LED (pronounced el-ee-dee) lights are technologically vastly different from traditional incandescent, fluorescent, and neon light sources. They cost several times more, but can use as little as 20 percent of the electricity.

Manufacturers such as GE and Philips make LED lamps that directly replace conventional ones, with a fraction of the energy use and heat output. (GE photo)

Luminaires that use LEDs also emit considerably less heat than conventional lamps -- they're even cooler than compact fluorescent -- and that reduces cooling loads when installed on a large scale.

LED luminaires require much less maintenance than do conventional lighting systems. The light element in an LED luminaire retains its brightness many times longer, so it doesn't need to be changed as often.

For general area lighting, LEDs can deliver a 30 percent energy savings compared to traditional metal halide high-intensity discharge (HID) lighting. An LED replacement has an estimated 10-year service life -- about four times the recommended service interval of a standard HID system.

The greatest penetration of LEDs in buildings, however, has been in exit signs. LEDs are also popular for traffic signals, parking lot lights, and other applications where the light stays on at least half of the time.

Some cities are trying out LED streetlights like this one from LEDway. (City of San Jose photo)

Most LEDs give off a cool, white light. Lamps tend to be directional, so they're great for certain applications, such as highlighting plants, or for small areas that need accent illumination.