Glossary · ☀️ Heat & UVB
UVB
UVB is the band of ultraviolet light reptiles need to make vitamin D3 in their skin, which lets them absorb calcium — without it, most reptiles develop metabolic bone disease.
UVB is provided by a proper reptile lamp (usually a linear T5 HO tube), not a household bulb, and it must be the right strength for the species and replaced roughly yearly as output fades even while the light still glows.
How much a species needs is set by its Ferguson Zone. Even species once told "don't need UVB" (like leopard geckos) now benefit from low-level UVB.