Light at the Right Time
30 April 2020
Sensory Perception (Vision, taste, hearing, speech)
Time your outside activity during the lockdown to take place in the morning hours.
Light exposure affects us profoundly. The clocks in our brains and bodies are exquisitely sensitive to light, and synchronise with light during the day and darkness during the night. On the flipside, light exposure at the wrong time can disrupt our body clock. For example, looking at the glaring light of a smartphone in bed at night can shift our body clock to later times. Our circadian physiology is complex and an active research, but there are a few things we know for sure. In general, bright light during the day and no light during the night – just like the “natural” cycle of illumination by daylight – enables our clock to stay “on time.”
What happens when our circadian rhythms are out of sync with the day and night cycle? There is mounting convincing evidence that disruption of our circadian rhythms can be bad for our general health. Shift workers, who experience irregular patterns of light exposure, have higher rates of chronic diseases. But also in people working more classical daytime hours, there is link between circadian rhythms, and mental and physical health.
As the UK is entering the 7th week of lockdown measures, our personal and professional lives remain upended by the COVID-19 pandemic. Schools, pubs, restaurants, gyms and many other places where we usually go to meet other people remain closed and the lifting of lockdown measures is all but uncertain. Many of us are simply staying at, working from home and, in the absence of a dedicated “study” room, are turning kitchen tables into desks where we connect with our colleagues using conference calls. It is important to take stock of how the lockdown has affected not only our social lives, but also how our spectral diet – the total amount of light that we receive throughout the day and night – has changed, and what we can do to help our rhythms stay on time.
We can quantify how much light we are exposed to using a simple number with a complicated name: the melanopic equivalent daylight illuminance (EDI) expressed in lux. Outdoors on a sunny day with clear blue sky, we can reach values over 50,000 lux melanopic EDI, but these values are lower when the sky is overcast, or in the shade. Indoors, the values can be 100 to 1000 times lower. This is true even without lockdown measures: indoor workers simply receive much less light than outdoors workers. Now that many people are working from home, it would be expected that spectral diet has also changed, with less light exposure during daytime hours.
But it’s not only how much light that we get that matters – but also when. Light exposure in the morning advances our circadian rhythm and can gives us a boost of alertness that can kickstart the day. Many people would get this natural exposure to light during their commute to work, which for many now has been cut short.
To get this natural boost from daylight, it is best to perform our daily allowed outdoor activity in the morning, if possible. When that isn’t possible, sitting by the window would be recommended.
Ultimately, light exposure is just one piece to ensure that our body clock is not out of sync. The Society for Light Treatment and Biological Rhythms (SLTBR) recommends the following simple strategies:
- set up routines where possible
- wake up at the same time and go to sleep every day
- spend time outdoors, especially in the morning; or spend at least 2 hours next to window
- schedule in regular activities, such as exercise, social interactions
- avoid naps during daytime (or limit 30 minutes)
- avoid exposure to screens in the evening and at night
It’s important to keep in mind that the lockdown is a “marathon, not a sprint” and developing these habits can support us and our well-being in the long-run.
About the author: Manuel Spitschan PhD, is a Sir Henry Wellcome Fellow at the Department of Experimental Psychology and a Biomedical Sciences Junior Research Fellow at Linacre College at the University of Oxford. You can find him on Twitter (@mspitschan) and ORCID (0000-0002-8572-9268).