Global light pollution is doubling, and more than a third of people don't see the effects of the Galaxy's brighter Earth that is hard to ignore

(Xinhua News Agency/Photo)

Globally, the nights are brighter due to accelerated urbanization. Wherever our gaze goes, we can see different types of lights contributing light. But scientists have found that light that occurs at the wrong time, or the amount of light exceeds what humans need, can cause light pollution. In recent years, this phenomenon is growing at an alarming rate, and it is getting worse due to the popularity of LED (light-emitting diode) illumination.

A new study in September 2021 showed that global light pollution has increased by at least 49% over the past 25 years, and that number includes only visible light through satellites, and scientists estimate that the real growth is likely to be much higher — a growth rate of up to 270% globally and up to 400% in some severe areas.

Before the age of artificial light, clouds masked the light from the stars. But now, as clouds roll in, the sky gets brighter, potentially adversely affecting animals and plants.

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The dangers of light pollution may not be as immediate as chemical spills, but it is now one of the most chronic environmental disturbances on the planet.

A 2016 world atlas of artificial sky brightness shown in a study published in Science Advance showed that more than 80 percent of the world's population lives under light-polluted skies, and more than a third can't see the Milky Way. In 2017, another study in the same journal showed that global light pollution increased by about 2% per year between 2012 and 2016. In September 2021, new research published in Remote Sensing once again refreshed the rate of growth of light pollution. The report shows that from 1992 to 2017, the power of observable light emissions from global satellites increased by at least 49%, and light pollution in Asia, South America, Oceania and Africa continued to increase and worsened at an increasing rate.

Notably, the study found that in Europe, the light detected by satellites leveled off after increasing to around 2010, while in North America it appeared to be decreasing. This is not to indicate that the problem of light pollution is decreasing, but mainly due to the fact that the shift in human light to blue-rich LEDs masks the fact that light pollution is gradually increasing in most areas. With the advancement of technology, LEDs have driven the lighting revolution to take place, causing individual consumers and entire cities to significantly reduce energy consumption. Compared with previous lighting technologies, LEDs emit more blue light, but satellite sensors "can't see" this blue light, so multiple previous studies have underestimated the "emission level" of human light pollution. This time the study, which took into account the contribution of LEDs, found that the actual increase in energy released by outdoor lighting and the resulting light pollution could be as high as 270%.

Over the past 25 years, the transition to LED lighting has been accompanied by a rapid increase in global light pollution, and the impact on the natural environment will accelerate if concerted action is not taken to reverse this trend. When in over-illuminated areas, without proper shielding, these brighter bulbs cast a lot of wasted light in all directions. What's more, the blue wavelengths emitted by white LEDs commonly found in street lamps reflect back and forth in the atmosphere, potentially increasing the brightness of the sky, and these wavelengths have a more pronounced effect on animals (including humans) than light emitted by other parts of the spectrum.

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The transformation of circadian rhythms affects the physiological processes of organisms, the advent of electric lights has completely changed our lives, and the effects of light pollution on plants and animals in the environment are multifaceted and have become more and more known over time.

Light pollution can directly affect the migration, reproduction, hunting and feeding behavior of animals. One of the best-studied examples is sea turtles. Before humans invented electric lights, starlight reflected on the ocean was the brightest thing on the beach, so turtle pups would instinctively move toward the brightest light source. But as the bright lights of coastal cities shine at night, the newly hatched baby turtles become confused and disoriented, heading toward the city rather than the sea, eventually dying of dehydration or prey for other predators, with hundreds of thousands of hatching losses in Florida alone. Migratory birds and nocturnal birds use the light of the moon, stars and sunset to navigate their twice-yearly migrations. Light pollution hides all their navigation tools. Every year, millions of birds crash into glowing buildings and die. A large number of insects are the main food source for birds and other animals, they are also attracted by artificial light sources, moths rushing up like fire, which will make many birds face the danger of food shortages, so many cities now have adopted a "lights out" program, that is, turn off the building lights during bird migration.

Nighttime lights can also affect the entire network of plants and pollinators. In 2017, researchers installed street lights on remote grasslands in Switzerland, far from city streets, to simulate the effects of artificial light pollution. In their study, published in Nature, they found that in fields with lights at night, flowers had 62 percent fewer visitors at night than flowers on dark meadows. In the test field, nocturnal pollination is more than just an activity of several special moth-loving plants. The flowers provide food for a wide variety of nocturnal visitors, while also attracting a wide variety of daytime pollinators. If insects during the day can't make up for the loss at night, plants illuminated at night will produce 13 percent fewer seeds than their counterparts in naturally dark places.

For humans, nocturnal light interferes with sleep and disrupts circadian rhythms. Circadian rhythm is the 24-hour biological clock inside the human body, which guides human circadian activity and affects almost all physiological processes, of which melatonin production is particularly important. Melatonin usually begins to rise at sunset and peaks around midnight, releasing a series of reactions that regulate the sleep-wake cycle, lower body temperature, slow metabolism, and increase leptin. Whether it's a computer screen, a bright bathroom light, or a glare of street lights, indoor and outdoor electric lights can hinder the normal secretion of melatonin, thus interfering with the circadian rhythm. Obesity is one of the consequences of light interfering with our nocturnal physiology, as it may be associated with persistently low leptin levels. According to a 2013 study published in the American Journal of Preventive Medicine, low melatonin levels and circadian rhythm disturbances are also thought to be contributing factors to heart disease, diabetes, depression and cancer, especially breast cancer. In 2016, the American Medical Association responded to the growing amount of evidence that light pollution has obtained from scientists that harm human health, suggesting that strong LEDs are harmful to human health, recommending that communities replace street lights to "minimize and control lighting of blue-light-rich environments."

If light bulbs have a dark side, they steal the night. The excess light that humans dump into the environment harms animals whose life cycle depends on darkness, and is endangering entire ecosystems, including ourselves, of course.

Southern Weekend contributed to Zhu Yehua