Friday, January 30, 2009

Cheap, Super-Efficient LED Lights on the Horizon

The race towards better, more affordable solid state lighting is heating up quickly. The U.S. government has sponsored a $20M USD prize for the first team of researchers to come up with solid state lighting that meets a strict set of standards. New research has finally helped to eliminate the LED droop typically associated with the higher currents needed to provide greater efficiencies.

Now a team at Cambridge University may be close to having a winning design on their hands, perhaps for the L Prize, if they're eligible, and for the consumer market. The university has produced a new design which costs a mere $2.85 USD and despite being the size of a penny, produces similar light to a fluorescent bulb while lasting over four times as long with a lifetime of 60 years.

The new design triples fluorescent bulb efficiency and is 12 times more efficient than incandescent designs. Also, it’s capable of instantaneous illumination, so the light lag associated with fluorescent bulbs may soon be a thing of the past.
I am a big fan of these contests to promote innovation. If they can produce these for $2.85, this will be well worth the $20 million. Of course if they do last 60 years, it might be the last light bulb you ever buy, and worth waiting a couple more years to make sure it is as good as its going to get.

So what was the breakthrough?
Gallium nitride cannot be grown on silicon like other solid-state electronic components because it shrinks at twice the rate of silicon as it cools. Crystals of GaN must be grown at 1000°C, so by the time a new LED made on silicon has cooled, it has already cracked, rendering the devices unusable.

One solution is to grow the LEDs on sapphire, which shrinks and cools at much the same rate as GaN. But the expense is too great to be commercially competitive.

Now Colin Humphreys's team at the University of Cambridge has discovered a simple solution to the shrinkage problem.

They included layers of aluminium gallium nitride in their LED design. These layers shrink at a much slower rate during cooling and help to counteract the fast-shrinkage of pure gallium nitride. These LEDs can be grown on silicon as so many other electronics components are. "They still work well as LEDs even with those extra layers inside," says Humphreys.

Growing the LEDs on silicon was assisted by a number of advances at other U.S. and European research institutions.

A 15-centimetre silicon wafer costs just $15 and can accommodate 150,000 LEDs making the cost per unit tiny.

via Daily Tech and New Scientist

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