The Effect of Background Luminance on the Perception of Discomfort Glare from Vertical Surface Light Sources

Vertical surface light sources, widely applied in public spaces, easily trigger discomfort glare due to direct visual exposure. As a core lighting parameter, background luminance (Lb) strongly regulates glare perception, yet relevant research mainly focuses on single-variable analysis for horizontal lighting. The mechanisms through which Lb influences discomfort glare in the presence of vertical surface light sources remain insufficiently understood. This study takes Lb, and vertical light source luminance (Lsv)-induced luminance contrast (Lcontrast) as core variables, and combines subjective glare assessment and pupil diameter monitoring to explore their independent and coupled effects on vertical glare perception and visual adaptation. The results indicate that Lcontrast, Lb, and their interaction all exert significant effects on subjective glare perception. The interaction effect suggests that the glare induced by one factor intensifies as the level of the other factor increases. In addition, the luminance of vertical light sources influences visual adaptation levels. Vertical illuminance at the eye (Ev) shows a stronger association with subjective glare responses under the present experimental conditions, supporting its potential as a saturation-related indicator for vertical surface light sources. Among the variables examined, Lcontrast exerts the strongest influence on discomfort glare. Furthermore, the pupil diameter change rating (PDCR) shows higher sensitivity to subtle visual stress under low Lb conditions. These findings provide preliminary support for refining discomfort glare evaluation of vertical surface light sources and inform future research on their application and design across diverse lighting environments.