Horti Gear 400w Magnetic Ballast class leading magnetic ballast Theses fixed power magnetic ballasts are thee leader of the pack when it comes to power and stability. Without a ballast to regulate voltage, compact fluorescent lights and high-intensity discharge (HID) lights uncontrollably draws so much current from a high-voltage source all at once that they will often overheat and burn out within seconds. Magnetic ballasts have been around for years and basically use an electromagnetic system to regulate the voltage of the lighting. They have a 92% energy efficiency and incorporate a 10a fuse for old bulb and surge protection they put out a true 400w to HPS lamps as well as metal halide.