The following is a description of the four IES cutoff classifications.

Full Cutoff

A luminaire is classified by the IESNA as Full Cutoff if there is no light emitted towards or above the horizon and if the maximum luminous intensity of the luminaire at 80 degrees above nadir (straight down) is less than or equal to 10% of the initial lumen rating of the bare lamp(s).

Cutoff

A luminaire light distribution where the candela per 1000 lamp lumens does not numerically exceed 25 (2-1/2%) at or above a vertical angle of 90° up from nadir, and 100 (10%) at or above a vertical angle of 80° up from nadir.  This applies to all horizontal angles around the luminaire.

Semi-cutoff

A luminaire light distribution where the candela per 1000 lamp lumens does not numerically exceed 50 (5%) at or above a vertical angle of 90° up from nadir, and 200 (20%) at or above a vertical angle of 80° up from nadir.  This applies to all horizontal angles around the luminaire.

Noncutoff

A luminaire light distribution where there is no candela limitation in the zone above or below the beam of maximum candelas.