Incandescent Comeback

Here’s another example of how applying new solutions to old problems can lead to exciting new products. With incandescent bulbs being phased out in favor of more efficient compact fluorescent lights (CFLs) and light-emitting diodes (LEDs), most of us have come to miss the soft, warm glow of a light that didn’t need time to heat up and could be dimmed to virtually any level. Now, as the result of a clever application of nanophotonics, incandescents may make a comeback.

The reason that incandescent bulbs are so inefficient is that much of the energy emitted by the filament is in the form of infra-red (IR) radiation – more commonly known as heat – rather than visible light. Prior experiments have sought to capture some of this IR radiation and reflect it back to the filament by coating the inside of the bulb, but the results have been marginal.

The latest bright idea involves coating the filament itself with a crystalline structure similar to those applied to glasses. The coating is made up of thin layers with different indices of refraction and arranged in a specific way so that visible light passes through but the heat is reflected back.

While the luminous efficiency of conventional incandescent bulbs is only 2 to 3 percent, the proof-of-concept models achieved 6.6 percent, making them comparable to some CFLs (which range from 7 to 15 percent) and LEDs (which range from 5 to 20 percent). However, the researchers anticipate that the new design (referred to as a two-stage incandescent) could reach as high as 40 percent efficiency with a little more tweaking.