Thanks, the light from the bulbs cast on the table was dimmer than the matching incandescent and bluer than it seemed it should be because the package indicated a warmer light. I guess the bulbs are going to be hit and miss for a while.
Thanks for the input, eeisgood. Sounds like it's a wise move to keep LED receipts, especially since the purported advantage is long life. I'm curious...when you say that LEDs were "not as bright or nice as incandescent bulbs," was it because of the color of the light? I know that some people don't like the bright white apperance of some LEDs.
Quite an optimistic article with little substantial consistent and complete information, it has a lot of disconnected tidbits. Like one of the other comments I read, some more complete information would be nice.
In any event I just keep track of what I find in the store, some failures, abject failures, and successes. One recent failure was a set of six bulbs just installed in a dining room fixture, after about 1/2 hour operation one bulb went really dim, the rest have been OK for a couple months. They are not as bright or nice as the incandescent bulbs they claim to match. One nice success was some under counter lighting we got, very bright, and only a little warm temperature wise, we really like them.
Life expectancy is the truly vital part of the LED discussion. Unless they last long enough to pay for the reduced maintenance costs there is really not that much motivation to choose an LED device. So quality is the very vital parameter.
The discussion about the actual life of the LED lamp versus the rated life of a single emitter is a good one. I have been designing LED lamps for many years, and the potential is there to reach very long life lamps. However it takes very careful design and high-quality components to reach that potential. In an effort to shed some light on the subject, DOE has been doing testing of various consumer LED lamps for the past several years. See http://www1.eere.energy.gov/buildings/ssl/caliper.html Their summary report #15 concentrates on flood lights. Brand names are not mentioned, but they do include pictures of the products, which might let you distinguish the brands.
Consumer Reports has also tested a range of LED bulbs. They do mention brand names, and clearly some brands are much better than others.
Perhaps the datasheet for a single emitter does say 50K hours, and that may even be accurate (if the LED is adequately heat sinked and isn't overdriven to maximize light output for least cost). But it just doesn't translate to the MTBF for the bulb, which may contain many emitters (along with other components including PCB and connectors). The MTBF of the LED light bulb itself is much, Much, MUCH lower.
To be precise, an emitter is a single LED. An LED bulb is an assembly that will contain one or more emitters.
I've seen more than one LED bulb advertised citing the emitter MTBF to imply that the bulb MTBF is the same (in the 20K to 50K hours MTBF range). This is, to be polite, not true. Excusable for marketing types, but not appropriate for an Engineering blog.
The calculated lifetime of an LED emitter is, truly 50,000 hours. The observed lifetime of the circuitry that drives the LED is about the same as the life expectance of a couple of incandescent bulbs. I have found the net cost of LEDs is roghly three times the cost of incandescants, plus the color is much different. Dinner just isn't as appetizing when displayed under a recently purchased LED and you can't take them back if you don't like the color. I did read a suggestion that to restore incandescent colors to LED environments, try buying tinted glasses (must have been a government spokesman).
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