Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Flickering
Name: Hui H.
Status: Other
Age: 20s
Location: N/A
Country: N/A
Date: December 11, 2002


Question:
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?
Also, 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 monitors?
Are these comparable?



Replies:
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 light.

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 per second.

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.

Tim Mooney


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 30 frames/second.

Best, Dick Plano...



Click here to return to the Environmental and Earth Science Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (help@newton.dep.anl.gov), or at Argonne's Educational Programs

NEWTON AND ASK A SCIENTIST
Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory