Dark room is a room made completely dark to allow processing of light sensitive photographic materials. It requires a light-tight door, often with a lock, to prevent light from entering. There are four main types of doors for dark rooms - revolving, single, double, and maze. Revolving doors are the most efficient but also most expensive, while maze doors provide no protection from accidental light exposure. The purpose of the dark room is to process film and photographic paper in complete darkness.