This long but interesting ieee Spectrum article takes an in-depth – and very scientific – look at the mystery surrounding the drive to make our LED lamps more efficient. The problem, known as droop in the trade, means that LEDs cannot be manufactured to emit more light, because the output drops off significantly above a certain wattage. That’s apparently why most household LED lamps only go up to 20W or so.
It’s a fascinating, albeit geeky, tale which shows how much science funding gets poured into problems with potentially massive commercial payoffs. Once they crack this problem – and it seems we’re talking quantum mechanics in there somewhere – the incandescent and fluorescent bulb business is going to be rather dead in the water, and we’ll all be using less power to receive more light.
Today’s garden-variety incandescent bulbs aren’t much different from the ones Thomas Edison sold more than a century ago. They still waste 90 percent of their power, delivering roughly 16 lumens per watt. Fluorescent tubes do a lot better, at more than 100 lm/W, but even they pale next to the best LEDs. The current state-of-the-art white LED pumps out around 250 lm/W, and there’s no reason why that figure won’t reach 300 lm/W.
Unfortunately, these LEDs perform at their best only at low power—the few milliamps it takes to backlight the little screen on your mobile phone, for instance. At the current levels needed for general lighting, droop kicks in, and down you go, below 100 lm/W.