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A lumen is the standard scientific unit used to measure how much visible light a source produces in all directions. It matters because it helps people compare the brightness of different light sources—like light bulbs—in a consistent, standardized way.
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Wikidata facts
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- derived from base unit
- candela
- measured physical quantity
- luminous flux
- conversion to SI unit
- 1
- unit symbol
- lm
- Wikidata SPARQL query equivalent
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- different from
- Lumen
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- Wikipedia:Vital articles/Level/4
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Encyclopedic overview
The lumen (symbol: lm) is the SI unit of luminous flux, which quantifies the perceived power of visible light emitted by a source. Luminous flux differs from power (radiant flux), which encompasses all electromagnetic waves emitted, including non-visible ones such as thermal radiation (infrared). By contrast, 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.
The lumen is defined as equivalent to one candela-steradian (symbol cd·sr):
Excerpted from Wikipedia’s “lumen” article, available under the CC BY-SA 4.0 licence.
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