# spectral-total hemispherical emissivity

[2.13.8.2] ε(x,y,2π,T), (at a point on the surface of a thermal radiator)
The ratio of the radiant exitance of the thermal radiator at temperature T, at the given point on the surface, to that of a blackbody at the same temperature T.

$\epsilon \left ( x,y,2\pi ,T \right )=\left ( 1/\pi \right )\int _{2\pi } \epsilon \left ( x,y, \theta,\phi ,T \right ) cos \theta d \omega$
$=\left ( 1/\pi \right )\int_{0}^{\infty }\int _{2\pi } \epsilon \left ( \lambda ,x,y, \theta ,\phi ,T \right ) cos \theta d\omega d\lambda$
$= M\left ( x,y,T \right )/M_{bb}\left ( T \right )$
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