| Definition: | quantity defined by the formula where dΩ is the solid angle of each elementary beam passing through the given point and Le its radiance at that point
unit: W • m-2
NOTE 1 – This quantity is the quotient of the radiant flux of all the radiation incident on the outer surface of an infinitely small sphere centred at the given point, by the area of the diametrical cross-section of that sphere.
NOTE 2 – The analogous quantities spherical illuminance Ev,o and photon spherical irradiance Ep,o are defined in a similar way, replacing radiance Le by luminance Lv or photon radiance Lp.
NOTE 3 – The term "spherical irradiance", or scalar irradiance, or similar terms maу be found in the literature, in the definition of which the area of the crosssection is sometimes replaced by the surface area of the spherical element which is four times larger.
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