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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]
The viewer does not see the transition, thus tricking the brain into believing a moving image is on screen. Modern shutters are designed with a flicker-rate of two times (48 Hz) or even sometimes three times (72 Hz) the frame rate of the film, so as to reduce the perception of screen flickering. (See Frame rate and Flicker fusion threshold ...
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 ...
These frame rates were enough for the sense of motion, but it was perceived as jerky motion. To minimize the perceived flicker, projectors employed dual- and triple-blade shutters, so each frame was displayed two or three times, increasing the flicker rate to 48 or 72 hertz and reducing eye strain.
The flicker of a CRT monitor can cause various symptoms in those sensitive to it such as eye strain, headaches [9] in migraine sufferers, and seizures in epileptics. [10]As the flicker is most clearly seen at the edge of our vision there is no obvious risk in using a CRT, but prolonged use can cause a sort of retinal shock where the flickering is seen even when looking away from the monitor.
Flicker (light), the study of directly visible change in brightness of a light source; Flicker fusion threshold, the frequency at which an intermittent light stimulus appears to be completely steady to the average human observer; Tachometer, an instrument measuring the rotation speed of a shaft or disk,
flicker fusion threshold floodlight focal length focus focus puller Foley artist follow focus follow shot followspot light forced perspective A technique which employs optical illusion to make an object appear farther away, nearer, larger or smaller than it actually is.