Mercury Vapor Bulbs provide heat and ultraviolet light, both UVA and UVB. Reptiles require external heat in order to properly digest their food. UVB, normally provided by the sun, is needed to produce Vitamin D, without which reptile cannot utilize calcium. UVA promotes natural activity, and may aid in breeding. Josh's Frogs strongly recommends using a Wire Clamp Lamp with Mercury Vapor Bulbs to extend bulb life.