Diode lasers for lighting looks promising, still a ways away
Recent research at Sandia National Laboratories has shown the human eye is as comfortable with white light generated by diode lasers as with that produced by increasingly popular LEDs. Why is this significant? While laser diodes may be farther from being ready for the commercial market, they have improved efficiencies at higher currents than LEDs.
The basis of both technologies is similar — electrical current is passed through a material and generates light. LEDs emit light through spontaneous emission, while diode lasers bounce light back and forth inside before releasing it. Laser diodes use four colors — blue, red, green and yellow — to come up with the pleasant white light.
“What we showed is that diode lasers are a worthy path to pursue for lighting,” said Sandia researcher Jeff Tsao, who proposed the comparative experiment. “Before these tests, our research in this direction was stopped before it could get started. The typical response was, ‘Are you kidding? The color rendering quality of white light produced by diode lasers would be terrible.’ So finally it seemed like, in order to go further, one really had to answer this very basic question first.”
Little research had been done on diode lasers for lighting because of a widespread assumption that human eyes would find laser-based white light unpleasant. It would comprise four extremely narrow-band wavelengths — blue, red, green, and yellow — and would be very different from sunlight, for example, which blends a wide spectrum of wavelengths with no gaps in between. Diode laser light is also ten times narrower than that emitted by LEDs.
Although these results probably won’t turn LEDs into collector’s items anytime soon, since diode lasers cost more to make because their components need to have fewer defects than what is acceptable in the LED world. But Tsao sees a future since these types of substrates are likely to become more available in the future because they improve LED performance as well.
At this point blue diode lasers are above and beyond performance found in the other colors, so much more that BMW is planning their use in its next-generation white headlights. Red laser performance is not as good but the yellow and green lasers have a ways to go before they are efficient enough for commercial lighting opportunities. The research was published in the July 1, Optics Express.