Evaluating discomfort glare from non-uniform electric light sources

Abstract

This study tested the appropriateness of unified glare rating (UGR), CIE glare index (CGI), British glare index (BGI), and visual comfort probability (VCP) for evaluating discomfort glare from common non-uniform electric light sources. An experiment was conducted in a windowless room. High dynamic range photogrammetry was used for measuring three non-uniform fluorescent glare sources. The luminance and geometry data were acquired to calculate the glare ratings. The sub-divisibility and additivity of UGR, CGI, BGI, and VCP were tested via numerical method. Their predictability was evaluated using 67 subjects in two sessions. It was found that UGR, CGI, BGI, and VCP all have valid additivity, but only UGR and CGI have valid sub-divisibility. Current formulae of UGR, CGI, BGI and VCP all overestimate the glare sensation from non-uniform sources that young people may feel. © 2012 The Chartered Institution of Building Services Engineers.