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As radiance ( English luminous exitance , outdated: luminous emittance ) M v is called the light flux emanating from a surface member of a light source.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