Name: Hui H.
Date: December 11, 2002
I know that lights blink on and off 60 times each second
and that flicker is not noticeable. Incandescent lights especially
appear steady but fluorescent bulbs sometimes appear to flicker. Also
monitors flicker at a refresh of 60hz. What is flicker noticeable on
monitors and fluorescent bulbs but not on a incandescent bulbs?
what is the human visual persistence cut-off? I hear it's 60hz in
physics class but hear it's about 70-85hz when people talk about
Are these comparable?
Incandescent lights do not appear to flicker because they do not flicker.
Although the current going through them rises and falls, it changes too fast
to really affect the temperature of the filament, which is what makes the
The human eye can notice a change of about 1/20 second. Motion pictures
change at a rate of about 25 frames per second, and television at 30 frames
Richard E. Barrans Jr., Ph.D.
PG Research Foundation, Darien, Illinois
The filament in an incandescent bulb cannot cool off quickly enough to
flicker at 60 Hz.
Human visual persistence is variable, depending on the person, the
conditions, and the image.
The reason that incandescent lights do not flicker is that the filament
is heavy enough that it does not cool appreciably in 1/120 second
(60 Hz power has two maxima each cycle as the electricity rushes back
and forth). Fluorescent lights and monitors emit light from
individual molecules which stop emitting light immediately that the
voltage on them reduces below a certain point.
I have always heard that human visual persistence is of the order of
1/30 second, which is why movies (and television sets) show close to
Best, Dick Plano...
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