You don't need to run out and spend hundreds of dollars here. I never worry about ambiant temps too much. Acurite thermometers (about 12 bucks) come with a probe. Just place the probe on the surface of the substrate at the warm end (mine are actually in the warm side hide). And, stick the unit at the other end on the glass and down low. The first reading on the acurite will be your cool side ambient temp (80), the second reading will be the hot side surface temp (90) and the third reading will be humidity (50-60). Heat lamps suck.... the humidity out. Plug your uth into a thermostat and set for as close as you can get to the above readings. Ambiant temps can be raised by insulating the tank. Humidity can be increased by covering the top. There are tons of great threads on the proper set-up.