UVB

UVB is a specific band of ultraviolet light that many diurnal and crepuscular reptiles need to synthesize vitamin D3 in their skin, which in turn lets them absorb calcium from their diet. Without adequate UVB, a species that needs it can still eat a calcium-rich diet and still develop weak bones, because the body cannot use the calcium properly without the D3 pathway UVB provides.

UVB bulbs are sold as compact coils, linear fluorescent tubes, and mercury vapor bulbs, and the right choice depends on enclosure size and the species' natural sun exposure. Coverage matters as much as strength, since a bulb needs to run most of the length of the enclosure so the animal can move in and out of UVB exposure the way it would move in and out of sunlight, and screen tops or plastic covers can significantly cut how much UVB reaches the animal even from a rated bulb.

The biggest and most common mistake is treating a UVB bulb as permanent. Output drops well before the light stops working visibly, so bulbs need replacing on a schedule, typically every six to twelve months depending on the bulb type, regardless of whether they still glow normally. A UV index meter is the only reliable way to know actual output rather than guessing from the bulb's age or the manufacturer's rated lifespan.