Artificial light at night, skyglow, glare, light trespass, circadian rhythms, wildlife, astronomy, energy use, outdoor lighting, and dark-sky design
Light pollution
Light pollution is excessive, misdirected, or poorly timed artificial light at night. It can brighten the night sky, create glare, disrupt sleep and wildlife, waste energy, and make it harder to see stars, while better lighting design can reduce many of its effects.
What light pollution is
Light pollution is artificial light at night that goes where it is not useful or needed. It includes light that shines upward into the sky, spills into homes or habitats, causes harsh glare, or creates visually confusing clusters of bright signs and fixtures. The problem is not light itself, but wasteful and poorly controlled light.
How skyglow forms
Skyglow happens when light is scattered by air molecules, aerosols, clouds, and dust above a town or city. Some light travels directly upward from fixtures, while some reflects from roads, buildings, and other surfaces. The result is a brightened night sky that can be visible far from the original light sources.
Glare and light trespass
Glare is light that is bright enough to reduce comfort or visibility, such as an exposed lamp shining into a driver's eyes. Light trespass is light spilling across property lines or into places where it is unwanted, such as a bedroom window, nesting beach, or natural area. Both can happen even when the total amount of light is modest.
Effects on people
Artificial light at night can affect human comfort, sleep timing, and nighttime visibility. Bright or blue-rich light in the evening can influence circadian signals that help the body distinguish day from night. Poorly aimed lighting can also make streets or work areas feel less safe by creating glare and deep shadows.
Effects on wildlife
Many animals use darkness, moonlight, or starlight to navigate, feed, migrate, hide, or reproduce. Artificial light can disorient migrating birds, affect insects, alter predator-prey relationships, and confuse sea turtle hatchlings that normally move toward the brighter ocean horizon. The impact depends on species, wavelength, timing, and location.
Astronomy and culture
Light pollution reduces the number of visible stars and can make faint astronomical objects difficult to observe. That matters for observatories, amateur astronomy, education, navigation traditions, and cultural relationships with the night sky. Dark-sky parks and lighting ordinances try to protect places where people can still experience natural darkness.
Better lighting design
Reducing light pollution usually means using the right amount of light, aiming it downward, shielding fixtures, choosing warmer colors when possible, and turning lights down or off when they are not needed. Motion sensors, timers, curfews, adaptive street lighting, and careful sign standards can preserve visibility while reducing wasted light.
Why it matters
Light pollution matters because it is a visible environmental problem that can often be reduced without giving up useful lighting. Better night lighting can save energy, improve comfort, protect wildlife, support sleep-friendly environments, and restore access to the stars. It asks cities and households to treat darkness as a resource, not just an absence.