If you have a MegaRay or other MVB, the recommended distance for the 100w bulb is 12" from the basking spot, for the 160w bulb, its 18" from the basking spot. You will probably need to purchase both bulbs, experiment with them and basking spot heights. I have found the best thing to use for basking spots is Slate, it retains heat very well, and if you elevate it on two pavers, it can double as a low hide for the Uro.
I hope that answers your question.

