Unified Glare Rating (UGR)

A measure of the discomfort produced by a lighting system along a psychometric scale of discomfort. The Unified Glare Rating formula is a discomfort glare likelihood assessment method developed, published, and recommended by the CIE in 1995. The UGR formula produces a glare rating which is a psychophysical parameter estimating the discomfort in response to glare in a visual environment containing light sources. The practical UGR range is from 10 to 30 with most lighting systems producing values in that range. A high value indicates likelihood of significant discomfort glare, while a low value indicates little likelihood of discomfort glare. The development of UGR predated the application of LEDs in general lighting, and studies have reported that the original UGR formula tends to underestimate the discomfort sensation provoked by the highly non-uniform source luminance from some LED luminaires. A correction term to the original UGR formula was consequently formalized in a CIE report in 2019 taking into consideration the effects of non-uniform glare sources. Due to the recency of this new development, UGR in the remainder of this policy refers to the 1995 UGR formula, and the DLC will consider adopting UGR with the correction term in future updates when standards are available.