Variable set points of glare control strategy for side-lit spaces: Daylight glare tolerance by time of day

Abstract

Too much natural light in the form of glare causes visual discomfort of building occupants, and many owners choose direct shading for glare control in the building operation management. Traditionally, automated glare control strategy is based on a constant set point. Early findings approved that subjects’ glare sensations are not at a constant level, hence, simple shading control logic could be unreasonable and inaccurate. The purpose of this paper is to quantify the tendency of glare intolerance by the time of day, and based on which, the variable set points of glare control are proposed. 42 subjects participated in the subjective evaluation in a controlled laboratory setting from morning to afternoon on sunny days. The light environment parameters and HDR images in the subject’s view field were collected at each glare sensation vote. After statistical analysis, the experiment results shows that: (i) the results reinforce the previous findings that tolerance to discomfort glare increases as the day progresses; (ii) DGP metric defined thresholds for GSV (Glare Sensation Vote) scales were validated by this investigation in midday; (iii) the set points of Ev based glare control strategy should be 1700 lx for Noticeable/2400 lx for Disturbing/3500 lx for Intolerable in morning; 2000 lx for Noticeable/3000 lx for Disturbing/4000 lx for Intolerable in midday; 2200 lx for Noticeable/3200 lx for Disturbing/4200 lx for Intolerable in afternoon.