Luminous flux 581888 220761150 2008-06-21T13:11:57Z TXiKiBoT 3171782 robot Adding: [[bar:Liachtstrom]] [[Image:Luminosity.png|thumb|right|400px|Photopic (black) and scotopic [http://www.cvrl.org/database/text/lum/scvl.htm] (green) luminosity functions. The photopic includes the CIE 1931 standard [http://www.cvrl.org/database/text/cmfs/ciexyz31.htm] (solid), the Judd-Vos 1978 modified data [http://www.cvrl.org/database/text/lum/vljv.htm] (dashed), and the Sharpe, Stockman, Jagla & Jägle 2005 data [http://www.cvrl.org/database/text/lum/ssvl2.htm] (dotted). The horizontal axis is wavelength in nm.]] [[Image:Spectrum4websiteEval.png|thumb|right|400px|]] In [[photometry (optics)|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 light emitted, in that luminous flux is adjusted to reflect the varying sensitivity of the human [[eye]] to different [[wavelength]]s of light. ==Units== The [[SI]] unit of luminous flux is the [[lumen (unit)|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 (physics)|power]]. ==Weighting== 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 band. Light outside the visible band does not contribute. The ratio of the total luminous flux to the radiant flux is called the [[luminous efficacy]]. ==Contexts== Luminous flux is often used as an objective measure of the useful power emitted by a [[Light#light sources|light source]], and is typically reported on the packaging for [[Lamp (electrical component)|light bulbs]], although it is not always prominent. Energy conscious consumers commonly compare the luminous flux of different light bulbs since it provides an estimate of the apparent amount of light the bulb will produce, and is useful when comparing the [[luminous efficacy]] of [[Incandescent light bulb|incandescent]] and [[Compact fluorescent lamp|compact fluorescent]] bulbs. Luminous flux is not used to compare [[brightness]], as this is a subjective perception which varies according to the distance from the light source. {{SI_light_units}} [[Category:Physical quantity]] [[Category:Photometry]] [[be:Светлавы паток]] [[bar:Liachtstrom]] [[cs:Světelný tok]] [[de:Lichtstrom]] [[es:Flujo luminoso]] [[fr:Flux lumineux]] [[is:Ljósflæði]] [[it:Flusso luminoso]] [[lt:Šviesos srautas]] [[hu:Fényáram]] [[ms:Fluks berkilau]] [[nl:Lichtstroom]] [[ja:光束]] [[pl:Strumień świetlny]] [[ru:Световой поток]] [[sl:Svetlobni tok]] [[fi:Valovirta]] [[sv:Ljusflöde]] [[vi:Quang thông]] [[uk:Світловий потік]] [[zh:光通量]]