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Why do we sleep so late?

A couple of our science advisors wrote some blogs about Good Light. In this blog Daan Van Der Veen, Science Advisor of the Good Light Group, watched and summarized the new animation ‘Why do we sleep so late’.

In a new animation by researchers at the University of Surrey, UK, it is explained how artificial light exposure at night is driving us to delay our bedtime and leaves us tired and reluctant to start the day when the alarm clock wakes us the next morning.

Humans – and many other species on our planet – have evolved internal biological clocks that drive daily rhythms in our sleep and activity patterns. But in contrast to our wrist watches or alarm clocks these biological clocks do not run to exactly 24 hours - depending on the species, biological clocks express a period that is slightly shorter or longer than 24 hours. To ensure that these biological clocks stay synchronised with the 24-hour day on earth, a mechanism evolved by which daylight adjust the timing of these internal clocks each day. If morning light exposure falls earlier than expected, humans move the arm of their internal clock forward to catch up; if evening light falls later than expected, the arm of the clock is moved back to delay starting the restful evening and subsequent sleep.

In the modern world we are exposed to electrical light late in the evening, and as a result we are delaying our biological clocks and holding back on a timely start of our sleep. If late sleep then also leads to late waking (but this is often only in weekends for many people in e.g. daytime employment or school-going children), we miss out on the important morning light that synchronises our clocks and rhythms to drive active wakefulness. The solution, Professors Dijk and Skeldon indicate, is to actively seek bright morning light exposure and avoid bright light in the evening. This will keep our biological clocks synchronised and promote timely sleep and waking.

This animation nicely shows why good timing of daily light exposure is so important for sleep, and by extension also suggests that regularity of this light exposure is key to good synchronisation of biological clocks. It’s not just about the timing - the characteristics of the light will have an impact on both the response of the biological clock, as well as the direct effects of light on sleepiness. As the authors say: light is both the problem and the solution, and tailoring timing and quality of artificial light exposure in our urbanised, 24-hour society will be hugely important to driving timing of good quality sleep, and many other daily behaviours that contribute to health and wellbeing.



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