NIF and IF effects of different light scenarios in a real-life office setting

BackgroundEffects of light on well-being and performance are often studied in the controlled confines of a laboratory. In real-life, we need to optimally balance circadian and acute effects on the one hand and visual comfort on the other, as both impact human daytime functioning and wellbeing. Objective Our aim was to investigate concurrent IF and NIF effects of three contrasting light scenarios on alertness, mood and comfort in a real-life office context. Method Two field studies were performed (summer vs. winter) in an office in The Netherlands. The study received approval of the local ethical committee. In summer 12 office workers (1 female, Mage = 45) participated, in winter 11 (1 female, Mage = 43). Each study lasted 3 weeks - one for each scenario. In contrast to a constant neutral electric light scenario (300 lx on desk, 100 lx at the eye, 4000 K), we tested a scenario with morning bright light (900 lx on desk, 300 lux at the eye) and a scenario with afternoon bright light. On top of these electric scenarios, the daylight added substantially to illuminances at desk and eye.We employed experience sampling (alertness (KSS), vitality, mood and light and temperature appraisals, 10 times per day) in combination with continuous person-worn and office-bound sensors (objective light exposure, skin temperature and actigraphy). FindingsPreliminary results indicate that bright electric light was perceived as less pleasant in summer. Moreover, alertness and vitality scores were lower throughout days with bright morning light. In contrast, pleasantness was not affected by the conditions in winter, and vitality and mood significantly dropped after morning bright light in the first week. Conclusions and ImplicationsWhen designing light interventions it is important to take both NIF and IF effects into account. Brighter light is not always better, particularly in real-life environments.