UVB And Reptiles
UVB is an essential part of how vitamin D3 is synthesized in the skin in all humans and even animals; this includes reptiles and mammals. UVB is responsible for sunburn in humans, but animals tend to have more protection from this than we do. Vitamin D3 produced in the body is vital in its role in regulating how calcium is metabolized, D3 is obtained either by ingestion in the diet of living things and also exposure to UVB radiation. Most reptile species are unable to utilize vitamin D3 through dietary methods, which is why they must have access to UVB. A lack of UVB in humans can cause rickets, while in reptiles, it can contribute to Metabolic Bone Disease (see Metabolic Bone Disease In Bearded Dragons).
Pretty much any animal that is active during the day is exposed to levels of UVB. Lighting has evolved over the time we have been keeping reptiles in captivity; in the early days, not too much was known about the type of lighting that we would need to keep our captive friends healthy. Along with the fact that technology wasn't as advanced as it is now, this meant that we did not have the means to look after them as well as we do now. Reptiles that we kept indoors did not have access to the UVB that they needed, and metabolic bone disease was much more prevalent. The effects of MBD are pretty severe, where it causes reptiles' bones to go soft, opening them up to become easily injured, resulting in severe permanent deformities of the spine, softened jaws that impede their ability to eat and broken limbs.
It was observed over time that reptiles that were housed outdoors did not develop MBD nearly as much as those housed indoors, and the connection was made that outdoor reptiles were getting something that indoor reptiles were not, the obvious was rays from the sun. This prompted experts to experiment with UVB production in fluorescent lighting, and artificial UVB lighting was born. It was soon learned that MBD was reversible with exposure to the correct artificial lighting, as well as MBD being preventable by exposure from birth throughout the life cycle of a reptile.
Awareness of the fact that diurnal reptiles need exposure to UVB enabled studies to be done on various species. Including the effects of different types of UVB lighting duration of exposure, the distances, and how often bulbs needed to be changed. All these factors led us to be able to determine the exact needs for the various species and be able to apply them to prevent MBD and promote healthy vitamin D3 synthesis in all the different reptiles we keep.
UVA is actually on the visible spectrum for reptiles and amphibians, as well as for birds and fish, unlike humans who lack this particular cone of vision. In reptiles, UVA is essential for them to be able to see color at all; without it, they are essentially colorblind. While they don't need to absorb UVA like they do with UVB, it is essential for their comfort and psychological wellbeing; it would be cruel to deny them UVA.