This is a flickering effect which results in the apparent change in the speed of moving objects. This can even go so far as to make objects appear to be stationary or move in the opposite direction. It is caused by light pulsating at or close to mains frequency. Stroboscopic effects can occur when lighting is provided by discharge lamps. It can be remedied by phase-shifted operation (lead-lag circuit, connecting to a three-phase power network) or by high-frequency electronic control gear.