Cold Light of Day is a 1989 British horror film written and directed by Fhiona Louise, and starring Bob Flag, Martin Byrne-Quinn, and Geoffrey Greenhill. Based on the crimes of serial killer Dennis Nilsen, the film is a fictionalized account of his various murders leading up to his apprehension by authorities. Louise, who was 21 years old at the time of the film's release, was the youngest woman ever to direct a feature film.