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Re: prove it objectively



Clarification! My posting is most unclear. When I refer to trying "the
experiment" in a room with only fluorescent illumination I mean *without*
illumination from a computer display! Just shake your finger between your
eyes and a blank wall! The effect goes away, of course, because the
flicker fusion frequency (~15 Hz) is less than the frequency (120 Hz) of
the variation in luminance.

Place your hand, fingers open, between your face and the computer display
screen. Shake your hand gently. You are looking at a stroboscopic effect.
Do the same thing with one finger only. The effect is still there. Now
try the experiments in a room with only fluorescent illumination. The
effect seems to be there when I shake all the fingers, but it goes away
when I shake one finger. It is not as good an effect (if there is an
effect at all), and I think the reason is that the motion stopping effect
depends on there being a shutter speed or flash interval shorter than the
period of the illuminat - a smooth sinusoidal variation won't do.

Fluorescent lights give only a weak effect. The computer display works
because the phosphor persistence time is short compared to 1/60 s (or
1/75 s in the case of my display). An experiment I did last year is
illustrative of a related effect I think worth relating to the group.