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The flicker fusion threshold, also known as critical flicker frequency or flicker fusion rate, is the frequency at which a flickering light appears steady to the average human observer. It is a concept studied in vision science , more specifically in the psychophysics of visual perception .
Impressions of several natural phenomena and the principles of some optical toys have been attributed to persistence of vision. In 1768, Patrick D'Arcy recognised the effect in "the luminous ring that we see by turning a torch quickly, the fire wheels in the fireworks, the flattened spindle shape we see in a vibrating cord, the continuous circle we see in a cogwheel that turns with speed". [8]
Up to about 80 Hertz or the flicker fusion threshold it is called visible flicker. From about 80 Hertz to 2000 Hertz it is called the stroboscopic effect (this article). Overlapping in frequency, but from 80 Hertz up to about 6500 Hertz a third effect exists called the phantom array effect or the ghosting effect , an optical phenomenon caused ...
To avoid brightness flicker, a double-bladed rotary disc shutter admits light two times per frame of film in 24 fps projection, resulting in 24 * 2 = 48 Hz, which is the lower brightness flicker fusion threshold.
In visual perception, flicker is a human-visible change in luminance of an illuminated surface or light source which can be due to fluctuations of the light source itself, or due to external causes such as due to rapid fluctuations in the voltage of the power supply (power-line flicker) or incompatibility with an external dimmer.
The frequency at which flicker becomes invisible is called the flicker fusion threshold, and is dependent on the level of illumination and the condition of the eyes of the viewer. Generally, the frame rate of 16 frames per second (frame/s) is regarded as the lowest frequency at which continuous motion is perceived by humans.
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