17-958

Planck's law

law giving the spectral concentration of radiance of a Planckian radiator as a function of wavelength and temperature

       

where

Le is the radiance;

λ is the wavelength in vacuum;

T is the thermodynamic temperature;

h is the Planck constant;

c0 is the velocity (speed) of light in vacuum;

k is the Boltzmann constant

NOTE 1 The formula is sometimes written with instead of  , where Ω0 is the solid angle of magnitude 1 sr.

NOTE 2 For a detector in a medium of refractive index n, the measured radiance is: n-2Le,λ(λ, T).

NOTE 3 Planck's law can be also expressed to give the spectral concentration of radiant exitance Me,λ(λ, T); the first factor in the formula is then c1 instead of  .

NOTE 4 Both quantities (radiance and radiant exitance) apply to the unpolarized radiation as emitted.

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