On 27/02/2013 10:28, Arfa Daily wrote:

I got it originally from a long paper on driving LEDs for best
efficiency, from one of the big manufacturers' websites - though I'm
struggling to remember which one now, but it was one of the big boys
like Cree or Osram or Kingbright. As far as I remember, it had to do
with light output from the die being proportional to current, but if you
tried to feed it with a steady current that was high, heating became an
issue, and that this led to fairly rapid deterioration of the light
output. By pulse driving, you could force a current of several times the
maximum steady state current, through the die, producing very bright
'flashes' of light, without the problems of heat deterioration. This, I
recall it saying, could lead to 50% lifetimes of over 100,000 hours,
compared to as little as 10,000 from DC driving.

I'm sure that I downloaded the paper and archived it somewhere. I'll see
if I can find it.


Ah, Sounds like the kind of thing they do for infra-red comms type
applications where they keep the duty cycle low so they can drive the
emitter with high peak power. The detectors are fast enough to see the
short pulses so you get a big improvement in effective transmitter
power. I didn't think the human eye behaved the same way, but I could be
wrong...

Still, I guess it's something that'll only get used on mega hidh-end,
"ultra-reliable" lights. Probably not something I need to worry about on
Chinese cheapies.

Cheers,

Colin.