Light pollution: dangerous, but easy to reduce

A hundred years ago, if you looked up at the night sky, you were guaranteed to see stars. But today, light pollution means that you can hardly see anything, especially in cities. Read more about the importance of light pollution, which not only impairs our view of the starry sky, but also endangers our environment, our safety, our health and that of wild animals.

Light pollution is caused by the inappropriate or excessive use of artificial light. It can have serious environmental impacts on humans, wildlife and the climate. Night-time light from cities in particular leads to excessive brightness, which causes visual discomfort, a brightening of the light sky and so-called “light pollution”. Light falls where it is not intended or needed.

This type of pollution is a side effect of industrialization. Sources include both outdoor and indoor lighting, advertising, commercial properties, offices, factories, sports and event venues and street lighting. Many outdoor night lights are inefficient and excessively bright. They are poorly aimed or inadequately shielded and are often unnecessary. This results in wasted electricity and light shining into the sky instead of focusing on the objects to be illuminated.

Excessive lighting is an international problem. Anyone living in an urban or suburban area can recognize light pollution when they look up at the sky at night. According to the 2016 World Atlas of Artificial Night Sky Brightness, 80 percent of the world’s population lives under skies that are too bright. And in the USA and Europe, as many as 99 percent of people are unable to experience a natural night.

For billions of years, life on earth was dominated by the light of the sun, the moon and the stars. Today, artificial lights overlay the darkness so that cities glow at night. This disrupts the natural day-night rhythm and shifts the balance in the environment. But light pollution also has a negative impact on the climate: it increases energy consumption, disturbs ecosystems and wildlife and can damage human health.

The extent of light pollution depends on the area, brightness and number of light sources, as well as the proportion of light that escapes over the horizon. The reflectivity of surfaces near light sources, such as walls or windows, and atmospheric conditions also have an effect on light pollution. There are formulas for calculating the so-called skyglow values depending on the number of inhabitants and the distance to the observer: Values that are more than ten percent above natural light conditions mean that a significant brightening of the sky has occurred. This can even be the case in small towns with around 3,000 inhabitants, where observers ten kilometers away can still see the effects of light pollution.

One of the main problems with light pollution is that it disrupts the natural body rhythms of humans and animals. Night-time lighting can interrupt sleep and disrupt the internal clock that controls the activities and physiological processes in living organisms. Most important is the production of the hormone melatonin, which the body releases in the dark. Reduced melatonin production due to more light at night can lead to sleep deprivation, fatigue, stress, anxiety, headaches and other health problems. Blue light in particular reduces melatonin levels. This light source comes from phones and computers as well as LEDs found in homes, industrial and street lighting.

Animals also suffer from light pollution: migratory birds, for example, usually fly at night and orient themselves by the light of the stars and the moon. The glare of artificial lighting disturbs them. Sea turtles and bats also rely on natural light to find their way around. In addition, urban birds generally wake up earlier in the day than birds in the wild and sing hours earlier, which can disturb humans. At the same time, peregrine falcons and pigeons benefit from brightly lit cities and choose them more often as breeding grounds, further unbalancing the ecosystem.

Similarly, caterpillars and other insects suffer from slower development in light-polluted areas. As the main food source for birds and other animals, insects are central to the ecosystem. However, as they are attracted to artificial light and die immediately on contact with light sources, they are endangered in cities.

Light pollution affects everyone. The good news is that, unlike many other forms of pollution, it is reversible. Everyone can help make the sky less polluted at night, starting with minimizing the light that emanates from his/her own home. Properly shielding outdoor lighting, drawing blinds and educating others about the problem can help reduce light pollution.

Curbing light pollution helps to save energy, which has a positive impact on climate change, and also helps citizens to save money. The immediate problems caused by excessive light, such as the visibility of stars or people’s ability to concentrate and sleep well, can also be mitigated by reducing light pollution. Better control of night-time lighting has a positive effect on birds and other animals. Many cities have started a “Lights Out” program that reduces lighting on buildings during bird migration.

Well-designed lighting fixtures with modern controls help to direct the light downwards and use as few watts as possible. The idea is to illuminate only those areas that are necessary for safety and orientation. Trees should remain dark at night so as not to disturb nesting birds or bats. Ground lights and bollards, especially near reflective surfaces, are another potential hazard for animals and contribute to night-time pollution. Overall, warmer light and warm white light bulbs are better than cold light.

By the way: You can read more about how energy-saving measures have affected light pollution since 2022 in light of the war in Ukraine here.