6 best reptile UVB bulbs (2026), judged by UVI at a stated distance

Why the percentage on the box tells you almost nothing

A 12% T5 HO lamp is not a UV index. It becomes one only once you add a fixture with a reflector, a mount distance, and a correction for how much of the output your mesh lid absorbs. Published mesh corrections in the sources we cite assume somewhere between a 30% and a 45% block, which is a wide enough spread that two keepers running identical lamps at identical heights can be exposing their animals to meaningfully different UVI.

That is why this roundup ranks on "can it hit the target at a distance your enclosure allows" rather than on output. A lamp that needs 17 inches of clearance is the wrong lamp for an 18 inch tall enclosure no matter how good it is.

Targets by species, with the published distances

Four rules that apply to every lamp on this list

1. Linear tube, never a compact coil. A coil lights a point; a basking area is a zone. Every published distance figure assumes a linear tube in a reflector.
2. No glass or plastic over the lamp. Both block UVB completely. A fixture with a protective shield renders the bulb useless for its actual purpose while the visible light continues to look fine.
3. Replace every 12 months. UVB output declines long before the visible light does. Still glowing is not still working. Details here.
4. Tube length matters. The published guidance for a bearded dragon is a tube about half the length of the enclosure, on the same side as the heat lamps - 22 inches for a 4 ft enclosure, 34 inches for a 6 ft.

What to avoid

• LED UVB. Reptile lighting researchers have concluded the technology is not yet ready for safe use with reptiles, regardless of manufacturer claims. This is not a performance quibble; it is a safety position.
• Compact coil bulbs as the primary UVB source. The output profile is wrong for a basking zone and the historical burn record for this product class is poor.
• Any "UVB and heat in one" mercury vapor bulb run without a meter. Combining the two functions removes your ability to adjust one without moving the other.
• Measuring UVI with anything other than a Solarmeter 6.5 or 6.5R. The care guidance is explicit that no other device measures reptile UVI accurately.

One question about your own exposure

These lamps emit real ultraviolet, so it is reasonable to ask what that means for the people in the room. The short answer is that distance and duration do the work, and that switching the lamp off before you put your head inside the enclosure removes the question entirely. We set out what is established and where the evidence runs out.