Light, Alertness, and Alerting Effects of White Light: A Literature Overview

Abstract

Light is known to elicit non–image-forming responses, such as effects on alertness. This has been reported especially during light exposure at night. Nighttime results might not be translatable to the day. This article aims to provide an overview of (1) neural mechanisms regulating alertness, (2) ways of measuring and quantifying alertness, and (3) the current literature specifically regarding effects of different intensities of white light on various measures and correlates of alertness during the daytime. In general, the present literature provides inconclusive results on alerting effects of the intensity of white light during daytime, particularly for objective measures and correlates of alertness. However, the various research paradigms employed in earlier studies differed substantially, and most studies tested only a limited set of lighting conditions. Therefore, the alerting potential of exposure to more intense white light should be investigated in a systematic, dose-dependent manner with multiple correlates of alertness and within one experimental paradigm over the course of day.

Daytime melatonin and light independently affect human alertness and body temperature

“…Underlying neuronal mechanisms therefore differ. Studies investigating alerting effects of light during daytime after sleep deprivation found significant effects while several studies in rested individuals did not for a review see . Sleep deprivation alters sleep pressure, suggesting that these levels are important for alerting effects of light .…”

“…Our study did not demonstrate alerting effects of light after placebo ingestion, indicating that light under these circumstance does not induce alertness during daytime, confirming previous observations . This emphasizes differences between night and day, since alerting effects of light during the night have been reported (reviews in Ref …”

“…Alertness is known to affect many functions, such as performance, psychological and physiological well‐being, caloric intake, and pain sensitivity . Displaying optimal alertness is thus beneficial, and many studies have attempted to improve alertness using monochromatic or polychromatic light (for review see,). Exposure to light improves alertness during nighttime, when melatonin concentrations are usually high and CBT decreases .…”

“…Exposure to light improves alertness during nighttime, when melatonin concentrations are usually high and CBT decreases. [9][10][11]16,[20][21][22][23][24][25] However, several studies report absence of light-induced alertness during daytime, when alertness and CBT levels are high and melatonin is absent, 18,20,[26][27][28][29][30][31][32][33][34][35][36][37][38][39][40] , although other studies report contradictory data. 10,41,42 These paradoxical findings can be reconciled when an alertness ceiling level during daytime is considered, which prevents light to further increase alertness.…”

Assessment of visual fatigue under LED tunable white light with different blue components

“…Light exposure has a great neurobiological effect on humans such as pupil constriction and brain cognition . The intensity, timing, duration, and spectral characteristics of light all contribute to these effects . However, the related mechanism is still unclear, particularly the spectral influence on the neurobiological system.…”