Lighting for circadian rhythms

Lighting for circadian rhythms was written by Dr Paul Littlefair and Dr Cosmin Ticleanu and was published by the BRE Trust in October 2019.

People have circadian rhythms linked to the natural light/dark cycle of the day. These control patterns of alertness and sleep as well as other factors such as body temperature and the release of various hormones. Light and dark patterns act as the most important signal to entrain (synchronise) the circadian clock to the solar cycle and cause waking and sleeping to occur at consistent times.

A combination of bright light during the day and darkness at night helps maintain the daily cycle of waking and sleep. However, exposure to artificial light at the wrong times of day can have an adverse effect on circadian rhythms. Light at night time can alter the body clock, suppressing melatonin production and keeping people awake at night, and making them more sleepy during the day.

Circadian lighting varies in colour and intensity during the day. The aim is to improve alertness during working hours using bright light, but to switch to lower brightness, warmer coloured light before it is time to relax.

This report presents the results of an experiment to assess circadian lighting and provides guidance for building owners and occupiers, lighting designers, lighting manufacturers and installers.

Its contents are:

• Abstract.
• Introduction.
• Colour of light.
• Dynamic lighting: previous studies.
• Existing recommendations.
• An experiment to assess variable lighting.
• Results.
• Discussion.
• Conclusions and recommendations.
• Acknowledgements.
• References.

--BRE Group

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