I'm glad I took the time to fix the scaly croissant's lizard enclosure sensors. I find the resulting nerdy plots quite interesting in several ways, especially the 3 temperature sensors.
The cool end sensor is an air temperature monitor in the rear left corner of the glass enclosure, and pretty much follows the ambient air temperature. Anything between about 21°C and 29°C is OK here for daytime, and down to 18°C or so is fine at night.
The warm end sensor also measures air temperature, but in the rear right corner of the enclosure, near the heat lamp. This is quite close to the air temperature sensor of the thermostat that controls the heat lamp, so the temperature measured here is fairly consistent and constant during the day. The actual temperature here doesn't matter very much, though
The basking temperature sensor in an infrared sensor measuring the surface temperature of Jerry's basking rock directly under the heat lamp. This is the temperature that's most important but it's also the one that varies the most, despite the use of a thermostat. The exact temperature isn't critical, but ideally it should be in the range 40-46°C.
The brief dips in basking rock temperature are a nice bonus of having this sort of sensor. They're an indication that a cool lizard has just plonked himself under the sensor to bask, so the frequency of dips in the data are an indirect indication of how active he's being.
The slower changes, on the other hand, are driven by changes in the ambient temperature in the room. When the room warms up the amount of heat escaping the enclosure decreases, the warm end air temperature starts to rise, so the thermostat turns down the heat lamp to compensate, and the basking spot temperature drops. It's important to have the thermostat's temperature sensor as close as practical to the basking spot in order to minimise this effect, but it's still pretty strong. Consequently, and counter intuitively, if I let the room get too hot them my lizard will end up with not enough heat rather than too much.
Ideally the thermostat controlling the heat lamp would use an infrared surface temperature sensor but all the commercially available ones just use an air temperature sensor. Maybe one day I'll make my own thermostat, with blackjack & direct surface temperature control.