When the days are short, the sun barely shines through urban canyons, and office lighting becomes our only source of light, rese\u00adar\u00adchers speak of \u2018living in biolo\u00adgical dark\u00adness\u2019. In fact, parti\u00adci\u00adpants 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 compa\u00adrison, in bright sunlight outdoors, 50,000 lux or more would be normal.<\/p>\n
But what is so special about light condi\u00adtions in the city? The many buil\u00addings, 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 invi\u00adting, only a frac\u00adtion of it reaches our eyes. This can easily increase in urban envi\u00adron\u00adments. You leave your apart\u00adment in the dark in the morning, take the under\u00adground to the office, sit far away from the window during the day (or are comple\u00adtely shielded from it), and possibly go home in simi\u00adlarly dismal dark\u00adness in the evening \u2013 day after day.<\/p>\n
What does this mean for our body? Along with sleep and food, light is one of our most important zeit\u00adge\u00adbers, control\u00adling the day-night rhythm, influen\u00adcing hormones and thus our mood. This is parti\u00adcu\u00adlarly evident in the study of REM sleep, a sleep phase that is highly depen\u00addent on the internal clock. Those who expe\u00adri\u00adenced extre\u00admely little light at midday showed a noti\u00adceable shift in REM phases at night: shor\u00adtened REM latency, more REM at the begin\u00adning of sleep \u2013 a pattern that was once considered a possible \u2018depres\u00adsion biomarker\u2019.<\/p>\n
We don\u2019t all fall prey to winter depres\u00adsion, but the results show how sensi\u00adtively our brain reacts to slight diffe\u00adrences in light. A lack of moti\u00adva\u00adtion, tired\u00adness and lethargy, as well as the need for more sleep, are just some of the possible reactions.<\/p>\n
A short walk or at least a place by a window, even in an urban envi\u00adron\u00adment, can help to improve your \u2018light balance\u2019. Arti\u00adfi\u00adcial light should be of high quality and as bright as possible \u2013 daylight lamps, with around 5,000\u20136,500 Kelvin, similar to natural daylight, can help. Those who are parti\u00adcu\u00adlarly sensi\u00adtive or feel list\u00adless 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 profes\u00adsional lamps provide at least 10,000 lux.<\/p>\n
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Nowozin C et al. Living in Biolo\u00adgical Dark\u00adness II: Impact of Winter Habi\u00adtual Daytime Light on Night-Time Sleep. Eur J Neurosci. 2025;61(2):e16647.<\/p>\n