Can you imagine the holidays without a star? Like all of us, we probably can't. The Star of Bethlehem is, in a sense, an icon of Christmas. It guided the three wise men to the newborn Christ. What if this story took place today? Would it be just as easy for them to reach their destination? Thanks to the advancement of civilization, they might have a real problem… Because the star shines, but unfortunately, it's invisible from Earth.

Artificial nighttime lighting and its negative consequences are a subject of interest in the fields of astronomy, human geography, ecology, and human health. There are numerous studies focusing on the impact of light pollution on our ability to view the night sky, as well as on biodiversity, ecosystems, and humans. However, most people are unaware of air, soil, and water pollution caused by hazardous chemicals and plastics. But light? It sounds like a complete abstraction.

Did you know that in the Bieszczady Mountains you can see over 7,000 stars? In a large city like Warsaw, however, you'll see a maximum of 200.

Light pollution is mainly a problem in large cities, where the sky is up to 80 times brighter than in rural areas.  Shop windows, clubs, pubs, restaurants, and, of course, nightlights, most of which are designed so that instead of illuminating only the streets, they also direct light into the sky. This causes the light to be scattered by smog, making stargazing impossible.

However, it's not the lack of stargazing that's the biggest problem. The consequences of nighttime light pollution are much greater and aren't limited to nighttime.

There are many types of light pollution. Among them, so-called "light intrusion" is a significant problem for people living in large cities. Unwanted illumination from neon signs on neighboring buildings or streetlights can intrude into a room where someone is trying to fall asleep. Unfortunately, the sleep hormone melatonin is very sensitive to light. The pineal gland, a small structure in our brain, cannot initiate melatonin production when a light impulse, which inhibits the secretion of this substance, reaches it through our eyes. But our eyes are closed. Yes, but through the thin skin of the eyelids, enough light reaches the retina to make falling asleep difficult, and if sleep does occur, it is shallow and unsatisfying. Furthermore, photoreceptors are also present in our skin, specifically in melanocytes. Melanopsin is highly sensitive to light, so inappropriate lighting at inappropriate times of the day can wreak havoc on our circadian rhythm, sleep, and consequently, our health. A recently published study in mice also demonstrated that neuropsin, present in the hair follicles of these animals, synchronizes the skin's circadian clock with the light-dark cycle independently of the eyes and brain. Therefore, we know that light can directly influence circadian rhythms, thus disrupting them and negatively impacting sleep when it occurs at inappropriate times of the day.

Aleksandra Karykowska, chronobiologist, member of the Polish Sleep Research Society

Find out how to effectively “turn off the lights”