Zilla T8 Fluorescent Bulbs Desert 15 WattsZilla Tropical 25 Bulbs provide a full dosage of UVB (25 micro watts per. second cm2) along with essential UVA light. Zilla Desert 50 Bulbs provide a full dosage of UVB (50 micro watts per. second cm2) along with essential UVA light. Provides UVB light rays which are required for many reptiles to metabolize essential calcium Full spectrum lighting enhances natural colors of the animal and environment Replace every 12 months to ensure proper UVB levels