What Is Light Pollution?

Medically Reviewed by Carol DerSarkissian, MD on November 11, 2021
Written by Alexandra Benisek
4 min read

Light pollution is when artificial light (usually from outside) is excessive, unnecessary, or obtrusive. Lights at homes and businesses, streetlamps, neon signs, and billboards are among the things that cause it.

While artificial light helps people stay productive after dark, light pollution can have harmful effects on humans, wildlife, the environment, and the economy.

There are several forms of light pollution:

Sky glow. This is the bright halo you see above a city at night. This happens when water droplets and other particles in the air scatter the light around.

Light trespass. This happens when light from a floodlight or streetlamp spills over into another area where it's not wanted or needed.

Glare. This is light that gets into your eyes and causes discomfort.

Over-illumination. This is the use of light where it's not needed, such as lights left on overnight in an empty office building.

You need darkness to live a healthy life. Before the invention of artificial light, humans were adjusted to a natural 12 hours of daylight and 12 hours of darkness.

This cycle is part of your circadian rhythm, your body’s internal "clock" that helps you fall asleep at night and wake up in the morning. Manmade light at night disrupts it.

Circadian rhythm disruptions may lead to problems like:

Too much light at night can also hinder your body’s production of melatonin. Melatonin is a hormone that helps regulate sleep patterns. Too little melatonin has been linked to:

One study found a link between lower levels of melatonin in the developed world and rising rates of breast cancer. Another showed that women living in communities that are brightly lit at night had a 73% higher chance of getting breast cancer than those from areas with little outdoor lighting. But that same study found that light pollution had no effect on the risk of lung cancer. We need much more research into this.

Light pollution also affects animals, especially species that are most active at night. Artificial light can interfere with migration, hunting, feeding, and reproduction. It gives nocturnal animals less time to find food, shelter, and mates. And it helps predators to see prey animals around the clock.

Think about sea turtles, for example. Newborn sea turtles' instincts tell them to move from their nests to the brightest source of light. That's because, in the natural world, starlight reflected on the ocean is the brightest thing on the beach. But when baby sea turtles see artificial light from coastal cities, they crawl toward land instead. There, they die of dehydration or become prey for other animals. Hundreds of thousands of turtle hatchlings die each year in Florida alone.

Light pollution has led to a lower lightning bug population, the deaths of many birds that become confused during migration, and habitat loss for many species. It may also increase the risk of algae blooms in bodies of water, which can harm fish and aquatic ecosystems.

In addition, unnecessary light contributes to air pollution. First of all, it wastes energy. Power plants that are mostly fueled by coal put tons of carbon dioxide pollution into the atmosphere every year. By some estimates, reversing light pollution would equal removing 9.5 million cars from the roads, in terms of air quality.

Further, nighttime light in urban areas appears to interfere with a compound called nitrate radical that naturally cleanses air of pollutants when it's dark.

Light pollution also has an economic effect. In the United States, we spend billions of dollars each year to light roads, stores, offices, and other areas. But much of this money goes to waste because many of these lights are badly designed. Often, light shines up into the sky instead of toward the ground, where we need it.

The International Dark-Sky Association estimates that about a third of all lighting is wasted. This amount of light costs about $2.2 billion a year.

The best way to fix light pollution is to turn on lights only when you truly need them, and avoid overly bright lighting. Use shields on outdoor fixtures to keep light out of the sky and direct it where it's needed.

Other ways to lessen light pollution include:

  • Use dimmers, motion sensors, and timers.
  • Use LEDs and compact fluorescent bulbs to save energy, but only the warm-colored ones.
  • Avoid using lights with blue tones at night. This worsens glare and sky glow, may harm your vision, and could make driving unsafe.