Artificial light at night is one of those inventions that is hard to dispute. It makes it easier to move around, extends city activity, increases the sense of safety, and allows people to work and rest after dusk. The problem is that in recent decades we have started to shine light not only where it is needed, but also “just in case”: brighter, longer, and across wider areas. From an environmental perspective, this is a change comparable to modifying a local climate—except it concerns not temperature or humidity, but a basic biological piece of information: is it night, or is it day?
Light pollution (often referred to by the acronym ALAN – Artificial Light at Night) includes the brightening of the sky above cities, glare, unwanted light entering windows, and excessive illumination of spaces that no one is using at a given moment. For humans, this may be “only” discomfort or worse sleep. For many species, it is a signal that the world has stopped working according to a rhythm they have adapted to for thousands of years.
Night Ecology: Why Darkness Is a Resource
For a long time, we treated night as an empty break between daytime activities. Meanwhile, for nature, night is a fully-fledged environment. Many animals live nocturnally: insects, amphibians, numerous mammals, and also some migratory birds. Darkness regulates behaviors related to foraging, reproduction, rest, and migration. If night becomes “brightened,” organisms lose their reference point.
In practice, ALAN acts like an environmental pressure. It creates zones that some species avoid, while others exploit. This changes the composition of local communities: some populations decline, others increase. Predator–prey relationships change, activity timing shifts, and even reproductive success can be affected. This is especially important because in nature many processes are synchronized—and light is one of the main “clocks.”
Nocturnal Insects: When a Streetlamp Becomes a Trap
The most familiar image is a moth circling a lamp. This is not just coincidence. Many insects use natural sky light for orientation. Strong, point-like light sources disrupt this mechanism: insects lose direction, circle, become exhausted, or become easy prey. At the scale of a single lamp it may look trivial, but at the scale of a city it means hundreds of thousands of such “traps” operating every night.
The consequences spill across the entire ecosystem. Insects are the foundation of many food webs. If their numbers drop, insect-eating species suffer: bats, birds feeding chicks, and even some small mammals. Moreover, some pollinators operate at night—and although daytime pollinators get the most attention, nighttime plant–insect interactions are important for maintaining biological diversity.
Field studies show that street lighting can reduce the abundance of caterpillars and other insect life stages near lamps, which translates into food availability during crucial parts of the season. This is an example of an effect that does not scream in headlines, but steadily weakens local networks of dependencies.
Migratory Birds: Night Light That Shortens Life’s Journey
For many birds, night is migration time. It is an energy and safety strategy: cooler air, fewer predators, different weather conditions. The problem is that strong nighttime light can disorient birds, especially during cloud cover and fog, when the urban glow creates a bright “dome” over the city. Disoriented birds circle, lose energy, and increase the risk of collisions with buildings—especially glass-covered ones.
In practice, this means that lighting infrastructure—combined with architecture—can become a mortality factor. In many countries, programs exist to reduce light emissions during migration periods, especially in city centers and around tall buildings. This does not require eliminating lighting, only management: dimming, switching off parts of illumination, and using solutions that minimize emission into the sky.
Plants and Trees: A Night That Extends the Day
Light pollution also affects plants. Trees and shrubs respond to day and night length, and photoperiod influences their phenology: flowering time, entering dormancy, leaf drop. If a plant “sees” a brightened night, it may maintain physiological activity longer, enter dormancy later, and be more exposed to frost damage. In cities, situations are observed where trees near streetlights keep leaves longer, and the seasonal cycle becomes less coherent.
This is not only an aesthetic issue. A phenology shift can cause timing mismatches between plants and organisms that depend on them. If a plant flowers earlier or longer, while the pollinator keeps an “old” rhythm—reproductive success declines. An ecosystem works well when elements are synchronized. ALAN loosens that synchronization.
LED: Progress That Requires Standards
In recent years, LED lighting has become widespread. This is good news from an energy-efficiency perspective, but not always from a night-ecology perspective. Cheap light tempts us to use more: brighter, longer, on more streets and squares. In addition, many LEDs have a significant blue-light component, which strongly affects circadian clocks biologically for many organisms (including humans). This does not mean LEDs are “bad”—it means we need design criteria, not only price criteria.
Key parameters are: directionality (light on the sidewalk, not into the sky), intensity (no excess, no glare), operating time (dimming in the middle of the night), and spectrum (warmer colors where possible). Well-designed lighting can simultaneously improve human comfort and reduce pressure on nature.
What Can Be Done Without a Revolution: Simple Rules to Reduce ALAN
The biggest advantage of tackling light pollution is that many solutions can be implemented quickly. They do not require major social campaigns or years of investment. They require awareness and decisions on the part of space managers.
- Use full cut-off fixtures that do not emit light upward and minimize skyglow.
- Set intensity according to the real function of the place, avoiding “over-lighting” that often increases glare.
- Implement dimming after hours of the lowest traffic, and motion sensors in low-activity zones.
- Limit decorative illuminations in the middle of the night and during sensitive periods (e.g., migrations).
- Avoid lighting ecological corridors: riverbanks, forest edges, and green zones that serve as animal movement routes.
This approach is not “anti-human.” On the contrary: reducing glare and better directing light can improve safety and comfort. In many places, the problem is not lack of light, but its quality.
Light Pollution and Pro-Environmental Actions: A Missing Element in Biodiversity Thinking
In environmental projects, we often focus on “adding good”: planting trees, creating meadows, protecting habitats. This is important, but sometimes just as important is “removing pressure.” If we want to support biodiversity, we must consider 24-hour conditions. A tree grows in a landscape where it is not only soil and water that matter, but also the lighting regime. Lighting can reduce insect presence, change bat behavior, and affect plant phenology. As a result, part of the benefits of greening may be weaker than we assume.
That is why the topic of night ecology complements the mission of organizations that operate in the field, engage people in practical projects, and build awareness that ecology is real decisions—not only declarations. If you are looking for examples of actions combining tree planting with corporate team engagement, it is worth seeing One More Tree’s employee volunteering initiatives
Summary: Darkness as a Resource Worth Protecting
Light pollution is a quiet problem because it seems harmless and “modern.” But in ecosystems, night is not emptiness. It is an environment that regulates life—from insects, through birds, to trees. When we brighten the night, we change the rules of the biological game.
The good news is that this is one of those areas where results can be achieved quickly: better fixtures, sensible intensity, dimming, and limiting emissions into the sky. In practice, that means protecting nature without losing quality of life. Sometimes, to do something important for the environment, you do not need to build anything or plant anything. Sometimes it is enough to stop shining light where nature needs darkness.
