The problem of light pollution has grown dramatically with the spread of LED lighting. Its effects are clear: the night sky loses its stars, wildlife such as birds and other species that depend on darkness is harmed, and human health can be affected as well.
Alicia Pelegrina, who spoke at the opening of the CSIC Andalusian Institute for Astrophysics Sky Quality Office, explains that light pollution results from how society uses artificial illumination. The latest volume in a CSIC collection warns about both causes and consequences. It notes that people often equate light with wealth, joy, and safety, but misused lighting becomes a serious environmental issue. It is a form of pollution that cannot be smelled, heard, or touched, yet it impacts ecosystems, contributes to insect declines, and disrupts biological rhythms in humans and other organisms.
The author emphasizes that excessive light can lead to a high bird mortality rate, destabilize ecosystems, and influence physiological processes. This is not merely an abstract problem; it affects real lives and the balance of living systems.
The new world atlas of sky brightness warned in 2016 that 80 percent of the planet’s population lives under polluted skies, and about a third cannot see the Milky Way. In Europe and the United States the situation is stark: nearly everyone is deprived of a view of the starry sky.
So, what is light pollution and how does it occur? In Spain, the Cel Fosc association defines it as the replacement of natural night darkness by artificial light sources. Two properties make artificial light especially dangerous: its tendency to spread in all directions and the speed at which it propagates. It travels at about 300,000 kilometers per second in vacuum, and atmospheric particles scatter light, producing a secondary glow. These insights come from a CSIC expert who highlights the need to understand this process and its consequences.
Too much light power and poorly directed lighting
The astronomy community has long warned about light pollution. Beyond diminishing the night sky, it alters how we explore the cosmos and manifests in several practical ways. Excess luminance floods areas beyond the target zone, with streetlight emissions intruding into bedrooms or coastal waters where light spills over into the sea. Another facet is flare, which happens when lights are directed toward the eyes or when lighting is excessive in a given area.
In practice, most of the problem comes from misaligned street lights and fixtures, with light directed upward or to the sides rather than downward. Excessive brightness and long operating hours also contribute to the pollution problem.
The description of street lamps, lamps themselves, and fixtures helps explain how city lighting is designed and where missteps occur. Proper design of both components is essential for effective and considerate illumination.
Experts advise using lamps with longer wavelengths that emit orange light, which is less scattered and gentler on the atmosphere. Lights should minimize skyward emission and avoid white or bluish tones, which cause greater scattering and brightness in the night sky.
Artificial light: the rules of the game are broken
Natural light cycles regulate living systems, supporting processes like reproduction, foraging, migration, and flowering. Artificial light disrupts these cycles and can affect distant natural areas because light from concentrated city centers travels far. The International Union for Conservation of Nature notes that light pollution already affects two-thirds of key biodiversity areas globally.
About 30 percent of vertebrates and 60 percent of invertebrates are nocturnal. The result is imbalances when light appears in unintended places or times. Nocturnal animals rely on darkness for safety and orientation, so artificial light can disrupt migratory movements and the feeding patterns of many species.
Birds and other wildlife are affected as well. Seabird chicks can be drawn to lights during their first flights, and in some places, chicks wander onto streets and highways. Turtles may fail to reach nesting beaches due to artificial lighting. A 2021 University of Plymouth report estimates that at a depth of one meter, almost two million square kilometers of coastal oceans are exposed to artificial light at night.
The rhythm doesn’t stop and our health suffers
People often know about the biological clock that governs daily rhythms. Artificial lighting can disrupt this clock, creating what some researchers call chronodisruption. Cities that operate around the clock intensify this disruption, sending night signals during daytime hours. Many studies connect chronodisruption with cardiovascular disease, insomnia, concentration problems, fertility issues, dietary changes, and even certain cancers.
In Spain, a large study involving more than 40,000 adults across multiple regions found a link between high blue light exposure at night, common in LED lighting and screens, and increased risk of breast and prostate cancer.
Towards sustainable lighting
Addressing the problem does not require stepping back to bonfires. Environmental science specialists suggest practical steps toward sustainability: reduce skyward light, illuminate only what is needed, and use lighting within the visible spectrum that humans can detect efficiently. Timing and direction matter—lights should be aimed downward and used only as required.
Legislation plays a crucial role. While some European countries have advanced dark-sky protections, a national law on light pollution is lacking in many places. Regions like the Canary Islands and Catalonia have enacted measures, and broader regulatory schemes are being considered. A recent decree to curb lighting in shop windows and public buildings is expected to influence local pollution levels, but the challenge remains substantial and calls for a comprehensive, action-oriented plan.
Light pollution is not just an environmental issue; it has a strong social component. Raising awareness and sharing information with citizens is essential. A collective responsibility exists to protect the starry sky for current and future generations.
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