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My son has a ceiling fan in his room and one Christmas, while he had blue snowflake lights strung up, we noticed that if we turned the fan on high with the blue lights on, we could see every blade.

Does the color of light effect the speed of the object your eye can see? I would love to know what was going on.

This is almost along the same lines as this post, but we've figured out a way for the eye to not see the blades as transparent:

Why does a moving fan seem transparent?

Thanks in advance

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  • $\begingroup$ Oh, by the way, this is almost along the same lines as this post: $\endgroup$ – jmt Nov 3 '16 at 2:21
  • $\begingroup$ Your previous comment doesn't have any link? $\endgroup$ – rob Nov 3 '16 at 3:12
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This is a known phenomenon, called stroboscopic effect. It is caused by the fact that you lights are emitting fluctuating light with a certain frequency, probably with the power net frequency 60 Hz (cycles/second) or the double, i.e. 120 Hz. Depending on the number of blades of your fan, the blades seem to stand still when the time between the light fluctuations corresponds to the time it takes for on blade to be in the position of the next blade.

You can also see this in movies when wheels or propellers are apparently standing still when actually moving due to the camera frames per second coinciding with the propeller frequency.

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