The yellow light-emitting diode (LED) gap always trouble Philips till now. Recently, researchers with Philips Lumileds (San Jose, CA) have developed a monochromatic nitride diode to closes the gap. The phosphor-converted (PC) amber LED demonstrated by Regina Mueller-Mach and her colleagues uses the down-conversion of blue light from an indium-gallium-nitride (InGaN) LED to longer-wavelength light by a phosphor, in a variation of a well-established process for producing cold or warm white light from blue LED light (see also "Fluorescent microspheres create white-light LEDs").
Monochromatic light-emitting diodes cover a large part of the visible spectrum with high efficiency. For blue light, nitride diodes achieve external quantum efficiencies in excess of 65%. For red light, phosphor diodes achieve efficiencies of approximately 50%. However, so far no highly efficient monochromatic LEDs have been available for the "yellow gap" at around 560 nm.
Leveraging previous research on warm white light, the researchers succeeded in down-converting blue LED light into monochromatic amber light with a 595 nm wavelength and a color purity of 98.7%. The external quantum efficiency of the PC amber LED is at 30-40%, depending on temperature. Compared to direct amber LEDs, the new PC amber LED is two to five times as bright. It achieves a light output of 70 lumens at a 350 mA current.
There are numerous applications for the LUXEON Rebel PC Amber LED. It can be used in yellow traffic lights or signals as well as in cars' turn signals or warning lights for construction sites. They could also be used in consumer electronics and their high efficiency makes them inexpensive.