quotient of the radiance of a thermal radiator in a given direction and the radiance of a Planckian radiator at the same temperature
Note 1 to entry: The symbols
Note 2 to entry: The directional emissivity has unit one.
Note 3 to entry: This entry was numbered 845-04-08 in IEC 60050-845:1987.
Note 4 to entry: This entry was numbered 17-328 in CIE S 017:2011.