Since this thread started a decade ago, and is still getting responses up to just a couple months ago I had to join just to respond to this thread. You guys saying using a 1000 watt bulb to a 600 watt ballast is a bad idea...are you also saying I should never dim my ballast? Because I run my digital ballast at 600 watts which is it's lowest setting. You saying I should put a 600 watt bulb in even though the ballast is a 1,000 watt? Come on ppl I'm sure you have dimmed your ballast before. Same thing, 600 watt dimmed down to 400 you still use your 600 watt bulb also.