Lumen (unit)
SI derived unit of visible light emission / From Wikipedia, the free encyclopedia
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The lumen (symbol: lm) is the unit of luminous flux, a measure of the perceived power of visible light emitted by a source, in the International System of Units (SI). Luminous flux differs from power (radiant flux) in that radiant flux includes all electromagnetic waves emitted, while luminous flux is weighted according to a model (a "luminosity function") of the human eye's sensitivity to various wavelengths; this weighting is standardized by the CIE and ISO.[2] One lux is one lumen per square metre.
lumen | |
---|---|
Unit system | SI |
Unit of | luminous flux |
Symbol | lm |
Conversions | |
1 lm in ... | ... is equal to ... |
SI base units | cd⋅sr[lower-alpha 1] |
The lumen is defined in relation to the candela as
A full sphere has a solid angle of 4π steradians,[3] so a light source that uniformly radiates one candela in all directions has a total luminous flux of
- 1 cd × 4π sr = 4π cd⋅sr ≈ 12.57 lm.[4]