White light shines for HP’s LEDsSteve Bush
Hewlett-Packard has joined Nichia and Siemens, the select few companies that have white LEDs in production.
Whereas Siemens is concentrating solely on surface mount components for back lighting, HP has taken the Nichia route and is making 5mm white LEDs for more general purpose uses. White LED comparison Manufacturer
120 o Luminous
0.04 (10mA) Colour
“Flashlights and other applications including signs that need efficiency and reliability. Outdoor path lights use incandescent bulbs and solar cells at the moment. White leds should increase run time,” said HP’s LED spokesman Northe Osbrink
Reliability is certainly higher in leds, and they are far more vibration resistant than incandescent bulbs, but the efficiency claim for white LEDs is a little premature. HP’s whites offer 3.4lm/W, Nichia claims over 7.5. Flashlight bulbs are above 10lm/W, although bulbs in long-life applications are under-run and produce less than this.
Colour is good in HP’s LEDs. Like Nichia, it uses a GaInN blue LED chip (Siemens uses GaN) with a YAG (yttrium aluminum garnet) inorganic phosphor to fill out the spectrum and provide white light. HP’s is nominally x=0.31, y=0.32 on the CIE (Commission Internationale de l’Eclairage) 1931 chromaticity diagram. This, says HP, represents a colour temperature of approximately 6500K. This is bordering on blue-white; ‘pure white’ in US TV speak. And whiter than photographic (5,500K) and printing (5,000K) whites.
To get consistency, something that the industry has not yet properly cracked in production, HPis sorting its white LEDs for both colour temperature and brightness. This, if price differentials are not too high, could be the major selling point. Mismatched LEDs are a cosmetic disaster.
In the future, Osbrink is looking for more efficiency and brightness. “One of the breakthroughs in white LEDs would be a violet or ultraviolet chip. The shorter wavelength would give better phosphor excitation. Bigger dies can also be used to produce more light, and heat sunk packages allow the chips to be driven harder.”
Heatsinking gets important as current rises above the conventional drive value of 20mA. Efficiency drops with temperature increase. Blue and green (GaInN) LEDs are far more prone to this than the best red and yellow (AlInGaP) types. Good package design can help remove heat to minimise temperature increase. “HP is involved with Philips in a company called Lumiled Lighting. It has a surface mount package that dissipates a lot of heat. With it, and using a metal-cored pcb, 12 red LEDs can be used instead of the usual 80 to 100 to make a red traffic light ,”said Osbrink.
HP’s white LEDs cost $0.95 in quantities of 100,000.