Originally posted by sfen
You are right! There is a difference, I first didn't notice.
But wasn't my explanation right?
In front of a screen, you are right about the stroboscopic effect
Yes, sometimes we see six fingers instead of five when we move our hand in front of tv screen with fingers spread apart. This happens due to the combined effect of the following two phenomena.
(a) TV Screen flickering @ 24 pictures per second with darkness
(b) Persistence of vision of our own visual system, which lasts for
approximately 1/10 seconds.
By the time one sequence of brightness is replaced , after the brief spell of darkness , by the next sequence of brightness, the fingers have moved to a new position. The first finger thus appears to the left( assuming the movement was towards left) of its earlier position and so on for each of the five fingers. But at the rightmost finger's older position,where it is no longer there , you still see a finger due to persistence of vision. Thus in all you see six fingers.
If the speed of the movement is very fast ,sometimes you can see seven fingers, due to this same effect.