Well, my first thought is he wants his tan to be even so is exposing his underside to the light as well... Seriously, I don't know what is going on. Maybe someone with more experience will know. As for the hanging from the top of the cage and walking about like Sukei is, Timber does that also and it is not related to the light. Why? Who knows, but he does it at times. If I forget to raise the light when Timber is out of the cage, he will try to chew the fixture. I don't think it has anything to do with it being the light, I think it is "just because it is there" and he wants to get his beak on anything he can.
I think Timber likes his light. He seems to make a point of sitting in its range when napping or preening. When he is sprayed, he always makes a beeline for the light. Wish I had a better answer for you!