Magnetic chokes
Magnetic ballasts - compact and cost-effective devices that are suitable for "igniting" lamps from 250W to 1000W. It is recommended that ballasts be placed outside of smaller grow rooms, as they convert some of the electricity they absorb into heat and can thus contribute to an increase in temperature.
See: magnetic ballast for HPS and MH lamps, Tomax magnetic ballast , EuroGear Pro ballast , magnetic ballast 250W, 400W, 600W, 1000W and more.