Effects of light on daytime alertness

What is it about?

Broad-spectrum light applied during the night has been shown to affect alertness in a dose-dependent manner. The goal of this experiment was to investigate whether a similar relationship could be established for light exposure during daytime. 50 healthy participants were subjected to a paradigm (07:30 AM - 5:30 PM) in which they were intermittently exposed to 1.5 hours of dim light (DL, <10 lux) and 1 hour of experimental light (EL, ranging from 24 to 2000 lux). The same intensity of EL was used throughout the day, resulting in groups of 10 subjects per intensity. Alertness was assessed with subjective and multiple objective measures. There was a significant effect of time of day in all parameters of alertness (p<0.05). Significant dose-response relationships between light intensity and alertness during the day could be determined in a few of the used parameters of alertness on some times of the day; however none survived correction for multiple testing. We conclude that artificial light applied during daytime at intensities up to 2000 lux does not elicit significant improvements in alertness in non-sleep deprived subjects.

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Why is it important?

Humans are diurnal, with optimal psychological and physiological performance during daytime. Alertness is known to affect many functions, such as performance, psychological and physiological well-being, caloric intake and pain sensitivity. Thus, displaying optimal alertness is beneficial in many facets of everyday life.