MassiveProng wrote:
On Tue, 10 Apr 2007 08:14:24 -0500, "Anthony Fremont"
Gave us:

Look again. Please refer to Figure 6 (Maximum Tolerable Peak
Current vs. Pulse Duration) It goes without saying, that you can't
keep Tj at 25C once you turn it on.


Max Tolerable is NOT the recommended operating current for 100%
duty.

Well duh. I was just showing you that there truly is a spec stated for a
duty cycle less than 100%.

Nearly ALL visible spectrum LEDs are meant to be ON ALL the time
without detriment to lifespan. I would actually bet that it IS ALL.

They are meant to be used as indicators, whether in a panel, or on
the rear of a car.

It is silly to think otherwise. Their original purpose was as a
replacement for panel lamps, and as a replacement for digit segments
in gas numeric digital displays. Among many other applications.

I never said that there were LEDs that couldn't be operated 100% duty cycle.
I imagine that they all will take it as long as current is low enough. I am
saying that many LEDs are manufactured with the forethought that the end
user may be overdriving them for short times. That's why they come up with
pulse specs.

High brightness LEDs are just now coming into being, and had to have
many years of field level testing to iron out deficiencies in physical
design and packaging as well as chemical makeup. In those cases, a
less than 100% duty rate MIGHT be a particular of a given makers' spec
on a device. Not likely though since they are fighting to win a
particular market that IS 100% duty rate. It matters not how long
some biker "typically" leaves his "gang boy" lights on his bike
running.

It's not the LED that is to blame on these failures. It is the lamp
assembly manufacturer that couldn't resist driving them just a little harder
than necessary. Otherwise they wouldn't dim/burn out like that.

I would never insinuate that the pulse spec duty cycle could be extrapolated
to hours of length. I'm just saying that the lights I saw on display at the
shop were being driven too hard from something. Chances are that the
display was only being driven by 12V. Just imagine how long they would last
in a vehicle seeing 14V all the time.