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# What is the critical flicker fusion frequency?

Wiki User

2009-04-19 22:32:56

By definition, the CFFF is "the highest or lowest temporal frequency, at a given percentage modulation, that can be resolved." (Schwartz, Visual Perception, 3rd ed.) In other words, the limits of distinguishing a flashing light from a steady one (at both the slow and fast end limits). Percentage modulation is calculated using the amplitude of the luminance of the light source, and the time-averaged luminance of said light source. In other words, the difference between the brightest/dimmest points in the cycle, averaged over the speed it takes to vary between the two points. Percentage modulation is used to calculate Relative Sensitivity, which is (1 / Percentage Modulation). For example: A lightbulb powered by Alternating Current (AC) is flickering. This is not visible to the normal human eye for two reasons (both variables in the definition of CFFF.) The temporal frequency of the AC in most American homes is 60Hz. The high temporal frequency cut-off for human sensitivity varies, and some cells are known to be sensitive to frequencies as high as 250 Hz, but for general daytime vision, it is lower than 60Hz. Also, the percentage modulation of a light bulb is low, since the change in brightness of the filament is very small. Relative sensitivity is the inverse of the percentage modulation. For flicker to be visible, a light source must have a relatively large change in level of brightness, and flicker at a rate within the human sensitivity range, somewhere between 2 and 50Hz. By definition, the CFFF is "the highest or lowest temporal frequency, at a given percentage modulation, that can be resolved." (Schwartz, Visual Perception, 3rd ed.) In other words, the limits of distinguishing a flashing light from a steady one (at both the slow and fast end limits). Percentage modulation is calculated using the amplitude of the luminance of the light source, and the time-averaged luminance of said light source. In other words, the difference between the brightest/dimmest points in the cycle, averaged over the speed it takes to vary between the two points. Percentage modulation is used to calculate Relative Sensitivity, which is (1 / Percentage Modulation). For example: A lightbulb powered by Alternating Current (AC) is flickering. This is not visible to the normal human eye for two reasons (both variables in the definition of CFFF.) The temporal frequency of the AC in most American homes is 60Hz. The high temporal frequency cut-off for human sensitivity varies, and some cells are known to be sensitive to frequencies as high as 250 Hz, but for general daytime vision, it is lower than 60Hz. Also, the percentage modulation of a light bulb is low, since the change in brightness of the filament is very small. Relative sensitivity is the inverse of the percentage modulation. For flicker to be visible, a light source must have a relatively large change in level of brightness, and flicker at a rate within the human sensitivity range, somewhere between 2 and 50Hz.

Wiki User

2009-04-19 22:32:56
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