Ballast Function

In order to produce light, metal halide lamps ionize gas within an arc tube. Once an arc has been struck, resistance to the current flow in these lamps is virtually nonexistent. As a result, without a ballast to control the current, the lamp would be destroyed. For this reason, the lamps require a ballast to provide certain operating characteristics:

a) Starting Voltage: An H.I.D. lamp requires a minimum starting (open circuit) voltage to be applied to the electrodes to ensure reliable starting in normal and low temperatures. The ballast converts or transforms the line voltage to the voltage required to ionize the gas in the arc tube.

b) Regulation: Ballasts must provide operating characteristics as outlined by lamp manufacturers’ specifications and in accordance with ANSI specification C82.4. These criteria are to be met even though the line supply voltage varies ± 5% from nominal.

c) Current Crest Factor: Lamp current crest factor must be within a predetermined maximum in order for the lamp to provide rated lumen maintenance and lamp life.