A global evaluation of discomfort glare metrics in real office spaces with presence of direct sunlight

Abstract

Existing glare metrics are usually tested in controlled studies and have certain limitations when predicting extremely bright scenes typical of clear sky with great daylight availability. A field-based research was carried out, where 26 real offices with direct sunlight were evaluated. Different daylight glare metrics were selected (luminance and illuminance levels, luminance ratios, luminance distribution). These were divided into two categories: “absolute glare values” and “relative glare values” following a study made by Suk et al. [22]. The contributions of these metrics about glare sensation (GSV scale) were statistically analyzed. In addition, the DGP model and uniformity values were calculated to complement this analysis. This paper demonstrates that Suk's proposal is a viable alternative; however, the “percentage of central and near FOV with luminance greater than 2000 cd/m2” metric showed a better correlation with the subjective response. Finally, a glare equation based on an absolute and a relative glare factor was proposed. This model is recommended to be used specifically when direct sunlight is present in the work area.