Looking to build a better light bulb, Shuji Nakamura led development of the modern blue LED in 1994. Initially considered too expensive, the blue LED is now ubiquitous, found in light bulbs, car headlights and Blu-Ray disc players. Awarded the Nobel Prize in Physics in 2014 for his work, Nakamura has focused in recent years on his latest invention, the violet LED. The latest LED lamps from his company, SORAA, were on display at Lightfair 2015, held on May 5-7 in New York City.
Blue LEDs are made of a gallium nitride (GaN) layer on a sapphire or silicon carbide layer, with two color phosphors to create white light. Nakamura's new design overlays a gallium nitride layer atop another layer of gallium nitride. The GaN-on-GaN design can take a higher level of current than earlier LEDs, allowing for a third color phosphor to be added. This LED emits a more accurate white light, with better color response on the violet end of the spectrum. "We take a violet LED and add red, blue and green phosphors to make white light," says George Stringer, SORAA VP. "We're so efficient at the front end that we can accept the [brightness] loss for better color."
Nakamura developed the GaN-on-GaN LED in 2006, but SORAA launched its first full line of violet LED lamps at Lightfair 2015. The new LEDs have a price premium and are used mostly for specifying, but Stringer expects costs to drop.