Introduction
Nighttime light makes our cities safer, allows businesses and public services to function while others sleep, and improves daily life and overall efficiency. In many ways, it reflects the level of development of modern urban civilization.
But this progress does not come without cost. A growing body of research on artificial light at night (ALAN) has documented adverse health effects associated with excessive exposure:
Various effects of excessive artificial light at night exposure on health have been reported, such as increased risks of cancer, obesity, skin and other diseases, mood disorders, and sleep disorders.
Effects of outdoor artificial light at night on human health and behavior: A literature review – Environmental Pollution (web link)
With this context in mind, this study explores how much of the population in some of the most livable cities in Europe and the United States is exposed to high levels of nighttime light, how this exposure compares between continents, and how it relates to each city’s position in livability rankings.
Setup
For the purposes of this study, we define high nighttime light exposure as areas with radiance ≥ 40 nW/cm²/sr (VIIRS nightlights). This threshold is used as an operational definition to isolate high-brightness urban areas where nighttime light is most intense and where cross-city differences are easier to compare.
We selected the top five cities in Europe and the top five cities in the United States from global livability rankings. In addition, New York City was included as a reference point due to its cultural image as “the city that never sleeps” and its relevance to the topic of nighttime activity.
Europe
- Copenhagen, Denmark (1st in the Livability Ranking)
- Vienna, Austria (2nd)
- Zurich, Switzerland (2nd, same score as Vienna)
- Geneva, Switzerland (5th)
- Luxembourg City, Luxembourg (11th)
United States
- Honolulu, Hawaii (23rd)
- Atlanta, Georgia (29th)
- Pittsburgh, Pennsylvania (30th)
- Seattle, Washington (34th)
- Washington, D.C. (38th)
- New York City, New York (69th)
While US cities rank lower than European cities in this list, this does not affect the validity of the study. The goal is not to establish a new ranking, but to examine how nighttime light exposure relates to existing livability positions — including relative differences between cities and broader continental patterns.
City boundaries were extracted from OpenStreetMap. Population distribution data comes from WorldPop, and nighttime light data comes from NASA / NOAA VIIRS Nighttime Lights products (VNL).
With these components in place, we can now move to the results.
Outcome
The two maps below provide context by showing the selected cities in Europe and the United States. Click the picture to explore the interactive widget, hover over a city to see additional details such as surface area and population.
Having outlined the selected cities, we now examine the results of the nighttime light exposure analysis for each location. For each city, the maps below show:
- the city boundary,
- nighttime light intensity,
- population distribution, and
- areas exceeding the defined harmful nighttime light threshold (marked with red borders).
The visual extent of the red-bordered areas gives an initial impression of nighttime light impact. However, the bar chart at the end of this section provides a clearer picture of how many residents are actually affected relative to the total population.
Europe
United States
The bar charts below shows the proportion of each city’s population living in areas exceeding the pre-selected nighttime light threshold. Cities are ordered by the Livability Ranking.
Click the map to open an interactive widget
New York City has been excluded from this chart because its population is nearly four times larger than Vienna — the second-largest city in the sample — which makes the visualization difficult to interpret when included.
Click the map to open an interactive widget
Detailed numbers and interactive versions of the charts are available in the Study Summary widget.
Conclusions
The results indicate a strong correlation between the share of population living in high-brightness areas and a city’s position in the Livability Ranking. This suggests that nighttime light exposure may be indirectly reflected in broader livability assessments.
Atlanta appears as a clear outlier in the dataset. Investigating the underlying reasons for this deviation would be an interesting direction for further research, although it falls outside the scope of this study.
Overall, European cities in the sample demonstrate lower population exposure to high nighttime brightness than their US counterparts. This aligns with their higher positions in the Livability Index.
Finally, New York City’s unofficial title as a “City That Never Sleeps” appears well deserved in this context, as it records the highest share of population living in high-brightness areas. A deeper comparison between New York and cities closer to it in the Livability Ranking would provide additional insight, but such analysis is beyond the scope of this study.
Limitations
This study relies on satellite-derived nighttime light data, which measures surface radiance rather than direct indoor light exposure. High radiance values do not necessarily translate to individual sleep disruption, as building design, window orientation, shading, and personal habits significantly influence actual exposure.
The threshold of 40 nW/cm²/sr is based on published research, but applying a single global cutoff to cities with different urban forms and lighting policies introduces simplification.
Population data is modeled at raster resolution and represents estimated distribution rather than exact residential counts. While sufficient for comparative analysis, it does not replace detailed census-level microdata.
Finally, correlation with livability rankings does not imply causation. Nighttime light exposure is only one of many factors that may influence overall urban livability.
Technical Notes
Although this study focuses primarily on nighttime lighting and its relationship to livability, a brief note on the tools used is warranted.
Both data processing and visualization were conducted using the GeoForm platform, which integrates and orchestrates open-source technologies for geospatial data management, processing, and visualization.
The data processing pipeline involved clipping, extracting, and summarizing raster cell values using GDAL (gdalwarp, gdal_calc, gdal_polygonize) and PostGIS for low-level spatial operations.
Maps are implemented with Mapbox. Vector data is loaded from S3 via the GeoForm platform, while raster data is served from S3 to Mapbox through TiTiler, also orchestrated by GeoForm.
Questions?
Any questions, comments, or suggestions? Reach out at jacek@geoform.io.
If you would like to see specific topics covered in future studies, commission a similar study for your organization, or collaborate on geospatial analysis or software development, feel free to get in touch.
References
- Tongyu Wang, Naoko Kaida, Kosuke Kaida, Effects of outdoor artificial light at night on human health and behavior: A literature review, Environmental Pollution (web link).
- The Global Liveability Index 2025, The Economist Intelligence Unit (web link).
AI Disclaimer: This study and accompanying article were designed and written by a human author. AI tools were used solely for grammar and style review.