Used by Ultraviolet Light (UV) is form of electromagnetic radiation that is naturally occurring in sunlight. Vampires in the Underworld universe suffer from a highly aggressive and acute form of photosensitivity; they are allergic to the ultraviolet radiation inherent in natural sunlight. Because of this allergic reaction, the movements of Vampires are restricted to the night. As shown in the first and third instalments, cremation via sunlight was used as a form of execution in the Old World Coven, as the ultimate deterrent against breaking the Coven's laws, the "Covenant".