LEDs should be lighting the way to a greener future: They use 75 percent less energy and last 25 times longer than incandescent light bulbs, and they do so at a cooler temperature. But right now, we mostly use LEDs in electronics, because they have a bit of a drooping problem: at higher currents, the amount of light they produce takes a nose-dive.
The efficiency droop has baffled scientists for years, but researchers at the University of California, Santa Barbara and France's École Polytechnique say they've finally solved the mystery.
Their work, published in a forthcoming issue of the Physical Review Letters, identifies the source of the droop as a process called Auger recombination, a non-radiative process that produces heat. Previous research at UCSB theorized that Auger recombination might be the culprit, but this is the first study to measure the effect conclusively.
LED-based lights contain a microchip with a positive-type and a negative-type semiconductor made of gallium nitride. Between the two, in a quantum well, the negative electrons from one semiconductor and the electron holes from the other combine, producing a photon of light. When you apply more electricity, it produces more photons--to a point.
In low power situations, like in your cell phone, the process works great. But when you raise the current up to the level it takes to light a room, nitride-based LEDs stop producing photons at the same rate. According to the research from UCSB's Center for Energy Efficient Materials, it's because the electrons collide with each other and lose their energy through heat instead of light.
If we could make LEDs that circumvent that issue, they could replace compact fluorescent lights as the energy-efficient bulb of the future. Theoretically, LEDs should produce about 300 lumens per watt, making them three times more efficient than CFLs, as well as easier to dispose of since they don't contain mercury. Widely adopting LED lighting could save the country $265 billion and reduce our electricity demand by one third in the next 20 years, according to a 2010 estimate from the U.S. Department of Energy.
But it does cost more upfront, so until LED technology can live up to their theoretical efficiency at higher currents, it's a tough sell. While the U.S. is already phasing out energy-sucking incandescent light bulbs, LEDs have yet to take over the commercial and residential lighting market.
So far, we don't have a solution to the droop, but now that they've identified the source of the problem, the researchers hope to design LEDs that will minimize the effect and produce more light, making the technology a more attractive choice for home and office lighting.
So just as a curiosity, why is it that my cheap little battery powered diode lasers can emit so many photons per Watt, while a diode without anything to parallelize the light can't? Should we be putting a mild pump behind them?
quasi44 - lasers put out photons in a concentrated direction and in a single color energy. Bright white light is the most energy intensive and difficult spectrum to produce. red lasers use significantly less power than green or violet and we are also talking about light in all directions.
I think the photography and Video lighting industry will jump on this and jumpstart the adoption of LED lighting. Especially because LEDs run so much more cooler than incandescents - temperature wise. There is already a healthy market of LED lights for video and photography. So this is probably very good news for that industry.
So just out of curiosity would it not be a good idea to upgrade the recessed lighting in my home with the current LED lights that are available in stores now? A product like the EcoSmart line that is available at Home Depot?
Almost all the lights in my home are LED. If you go to home depot you will notice that LED lights have about equal share of shelf space with CFL bulbs. We have had a workaround for years, if you cant make a brighter LED then make a bigger one or use several smaller ones.
@jMac029 - It really depends on the product I think.
There are two ways to deal with the current droop issue.
1) Add more diodes in parallel to divide the current and keep efficiency up.
2) Lose efficiency and just deal with the additional heat with heatsinks.
The first generally results in a more expensive product but you get all of the advantages of LED.
The second won't save you quite as much on electricity and they won't last as long, so I've been avoiding those models.
In reality even if they do figure out how to solve the issue with Auger recombination, it will be years before any of these ideas become commercialized, so I wouldn't let something like that stop you if you can afford the upfront cost of good LED bulbs now.
Today's LED's for home are poor choices in color and appeal. They are very expensive and my not prove to last as long as stated. I put many of the original CFL bulbs in my home 20 years ago and except for one or two, they are all working still. Maybe I have grown used to their light but I have tried the new LED's and they suck. Even the so called yellow ones from the P company.
However, it would be nice to get an LED to compete with and greatly outperform the true electric use when compared to normal tube florescent or sodium or metal halide.
if you want an led bulb then just build it yourself, allied electronics has an excess inventory section where they have many of the 3mm and 5mm leds for maybe 2 cents each, if that. these most commonly run on 3 volts, using a resistor and a large enough capacitor to offset the power factor and increase the impedance you could build your own led bulb that was brighter and costs maybe 5 dollars.
and you'd be able to say that you built it.
to mars or bust!
I think you might want to take another look @ LED bulbs. The cree LED bulbs just released (home depot) cost $13, turn on instantly and only use only 9.5 watts (60 watt equivalent brightness)I have a bunch of them and lighting wise you can't pick them out from other 60w bulbs
I bought a case of 100 100W incandescent bulbs before the Marxist ban took hold. Will do that for every size bulb they target. will be set for life with good bulbs.
I didn't know that even LED's contained a kind of mystery.
Presumably this problem would not occur until higher current if the single LED were replaced by a larger number of LEDs in series. If that is more expensive, then LED designers might be able to make a large LED behave more like several smaller ones.
I have a 46" LED Tv and it appears plenty bright to me excellent picture. But arent OLED organic light emitting diodes suppose to be better and possibly replace LED? I have not heard much lately about the OLEDS.
By saving all of this energy with LED lights the power companies will have jack up the rates so there will be no savings after all.
I am all for the time when LEDs will replace my current lighting, assuming that they will give a decent longevity vs price.
I have been replacing my incandescent lamps (last one was 10 years old), with CFLs and have found them to be expensive and unreliable.
I have had them fail in just a few weeks. Good luck getting a refund.
Why are the environmentalist gurus so much against incandescent? I live in a modern house (cold Canada) that is very well insulated. Any heat generated above the luminescence value is retained in the building.
Just think of the hundreds of thousands of houses that use electric radiators for either primary or supplementary heat.
Are the enviros next going to want radiant heaters banned??
At least I get light from my incandescent lamps. A dumb idea to outlaw them.
Just my humble opinion.