irradiance (at a point of a surface) [*E*_{e}]

1. quotient of the radiant flux d*Φ*_{e} incident on an element of the surface containing the point, by the area d*A* of that element

2. equivalent definition: integral, taken over the hemisphere visible from the given point, of the expression *L*_{e}cos*θ*d*Ω*, where *L*_{e} is the radiance at the given point in the various directions of the incident elementary beams of solid angle d*Ω*, and *θ* is the angle between any of these beams and the normal to the surface at the given point

Unit: W⋅m^{-2}

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