This is a week of public awareness about a problem that is current, but not yet fully recognised by society, nor by our decision-makers
– says Prof. Edyta Reszka from the Faculty of Biology and Environmental Protection, University of Lodz.
The so-called light smog, or light pollution is the problem. It's especially visible in cities above streets, advertisements, office buildings and parking lots. Night ceases to be night, because there is light everywhere, twinkling, reflecting off windows and spreading a bright glow across the sky. This is why it's becoming increasingly difficult to see the stars in many places and for many people, the Milky Way is becoming something known more from photographs than from personal experience.
However, the issue isn't just about astronomy. It's also about health. Our bodies love rhythm and rhythm is a biologically determined process. Daytime is for activity, nighttime for calm. Artificial light disrupts this rhythm, especially when it contains a high blue component, typical of modern LED lighting.
In the evening and at night, it stimulates us, alters and modifies our circadian rhythm
– – explains Prof. Reszka and adds that the effects are noticeable very quickly:
This is a problem with falling asleep, a problem with staying asleep.
In practice, this means that even when we're tired, our bodies receive a misleading signal: "It's not bedtime yet" and nighttime awakenings and exposure to light only exacerbate this problem.
Exposure to light inhibits this synthesis
– the researcher talks about melatonin, a hormone secreted at night. This is why it's so important for the bedroom to be truly dark.
It's even more difficult to defend ourselves against outdoor light. Street lamps, illuminated signs and brightly lit buildings affect not only humans but entire ecosystems. This is especially true for nocturnal animals, for whom darkness isn't a lack of light, but a necessary condition for life.
Prof. Reszka recalls the well-known example of turtles that come out at night to lay eggs. Too much light disrupts their natural behaviour. However, there are more similar stories, including those involving birds.
The birds are attracted to this light
– says the researcher, citing the example of two powerful beams of light activated during the 11 September anniversary commemorations in New York.
For migrating birds, such light columns become a trap. The animals lose their orientation, circle, collide with buildings and waste energy needed to continue their journey.
Light also indirectly affects plants and crops by disrupting insect life. And when the insects' rhythm becomes unstable, something much larger begins to falter.
Can we do anything about this?
Yes, we can – and there's no need to plunge cities into darkness. Rather, it's about using light wisely. Where it's needed, only when it's needed and so that it shines downward, not into the sky or into apartment windows.
The most important thing is that outdoor lighting is purposeful, meaning it's actually needed where it's needed
– underlines Prof. Reszka. She explains that lower light intensity, using timers and choosing warmer colours are also important.
International Dark Sky Week has a very simple meaning. It's meant to teach us that light doesn't always mean progress and darkness isn't always a bad thing. Sometimes, darkness itself proves to be essential for healthy sleep, safe bird migration and the simple experience of nighttime.
Acknowledging this problem, not only for us humans, but also for other ecosystems, is the most important thing
– says the researcher.
Night isn't just a backdrop for the city. It's a world all its own. Quieter, more delicate and increasingly being replaced by the white glow of streetlights. Dark Sky Week reminds us that it's still worth preserving – for nature, for our health and for all those moments when we raise our heads and truly see the sky. So, we encourage you to turn off the lights this week and gaze up at the sky (if you can still see the stars through the smog).
The Light Pollution Think Tank Foundation is organising a series of weekly evening webinars (starting at sunset) to mark International Dark Sky Day 2026.
Source: Prof. Edyta Reszka, Faculty of Biology and Environmental Protection, University of Lodz
Edit: Kacper Szczepaniak, Centre for Brand Communications, University of Lodz
