What is light pollution?

Starting with gaslit outdoor lamps in the late 1700’s, outdoor lighting is a staple of modern society, allowing people to work and play outside when it’s dark. But the widespread use of outdoor lighting has altered our view of the night sky. 

Identified by astronomers as a problem in the early 20th century, light pollution refers to human-produced modifications to outdoor light that exceed naturally occurring light levels. Light pollution is created when outdoor light escapes upwards or sideways, causing a brightening effect in the night sky. Nearly 80 percent of the world’s human population live under night skies that have been artificially brightened. 

There are four main types of light pollution: glare, clutter, light trespass and night glow. 

• Glare occurs when light shine interferes with the observer’s vision. It refers to the effect of a “bright light against a dark background.” This effect is common with street lights. 
• Clutter occurs with excessive groupings of artificial light sources such as electronic advertisements. 
• Light trespass, the unintended spill of light from one source onto property or space, is also a common by-product of advertising and unshielded light.
• Night glow refers to the overall lightening of the sky. 

While light pollution tends to be most intense in urban environments, nighttime light comes from many sources that are found across the world. Streetlights and electronic advertising typically use LED bulbs that often produce glare, light trespass, and tend to be cluttered. Similarly, houses, buildings, and landscaping often use lighting that contributes to artificial light in the sky. 

Effects of Light Pollution 

Light pollution harms wildlife, wastes energy, and can have adverse health effects on humans.

Wildlife

For nocturnal species – approximately 30% of all vertebrates and 60% of invertebrates – disruption of the darkness can affect foraging patterns and reproduction cycles, and hence their roles in the larger ecosystem.

Animals can experience disturbances to mating patterns, sleep, and hunting behaviors due to artificial light. 

Light pollution leads to millions of bird deaths each year. Light can affect the migratory patterns of birds as birds may misinterpret excess light as a continuation of daylight. This can cause exhaustion, predation, and lethal collision. Birds may also leave their wintering sites earlier creating migration mistiming as resources and the conditions may not be suitable along their migratory path. 

Light pollution has a major impact on species of endangered or threatened sea turtles that nest on developed beaches. Sea turtles have naturally evolved to locate the sea by seeing the brighter horizon over the ocean. Exterior lighting on beaches can cause disorientation in hatchlings causing them to wander inland, where they often die of predation.

About 50% of insect species are nocturnal, so artificial light severely impacts their life cycles. The unnaturally bright environment disrupts bioluminescent communication, light-based navigation, and where insects lay their eggs. Insect diversity is critically important for vital environmental functions— by losing insect diversity, entire ecosystems are at risk.

Similarly, light pollution can interfere with plant pollination and reproduction. Plants under artificial light experience changes to budburst, flowering, and leaf coloring which have significant effects on the health, survival, and reproduction of plants. 

Energy

DarkSky estimates that at least 30% of all outdoor lighting in the U.S. alone is wasted, mostly by lights that aren’t shielded, as the light levels are higher than necessary and shine both where and when it is not needed. The main culprits driving the increasing brightness of the night sky are urbanization and the growing use of LEDs. One study found that white LEDs attracted 48% more flying invertebrates than existing HPS (high-pressure sodium) lamps. 

Human Health

Light pollution can cause significant health problems in humans as it decreases melatonin production which results in fatigue, stress, and can contribute to other health issues. Melatonin is a natural hormone that induces sleep and supports the immune system. Light pollution can also potentially influence human circadian rhythms which are key to sleep cycles.  

According to the American Medical Association, “High-intensity LED lighting designs emit a large amount of blue light that appears white to the naked eye.” These lights can create nighttime glare that is worse than lighting used outdoors pre-LEDs. Blue-rich LED lighting can decrease visual acuity and safety, resulting in concerns and creating road hazards for drivers at night in addition to over-illuminating skies. 

Solutions 

To reduce light pollution, we can make small changes such as using light only where needed, decreasing the brightness of bulbs, utilizing warm lighting, and using timers or motion sensors. This in combination with city ordinances and state policy will pave the way for the return of darker skies.