Ultraviolet B light is essential for vitamin D synthesis and calcium metabolism in many reptile species, and its absence in captive reptile environments causes severe metabolic bone disease and welfare suffering.
Reptile UV-B welfare illustrates how invisible deficiencies can cause profound suffering. Metabolic bone disease from insufficient UV-B causes soft, deformed bones that fracture under normal movement. Affected reptiles experience chronic pain and mobility limitation. The insidious nature of the deficiency - symptoms develop slowly over months - means owners may not notice until disease is advanced and irreversible. UV-B bulbs that appear functional may have lost their UV-B output while maintaining visible light. Regular bulb replacement schedules, UV-B solarmeter measurements, and species-appropriate positioning of UV-B sources are essential welfare practices for reptile keepers.