 2004 to around $50/klm in 2006 (based on manufacturer estimates for volume purchases). By comparison, conventional light sources (incandescent, fluorescent, etc.) cost around $1/klm.
Developmental versions of white LEDs from Japan's Nichia have produced 150 lm/W of output light. Now, commercial versions are ready for market introduction. Market data by Lumileds Lighting (a joint venture by Philips Lighting and Agilent Technologies) supports the favorable efficacy rating of white-light LEDs compared to other conventional light sources (Fig. 2).
According to DoE projections, the market penetration and energy savings potential of solid-state lighting will be driven primarily by economics that incorporate the initial light source price, operating cost, maintenance, and lifetime (see "Major Challenges Lie Ahead For LED Acceptance").
The DoE expects more of the 348 terawatt-hours (TWh) of energy saved by 2027 to be derived from LED lamps and fixtures. They will displace incandescent lamps with very high color-rendering indexes (CRIs), particularly in commercial and residential sectors (Fig. 3). For outdoor and industrial areas, savings in energy will be seen from LEDs with low and medium CRIs, respectively, for the same year.
Civic Service Municipal governments have taken notice of the LED's potential for huge energy savings in general illumination. For example, Raleigh, N.C., will become the first "LED City" in the U.S., using LEDs supplied by Cree Inc. Raleigh will deploy LED lighting through its living laboratory initiative to serve a number of applications, including garage and parking lot sites, street lights, architectural and accent lighting, portable lighting, and pedestrian and walkway lighting over the next 14 months (Fig. 4).
"LED technology provides a clear benefit to a municipal infrastructure, as well as the citizens it serves," says Charles Meeker, the mayor of Raleigh. "The economic benefits for municipalities to invest in LEDs are clear. They save energy, reduce environmental impact, and improve the quality of light."
Cree's latest LED lamps, the warm-white XLamps, can produce 124 lm of output at a correlated color temperature of 300K when driven at 700 mA.
Raleigh isn't the only city embracing solid-state lighting. Two years ago, LED lights from Ledtronics began illuminating San Pedro's mile-long Vincent Thomas Bridge over Los Angeles Harbor, the third-longest suspension span bridge in California (Fig. 5). The bridge is lit by 160 lamps, with 360 LEDs per lamp. Taking green lighting even further, they're powered by a 4.5-kW solar panel system.
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