lumen second

SI coherent derived unit whose name and symbol includes an SI coherent derived unit with a special name and symbol

Name	Symbol	Derived quantity	Expressed in terms of SI base units
lumen second	lm s	luminous energy	s cd
Definition The lumen second, symbol lm s, is the SI coherent derived unit of luminous energy, a measure of the total quantity of visible light emitted by a source.

Luminous energy

Luminous energy is a measure of the total quantity of visible light emitted by a source.

The lumen second is analogous to the watt second, or joule.

Luminous energy differs from radiant energy, in that radiant energy includes electromagnetic waves at all emitted frequencies, while luminous energy is weighted according to the human eye’s sensitivity to different frequencies, or wavelengths.

Photometry units

Name	Symbol	Quantity	Expressed in terms of SI base units		Expressed in terms of other SI units
candela	cd	luminous intensity	cd		lm/sr
lumen	lm	luminous flux	cd		cd sr
lux	lx	illuminance	m-2 cd		lm/m2
candela per square metre	m-2 cd	luminance	m-2 cd		cd/m2
lumen second	lm s	luminous energy	s cd		lm s
lumen per watt	lm W‑1	luminous efficacy	kg‑1 m‑2 s3 cd		lm/W