Hi i am setting up a new bearded dragon setup for a baby, i have a 100 Watt UVB/UVA powersun bulb for him/her to bask in, how far away should i keep it from the tank? the tank is 12 inches tall thanks.
That may be a bit too intense.. how big is the tank? I personally wouldn't recommend having a MVB on any tank less than a 75 or 55 gallon.
I'd also recommend going for a tube light instead, this way you can control the two desperately rather than risking your beardies health by putting the light way too close and harming the reptile with an overexposure of UVB trying to get to correct temps as MVB's suck at heating.
At that range you may get pretty good temps, espially if the tank is small... but then you now risk overheating because small tanks heat up fast. You also risk overexposure of UVB at that height because of how close it is. And if you move it farther away your not going to get good temps.
Just use it for a portable basking spot, not a enclosure lighting source.