Alerting Effect of Light: A Review of Daytime Studies

Light affects humans beyond only image formation. Several studies have reported that light can increase daytime alertness and can therefore be positively utilized to counter daytime fatigue and increase productivity in workspaces. This systematic review summarized and analysed relevant literature that investigated the daytime alerting effect of light. Using keywords “alertness” and “light” in the title we retrieved a total of 142 studies via three search engines. Out of 142 studies, only 26 investigated the alerting effect of light during daytime. Six studies were excluded from the review based on the exclusion criteria. We reviewed twenty articles from the year 1991 until 2022 that have investigated the alerting effect of polychromatic and monochromatic light sources. Only seven out of twenty studies found an alerting effect that was recorded through positive self-assessment or enhancement of cognitive processes. The studies in which the lighting application would be transferrable for office use were highlighted. A specific common trend regarding the enhancement of alertness was not detected, as different lighting conditions and protocols were applied in the reviewed studies. More studies that investigate the effect of polychromatic light with intensities and spectral compositions that are suitable for application in realistic working environments are necessary to determine whether the daytime alerting effect of light will be significant.