# 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 .