Perceived dimming (pulsing) of lights, usually due to rapid small changes in voltage on a distribution system. Flicker is also the term used for intermittent light dimming. EG: a large load goes on, the voltage sags for the duration of that load operation, and the lights dim, then brighten again when the load goes off. While not physically harmful to personnel, flicker can be very annoying. Due to the fact that the human eye can easily detect very small changes in light level, flicker is of great concern to the power quality industry.