On Tuesday, May 25, 2004, at 17:22 US/Pacific, Russell McMahon wrote:

>> If a white LED burns out or dims out after a few hundreds or
>> thousands of hours, it isn't that much of an improvement over a small
>> incandescent bulb except maybe for the energy efficiency factor.
>
> FWIW a good LED is not more efficient than the best incandescent bulbs
> (generally higher wattage halogens) and a good smaller bulb can be of
> similar efficiency - notwithstanding general belief to the contrary :-)
>
Yeah, if you're talking about overall light output.  If you're talking
about how bright a spot or indicator you can get (small viewing angles)
at something like 5mA of average current, I think the LED comes out WAY
ahead.  Filaments, and their usual housings, are terribly
omnidirectional  (of course, there have been lots of people trying to
use highly-directional LED for applications where an omnidirectional
filament bulb would have worked much better, but that's a separate
issue!)  And of course the chromicity of LEDs is much nicer...

The nichia datasheet I just looked at said 0 failures after 1000 hours,
which was a reliability test rather than a lifetime spec.  I didn't see
any lifetime specs.  For the "premier" white LED vendor, Nichia's
information and distributer network certainly sucks...

I have a chinese (Chi-wing LED shop on eBay, I think) "UV" LED that's
part of a nightlight string whose output has steadily decreased over
the 6 months it's been in operation, and it doesn't have any phosphor.
I'm not sure if I'm overdriving it (The other 5 LEDs (of various
colors, including white) in the series string (same current) are still
outputting at original brightness (as far as I can tell.))  So phosphor
failure isn't the only thing you have to worry about.

BillW

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