175 Watt Electromagnetic M57 4-Tap Metal Halide Ballast KitHigh Intensity Discharge (HID) lamps require a ballast to apply starting voltage to the lamp and establish current flow an arc between the lamp electrodes. Without a ballast, the arc will extinguish or draw increasing current until some circuit element burns up. Ballasts provide system stability by limiting the current that can be drawn. Core and Coil metal halide HID ballasts are used in over 90% of all HID lighting. Replacement ballast kits contain