Im guessing that's 2x4x5 or something similar.. I have a 2x4x5 with a 125w qb that does well on its own.. The average high end watts per sq with qb's is about 25w per sq. That driver tells me that your lights are wired in parallel, and are probably pushing about 150w a piece. To dim the light, use the "IO" knob. Remove the plastic cover and use a screwdriver/knife to slowly dim it. And important tool to have when using qb's and drivers, is a wattage meter. Most drivers only dim to 50% so keep that in mind. Turning the dimmer as low as possible will only be 50% of the total wattage.. So if one light is running at 150w right now, turning the dimmer all the way down will get you 75w, if that makes since. If you haven't made any adjustments to the driver, im pretty sure it came out of the box set to more power than you actually need. But the only way to know how many watts your pushing is with a watt meter.. 10-25 bucks on Amazon.