The life of a reptile looks like easy street – besides mating and eating, much of the time is spent sunbathing. But for many reptiles, basking in the sun is essential to their health. It provides warmth, stimulates their appetite and encourages growth. Even reptiles kept in captivity need the sun's rays to maintain proper health.
What is so special about the sun? All animals need calcium in their system in order to survive. This mineral is crucial in maintaining muscle function, nerve function and overall body health. Vitamin D is important in controlling calcium levels and calcium metabolism. Without vitamin D, the calcium in the body cannot be properly utilized.
Reptiles are unable to form vitamin D without the help of ultraviolet rays. Within their bloodstream and in their skin, reptiles have a compound known as provitamin D3. This is a precursor to vitamin D3. With the help of ultraviolet B rays, this provitamin is converted to previtamin D3, which the reptile is able to convert into vitamin D3 – with the help of a proper body temperature. (By the way, this isn't true for all reptiles. Snakes have been found to thrive without either natural sunlight or an artificial alternative.)
Although UV-B light can suffice during the cold times of the year, direct sunlight is the best source for these rays. "Direct" means the sunlight does not pass through glass or other clear material; the glass blocks the necessary rays while admitting the heat. Placing your reptile in an aquarium near a window won't give him what he needs, and may just cause him to overheat.
Sunlight is the optimum source of ultraviolet rays for reptiles, and basking in the sun is a favorite past time. But too much can be dangerous. Always make sure you provide a hiding place or shade for your reptile in case he becomes overheated and needs to escape the sun. There are many brands of UV-B lights available specifically for reptiles. Be aware that the UV-B rays of the lights tend to only last about 6 months. The light will still glow but the ultraviolet rays will be gone. For optimal health, change your UV-B light source every 4 to 6 months.