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In article <2427@ttidca.TTI.COM> hollombe@ttidcb.tti.com (The Polymath) writes:
|According to my psych. course in Sensation and Perception, under ideal
|circumstances the maximum flicker rate detectable by the typical human eye
|is about 60 hz.  That's why projectors in movie theaters open and close
|their shutters 3 times per frame, yielding an undetectable flicker rate of
|72 Hz (and why movies were called the "flicks" before they discovered that
|trick).
|
|Therefore, if fluorescent tubes strobe at 120 Hz, they can't be causing
|your headache problems.  Your eyes are physiologically incapable of
|detecting the flicker.

I think this is more of an average and may be affected by "point of
view".  For instance, I can quite definitely detect a flicker in
florescent lights and also with color televisions.  While this flicker
is undetectable when I'm looking right at the source, it is
periferally detectable.  It's a tremendous annoyance when you're
talking to someone over a glass-topped display case that's lit
internally (such as at a jeweler's).

One way to see if something is producing a slightly out-of-visibility
flicker is to wave your hand quickly in front of it.  If you see
multiple images of you hand, it is.  Under sunlight you will see a
continuous motion.  Try it in front of a color television in a dark
room.

Worse (I think) than flickering is CRT noise.  No one seems to care
that about 10% of the population (my estimate based on experience) can
hear most CRTs the entire time they are on.  This is terribly
annoying!  On the plus side, it enables me to find equipment that is
left on at night by walking around and listening.

jim frost
madd@bu-it.bu.edu