People warm to white light from four-color diode lasers
ALBUQUERQUE, N.M. – Step aside LEDs, there’s a new light source in town. A new four-color laser source can produce high-quality white light that is appealing to the human eye.
LEDs – widely accepted as sturdier, more efficient replacements for incandescent bulbs – lose efficiency at electrical currents above 0.5 A. Diode lasers, however, improve at higher currents to provide even more light than LEDs.
In the test setup, similar bowls of fruit were placed in a lightbox with a divider in the middle. The bowl on the left side was illuminated by a diode laser light and the one on the right, by a standard incandescent bulb. The aesthetic quality of the diode laser lighting compares favorably with the standard incandescent light.
To test whether the white light produced by the diode lasers is pleasing to the eye, researchers at Sandia National Laboratories developed a series of tests that were carried out at the University of New Mexico’s Center for High Technology Materials. One by one, 40 volunteers sat before two near-identical scenes of fruit in bowls, housed in adjacent chambers. Each bowl was randomly illuminated by warm, cool or neutral white LEDs, by a tungsten-filament incandescent lightbulb, or by a combination of four lasers (blue, red, green, yellow), tuned so that they produced a white light.
The participants were instructed to choose the lit scene with which they felt most comfortable. The pairs were presented 80 times in random order, and the light sources providing the illumination were not revealed, to ensure that only the lighting itself and not sequence or tester preconceptions played a role in subject choices.
Sandia researcher Jeff Tsao examines a setup used to test diode lasers as an alternative to LED lighting. Skeptics believed that laser light would be too harsh to be acceptable, but research by Tsao and colleagues suggests that the skeptics were wrong. Images courtesy of Randy Montoya.
The result was a statistically significant preference for the diode-laser-based white light over the warm and cool LED-based white light, but no statistically significant preference between the diode-laser-based and either the neutral LED-based or incandescent white light.
“Since the tests show that diode laser light is as pleasing as its competitors, we expect we’ve removed some of the roadblocks to further research in this area,” said Neal Singer, a science writer at Sandia, adding that more research to compact various diode laser light sources must be conducted.
Four laser beams – yellow, blue, green and red – converge to produce a pleasantly warm white light. Results suggest that diode-based lighting could be an attractive alternative to increasingly popular LED lighting, itself an alternative to compact fluorescent lights and incandescent bulbs.
Diode lasers are slightly more expensive to fabricate than LEDs because their substrates must have fewer defects than those used for LEDs. Still, such substrates are likely to become more available because they improve LED performance as well, the researchers say.
Although blue diode lasers perform well enough that BMW AG plans to use them in its vehicles’ next-generation white headlights, the performance of red diode lasers is not as good, and yellow and green have a ways to go before they are efficient enough for commercial lighting.
The study was published in Optics Express (dx.doi.org/10.1364/OE.19.00A982) on July 1, 2011.
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