Three zones, one long tank
A bearded dragon is a desert animal built around contrast. In the wild he basks on hot rock until his body reaches working temperature, then slips into shade to stop cooking, and your vivarium has to offer the same choice. Set the basking surface at one end to 100–110°F: that is the temperature of the tile or branch itself, not the air hanging above it. Around that end the air should sit in the mid-90s. At the far end, let the temperature fall to 80–85°F, and put a hide there so that retreating also means feeling hidden. Babies and juveniles run a few degrees hotter, basking at up to about 115°F, because small bodies heat and cool quickly and a growing dragon digests almost constantly. Adults are content nearer 100–105°F on the basking spot itself.
Building the gradient in practice
One heat source, placed at one end — that is the whole trick. A basking lamp over a slate tile or a sturdy branch at the warm end creates the hot spot, and the length of the enclosure does the rest, which is why a long vivarium holds a gradient far better than a tall, short one. Run the lamp on a dimming thermostat so the spot holds steady instead of swinging with the temperature of the room, and pair it with a proper UVB tube along the warm end: a dragon goes where the heat is, so the ultraviolet light needs to be waiting there too. Measure with tools that match the job — an infrared temperature gun for the basking surface, and digital probe thermometers for the warm-end and cool-end air. Stick-on dial gauges read the glass rather than the lizard's world and can be out by several degrees. At night the whole enclosure can drift down towards the high 60s or low 70s; a healthy dragon expects that drop and needs no night heating in a normally warm home.
What his behaviour tells you
A dragon using his gradient properly shuttles through the day: basking flat with legs splayed after a meal, gaping slightly at peak heat to dump warmth, then ambling down to the cool end as the afternoon goes on. Constant gaping, frantic glass-surfing, or hiding all day at the cool end usually means the hot end has overshot. A dragon who never leaves the basking spot, stays dark in colour, and digests slowly is telling you the spot is not reaching temperature, or that the cool end has become so cold he cannot afford to use it. Digestion is the clearest readout of all: a beardie who cannot reach his preferred body temperature cannot digest properly, and undigested food appearing in the droppings is a gradient problem until proven otherwise.
The vet threshold for this dragon
Heat problems creep up slowly, so treat appetite as your alarm. A dragon who stops basking, refuses food for several days outside of brumation, loses weight, or produces persistently runny droppings needs a reptile vet — and take your temperature readings along, because they are the first thing the vet will ask about. Burns are the other gradient emergency: a lamp a dragon can reach, or an unregulated heat rock under his belly, can scorch skin before he bothers to move, and any blistered or discoloured patch is a same-week vet visit. Keeping a simple written log of the three readings makes patterns obvious; on KinsLe, that log sits inside his Care Teams record, so the person who checked the cool end this morning and the person feeding tonight are working from the same numbers.