The world is getting brighter at night but some places are going dark

"Although there has been a total increase of 16 percent worldwide, that does not mean that lighting is increasing everywhere," explained Christopher Kyba. "In areas where lighting increased, we found global emissions rose by 34 percent. This was offset by an 18 percent decrease in emissions from other areas."

These findings reveal that changes in nighttime lighting are more dynamic and localized than previously understood. Rapid urban growth made countries like China and India significantly brighter during the study period. In contrast, some industrialized nations saw declines in light emissions, often linked to the adoption of LED technology and policies aimed at reducing light pollution.

Regional Shifts Reflect Policy and Conflict

Not all changes are gradual. Ukraine experienced a sharp drop in nighttime lighting after the Russian invasion. France also saw a major reduction, with nighttime brightness falling by 33 percent as many cities turn off streetlights after midnight to conserve energy and limit light pollution.

"In Germany, light emissions remained almost constant overall despite local variations," Kyba reports. "While light emissions rose by 8.9 percent in brightening German regions, they fell by 9.2 percent in dimming areas."

Across Europe as a whole, satellite measurements show a four percent decrease in nighttime light emissions. However, this decline may not fully match what people perceive on the ground, since the satellite detects light differently than the human eye.

High Resolution Data Reveals Faster Changes

A key advance in this study is the use of full resolution nightly data. Earlier analyses relied on monthly or yearly averages, which made it harder to spot short term or localized changes.

"Until now, no global analysis had been conducted using the full-resolution nighttime data," Kyba emphasizes.

The research team also applied a new algorithm that accounts for the angle at which the satellite views the Earth. For instance, residential neighborhoods tend to appear brighter when seen at an angle, while dense city centers often look brighter from directly overhead. Incorporating these differences allowed for a more accurate picture of how light emissions are changing.

How the Satellites Track Earth at Night

The study is based on data from the Visible Infrared Imaging Radiometer Suite (VIIRS) Day/Night Band (DNB), carried by the Suomi NPP, NOAA-20, and NOAA-21 satellites operated by NOAA and NASA.

These satellites collect images after midnight, usually between 1:00 a.m. and 4:00 a.m. local time, and scan nearly the entire planet each night between 70° North and 60° South. Each pixel in the imagery represents about 0.5 square kilometers.

To ensure accuracy, researchers focused only on artificial light sources. Natural phenomena such as wildfires and auroras, which the satellites can also detect, were excluded from the analysis.

A Push for a Next Generation European Satellite

Understanding how nighttime lighting is changing has practical importance. "Artificial light is a major consumer of electricity at night, and light pollution harms ecosystems," says Christopher Kyba. "It is therefore important to understand how both of these are changing."

Kyba is leading efforts to develop a new satellite designed specifically to monitor night lights, as part of the European Space Agency's (ESA) "Earth Explorer 13" mission. This proposed system would detect much fainter light sources and offer significantly higher resolution, reducing uncertainty about global lighting trends.

"While the U.S. and China each have multiple satellites that observe nighttime light, there is currently no European satellite designed for this purpose," says Kyba.