Pupil dynamic adaptation in response to environmental luminance: A controlled laboratory study

Unlike most human factor studies on environmental exposure, where environmental parameters can be directly linked to human responses, the luminous environment involves a unique regulatory process. By controlling luminous stimuli, the pupil serves as a crucial intermediary connecting lighting conditions with human visual perception, circadian regulation, and emotional responses. This study employed an innovative adaptive experimental approach to examine how periodic luminance changes influence the dynamic adaptation of the pupil to identify the underlying principles of pupillary adaptability. Additionally, a longitudinal study was conducted to observe the differences in pupil responses based on varying exposure histories. The results demonstrate that the relative pupil diameter is strongly correlated linearly with the logarithm of luminance. As luminance increases, each unit increase in the logarithmic luminance value caused the pupil to constrict by an additional 70%. Interestingly, as luminance decreases, the pupil dilates by 82% per unit decrease in logarithmic luminance. A progressive increase in relative pupil diameter at identical luminance levels across successive cycles is observed when luminance undergoes periodic cycles of alternating bright and dark. This adaptation continues until stabilization is achieved, typically within the third to fourth cycle. These findings provide new insights into short-term light adaptation in the human visual system and highlight the importance of incorporating pupillary dynamics into the design of indoor lighting strategies for health and comfort.