All my lizards have always had the Reptisun 10.0 tubes....first was T12...then T8. Now (in Canada) T8s are being phased out and are no longer readily available. With my T8s they are at a distance of 6 inches on top of the screen top. I am now getting T5s using a Sun Blaster ballast which is mountable. If I place this on top of the screen should my distance remain the same. I could also potentially mount to the inside of the vivs. What should the distance be then....10 inches or 12 inches from basking. 2 vivs are 75 gallon...one is custom 2ft H by 18in W by 36ft L and the other is a 40 gallon breeder.
The T5 will be a very nice upgrade. If it's shining through a mesh top I'd mount it about 10-12'' above the main basking area. The amount intercepted depends on how fine the mesh is though. If you mount it inside the tank, 12-14'' is about right. You can have some areas (branches etc) allow closer access but you also want some shade areas away from the bulb too so you have a nice gradient to choose from.