form factor, <between two surfaces>
quotient of the average radiant flux density or luminous flux density,
or
with
where
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.