Alerting and vitalizing effects of color temperature during daytime: findings on subjective and objective indicators

We investigated the effects of correlated colour temperature on alertness, vitality and performance during daytime. Results of a within-groups experiment demonstrate time dependent effects on subjective indicators; objective measures are still being analysed

Non-image forming effects of illuminance level:exploring parallel effects on physiological arousal and task performance

\u3cp style= margin: 0px 0px 9px; padding: 0px; border: 0px currentColor; border-image: none; color: rgb(46, 46, 46); font-family: Arial, Helvetica, "Lucida Sans Unicode", "Microsoft Sans Serif", "Segoe UI Symbol", STIXGeneral, "Cambria Math", "Arial Unicode MS", sans-serif; font-size: 16px; word-spacing: -0.15ex; vertical-align: baseline; \u3eThis 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; \u3cem style= margin: 0px; padding: 0px; border: 0px currentColor; border-image: none; vertical-align: baseline; \u3eSD\u3c/em\u3e = 2.1; 11 male) completed three 90-min sessions (165 vs. 600 lx vs. 1700 lx at eye level) either in the morning (\u3cem style= margin: 0px; padding: 0px; border: 0px currentColor; border-image: none; vertical-align: baseline; \u3eN\u3c/em\u3e = 18) or afternoon (\u3cem style= margin: 0px; padding: 0px; border: 0px currentColor; border-image: none; vertical-align: baseline; \u3eN\u3c/em\u3e = 21). During each session, participants completed four measurement blocks (incl. one baseline block) each consisting of a 10-min 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.\u3c/p\u3e\u3cp style= margin: 0px 0px 9px; padding: 0px; border: 0px currentColor; border-image: none; color: rgb(46, 46, 46); font-family: Arial, Helvetica, "Lucida Sans Unicode", "Microsoft Sans Serif", "Segoe UI Symbol", STIXGeneral, "Cambria Math", "Arial Unicode MS", sans-serif; font-size: 16px; word-spacing: -0.15ex; vertical-align: baseline; \u3eThe results revealed significant improvements in performance on the BDST difficult trials under 1700 lx vs. 165 lx (\u3cem style= margin: 0px; padding: 0px; border: 0px currentColor; border-image: none; vertical-align: baseline; \u3ep\u3c/em\u3e = 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 lx vs. 165 lx during PVT performance (\u3cem style= margin: 0px; padding: 0px; border: 0px currentColor; border-image: none; vertical-align: baseline; \u3ep\u3c/em\u3e = 0.05), while during BDST performance, HR was only slightly higher under 600 vs. 165 lx (\u3cem style= margin: 0px; padding: 0px; border: 0px currentColor; border-image: none; vertical-align: baseline; \u3ep\u3c/em\u3e = 0.06). SCL was significantly higher under 1700 lx vs. 165 lx during performance on BDST easy trials (\u3cem style= margin: 0px; padding: 0px; border: 0px currentColor; border-image: none; vertical-align: baseline; \u3ep\u3c/em\u3e = 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 seemed to be affected independently, via unique pathways.\u3c/p\u3

Shining light on memory:Effects of bright light on working memory performance

This study examined whether diurnal non-image forming (NIF) effects of illuminance level on cognitive task performance depend on task difficulty and time of day. We employed a balanced crossover design with two 60-min sessions of 200 vs. 1000 lux at eye level. Digit-span task difficulty was manipulated\u3cbr/\u3ewithin subjects (forward (FDST) vs. backward (BDST) digit-span task), n-back task difficulty was manipulated between subjects (n = 1, 2, or 3). Bright light exposure improved FDST performance during the final measurement block, especially in the afternoon. In contrast, BDST performance deteriorated slightly under bright light in the afternoon. Two-back performance was significantly worse under bright lighting the afternoon, while no effect of illuminance level was found on 3-back performance. Thus, the more difficult BDST was affected differently by light intensity as compared to the easier FDST. N-back accuracy, however, did not confirm this role of task difficulty. Future studies should investigate whether similar results hold for other types of tasks and how other variables (e.g., time of day, physiological arousal, or other task characteristics) may influence the direction and magnitude of NIF effects on performance

Higher light intensity induces modulations in brain activity even during regular daytime working hours

We investigated the effect of exposure to bright white light as compared to a commonly experienced illuminance (1000 lx vs. 200 lx at eye level, 4000 K) on electroencephalography spectral power density during daytime. Spectral power density was measured during one hour of exposure in the morning and in the afternoon. Results showed a lower relative power density in the theta range under bright light. In the morning, relative alpha power was also lower under exposure to 1000 lx. The current findings extend earlier results on the effect of illuminance on alertness and arousal in the late evening and at night. Moreover, they largely corroborate results on subjective experience and sustained attention during daytime, and together suggest higher alertness under brighter light even for daytime exposure in everyday situations

Seasonal and time-of-day variations in acute non-image forming effects of illuminance level on performance, physiology and subjective well-being

This study investigated seasonal and time-of-day dependent moderations in the strength and direction of acute diurnal non-image forming (NIF) effects of illuminance level on performance, physiology and subjective well-being. Even though there are indications for temporal variations in NIF-responsiveness to bright light, scientific insights into potential moderations by season are scarce. Moreover, it is still unknown whether effects of time-of-day influences on NIF effects are persistent throughout the year.\u3cbr/\u3eWe employed a mixed 2 (Light: 165 vs. 1700 lx at eye level, within) x 2 (Season: autumn/winter vs. spring, between) x 2 (Time of day: morning vs. afternoon, between) mixed-model design. During each of the two 90-min experimental sessions, participants (autumn/winter: N=34; spring: N=39) completed four measurement blocks (incl. one baseline block of 120 lx at eye level) each consisting of a 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) and skin conductance level (SCL) were measured continuously. At the end of each lighting condition, subjective sleepiness, vitality and mood were measured. \u3cbr/\u3eResults revealed a clear indication for significant Light * Season interaction effects on both subjective sleepiness and vitality, which appeared only during the morning sessions. Participants felt significantly more vital and less sleepy in winter, but not in spring, after bright light exposure in the morning. In line with these subjective parameters, participants also showed significantly better PVT performance in the morning in autumn/winter but not in spring under bright light exposure. Surprisingly, for difficult working memory performance the opposite was found, namely worse performance during bright light exposure in winter but better performance when exposed to bright light in spring. Effects of bright vs. regular light exposure on physiology were quite subtle and largely nonsignificant. Season did not seem to play an important moderating role in these effects. Overall, it can be concluded that acute illuminance-induced NIF effects on subjective alertness and vitality as well as objectively measured vigilance in the morning are significantly moderated by season. Possibly, these greater illuminance-induced benefits during the morning sessions in autumn/winter compared to spring occurred due to increased responsiveness to bright light as a function of a relatively low prior light dose in autumn/winter.\u3cbr/\u3