Re: LED at 60 HZ? (was RE: Radio Shack Strobes)

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: Ed Phillips <evp-at-pacbell-dot-net> 

"Hi Terry, Dave

As an experiment, I built this simple LED strobe to compare it to my
xenon
flash tube based strobe which I have already built.  The xenon strobe is
built around a UJT based zero-crossing detector, an SCR and a trigger
transformer.

The reason I did the comparison is because of the inherent problems with
xenon flash based strobes - i.e. short run times, about 10 seconds max.,
before things start overheating and the strobe starts to flicker.  Both
the
tube, and the series load resistor on the xenon positive output gets
very
hot very quickly.

The LED strobe works reasonably well, but there is some smearing of the
image of the SRSG platter - about an inch or so at the platter
electrodes in
my case.  The xenon strobe leaves the platter image rock steady
stationary.

Is the smearing really caused by LED persistence, or is it something to
do
with the type of LED I was using (a water-clear ultra-bright 5mm red
LED)?

Regards
Ian"

	Smearing in this case is due to the length of the LED current (couple
of msec +/- ?) rather than any "persistance" in the LED.  The circuit is
quite adequate to measure synchronism, but not to freeze motion.

Ed