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LEDs vs. Lightbulbs
zymano writes "www.technologyreview.com has this nice article on LEDs vs lightbulbs" Follows the exploits of one Shuji Nakamura, the same man who brought you the practical violet laser.
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...LEDs are more fun to play with. I remember messing with them when I was younger and had one of those "300-in-1" kits from Radio Shack. I read the little book for ideas and then tossed it aside and had my own version of mayhem. At that point, my dad's own experiment was finished, and the results were startling...his son was a nerd.
Only in slashdot are posts of solidarity modded at -1 Redundant, while posts of antagonism are modded as -1 Flamebait.
I have a DORCY solid state LED Flashlight--actually, I have two. I liked it so much I bought it twice (one for home and one for my car). It works great. It doesn't difuse as badly as normal flashlights so it can shine further. Walmart seems to have stopped carrying it, but I got my second one at Sears for about $13.00 (no sales tax).
At the next eco-hypocrisy-meeting, count the private jets used to get to the meeting. Should be interesting to see that
I've a friend who works for Coleman (he's one of their webmonkeys, let's give him a heart attack by putting some "referrer=http://slashdot.org"'s in his logs).
He gets plenty of fun stuff from work. One of the things they have is a little crank powered flashlight that uses a Brinkman style little incand.
It will run for a fair length of time on the batteries, but I have to wonder how much longer it would run with an LED.
Perhaps next generation....
www.eFax.com are spammers
This article, like most articles that tout LEDs as a replacement for light bulbs, confuses efficacy and efficiency.
Luminous efficacy is defined as the power of radiated visible light (visible luminous flux) divided by the dissipated electrical power. Given in lumens per watt, efficacy provides a useful means of comparing which source provides the most useful illumination for a given power.
Efficiency on the other hand is defined as the power of radiated visible light (visible luminous flux) divided by the power of all radiated light (total luminous flux). Ideally given as a unit-less ratio, efficiency provides the ratio of useful light to wasted light and does not necessarily correlate with efficacy. It is possible to have simultaneously high efficiency and low efficacy.
The question of why LEDs haven't already replaced all lights can be answered quickly by comparing the efficacy of different sources of light. All numbers below are approximate.
Filament light: 10 lm/W
White LED: 20 lm/W
Halogen light: 25 lm/W
Red LED: 40 lm/W
Florescent light: 100 lm/W
Sodium light: 150 lm/W
It can be seen why red LEDs have replaced halogen bulbs with red filters in stop lights -- red LEDs have a much higher efficacy. Note that the efficacy of LEDs are still well below that of florescent lights. If you feel frustration in seeing how far LED technology still has to go to compete with the boring lighting technologies of yesteryear, assuage your sorrows in the knowledge that you can save billions in energy costs right now, simply by switching to florescent lighting.
Michael.
Linux : Mac
Whoever does the traffic lights over here (I think it's the LTSA, but whoever it is doesn't really matter) is slowly changing traffic lights (busted ones and new ones) over to using LEDs instead of the traditional light-bulb.
The change is quite noticeable (when you see 500 LEDs peering back instead of a large bulb), but the LEDs seem to provide greater brightness in addition to a longer-life and better energy efficency (which is always good during our annual energy-crisis).
A white led today has about twice the efficiency of a normal ligthbulb. That sounds great -- until you consider:
- The brigthest white led existing (in a lab environment, not on the shelves) is a 5 watt led, equivalent to a 10W ligthbulb, yay !
- Twice the efficiency ain't that good, this still means only about 10% of the energy-input gets turned to ligth, even halogen can do better than that and fluorescent has it beat into the ground with like 20-30%.
- The prices are out of this world, no, each LED ain't that expensive, but it also has a tiny ligth-output, try calculating the price for reasonably ligthing a single room.
- The color-spectra suck. Seriously, led is inherently monochromatic. Yes they can remedy this with various phosphors and the like, but those reduce efficiency (which was supposed to be the advantage of leds, remember?) and even with those it's hard getting a natural full ligth-spectrum.
In the meantime pluorescents are developing at a breakneck pace. Today you can buy pluorescents compact-bulbs that fit in a normal bulb-socket, are 5 times as efficient as a standard bulb, cost around 2$ a piece, are available in wattages up to 25 W (equivalent to 125W standardbulb), and last for around 10000 hours.This is a no-brainer people. Replace a single 100W ligthbulb with a 20W energy-saver and the math looks like this over the 10000hour lifetime:
You pay 1$ extra for the bulb, and you save 800Kwh over the lifetime of the bulb. With an energy-price of 13 cent (most pay more!) you will save over 100 dollars over the lifetime of that single bulb.
How about this: since LED's are pretty much monochromatic, and they seem to be more efficient if you only need one wavelength, use them to drive flourescent tubes. Use a UV LED (heh... these may not exist cheaply), and the tube should be able to convert from UV to visible for you.
Problems: How do you fit enough LEDs into the tube to make a bright light? How do you arrange them, so that no photons are lost before they hit the phosphors on the side of the tube? Putting them in a plane on the ends of the tube (so the LEDs are pointing to the other end) would probably lose quite a bit to hitting the other end of the tube first. One LED every X inches would look strange.
Conversion losses may also be too high, though fl. tubes are pretty efficient with the standard gas discharge tech.