On Feb 23, 2006, at 2:45 PM, G=F6khan SEVER wrote:
>
> I have confirmed that the correct Vf bin code ranges in
>  3.51 - 3.75[V] for my white Luxeon III Emitter power led.

Huh.  Then I'm not sure why you are under the current you expected
based on assuming 3.9V each.  Unless the bin Vf is at 700mA rather
than the 1A you expect, but even then it sounds like you had less
current than I would have thought...


> Another question for red color Lux3 power leds; Whats the wiser
> solution to get the best current /  normalized luminous flux
> trade-off?  ( If i want to get maximum flux i have to drive
> the led at 1400mA but that will cause overload on dissipated power

Are  you sure?  Don't forget that the red LEDs have significantly
lower Vf.  I thought that was why they were spec'ed at 1400mA in
the first place: the Lux III packaging is essentially capable of
of dissipating about 4W into appropriate heatsinks, which means about
1A for the about 4V blue/white/etc LEDs, and about 1400mA for the
about 3V red LEDs.


> Do you think the result predictable, in other words do we say
> that we get stable 0.7[A] current or at the start we get 0.5[A]
> and increasing to 0.7[A] slowly?

I think the current will change as the junctions heat up to an
equilibrium temperature; I don't think that's avoidable...

Most resistor-based LED schemes are less than optimal.  A matter of
being within spec and "bright enough" rather than exactly AT some
spec point and optimal brightness.  That's one reason why there's
such a market for LED driver chips that achieve constant current at
high efficiencies...

BillW

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