Definition: | representation in space, in the form of a surface expressed in polar coordinates, of the angular distribution of (relative) radiant or luminous intensity or of (relative) radiance or luminance of an element of surface of a medium that diffuses by reflection or transmission
NOTE 1 – For a narrow incident beam of radiation, it is convenient to represent the indicatrix of diffusion in Cartesian coordinates. If the angular distribution has rotational symmetry, a meridian section of the surface is sufficient.
NOTE 2 – The term indicatrix is often used to denote, instead of the surface, the curve obtained in a similar manner in a plane normal to the element concerned.
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