uhh, yes, there is proof it is needed. Why else is it essential for iguanas, BTS, lots of monitors, and even many exotic geckos.
A friend of mine was telling me he had a female G. Vorax basicly on her death bed, laying on the ground, not eating, so he just lowered the UV lighting right up against the screen, and within a couple days, she was completely fine and healthy with no medical aid what so ever.
I think thats proof enough.
1.1 Gehyra Vorax 1.0 Golden Gecko 1.0 Oedura Monilis 1.1 Green Tree Frogs