| Definition: | quotient of that part of the radiant flux or luminous flux from a surface, the radiance or luminance of which is the same at all points and for all directions, which falls on the surface itself, and the radiant exitance or luminous exitance of the surface Note 1 to entry: The self-exchange coefficient of a surface, S, limited by a flat curve, C, and situated on only one side of the plane of this curve is equal to the surface area of S minus the flat surface area limited by C. Note 2 to entry: The self-exchange coefficient is expressed in square metre (m2). Note 3 to entry: This entry was numbered 845-09-74 in IEC 60050-845:1987.
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