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The CIE Unified Glare Rating (UGR) metric has been use by the architectural lighting industry since it was first published by the CIE a quarter-century ago (CIE 117-1995, Discomfort Glare in Interior Lighting). Originally popularized by European lighting manufacturers, UGR has recently been adopted by the DesignLights Consortium, the US Green Building Council (LEED), and the WELL Building Standard.

It is easy enough to calculate UGR metrics using commercial lighting design and analysis programs, and luminaire manufacturers are increasingly providing UGR values for their products. However, UGR is a much more complicated metric than for example illuminance. It is the responsibility of lighting designers to *understand* the metric, rather than just blindly (no pun intended) use it in their specifications and designs.

There have been many dozens of research papers written on visual glare since CIE 117-1995 was published, but these have been of little use for day-to-day lighting design. I am therefore both pleased and proud to recommend this just-published white paper from the National Electrical Manufacturers Association (NEMA):

NEMA LS 20001-2021, White Paper on Unified Glare Rating (UGR)

UGR analysis images generated by SunTracker Technologies’ Cerise365 / (c) 2021 National Electrical Manufacturers Association

I am pleased because this authoritative 34-page document “explains the original intent of Unified Glare Ratio (UGR), its proper uses, and common misuses of the Standard.” It provides detailed information on how the metric works, and how it should (and should not) be used.

I am proud because I (ahem) contributed roughly a quarter of the text, including Annex C, UGR Computer Simulations. If you *really* want to know all the gory details of how a lighting design and analysis program should calculate the UGR metric, this annex provides the answers. (Note the qualifier “should” — some programs may surprise you.)

One final comment: the white paper is free, but you have to register with NEMA in order to download it. This may be an annoyance, but I can promise that it will be worth the effort. This white paper is an essential resource for today’s lighting designers.