I've never had an aquatic turtle before, I'm not sure what kind of UVB bulb would be best for the little dude. Does it matter if it will be sitting on top of a screen lid?
I've never kept painted turtles, although I've kept mud and musk turtles in aquariums indoors and a tortoise outside.
I'm not sure what to suggest, since I don't know much about the painteds, but I'm hoping some more knowledgable people will be along soon!
I've been using the Zoo Med PowerSun 100W UVB suspended just above a black metal screen lid, for my three-striped mud turtles (in their 20 long tank) and for our year-old bearded dragon (in a 40 breeder tank).
The black metal screen lid does reduce the amount of heat and UVB that gets to the basking area in the enclosure, but I take that into account. In other words, I would probably go with a lower wattage bulb (or a greater distance from the basking area) if it were an open top tank.