# 17-29-092

mutual exchange coefficient, <of radiance or luminance between surfaces>

exchange coefficient, <of radiance or luminance between surfaces>

g

quotient of the radiant flux or luminous flux Φ2 (or Φ1) that surface S1 (or S2) sends to surface S2 (or S1) and the radiant exitance or luminous exitance M1 (or M2)

Note 1 to entry: Since M = πL, and in the particular case where all points on S1 are seen from all points on S2

where l is the distance between the elements of areas dA1 and dA2 on the surfaces S1 and S2, G is the geometric extent of the beam delimited by the boundaries of S1 and S2, and θ1 and θ2 are the angles between the surface normals of the two elementary areas dA1 and dA2 respectively and the line joining the two elementary areas.

Note 2 to entry: For two elementary areas dA1 and dA2

where dΩ1 (or dΩ2) is the solid angle which the area dA2 (or dA1) subtends from the centre of dA1 (or dA2).

Note 3 to entry: The radiance or luminance L of the beam delimited by the boundaries of dA1 and dA2 is
.

Note 4 to entry: The mutual exchange coefficient is expressed in square metre (m2).

Note 5 to entry: This entry was numbered 845-09-71 in IEC 60050-845:1987.

Note 6 to entry: This entry was numbered 17-797 in CIE S 017:2011.

Publication date: 2020-12