LED versus Light Bulb

After more than a century, the light bulb is about to go the way of the whale-oil lamp. The contender is the LED (light-emitting diode).

The newest member of the family, white-light LED’s, emit light at frequencies across the entire visible spectrum, which means they can illuminate our surroundings with a clarity that's comparable to nature's original incandescent - the Sun.

The switch from light bulbs to LED’s is being driven by more than America's fondness for the latest technology. We simply do not like to be left in the dark.

Almost all of this electricity creates heat rather than light. Producing the white light needed to show the natural gamut of colors requires heating the filament of a light bulb to metal-melting temperatures. As a result, a typical 100-watt light bulb radiates roughly 95 watts into its surroundings as waste heat.

The LED’s could reduce the nation's electrical consumption by 10 percent.

A more significant advantage is convenience. The absence of a filament and its surrounding vacuum-containing bulb makes LED’s extremely durable and last a long time. Engineers from a company that makes the worlds brightest white-light LED, estimates that their Luxeon Star model, will shine for 100,000 hours.

Between 1962, when they were first demonstrated by General Electric, and about 1985, LED’s produced too little power to be useful for anything other than tiny red signaling lights on electronics. In 1993, researchers at several universities perfected a high-efficiency blue-light LED. By combining different colors and using colored coatings, LED’s now can produce colors as pleasing as the best incandescent bulbs.

Despite considerable progress in 2002, a serious hurdle remains. LED’s are expensive, and for years to come they will cost more than both incandescent and fluorescent lighting.

For applications like traffic lights, railroad signals and aircraft lighting - places where dealing with a burned-out bulb can pose a serious safety concern - cost is a minor consideration. Spurred on by the federal Next Generation Lighting Initiative, major lighting manufacturers, including General Electric, Philips and Osram, have formed consortia with semiconductor producers to mass-produce LED’s.

White-light LED’s could capture a quarter of the existing incandescent and fluorescent lighting markets as early as 2012.

The energy savings of LED’s is only the start.

In the course of looking into new ways to manufacture better LED’s, researchers have stumbled onto a remarkable light-related phenomenon. When they assembled the tungsten used in bulb filaments into a lattice structure, they found they could essentially transmute wasted heat into light.

There are several approaches to generating light with LED’s. All are based on the same underlying physics - a phenomenon called radiative recombination. When an electric charge is applied to certain semiconductors, the interaction between the electrons and the so-called electron holes releases photons, or packages of light. The nature of the semiconductor material used to make the diode determines the frequency of the photons, hence the color of its light.