Less is more?  : Effects of more vs. less electric light on alertness, mood, sleep and appraisals of light in an operational office

Given the fact that most office workers spend substantial parts of their working day – and life – indoors, it is important to provide healthy conditions in the office. An important factor in this respect is lighting. Many laboratory studies have investigated acute effects of light on people’s alertness and cognitive performance, as well as effects on sleep. Yet, little is known about how these effects translate to experiences in operational work environments. In two field studies, performed in spring and winter respectively, we investigated the effects of daytime exposure to more intense light in the morning or afternoon for relatively long exposure times (i.e., each light condition lasted 4 hours a day for one workweek) on subjective sleepiness, vitality, mood, and fatigue, sleep and light appraisals. The results indicated that at no time did adding more light lead to positive results. On the contrary, especially in spring, participants experienced both acute and delayed negative effects of more electric light on sleepiness and vitality. In spring, the conditions with more electric light were also experienced as less pleasant. In winter, participants reported going to sleep later in the conditions with more electric light. Importantly, the effects on affective state and sleep in this study were very modest, whereas those on light appraisals were more substantial and robust, which emphasizes that we should never disregard visual effects, even if we are aiming for light-induced effects beyond vision.