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A foot-candle (sometimes foot candle; abbreviated fc, lm/ft 2, or sometimes ft-c) is a non-SI unit of illuminance or light intensity. The foot-candle is defined as one lumen per square foot. This unit is commonly used in lighting layouts in parts of the world where United States customary units are used, mainly the United States. [1]
A foot-lambert or footlambert (fL, sometimes fl or ft-L) is a unit of luminance in United States customary units and some other unit systems. A foot-lambert equals 1/π or 0.3183 candela per square foot, or 3.426 candela per square meter (the corresponding SI unit).
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.
Starlight overcast moonless night sky [1] 140 microlux: Venus at brightest [1] 200 microlux: Starlight clear moonless night sky excluding airglow [1] 10 −3: 1 millilux: 2 millilux: Starlight clear moonless night sky including airglow [1] 10 −2: 1 centilux: 1 centilux: Quarter Moon 10 −1: 1 decilux: 2.5 decilux: Full Moon on a clear night ...
The foot-candle is a non-metric unit of illuminance that is used in photography. [5] Illuminance was formerly often called brightness, but this leads to confusion with other uses of the word, such as to mean luminance. "Brightness" should never be used for quantitative description, but only for nonquantitative references to physiological ...
Narrow-beamed lights of all sorts can have very high candlepower specifications, because candlepower measures the intensity of the light on a target, rather than the total amount of light it emits. A given lamp has a higher candlepower rating if its light is more tightly focused. [2] Candlepower is still used today in law.
A tea light-type candle, imaged with a luminance camera; false colors indicate luminance levels per the bar on the right (cd/m 2). Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. [1]
The design day for daylight factor calculations is based on the standard CIE overcast Sky for 21 September at 12:00pm, and where the Ground Ambient light level is 11921 Lux. CIE being the Commission Internationale de l´Eclairage, or International Commission on Illumination.