UVB Lamps for Aquatic Turtles
A completely different UV lamp from the UV-C sterilizer: basking turtles need UVB to make vitamin D3 and absorb calcium, or they develop metabolic bone disease. Learn the requirements and pitfalls.
Confusingly, the word ultraviolet covers very different lamps. The UV-C of a sterilizer is germicidal and goes in the water; UVB is a longer wavelength used over a basking area for the animal's own health. For basking aquatic turtles such as sliders, painted, musk and map turtles, a UVB lamp is not optional lighting, it is essential to prevent serious bone disease.
The UV bands are not the same
Ultraviolet is divided by wavelength into UV-A (315 to 400 nm), UV-B (280 to 315 nm) and UV-C (100 to 280 nm). UV-C is the germicidal band used to disinfect water. UVB is the band that drives vitamin D synthesis in skin. They are different tools with different jobs, and a water sterilizer does nothing for a turtle's bones.
Why turtles need UVB
Reptiles use UVB of roughly 290 to 315 nm to synthesise vitamin D3 in their skin, and vitamin D3 is required to absorb and use dietary calcium. Without adequate UVB, dietary vitamin D alone is often insufficient, and the animal cannot maintain calcium balance. The result is metabolic bone disease, also described as nutritional secondary hyperparathyroidism, which causes a soft or deformed shell, distorted jaw and long bones, and even pathologic fractures.
Setting it up correctly
- Shine it directly: ordinary glass and plastic block UVB (window glass passes very little light below 300 nm), and water absorbs it too, so the lamp must shine onto a dry basking spot with nothing in between.
- Pair it with heat: place a basking heat lamp beside the UVB lamp so the turtle basks in both and gets a proper temperature gradient.
- Set the right distance and duration: follow the lamp's instructions, since UVB intensity falls steeply with distance; older non-mercury-vapour bulbs typically need 30 to 120 minutes of exposure a day.
- Replace on schedule: UVB output declines with use before the visible light fades, so replace the bulb regularly, commonly about once a year.