Light and alertness

Acute effects of light on alertness

Alertness (or at the other side of the spectrum: sleepiness) is a human feature largely studied given its relevance for human wellbeing and performance. Alertness can be assessed either by subjective or objective measures. Although the first studies were conducted during the biological night, recent studies have shown that light can have an acute alerting effect both when applied during the night as well as during the day (Phipps-Nelson et at, 2003, Rüger et al, 2006; Smolders et al, 2012). The relationship between light and alertness, either measured with subjective scales or with objective methods, shows a clear dose response curve with light levels; with higher light intensities having a higher alerting effect (Cajochen et al 2000, Hommes & Giménez 2015).


Effects of light on cognition

Light can have a direct positive effect on cognitive performance as well as an indirect positive effect via synchronization of the sleep-wake cycle to the optimal time of the 24h day. Direct effects were shown throughout several studies using cognitive performance tests as a tool. Moreover, recent studies with fMRI have shown how specific brain functions are enhanced with light exposure during specific cognitive tasks  (see review, Chellappa et al., 2011). Indirect effects throughout sleep are based on the observations that disrupted sleep can disturb memory consolidation and lead to cognitive impairment (see review, Chellappa et al., 2011; Astill et al, 2012).

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