Flicker is a visually perceptible disturbing effect that occurs with periodically repeating image displays. It occurs when the repetition rate of the periodically displayed images falls below a certain value. In this case, the inertia of the eye, the so-called afterimage effect, can no longer compensate for the flicker effect that occurs.
The repetition rate depends on the light. In bright light, flicker can be perceived at a frame rate of 50 Hz to 60 Hz; in darker light, the repetition rate is about 20 Hz. In addition, the perception appears more pronounced with uniform large- area image areas and large screens than with small image details. This is referred to as large area flicker. The lower limit at which the human eye integrates periodic sequences to form a moving image is around 20 frames per second. Accordingly, movies are displayed at 24 frames per second, television at 25 or 30 frames per second, and monitors at 60 to 100 frames per second. In the case of television, the interlaced scanning method simulates a higher repetition rate for the eye.
To achieve flicker-free viewing, the refresh rate can be increased until the flicker effect has completely disappeared. The refresh rate must be at least 75 Hz. In television technology, 100 Hz technology and sometimes also 200 Hz technology are used, with which 50 or 100 full frames per second are displayed.