Specific light emission

Physical size
Surname	Specific light emission
Formula symbol	${\displaystyle M_{\mathrm {v} }}$
Size and unit system unit dimension SI lm · m -2 L -2 · J

As radiance ( English luminous exitance , outdated: luminous emittance ) M _v is called the light flux emanating from a surface member of a light source.

If a uniformly luminous surface emits the luminous flux , the specific light emission of the surface is equal to the quotient of the emitted luminous flux and the area : ${\displaystyle A}$ ${\displaystyle \Phi _{\mathrm {v} }}$ ${\displaystyle \Phi _{\mathrm {v} }}$ ${\displaystyle A}$

${\displaystyle M_{\mathrm {v} }={\frac {\Phi _{\mathrm {v} }}{A}}}$

If the specific light emission varies over the area, the local variation of the specific light emission can be described in detail using the differential quotient:

${\displaystyle M_{\mathrm {v} }={\frac {\mathrm {d} {\Phi }_{\mathrm {v} }}{\mathrm {d} A}}\,}$.

It is in the unit lumens by square meter measured. The lux unit, which is formally identical to it, should not be used because it is reserved for the illuminance (luminous flux through the receiver surface).

The corresponding term in radiometry is specific radiation or . The specific light emission also contains a physiological component (taking into account the sensitivity curve of the human eye). ${\displaystyle M}$ ${\displaystyle M_{\mathrm {e} }}$

Relationship with other radiometric and photometric quantities

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.