I'm actually not using mine. Bought it last year on the black Friday sale and haven't had a use for it yet. Exo Terra makes a lamp that fits in that plastic frame on top. It's only 7" across and made specially for these cages. You can fit 2 of them in each part of the frame if you needed to. This fixture holds up to 150w just like your 8.5". The catch us that this fixture is 29.99$ at PETsMART. It's actually on sale right now for 23.99$. I know because I'm a PETsMART employee.