It depends on the Ballast manufacture. The ballast in the Orbit fixtures are Work Horse 5 or 7 and if you go to there website they have multiple wiring diagrams for T5HO, VHO and Compact Fluorescent lamps. Most ballast are self leveling(Not sure if that is the right terminology?) In other words you can run up to a cetain amount of wattage of lamps as in 1 96 watt CF or 2 65w or 2 T5HO. If your ballast isn't listed for multiple lamps, just because it works you could cause an electrical fire down the road.