[sdiy] The Humble LED.

[Theo]

There are  HP/Alligent (sp?) application notes on pulsed led use.
Application brief # I-024, # D-007 and AN 1005 (sorry no links )
According to these documents a pulse frequency below 1khz lowers the
efficiency of the LED.
The pulse frequency of 1khz or more is needed to keep the junction
temperature of the LED on level.
Tables and formula on current & pulse duration vs. apparent brightness vs.
lifetime are also in there.

HTH
Theo


----- Original Message -----
From: Batz Goodfortune <batzmanx at all-electric.com>
To: <synth-diy at dropmix.xs4all.nl>
Sent: Saturday, July 12, 2003 5:55 AM
Subject: [sdiy] The Humble LED.


> Y-ellow All.
>          I have this crazy idea. I think it's been done before but for
> power saving rather than brightness. I want to get real light out of an
> array of LEDs. (Yellow in this case) I've pushed the array to the limits
of
> reasonable reliability (IE:35mA per LED) but still it's not bright enough.
>
> I would assume, rightly or wrongly, that heat is the killer with these
> devices as with many other semiconductor materials. I remember that one of
> the things Sinclair did when he (allegedly) invented the digital wrist
> watch, was to pulse the circuit. The LEDs were not on 100% of the time.
> Though I have no idea of the duty cycle. For him, it meant the same
> brightness but for a fraction of the battery usage. I'm thinking the
opposite.
>
> In theory, should I not be able to pump significantly more current through
> the LEDs so long as that current was pulsed. Like a LED bike tail light.
> I'm thinking here about 50% duty cycle @ 3 or 4 Hz and pumped at between
60
> & 80mA per LED.
>
> The reason I'm putting out this general question is that I can find no
> precedence for doing this. Other than some very expensive and specialized
> LED technology that's now kicking round.
>
> Does anyone have any compelling evidence or caveats they'd like to share?
> I'd most appreciate it.
>
> Strangely, this is the first time I've ever been able to feel any heat
from
> a LED. Or should I say, a slight warmth. It's winter time and I can just
> feel a bit of a warmth in the glow. I guess I've been a fairly
conservative
> LED user up until now but I'm also figuring that with every extra mA at a
> constant on-time, the reliability and longevity of the devices will be
> reduced. The only good thing about incandescent bulbs VS a LED array is
> that at least Bulbs are easy to change.
>
> Anyway, before I go to all the trouble of building up a triple5 (or
> something), I just thought I'd ask if someone has any experience or
> knowledge of doing this kind of thing.
>
> Thanks very much in advance.
>
> Be absolutely Icebox.
>
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