Jim wrote:

>
>PS. What is the upper limit/frequency response of the human eye
>to 'impulse' or on/off cycled light sources?
>
The eye will blend light that is faster than ~30Hz, but depending on the
pulse width and the device emitting light you can detect flicker (given
no other aid or light source) up to ~45Hz (determined
experimentally/informally/non-scientifically) when the source is an LED
and the signal is a square wave of 50% duty cycle.

The flickering is also detectable when there are other light sources
which flicker - they beat against each other and produce another slower
more easily detectable beat.  This is one of the reasons viewing a CRT
under flourescents at a low refresh rate is so annoying.  You may see
the flicker out of the corner of your eye (where there are fewer color
receptors, and more rods).

There is a lot of information about this out there, though, and you'll
find some disagreement among different studies.

-Adam

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