Earth’s nights are steadily getting brighter. However, these changes vary dramatically by region. In terms of areas becoming brighter, rapid urban growth is lighting up countries like China and India. In contrast, parts of Europe are dimming due to energy-saving efforts and new lighting technologies. Beyond these two poles, global trends often mask sharp local contrasts, from war-related blackouts to deliberate reductions in light pollution.
An assessment of detailed satellite analysis, from Ruhr-University Bochum, shows these shifts happening faster and more unevenly than expected. Data was collected from the VIIRS DNB instrument, covering the years 2014 to 2022. The overall trends indicate that global night time lighting has been increasing by roughly two percent each year.
The Visible Infrared Imaging Radiometer Suite (VIIRS) Day-Night Band (DNB) is a key instrument aboard the Suomi National Polar-orbiting Partnership (Suomi NPP) satellites, designed to collect visible and near-infrared light data. It operates over wavelengths from 0.5 to 0.9 micrometres, providing high-resolution imagery and radiometric measurements of Earth’s surface in both day and night time conditions.
The satellite collects 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 kilometres.
To harness insights from the images, the research team applied a new algorithm that accounts for the angle at which the satellite views the Earth. For instance, residential neighbourhoods tend to appear brighter when seen at an angle, while dense city centres often look brighter from directly overhead. Incorporating these differences allowed for a more accurate picture of how light emissions are changing.
Brightness Linked To Global Emissions
Although there has been a total increase of 16 percent worldwide, that does not mean that lighting is increasing everywhere. The scientists found that in areas where lighting increased, 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 night time lighting are more dynamic and localised 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 light emitting diode (LED) technology together with policies aimed at reducing light pollution.
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.
Light pollution is the excessive or misdirected artificial light that disrupts natural darkness, affecting the environment, human health, and visibility of the night sky.
Regional Shifts Reflect Policy and Conflict
Not all changes are gradual. Ukraine experienced a sharp drop in night time lighting after the Russian invasion. France also saw a major reduction, with night time brightness falling by 33 percent as many cities turn off streetlights after midnight to conserve energy and limit light pollution. Whereas, in Germany light emissions remained almost constant overall despite local variations.
Across Europe as a whole, satellite measurements show a four percent decrease in night time 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.
Ecological Impact
Artificial light is a major consumer of electricity at night, and light pollution harms ecosystems. Here, satellites are capturing human civilization’s glowing pulse, yielding a spectrum of information and shifts over time.
The research features in the science journal Nature with the research paper headed “Satellite imagery reveals increasing volatility in human night-time activity.”
