Yeah it can run at 250 - 400 - 600 so i can dim it and put a 400w bulb in. I can dim a 600w bulb but then it wont put out the correct par
I have 2 of these, one set at 250 with a mh bulb in the veg side and the other at 600w with the hps, i also kept my old 600w magnetic as a spare in case one of them stops working and needs to go back under warrenty.
http://www.hydroculture.co.uk/sunmaster-600w-digital-ballast
"The ballast will power 250W, 400W or 600W HPS or Metal Halide bulbs and includes a boost mode that increases output to 660W which is really beneficial during the flowering/fruiting phase. Be sure to pair the correct lamp to the output selected, so don’t be tempted to run a 400W lamp at 250W for example. This will save energy, but is a pretty pointless exercise as your plants will not receive the full PAR (usable light) range."