17-1245

spherical irradiance (at a point) [Ee,o]

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

Equivalent term: “fluence rate”, “radiant fluence rate”

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” (also termed “photon fluence rate”), Ep,o, are defined in a similar way, replacing radiance, Le, by luminance, Lv, or photon radiance, Lp.

NOTE 3 This is the appropriate radiometric quantity for describing a dose rate for a photobiological or photochemical effect in a scattering medium (e.g., light in skin). It is also the appropriate quantity for describing the irradiation of microorganisms. It is frequently used incorrectly as a substitute for irradiance in some publications.

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