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This study investigated diurnal non-image forming (NIF) effects of illuminance level on physiological arousal in parallel to NIF effects on vigilance and working memory performance. We employed a counterbalanced within-subjects design in which thirty-nine participants (mean age = 21.2; SD = 2.1; 11 male) completed three 90-minute sessions (165 vs. 600 lux vs. 1700 lux at eye level) either in the morning (N=18) or afternoon (N=21).During each session, participants completed four measurement blocks (incl. one baseline block) each consisting of a 10-minute Psychomotor Vigilance Task (PVT) and a Backwards Digit-Span Task (BDST) including easy trials (4-6 digits) and difficult trials (7-8 digits).Heart rate (HR), skin conductance level (SCL) and systolic blood pressure (SBP) were measured continuously.The results revealed a significant improvement on the BDST difficult trials under 1700 lux vs. 165 lux (p = 0.01), while illuminance level did not affect performance on the PVT and BDST easy trials. Illuminance level impacted HR and SCL, but not SBP. In the afternoon sessions, HR was significantly higher under 1700 lux vs. 165 lux during PVT performance (p = 0.05), while during BDST performance, HR was only slightly higher under 600 vs. 165 lux (p = 0.06). SCL was significantly higher under 1700 lux vs. 165 lux during performance on BDST easy trials (p = 0.02) and showed similar, but nonsignificant trends during the PVT and BDST difficult trials. Although both physiology and performance were affected by illuminance level, no consistent pattern emerged with respect to parallel changes in physiology and performance. Rather, physiology and performance seem to be affected independently, via unique pathways.

Dynamic lighting is designed to have positive effects on well-being and performance. In a field experiment we tested whether these effects are detectable and stable over time when employed in actual work settings. The study consists of two tranches, one following a monthly alternating experimental design, the other a yearly alternating one. This paper reports on the first tranche. In a dual balanced design, office workers experienced dynamic or static lighting according to an a-b-a /b-a-b scheme over three consecutive periods (N = 142, 90, 83). Questionnaire data suggest no significant differences for need for recovery, vitality, alertness, headache and eyestrain, mental health, sleep quality, or subjective performance, although employees were more satisfied with the dynamic lighting. Implications and limitations of the study are discussed.

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