(4) QUANTUM 600W Watt HPS & MH Dimmable Digital Grow Light Lamp Ballasts | QT600 Run at 100%, 75% or 50% power Strike both Metal Halide and High Pressure Sodium Bulbs Accepts 120v or 240v (Both cords included) Allows 50 Hertz to 60 Hertz Runs 15% cooler than other digital ballasts on the market