80 per cent of the world's population and 99 per cent of the population of the United States and Europe lives beneath a sky polluted by artificial lights. The Milky Way, declared a Unesco world heritage site, is invisible to more than a third of humanity, including 60 per cent of Europeans and 80 per cent of North Americans. But the worst news concerns Italy, which is the developed country with the highest percentage of territory polluted by artificial light in the world. Eight out of ten Italians cannot see an unspoilt starry sky. This is what the world atlas of light pollution (The new atlas of artificial night sky brightness), published in the journal Science Advances, reports.

What is light pollution

Light pollution is the direct or indirect introduction of artificial light into the environment and is one of the most widespread forms of environmental alteration. The phenomenon also affects unspoilt sites that during the day appear untouched by human activity, while at night they fall victim to light pollution. Light, in fact, travels hundreds of kilometres from its source, thereby damaging nocturnal landscapes, even in protected areas such as national parks. One example above all: the light domes of Las Vegas and Los Angeles can be seen even from Death Valley National Park.

The main cause of light pollution is emissions from non-compliant outdoor lighting systems — that is, systems that do not emit only the light needed for night-time vision, but disperse a good portion of it in other directions.

LEDs and light pollution

LED lamps are becoming increasingly widespread, particularly in the public lighting sector, thanks to their low energy consumption. LEDs themselves would appear to play an important role in the level of light pollution in the blue part of the spectrum. This is linked to the fact that they use light with strong blue-white components, which is scattered far more by atmospheric molecules than light with a predominantly yellow component, such as that of high-pressure sodium lighting systems. The phenomenon causes an increase in the level of light pollution close to the sources, up to several tens of kilometres away, while reducing it at greater distances, since the blue light has already dispersed.

The atlas of light pollution

The world atlas of light pollution, published in the summer of 2016 by Fabio Falchi — one of the world's leading experts on the subject — who led a group of international researchers, brought the problem of light pollution to the fore. Practically all Europeans and Americans are unable to see a starry sky during the night-time hours due to excessive illumination of the sky.

According to the atlas, the countries with the populations least affected by light pollution are Chad, the Central African Republic and Madagascar, where more than three quarters of the inhabitants live under unspoilt sky conditions. The countries and territories with the highest areas unaffected by light pollution are Greenland, where only 0.12 per cent of the surface area has no unspoilt skies, the Central African Republic with 0.29 per cent, Niue with 0.45 per cent, Somalia (1.2 per cent) and Mauritania (1.4 per cent).

By contrast, the country most affected by light pollution is Singapore, where the entire population lives beneath skies so bright that the human eye is unable to fully adapt to night-time vision. Singapore is not alone. There are other countries where high levels of light pollution are recorded and where more than 50 per cent of the population lives beneath very bright skies: Kuwait (98 per cent), Qatar (97 per cent), the United Arab Emirates (93 per cent), Saudi Arabia (83 per cent), South Korea (66 per cent), Israel (61 per cent), Argentina (58 per cent), Libya (53 per cent), and Trinidad and Tobago (50 per cent).

The possibility of seeing the Milky Way is denied to all citizens of Singapore, San Marino, Kuwait, Qatar, and the inhabitants of Malta; but also to almost the entire population of the United Arab Emirates, Israel and Egypt.

Among the G20 countries, Saudi Arabia and South Korea have the highest percentage of population exposed to extremely bright skies, while Germany is the least polluted. The territories of Italy and South Korea are the most polluted among the G20 countries, while Australia is the least polluted, a factor also linked to population density.

The classification of light pollution levels

Based on the percentage of the population exposed to light pollution and the percentage of territory exposed to different levels of light pollution, researchers drew up the following classification:

• light pollution level of 1 per cent: unspoilt sky (black)
• light pollution level between 1 and 8 per cent: relatively polluted sky (blue)
• light pollution level between 8 and 50 per cent: polluted sky with a level of pollution that degrades towards the zenith (green)
• light pollution level above 50 per cent, where the Milky Way is not visible and the natural appearance of the night sky is lost (yellow)
• from the loss of visibility of the Milky Way to a high stimulation of the visual cone (688 to 3000 μcd/m2) (red)
• intense night-time light, the human eye is no longer accustomed to adapting to night-time vision (white).

The consequences of light pollution on health

Under normal conditions, our biorhythm is programmed to alternate between day and night. This alternation is known as the circadian rhythm. The body behaves differently depending on whether it is in conditions of light or darkness. The pineal gland produces serotonin during the day and melatonin at night. A well-synchronised circadian rhythm is fundamental to psychophysical balance; otherwise there is a risk of negative health effects, such as: depression, cancer, diabetes, obesity, and suppression of the immune system. If a light source is present during the night-time phase, melatonin production is affected, and with it the quality of sleep. It is well known that light — in particular the blue light emitted by LED-backlit devices such as tablets, computers and smartphones — can interfere with the quality of our sleep, and the repercussions can be very serious. The World Health Organisation has found that people exposed to artificial light for many hours a day, such as those who work at night or airline staff, have a higher incidence of cancer, to the point that it has classified light pollution among the factors considered "probably carcinogenic". Scientific studies have highlighted a higher incidence of breast cancer in women working night shifts, while in men an increased risk of prostate cancer has been identified.

What is more, light pollution also has effects on migratory patterns, mating rituals, hunting and many other processes that are essential to the lives of plants, insects and animals.

Waste of energy and economic resources

According to the International Dark-Sky Association, in one year in the United States, outdoor lighting uses approximately 120 terawatt-hours of energy, mostly used to illuminate roads and car parks. This is an amount of electricity that would be sufficient to meet the electricity demand of a city like New York for two years. Unfortunately, around 50 per cent of all this lighting is wasted. In cost terms, the figures amount to around 3.3 billion dollars, with the emission of 21 million tonnes of CO2 per year. To offset these emissions, we would need to plant 875 million trees every year.

Italian municipalities spend one billion and 800 million euros on electricity every year, two thirds of which goes on public lighting. We are the country in Europe that spends the most on public lighting. Each of us consumes 100,000 kWh every year — twice as much as Germans and the British, and a third more than the French.

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