One-way perspective film (also called unidirectional film, mirror film, etc.) is a kind of film which can give the glass high reflectance to the visible light. 2) Service condition. This film is often misunderstood that it can allow you see through the window indoors without letting someone see indoors from outside. In fact, there is certain requirement that should be met to make it work. When the outdoors is brighter than the indoors, this film acts like a common mirror. The scene indoors can't be seen from the outdoors. The reverse is not true. But when the outdoors is darker than the indoors, the scene indoors can be seen from the outdoors and vise versa. The clarity depends on the illuminance outdoors. At present, this film is mainly used as observation window and hole with high level of concealment. The product can be used in Public Security Bureau, detention house, prison, court, karaoke, office, kindergarten, psychiatric hospital and other special sites.