In photometry, luminous flux or luminous power is the measure of the perceived power of light. It differs from radiant flux, the measure of the total power of electromagnetic radiation (including infrared, ultraviolet, and visible light), in that luminous flux is adjusted to reflect the varying sensitivity of the human eye to different wavelengths of light.
1 Units 2 Weighting 3 Context
3.1 Relationship to luminous intensity
4 Examples 5 References
The SI unit of luminous flux is the lumen (lm). One lumen is defined
as the luminous flux of light produced by a light source that emits
one candela of luminous intensity over a solid angle of one steradian.
In other systems of units, luminous flux may have units of power.
The luminous flux accounts for the sensitivity of the eye by weighting
the power at each wavelength with the luminosity function, which
represents the eye's response to different wavelengths. The luminous
flux is a weighted sum of the power at all wavelengths in the visible
SI photometry quantities
v t e
Quantity Unit Dimension Notes
Name Symbol[nb 1] Name Symbol Symbol[nb 2]
Luminous energy Qv [nb 3] lumen second lm⋅s T⋅J The lumen second is sometimes called the talbot.
candela (= lm/sr)
candela per square metre
lux (= lm/m2)
Luminous exposure Hv lux second lx⋅s L−2⋅T⋅J Time-integrated illuminance
Luminous energy density ωv lumen second per cubic metre lm⋅s⋅m−3 L−3⋅T⋅J
Luminous efficacy η [nb 3] lumen per watt lm/W M−1⋅L−2⋅T3⋅J Ratio of luminous flux to radiant flux or power consumption, depending on context
See also: SI · Photometry · Radiometry
^ Standards organizations recommend that photometric quantities be denoted with a suffix "v" (for "visual") to avoid confusion with radiometric or photon quantities. For example: USA Standard Letter Symbols for Illuminating Engineering USAS Z7.1-1967, Y10.18-1967 ^ The symbols in this column denote dimensions; "L", "T" and "J" are for length, time and luminous intensity respectively, not the symbols for the units litre, tesla and joule. ^ a b c Alternative symbols sometimes seen: W for luminous energy, P or F for luminous flux, and ρ or K for luminous efficacy.
Table of comparative luminous flux of several light sources
37 mW "Superbright" white LED 0.20
15 mW green laser (532 nm wavelength) 8.4
1 W high-output white LED 25–120
Kerosene lantern 100
40 W incandescent lamp at 230 volts 325
7 W high-output white LED 450
6 W COB filament LED lamp 600
18 W fluorescent lamp 1250
100 W incandescent lamp 1750
40 W fluorescent lamp 2800
35 W xenon bulb 2200–3200
100 W fluorescent lamp 8000
127 W low pressure sodium vapor lamp 25000
400 W metal-halide lamp 40000
Values are given for newly manufactured sources. The output from many sources decreases significantly over their lifetime.
^ http://www.cvrl.org/database/text/lum/scvl.htm ^ http://www.cvrl.org/database/text/cmfs/ciexyz31.htm ^ http://www.cvrl.org/database/text/lum/vljv.htm ^ "Sharpe, Stockman, Jagla & Jägle (2005) 2-deg V*(l) luminous efficiency function". Archived from the original on 2007-09-27. Retrieved 2007-05-10. ^ Szokolay, S. V. (2008). Introduction to Architectural Science: The Basis of Sustainable Design (Second ed.). Routledge. p. 143. ISBN 9780750687041. ^ BeLight. 3. Trendforce. 2010. pp. 10–12. ^ Jahne, Bernd (2004). Practical Handbook on Image Processing for Scientific and Technical Applications (Second ed.). CRC. p. 111. ISBN 97808493