Originally posted by robvia
Your watts is set by your bulbs. If you hook a 100W light to a 400W ballast you still get 100W of light. The ballast just needs to be able to run at least the lights you have. It (the ballast) can be bigger, but not smaller. Hooking a 400W light to a 100W ballast will not work.
not true, a 100w ballast will overdrive a 65w bulb. You can exceed the bulb wattage to a point, get too high and POW! no more bulb. In addition, you can also underdrive bulbs with less wattage but the given example won't work, just too big of a difference.
anyway, this is just a ballast. It powers a bulb. you can add it but it won't do any good unless you add another bulb to your system