A perceived rapid fluctuation of a displayed image, usually one on a cathode-ray tube such as a television or computer screen. The threshold for perceiving flicker is dependent on the brightness of the observed light and the angle that it subtends to the optic axis. In television flicker prevents complete continuity of the images. In colour television flicker can result from either unwanted variations in the luminance signal – luminance flicker – or in the chrominance signal – colour flicker.