UVB (ultraviolet B) — A band of ultraviolet radiation involved in vitamin D3 synthesis and calcium use in many reptiles. It differs physically from visible brightness and heat, so a bright or hot lamp does not necessarily provide adequate UVB.
Understanding by example
Distance, mesh, reflector design and installation angle all change the radiation that reaches the animal. A bulb’s UVB percentage and the UV Index at the animal’s position are not the same number. Check both manufacturer installation conditions and a species-appropriate exposure range.
Common misconceptions
Nocturnality does not automatically make UVB irrelevant, and higher exposure is not always better. Animals need shade where they can avoid the light. Dietary vitamin D3 and lighting should be assessed with diet, age and health rather than simply added together.
Related reading and sources
For species-specific context, see UVB Setup and Humid Hides. Browse the full glossary.
Basic reference: Merck Veterinary Manual: Nutrition in Reptiles.