One night in 1994 , an earthquake caused a blackout in Los Angeles . Many switchboards of the single number for emergencies in the United States, 911, received alarmed calls: citizens were frightened because of a ” silver cloud ” in the sky . It was the Milky Way, our galaxy, which until that moment had been invisible to the eyes of the inhabitants because of the excess of artificial lights that screened the sky.
Although light pollution may seem like a minor problem, it actually causes damage to many living beings, including humans . The unnatural presence of light, in fact, affects the biological rhythms of organisms, interfering with migration, reproductive cycles, sleep and other activities. It is estimated that light pollution contributes significantly to the decline of some species and compromises the quality of life of millions of people. Scientists suggest that nighttime brightness may be one of the factors that has contributed to the increase in cases of cancer , cardiovascular disease and diabetes observed in the last century.
Definition of light pollution
What is meant by light pollution?
This term refers to the excessive amount of artificial light in the sky . The light emitted by street lamps, buildings, signs, cars, ships, fireworks and other artificial light sources is scattered in the sky by particles in the atmosphere. Because of this phenomenon, the skies of some cities are brightly lit even after sunset. In this way, the visibility of celestial objects is reduced : in the most polluted areas of the world, such as Singapore and Kuwait, 99.5% of the stars are invisible. Light pollution mainly affects cities , but not only . In fact, even a small town can light up the sky tens of kilometers away.
What are the types of light pollution?
The phenomenon can be divided into 4 categories.
- Urban glow is the bright halo that appears over inhabited areas at night. It is caused by particles in the air that reflect light;
- Light spillover occurs when light rays are scattered in areas outside the area that should be illuminated. For example, this is the case of the light from a street lamp illuminating a nearby garden ;
- Glare is the brightness given off by lighting systems that emit light horizontally;
- Overlighting is the use of lights where they are not needed, such as in empty buildings .
But why do we talk about light pollution?
This phenomenon causes damage to wildlife and humans . About 80% of the world’s population, and 99% of Europeans, live in areas with light pollution, with significant consequences for their health.
Effects of light pollution on animals
By blocking the view of the Milky Way, this phenomenon does not only harm astronomers and romantics. Light pollution causes damage to living beings: studies have found damage to plants , birds , bats , reptiles , amphibians , insects , marine animals (including coral ) and some primates, including us . Due to the prolongation of the illuminated phase of the day, some plants are unable to adapt to seasonal variations. This affects their survival and that of the species that depend on them, for example because they live on them. Animals that use the stars to orient themselves are distracted and misguided by artificial lights, sometimes with fatal effects. Newborn sea turtles follow the brightest sources, such as stars reflected in the sea; but they can be attracted by city lights : they then proceed in the opposite direction, risking dehydration or being run over. In the United States alone, it is estimated that 4 million migratory birds die every year due to collisions with illuminated buildings .
This excessive brightness also causes the death of many insects , so that the fauna that feed on it has difficulty obtaining food. In many species, including humans, light pollution alters the circadian cycle , the biological system that guides the rhythms of the organism. In fact, light is a parameter according to which organisms regulate their activities: this is how plants and animals understand the passing of the seasons, regulating their reproductive, feeding, hibernation periods and so on accordingly. The main problem is that if an organism changes its habits it may not be synchronized with other environmental events: for example, the early birth of a litter may precede the availability of food in that environment. This puts the survival of the species at risk .
Light pollution: effects on human health
Night light can distract us while we are driving or walking on the street, increasing the risk of accidents. But the negative effect of light pollution is mainly inside our body. In particular, the American Medical Association and other experts warn against blue light , present in particular in electronic devices but also in city lighting systems. Melatonin is a hormone produced by the pineal gland, a structure as large as a phalanx, located in a cavity of the brain. This hormone regulates the rhythms of our body, modulating brain rhythms and hormones. In particular, it affects :
- Our sleep-wake cycle ;
- Hunger ( which disappears at night);
- Metabolism ( slowed down by melatonin);
- Body temperature ( which drops at night) .
The production of this hormone depends on the brightness we perceive : when our retinas receive light, our brain blocks the production of melatonin. Normally, this hormone should be produced starting at sunset with a peak at midnight, but artificial lights, in our homes and from outside, cause an alteration of this cycle. This can also happen indirectly , disturbing people who are sleeping and who get up and turn on the lights.
The consequences of exposure to light during the night are:
- Insomnia ;
- Shift work sleep disorder (SWSD) , a condition that causes people with frequent changes in work schedules to be sleepless when they can sleep and sleepy when they would like to be active ;
- Delayed sleep phase syndrome , a disorder in which a person falls asleep and wakes up later than normal;
- Fatigue ;
- Heachache ;
- Overweight and obesity ;
- Cardiovascular problems;
- Anxiety , depression and other mood disorders . According to some research, in fact, stargazing improves mood and altruistic behavior and decreases attachment to material things ;
- Recent studies show that melatonin deficiency may contribute to the risk of cancer, especially breast cancer. In fact, it seems that the natural presence of this hormone in the blood slows tumor growth ;
- According to some authors, constant exposure to artificial light in neonatal intensive care units could disrupt the circadian cycle of children , predisposing them to mood disorders, including depression.
The consequences are evident in night workers, such as truck drivers, flight crews and night janitors: in 2007, the World Health Organization declared night work a risk factor for cancer.
Causes and remedies of light pollution
The main cause of light pollution is non-compliant outdoor lighting systems, which disperse light in directions where it is not useful. For example, a street lamp that not only emits light toward the street, but also upwards , is a major factor that contributes to this problem.
How is light pollution calculated?
The amount of light pollution in an area depends on several factors .
- Emitted brightness : If the brightness levels in the sky are more than 10% higher than the natural brightness level, the light from a small town can affect the quality of the sky even 10 kilometers away;
- The amount of light scattered upwards by street lamps and other light sources;
- The ability of the environment (streets, windows, walls, etc.) to reflect light;
- The weather conditions .
How to reduce light pollution
Limiting the problem would also mean energy and therefore economic savings . Furthermore, since artificial light is produced mostly through the use of fossil fuels, the reduction of light pollution would also lead to a decrease in air pollution. The phenomenon of light pollution is also growing due to the spread of LEDs . In fact, these, being much cheaper than traditional light bulbs, lead to overuse and therefore excessive lighting. Furthermore, these are cold lights: blue lights, in addition to being the worst for human health, spread further into the atmosphere, worsening the condition of light pollution. Reducing the use of LEDs to what is necessary, shielding them and making them warmer would be positive. To limit light pollution, we can act at the city level but also in homes. The general rule is to illuminate as little as possible , but there are other targeted solutions.
- Use low and shielded light sources so that the light does not disperse upwards. According to studies, in unshielded or directional lamps only 40% of the light is exploited: the rest is dispersed into the atmosphere ;
- Use motion sensors, timers or other tricks to turn off outside lights when they are not needed ;
- Turn off lights in buildings, especially at night. It is recommended to turn them off an hour before bedtime for good sleep hygiene;
- Prefer low -temperature LED or sodium lamps, among the most efficient available, preferably in warm colors. At night, the use of red lighting is recommended, which interferes less with the body;
- Use curtains to prevent light from spilling out of your home at night. This also reduces bird collisions with glass.
Many cities have adopted a lights – out program for the evenings when birds migrate, and more and more countries are implementing solutions to reduce light pollution. Lighting sustainability is also one of the sustainable development goals of the UN Agenda 2030, which estimates that if more efficient light bulbs were used worldwide, we would save 120 billion dollars every year .
