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Integrated Reflector Could Lead to Ubiquitous LEDs
Andreas writes "Professor Schubert says he has found a way to raise the efficiency of LEDs to 99%. From an article on Advanced Technology: "Until now, all lighting systems, especially incandescent bulbs, generated more heat than light. But our 99-percent efficient reflectors for LEDs makes them the first candidate for light-bulb replacement that generates more light than heat," said Schubert."
"LED technology has the advantage of longer life than fluorescent. With the increase in efficiency from reflectors, they could cut power costs below fluorescent and become the TCO winners."
Also something to keep in mind is that LEDs are far more robust than fluorescent and incandescent lights. Incandescent lights can't take shocks very well, and the huge temperature delta between an on/off state reduces its lifespan significantly. Fluorescent lights are also relative fragile (ever tried replacing fifty or so of those tubes without shattering at least one of them?), and the ballast used to generate the required high voltage (most types of ballast) create quite a lot of EMI, which is bad for sensitive equipment and cables like Cat-5 etc.
LEDs generate very little heat, require only a very small current (tens of mA!) at equally low voltages, produce no EMI, are unaffected by all but the most severe shocks and last virtually forever (100,000 hours for red, green, etc. with ease).
If LEDs are made brighter, even if this makes them more expensive than other technologies, there are always some (less friendly) places where they would work very well and would be cheaper in the long term.
Site & blog: http://www.mayaposch.com
These lights use a Fresnel Lens to direct the light from the bulb or LED cluster to only the lane for which it is intended.
wikipedia link
Unfortunately DC power doesn't transmit over any kind of distance very well. AC is much more efficient for that. (Esp. at high voltages... 20,000V+)
Also, all flourecent lights have transformers in them, so suddenly it's not too unreasonable for each light fixture to have its own little transformer in it!
=Smidge=
Electronics 101: when you connect 2 circuits in series each sees half the total voltage. Connect 24 LEDs in series to a 120 volt line and each sees 5 volts! By definition there is no need to transform the AC into DC - the D in LED stands for diode, which is what you use to turn AC into DC! In the real world you are likely to use 48 LEDs, in two different strings, so that you get light from both sides of the wave.
If you have 2v LEDs, you only need wire about 60 of them in series and you've taken care of the voltage problem. Well, except they'll blink at 60hz, quite strongly...and if one failed, they'd all go out. But in any case, it's hardly rocket science to make use of the higher voltage level, especially since LEDs will tolerate A/C. Incidentally, look at a screw-in fluorescent bulb some time- they've gotten the whole thing down to $10 or so, and that includes a transformer and electronics to raise the voltage. Transformers etc are very cheap.
However, there's an increasing number of appliances in a modern household that would be much better served by a 12V DC supply. How long do you think it'll be before we start changing over?
Never. The whole point behind A/C is that it is very easy to step up/down, and as a result, you can use a higher voltage for transmission and distribution. Higher voltages mean less current flow for the same amount of energy, which means reasonably sized wiring and such.
Even in the short distances involved in a house, losses from wiring can be substantial at such a low voltages as 12v. 48v might be a better choice, but I can't see it ever taking off.
Please help metamoderate.
> Unfortunately DC power doesn't transmit over any kind of distance very well.
Looking at just the wire itself, transmission losses aren't worse for DC. There are a few HVDC transmission lines in operation now. Some are used for 50/60Hz conversion.
The reason AC is used because it's easier/cheaper to efficiently step up (and down) the voltage to useful levels, as per your power transmission example.
If you read the article you will see that there is no claim on 99% efficiency of the LED. The claim is 99% efficiency on the reflector. No LED anywhere in the world comes even close to 220 lumens/watt. The best I've seen in the real world is about 80 lumens from the 3 watt Luxeon devices put out by Lumileds. These devices are very hot and need a lot of heat-sinking to avoid destroying themselves in any confined application. You have to remember that LEDs aren't magic. They are just full of inefficiencies and the back reflector issue is only one of them. I work with high intensity white LEDs every day and if you know of some that can give the output you talk about that don't need active cooling for God's sake tell me where I can buy them.
-Pinkoir