Bearded dragon basking setup

Three variables, not one

A basking spot is usually adjusted by swapping bulb wattage. That is the least precise of the three controls available:

Use the thermostat for the fine control, the height for the coarse control, and pick the slab once.

The slab

Flat stone, slate or tile. Three reasons: it stores heat so the animal gets radiant warmth from below as well as above, it gives you a flat defined surface to point an infrared gun at, and it sits level without sinking into the substrate if you bed it on a clay-containing mix.

It should be the highest point in the enclosure and directly under both the heat lamp and the UVB fixture, because the published UVB distances are measured to the animal's back at the basking position.

Setting it, step by step

1. Place the slab at one end, as the highest point, on a stable base.
2. Mount the halogen lamp above it in a guarded fixture, mechanically secured.
3. Put the thermostat probe at the slab surface, secured so it cannot fall off - a loose probe is the failure mode that drives a lamp continuously.
4. Set the thermostat conservatively low and let the enclosure stabilize for an hour.
5. Take an infrared reading of the slab. Raise the setpoint in small steps until the reading sits in the 108-113 F (42-45 C) surface temperature band.
6. Check the air temperature in the basking area with a probe - a warm surface with cold air does not work, and air that is too hot causes heat stroke.
7. Check the cool end reads 77-85 F (25-29 C) surface, 72-99 F (22-37 C) air gradient. If it does not, the enclosure is too short for the lamp you are running.
8. Mount the UVB at its published distance measured to the animal's back on the slab.

Zone size, not just temperature

A narrow spot produces a hot patch the dragon cannot fit on rather than a basking site. The slab should be large enough for the whole animal, and if a single lamp cannot heat that area evenly, two lamps placed close together is the published approach for larger enclosures - it is how the ball python guidance handles the same problem in a 4 ft enclosure.