[time-nuts] time-nuts Digest, Vol 98, Issue 77

[Dan Kemppainen]

On 9/18/2012 1:48 PM, time-nuts-request at febo.com wrote:
> In the old CRT type TV sets, the phosphor has some persistence.
> Movies are modulated with a square waves, the frame blinks off and
> goes dark then blinks on.   But the LED's brightness is fast enough to
> track the sine wave and would be bright only for an instant with quick
> pulses of light.
>
> But just as bad as the flicker is that the LED is wasted and spends
> most of the time being dim.
White LED's have phosphor in them also. That's how they convert the 
typically blue output to 'near full spectrum' white. I'm not sure 
about persistance in them though. I have some Cree XML's around here, 
and may try to see what a Photodiode can see when bursting them with 
PWM at various frequencies.

  I believe this also allows PWM dimming at relatively low 
frequencies. (<--- See, frequency is time related ! :) )

Dan