Light pollution  in the Marina Bay area, Singapore, Photo: The Independent

Hello again! In the previous post, we talked about the general trends of light pollution, and it being a global phenomenon, with 83% of the world’s population living under light-polluted skies. You might be wondering, which areas in the world are light-polluted, and to what extent are they so?

In 2016, a study by Science Advances measured light pollution on a global scale, using data from the Visible Infrared Imaging Radiometer Suite (VIIRS), an instrument from the Suomi National Polar-orbiting Partnership (NPP) satellite. It has shown that while parts of the least developed world enjoy unpolluted skies, a significant majority of the developing and developed world live under starless skies.

 

Figure 1: World map of artificial sky brightness, Photo: Falchi et al.

The zenith sky brightness (in μcd/m²) was computed to indicate light pollution. With the natural sky brightness (light from the milky way, stars, and airglow) at 174 μcd/m², Figure 1 illustrates the levels of light pollution measured, as a fraction above the natural sky brightness. The areas in blue represent the approximate minimum level where light pollution is considered present. As your eyes can tell,  large swathes of the developing and developed world have already reached that level – most of the United States, Mexico, parts of South America (Brazil, Chile, Venezuela, Argentina), parts of Africa (South Africa, Libya), the Middle East (Saudi Arabia, Iraq), Europe (Germany, France, Spain, Italy), parts of Russia, most of India, most of China, South Korea, Japan, and Southeast Asia. Wow, that was a really long list! But we’re not done yet.

 

Figure 2: Map of North America’s artificial sky brightness, Photo: Falchi et al.

Figure 3: Map of Europe’s artificial sky brightness, Photo: Falchi et al.

In the areas coded yellow and orange, the milky way cannot be seen due to light pollution. Finally, people living in the red areas will “never experience conditions resembling a true night because it is masked by an artificial twilight”. From this global map of light pollution, we can already witness the extent to which light pollution is experienced by the world at large. In Figures 2 and 3, highly developed countries, such as the United States and Europe, have already reached those levels.

The 20 least polluted countries identified in the study are poor, underdeveloped African countries (coded in grey). However, as the world continues to urbanize and develop, it may not be a surprise that these countries would also light up in the future, just as the industrialized and developing countries of China and India have.

One limitation of the study is that the VIIRS instrument does not measure the blue-wavelength of light emitted by LED lights, which significantly brightens the sky and causes harmful effects to human health and ecology (which we will explore on a separate post). Thus, what we are seeing in the skies right now may actually be brighter than what the global map of light pollution depicts. With the rising adoption of LED street lighting, our nights might just get brighter and brighter.

Coming from a little red dot in the world, never did I realize the prevalence of how others, in their own corners of the globe, are also looking up at starless skies, or skies with slowly disappearing stars. How did this study make you feel and what are your thoughts on it? Let me know in the comments below!

 

Source: Falchi, et al. (2016). The new world atlas of artificial night sky brightness. Science Advances 2(6).