Light Pollution and Dark Skies: Glare, Skyglow and the NPS Six-Step Lighting Check
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How we wrote this: A plain-English summary of the National Park Service Night Skies program pages, checked October 29, 2026. Local lighting ordinances may also apply to your property.
Can't see the Milky Way from home? Light pollution is the likely reason. Here's what the National Park Service (NPS) says about it, and what you can change in your own yard.
What light pollution is
NPS defines light pollution as excess or inappropriate artificial light outdoors. It shows up three ways:
- Glare: bright, uncomfortable light shining straight at you that interferes with your vision.
- Light trespass: unintended spill of light onto someone else's property, often a source of neighbor conflict.
- Skyglow: the brightening of the night sky from human-caused light scattered in the atmosphere.
NPS has documented the glow of cities at distances over 200 miles.
It's growing
NPS cites satellite data showing that from 2012 to 2016, continuously lit areas brightened by 2.2% per year, and Earth's artificially lit outdoor area grew by 2.2% per year. Exceptions include places with enforced lighting rules, such as Tucson and Flagstaff, Arizona.
Clouds and air pollution make it worse. NPS says clouds over a city's light dome can make the sky up to 1,000 times brighter than on a clear night.
Why it matters
- Stargazing: skyglow cuts contrast, hiding stars and planets, and keeps your eyes from fully dark-adapting.
- Sleep and health: NPS notes dark nights (and bright days) help keep circadian rhythms in sync.
- Safety: glare can create blind spots.
- Wildlife: nearly half of Earth's species are nocturnal. Light can disrupt predator and prey relationships, reproduction, navigation and migration. On the coast, it disorients sea turtle hatchlings (see sea turtle nesting beaches).
The NPS six-step lighting check
NPS recommends evaluating each outdoor light this way:
- Light only if needed.
- Light only when needed. Use motion sensors or timers.
- Light only where needed. Shield fixtures and point them down.
- Use warm-white or amber light. Avoid blue-white light.
- Use the minimum amount of light needed.
- Use energy-efficient lights.
NPS adds that efficient warm-white LEDs save energy and money and cut replacement costs.
Get the most from a dark sky
Pick a moonless night (check our moon phases guide), get away from city light domes, and give your eyes time to adjust. Then try a meteor shower or watch for the space station.