Since the inception of electric lighting, the dimming and flickering of lights has been a reality for most consumers. In general, the main cause of these effects is switching operations of industrial processes and electrical appliances connected to the supply system. As shown in Figure 1, the current drawn by an appliance causes a voltage drop across the impedance of the electricity supply network, which results in a lower voltage supplied to the lighting system.

Electrical equipment can often have complex program cycles which cause the current drawn from the supply to fluctuate. For example, a washing machine will switch on and off current to heat the water; there will be a surge of current as the motor starts to turn and varying current as the motor speed is controlled. The fluctuating current flows through the network impedance and induces a voltage drop which changes at the same rate as the current.

Figure 1: Electrical Appliances Inducing Light Flicker

At particular repeat rates, these changing voltage drops can be sufficiently large that people can be affected by a flickering of the electric lighting in the office or in the home. The effects of this can range from minor irritation to a health risk, particularly for those who are prone to epilepsy.

The extent to which people find flicker annoying is the natural way to assess how a given piece of equipment effects power quality. The magnitude of light change has an obvious relationship to the perceived annoyance to the observer. The rate of fluctuation also affects people but its perception is more subtle; intuitively, a lamp flickering tens of times per minute will be more annoying than a lamp that flickers one or twice per minute or indeed one that flickers a few hundred times per minute.

The present trend towards improving the quality of the power supply has led electricity supply companies and regulatory bodies to recognize the problem of flicker and the proliferation of the type of equipment which causes these problems.

Regulating Flicker >>