Discharge lamps – e.g. fluorescent lamps – require a ballast. This is because ignition is followed by massive ionisation of the inert gas or metal vapour, which causes a surge in current in the lamp. This would destroy the lamp within a short time, so a ballast is used to limit the lamp current (also during operation).

A distinction needs to be made between conventional ballasts (CBs), low-loss ballasts (LLBs) and electronic ballasts (EBs). EBs are available in dimmable and non-dimmable designs. In energy-saving lamps, ballasts are integrated into the screw base; otherwise they form part of the luminaire.

Ballasts are classified by the Energy Efficiency Index (EEI). Energy-wasting CBs are no longer admissible (Class D ballasts since the end of 2002, Class C ballasts since the end of 2005).