IDK. :dontknow: Z's basking surface (T5 10.0) is 9" from the bulb. The UVI @ surface is 3.0. One inch higher--the average height of his back while lying on his belly basking--the UVI is 3.5.
I should know whether UVI values are geometric, algebraic, or logarithmic, but I don't. I know they are what they are, and AFAIK, should fall between 3.0 and 4.0 for BDs. (Please correct me if wrong.)
I would also think that UVI zones with a T8 would be condensed somewhat (more so/less so with other types of UVB bulbs), but perhaps not enough to get pedantic about (as I am wont to do :roll: ).