From: "Spehro Pefhany"
Subject: Re: What is maximum current for LED?
References: <email@example.com> <firstname.lastname@example.org>
User-Agent: tin/pre-1.4-19990216 ("Styrofoam") (UNIX) (Linux/2.2.14 (i586))
Date: Thu, 03 Oct 2002 15:08:09 GMT
NNTP-Posting-Date: Thu, 03 Oct 2002 11:08:09 EDT
The renowned Wouter van Ooijen (www.voti.nl) wrote:
>> As for pulsing the light so fast that it appears to be steadily on,
>> you are correct, this does not enhance the apparent brightness.
> So, in an attempt to kill a urban legend (which is, of course,
> - for *signaling* it is a good idea to flash a LED (optimal frequency?
> optimal P/P?)
I'm not sure there is an optimal frequency/duty cycle. It's easy to miss
very slow flashes. I suspect that a few Hz with perhaps 70% on time would
be optimal when it's important to pick it up fast. Maybe Win can dredge
some ballpark numbers out of his head?
> - for *illumination* flashing a *modern* LED at a high frequency (you
> would not want your illumination to flicker visibly, would you?) makes
> no difference (no good, no harm)
Ignoring the drive circuitry (which could be simpler or more complex,
depending), the additional I^2R heating in the LED could have negative
effects on the reliability of a LED run close to the maximums. At low
frequencies, possibly thermal fatigue failures of the die bond and
subsequent damage from overtemperature.
> I guess the same question will pop up within a week from now...
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