# 17-29-094

form factor, <between two surfaces>

f12; f21

quotient of the average radiant flux density or luminous flux density, Φ2/A2 (or Φ1/A1), received over surface S2 (or S1) from surface S1 (or S2) and the radiant exitance or luminous exitance, M1 (or M2), of surface S1 (or S2)

or

with

where Φ2 (or Φ1) is the radiant flux or luminous flux received over surface S2 (or S1) from surface S1 (or S2), A2 (or A1) is the area of surface S2 (or S1) and g is the mutual exchange coefficient

Note 1 to entry: The form factor has unit one.

Note 2 to entry: This entry was numbered 845-09-73 in IEC 60050-845:1987.

Note 3 to entry: This entry was numbered 17-468 in CIE S 017:2011.

Publication date: 2020-12