The 1000 watt Cali grow light ballast is a dimmable ballast, which allows you to reduce your output voltage from 100% to either 75% or 50%. The benefit of this feature is that you can run either a 1000 watt, 600 watt, or 400 watt lamp with this ballast, HPS or Metal Halide. Although many growers will use this feature to reduce output of their 1000 watt bulbs, we do not recommend this use as the lamp life will be dramatically reduced. We have found our customers are much more satisfied when they purchase appropriate wattage lamps, either metal halide or high pressure sodium, to use with the dimmed ballast. These means you will use a 1000 watt lamp at 100%, a 600 watt lamp at 75% strength, and a 400 watt lamp at 50% strength. These features at this price is a bargain! Set the desired percentage on your ballast and then use the appropriate wattage lamp. It is compatible with every reflector we carry. The three year manufacturer’s warranty ensures long term trouble-free operation. A practical ballast at an economical price. Dimensions are 11.5” x 5.5” x 2.25”