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Home » Blog » Between high-rise buildings and winter grey: living in biological darkness

Between high-rise buil­dings and winter grey: living in biolo­gical darkness

When the days are short, the sun barely shines through urban canyons, and office lighting becomes our only source of light, rese­ar­chers speak of ‘living in biolo­gical dark­ness’. In fact, parti­ci­pants in a Berlin study received little more than 80 lux for around 70 per cent of their active time on winter days. The values were only just over 500 lux for 36 minutes a day. By way of compa­rison, in bright sunlight outdoors, 50,000 lux or more would be normal.

But what is so special about light condi­tions in the city? The many buil­dings, narrow streets and the fact that we often spend time indoors ensure that we get even less natural daylight here than we usually do at this time of year. Even when the light outside is invi­ting, only a frac­tion of it reaches our eyes. This can easily increase in urban envi­ron­ments. You leave your apart­ment in the dark in the morning, take the under­ground to the office, sit far away from the window during the day (or are comple­tely shielded from it), and possibly go home in simi­larly dismal dark­ness in the evening – day after day.

What does this mean for our body? Along with sleep and food, light is one of our most important zeit­ge­bers, control­ling the day-night rhythm, influen­cing hormones and thus our mood. This is parti­cu­larly evident in the study of REM sleep, a sleep phase that is highly depen­dent on the internal clock. Those who expe­ri­enced extre­mely little light at midday showed a noti­ceable shift in REM phases at night: shor­tened REM latency, more REM at the begin­ning of sleep – a pattern that was once considered a possible ‘depres­sion biomarker’.

We don’t all fall prey to winter depres­sion, but the results show how sensi­tively our brain reacts to slight diffe­rences in light. A lack of moti­va­tion, tired­ness and lethargy, as well as the need for more sleep, are just some of the possible reactions.

A short walk or at least a place by a window, even in an urban envi­ron­ment, can help to improve your ‘light balance’. Arti­fi­cial light should be of high quality and as bright as possible – daylight lamps, with around 5,000–6,500 Kelvin, similar to natural daylight, can help. Those who are parti­cu­larly sensi­tive or feel list­less often benefit from adding half an hour of light therapy with such a lamp to their usual shower in the morning. 2,500 lux is helpful for this, but profes­sional lamps provide at least 10,000 lux.

 

Nowozin C et al. Living in Biolo­gical Dark­ness II: Impact of Winter Habi­tual Daytime Light on Night-Time Sleep. Eur J Neurosci. 2025;61(2):e16647.

https://onlinelibrary.wiley.com/doi/10.1111/ejn.16647