There is project where the only exterior lighting is two ceiling recessed downlighting fixtures installed at the outdoor canopy of the main entrance. According to the BUG method, B (backlight) and U (uplight) would already be 0. Not only are they downlighhts but they are flushed no less than 1.25" inward, how would that affect the G (glare) part of the BUG rating for these fixtures. The cutsheet does not provude a BUG rating, but I would assume it would be B=0 U=0 G=0. Would this method work to comply with the Light Pollution Reduction credit?
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Bill Swanson
Sr. Electrical EngineerIntegrated Design Solutions
LEEDuser Expert
734 thumbs up
November 7, 2023 - 1:47 pm
The Uplight does sound like it would be U=0.
You are incorrect with the others. Look at this graph to see how the light sphere is divided up. https://www.accessfixtures.com/what-is-bug-rating-and-why-does-it-matter/ The light output within any region will determine B, U, and G ratings. The same fixture at different wattages will likely have different ratings.
Acuity brand has this free tool for getting an BUG rating from any IES file. Either look up one of theirs or upload your saved file from "My Computer". https://www.visual-3d.com/tools/photometricviewer/
Make sure the 'LCS Table' is on in the options so you can see the BUG rating. Default was off for some reason.
The first downlight I quickly checked had B2, U0, G0. This makes sense since the "back" half of a fixture has stricter limits than the front half. And the downlight is uniform on all sides. But don't worry. The B rating is not applicable to building mounted fixtures.
Glenn Heinmiller
PrincipalLam Partners
100 thumbs up
November 7, 2023 - 1:54 pm
Edgar,
Don't assume anything. The only way you can determine the BUG rating if you can't get it from the manufacturer is to download the ies file and open it in a photometric viewer that generates BUG rating from the data file.
But yes, U obviously = 0.
B doesn't matter because your fixture is building-mounted and per credit language: "Building-mounted luminaires with the backlight oriented toward the building are exempt from the backlight rating requirement."