Units of Light
Luminous intensity is a base dimension in the International System of Units. The SI unit of luminous intensity is the candela, which is defined as the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 5.4×1014 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian (16th CGPM, 1979).
Luminous flux has the dimension luminous intensity solid angle. The SI unit of luminous flux is the lumen, which is defined as a candela steradian.
Luminous luminance has the dimension luminous intensity per length squared. The SI composite unit of luminous luminance is the candela per meter squared.
Illuminance has the dimension luminous intensity solid angle per length squared. The SI unit of illuminance is the lux, which is defined as a candela steradian per square meter.
Maple knows the units of light listed in the following table.
An asterisk ( * ) indicates the default context, an at sign (@) indicates an abbreviation, and under the prefixes column, SI indicates that the unit takes all SI prefixes, IEC indicates that the unit takes IEC prefixes, and SI+ and SI- indicate that the unit takes only positive and negative SI prefixes, respectively. Refer to a unit in the Units package by indexing the name or symbol with the context, for example, candela[SI] or lx[SI]; or, if the context is indicated as the default, by using only the unit name or symbol, for example, candela or lx.
The units of light are defined as follows.
A carcel is defined as 10 candelas.
A Hefner unit is approximately 0.903 candela.
The only unit of luminous flux is the lumen.
A nit is defined as a candela per square meter.
A stilb is defined as a candela per square centimeter.
A lambert is defined as 1π candela per square centimeter.
A footlambert is defined as 1π candela per square foot.
An apostilb is defined as 0.0001 lambert.
A skot is defined as 1.×10−7 lambert.
A phot is defined as a kilolux.
A nox is defined as a millilux.
A footcandle is defined as a lumen per square foot.
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