The flicker chart below shows one measure of how power disturbances can affect power users. At any point above the orange line, light flicker will be noticeable, while above the purple line people will begin to become irritated by the intensity and frequency of the flicker.

Flickering of the lights is a definite indication that there are voltage variations in the distribution system. While this chart is intended for use with incandescent fixtures, it may be applied to fluorescent fixtures with a suitable scaling factor, as fluorescents are not as sensitive to voltage variance.

The chart is not as accurate for high-intensity-discharge (HID) sources since a dip in the supply voltage does not result in the same reduction in intensity of the lamp output as it does with incandescents. Also, if the voltage dips too much, the HID lamp will completely extinguish-requiring it to restrike-while the incandescent or fluorescent lamps will immediately turn back on.

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