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| lumen | |
|---|---|
| Unit system | SI |
| Unit of | luminous flux |
| Symbol | lm |
| Conversions | |
| 1 lm in ... | ... is equal to ... |
| SI base units | cd⋅sr[a] |
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.
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]
- ^ The International System of Units (SI) (PDF) (9th ed.). Bureau International des Poids et Mesures. 2019. pp. 137–138.
- ^ ISO/CIE 23539:2023, CIE TC 2-93, Photometry — The CIE system of physical photometry. ISO/CIE. 2023. doi:10.25039/IS0.CIE.23539.2023.
- ^ "Lesson introduction to solid angles". Retrieved Oct 4, 2010.
- ^ Bryant, Robert H. "Lumens, Illuminance, Foot-candles and bright shiny beads…". The LED Light. Retrieved Oct 4, 2010.
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