We humans have turned night into day: our artificial lighting makes our planet brighter and brighter at night. Now, for the first time, a new analysis of high-resolution satellite data not only reveals long-term trends in this light pollution, but also makes abrupt changes in nighttime light pollution visible. It shows, for example, that the war in Ukraine had an impact on the nighttime brightness of all of Europe within a very short period of time. At the same time, the data also shows that there are large regional differences in the gradual brightening of the night – and that the nights are even becoming darker again in some regions.
Illuminating streets, buildings and industrial facilities not only brightens the surrounding area, but also the night sky. As a result, around 80 percent of the world’s population no longer sees a really dark night sky and even in remote areas the nights are becoming brighter. In recent years, nighttime sky brightness has increased worldwide, as satellite measurements show. This brightening of the nights not only hinders astronomical observation of the sky, it also disrupts the internal clock of humans and animals. Studies show that migratory birds can deviate from their course in brightly lit areas. In corals, mass spawning, which is normally synchronized by moonlight, is disrupted by artificial light. For us humans, night-time light can disrupt our natural sleep-wake rhythm and cause long-term health damage.
It is therefore important to keep an eye on the extent of light pollution. Until now, this has been done using satellites that measure the nighttime brightness of various regions on a weekly or monthly basis. To evaluate light pollution, data from several satellites and times are usually combined. However, these surveys were unable to capture short-term changes. That has now changed. A team led by Tian Li from the University of Connecticut has now mapped the nighttime illumination in high resolution and in daily time resolution for the first time. “For the first time, daily satellite images were used on a global scale for this purpose,” says co-author Christopher Kyba from the Ruhr University Bochum. Specifically, the researchers used the NASA “Black Marble” data set from 2014 to 2022, which is based on measurement data from a standardized infrared sensor on three different satellites. Together, these record the earth’s surface in the area between 70 degrees north and 60 degrees south every night between one and four o’clock local time. Each pixel covers around 0.5 square kilometers.
China is getting brighter, Europe is getting darker
The evaluations showed that nighttime light pollution increased by around 16 percent globally from 2014 to 2022. “But that doesn’t mean that there will be brightening everywhere,” emphasizes Kyba. Instead, nighttime lighting increased in some regions, by a total of 34 percent, while in others night light decreased, by a total of 18 percent. “The overall value therefore conceals a widespread coexistence of brightening and darkening,” write Li and his colleagues. According to their analysis, changes have intensified in both directions in recent years: “The global nighttime landscape is becoming more dynamic and volatile,” according to the team.
Nocturnal scattered light has increased in many parts of China and India due to the expansion of metropolitan areas and increasing industrialization. In other regions, including Europe, night light levels tended to decrease. “These reductions are particularly pronounced in France with a 33 percent decrease in brightness, in Great Britain with a 22 percent decrease and in the Netherlands with around 15 percent decrease,” the researchers report. They attribute this to the switch to LED lighting, energy conservation measures and targeted reductions in light pollution in many developed countries. “In Germany, light emissions remained constant overall despite local changes,” reports Kyba. “While in some areas of the country light emissions increased by 8.9 percent, in other areas they decreased by 9.2 percent.”
Creeping change and abrupt changes
But in addition to such regional differences, the data also revealed previously largely ignored temporal rhythms: “Human activities and the resulting changes in nighttime illumination are not uniform, linear, or continuous processes,” report Li and his colleagues. “Instead, they show a broad temporal spectrum – from gradual changes such as the expansion of cities or
from switching to LED technology to abrupt events such as industrial construction sites, changes in municipal lighting regulations, power outages due to disasters and disruptions or destruction of infrastructure.”
The corona pandemic provided an example of such sudden changes in brightness: in 2020, there was a decrease in night-time lighting across almost the entire globe; this was particularly noticeable in Asia. “This sudden darkening coincides perfectly with the widespread lockdowns and restrictions on economic and social activity during the first wave of the pandemic,” the team writes. Another example of abrupt changes in brightness occurred in Europe in 2022: “Here we see a strong and sustained decrease in nighttime lighting, contrary to the trends on most other continents,” the researchers report. “This timing coincides with the start of the Russia-Ukraine conflict and the resulting energy crisis in Europe.”
Overall, the nighttime illumination of our planet reveals a lot about its inhabitants. “The data expands and deepens our understanding of how we humans change the night,” write Li and his colleagues. “Our results show that the human light footprint does not just expand uniformly. Instead, this is a dynamic system in which brightening and darkening, abrupt and gradual processes, take place side by side.”
Source: Tian Li (University of Connecticut, Storry) det al., Nature, doi: 10.1038/s41586-026-10260-w