Basking setup for dehydrated bearded dragons

Bad lighting is the most common husbandry mistake with bearded dragons — incorrect UVB or basking temperatures cause metabolic bone disease and chronic illness that many owners don't recognise until significant damage is done. You've got a dehydration history to factor in as well, which makes getting the basking setup right even more important — too much radiant heat from the wrong bulb type will pull moisture out faster than the dragon can compensate. To help properly: what size is the enclosure, what bulbs are you currently running (brand and wattage), and how old is your dragon?

Your UVB is solid — the Reptisun T5 HO 10.0 is the right choice for a 4x2x2. The problem is almost certainly that unbranded 100W spot bulb. Cheap ceramic or standard incandescent spots emit a very broad, unfocused heat that bakes the ambient air around the basking zone, raising overall enclosure temperature and humidity-stripping the air without giving you a tight, controlled hotspot. For a 3-year-old adult in that enclosure you want a basking surface temp of around 40–42°C and an ambient cool side no higher than 27°C. Is she actually hitting those numbers currently, and where are you measuring — surface or air?

That's the gap — air temp of 38°C on the warm side is too high and it's exactly the kind of reading that masks what's really happening. Surface temp at the basking spot could easily be 48–52°C with a diffuse cheap bulb, which is dangerously hot and extremely desiccating. A tight halogen flood rather than a broad-spectrum spot is the right switch here. Halogens produce a dense, focused beam of radiant heat — the dragon absorbs it directly, the surrounding air stays cooler and less dry, and you get far more predictable surface temps. The one I'd recommend is the Arcadia Halogen Basking Flood 75W. It's specifically designed for reptile basking, gives a focused hotspot without cooking the ambient air, and in a 4x2x2 it typically lands your basking surface around 40–43°C when mounted at the correct distance. Pair it with a dimming thermostat if you haven't already — that's the final piece that protects against temperature spikes that would worsen the dehydration risk.

The halogen swap is the main fix on the lighting side. Keep the Reptisun T5 HO 10.0 exactly as it is — that's doing its job. On the dehydration front: make sure she has a shallow lukewarm bath two to three times a week for 10–15 minutes, which is the most reliable way to rehydrate adult bearded dragons passively. Fresh leafy greens daily help too — their natural moisture content matters more than most people realise. Watch for early signs: sunken eyes, skin that doesn't snap back quickly when gently pinched near the shoulder, or wrinkled skin along the sides. If those appear, back to the vet promptly. Get yourself a cheap IR thermometer as well so you can actually verify that basking surface temp once the new bulb is in — it removes all the guesswork.

Good plan. Once it's installed, give it 48 hours before drawing conclusions — the vivarium needs to settle to its new equilibrium. Aim for 40–42°C surface at the basking spot, cool side 24–26°C, and UVB index of around 3–4 in the basking zone with the Reptisun T5. If anything reads outside those ranges after settling, adjust the mounting height of the halogen rather than the wattage. She should be in a much better position, and the reduction in ambient heat stress will genuinely help with hydration retention too.