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cut-off angle, <of a luminaire>
angle, measured up from nadir, between the vertical axis and the first line of sight at which the light source(s) and the surfaces of high luminance are not visible
Note 1 to entry: The cut-off angle is expressed in radian (rad) or degree (°).
Note 2 to entry: This entry was numbered 845-10-30 in IEC 60050-845:1987.
Note 3 to entry: This entry was numbered 17-270 in CIE S 017:2011.