Evening light: disrupts sleep and the biological clock. New clues to why we go to bed so late

Friday 4 November 2011

Researchers at the Surrey Sleep Research Centre at the University of Surrey have found that the evening light we are exposed to in an indoor environment affects our biological clock and disrupts sleep quality.  

The ordinary, artificial indoor-light we are exposed to in the evening suppresses the rise of the sleep-inducing hormone ‘melatonin’.  Artificial light exposure makes us feel less sleepy and, therefore, we may be inclined to delay bedtime.  However, we still have to get up early in the morning and deal with sleep deprivation and the negative health implications associated with it.

The researchers studied daily light exposure at home and then investigated the effects of that light on sleep and biological rhythms.  The spectral composition – the colour of light – was also investigated in terms of what can be engineered to minimise these disruptive effects.  The approach is based on a recently discovered blue-sensitive photoreceptor, which specifically targets the biological clock.  The research team found that by reducing overall light intensity or using yellow light with minimal blue content, or both, the disruptive effects of evening light can be minimised.

The research, which is published in the Journal of Pineal Research, provides a better understanding of these phenomena. It also informs the discussion about double summertime, later school start times and other decisions to be made about when we sleep and wake relative to the natural light-dark cycles.

Professor Derk-Jan Dijk, senior investigator on the study, comments: “During the evening, the availability of electrical light indoors has not only led to a delay of sleep relative to the natural light-dark cycle, but also contributes to sleep deprivation in our society. A better understanding of the mechanisms by which light affects our sleep and biological rhythms may lead to new ways to minimise some of the unwanted effects of artificial light.”

Dr Nayantara Santhi, lead investigator, comments: “It was quite remarkable to see the individual differences in the response to light and we wonder how this may relate to differences in sleep patterns.”

Dr Luc Schlangen, Senior Principal Scientist at Philips Lighting and co-author on the paper said: “The study findings show us that an optimised and more sleep-friendly definition of the indoor light environment in the evenings is desired.’’

The research was part of a collaborative project between the University of Surrey and Philips (and has been funded by Philips).

Editors' Notes

The research is published in The Journal of Pineal Research entitled “The spectral composition of evening light and individual differences in the suppression of melatonin and delay of sleep in humans.” – Santhi N, Thorne HC, van der Veen DR, Johnsen S, Mills SL, Hommes V, Schlangen LJ, Archer SN, Dijk DJ.  J Pineal Res. 2011 Sep 20. doi: 10.1111/j.1600-079X.2011.00970.x

Media Enquiries

Peter La, Press Office at the University of Surrey, Tel: +44 (0)1483 689191, or Email mediarelations@surrey.ac.uk

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