Many people don't understand the need for 600W ballasts when 1000W units are not much more expensive. Those people aren't commercial growers. 400W is 40% less power than 1000W, so if your plants don't need the extra oomph of a 1000W ballast you're either wasting your money or actually making thigs worse by light-saturating your canopy and harming your yields.
Dimmable: 100%, 75%, or 50% power
Metal Halide and High Pressure Sodium Bulb compatible
Accepts 120v or 240v (Both cords included)
Allows 50-60 Hertz
Runs 15% cooler than most other electronic ballasts