entrance angle, <of a retroreflector>
angle between the illumination axis and the retroreflector axis
Note 1 to entry: The entrance angle is expressed in radian (rad) or degree (°).
Note 2 to entry: This entry was numbered 845-04-95 in IEC 60050-845:1987.
Note 3 to entry: This entry was numbered 17-386 in CIE S 017:2011.