|“||Daylight... harnessed as a weapon!||”|
Selene takes a Desert Eagle loaded with the special bullets off a Lycan warrior, Trix, in the beginning of Underworld. Realizing that the bullets emitted UV radiation, she brought them back to the mansion. When Selene shows Kahn the bullets, Kraven scoffs at the possibility of the Lycans developing such technology from scratch. However, Kahn theorizes that it was originally some sort of advanced tracer-round technology developed by a human military, which the Lycans then stole and adapted to their own uses, i.e. to emit specifically ultraviolet light. They have been shown to be fatal to Werewolves as well.
The advent of Ultraviolet ammunition gives the Lycans a significant leg up in the arms race against the Vampires, equaling how the Vampires use silver ammunition against them. The Vampires (specifically Kahn) respond by making new advances in silver weapons, specifically bullets tipped with a silver nitrate solution, which immediately disperses into the bloodstream.
Underworld: Evolution reveals that it was actually Andreas Tanis who provided the Lycans with the UV ammunition. He manufactured and sold them to Lucian in exchange for luxuries, including Lycan bodyguards to protect his home.
In Evolution, the Cleaners and Selene arm themselves with machine guns loaded with UV rounds. Samuel states that UV rounds can't kill William Corvinus, but Selene believes them to be capable of at least slowing him down. Despite being designed for use against Vampires only, Selene is able to kill several Werewolves with the Cleaners' UV rounds.
Underworld: Blood Wars
In Underworld: Blood Wars, Varga kills many aspiring Death Dealers of the Eastern Coven with ultraviolet ammunition to pin the blame on Selene. The Lycans also use the ammunition in the battle with the Nordic Coven and the Eastern Coven. At one point, Marius shoots David repeatedly with UV rounds, but he proves to be immune, as he is a Vampire-Corvinus Strain Hybrid. In a show of power, David ejects the UV rounds from his body while Marius does the same with David's silver nitrate rounds.
- In Blood Wars, the Vampires killed with ultraviolet ammunition catch on fire and burn into charred corpses. This effect was absent from when Rigel was killed in Underworld.