[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\,\mathrm{d}\omega

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

\equiv M\left ( x,y,T \right )/M_{bb}\left ( T \right )

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