Tired of dealing with those newfangled fluorescent and halogen bulbs that tend to blow out and can't quite handle dimmer switches? You might just find solace from an old and trusted source: incandescent lights. A team of physicists has discovered a way to double the efficiency of these ordinary light bulbs. All it takes is a superfast laser blast to their filaments.
The old-fashioned light bulb, invented in the 19th century by Thomas Edison, seems to be heading the way of the horse and buggy. Cheap, conventional bulbs require more electricity per lumen, or unit of light output, than compact fluorescent or halogen bulbs, something that makes them increasingly unpopular for efficiency-oriented consumers. Yet fluorescent and halogen bulbs carry their own problems. Fluorescents contain mercury, which makes their disposal problematic, and halogens burn very hot, creating the potential for a fire hazard. And neither emits the warm, yellow glow with which people have grown so comfortable.
Chunlei Guo of the University of Rochester in New York state, along with colleagues both at the university and in Russia, were experimenting with the effect of ultrafast laser pulses on metals when they noticed that pulses lasting only a few femtoseconds--quadrillionths of a second--could fundamentally change the molecular arrangement of metals without melting them. They also found that the altered metals became very good at capturing radiation in the form of heat, and they wondered if the opposite could be true as well. So they tried a simple experiment. They fired a femtosecond laser beam through the glass of an off-the-shelf incandescent bulb. As expected, the lightning-fast beam rearranged the molecules of the bulb's tungsten filament, turning it dark black. But then, when the researchers turned the bulb on, the part treated with the laser shone considerably brighter than the rest of the filament. As the team reports in an upcoming issue of Physical Review Letters, further tests showed that treating the entire filament this way made a 60-watt bulb as bright as a 100-watt bulb without increasing its power requirements.
The process could have immediate commercial potential, Guo says. Femtosecond lasers are expensive but readily available, and on a mass-production scale the costs of treating bulb filaments "could come down dramatically," he says.
Physicist William Stwalley of the University of Connecticut, Storrs, says it's remarkable that something as well-studied as a tungsten light-bulb filament can be fundamentally changed by a femtosecond laser. He adds that the technique offers "very exciting possibilities for changing the structure of and blackening other metals," such as those used in solar-energy collectors and radar-evading materials. As far as residential lighting, Stwalley says the efficiency improvement might not be enough to stop the conversion to alternative lighting, but for industrial applications, "it could be really helpful."