Perceived brightness is proportional to average physical power output
of flashing light sources except for relatively low flash rates.
Above the critical flicker fusion rate (the flashing rate above which
the source does not appear to pulsate), the visual system responds
only to average power, not peak power. Consequently, there is no
perceptual advantage to pulsing LEDs at high rates. However, LEDs
themselves do not have output directly proportional to current, and
this fact can sometimes be used to improve physical power output by
pulsing. For example, if a particular LED has its highest flux output
per milliamp input at 100 milliamps, and the available current is
10mA, then the LED will have higher output pulsed 100mA with 10% duty
factor than operated with DC at 10mA. In other words, if you're
application requires operating the LED at an average current below its
point of highest efficiency, pulsing can be advantageous. On the
other hand, if you're trying to get the absolute maximum amount of
brightness from a given LED within its ratings, DC is always best.
This point has been debated thoroughly in sci.electronics.design and
elsewhere, and you can find more info he

http://www2.whidbey.net/opto/LEDFAQ/...Q%20Pages.html

Lighting for electronic cameras (as in the Stocker and Yale link) is
an entirely different matter. Flashing LEDs in sync with camera
frames is an obvious way to reduce power dissipation in the LEDs, but
there is no human visual parallel.

Paul Mathews


Old Nick wrote in message . ..
On Sat, 27 Nov 2004 08:03:59 +0100, "Meindert Sprang"
vaguely proposed a theory
......and in reply I say!:

remove ns from my header address to reply via email

"dazed and confuzed" wrote in message
...
I believe he wants to strobe them faster than the eye can percieve.
something like 50 hz would do it.

Ah, now I understand. But this has no benefits. A LED that is continuously
on at, say 20mA, will appear to have the same brightness as when strobed
with a 20% duty-cycle (1/5 of the time) at 100mA (5 times the current).

Meindert



Actually not quite. If you talk energy consumption then you are right.
But you can viciously overdrivve LEDs to get far more brightness out
of then than they normally can give.

see:
http://www.stockeryale.com/i/leds/lit/app001.htm

There is also argument that your eye and brain think that the led is
still alight and this can fool you into seeing a brighter LED. I would
reckon this would work best for LEDs being looked _at_, rather than
thiose used as a source of illumination.