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Reference.org
Flicker fusion threshold
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<p>The flicker fusion threshold, also known as critical flicker frequency or flicker fusion rate, is the frequency at which a <a href="/facts/Flicker_(light)/bF2d3VNL">flickering light</a> appears steady to the average human observer. It is a concept studied in <a href="/facts/Vision_science/M2ANjNn7">vision science</a>, more specifically in the <a href="/facts/Psychophysics/yDPmvvGf">psychophysics</a> of <a href="/facts/Visual_perception/g7Tfaq2l">visual perception</a>. A traditional term for "flicker fusion" is "<a href="/facts/Persistence_of_vision/JqdeCeVT">persistence of vision</a>", but this has also been used to describe <a href="/facts/Afterimage/C93egAYk">positive afterimages</a> or <a href="/facts/Motion_blur/e6zkU22k">motion blur</a>. Although flicker can be detected for many waveforms representing time-variant fluctuations of intensity, it is conventionally, and most easily, studied in terms of sinusoidal modulation of intensity. </p><p>There are seven parameters that determine the ability to detect the flicker: </p> <ol><li>the frequency of the modulation;</li> <li>the amplitude or depth of the modulation (i.e., what is the maximum percent decrease in the illumination intensity from its peak value);</li> <li>the average (or maximum—these can be inter-converted if modulation depth is known) illumination intensity;</li> <li>the wavelength (or wavelength range) of the illumination (this parameter and the illumination intensity can be combined into a single parameter for humans or other animals for which the sensitivities of rods and cones are known as a function of wavelength using the <a href="/facts/Luminous_flux/Sfya3RXh">luminous flux</a> function);</li> <li>the position on the retina at which the stimulation occurs (due to the different distribution of photoreceptor types at different positions);</li> <li>the degree of light or dark adaptation, i.e., the duration and intensity of previous exposure to background light, which affects both the intensity sensitivity and the time resolution of vision;</li> <li>physiological factors such as age, sex, and fatigue.</li></ol>