Defining the Actual Luminous Surface in the Unified Glare Rating

ABSTRACT

A nonuniform luminance distribution produces more discomfort glare than a uniform one of equal average luminance. Because the standard unified glare rating (UGR) generally considers the average luminance level of the total luminaire surface, its applicability for nonuniform light sources is under discussion. With a growing market share of highly nonuniform light emitting diode (LED) luminaires, a valid discomfort glare metric becomes essential. The UGR can elegantly be improved by discriminating between background and luminous part(s) of a luminaire. A luminance threshold identifies the high-luminance pixels in a luminance map as an actual light emitting surface. Two subjective visual experiments, encompassing commercially available recessed office luminaires and custom-designed luminaires, validate the improved UGR method. With a coefficient of determination of 0.45, the standard UGR fails to predict visual glare sensation. Also covering nonuniform light sources, the improved UGR, with a coefficient of determination of up to 0.91, elegantly ameliorates the visual discomfort calculation from a luminance map.

KEYWORDS:

• discomfort glare
• luminance map
• magnitude estimation
• paired comparison
• unified glare rating

ACKNOWLEDGMENTS

The authors thank Gilles Vissenberg, Leonie Geerdinck, and Maurice Donners from Philips Research for the perspicacious comments.

FUNDING

The authors thank the Hercules Foundation for funding the near-field goniophotometer as medium-scale infrastructure project (AKUL-35) and KU Leuven for funding (BAM, internal funding).

Additional information

Funding

The authors thank the Hercules Foundation for funding the near-field goniophotometer as medium-scale infrastructure project (AKUL-35) and KU Leuven for funding (BAM, internal funding).