LED Lights shine at saving energy

The same innovation that makes laptop screens thinner turns out to be one of the best energy-saving technologies on Earth - and it's all thanks to new tricks that make it possible to create more illumination using the most humble member of the semiconductor family, the light-emitting diode, or LED.

Semiconductors, you will recall, are materials that can be coaxed into either conducting or not conducting electricity. Computer chips, which turn on and off, or count to zero and one, are the most common type of semiconductor. Solar cells, which emit electrons when struck by the photons in light beams, are another well-known semiconductor.

The LED is a solar cell in reverse, said Steven DenBaars, a professor of materials science at UC Santa Barbara. "When we put in electricity, it comes out as light," he said.

Although the LED has been in commercial use since the late '60s, it has ever been the blinking idiot of the semiconductor world. Costly to make and emitting only tiny amounts of light, the LED was at first useful only in expensive instruments such as calculators, watches and eventually those old VCRs that used to flash 12:00.

But in a world that is warming globally, this all-but-forgotten semiconductor may finally get its day in the sun, according to technology analyst Sweta Dash, who noted the growing importance of LEDs in a recent report for market research firm iSuppli Corp.

Writing about the display screens on electronic devices from wall-size to wrist-size televisions, Dash noted that one of the most important trends is a switch in the type of backlight that helps brighten the screens and increase the color range. Increasingly, Dash wrote, laptop and PDA makers are opting to use LEDs as backlights. Why? LEDs are thinner and use less energy than the fluorescent tubes inside today's flat-panel screens, she said.

As Dash explained, behind the flat-panel display in a typical laptop there sits a thin fluorescent lightbulb that illuminates the back of the screen. Dash's report noted how designers increasingly are using LEDs in this backlight function.

"In notebooks, everyone is trying to get more battery life," said Dash, adding that the solid state LED also takes up less space than today's fluorescent backlight. And that allows for sleeker products like Apple's MacBook Air, which is about three-quarters of an inch thick at the hinge.

Thanks to this happy confluence of low-power consumption and thinness, Dash predicted that "in the next few years we will see this major change where these LED backlights are going to be everywhere."

John Peddie, whose Tiburon consulting firm has tracked graphics and multimedia for three decades, said LED backlighting will not only yield thinner electronic devices but a more vibrant palate of colors on display screens. Current display technology can represent a palate of about 24 million colors. "We need close to a billion colors, our eyes are that sensitive," said Peddie, adding that LED backlighting will enrich visual display.

But snazzier graphics and thinner gizmos are just the beginning of the LED revolution. The same power-saving characteristic that drives computer design is already making LEDs economical as a source of illumination in real world applications like traffic lights, according to DenBaars, the UCSB professor who works at that school's Solid State Lighting and Energy Center.

"Cities are saving hundreds of dollars per intersection per year with LED traffic lights," said DenBaars, who broke down the savings as follows.

The 100-watt incandescent bulb in a streetlight might cost $2 to buy, $40 to install and $73 a year to run, plus the cost of electricity. The bulb will likely last just six months, he said, pushing the cost to about $160 per year - two bulbs, two installations and the electric bill.

A 15-watt LED stoplight could throw off the same illumination at an annual electricity cost of about $11 - more than enough to offset the $50 cost of the solid state lamp, which should last five years, he said.

Because of the favorable economics, cities have led the charge on using LEDs in traffic lights and other round-the-clock situations in which the initial cost of the solid state device is still quite high relative to other light sources such as compact fluorescent bulbs. But it will be a while before consumers can justify the higher costs of LEDs as energy-saving replacements for older household fixtures.

"A room light is on about four to six hours a day," DenBaars said, and that works out to a payback period on the order of three to six years.

So while LEDs may be ready to make computers smaller and sleeker, the technology will have to come down in price before it can find wider household application. But DenBaars said LEDs will eventually have a big role to play in reducing electricity consumption. And in the short term it may even find applications where its benefits outweigh its installation costs, such as in outdoor lighting for decks and patios.

"LED lights don't attract bugs," DenBaars said. "They don't emit ultraviolet light like incandescent and fluorescent lights. And it's the ultraviolet light that attracts the bugs."