The difference between day and night is becoming less and less obvious as artificial light spreads across the planet.
According to a study published in Science Advances yesterday (22 November), light pollution is increasing rapidly.
The outdoor area of the planet illuminated by artificial light grew by 2.2pc per year from 2012 to 2016, with a total radiance growth of 1.8pc per year.
A dramatic environmental change
The study was led by physicist and ecologist Christopher Kyba of the German Research Centre of Geosciences in Potsdam, who described artificial light as “one of the most dramatic physical changes human beings have made to our environment”.
The research team used the US’s Suomi NPP satellite, which is jointly operated by NASA and the National Oceanic and Atmospheric Administration, to track and map night-time illumination on Earth for four years, recording which square miles remained in darkness and which were lit up.
The researchers filtered out data that could affect the study – such as areas ravaged by wildfires appearing darker because flames had been extinguished, or cloud cover – so they could correctly analyse artificial illumination only.
Lighting up the world
There were large variations in the illumination rates between countries, with Spain and the US remaining the same while most nations in Africa, Asia and South America have seen an increase in brightness.
A handful of countries, including Syria and Yemen, experienced a dip in brightness, which can be attributed to the devastation unrest has caused in these regions.
Kyba told BBC News that the team had expected brightness in wealthy countries to show a decrease as they switched from sodium lights to energy-efficient LEDs.
Instead, they found brightness in the US to have stayed static, while the UK and Germany grew brighter.
The negative effects of artificial light are well documented. A study from the American Medical Association this year showed that blue-white light emitted from LEDs is associated with “reduced sleep times, dissatisfaction with sleep quality, excessive sleepiness, impaired daytime functioning and obesity” while another study from ScienceDirect showed a clear link between brighter light over beach areas and a large decline in the sea turtle population.
Crops and plants are also being affected, as artificial light can cause irregularities in growth patterns – for example, tree buds bursting too soon.
What’s more, the satellite’s sensor does not see the bluer light that humans can see, so the increase in brightness that we notice is in fact greater than what the scientists could measure for this particular study.
Kyba said that humans could make urban areas less bright quite easily, as humans rely on contrast to see as opposed to the quantity of light itself. “That could mean big energy savings but our data show that, on a national and global scale, this is not the direction we are heading.”
A co-author of the study, Franz Hölker of the Leibniz-Institute of Freshwater Ecology and Inland Fisheries in Berlin, said the issue is serious. “Many people are using light at night without really thinking about the cost.”
Aside from the economic implications, ecology, human health and the environment are also paying a high price.