The lumen (symbol: lm) is the SI unit of luminous flux. Cover of brochure The International System of Units. ... Luminous flux is a measure of the energy emitted by a light source in all directions. ...

Definition

1 lm = 1 cd·sr = 1 cd·m²·m^–2

SI multiples

Explanation

If a light source emits one candela of luminous intensity into a solid angle of one steradian, the total luminous flux emitted into that solid angle is one lumen. Alternatively, an isotropic one-candela light source emits a total luminous flux of exactly 4π lumens. The lumen can be thought of casually as a measure of the total "amount" of visible light emitted. The candela (symbol: cd) is the SI base unit of luminous intensity (that is, power emitted by a light source in a particular direction, with wavelengths weighted by the luminosity function, a standardized model of the sensitivity of the human eye). ... Luminous intensity is a measure of the energy emitted by a light source in a particular direction. ... The steradian (ste from Greek stereos, solid) is the SI derived unit of solid angle, and the 3-dimensional equivalent of the radian. ... Luminous flux is a measure of the energy emitted by a light source in all directions. ... Isotropic means independent of direction. Isotropic radiation has the same intensity regardless of the direction of measurement, and an isotropic field exerts the same action regardless of how the test particle is oriented. ...

A standard 100 watt incandescent light bulb emits approximately 1700 lumens. See the article on incandescent light bulbs for the specific efficiency of various types of electric light sources. The watt (symbol: W) is the SI derived unit of power. ... An incandescent light bulb and its glowing filament. ...

SI photometry units

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Cover of brochure The International System of Units. ... luminous energy : visible radiant energy, visible light ; units are lumen*seconds or Talbots (T = lm*s) ; lumen = candela*steradian ... Look up second in Wiktionary, the free dictionary. ... Look up second in Wiktionary, the free dictionary. ... In photometry the Talbot (T) is a nonstandard unit of luminous energy. ... Luminous flux is a measure of the energy emitted by a light source in all directions. ... The candela (symbol: cd) is the SI base unit of luminous intensity (that is, power emitted by a light source in a particular direction, with wavelengths weighted by the luminosity function, a standardized model of the sensitivity of the human eye). ... The steradian (ste from Greek stereos, solid) is the SI derived unit of solid angle, and the 3-dimensional equivalent of the radian. ... In photometry, Luminous flux or luminous power is the measure of the perceived power of light. ... Luminous intensity is a measure of the energy emitted by a light source in a particular direction. ... The candela (symbol: cd) is the SI base unit of luminous intensity (that is, power emitted by a light source in a particular direction, with wavelengths weighted by the luminosity function, a standardized model of the sensitivity of the human eye). ... The steradian (ste from Greek stereos, solid) is the SI derived unit of solid angle, and the 3-dimensional equivalent of the radian. ... The candela (symbol: cd) is the SI base unit of luminous intensity (that is, power emitted by a light source in a particular direction, with wavelengths weighted by the luminosity function, a standardized model of the sensitivity of the human eye). ... The SI system of units defines seven SI base units: physical units defined by an operational definition. ... Luminance (also called luminosity) is a photometric measure of the density of luminous intensity in a given direction. ... The candela (symbol: cd) is the SI base unit of luminous intensity (that is, power emitted by a light source in a particular direction, with wavelengths weighted by the luminosity function, a standardized model of the sensitivity of the human eye). ... A square metre (US spelling: square meter) is by definition the area enclosed by a square with sides each 1 metre long. ... The candela (symbol: cd) is the SI base unit of luminous intensity (that is, power emitted by a light source in a particular direction, with wavelengths weighted by the luminosity function, a standardized model of the sensitivity of the human eye). ... A square metre (US spelling: square meter) is by definition the area enclosed by a square with sides each 1 metre long. ... This article is about the unit of measure. ... Illuminance is the total luminous flux incident per unit area. ... The lux (symbol: lx) is the SI derived unit of illuminance or illumination. ... A square metre (US spelling: square meter) is by definition the area enclosed by a square with sides each 1 metre long. ... The lux (symbol: lx) is the SI derived unit of illuminance or illumination. ... In photometry, illuminance is the total luminous flux incident on a surface, per unit area. ... The lux (symbol: lx) is the SI derived unit of illuminance or illumination. ... A square metre (US spelling: square meter) is by definition the area enclosed by a square with sides each 1 metre long. ... The lux (symbol: lx) is the SI derived unit of illuminance or illumination. ... Luminous efficacy is a measure of the proportion of the energy supplied to a lamp that is converted into light energy. ... The watt (symbol: W) is the SI derived unit of power. ... The watt (symbol: W) is the SI derived unit of power. ... Luminous flux is a measure of the energy emitted by a light source in all directions. ... Luminous flux or luminous power is the measure of the perceived power of light. ...

See also

• Video projector for a discussion on lumen ratings of projectors.