i may be wrong, but the bulb doesnt know what size it is. almost all HID bulbs are able to run 120,240, or 440. its the ballast that matters. if you have a multi tap ballast you can rewire it for 120(if thats what your wanting to do).or like 4:20 said 'it may have a switch". if its not a multi tap then your stuck useing a 240 supply. but you should be cool with any 600watt MH bulb,,, (i think) lol