How often should I replace my UVB bulb?

T5 HO, T8, and compact fluorescent UVB bulbs should be replaced every 6 months. Mercury vapor bulbs last up to 12 months.

Can I tell when a UVB bulb needs replacing by looking at it?

No. UVB output degrades invisibly — the visible light stays normal long after UV levels have dropped.

Husbandry tool

UVB Bulb Replacement Calculator

UVB bulbs lose most of their UV output before they stop glowing. Enter your install date and get reminded when it's time.

Your bulb

Bulb type

Why timing matters

UVB fluorescent tubes use phosphors that degrade over time. The phosphors responsible for UV emission degrade significantly faster than visible-light phosphors — which is why a bulb can appear bright while delivering almost no usable UVB to your animal.

Without adequate UVB, reptiles cannot synthesize vitamin D3, leading to metabolic bone disease (MBD) — soft bones, shell pyramiding, and in severe cases organ failure.

Replacement intervals

T5 HO Linear (Arcadia, Reptisun)6 months

T8 Linear6 months

Compact Fluorescent6 months

Mercury Vapor Bulb12 months

More husbandry tools

Feeding Schedule Growth Tracker Brumation Calendar Substrate Calculator

Save results & track over time

Create a free Basking account to keep your pet's schedule, log feedings, and build grocery lists.

Basking is here to help you learn — it isn't veterinary advice. For anything specific to your animal, talk to a qualified exotic-animal vet.