UVB 5.0, 10.0, 12.0 — what the numbers mean, how far UVB actually penetrates, and how to build a healthy basking gradient for desert and forest species.
UVB radiation between 290 and 315 nanometres is what allows reptiles to synthesise vitamin D3 and, in turn, metabolise calcium. Without it, captive lizards, tortoises and snakes develop metabolic bone disease within months.
The numbers on UVB lamp labels — 5.0, 10.0, 12.0 — describe the percentage of the lamp's UV output in the UVB band. UVB 5.0 is correct for tropical and forest species that would receive filtered sunlight in the wild. UVB 10.0 is standard for desert species. UVB 12.0 is for species that bask in intense equatorial sun.
T5 High-Output tubes deliver roughly twice the UVB flux of T8 tubes at the same length. In tall terrariums — anything over 45 cm — a T5 HO is the only reliable way to deliver a therapeutic UVB dose at basking height.
Replace UVB tubes every six to twelve months. The visible light output remains almost unchanged as the phosphor degrades, but UVB emission drops steadily; a lamp that still looks bright can be delivering effectively zero UVB.