Light Pollution: What We Lose When the Night Sky Disappears, and How to Dim It

Imagine a quiet evening at home when the power goes out. Your neighborhood — usually full of house lights and streetlights — goes dark, and looking up you see something you rarely do: thousands of stars splashed across the sky — the Milky Way. Light pollution keeps a large share of the world's people from seeing it from their own backyard; see how bright your area is on this light pollution map.

A building under a brilliant night sky, with the Milky Way visible. Image from the Park Service's page.

The night sky has inspired people for generations: the Milky Way over a lake in Yellowstone National Park. NPS / Neal Herbert.

What light pollution does

The obvious loss is the night sky itself, and the awe and wonder of looking up at the stars. Less obvious effects are being uncovered by scientists studying nocturnal (night-active) and even diurnal (day-active) wildlife:

• Nocturnal and migratory animals depend on darkness; artificial light can disrupt their breeding and feeding.
• It can lure sea turtle hatchlings away from the ocean.
• City light attracts migrating birds, throwing them off course, making them collide with lit buildings, or leaving them circling until exhausted and starving — millions of birds die this way each year.
• Birds read cues from their surroundings to know when to migrate; artificial light can distort them, so they leave too early or too late.

What you can do

The good news: light pollution is completely reversible — all it takes is turning lights off.

• Light only if needed — do you really need or use that light?
• Light only when needed — use timers or motion sensors.
• Light only where needed — shield lights and point them down; shades, blinds and curtains keep light in. More: reducing unwanted lighting.
• Color matters — white and blue light affects wildlife more than warmer colors; use warm-white or amber light.
• Use the least light you need — fewer lights, or lower-wattage bulbs.
• Use energy-efficient lights, which also shrink your carbon footprint.

Pass it on

Protecting night skies is everyone's job, and sharing what you know helps: the next time a neighbor puts up a light that isn't dark-sky friendly, you can tell them — and it's fine to admit, "I didn't know that!" Learn more by becoming a Junior Ranger Night Explorer, or explore other I Didn't Know That! topics.

Sources

Based on "I Didn't Know That!: Light Pollution," National Park Service; a work of the United States government in the public domain. The source gives the share of people who can't see the Milky Way as both 80% of the world's population (in its text) and one third of humanity (in its graphic), so neither figure is repeated and the graphic is not shown. Its photograph of sea turtle hatchlings, credited to Colorado State University, is not reproduced.