Light pollution: causes, examples, and mitigation strategies

Light pollution is one of those environmental problems that, although it may go unnoticed by many, directly impacts the lives of people, animals, and ecosystems themselves. Just look at the sky in a large city to see that the stars have almost completely disappeared under artificial light. This situation, far from being harmless, leads to a series of little-known consequences that affect everything from our health to nocturnal biodiversity.

Over the past few decades, urban areas have significantly increased their nighttime lighting, and not always for the best. Despite technological advances, the indiscriminate and poorly managed use of artificial light poses a real challenge to sustainability, energy efficiency, and the conservation of the night sky. In this article, we delve deeper into the causes, examples, effects, types, and the most effective strategies to mitigate this phenomenon, integrating the most accurate and up-to-date knowledge provided by leading sources on the subject.

What is light pollution?

Light pollution refers to the alteration or degradation of the natural nighttime environment due to the excessive, unnecessary, or misdirected use of artificial outdoor light. This phenomenon manifests itself primarily through the glare in the night sky caused by light sources installed in cities, commercial and industrial areas, and on highways.

The problem arises when the light is not adequate or limited to actual needs, projecting into the sky or dispersing into areas that do not require it. This nighttime glare obscures the view of stars, alters day-night cycles, and generates negative consequences in many areas: from energy waste to the alteration of ecosystems and a direct impact on our health.

In the words of the Mexican Geological Service, light pollution involves the emission and reflection of artificial light into the atmosphere, scattered in all directions by air particles. This reduces the natural darkness of the sky, making everyday phenomena such as observing the Milky Way impossible for the majority of the population in many countries.

Main causes of light pollution

The rise of urbanization, the lack of planning, and the indiscriminate use of artificial light at night are largely responsible for this phenomenon. There are several causes that often combine to aggravate the problem, especially in urban environments:

• Excessive and uncontrolled lightingMany urban and rural areas experience an over-use of outdoor lighting, which often fails to take into account both the necessary volumes and proper orientation. Streetlights, advertising signs, and illuminated buildings waste energy and project unnecessary light into the sky and unintended areas.
• Inefficient installation of lighting fixtures: Poor design or installation of streetlights and other lighting systems, especially those without shielding or protection, causes much of the light to scatter upwards or to the sides.
• Overlighting: This involves lighting with more intensity than the actual activities required. This occurs in residential streets, workplaces, and even homes, often due to a false sense of security or simply due to ignorance.
• Excessive advertising and decorationThe use of huge neon signs, neon advertisements, and overly illuminated facades and decorative monuments exacerbates the problem, especially in tourist and commercial areas.
• Lack of responsible habits and lack of knowledge: A lack of training and awareness leads to poor practices at the personal, institutional, and business levels, perpetuating ineffective or unnecessary habits and lighting systems.
• Reflections and shiny surfaces: Glass surfaces, asphalt, facades and other highly reflective elements increase dispersion and unnecessary glare.
• Lack of night shutdown and automationMany lights remain on senselessly for hours with little or no human use, intensifying energy waste and the impact on the skies and wildlife.
• Urban expansion and proliferation of new infrastructureThe growth of large cities and the lack of environmental criteria in planning are increasing the number of light-emitting sources, exacerbating the problem globally.

Ultimately, light pollution is the result of a combination of excess, poor management, and lack of information. Today we have the technology to prevent this, but a change in habits and policies is necessary.

Types of light pollution: forms and specific examples

Light pollution can manifest itself in different ways, depending on how and where artificial light sources act. Among the main types are:

• Skyglow: It appears as an orange or whitish halo over cities and urban areas, especially visible on cloudy nights. It is generated by the scattering of light in the atmosphere, making it extremely difficult to observe stars and celestial bodies.
• Glare: It occurs when intense light, direct or indirect, reduces visual capacity and causes discomfort or danger, for example, to drivers or pedestrians.
• Light intrusion: It occurs when light enters spaces where it is bothersome or harmful, such as the light from a street lamp entering a home through a window, preventing rest or modifying biorhythms.
• Excessive grouping and lighting clutter: The presence of areas with different types of lights, colors and powers, poorly distributed, generates confusion and can cause orientation problems and dangerous distractions.

Common examples of light pollution include streets and avenues with unshielded globe-style streetlights, sports stadiums fully lit when there are no matches, monuments or facades lit up all night, or neon signs and LED screens operating for hours without real need.

Impacts of light pollution: beyond the starry sky

The consequences of light pollution are much more profound than one might expect at first glance. It's not just about losing the spectacle of the night sky, but about wasting resources unnecessarily and directly affecting human health, safety, ecosystems, and scientific research:

1. Effects on human health

Prolonged exposure to artificial light at night disrupts circadian rhythms and affects sleep quality. Excessive light—especially blue light, such as that from screens and white LEDs—inhibits the production of melatonin, a hormone essential for regulating sleep and wakefulness, increasing the risk of insomnia, anxiety, fatigue, headaches, and metabolic disorders.

Various studies link light pollution with the increase in pathologies such as obesity, depression or even certain types of hormone-dependent cancers (breast, prostate), in addition to aggravating mental health problems and affecting general well-being.

2. Environmental and biodiversity impacts

Life on Earth evolved following natural cycles of light and darkness.Artificially altering these cycles has a profound impact on all types of organisms, especially those that depend on the night for their essential activities.

• WildlifeNocturnal animals, such as bats, owls, and foxes, see their hunting, movement, and reproductive patterns altered. Birds can become disoriented during migration and collide with illuminated structures, while insects tend to gather around artificial lights, becoming easy prey or even losing their reproductive capacity.
• Reptiles and amphibians: A paradigmatic case is that of sea turtles (Caretta caretta), whose young depend on moonlight to navigate the sea. The presence of artificial lights on beaches can disorient them, driving them inland and exposing them to predation or death.
• Zooplankton and aquatic organisms: The daily vertical migration of these organisms is altered by the presence of light, conditioning the feeding and food chain of many aquatic ecosystems.
• Plants and nocturnal pollinators: Certain plant species, such as Selenicereus (cactus family) open their flowers only at night to be pollinated by moths. The disruption of the dark cycles impacts their flowering patterns and the very survival of pollinators.
• Predator-prey relationships and trophic circuitsExcessive light alters the relationship between species, giving advantages to some and endangering the survival of others, with serious consequences for biodiversity.

Disruption of day-night cycles can make nocturnal and crepuscular species vulnerable, distorting reproductive patterns and feeding habits.

3. Obstacles to astronomical observation and scientific research

Light pollution is the number one enemy of astronomy, both professional and amateur. Sky glare reduces contrast and makes stars, planets, and galaxies invisible to the human eye and telescopes. Therefore, large observatories are increasingly being built in more remote and protected locations, with specific regulations.

Spain, for example, enacted pioneering regulations in the Canary Islands to safeguard the astronomical quality of the skies, and today there are international initiatives such as the Starlight Declaration (La Palma, 2007) supported by UNESCO, which recognizes the universal right to observe the starry sky.

4. Energy waste and economic consequences

Poorly managed electricity involves a considerable waste of economic and energy resources. In countries like Spain alone, annual spending on public lighting exceeds €950 million. It is estimated that a significant portion of this energy is lost illuminating unnecessary areas or escaping into the sky.

Investing in responsible solutions not only reduces environmental damage, but can also lead to savings of 25% to 75% in electricity consumption and billing, while reducing COXNUMX emissions.₂ and other contaminants.

5. Other negative consequences: road safety, air/sea traffic and cultural heritage

Glare, reflections and misdirected light create risks to driving and road safety., affecting both pedestrians and drivers. In the field of air and sea traffic, visibility can be impaired by inadequate or dazzling lights.

The loss of the night sky also means the disappearance of an invaluable cultural and scientific heritage. The starry sky has been declared a World Heritage Site by UNESCO, highlighting its importance for culture, science, and education.

Cities and regions most affected by light pollution

The problem is global, but it has a particular impact in densely populated areas and developed urban and industrial zones. More than 80% of the world's population already lives under skies polluted by artificial light.

Europe and the United States: the epicenters of light pollution

60% of Europeans and almost 80% of North Americans have lost the ability to see the Milky Way. Cities like Madrid, London, Paris, Berlin, Rome, Athens or Milan They are among the most polluted in Europe, partly due to their intense nightlife and poor lighting infrastructure.

On the other hand, there are notable contrasts: vast regions of Africa, Australia, and Russia still maintain areas relatively free of artificial light, allowing for better preservation of the night sky.

Spain: one of the most enlightened countries in Europe

In the Spanish case, Madrid, Barcelona, ​​Valencia, Seville, Malaga, Zaragoza and Palma de Mallorca They stand out for their high levels of lighting output and number of streetlights per inhabitant. Inadequate management of public lighting places Spain as the third most affected European country, behind only Greece and Malta.

Cities with the worst night sky quality

The international ranking indicates that Moscow, London, Rotterdam, Paris, Athens, Rome, Stockholm, and Milan top the list in Europe, although peripheral neighborhoods of major cities and industrial areas have even higher scores in some cases.

Impact of temporary changes: the case of the pandemic

During the COVID-19 pandemic, reduced human activity and lockdowns led to a significant decrease in light pollution. Cities like Berlin and Granada experienced darker skies and improved star visibility. The improved air quality, with fewer suspended particles, facilitated the direct scattering of light into space and allowed us to observe the profound link between the presence of artificial light and the degradation of the nighttime environment.

Global and local regulations, policies and initiatives

Advances in awareness about light pollution have led to a growing number of regulations and citizen movements to protect the nighttime environment. In some countries, such as Chile, very specific regulations have been enacted, restricting the emission of blue light nationwide (maximum 7%, or 1% in protected or astronomical areas) and strictly limiting the illumination of commercial and advertising signs after hours.

In Spain, in addition to the pioneering Canary Islands law, autonomous communities such as Catalonia, the Balearic Islands, Navarre, Cantabria, Andalusia, Extremadura, and Castile and León have their own regulations, and a growing number of municipalities are committed to combating light pollution.

International initiatives such as Stars4All or the "Starlight Declaration" address global awareness and promote the collective defense of the starry sky as a universal right. In parallel, municipal projects and citizen associations are working to reduce inefficient lighting, optimize lighting, and install control and automation systems.

Solutions and strategies to reduce light pollution

The good news is that there are effective measures to control and reverse light pollution, both at the institutional level and in the daily lives of individuals. Some of the most effective solutions, endorsed by organizations such as the International Commission on Illumination (CIE), are:

• Use of shielded and directional luminairesInstalling streetlights, lamps, and devices that project light exclusively downward limits dispersion into the sky and unintended areas. Shielding is essential to prevent light leakage.
• Limiting luminous flux and adjusting intensity: Regulate the power of each light point according to the area to be illuminated, following scientific criteria and technical recommendations.
• Reduction of the polluting spectrum and preference for warm lights: Minimize the use of cool white LEDs and opt for narrow-spectrum lamps (such as sodium), which have less impact on biological rhythms and lower atmospheric dispersion.
• Ban or reduction of cannons, laser projectors and intense sources: Eliminate the use of devices that send light directly into the sky, as well as limit ornamental and advertising lighting outside of necessary hours.
• Implementation of sensors, timers and automatic systems: Automate switching on and off, regulate intensity based on activity and the presence of people, and promote nighttime shutdown during periods of low activity.
• Harnessing technological innovation and smart planning: Invest in efficient, low-consumption LED systems with intelligent control (Smart Lighting) to adapt lighting to real needs and avoid waste.
• Education and citizen awareness: Promote awareness of the issue in society, in educational centers, and through institutional campaigns, so that everyone adopts responsible habits, such as avoiding unnecessary use of electricity at home and not leaving unused outdoor lights on.
• Legislation and compliance control: Ensure the existence and monitoring of specific environmental regulations for public and private lighting, with authorities responsible for certification and the imposition of sanctions.
• Sustainable urban design: Guide the planning of cities and inhabited areas through lighting sustainability criteria, with professionalization of those responsible and the use of intelligent management technologies.

Good practices at individual and collective levels

Beyond policies and regulations, The sum of small individual and community gestures can make a notable difference:

• Use blackout curtains or blinds to minimize the intrusion of outside light into homes.
• Avoid using electronic devices that emit blue light before sleeping.
• Turn off the lights whenever they are not essential, both inside the house and in gardens or patios.
• Opt for low-consumption, warm-light bulbs.
• Get informed and participate in consultations and public processes related to lighting in your neighborhood or municipality.
• Support neighborhood initiatives to reduce unnecessary lighting and demand efficient systems for facades, monuments, and public spaces.

Success stories, initiatives and the role of citizens

In recent years there has been a proliferation Local, national and international movements and projects that demonstrate that it is possible to reverse the trendEarth Hour, promoted by WWF, demonstrates the symbolic power of a global blackout, although the key lies in the daily commitment of governments, institutions, and individuals.

Citizen associations, NGOs, and scientific platforms actively collaborate to raise awareness and participate in urban planning, project evaluation, reporting cases, and lobbying for regulatory improvements. Interactive tools (such as online light pollution maps) facilitate access to data and contribute to raising awareness about the severity and scope of the problem.

It is essential to recognize that protecting the night sky, biodiversity, and human health is a shared responsibility. Only by joining forces can we ensure the recovery of the night, energy savings, and the perpetuation of one of humanity's most beautiful heritage sites: the starry sky.