So you want something that dims on it's own. This functionality is going to cost you. There are LED
vendors here that are sponsors for this site who can hook you up with whatever you need. AQ-LED
is one of them. Scroll up to the "vendor spotlight" and you'll find his store.
There are a few others I have heard good things about-
Aqua Illuminations SOL Blue
Though very expensive, any one of those will allow you to do virtually anything.