Originally Posted by tomcannon
But that's not right, they should be in the cool end! I'm joking with you! If we've all got temps that are correct then what's the issue.
The reason some people place the stat probe in the cool end is because many thermostats are badly designed for running bearded dragon vivs. The temperature scale doesn't go high enough to control the hot end properly. Somebody realised that a way around this is to place the probe in the cool end - and this has become adopted as "the way to do it". However, it isn't the best way to use a thermostat.
A thermostat is a simple device (God knows why they are so expensive - but that's another issue!). There are various ways they control the heating element, but the principle is most easily illustrated with an on/off device.
If the stat probe is in the cool end, the heater will continue heating until the set-point temperature is reached in the cool end. By this time, it could be very hot in the hot end. The thermostat would then cut the power, but since it is now very hot at the warm end, the heat continues to drift towards the cool end due to the high thermal gradient that exists. It therefore takes some time before the cool end drops back below the thermostat's lower set-point temperature, which switches the heat back on. Crucially, during this time, the temperature in the cool end can rise significantly above the thermostat control value. The further away from the heat source the probe is, the worse this effect becomes.
In order to control a heat source properly, the thermostat probe needs to be fairly close to the heat source. A good compromise (because thermostats are mostly rubbish designs) is to place the probe in the warm end, but not in the basking spot.
The whole set-up is a compromise to be honest. The long, but narrow shape of most vivs helps us with setting up a gradient, though. Ideally, we would also fit a cooling system in the cool end as well in hot weather, but since it is very rare that this is a problem in this country, most people don't do it.