Capacitors are fitted to luminaires that operate with discharge lamps either to improve the power factor Power Factor Correction (cf. Circuit Types) or to suppress radio noise voltage in the long and medium-wave ranges.

It is a legal requirement that luminaires that operate with fluorescent and compact fluorescent lamps be fitted with radio interference suppression for switch start operation. This is done by incorporating a radio interference suppression capacitor, which is connected in parallel between the phase and the neutral. The compensating capacitor provides the necessary radio interference suppression for luminaires with parallel compensation.