The visual and non-visual effects of annual daylighting performance on middle school students: A longitudinal field survey of classrooms in Eastern China

Daylight can not only render a visual comfort environment but also enhance the productivity, mood, and health for occupants in educational buildings. A set of objective metrics (daylighting and circadian metrics) were evaluated by field studies in six classrooms with different building parameters among three schools in eastern China. Ladybug, Honeybee and Lark based on Radiance were used to calculate four daylighting metrics and two circadian metrics, respectively. Considering integrative lighting, a long-term field survey was conducted over winter, spring, and summer to assess students' visual and non-visual health. The survey involved four dimensions including daylight provision, daylight comfort, satisfaction, and perceived productivity. A correlation analysis was performed on the objective metrics and students' health perception. The results showed that window characteristics (glass transmittance and window to floor ratio) had a substantial impact on achieving target horizontal illuminance in classrooms, while the reflectance of interior surface enhanced vertical illuminance, potentially promoting non-visual health. The students' rating substantially increased with the improved external view quality. Among objective metrics, the Spatial Daylight Autonomy at 500 lx for 50 % of annual hours (sDA500,50%) demonstrated a strong correlation with students' daylight comfort, satisfaction and perceived productivity, while the Useful Daylight Illuminance (UDI) autonomous (UDI300-3000) showed a moderate correlation with the four dimensions of students' health perception. It was also found the Melanopic Equivalent Daylight Illuminance (mel-EDI) could indicate students' health perception. In this study, Circadian Frequency (CF) was proposed as an annual circadian metric for assessing students' non-visual health. Floor levels exhibited a significant positive correlation with students' satisfaction, while corridor width demonstrated a notable negative correlation. The study provides insights for the early design phase of educational buildings, and recommendations for promoting both visual and non-visual health of adolescents, improving human-centered healthy lighting conditions in classrooms.