No problem. I'd say its worth a shot, if the top is completely open it probably will hold an ambient close to the room its in to be honest, the bulb may heat it a bit. I know that when I open both doors on the front of my cage it drops a couple degrees, but still stays higher then the ambient of the room. I know opening the front isn't the same as opening the top per say since the heat will still get trapped in the on the ceiling. The other reason I stayed away from MVBs is because I would go broke buying them haha. My T5HOs say that the bulb can be more than 2ft away and still deliver UV, that being said I don't currently have a meter so I can't give you any hard data, just going off what I have read about the fixture and bulbs. The only other thing I would check is do the MVBs have a "replace by date"? I know on regular UV bulbs they say replace every 6 months because the UV output drops drastically, even if the bulb is still turning on. Not sure if that is the same with MVBs or not to be honest but may be worth researching, down here they are pretty pricey.