Nighttime Light Emissions
The class of terrestrial-technosignature consisting of artificial light emitted by human civilization at night, measured from orbit and used as a working model for what an alien observer could detect from a comparably industrialized exoplanet.
Measurement
The primary global instrument is VIIRS DNB aboard suomi-npp, NOAA-20, and NOAA-21 — sensitive enough to detect city lights, fishing fleets, and wildfires at ~0.5 km² per pixel, with full-disk nightly coverage between 70°N and 60°S. A successor — esa earth-explorer-13 — is proposed for higher resolution and fainter sources.
2014–2022 trajectory (christopher-kyba)
Per src-terrestrial-technosignatures-satellites-2026-04, global emissions rose ~16% over the 2014–2022 period (~2%/year), decomposing as:
- +34% in brightening regions (urbanization-driven)
- −18% in dimming regions (regulation, LED conversion, conflict)
Regional patterns:
- China, India — strong brightening; urbanization and industrialization.
- France — −33%, attributed to post-midnight streetlight curfews and LED conversion (which can reduce upward-spilled flux per fixture).
- Europe overall — −4%.
- Ukraine — sharp post-invasion collapse.
- Germany — roughly flat (+8.9% bright / −9.2% dim).
Significance
- Energy policy: artificial light is a major nighttime electricity sink.
- Ecology: see light-pollution.
- Astrobiology: functions as ground-truth calibration for terrestrial-technosignature detection limits in seti and exoplanet direct-imaging strategies.