Measure of how well a light source produces visible light
Luminous efficacy
Common symbols
K
SI unit
lm⋅W−1
In SI base units
cd⋅s3⋅kg−1⋅m−2
Dimension
Luminous efficacy is a measure of how well a light source produces visible light. It is the ratio of luminous flux to power, measured in lumens per watt in the International System of Units (SI). Depending on context, the power can be either the radiant flux of the source's output, or it can be the total power (electric power, chemical energy, or others) consumed by the source.[1][2][3]
Which sense of the term is intended must usually be inferred from the context, and is sometimes unclear. The former sense is sometimes called luminous efficacy of radiation,[4] and the latter luminous efficacy of a light source[5] or overall luminous efficacy.[6][7]
Not all wavelengths of light are equally visible, or equally effective at stimulating human vision, due to the spectral sensitivity of the human eye; radiation in the infrared and ultraviolet parts of the spectrum is useless for illumination. The luminous efficacy of a source is the product of how well it converts energy to electromagnetic radiation, and how well the emitted radiation is detected by the human eye.
^Allen Stimson (1974). Photometry and Radiometry for Engineers. New York: Wiley and Son. Bibcode:1974wi...book.....S.
^Franc Grum; Richard Becherer (1979). Optical Radiation Measurements, Vol 1. New York: Academic Press.
^Robert Boyd (1983). Radiometry and the Detection of Optical Radiation. New York: Wiley and Son.
^International Electrotechnical Commission (IEC): International Electrotechnical Vocabulary, ref. 845-21-090, Luminous efficacy of radiation (for a specified photometric condition)
^International Electrotechnical Commission (IEC): International Electrotechnical Vocabulary, ref. 845-21-089, Luminous efficacy (of a light source)
^Roger A. Messenger; Jerry Ventre (2004). Photovoltaic systems engineering (2 ed.). CRC Press. p. 123. ISBN 978-0-8493-1793-4.
^Erik Reinhard; Erum Arif Khan; Ahmet Oğuz Akyüz; Garrett Johnson (2008). Color imaging: fundamentals and applications. A K Peters, Ltd. p. 338. ISBN 978-1-56881-344-8.
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