UV Lighting is absolutly necessary in the synthesization of Vitamin D3. This is done thru the chemistry of Keratonin and Melmine in the cell structure of the skin/scales into the blood stream. A natural process. Information can be found in Mader's Reptile Medical book and lizard biology books availiable. Calvin rating of 90 and over in UV lighting along with UVA & UVB wave lengths stimulate activity.