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Related Experiment Video

Updated: Feb 5, 2026

Transcranial Electrical Brain Stimulation in Alert Rodents

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Published on: November 2, 2017

White Light During Daytime Does Not Improve Alertness in Well-rested Individuals.

Renske Lok¹, Tom Woelders¹, Marijke C M Gordijn^1,2

¹University of Groningen, Chronobiology Unit, Groningen Institute for Evolutionary Life Sciences, Groningen, the Netherlands.

Journal of Biological Rhythms

|September 8, 2018

Summary

Daytime light exposure up to 2000 lux did not significantly improve alertness in healthy adults. Time of day impacted alertness, but light intensity did not show a consistent dose-response relationship during the day.

Keywords:

alertness daytime dose-response curve human light

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Area of Science:

Chronobiology
Human Physiology
Light and Health

Background:

Nighttime broad-spectrum light affects alertness in a dose-dependent manner.
The impact of daytime light exposure on alertness requires further investigation.

Purpose of the Study:

To determine if daytime light exposure influences alertness similarly to nighttime exposure.
To investigate the dose-response relationship between light intensity and alertness during daytime.

Main Methods:

Fifty healthy participants were exposed to intermittent dim and experimental light (24-2000 lux) between 0730 and 1730 h.
Alertness was measured using subjective and objective assessments.
Participants were grouped by light intensity, with 10 subjects per intensity level.

Main Results:

Time of day significantly affected all measured parameters of alertness (p < 0.05).
Few dose-response relationships between light intensity and alertness were observed during the day.
No significant dose-response relationships between light intensity and alertness persisted after correction for multiple testing.

Conclusions:

Artificial light up to 2000 lux during daytime does not significantly enhance alertness in non-sleep-deprived individuals.
Time of day is a more critical factor for alertness than light intensity during daytime in healthy adults.