Diode lasers "can be tolerated by human eyes"
By Adrian Galbreth
The human eye is as comfortable with white light generated by diode lasers as with that produced by increasingly popular light-emitting diodes (LEDs), according to tests conceived at Sandia National Laboratories which could result in diode lasers eventually challenging LEDs for home and industrial lighting supremacy.
Currently, both technologies pass electrical current through material to generate light, but the simpler LED can only emit lights through spontaneous emission, while diode lasers bounce light back and forth internally before releasing it.
Experts claim the finding is important because LEDs lose efficiency at electrical currents above 0.5 amps, while the efficiency of diode lasers improves at higher currents, providing even more light than LEDs at higher amperages.
Sandia researcher Jeff Tsao, who proposed the comparative experiment to measure the impact on, and tolerance of, the human eye, said it showed that diode lasers are a "worthy path to pursue" for lighting.
"Before these tests, our research in this direction was stopped before it could get started. The typical response was, 'Are you kidding? The colour 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," he explained.
In tests that took place at the University of New Mexico's Center for High Technology Materials, 40 volunteers were seated one by one before two near-identical scenes of fruit in bowls, housed in adjacent chambers, with each bowl randomly illuminated by warm, cool, or neutral white LEDs, a tungsten-filament incandescent light bulb or a combination of four lasers tuned so their combination produced a white light.
The result was that there was a statistically significant preference for the diode-laser-based white light over the warm and cool LED-based white light, explained Sandia scientist Jonathan Wierer, who helped plan, calibrate and execute the experiments.
However, he said there was no statistically significant preference between the diode-laser-based and either the neutral LED-based or incandescent white light - results which are unlikely to start "a California gold rush" of lighting fabricators into diode lasers.
Nonetheless, the experts said the results make potential further efficiencies for the multi-billion pound lighting industry.
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