LED researchers at NREL think they are on the road to creating super-white LEDs thanks to a breakthrough in fabricating a reliable efficient green LED using indium gallium phosphide.
To make an LED that appears white, researchers minimally need the colors red, green and blue. Red proved easy to generate, and about 15 years ago, Japanese scientists found a way to generate blue, thus providing two of the key colors from the spectrum of white light.
But green has been elusive. In fact, commercial LEDs now are made to look white by aiming the blue light at a phosphor, which then emits green. The process saps a big chunk of the efficiency from the light.
The aim now is to provide a fourth color to make that white light even whiter.
NREL plans to use a slightly deeper red and a lemony green, which would then be combined with a blue and a deep green made using its gallium nitride technology.
In three years, NREL thinks it will have a bi-colored device that, when teamed with blue and deep green, can produce an LED with a color-rendering index well over 90, NREL scientist Angelo Mascarenhas said.
"It will give you one of the finest color-rendering white lights" and the manufacturing costs shouldn't increase, he maintains.
"We have a patent on a device that will provide these two colors, as one unit, " says Mascarenhas. He says the configuration will be like a fly's eye with units side-by-side with the blue and deep green combination, alternating in a pattern.
"From afar, it will look like white. You won't be able to see the individual colors of the mosaic structure."
The resulting white light LED will be intelligent. "We'll be able to electronically control the hue of the lamp," he said. "We can vary the combination of intensities of these four colors on an electronic circuit. By slightly increasing the blue, we can make it more suitable for daylight. By turning down the blue and increasing the reddish yellow, we can make it softer, more suitable for night. We can smoothly control the hue throughout the day like nobody has imagined. " More information can be found on the NREL release: