Lighting ratio in
photography
Photography is the visual arts, art, application, and practice of creating images by recording light, either electronically by means of an image sensor, or chemically by means of a light-sensitive material such as photographic film. It is empl ...
refers to the comparison of
key light (the main source of light from which shadows fall) to the total
fill light (the light that fills in the shadow areas).
The higher the lighting ratio, the higher the contrast of the image; the lower the ratio, the lower the contrast. The lighting ratio is the ratio of the light levels on the brightest-lit to the least-lit parts of the subject; the brightest-lit areas are lit by both key (K) and fill (F). The
American Society of Cinematographers
The American Society of Cinematographers (ASC), founded in Hollywood in 1919, is a cultural, educational, and professional organization that is neither a labor union nor a guild. The society was organized to advance the science and art of cinem ...
(ASC) defines lighting ratio as (key+fill):fill, or (key+Σ
fill):Σ
fill, where Σ
fill is the sum of all fill lights.
Light can be measured in
footcandles. A key light of 200 footcandles and fill light of 100 footcandles have a 3:1 ratio (a ratio of three to one) — (200 + 100):100.
A key light of 800 footcandles and a fill light of 200 footcandles has a ratio of 5:1 according to the lighting ratio formula — (800 + 200):200 = 1000 / 200 = 5 : 1.
The ratio can be determined in relation to
F stops since each increase in f-stop is equal to double the amount of light: 2 to the power of the difference in f stops is equal to the first factor in the ratio. For example, a difference in two f-stops between key and fill is 2 squared, or 4:1 ratio. A difference in 3 stops is 2 cubed, or an 8:1 ratio. No difference is equal to 2 to the power of 0, for a 1:1 ratio.
See also
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High-key lighting
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Low-key lighting
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 ...
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Silhouette
A silhouette (, ) is the image of a person, animal, object or scene represented as a solid shape of a single colour, usually black, with its edges matching the outline of the subject. The interior of a silhouette is featureless, and the silhouett ...
References
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Science of photography
Engineering ratios