An interesting look at LED Lighting
The author is Paul Rako who is the technical Editor of Electronic Design News so he probably knows a thing or two about them...
From
EDN:
LED lighting� yet more green BS
I haven�t done any green-baiting lately and I really miss reading the hundreds of comments from people that call me an idiot or a shill for the oil companies. Last week I was with my buddy Paul Tuttle at his monthly HP alumni gathering. One of the HP retirees bragged about how he was using LED bulbs in his house and how they lasted longer and saved energy. Now I try to keep up on LED lighting� it is a promising technology, but in 2008, the situation is this: Cree, a great outfit has managed to exceed the luminous efficiency of cold-cathode fluorescent but only in a tiny 20 mA LED. It puts out way less light than a CCF. OK, what Cree has done in their big lamps is to match the efficiency of halogen, at least in the lab. They are still a ways off from getting the same luminous efficiency as a fluorescent bulb. Now there are great applications for LED lighting. One is inside food coolers it the grocery store. Since fluorescents don�t work very well when it is cold they cannot be used. And the incandescent halogen lights might use the same power, but they also reject more heat into the cooler, and it takes refrigeration energy to make up for that. On top of that you don�t have to replace the LED lights as often and that is always good in a business situation.
Another great application for LED lights might be way up on a high ceiling where it is a real pain to get up there to replace the lamp. But be careful about lifetime claims for LEDs. First off, bear in mind that heat degrades an LED. The end-of-life may not be a failure, but rather, a reduction to 50% output. Also lets not forget you need a power supply to feed the LEDs. If you want any kind of efficiency, that has to be a switching supply with an IC and worse yet, electrolytic capacitors. You are not going to get 60,000 hours out of that in all cases. We all know that the early CFL lamps would die early if you switched them on and off a lot. That was not the phosphor or the bulb failing, it was the little power supply in the base. In addition to the lifetime issues of a power supply realize that the power supply is a big hit on efficiency. Yeah, you may run an LED string on AC with a resistor, but you will get really lousy efficiency. The same goes for making it dimmable, it will work but you will take an efficiency hit.
What really irks me is the plain old marketing BS surrounding LED lamps. Paul Tuttle told me about this great site, C Crane. We all gotta love a site that has short-wave radios and scanners on the home page. The problem is on the LED light page. There they have a little chart to show what a great deal LED lights are and how one bulb can save you 353 dollars and 25 cents. But it is a bald-faced lie and all it takes is a few minutes on the Internet to prove it. It took a few seconds to find this page with a halogen lamp that makes 840 lumens, uses 60 watts and lasts 3000 hours. When you plug this into the little chart at the bottom of the C Crane page you no longer get a $353.25 savings, you get a $217.50 penalty.
The Chart that Paul mentions in his last sentence is very simple, fact checkable and makes his point very eloquently.
Nice to see a balanced analysis of the costs and the benefits. Our living room has a cathedral ceiling and there are three lights that 'wash' the fireplace and chimney. A bear to replace the bulbs and when I saw the cost of equivalent LED luminaries, I am now planning to buy that 30' extension ladder that I had been meaning to get for the last couple years. The hassle-factor is a bit higher but the overall cost is lower and the end result is better (the circuit is on a dimmer).
Posted by DaveH at March 14, 2008 10:21 PM