9 February 2012
Combine blue, red, green, and yellow laser light and you will get white light, but perhaps a white light you wouldn’t want illuminating your living room. It’s long been thought that the extremely narrow band of wavelengths generated by the four lasers would create a harsh white light consumers would find unpleasant and uncomfortable.
But researchers at Sandia National Laboratory wanted to see if this was indeed true. So they conducted a survey in which participants looked at images illuminated with white light from one of five different sources: LEDs producing warm, cool, and neutral light; a tungsten-filament incandescent light bulb; and four lasers tuned to produce white light. Participants reported no significant difference between the light from the incandescent, the neutral LED, and the combination of four laser lights. Interestingly, they also put the cool and warm LEDs at the bottom of the list for ease of viewing and realism.
The Sandia researchers think the results could lead lighting engineers to develop laser-based home and industrial lighting. Laser diodes are more expensive to make than ordinary LEDs because their substrates must have fewer defects. But substrate quality, which also affects LED performance, has been constantly improving. There are also problems with the performance of yellow and green lasers. And while red lasers perform better, they are not as good as blue lasers, which are now good enough to let BMW use them in its next-generation white headlights.
The performance disparity could be addressed by creating hybrid lights — white lights that use lasers and ordinary LEDs. For example, blue and red diode lasers could be combined with yellow and green LEDs.
The advantage of laser diodes is that they can handle electrical currents above 0.5 A and create more light efficiently as the electric current increases. LEDs, on the other hand, lose efficiency at currents over 0.5 A.