This depends on what you are looking to do, Some people have shoved some chaeto in there with submersible lights or had a small pendent or light suspended above. I have not however heard of any success or for that matter failures with those magnetic lights that you attach to the back.
Here is a pic of mine. I had a LED Pendent above and mangroves and chaeto. Now in the Pics you can just see the Mangroves, but before I upgraded, it was pretty awesome to have them shooting out of the back. I just took the back lid off. As you can see it created some light spill but it had an interesting effect.
