Low-key lighting is a style of lighting for photography, film or television. It is a necessary element in creating a chiaroscuro effect. Traditional photographic lighting, three-point lighting uses a key light, a fill light and a back light for illumination. Low-key lighting often uses only a key light, optionally controlled with a fill light or a simple reflector.
Low key light accentuates the contours of the subject by throwing areas into shade while a fill light or reflector may illuminate the shadow areas to control contrast. The relative strength of key-to-fill, known as the lighting ratio, can be measured using a light meter. Low key lighting has a higher lighting ratio, e.g., 8:1, than high-key lighting, which can approach 1:1.
The term "low key" is also used in cinematography and photography to refer to any scene with a high lighting ratio, especially if there is a predominance of shadowy areas. It tends to heighten the sense of alienation felt by the viewer, hence is commonly used in film noir and horror genres. It is typically used in dark dramas/ thrillers. Low-key lighting is also associated with German Expressionism and later film noir.