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LEDs - Do the Benefits Outweigh the Cost?
7x7 asks: "We keep hearing about the latest and greatest thing to come out of LED technology, and every article seems to give an over-view of the topic. How LEDs consume little electricity and last a long time, etc. However the manufacturing process involves super hot ovens and expensive componants. Do the requirements necessary in the manufacture LEDs and LED componants out-weight the requirements for standard bulbs over 10 years? One LED light can last ten years, but contains dozens of LEDs. Has anyone seen or performed an evalutation to see if the trade-off is really anything to speak of?"
Previous Ask Slashdot discussions on LED lighting, LED Light Fixtures for the Home? and Which LED Flashlight Do You Use?
I've got a fever and the only prescription is more COBOL.
Incandescent light bulbs, as we all know, are highly inefficient, emitting ~95% of their energy as heat. Fluorescent bulbs are much better, but still emit radiation in a line-emission spectrum far wider than that of visible light. As far as I know, LEDs are geared to one frequency, and are therefore very power-efficient. No matter how much it takes to manufacture something (within reason), if it is more efficient, it will pay off in the end.
As always, it depends on the use.
I haven't seen anything about manufacturing costs, so maybe I'm not answering your question, but in use:
In traffic lights, a burned out bulb is a hazard, and expensive to change.
Brake lights and taillights are dangerous to lose, and they get shaken around. That's why in many cars if your brake or taillights go out, your dash lights go out too as a reminder.
Flashlights are typically low temperature bulbs where incandescents are more inefficient, especially after the battery voltage starts to drop off. Besides, they get dropped, so LEDs are a win there too.
Fluorescents are the most effecient, but for household lighting I don't like their color or sixty Hertz visible hum. (Any specific recommendations for a compact fluorescent that has a good color & a nice ballast that doesn't flicker sixty times a second?)
The LED geeks know LEDs aren't always better as far as power consumption goes.
http://www.pioneernet.net/optoeng/LED_FAQ.html#Q7
http://misty.com/people/don/lede.html
I saw a nice use of LEDs in a remote campsite. There were solar collectors on the roof of the bathroom, and little banks of a few LEDs that lit the bathrooms at night.
An LED seems smaller, but the incandescent in a mini-maglite puts out much more light than a white LED of the same size.
Assembly is the reverse of disassembly.
A high-efficiency red LED puts out about 2.5 mW of luminous energy in its emission band, and consumes 120 mW of power. That's 3% efficiency. The rest is dissapated as heat. Incidentally, that's why LEDs have a large footprint (the luminous area is very small); so the heat can spread out and the junction characteristics don't change. Incandescents emit light energy outside the visible band, unlike LEDs. This is where most of the power goes, not heat. Thus, incadescent lights achieve about 15 lumens per watt, flourscents get about 50 per watt. Contrary to popular belief, LEDs are in between, the high efficiency models get about 25 lumens per watt.
The most efficient LED right now is %32. You can't buy these yet... they will be used in lights that operate like flourescent lights since they emit UV. This will be the ideal, long-lasting but low power light source.
LEDs are not economical when a flourscent light with electronic ballast can be used in the same situation. In scenarios where the extra electronics required by a flourscent light are too bulky or not enough power is available- this is where LEDs shine. That is why they are the flash-light champs.
Fuck Beta. Fuck Dice
Bike lights (taillights, headmarkers and on some models of high-end headlights, instrument lights) have used LEDs for years. They really conserve on batteries and are quite bright (I can see the glare of my LED taillights on the road behind me in my helmet mirror at night). Most of the cities in northwest Oregon and ODOT have changed to LED arrays for traffic signals, since they don't burn out as often as incandescent, even when being bounced around by a storm (most intersections have traffic lights on overhead stringer lines, not poles, so they can properly position the signals over each lane). TriMet is phasing in LED signals on busses (they hate driving around busses with a burned out left blinker as much as you hate getting stuck behind them that way), and has
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LED lights are getting better
http:\\www.limileds.com
main points to know about lumileds
the light is cold to touch (heat is still generated - but through a heat sink)
coloured lights are alot more efficiant then any other type i know of
the 5W white leds are not rated for a very long life but all the other 5W and all the 1W are rated for 100,000 hours.
a swith mode power supply will probabily be need to drive them efficaintly which adds to the already high cost.
Did you misread the part where I said LEDs are the winner in flashlight choice? This is because they beat incadescent lights in lumens per watt numbers (the numbers get worse for incadescents too as they get smaller, like in flashlight bulbs). They don't beat flourescent lights, though. That was my point.
Light bulbs emit infrared, radio, microwave, and ultraviolet light (as they are blackbody sources). The heat from the filament is not easily conducted away into the base of the bulb or through the gas inside. Hence, much of it radiates away in the form of photons. The infrared radiation is re-absorbed by the glass in the bulb itself and causes it to heat up some (in addition to heat transfered by conduction). But it still passes much of the infrared, ultraviolet, etc. energy out into the room. They don't heat up as much PER WATT when compared to LEDs.
LEDs don't emit anything but a narrow wavelength. Unfortunately, many of the photons get re-abosrbed by the substrate. All of this gets converted into heat. Some of it is converted into microwaves and radio waves, but not much. This is because the large package area (and small power output compared to a light bulb) allow it to conduct the heat into the environment, either through the plastic package or through the thick metal leads allow into whatever its attached to. They don't get hot to the touch unless you put a lot in a small space.
Fuck Beta. Fuck Dice
People say this a lot here, but can you cite a source. A super-bright (2 candella) LED takes 15mA at 1.7 volts, that's about 25mW of power, so 1 Watt powers 40 LEDs. A standard 4-foot fluorescent tube is 40 Watts, so you can power 1,600 super-bright LEDs with the same power as the 40 Watt tube. I've never used more than 50 of the LEDs at once, but it sure seems like a few hundred would match the light output of the fluorescent.
From what I said, we know 40 Watts gives us 3,200 candella with the LEDs. What's the output of the 40 Watt tube? I have a 20 Watt ring-shaped compact fluoresent that gives under 1000 candella, so the LEDs are more efficient than that.
Jason
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