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In SI units illuminance is measured in lux (lx), or equivalently in lumens per square metre (lm·m −2). [2] Luminous exitance is measured in lm·m −2 only, not lux. [4] In the CGS system, the unit of illuminance is the phot, which is equal to 10 000 lux. The foot-candle is a non-metric unit of illuminance that is used in photography. [5]
1 lux < 1 lux: Extreme of darkest storm clouds, sunset or sunrise 10 1: 1 decalux: 40 lux: Fully overcast, sunset or sunrise 10 2: 1 hectolux < 200 lux: Extreme of darkest storm clouds, midday 400 lux: Sunrise or sunset on a clear day (ambient illumination) 10 4: 10 kilolux: 10–25 kilolux: Typical overcast day, midday 20 kilolux
The lux (symbol: lx) is the unit of illuminance, or luminous flux per unit area, in the International System of Units (SI). [ 1 ] [ 2 ] It is equal to one lumen per square metre. In photometry , this is used as a measure of the irradiance , as perceived by the spectrally unequally responding human eye, of light that hits or passes through a ...
lux (= lumen per square metre) lx (= lm/m 2) L −2 ⋅J: Luminous flux incident on a surface Luminous exitance, luminous emittance M v: lumen per square metre lm/m 2: L −2 ⋅J: Luminous flux emitted from a surface Luminous exposure: H v: lux second: lx⋅s L −2 ⋅T⋅J: Time-integrated illuminance Luminous energy density ω v: lumen ...
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.
In the US lighting industry, foot-candles are a common unit of measurement used by architects to calculate adequate lighting levels. Foot-candles are also commonly used in the museum and gallery fields in the US, where lighting levels must be carefully controlled to conserve light-sensitive objects such as prints, photographs, and paintings, the colors of which fade when exposed to bright ...
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Illuminant C does not have the status of CIE standard illuminants but its relative spectral power distribution, tristimulus values and chromaticity coordinates are given in Table T.1 and Table T.3, as many practical measurement instruments and calculations still use this illuminant. —