## radiant exitance, $$M$$

@R05046-1@, $$P$$, emitted at all wavelengths by an element of surface containing the source point under consideration divided by the area of the source. SI unit is $$\text{W m}^{-2}$$.
1. Mathematical definition: $$M = \text{d}P/\text{d}S$$. If the @R05046-2@ $$P$$ is constant over the surface area considered, $$M = P/S$$.
2. Equivalent to the integration of the @R05046-3@ leaving a source over the solid @A00346@ and over the whole @W06659@ range. Mathematical definition: $$M = \int_{\lambda}M_{\lambda}\, \text{d}\lambda$$, where $$M_{\lambda}$$ is the @S05825@ at @W06659@ $$\lambda$$.