Amount of light

Physical size
Surname	Amount of light
Formula symbol	${\displaystyle Q_{\mathrm {v} }}$
Size and unit system unit dimension SI Lumen second  ( lm · s ) T · J

Light quantity ( english luminous energy ) is the photometric weighted radiant energy .

If a light source emits the temporally constant luminous flux during the period, the amount of light generated during this period is the product of the luminous flux (the "light generation rate") and the duration : ${\displaystyle T}$ ${\displaystyle \Phi _{\mathrm {v} }}$ ${\displaystyle Q_{\mathrm {v} }}$ ${\displaystyle \Phi _{\mathrm {v} }}$ ${\displaystyle \Delta t}$

${\displaystyle Q_{\mathrm {v} }=\Phi _{\mathrm {v} }\cdot \Delta t}$

If the luminous flux varies over time, the amount of light generated must be calculated using the corresponding integral :

${\displaystyle Q_{\mathrm {v} }=\int _{\Delta t}\Phi _{\mathrm {v} }(t)\ \mathrm {d} t}$

The amount of light is given in the unit of lumen second (lm s, unofficially also called Talbot or Lumberg ).

Overview of photometric quantities and units

radiometric quantity	Symbol a)	SI unit	description	photometric equivalent b)	symbol	SI unit
Radiant flux radiant power, radiant flux, radiant power	${\displaystyle \Phi _{\mathrm {e} }}$	W ( watt )	Radiant energy through time	Luminous flux luminous flux, luminous power	${\displaystyle \Phi _{\mathrm {v} }}$	lm ( lumens )
Radiant intensity irradiance, radiant intensity	${\displaystyle I_{\mathrm {e} }}$	W / sr	Radiation flux through solid angles	Luminous intensity luminous intensity	${\displaystyle I_{\mathrm {v} }}$	cd = lm / sr ( candela )
Irradiance irradiance	${\displaystyle E_{\mathrm {e} }}$	W / m 2	Radiation flux through the receiver surface	Illuminance illuminance	${\displaystyle E_{\mathrm {v} }}$	lx = lm / m 2 ( lux )
Specific radiation emission current density, radiant exitance	${\displaystyle M_{\mathrm {e} }}$	W / m 2	Radiation flux through the transmitter surface	Specific light emission luminous exitance	${\displaystyle M_{\mathrm {v} }}$	lm / m 2
Radiance radiance, radiance, radiance	${\displaystyle L_{\mathrm {e} }}$	W / m 2 sr	Radiant intensity through effective transmitter area	Luminance luminance	${\displaystyle L_{\mathrm {v} }}$	cd / m 2
Radiant energy amount of radiation, radiant energy	${\displaystyle Q_{\mathrm {e} }}$	J ( joules )	by radiation transmitted energy	Amount of light luminous energy, quantity of light	${\displaystyle Q_{\mathrm {v} }}$	lm · s
Irradiation irradiation, radiant exposure	${\displaystyle H_{\mathrm {e} }}$	J / m 2	Radiant energy through the receiver surface	Exposure luminous exposure	${\displaystyle H_{\mathrm {v} }}$	lx s
Radiation yield radiant efficiency	${\displaystyle \eta _{\mathrm {e} }}$	1	Radiation flux through absorbed (mostly electrical) power	Luminous efficiency (overall) luminous efficacy	${\displaystyle \eta _{\mathrm {v} }}$	lm / W

^a)The index "e" is used to distinguish it from the photometric quantities. It can be omitted.

^b)The photometric quantities are the radiometric quantities, weighted with the photometric radiation equivalent K , which indicates the sensitivity of the human eye.

Individual evidence

1. ↑ Thomas Jüstel, Sebastian Schwung: Phosphors, light sources, lasers, luminescence . Springer, Berlin, Heidelberg 2016, ISBN 978-3-662-48455-5 , pp. 96 , doi : 10.1007 / 978-3-662-48455-5 .