A very starry sky

Starry Skies in the City? The Effects of Light Pollution

It’s 1957 in Long Island, New York. Michael goes out to his backyard with a pair of binoculars his dad gave him and an astronomy book of constellations in hand. He lies on the ground and stares up into the sky for hours, looking at the thousands of stars that were visible even in the outskirts of New York City.

In 1975, Michael was working at a daycare near Prospect Park in Minneapolis, where he focused his efforts on educating kids about the wondrous world of astronomy. He brought them to a nearby park to observe the stars in the sky when he realized they were less visible than they used to be. In order to give the students a full stargazing experience, he had to bring them on camping trips outside the city to view a darkly lit night sky.

The starry night sky in northern Minnesota. Photo by Makayla Mitchell.
The night sky in northern Minnesota. Photo by Makayla Mitchell.

While Twin Cities residents are fortunate to be able to drive a couple hours north to see a sky brightly lit with stars and full visibility of the Milky Way, it’s important to address why we can’t see nearly as much in our own backyards here in the metro. Metropolitan areas are affected by light pollution, which is defined as the brightening of the night sky by streetlights and other human sources. It has a disruptive effect on natural cycles and inhibits the observation of stars and planets.

Light pollution over the horizon coming from a nearby city. Photo by Makayla Mitchell.
Light pollution over the horizon coming from a nearby city. Photo by Makayla Mitchell.

The observation of light pollution began in the 1970s. According to the International Dark-Sky Association, research indicates that light pollution is increasing at a global average of 2 percent each year. This is evident here in St. Paul as a result of increased and misdirected commercial, residential and municipal lighting.

Longtime Mac-Grove residents brought up the topic with the Macalester-Groveland Community Council’s Community Building Team due to the difference they noticed in the night sky in the neighborhood over the past 40 to 50 years. In April, the Macalester-Groveland Community Council invited Bob Foucault, the vice president of Starry Skies North (the regional chapter of the International Dark-Sky Association), to attend the Community Building Team’s monthly meeting and explain more about what is being done — and what more can be done — to darken the skies.

What follows is a summary of the meeting.

Negative Effects of Light Pollution

Light pollution negatively affects both humans and wildlife.

  • For humans, light pollution can disrupt the natural circadian rhythm and sleep patterns, impair vision at night due to glares caused by misdirected street lighting and have lasting adverse effects on human health.
  • For wildlife, artificial light disrupts the world’s ecosystems, which has negative and deadly effects on plants, mammals, birds, amphibians and invertebrates.

For example, many birds are killed during migration because lighting from tall buildings and other metropolitan sources attracts them and disrupts their migration patterns. Light pollution also disrupts many animal and plant-life-sustaining behaviors such as reproduction, nourishment, sleep and protection from predators.

In addition to negative effects on human health and disrupting wildlife’s natural cycles, it is also important to address light pollution’s inequitable effects within the city. According to Foucault, lower income and racial minority neighborhoods are most impacted by light pollution due to the closer proximity to highways.

What Can Be Done About Light Pollution?

It may feel discouraging to live in a metropolitan area and wonder what impact you can have on light pollution. However, individuals can have an influence in many ways.

  1. Use warmer color LED light bulbs on your home’s exterior lighting.
    Color temperatures are measured in Kelvin; the lower the Kelvin, the warmer the light. Indoor lighting is typically around 2700 K and natural outdoor lighting at noon is about 5700 K. For exterior lighting, try to choose LEDs that are 3000 K or lower.
  2. Turn off exterior lighting when it is not being used.
  3. Educate yourself and others about what light pollution is and is not.
    Talk to your neighbors; let them know that the goal is not to eliminate lighting, but rather to reduce and redirect it to where it needs to be.
  4. Advocate for light pollution policies amongst city officials.
    Many cities have implemented various policies to redirect or change lighting to produce less light pollution.
    • The city of Duluth began switching streetlights to LED, but they were using 4000 K bulbs. The International Dark-Sky Association advocated for warmer color bulbs, and now Duluth doesn’t install anything above 3000 K.
    • In Tucson, Arizona, the city dims streetlights to 60% after 11 p.m., when traffic is lighter. Earlier in the evening, the lighting is at 80%, except in cases of emergency.
    • In Minnesota, streetlights could be dimmed, especially in the winter when there is an abundance of light reflectivity from snow.
  5. Reach out to local businesses, educational institutions and other commercial properties about lighting policies and ways in which excess lighting could be reduced.
    The International Dark-Sky Association is looking to partner with various businesses and organizations to work toward a less polluted sky. City officials in Duluth will be implementing a reward program for businesses that have efficient lighting.

Safety Concerns

A common misconception about implementing dark sky initiatives is that more lighting equals more safety, and therefore redirecting lighting will create more safety issues. However, lighting often is directed incorrectly, producing glares and creating hazards for driving and for pedestrians. When misdirected lighting creates a spotlight effect, it only allows for pedestrians to see areas that are illuminated and darkens the shadows beyond. “It’s how you use the lighting, not how much you use,” Foucault noted.

Similarly, it’s a common belief that more lighting provides more security and safety when it comes to theft and crime. However, bad lighting can actually cause a false sense of security. Bright and poorly aimed lights can hide danger by creating deep shadows where bad actors can hide. As Foucault said, “We are the Dark Sky Association, not the Dark Ground Association. We are advocating for more responsible and more efficient use of lighting.”

A hand blocking the light source in the lower photo illustrates how lighting can be focused better to reduce glare (author photos).

Measuring Light Pollution

Light pollution is measured using sky-quality meters, which give a basic measurement of the amount of light pollution in a given area. This is measured on what’s known as the Bortle scale, from 1 (which might be found in places like the Boundary Waters) to 9 (in the heart of a city). The International Dark-Sky Association and the Minnesota Astronomical Society will be setting up a network of eight sky-quality meters around the Twin Cities to gauge where pollution is the strongest and what is its source.

To learn more about dark skies, can watch the Macalester-Groveland Community Council’s April 2023 Community Building Team Meeting, or you can visit the International Dark-Sky Association website. Their site contains many different informational brochures, videos, policies, and ways to get involved. You can also visit the Starry Skies North website for more Minnesota-based information.

Additional Resources

Photo at top by Guille Pozzi on Unsplash

Alyssa Mitchell

About Alyssa Mitchell

Pronouns: She/her

Alyssa Mitchell is the Program and Events Specialist for the City of Vadnais Heights Parks and Recreation Department.