radiant flux areal density

[2.7] dΦ/dA, (at a point on a surface)
The quotient of the radiant flux incident on or emitted by an element of surface area at the point, by the area of the element. Radiant flux density emitted from a surface has been called emittance.iv The preferred term for radiant flux density leaving a surface is exitance (M). Radiant flux density incident on a surface is irradiance (E).

iv Deprecated.

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