Power-line flicker is a visible change in brightness of a lamp due to rapid fluctuations in the voltage of the power supply.
Flicker may also affect sensitive electronic equipment such as television receivers or industrial processes relying on constant electrical power.
[1] Flicker may be produced, for example, if a steel mill uses large electric motors or arc furnaces on a distribution network, or frequent starting of an elevator motor in an office building, or if a rural residence has a large water pump starting regularly on a long feeder system.
The likelihood of flicker increases as the size of the changing load becomes larger with respect to the prospective short-circuit current available at the point of common connection.
Long term flicker Plt is calculated as the cubic mean of several Pst values over a standardized two-hour period.