What is Light Pollution?

Why does it matter?

Light pollution impacts nearly every aspect of our lives, including our health, safety, and environmental justice. Humans have an innate connection with the night sky, spanning across generations, as societies relied on the seasonal patterns of constellations to pass down stories and important lessons. The Milky Way’s majestic presence also gives us an intimate introspective into the human experience. Beyond that, light also impacts the natural environment and disrupts entire community assemblages. Wasting light means wasting energy and financial resources that could be used for other projects. Below are just some examples of light pollution’s impacts, but a high-level overview is provided in DarkSky International’s 2023 State of the Science Report. 

• Human health - Like most life on Earth, humans adhere to a circadian rhythm — our master clock, which is crucial for our overall health. It interacts with our body systems, changes our hormone levels, and even modifies our genetic code. Natural light helps keep our clock in tune with Earth’s 24-hour cycle. Altering or interrupting our normal circadian rhythm can put us at risk for physiological and behavioral impacts. Long-term circadian disruption may increase our risk of obesity, diabetes, mood disorders, reproductive problems, and cancers. Additionally, light pollution impacts are not uniform. Recent studies have shown that poorer, non-white neighborhoods tend to be brighter, increasing the exposure intensity and duration of this pollutant.

• Safety - Outdoor lighting can have a significant impact on how people perceive and react to their environment. Lighting can help people to identify potential hazards, navigate safely, and read important signage. Properly lit sidewalks and streets can allow pedestrians, cyclists, and vehicles to traverse through urban areas at night. Lighting can also enhance situational awareness in public areas, such as parks and universities. Note that safety is a different topic than security. People may desire the need to protect their property with additional lighting. However, if the light source creates glare or is overly bright, it may reduce the user’s visibility to detect movement, or the light may make valuable property more visible and accessible to trespassers. While there are no conclusive studies that show adding more light reduces crime, they do show that lighting makes us feel safer. In light of this, we can provide preventive measures without negating safety or environmental health when lighting is responsibly used.

• Natural environment - Light pollution impacts organisms at multiple scales, from physiological changes brought by metabolic stress, to changes in individual behavior and population shifts, and has the potential to disrupt entire communities. Well-known examples of affected animals include migrating birds, hatchling sea turtles, predator-prey dynamics, and nocturnal pollinators like moths and bats, but the list does not stop there. Plants are impacted by light pollution as well; they will bloom earlier in the year when exposed to light, which creates a temporal mismatch with animals they depend on for pollination. The delicate interactions that evolved with the day-night cycle are shifting rapidly, and species most sensitive to the presence of artificial light are the most at risk.

• Energy - A 2022 report by the U.S. Department of Energy found that 99% of artificial light we produce is not used by the human eye to interpret its surroundings, and is therefore wasted. All of this wasted light adds up. Globally we spend at least $50 billion in energy costs each year to produce light that escapes into space. This waste can be solved with advanced lighting controls like dimming and motion sensors and transitioning to energy-efficient LEDs, which would save $15.4 billion per year in the U.S. alone.

All of these facets can be immediately improved by reducing wasteful and unnecessary light.

How to identify when artificial light is an issue

The easiest indicator is whether a light is obtrusive or excessive. If misused, artificial lights can actually reduce our visibility of the surrounding environment, making it less safe. If the light serves no clear purpose or task, it is wasteful and therefore polluting the nighttime environment. There are four main types of light pollution.

1. Glare is light striking your eye directly from the source. Glare, depending on the intensity, can result in reduced contrast, color perception, and visual performance. A common occurrence comes from overly bright vehicle headlights that cause visual discomfort.

2. Light clutter is the excessive grouping of bright lights that cause confusion and distract from oncoming or surrounding objects.

3. Light trespass, also known as spill light, occurs when a light fixture casts illumination beyond the property lines, unintentionally illuminating other homes, businesses, or areas. Many people experience this from streetlights without proper shielding or undirected floodlights from their neighbor’s property.

4. Skyglow originates from natural and man-made sources; however, poorly designed artificial lights are the main cause of skyglow. Light emitted into the sky and along the horizon accumulates to form a dome of light surrounding and expanding out past communities. This glow makes celestial objects difficult to see, even with a telescope. 

Solutions to light pollution 💡

The solution to light pollution is as easy as turning off lights we don’t need - that’s it! 

The National Audubon Society and chapters like the Tropical Audubon Society promote this every year with its Lights Out campaigns to encourage homeowners, businesses, and municipalities to turn off unnecessary lights during peak bird migration. 

If we can live without these lights for a few nights of the year, why not take it a step further and turn off unnecessary lights every night?

Because there are reasons to keep certain lights on at night, DarkSky International partnered with the Illuminating Engineering Society to promote the Five Principles for Responsible Outdoor Lighting. 

How do quality lights look in action? Here are a few examples of quality outdoor lighting taken by night sky advocates in other regions: