Alliance for Lighting Information

IESNA Luminaire Cutoff Classifications

by David M. Keith

The IESNA Roadway Lighting Committee has developed definitions for luminaire classifications for cutoff, published in the ANSI/IESNA pulication RP-8-00, American National Standard Practice for Roadway Lighting. The classification is intended to control glare by establishing the maximum allowable intensity - measured in candelas (cd) - for different elevations above nadir.

The classifications are Full cutoff (FC), Cutoff (CO), Semi-cutoff (SC) and Non-cutoff (NC). FC has the most stringent limits, and then CO and SC. There are no limits for NC classification.

The limits apply to intensity measured in candelas (abbreviated as cd) anywhere around the luminaire and within two separate and distinct elevation regions: from 80 to 90 degrees, and at and above 90 degrees. To be classified as FC, CO or SC, a distribution has to meet both limits: one for the "80 to 90 degrees" and another "at or above 90 degrees".

The value of the maximum allowable intensity is scaled to the lamp output by using the rated lamp lumens. The numerical value for each limit on intensity is determined by multiplying a factor times the rated lamp lumens. The factors are specific to the different elevations and classifications. The following diagram shows the numerical details.

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