🚀 go-pugleaf

"Jamie" <jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote in message
news:s9MTj.40$wj3.23@newsfe06.lga...
> 32 frames/Sec I believe is the minimum needed to prevent strobe flash in
> the human eye.. or some figure like that.

Depends on the nature of the "flash".  Film looks okay because it moves
quickly and smoothly between frames (at 24FPS).  A light scene moving to a
light scene without dark inbetween is a lot more pleasant than a really
bright scene flashed only every so often.  PWM LEDs will do that, because
they're very firmly either ON or OFF, within microseconds I mean.  You want
to minimize the apparent movement of a PWM cycle with respect to the eye's
movement, which might be...

Pffft... well lemme see here...  I can glance 60 degrees in 0.1 second
pretty easily, which is easily 10' travel at a distance of 8'.  An average
LED is 1/4" across, and you want to keep the "distance" between cycles
below a diameter or so.  The surface rate is around 100 FPS, or 1200 IPS,
or 4800 LEDs/s.  So the minimum duration is around 1/4800 LEDs/s = 1/4800Hz
frequency.  Which hey, that's pretty damn close to the earlier estimate in
this thread of about 5kHz minimum.  There ya go!  Of course, this frequency
can be lower for large LEDs, diffuse arrays, etc., or should be higher for
really close, fast moving stuff (uh, passing pedestrians a few feet away at
60MPH?!?).  And if nothing else, you can add a choke filter and recoil
diode (aka buck converter) to smooth out the pulses and get perfectly level
light output.  Hey, you could use an iron-core choke to justify the
switching loss savings of 400 Hz operation.  :^)

Tim

--
Deep Fryer: A very philosophical monk.
Website @ http://webpages.charter.net/dawill/tmoranwms