Magnetic Ballasts
Magnetic or coil grow light ballasts have been traditionally used to power High Pressure Sodium and Metal Halide grow lamps for many years now.
The magnetic ballasts convert mains electricity into the correct voltage and wattage to power the grow light bulb. When buying a magnetic ballast to power your grow light bulb you will need to match the wattage of your grow lamp to the ballast wattage or incorrect matching can lead to your grow light not working or at worst an electrical fire. Make sure when running traditional magnetic ballasts that you place them some where safe and that will not be a fire hazard as magnetic grow light ballast normally run pretty hot so place them on a fire proof surface with plenty of ventilation around the magnetic ballast.