Light emissions indicate how much nighttime light is emitted from Earth into space. Too much light can be detrimental to health and interfere with the biological clock. It leads to sleep disorders, heart rhythm changes and lower melatonin production, which stimulates the immune system and other body functions. Excessive light emissions can also adversely affect the habitats of nocturnal animals and have deadly consequences.
From 1994 to 1997, Switzerland’s light emissions rose by almost 40%. Then, they remained relatively stable with slight fluctuations until 2007, when they rose significantly again. The area of nocturnal darkness also shrank considerably (from around 30% in 1994 to around 20% in 2012, values for Switzerland as a whole). Naturally dark expanses of land have become especially rare in the Central Plateau and Jura regions. This is causing a dramatic change in our natural environment, such as the loss of the natural night landscape. That is why it is important to reduce light emissions and make nocturnal darkness possible again. One of the most effective measures would be to turn off illuminated advertising at night.
The “light emissions” indicator is based on analyses of satellite images taken by the Operational Linescan System (OLS) of the Defense Meterological Satellite Program (DMSP). The data have been continuously collected since 1992 and are processed and provided by the Geophysical Data Center (NGDC). For this indicator, sunlight data, glare effects, moonlight data, cloud observations and auroras are adjusted to produce a world map with brightness values between 0 and 63 (255 = no data) and a cell size of 30x30 arc-seconds. To attenuate annual peak values and inaccuracies, the data are averaged temporally over a 3-year period and spatially over 3x3 cells. The map is then projected onto the Swiss grid and converted into 1 km2 raster cells.