Comparing performance of discomfort glare metrics in high and low adaptation levels

Current discomfort glare prediction metrics usually account for at least one of the two categories of effects that induce discomfort glare – the saturation and contrast effects. Saturation-driven metrics (overall illuminance on the eye) are suited for brightly lit scenes in general. On the contrary, contrast-driven metrics (luminance ratio in the field of view) usually perform better in high contrast conditions such as with small-sized bright glare sources. Only a few existing metrics consider both effects, such as the Daylight Glare Probability (DGP). However, even these “hybrid” metrics may underperform in conditions other than those considered when they were developed, such as in dim scenes with high contrast glare. This paper investigates the ability of current glare indicators to predict perceived discomfort glare in user-evaluated scenes depending on two different adaptation levels. Towards this end, we used a composite dataset of six laboratory studies performed previously and separately in various parts of the world. According to Receiver Operator Characteristics (ROC) findings and complementary statistical research, the hybrid metrics DGP and Eccologit perform best in both investigated ranges (dimmer and brighter scenes). For the single-effect metrics, the contrast-driven metrics appear to perform better than saturation-driven metrics in lower adaptation levels (dimmer scenes), while the reverse is seen in higher adaptation levels (brighter scenes). As a result, metrics that only consider one effect should be used with caution. Although hybrid metrics continue to perform well in the investigated scenes, further research is needed to extend their applicability to a larger variety of lighting conditions that may be observed in work environments.