I have one but with two heat lamps instead of a UVB bulb. I have two so on extra hot days I can turn one bulb off so my cham don't get to hot.
I have the dual dome fixture housing two heating bulbs as well, although my reason is a little different.... One of the bulbs is a 60 watt incandescent, and the other side is a 100 watt incandescent plugged into a dimmer switch so I can manually adjust it up or down to make the combined temps of the two bulbs at 90 degrees +/- 2. Now, the reason I have two bulbs instead of one to achieve this, is because I used to only have one heat bulb on my cage but I've came home from work in the past, twice, to a heat bulb that stopped working at some point during the day and a cold chameleon. I mean he was fine, he was just not able to bask how he wanted ya know?
So now I use the two heat bulbs, in case one of them ever goes out, there is at least SOMETHING putting some heat onto his basking spot for him and he won't be cold. The 60 watt alone does not achieve the temps I want but it gets a little close, and I leave it on full blast, all the time. I didn't want a stronger bulb because on days the room temp fluctuates by 5 or 6 degrees, that basking spot temp will also rise or fall with the ambient room temp, and with a stronger bulb, that might make for a hotter-than-wanted basking spot at times. So I use the 60 watt on full blast to get the temps close to what I want, within about 8-10 degrees. The other bulb is my 100 watt and it's on a dimmer switch. I use it to make the basking spot a perfect 90 degrees, give or take a degree or two. The temps at my place fluctuate by about 5 degrees from morning lights on to evening lights out, depending on how warm it is outside during the day and how cold it got at night to let the place cool down. Never higher than 74 inside though during the day because my central air will kick on. So on colder days where my room temp is going to be a bit cooler, I just adjust the dimmer up a bit and make that 100 watt bulb a little hotter. On warmer days where my room temp might be a little more towards 74 degrees, I adjust the dimmer down a bit and make the 100 watt a little cooler. Works like a charm, and I can always have my basking spot within a couple degrees of where I want it, at all times, no matter how cool or hot the ambient room temps get. That, and I found that, with only one heat bulb, you could have a bulb that was the "perfect" basking temp, but if you opened a window or turned the heat or AC down/up 5 degrees... the ambient room temp changes, which in turn affects the basking spot temp... so you could never have that "perfect" basking spot temp.
Not that it has to be "perfect" at all times because in the wild, the temps from day to day fluctuate. I have two heat bulbs simply for the fact I stated that - I don't want to come home to a cold chameleon again. It happened twice, and it actually happened again, but not even to my own chameleon. I was cham-watching Kaliko the panther chameleon for my buddy Nick a couple weeks ago, when Nick was gone for a week or so... and one day I went to his house to check on it like normal and the heat bulb was blown out. Little dude looked cold, just like how my own cham looked when it happened to me. And you have no idea of telling how long that heat bulb has been out either unless you were there to watch it blow out. Cold is not particularly a good thing when you are wanting to feed them or when they are wanting to digest. 2 heat bulbs fixed that problem.
As for UVB... I use a quad fixture with a 22" UVB and other bulbs in it as well.
