How can I improve my bearded dragon's enclosure?

Well, it depends on the actual lamp and the actual reptile. Most of the high end aquarium lighting & "full spectrum bulbs" doesn't produce any UVB, which is specifically what we are talking about here. That is light waves above the visible light spectrum to humans, from 280nm - 315nm. Replies in particular benefit most from rays between 295nm - 305nm for vitamin D3 production. And with certain lizard species that really can't be replaced by dietary D3 supplements. They will still end up with a hist of problems, the worst being metabolic bone disease (MBD).