UVB lighting mimics the sun's natural ultraviolet rays. Not only is natural UV light responsible for tans, but it also allows the body to produce vitamin D3, which is vital for proper calcium absorption. Many species of reptiles (and amphibians!) have evolved to utilize UV light, and providing it in captive conditions is very important. There are several artificial means of providing UVB to your pets, including linear UV Fluorescent bulbs, Compact Fluorescent UV bulbs, Mercury Vapor bulbs, and new Metal Halide UV bulbs.