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What are LEDs for?

27-03-2009

I saw my very first �architectural� LED about twenty years ago. It was small, and it was dim � but it was intriguing. The very small size of the semi-conductor source made them ideal for indicator lamps, but for architecture? We couldn�t see it � almost literally, we couldn�t see it. Fast-forward to today and we are looking at the LED as a possible replacement for much of our home lighting.
How did that happen? 

The first architecturally-useful LED relied on the fact that the LED is a �natural� spotlight. All other light sources give out their light in all directions and have to be collected by a reflector in order to create a light beam. And there are much inefficiency in that method.
LEDs, on the other hand, project their light straight from the chip. Combine that with a lens system that fits directly over the chip and you end up with a far more efficient way of delivering light.

But for LEDs to be accepted as a true energy-efficient source their light output needed to become similar to that of the fluorescent lamp. If that could be achieved then we�d have an extremely bright source that could see the end of the traditional filament lamp in all its guises. We�re not there yet, but it�s clear that we�re not far away and it may be that, by the time you read this, the first commercially-available LED that matches fluorescent output will have been announced.

For me, the most exciting aspect of this is the possibility of a whole new application for the LED. Up to now, LEDs have either been incorporated into fittings � so should the LED fail you have to replace the entire fixture, or they have been replacements for small spot lamps, typically of those small 50mm diameter tungsten halogen reflector lamps. But the first LED replacements for �ordinary� light bulbs are almost with us. Lower wattages (up to 40W) are already available, and the 60W equivalent is almost in our grasp.
Why does this matter?

The �greening� of our lighting is a vital part of the strategy to reduce energy dependency. So far the only practical alternative we�ve been offered is the compact fluorescent lamp (CFL). Now � the CFL is a good light source, regardless of the negative publicity that�s been generated (and there�s been more heat than light in all of that), but I am concerned that CFLs still contain toxic materials that require the failed lamp to be disposed of as �hazardous material�. But how likely is this to happen? We�re talking about millions and millions of lamps eventually being thrown away and I fear that most of them will end up in landfill, eventually leaching this bad stuff into ground water. That�s a scary scenario.

I�m sure it�s only a matter of time before someone offers up some negative aspect of the LED lamp. At the moment there are issues around the brightness of the LED and risks to the eye should you look directly into the light beam. Hmmm � OK, I see the problem, but I don�t think it compares with the risk of poisoning our water supply.

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