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

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

Original poster: Terry Fritz <teslalist-at-twfpowerelectronics-dot-com>

Hi,

White LEDs bombard phosphors with UV light to make the bright white 
light.  Just like a CRT or common florescent tube.  They probably flash 
well at 60Hz but they may indeed be poor for a strobe that need to turn on 
and off in significantly less than 1mS.  I wonder what the frequency 
response of white LEDs is?  but don't want to drag it OT...  I note that 
the new electronic ballast florescent lights that operate from 50 to 100kHz 
can destroy IR communications, so the brighter phosphores may be very fast...

Since I got the stuff to test it...  I just flashed my 1GHz fiber probe 
input with one of those key-chain style white LEDs.

http://hot-streamer-dot-com/temp/WhiteLED-1.jpg

and the answer is...

http://hot-streamer-dot-com/temp/WhiteLED-2.gif

literally, as quick as lighting at 165nS ;-))  So the frequency response of 
white LEDs is probably a few orders of magnitude faster than any strobe 
light needs :-)))


Cheers,

         Terry


At 05:16 PM 2/24/2004, you wrote:
>On 24 Feb 2004, at 13:10, 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?
>
>The persistence can't be great considering LEDs are used to convert
>electrical impulses to light impulses at GHz frequencies. Any
>perceived persistence is probably a function of propagation time from
>eyes to brain or some other physiological thing to do with the eyes.
>
>Malcolm