Chronology | Current Month | Current Thread | Current Date |
[Year List] [Month List (current year)] | [Date Index] [Thread Index] | [Thread Prev] [Thread Next] | [Date Prev] [Date Next] |
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.