Best UVB for a bearded dragon (2026), by mount distance

The target, and why it makes this decision easy

A bearded dragon is Zone 3, edging into Zone 4, with a published basking figure of UVI 4.0-4.5 at the basking surface per the care reference. That is the highest target of any species we cover, and it rules out an entire shelf of products in one step: compact coils, mercury vapor bulbs behind glass, and every low-output shade-dweller lamp. What is left is a high-output linear T5 tube in a reflector, and the only remaining question is how far above the animal it sits.

So this page is organized around distance rather than brand. The lamp and the distance are one purchase decision, not two, and a lamp with no published distance figure is a lamp you cannot set correctly.

The published mount distances

Two things to carry away from that table. First, the mesh correction is large - roughly 5 to 6 inches of difference - so "11 inches" means nothing until you say whether the lamp is sitting on mesh or hanging inside. Second, the figures are per brand. Arcadia and Zoo Med both publish, and their numbers are not transferable.

Tube length, which is the mistake nobody warns you about

The lamp has to span the basking zone, and the usual advice - cover about two-thirds of the enclosure length - exists so the animal can move out of the UV as well as into it. In a 48 in enclosure that means a 34 in or 36 in tube, not a 22 in one. A short tube in a long enclosure produces a narrow UV column that a dragon has to sit directly under, which is the opposite of a gradient.

It also matters for where the heat goes. The basking lamp and the UVB tube should overlap, so the animal gets heat and UV in the same place and is not forced to choose. Our basking setup page covers the geometry, and UVB distance and Ferguson zones has the zone figures for every species.

The 40-gallon and 120-gallon question

People search for a UVB lamp by tank size, which is reasonable and slightly misleading. The lamp is chosen by the distance from the lid to the basking surface, not by the volume of the box. A 40-gallon breeder and a 4x2x2 are both 18 to 24 in tall, so the same 12% lamp suits both - what changes is the tube length and how high you build the basking platform. Our tank-size UVB page works through that conversion, and 40 gallon vs 120 gallon covers whether the box itself is big enough.

Replacement, which is a calendar item and not a judgment call

A T5 fluorescent is replaced every 12 months whether or not it still lights up. UVB output declines long before visible output does, so a bulb that looks fine can be producing a fraction of its original UVB. Write the install date on the tube in marker. The detail is on when to replace UVB bulbs, and if you want to verify rather than assume, the UV index meter the care references accept is covered here.