LIGHT POLLUTION: CHARACTERISTICS, CAUSES, EFFECTS, SOLUTIONS - ENVIRONMENT - 2025

The light pollution is the interference in the nature of artificial light sources causing negative impacts to living beings or affecting human interests. Little attention has been paid to light pollution, yet it has an impact by altering natural light-dark cycles.

For a long time, human beings have used the night for their activities, artificially illuminating and therefore affecting the natural environment. The awareness of light pollution only emerged in the 60-70s (20th century), when astronomers warned about it. This is because the glare of cities interferes with observations and measurements from astronomical observatories.

Light pollution of the planet Earth. Source: Dominic Alves

The artificial light diffuses into the environment and thanks to its reflection and refraction properties it ends up encompassing the surrounding space. Reflection determines that photons (elementary units of light) bounce off surfaces and particles that they impact.

The cause of light pollution is the generation of artificial light by human beings in excess and without control. The growth of the human population and its concentration in urban centers generates this growing demand for light.

Additionally, the unconsciousness regarding the capacity of light as a pollutant does not pose the need for its adequate control. Poorly directed street lighting, bright billboards, and nighttime motor vehicle traffic create excess light.

Light pollution varies depending on the type of lamp that generates it, the most polluting being those that provide bluish-white light. Light pollutes when projected into the environment, invading private areas and dazzling or cluttering areas.

According to the source that emits it, light pollution occurs from public or private lighting, advertisements, vehicle headlights and entertainment reflectors.

Light pollution has negative effects on humans by altering their biological clock. This affects health by generating nervous problems, insomnia and even hormonal imbalances.

Likewise, it hampers the activity of astronomical observatories, since the glare of the cities prevents the perception of the night sky. This likewise deprives citizens of this aesthetic experience.

On the other hand, light pollution implies a waste of electricity, which represents economic losses and wasting resources. In addition, in the process of producing that light that is wasted, other pollutants such as CO2 were generated.

Light pollution has negative effects on natural ecosystems and can affect migratory birds, as well as insects and frogs. The light alters the path to the sea of ​​the small turtles after hatching the eggs on the beaches.

In general, the alteration of the day-night cycle generates changes in the behavior of living beings. These changes affect their feeding, reproduction, and the predator-prey relationship. Plants suffer alterations in the photoperiod (response to the day-night duration), with consequences in flowering.

The greatest light pollution in the world occurs in the most developed countries and in large cities. The main sources of light pollution are on the east coast of the United States of America, Europe, northern India, Taiwan, Japan and China.

The solutions to light pollution are social, legal and technical. Socially, it is necessary to create awareness of the existence of this type of pollution and its effects.

In legal terms, strict laws are required to regulate the use of lighting. Likewise, it is necessary to prohibit excessive light above the horizon and guarantee the implementation of adequate technical measures.

Technically, there are lighting systems that include suitable lamps (monochromatic), as well as in the correct orientation. There are also timers that allow you to regulate the lighting time.

characteristics

Light pollution refers to artificial light when it is emitted in excess or outside the range in which it is functional. The characteristics of the diffusion of light, such as reflection, generate the so-called luminous glow of cities.

That is to say, the emitted light is reflected off surfaces and as it goes towards the atmosphere it bounces off the atmospheric particles that return it.

Bortle's scale of darkness in the sky

John E. Bortle created in 2001 a scale (from 1 to 9) to measure how bright the night sky is. Level 1 is the darkest sky that can be observed from earth, with the largest number of stars. While level 9 corresponds to the night sky seen from the center of a large city, where few stars are seen.

Causes

The fundamental cause of light pollution is the emission of light through artificial lighting. This in turn is determined by a number of human needs that include:

- Allow nighttime activities.

- Create conditions of citizen security.

- Facilitate the safety of vehicular traffic.

- Extend economic activity.

- Advertising lighting.

- Ornamental lighting.

This emission of light can cause pollution by the action of three main factors:

Direct issue

This is the primary factor of light pollution, as artificial light is emitted into the dark environment to illuminate it. It is a powerful source of pollution due to its intensity and it is usually multidirectional.

A modern city is a source of light, thanks to the combination of countless sources that include public and private lighting. This includes street and avenue street lamps or lamps, lights in homes and buildings for economic activity, lighted signs, billboards, and vehicle headlights.

This emitted light can exert its polluting effect directly, when it is directed towards a habitat of living beings. Likewise, it can do it secondarily by reflection or refraction.

Reflection on illuminated surfaces

The light emitted is reflected on the surfaces of the urbanized area such as streets, buildings, signs and any object in its range of action. When photons collide with these surfaces, they are reflected in different directions, generating the luminous glow of the city.

However, this secondary factor of contamination is obviously weaker than the first. In fact, in cities where light bulbs are properly directed, the polluting effect of reflection is significantly low.

Reflection in atmospheric particles

Finally, the emitted and reflected light is directed towards the atmosphere and there it collides with the suspended particles.

Types

Light pollution can be classified in various ways, depending on the type of lamp that produces it, its characteristics or the source that generates it.

- According to the type of lamp

Light pollution will vary depending on the type of lamp that provides the light. Monochromatic lamps such as sodium lamps will be less polluting than white light lamps such as fluorescent lamps or some LEDs.

- According to its characteristics

Projected light diffusion

It is the scattering of light that is diffused and contributes substantially to the glare emitted by urban centers.

Invasive light

It is when the external light source penetrates the houses or areas where its lighting function does not correspond, becoming a pollutant.

Glare or glare

It is an excessive or sudden lighting that causes glare in pedestrians and vehicle drivers, and can cause accidents. For example high beams of a vehicle.

Heterogeneous lighting or overcrowding

They are areas with irregular lighting, with different sources of light, causing disorientation, confusion, distraction and stress. For example, a large number of luminous signs and street lighting.

Likewise, areas with an excess of artificial lighting can be presented for the tasks that are carried out there.

- According to the source

Street lighting

This is the biggest source of light pollution that exists, especially when the lighting system is not designed properly. This source is responsible for 40 to 60% of light pollution, both by diffusion of projected and invasive light.

Light warnings

In some large cities such as New York or Tokyo this light source reaches high levels of incidence. It is a direct cause of contamination by diffusion of projected and invasive light since it emits above the horizon.

Vehicle headlights

This is a mobile and variable source and in cities with a high degree of night traffic it becomes an important factor of light pollution. Depending on the type of headlamp and if the rules for its use are not met, it is a cause of glare pollution.

Private lighting

The lights in homes, especially buildings in large cities, generate significant light pollution.

Reflectors

Generally this is a source of point light pollution, since it is the reflectors used in public shows. Pollution occurs by diffusion of projected and invasive light.

Effects edit

The effects of light pollution can be grouped into three broad categories:

- Effects on the night sky

The light pollution generated by the glare of cities makes the night sky invisible. We can see the stars thanks to the contrast of their brightness (own or reflected) in the context of celestial darkness.

Aspect of the sky at night with and without light pollution. Source: Jeremy Stanley

The glare of light from the cities increases the clarity of the celestial background above the brightness of the stars, making them invisible.

- Effects on humans and their habitat

Intrusion of external light

Outdoor lighting in cities often generates light pollution by invading the privacy of homes. Sometimes this can be beneficial, for example by allowing us to move around at night without turning on internal lights.

However, it limits those other circumstances where you want to keep the darkness without appealing to close the windows.

Impacts on health

Living beings respond to circadian rhythms, that is, physiological responses according to defined periods between 20 and 28 hours. Therefore, the alteration of the light and dark cycles generate physical, mental and behavioral changes. Light pollution causes serious sleep disorders and therefore behavior in humans.

Melatonin is a nocturnal secretion hormone produced by the pineal gland that helps regulate the biological clock and reduces the nocturnal production of estrogen.

It has been proven that when the human body is subjected to artificial lighting, the production of melatonin is drastically reduced. According to studies (not yet conclusive) this could increase the risk of certain types of cancer.

For its part, the French National Agency for Health Food Safety, Environment and Work (ANSES) has pointed out other risks of light pollution. For example, oxidative stress generated in the retina by the high incidence of certain types of lighting (eg: LED).

Economic impacts

Light pollution is a consequence of an excess of light that is scattered, therefore it implies a waste of it. An increase of no less than 20% has been calculated that leads to direct economic losses.

To the waste that results in light pollution is added all the economic cost involved in its production (resources and pollution from other sources).

Additionally, light pollution has forced the establishment of astronomical observatories in places far removed from populated centers. This has increased construction and operating costs, mainly related to the transport of materials, supplies and personnel.

Technical impacts

Astronomy has been affected by light pollution, due to the aforementioned effects on the night sky. In fact, astronomers were the first to warn about it and developed a magnitude to measure it.

This index is called the Luminance of the celestial background and it measures the increase in its clarity.

Aesthetic impacts

Anyone who has never been far from urban centers, has not been able to fully appreciate a starry sky. This implies the loss of a significant aesthetic and emotional experience, which can only be experienced by moving substantially away from cities.

Take into account that the light pollution generated by large cities extends for tens of kilometers, connecting with neighboring cities. Therefore, the same threat to our nocturnal landscape and some authors speak of the cultural loss of the "experience of the night"

- Effects on natural ecosystems and biodiversity

The cycle of day and night with their characteristic levels of illumination have governed the evolution of species. These therefore have adapted their behavior to that cycle in each particular environment on the planet.

Animals

Wild animals are even more sensitive to the effect of light pollution on their biological clock and ethology (behavior). Species with nocturnal habits such as bats and certain amphibians see their habitat seriously affected by night lighting.

When faced with unusual lighting, animals adapt well either through rejection or attraction. In any case, this implies changes in their feeding, migration, reproduction or predator-prey relationships.

For example, when sea turtle hatchlings go to sea after hatching, they lose their way to light sources. Nocturnal raptors such as owls require darkness to detect and stalk their prey.

Species of insects and frogs are attracted to light sources and their populations decline as a result. That is why very illuminated buildings near natural areas have a negative effect on these organisms.

Let us bear in mind that the species with an active night cycle are an important proportion of the Animal kingdom. It is estimated that about 30% of all vertebrates and more than 60% of invertebrates are nocturnal.

Plants

The flowering of plants is a process determined by the interaction of genetic and environmental factors, including the photoperiod. That is, they respond to the duration of day and night, and the alteration of these rhythms affects the flowering of certain species.

The relationship of living beings with the cycles of light and dark is so relevant that it has motivated the development of two disciplines of biology. One of them is escotobiology, which studies the relationship between life and darkness. The other is chronobiology that studies biological rhythms.

- Effects on other pollutants

Acid rain

Photochemical effects are essential for certain processes that are generated in the atmosphere. For example, NOx radicals in the presence of light generate acids and in the absence of light they decompose.

Therefore, continuous artificial lighting increases the production of acids and therefore acid rain. It is estimated that this increase reaches between 5 and 7%.

Greenhouse effect gases

As we mentioned when referring to the economic effect, about 20% of the light is wasted transforming into light pollution. But this also has implications in the generation of other pollutants, specifically in the production of CO2.

Most of the electricity is produced in thermoelectric plants and these emit CO2, which is the main greenhouse gas, causing global warming.

Examples of places with light pollution

The most striking cases of light pollution are the large cities of developed countries. Due to the high population concentration and the high economic level, the excess of night lighting is evident.

In terms of world regions, the greatest light pollution is found in North America, Europe and Asia.

Las Vegas (United States) at night. Source: EconomicOldenburger - Alles über den Las Vegas Strip

In North America, the United States stands out (especially the east coast), while in Europe Greece, Malta and Spain stand out, and in Asia Japan, Taiwan and China. At the city level in the United States, Las Vegas and New York stand out. Other notable cities are Moscow, Valencia, London, Rotterdam, Paris, Hong Kong and Tokyo.

In these cities, due to their magnitude and socioeconomic dynamism, the nightlife is intense, driving the demand for lighting in public and private areas. In the same way, there is an increase in motor vehicle traffic at night and commercial promotion through luminous advertisements.

Hong Kong

A high population density and a thriving economy make Hong Kong a city with a high level of light pollution. It has more than a thousand skyscrapers, which causes some to consider it the city with the highest light pollution in the world.

Tokyo (Japan) illuminated at night. Source: Moyan Brenn from Italy

According to a study by the University of Tokyo, the night in Hong Kong is a thousand times brighter than the established limit.

Las Vegas (USA)

The largest source of income in this city is tourism linked to gambling, promoting the largest concentration of luminous signs in the world. On the other hand, it is common to use high-power reflectors to directly illuminate the sky.

New York (USA)

This is one of the cities with the highest light pollution in the world, especially the commercial district of Manhattan. As a curious fact, about 90 thousand birds die annually when they collide with skyscrapers disoriented by the intense lighting.

Valencia Spain)

Valencia is the Spanish city with the highest light pollution and some place it as the largest in Europe. In 2007, this city spent 1.5 million euros more than Barcelona, ​​despite having half the inhabitants.

However, today a program is being promoted to replace inefficient street lamps in public lighting to reduce light pollution.

Solutions

Solutions to light pollution encompass social, legal and technical measures.

- Social

It is important to raise awareness about light pollution, its consequences and solutions, in order to achieve citizen support for its control. Support for related legislative measures and the rational use of lighting in the home and community is required.

- Legal

There is a diversity of legal rights, including rights that must be protected against light pollution. From the right to the protection of the vision of the night sky as part of the landscape, to the protection of natural habitats.

Therefore, it is essential to have laws that regulate the use of lighting, restricting light pollution. That is, to establish through regulations the periods of use of lighting and the implementation of adequate equipment for a rational use of light.

Especially relevant is the prohibition of light emission above the horizon, except for requirements of air navigation.

- Techniques

Teams

There are lamps with timers that allow the lighting periods to be adjusted to what is strictly necessary. In the same way, the luminaires must focus the light strictly to the required areas and avoid its dispersion.

This implies an adequate design of the lighting system and the use of the appropriate equipment for each case. Special attention must be paid to the inclination, direction, characteristics and type of luminaires.

So that the light does not exceed the horizontal line, there are suitable moldings that allow the lamps to be focused towards the ground.

Light type

The least polluting light is monochromatic, that is, that which, unlike white light, is made up of a single wavelength (or few lengths). The ideal are low pressure sodium lamps (yellow light), as they generate less light pollution by causing less interference.

Zoning

The zoning of the territory is important based on its real lighting needs and its vulnerability to light pollution. This allows the establishment of both regulations and other technical measures appropriate to each area.

References

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