LEDs might light up our lives

A better bulb? They are energy-efficient but quality is issue


February 25, 2005|By Frank D. Roylance | Frank D. Roylance,SUN STAFF

It was a bright idea, but the incandescent light bulb that illuminates most of our homes hasn't changed much since Thomas A. Edison invented the first practical model in 1879.

It's still fragile and grossly inefficient, wasting 90 percent of the energy we put into it producing heat instead of light.

"It's not really an elegant solution," said E. Fred Schubert, an engineering professor at Rensselaer Polytechnic Institute in Troy, N.Y. "It has been around for 100 years, yes. But now it's time for the better light bulb."

Researchers around the world think they've found one. Engineers in industry, academia and government labs are in a race to replace the familiar light bulb with solid-state light-emitting diodes, or LEDs.

Already used to illuminate telephone keypads, watches and Christmas lights, LEDs employ semiconductors to produce light with almost no heat. They last for years and operate on a fraction of the electricity incandescent bulbs need to produce the same amount of light.

Researchers are looking for ways to extract more light from LED chips - to make them larger, cooler, cheaper and more efficient - while improving the color of the light they emit.

If they can match the quality of conventional lights - and scientists are confident they can - LEDs might catch on in homes and offices, halving the amount of electricity we generate for lighting.

That's huge. Americans use more than 8 "quads," meaning 8 quadrillion British thermal units of energy, on lighting every year.

By 2025, according to the Department of Energy, solid-state lighting could knock as much as $15 billion from electric bills in the commercial sector, and $5 billion more from residential bills.

"If we had, say, 100 major power plants in the United States, we could switch 12 1/2 of them off," Schubert said. "It's an enormous amount, and it is the single biggest potential for ... electrical energy savings."

As a bonus, by 2025 the reductions would keep 28 million tons of carbon from power plant emissions out of the atmosphere each year. Mercury pollution from coal combustion also would be reduced.

"There's a lot of interest all over the world in this technology," said Jeff Tsao, a lighting researcher at the Sandia National Laboratory in Albuquerque, N.M.

The Department of Energy has provided more than $50 million for 45 LED research projects since 2002. Sandia recently sponsored a three-year "grand challenge" that brought together 30 of the nation's top scientists to tackle key challenges facing LED development.

"They made a lot of progress," Tsao said. But there is plenty of competition from Japan, Taiwan, South Korea and some institutions in Europe. "I would say the U.S. and Asia are sort of neck and neck," he said.

Traditional incandescent lights work by sending an electric current through a glowing filament, usually made of tungsten. They're cheap and produce a pleasing, warm, yellowish light. Engineers rate them close to the top of the 100-point "color-rendering index" (CRI) that measures a light's ability to render the true colors of objects and people.

But incandescent filaments don't glow until they're heated to more than 3,600 degrees Fahrenheit, which makes them wasteful and limits their life to a few thousand hours.

The second most popular fixture - the fluorescent bulb - is cooler, longer-lasting and far more efficient. It produces 83 lumens of light per watt of electricity, more than six times as much as an incandescent light.

Fluorescents work by passing electric current through a gas-filled tube, which causes mercury inside to emit invisible ultraviolet light. The UV light strikes a phosphorescent coating on the glass, making it glow.

They're cheap to buy and use, but not everyone likes the color of fluorescent light. "If you've ever tried to switch a really critical light in the house to a fluorescent or a compact fluorescent, your wife will say you can't do that," Tsao observed. "The color quality is not as rich and warm and true to what they're supposed to look like."

As a result, outside of the kitchen, homeowners have never warmed to fluorescents, even the efficient and durable "compact" variety designed for conventional house lamps.

Having witnessed that consumer resistance, LED researchers "don't want to go down that road again," Tsao said.

Hence the industry's challenge: produce affordable white LEDs that match the color-rendering quality of incandescent bulbs - and make them more efficient than fluorescents.

It's won't be easy.

Although costs are falling, the LEDs remain expensive to produce: $190 per 1,000 lumens of light (roughly equivalent to a 75-watt incandescent). That compares to 60 cents per thousand for incandescents and 73 cents for fluorescents, according to 2003 data from the Department of Energy. The price gap has limited LEDs to low-power and specialized applications.

On the plus side, the LED yields 30 to 50 lumens per watt - far better than incandescents, but not yet equal to fluorescents.

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