Coralvue DOES have dimmable ballasts for MH now. I'd be surprised if you couldn't dim T5's too. The dimmable MH ballasts that I was looking at take a 0-10v DC circuit to control the brightness of the ballast. I didn't look for dimmable T5 ballasts (I don't think they're even called ballasts, that shows how much I know about T5

)