photon exitance (at a point of a surface) [Mp]

1. quotient of the photon flux dΦp leaving an element of the surface containing the point, by the area, dA, of that element

2. equivalent definition: integral, taken over the hemisphere visible from the given point, of the expression LpcosθdΩ, where Lp is the photon radiance at the given point in the various directions of the emitted elementary beams of solid angle, dΩ, and θ is the angle between any of these beams and the normal to the surface at the given point


Unit: s-1·m-2

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