This makes objects look as if they are moving more slowly than their actual speeds – they may even appear stationary if the object is moving at the same rate as the flicker frequency (or a multiple of it). When objects move or rotate rapidly, they may be lit at or about the same position during each cycle or rotation. The light flicker may be detected by its stroboscopic effect. Flicker with LED lights may be more noticeable due to the fact that LED lights flicker between less than 10% and 100%, where as fluorescent lights dim to about 35% and back to 100%). Most people cannot notice the flicker in fluorescent lights that have a flicker rate of 120 cycles per second (or 120 Hz). This happens because the response to the light stimulus lasts longer than the flash itself. At this frequency – the critical flicker frequency or flicker fusion threshold – the flashes appear to fuse into a steady, continuous source of light. When a light is flickering at a frequency greater than 50 or so Hertz, most people can no longer distinguish between the individual flickers. The actual critical flicker frequency increases as the light intensity increases up to a maximum value, after which it starts to decrease. People can see lights flashing on and off up to about 50 flashes per second (50 Hz) – they are most sensitive to time-varying illumination in the 10-25 Hz range. It depends on the frequency of the flicker. Essentially, the power is turning on and off 120 times a second (actually the voltage varies from +120 volts to -120 volts, 60 times or cycles a second and is at zero volts twice in one cycle).
Lamps operating on AC electric systems (alternating current) produce light flickering at a frequency of 120 Hertz (Hz, cycles per second), twice the power line frequency of 60 Hz (50 Hz in many countries outside North America). The amount of light in the lighted area (ambient light levels).The kind of light – incandescent, fluorescent, LED (light emitting diodes), or HID (high intensity discharge lighting systems).How often and regularly the voltage fluctuates.The severity of the flicker depends on several factors such as: It is caused when the voltage supplied to a light source changes or when the power line voltage itself fluctuates. Light flicker refers to rapid or quick and, repeated changes in the brightness of light over time – light that appears to flutter and be unsteady.
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