Light pollution

Light pollution is excessive, misdirected, or poorly timed artificial light that brightens the night sky, disrupts ecosystems, or interferes with human activities.

Skyglow: A diffuse brightening of the night sky caused when artificial light scatters through the atmosphere. Upward and reflected light from cities creates this widespread loss of dark skies.
Outdoor lighting: Artificial illumination installed outside buildings and in public or private spaces. Its design and operation are the main controllable sources of light pollution.
Astronomy: The scientific study of celestial objects, space, and the physical universe. Skyglow reduces the contrast needed to observe faint astronomical objects from the ground.
Darkness: The absence or near-absence of visible light in a space or environment. Natural darkness is the environmental condition that excessive nighttime lighting displaces.
Glare: Excessive brightness that reduces visual comfort or a person's ability to see. Unshielded or overly bright fixtures can impair visibility even when they illuminate a small area.
Full cutoff fixture: A luminaire designed to emit no light above the horizontal plane through its lowest point. It directs light downward and limits direct emissions into the night sky.
Migratory bird: A bird that makes regular seasonal movements between breeding and nonbreeding areas. Artificial lights can disorient migrating birds and draw them into collisions with buildings.
Moonlight: Sunlight reflected from the Moon that illuminates Earth's night side. Its natural variation contrasts with the persistent artificial brightness that alters night environments.
Light trespass: Unwanted artificial light that spills into spaces where it is not intended. Poorly aimed outdoor lighting sends illumination into homes and neighboring properties.
Correlated color temperature: A measure, in kelvins, describing the apparent color of a light source relative to a reference radiator. Choosing warmer sources can reduce short-wavelength emissions associated with greater skyglow and biological effects.

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