Question, I have a zoo med uvb/heat lamp 125w mercury bulb, (hung 12" above my Russian tortoise's shell, in a deep fixture). How much ground is that covering with uvb in his encosure? Anywhere the light casts a shadow? Just the area below in the basking area? I use uvb testing cards to make sure the bulbs are putting out uvb, but I'm not sure how far it's reach is.