A standard PAL television will refresh the picture at a frequency of 50Hz or 50 Frames Per Second (FPS). The Frames Per Second are the number of frames needed to create the illusion of movement. On a 50Hz Cathode Ray Television (CRT), because the picture was produced by an electron scan, there was a visible flicker that could be detected by the human eye.
Our eyes are often aware of this frequency of picture change depending on the...