I always thought that it is the colour sensing cells in your retina that is
making those 25 frames/sec forms a continuous moving picutre.

The pigments reacts according to the intensity of the light, i.e. it takes
time to react, thereby giving the image persistence.

When light intensity falls below a certain threshold, these pigments fails
to react altogether. The other light sensitive cells becomes dominant,
giving you black and white vision at night.

On the other hand, the flickers you see on computer monitors are due to
interlacing, where image is displayed on alternate lines at a lower
refresh rate (say 35Hz) and filled in on the second pass, giving you a
virtually doubled refresh rate (70Hz). However, these "filling in" of the
picture is not perfect and is noticeable as flickers.

You can minimized this flickers by adjusting the size of the displayed
area, i.e. the smaller the less flicker, confirming that the flickers
are due to errors in the "filling in" process.

Rgds,

Peter Tiang
Design Engineer
Design & Applications Laboratory
Hitachi Semiconductor (M) Sdn Bhd