A Metal Halide Ignitor used to provide this additional voltage for a very small amount of time 1 to 5 microseconds. The voltage required to initiate the arc discharge on most high-pressure sodium lamps and some metal halide lamps is greater than the ballast open-circuit voltage. The mercury lamps do not require ignitors and the two distinct types of ignitor SUPERIMPOSED and IMPULSE. It offers SUPERIMPOSED the ignitor is situated less than 2m away from the lamp and works independently of the ballast – one wire of three to the ballast and IMPULSE the ignitor is situated more than 2m from the lamp. The winding of the inductive ballast is used to generate the required pulse voltage – two wires of three to the ballast.