Hello,
I have a few questions.
The first thing I was wondering is if that UV light fixture has a plastic shield over the light. If it does, you need to remove it. It is filtering out some of the UV.
What type of UV light are you using? (Brand)
How close to the UV Light can the dragon get? From the picture, it appears that he doesn't have a branch under the light allowing him to get close to it.
The dragon needs to be able to get within 12" of the light for the UV to be effective. The further away from the light he is, the lower the UV is that he can absorb. I would actually suggest he be able to get within 8" of the light. (Not the regular lightbulb. I am talking about the flourescent tube.)