Bearded dragons need ultraviolet (UV) lighting for physiological and behavioural well being. Ultraviolet lighting is not only needed for Bearded dragons to see better, but also aids in calcium absorption.
The ultraviolet light spectrum can be divided into UV-A, UV-B and UV-C. Image from aetaire.com
When looking at the spectrum of light emitted by the sun, only a small portion is visible to humans. One might recall the light spectrum (or the colours of the rainbow) from school, namely red, orange, yellow, green, blue, indigo, violet. Humans tend to see all these basic colours, but our eyes are not adapted to see the two extremes – the very short wavelengths called ultraviolet and very long wavelengths called infrared.
Ultraviolet rays are light with wavelength of less than 400 nm. It can be divided further into UV-A, UV-B and UV-C. Unlike humans, Bearded dragons can actually see into the UB-A spectrum of light. The UV-B spectrum is also very important for these, and other sun-basking lizards.
UV-A is more for sight
Photograph with and without UV enhancement. If humans were able to see the UV-A spectrum (315 – 400 nm wavelenghts), this is more or less what flowers will look like. Image from WiseGeek.com
The image above shows an ultraviolet enhanced photo of a flower. Generally much more details are visible. By being able to see the UV-A spectrum, Bearded dragons see more details and are for example able to distinguish better between smaller items such as food.
UV-B is more for calcium absorption
Calcium is absorbed through the intestines (with food) and plays a vital role in nerve and muscle function. Calcium is also stored in our bones. In order to be able to absorb calcium, vitamin D3 plays a vital role. If enough vitamin D3 is not supplied through the diet, e.g. from supplements (reasonable quantities) or from food (very small quantities), then not enough calcium will be absorbed. This is very often the case in Bearded dragons and can rapidly lead to metabolic bone disease. In Bearded dragons, vitamin D3 is produced by absorbing UV-B through the skin.
Health reasons
Apart from physiological well-being, skin diseases such as Yellow fungus disease is often diagnosed in Bearded dragons where the ultraviolet exposure were inadequate or absent. In theory, ultraviolet also serves as a natural disinfectant and will likely kill these, and other, micro-organisms.