Visual discomfort in four urban tunnel scenes evaluated by field measurements and small sample video replay

Visual discomfort may occur in urban road tunnels even when conventional lighting criteria are satisfied. This exploratory study combined field measurements in four urban tunnels with a small-sample laboratory video-replay study involving six licensed young adults. Field measurements characterized illuminance, surface luminance, along-route illuminance variation, threshold increment (TI), and a calculated de Boer rating. The questionnaire-based overall comfort rating was the dependent variable; field-derived photometric quantities were explanatory scene variables, while pupil response and area-of-interest (AOI) hit rate were laboratory process indicators. TI was used primarily to establish that all four scenes remained below the conventional disability-glare reference, whereas the calculated de Boer rating and other scene descriptors were examined for their correspondence with the human responses. Neither TI nor the calculated de Boer rating was participant-rated, and the projection system was not used to reproduce disability glare. Across the four scenes, lower overall comfort ratings were associated with greater field-measured illuminance variability, stronger pupil responses, and higher sidewall-related AOI hit rates. The calculated de Boer rating showed a positive scene-level association with overall comfort, whereas TI did not show a statistically significant association. These findings identify candidate variables for future controlled research but do not establish causal mechanisms or population-level thresholds because of the small sample, limited scenarios, and video-based presentation.