I've had Marta under a T10 tube light in a fixture that is on top of a screen all the time that I had her (Changing it every six months), but I read that you should have a T5 if you want to put it on top of a screen. Should I buy her a T5?
T10 tubes are even weaker than T8 tubes at any given UVA & UVB rating and even in visible luminance.
Only suitable for VERY shallow tanks (about 12" tall). The dragon would need to get closer than 6 inches to get sufficient UVA & UVB.