Lumen (unit)

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The lumen (symbol: lm) is the SI unit of luminous flux.

1 Definition
2 SI multiples
3 Explanation
4 SI photometry units
5 See also

[edit] Definition

1 lm = 1 cd·sr = 1 cd·m²·m^–2

[edit] SI multiples

Multiple	Name	Symbol	Multiple	Name	Symbol
10⁰	lumen	lm
10¹	decalumen	dalm	10^–1	decilumen	dlm
10²	hectolumen	hlm	10^–2	centilumen	clm
10³	kilolumen	klm	10^–3	millilumen	mlm
10⁶	megalumen	Mlm	10^–6	microlumen	µlm
10⁹	gigalumen	Glm	10^–9	nanolumen	nlm
10¹²	teralumen	Tlm	10^–12	picolumen	plm
10¹⁵	petalumen	Plm	10^–15	femtolumen	flm
10¹⁸	exalumen	Elm	10^–18	attolumen	alm
10²¹	zettalumen	Zlm	10^–21	zeptolumen	zlm
10²⁴	yottalumen	Ylm	10^–24	yoctolumen	ylm

[edit] 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 <math>4\pi</math> lumens. The lumen can be thought of casually as a measure of the total "amount" of visible light emitted.

A standard 100 watt incandescent light bulb emits approximately 1700 lumens. See luminous efficacy for the specific efficiency of various types of electric light sources.

[edit] SI photometry units

SI photometry units
[edit]
Quantity	Symbol	SI unit	Abbr.	Notes
Luminous energy	Q_v	lumen second	lm·s	units are sometimes called Talbots
Luminous flux	F	lumen (= cd·sr)	lm	also called luminous power
Luminous intensity	I_v	candela (= lm/sr)	cd	an SI base unit
Luminance	L_v	candela per square metre	cd/m²	units are sometimes called nits
Illuminance	E_v	lux (= lm/m²)	lx	Used for light incident on a surface
Luminous emittance	M_v	lux (= lm/m²)	lx	Used for light emitted from a surface
Luminous efficacy		lumen per watt	lm/W	ratio of luminous flux to radiant flux; maximum possible is 683.002