I bought a Lumtek electronic ballast yesterday, !k type but I can either dim it down to 600 or I can use a 600 or 750 HPS or MH bulb, I don't know if the 5x5 even with the nice inline fan I'm using will be able to handle a 1K though...the dude at the store had a used 1K MH he let me use to see what it does, now they are hotter than a HPS, just how much hotter I don't know. At 10 mins in with the outside room temp at 68 the tent was 73...going to check now, its been a half hour.