Lights out in cities: Why we need darkness

The energy crisis has inspired cities across Germany to turn off night lights at landmarks, monuments and prominent buildings such as city halls, museums and libraries.

In the capital Berlin, 200 landmarks including the Victory Column and the Berlin Cathedral are to remain unlit when the sun goes down.

Since September 1, the Energy Saving Ordinance has also officially prohibited the illumination of public buildings from the outside. Meanwhile, neon signs may only burn for a few hours a day.

The city of Weimar in central Germany has been saving energy during the summer months by turning street lights on 30 minutes later in the evenings, and turning them off 30 minutes earlier.

But beyond saving power and money, darker cities have many positives both for the climate and biodiversity.

Lights out helps against air pollution

The International Dark-Sky Association, a US-based non-profit, estimates that about one-third of all outdoor lighting burning at night has no benefit. 

Even before the global energy crisis and higher prices, turning off this unnecessary lighting would save $3 billion (€2.9 billion) a year and also help reduce air pollution and harmful emissions that contribute to climate change.

In India, for example, excessive lighting emits 12 million tons of carbon dioxide per year, according to climate change expert Pavan Kumar of the Rhani Lakshmi Bai Central Agricultural University in the state of Uttar Pradesh.

That's equivalent to about half of the total emissions produced by India's air and sea traffic annually. 

Today, more than 80% of people worldwide live under light-polluted skies. In Europe and the US, the figure is as high as 99%, meaning people no longer experience real darkness.

In Singapore, for example, nights have become so bright that people's eyes now struggle to adapt to real darkness.

Why we need darkness

As well as benefiting the environment, sufficient darkness at night is good for human health. Studies have demonstrated the link between artificial light and eye injury, sleeplessness, obesity and, in some cases, depression.

These side-effects are related to a lack of melatonin, a hormone that is released when it gets dark.

"When we don't get that hormone, when we don't produce that hormone because we're exposed to so much light in our apartment, or as a shift worker, then the whole working of this biological clock system becomes problematic," said Christopher Kyba, a scientist at the German Research Center for Geoscience.

A 2020 study from the US shows that children and adolescents who live in areas with an abundance of artificial light get less sleep and suffer more often from emotional issues.

The introduction of artificial light is "one of the most dramatic changes we've made to the biosphere," said Kyba. 

Throughout evolution "there was a constant signal coming from the environment," he explains. "This is daytime, this is nighttime, this is the lunar month. In areas that experience strong light pollution, that signal has been dramatically changed."

Scientists estimate our planet is becoming 2% brighter every year.

So dimming or partially turning off street lights could be a first step in counteracting light pollution. This is despite regulations that deem darkness influences accident or crime rates, an assumption contradicted by one study in England and Wales.

Animals and plants also like it dark

Other species also struggle to adapt to the use of artificial light at night. Corals, for example, don't reproduce as usual; migratory birds can lose their sense of orientation' and newly hatched turtles have been found walking inland, where they die, instead of scuttling toward the sea.

Insects are also affected. One study suggests that an estimated 100 billion nocturnal insects die in Germany each summer as a result of artificial lighting.

Usually reliant on the moon for orientation, some insects become so distracted by bright streetlamps, for example, that they fly around them all night. The ensuing exhaustion can make them easy prey for predators, interfere with their reproduction, or kill them outright. 

Several recent studies have showed that plants growing near streetlights are pollinated significantly less often at night and produce less fruit than when the same plants grow elsewhere in the dark. Even trees feel the impact of light at night — they produce buds earlier and their leaves fall later.

This article was originally published in German.