Gary Coffman wrote:
On Wed, 15 Oct 2003 19:08:29 GMT, "AL A." wrote:
I am looking to build a "task" lamp (think dentist-type light) that uses
high output white LEDs for a friend who often does
work for extended periods of time in very remote places. I was looking at
the NTE electronics "lightwave" flashlights
snip
They must. LEDs don't have the thermal lag that filament type bulbs have.
So they can pulse the LED with a reasonably low duty cycle. If they use
a 5% duty cycle, they can get average current draw down to 2.2 mA while
still producing the same peak output as running continuously at 44 mA.

Of course *average* output is also only 5%, but the eye has persistence,
and is fooled into thinking it is seeing a much brighter light. Some strange
effects would occur for rapidly moving objects, strobing, but for nearly
stationary scenes you'd see about as well as if they were actually drawing
40 mA.

Vision doesn't work that way.
If it doesn't flicker, then it's strictly linear.
50ma 10% of the time looks just like 5ma.
The only exception is where the frequency is low enough to create perceptible
flicker.
Some LEDs have a small efficiency gain when run at high currents.
(most modern white or blue ones do not)

--
http://inquisitor.i.am/ | | Ian Stirling.
---------------------------+-------------------------+--------------------------
He had been eight years upon a project for extracting sunbeams out of cucumbers,
which were to be put in vials hermetically sealed, and let out to warm the air
in raw inclement summers. -- Jonathan Swift, "Gulliver's Travels" (1726)