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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 ), which encompasses all electromagnetic waves emitted, including non-visible ones such as thermal radiation ( infrared ).
Luminous efficacy can be normalized by the maximum possible luminous efficacy to a dimensionless quantity called luminous efficiency.The distinction between efficacy and efficiency is not always carefully maintained in published sources, so it is not uncommon to see "efficiencies" expressed in lumens per watt, or "efficacies" expressed as a percentage.
lumen second per cubic metre lm⋅s/m 3: L −3 ⋅T⋅J: Luminous efficacy (of radiation) K: lumen per watt: lm/W: M −1 ⋅L −2 ⋅T 3 ⋅J: Ratio of luminous flux to radiant flux: Luminous efficacy (of a source) η [nb 3] lumen per watt: lm/W: M −1 ⋅L −2 ⋅T 3 ⋅J: Ratio of luminous flux to power consumption Luminous efficiency ...
The lux is one lumen per square metre (lm/m 2), and the corresponding radiometric unit, which measures irradiance, is the watt per square metre (W/m 2). There is no single conversion factor between lux and W/m 2; there is a different conversion factor for every wavelength, and it is not possible to make a conversion unless one knows the ...
For example, consider a 10 W transmitter at a distance of 1 million metres, radiating over a bandwidth of 1 MHz. By the time that power has reached the observer, the power is spread over the surface of a sphere with area 4 πr 2 or about 1.26×10 13 m 2 , so its flux density is 10 / 10 6 / (1.26×10 13 ) W m −2 Hz −1 = 8×10 7 Jy .
lumen second per cubic metre lm⋅s/m 3: L −3 ⋅T⋅J: Luminous efficacy (of radiation) K: lumen per watt: lm/W: M −1 ⋅L −2 ⋅T 3 ⋅J: Ratio of luminous flux to radiant flux: Luminous efficacy (of a source) η [nb 3] lumen per watt: lm/W: M −1 ⋅L −2 ⋅T 3 ⋅J: Ratio of luminous flux to power consumption Luminous efficiency ...
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 ...
lumen second per cubic metre lm⋅s/m 3: L −3 ⋅T⋅J: Luminous efficacy (of radiation) K: lumen per watt: lm/W: M −1 ⋅L −2 ⋅T 3 ⋅J: Ratio of luminous flux to radiant flux: Luminous efficacy (of a source) η [nb 3] lumen per watt: lm/W: M −1 ⋅L −2 ⋅T 3 ⋅J: Ratio of luminous flux to power consumption Luminous efficiency ...