On Sun, 8 Apr 2007 19:52:26 -0500, "Anthony Fremont"
wrote:

John Fields wrote:

I seriously doubt whether the LED manufacturers are the weak link in
the chain. If it exists at all, I suggest that it's somewhere down
the chain where the unscrupulous are trying to trim the
dollars-per-lumen bottom line by overdriving fewer than the number
of LEDs required to generate the desired light level reliably.

Exactly, not the LED manufacturer, but the light assembly manufacturer is
the one that I blame. Normally, these lights are not used continuously, but
are for looking cool while the bike is parked outside the bar for a couple
hours. These are targeted towards a market segment where they would likely
see much less than 100 hours. I suspect that on the display board they were
actually seeing a bit less voltage than it normally would installed, and
under allot better conditions. It's just that 12 hours per day operation in
a static display is an outrageously heavier than normal duty cycle.

---
I missed those last two sentences earlier.

If they were seeing a bit less voltage than normal then there's no
way their forward current could increase to the point where the
lifetime of the lamp would decrease. Other than reverse bias
failures, what causes LEDs to die is high junction temperatures, and
that comes about by forcing more current into them than they're
designed for. And that's caused by increasing the voltage across
them, not decreasing it.

Also, in other than high-power pulsed service, LEDs are designed to
be operated continuously. The example you cited in another post is
for high power operation.

Consider: If that weren't true, then the POWER ON LED on a device
designed to be ON 24/7 would have to be turned off every once in a
while, and that's just silly.


--
JF