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> 

Tesla list wrote:
 >
 > Original poster: "Daniel Kline" <daniel_kline-at-med.unc.edu>
 >
 > An engineering friend says a high-brightness LED on a
 > low-voltage transformer, like 6 Volts, connected through
 > a suitable resistance, should flash at 60Hz in sync with
 > the 60Hz mains. (50Hz for you all over there :)
 > It seems too easy to me...he thinks that the LED may have
 > a "persistence" issue. In other words, just because it
 > turns off quickly doesn't mean it stops emitting quickly.
 > Comments?
 > Thanks,
 > Dan K

	It will work just fine; "persistence" is measured in fractions (small
ones) of a microsecond at most.  Of course, the light will last for
around 8 msec each cycle so you'll get a pattern as with a neon lamp or
a fluorescent lamp.  I have a simple little stroboscope I built using an
NE555 timer for a variable frequency source pulsing three high-intensity
red LED's from Radio Shack.  Use a transistor to drive the LED, with
series limiting resistor.  Works quite well and plenty of light for my
purposes, running from a 9V "transistor battery".

Ed