A transformer is an electrical or electronic component required by low voltage lamps in order for these to operate correctly. A typical transformer for lighting applications converts the supply voltage from 230V (mains voltage in residential buildings throughout Europe) to 12V, which is the typical voltage required by tungsten halogen lamps. A ballast or control gear performs a similar function of a transformer, but it also incorporates additional electrical and electronic components required by other types of lamps in order for these to operate correctly. A control gear is required by linear and compact fluorescent lamps, metal halide lamps, cold cathode lamps and LEDs. In the case of the LEDs the control gear is more commonly called driver. The secondary or output voltage of the ballast varies depending on the specific type of lamp it is serving.