Downlight Cutoff Angle, UGR and Deep-Recessed Trims

Guide

Cutoff angle is the angle, measured from the horizontal at the fixture, above which the LED source is no longer directly visible inside the reflector; ERCO's lighting-technology glossary defines cutoff angle this way and separately defines shielding angle as the angle from horizontal to the edge of the visible light-emitting surface (erco.com). Deep-regressed or deep-recessed trims set the LED module or lens further up inside the housing than a flat trim, which raises this cutoff/shielding angle without adding a separate diffuser; Halo's RLD6 Deep Baffle trim publishes a 50-degree optical cutoff from this construction (cooperlighting.com) and WAC's Oculux Architectural trim publishes a 35-degree visual cutoff (waclighting.com). Where a manufacturer instead publishes Unified Glare Rating (UGR), as Cooper Lighting does for the Halo Commercial HC6 and HC4 downlight series (UGR 11.7 and 12.2 for their narrow-distribution reflectors), a lower UGR number indicates less discomfort glare for an occupant looking up toward the fixture, which is the viewing geometry created by a bed positioned under a downlight.