I'm soon to run into that same problem. I've got a massive 75-gallon tank that Shaggy will move into in a couple months. Trouble is, it's pretty tall, too...so if I put the UVB lights on top, they won't reach him very well when he's down on the floor. I'm either going to have to find a way to suspend the lights from inside the tank...(I have to customize my own lid anyhow)...or make some really tall basking platforms and branches for him to climb up on. Not sure yet which way I'm going to go.

Maarken, I have two problems with the PowerSUN bulbs. One: It's a spot, like a basking lamp...so you don't get a good UVB exposure throughout the enclosure...which is ok in a small one, but not so good in a large one. And Two: They can get really hot. If you have to use a dimmer switch to control the temperatures, then you are also dimming your UVB exposure. So, my personal preference is to use two different sources for UVB and heat.