Brief CommunicationLet there be no light: the effect of bedside light on sleep quality and background electroencephalographic rhythms
Introduction
Exposure to light at night is now considered to be ordinary. Artificial light certainly has beneficial aspects; it has extended the length of productive days of work and recreational activities. However, when it becomes unreasonably excessive, it can be considered as light pollution, negatively affecting human physiology [1]. It may disturb circadian organization; influence neuroendocrine systems; and cause many diseases, such as obesity [2], diabetes mellitus, depression, and even cancers [1].
Artificial lighting also is commonplace in bedrooms, and individuals with poor sleep hygiene often deliberately or unintentionally fall asleep with lights on. For example, one may fall asleep late night with the television light on, and children who are afraid of the dark may ask their parents to keep their lights on during sleep. Light exposure may affect sleep quality, but there have been no systemic comparative studies with objective measures. If any difference exists, it may be reflected in background brain oscillations. Here we performed two whole-night polysomnography (PSG) sessions, one with lights off and one with lights on, to investigate the effect of light on sleep quality and brain activity.
Section snippets
Methods
Ten young healthy volunteers (4 women; mean age, 27 years; range, 21–34 years) participated in our study, which was reviewed and approved by the local internal review committee. All participants gave fully informed written consent. They were all healthy sleepers without major health problems, including no neurologic, psychiatric, or endocrine disorders. Interviews and the Pittsburgh Sleep Quality Index [3] suggested normal and regular sleep–wake habits. First the PSG was performed with the lights
Results
All participants demonstrated normal patterns of sleep. With the lights on, nine participants reported higher scores in subjective feeling of frequent arousals and shallow sleep. We extracted PSG variables (Table 1) that were appropriate in evaluating sleep quality. There was no significant difference in total bed time, total sleep time, or sleep efficiency between lights-off and lights-on sleep. However, constant exposure to dim light affected sleep architecture, increasing the proportion of
Discussion
Unintentional or intentional light exposure during sleep is becoming increasingly more common due to the widespread use of artificial lighting, and its negative effect on health is a major theme of research. Whole-night light exposure demonstrated acute effects on sleep architecture and brain activity, including shallow sleep, frequent arousals, and reduction of power in SWA and spindle frequency bands during NREM sleep and theta frequency bands during REM sleep.
Light is the major synchronizer
Funding sources
This study is supported by a Grant of the Korean Health Technology R&D Project, Ministry for Health, Welfare & Family Affairs, Republic of Korea (No. A110097) and by a grant of the Korea Healthcare technology R&D Project, Ministry of Health and Welfare, Republic of Korea (HI10C2020).
Conflict of interest
The ICMJE Uniform Disclosure Form for Potential Conflicts of Interest associated with this article can be viewed by clicking on the following link: http://dx.doi.org/10.1016/j.sleep.2013.09.007.
Acknowledgment
The authors appreciate the effort of volunteers and technicians in their sleep clinic.
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