In lighting control circuitry, the power is sourced from the rectified AC mains as shown in the schematic. Pre-converters are also used in many ballast circuits and have a power factor approaching unity. The pre-converter supplies an output voltage that is regulated with very high accuracy. The filaments in florescent lamps require pre-heating followed by a very high start-up/ignition voltage to light the bulb. Once the ignition occurs and the lamp is conducting, the basic circuit appears as an inductor in series with a parallel resistor and a capacitor. Additionally, when the ballast section is operational, the current pump, consisting of the capacitor snubber and the diodes, limits the rise and fall time of the bridge output. The snubber is also used to reduce EMI.