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Proc Biol Sci. 2018 Jul 18;285(1883). pii: 20180989. doi: 10.1098/rspb.2018.0989.

Sustained effects of prior red light on pupil diameter and vigilance during subsequent darkness.

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Department of Sleep and Cognition, Netherlands Institute for Neuroscience, 1105 BA Amsterdam, The Netherlands
Sleep Disorders Center, CHU and FMTS, CNRS-UPR 3212, Institute of Cellular and Integrative Neurosciences, University of Strasbourg, 67084 Strasbourg, France.
Center for Chronobiology, Psychiatric Hospital of the University of Basel, CH-4012 Basel, Switzerland.
Department of Sleep and Cognition, Netherlands Institute for Neuroscience, 1105 BA Amsterdam, The Netherlands.
Department of Retinal Signal Processing, Netherlands Institute for Neuroscience, 1105 BA Amsterdam, The Netherlands.
Department of Neurogenetics, Academic Medical Center, University of Amsterdam, 1105 AZ Amsterdam, The Netherlands.
Departments of Integrative Neurophysiology and Psychiatry, Center for Neurogenomics and Cognitive Research (CNCR), Neuroscience Campus Amsterdam, VU University and Medical Center, 1081 HL Amsterdam, The Netherlands.


Environmental light can exert potent effects on physiology and behaviour, including pupil size, vigilance and sleep. Previous work showed that these non-image forming effects can last long beyond discontinuation of short-wavelength light exposure. The possible functional effects after switching off long-wavelength light, however, have been insufficiently characterized. In a series of controlled experiments in healthy adult volunteers, we evaluated the effects of five minutes of intense red light on physiology and performance during subsequent darkness. As compared to prior darkness, prior red light induced a subsequent sustained pupil dilation. Prior red light also increased subsequent heart rate and heart rate variability when subjects were asked to perform a sustained vigilance task during the dark exposure. While these changes suggest an increase in the mental effort required for the task, it could not prevent a post-red slowing of response speed. The suggestion that exposure to intense red light affects vigilance during subsequent darkness, was confirmed in a controlled polysomnographic study that indeed showed a post-red facilitation of sleep onset. Our findings suggest the possibility of using red light as a nightcap.


mental effort; post-illumination effects; pupil diameter; sleep propensity; vigilance

[Available on 2019-07-25]

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