What happens when something in view, a lamp, a window or a reflection, is far brighter than the level the eyes have adjusted to. Discomfort glare makes people squint, complain and turn away without necessarily reducing visibility; disability glare scatters light inside the eye, washing out contrast, as with oncoming headlights. It depends on source luminance, size, position and background luminance, and is controlled with shielding, diffusers, cutoff and lower-luminance optics.
Those high-bay lenses are pure glare from the forklift seat, put on the prismatic diffusers before the night shift starts.
Related terms
UGR
Unified Glare Rating: a calculated index of discomfort glare from interior luminaires, where lower numbers mean less glare.
Luminance
The brightness of a surface or source as seen from a particular direction, measured in candelas per square meter.
Cutoff
The angle above which a luminaire emits little or no light, used to classify glare and light pollution control.
BUG rating
An outdoor luminaire rating for backlight, uplight and glare, each scored 0 to 5, used in light pollution ordinances.