Light pollution: The dark side of keeping the lights on

April 10, 2019

If you look at a NASA picture of the Earth at night, most of the world—with the exception of such areas as North Korea and central Africa —is ablaze with artificial lighting. Now, scientists are having “a lightbulb moment” about the effect of this nearly ubiquitous illumination on natural life on the planet—and the news is not good.

In fact, researchers at the University of the Witwatersrand in Johnannesburg, South Africa, have found mounting evidence that increases in “light pollution” have resulted in a range of negative effects on all life on earth.

Light pollution is the excessive and obtrusive illumination produced by humans at night. This light is from artificial sources—mainly, from residences, offices, street lamps , billboards, and car headlights.

There are two types of light pollution: point source, which is light directly from a source; and skyglow, which is the combined and accumulated effect of point source lighting that spreads through the atmosphere. This is the slight glow one can see on the horizon if looking towards a city from a rural area.

Almost one-quarter of global land area on Earth is now under light-polluted skies, according to Bernard Coetzee, a conservation scientist at the Global Change Institute  of the University of Witwatersand. What’s more, 80% of the world’s population now lives under light polluted skies—meaning that fully one-third of humanity no longer can see the Milky Way.

This is a modern problem: Apart from the soft glow of celestial light, it is remiss of us to forget, Coetzee says, that 50% of the Earth always used to be, at any moment in time, in total darkness.

Where there are sunlight cycles and moonlight cycles, many species rely on them to time their behavior, activity, and sleep patterns; as well as when to mate and when to feed.

But now, the spatial coverage of light pollution is large, and its intensity is increasing—causing negative effects, among them, a disruption in the natural light cycles that species are cued into. These include changes in time partitioning such as singing, activity, and foraging in animals; or altering individual health.

And there is increasing evidence that lighting has negative effects on human health, as well, Coetzee reports. Melatonin is the hormone that regulates human sleep patterns and is expressed under light. Changes in light regimes away from day-night cycles caused by light pollution means that it can disrupt this vital hormone’s natural expression. This problem has been linked to obesity, reduced sleep quality, and impaired memory. In addition, because melatonin is an antioxidant that can remove free radicals, the disruption of its expression by artificial light may increase cancer risk.

A recent review in the journal, Science has outlined five key strategies to reduce lighting globally, which will not necessarily compromise its benefits. They are:

  • The introduction of light to previously dark areas should be avoided.
  • Lighting should be at the lowest usable intensity.
  • Lighting should only be used where it’s directly needed and shielded where possible.
  • Lighting should only be used when required.
  • Lighting should be “warmer”—meaning more orange colors should be used rather than in the harsh white spectrum.

“Given the extent and severity consequences, the dearth of light pollution research in Africa is a surprising oversight,” Coetzee comments, noting, “Africa still remains one of the least light-polluted continents, but this is rapidly changing with the expansion of lighting infrastructure, which it is closely tied with economic development. This is especially true for rural areas that may increasingly gain access to electrical grids and LED lights.”

While many Africans may still see the Milky Way, the expansion of lighting infrastructure is imminent. As with other global change drivers, the continent is at an important juncture to ensure that its economic trajectory does not compromise its human and environmental health. How best to do so for light pollution still remains to be decided.

Research contact: @BernardScience

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