mean value of illuminance on the outer curved surface of a very small (real or imaginary) sphere at a point in space
Note 2 to entry: The spherical illuminance is the quotient of the luminous flux of all the light incident on the outer surface of an infinitely small sphere centred at the given point and the area of the diametrical cross-section of that sphere.
Note 3 to entry: The analogous quantities "spherical irradiance",
Note 4 to entry: The spherical illuminance is expressed in lux (lx = lm·m−2).
Note 5 to entry: This entry was numbered 17-1244 in CIE S 017:2011.