Back in 1807, London became the first city on the planet to have a street illuminated by gaslight lamps. To the city's residents, it must have seemed like a wondrous thing to have evening turned into a simulated version of daytime.
But a little more than two centuries later, artificial lighting has spread across so much of the planet that the darkness of night is steadily vanishing. Today, 80 percent of the world's population now lives in places where the sky glows at night from lights on streets and buildings. Artificial light has become another form of pollution — one that scientists say poses threats both to the natural environment and to human health.
The extent of light pollution is evidenced by a November 2017 study in the journal Science Advances, in which researchers used measurements taken by satellites to study the artificial brightness of Earth's surface during nighttime. They found that between 2012 and 2016, the outdoor area that was artificially lit grew at a rate of 2.2 percent per year. As more spaces are being illuminated, they've become brighter as well, with the radiance of those areas increasing at an annual rate of 1.8 percent.
As this summary of the findings in USA Today explains, the researchers found nighttime brightness stayed the same in the U.S. and 38 other countries during the time period studied, while it increased in 79 countries — mostly in fast-developing areas in Asia, Africa and South America. Only 16 nations — including Syria, whose cities have been devastated by a brutal civil war — saw decreases in light. And artificial lighting seems to be growing the fastest in areas that didn't have a lot of it until recently.
But those increases are just part of the story. Christopher Kyba, a scientist at the GFZ German Research Centre for Geosciences and the study's corresponding author, says in an email that the increasing transition to high-efficiency LEDs for outdoor lighting, which have been touted as a way to reduce our dependence upon fossil fuels and slow climate change, may not be saving as much electricity as envisioned.
"Despite great success with reducing energy for lighting in specific projects — e.g., LED transitions in individual cities — cheaper light seems to be leading to increased use," Kyba explains. "That means that LEDs overall aren't reducing total energy consumption for outdoor lighting anywhere near as much as it would appear."
Worse yet, there's growing evidence that our excess illumination is having harmful effects on people. In 2016, the American Medical Association issued a warning that the conversion to high-intensity LED streetlights — which emit a large amount of blue light that increases glare — actually made it more difficult for drivers to see at night. The AMA added that the wavelengths at which the lights operate suppress melatonin, a hormone that helps us to sleep.
"It is estimated that white LED lamps have five times greater impact on circadian sleep rhythms than conventional street lamps," the AMA noted. Research indicates that such disruption may be a significant factor in obesity and other ailments.
And it's not just humans who are being affected.
Nocturnal Species Need Darkness
"Many terrestrial species are nocturnal, and electric lighting, especially dusk to dawn lighting, represents a complete disruption to the physical environment of these species," Dan Duriscoe, a retired physical scientist who worked at the National Park Service's Natural Sounds and Night Skies Division, explains in an email. "Imagine the daytime darkened artificially by a factor of 10, every day. What kind of impact would that have on diurnal species such as humans?"
An October 2017 study in Proceedings of the National Academy of Sciences, for example, found that powerful beams of light from the National September 11 Museum and Memorial altered the flight paths and speed of 1.1 million migrating birds over a seven-day period alone, with simulations revealing "a high probability of disorientation" and other effects. The behavioral problems disappeared when the lights were turned off.
And in Florida, light pollution along beaches is disrupting the hatchling behavior of sea turtles, causing thousands of young animals to die each year, according to the Florida Fish and Wildlife Conservation Commission. (For more information on the environmental effects, check out the HowStuffWorks article How Light Pollution Works.)
How Much Artificial Light Do We Need?
But perhaps the most glaring thing about light pollution is that much of it results from wasteful illumination that isn't really necessary, according to Kyba, who estimates that it could be reduced by a factor of five to 10. "I think we should be asking as taxpayers, why are we paying for lights that shine uselessly into people's windows and disturb their sleep?"
Chris Elvidge, a scientist with the National Oceanic and Atmospheric Administration's Earth Observation Group and a co-author of the Science Advances study on the extent of light pollution, says in an email that plenty could be done to reduce the over-illumination, including putting more shielding on lights, decreasing the brightness of outdoor lighting and using motion detectors to turn on lights only when activity nearby is detected.
An Italian light pollution researcher also thinks there's a possibility that the rise of self-driving vehicles — which could communicate wirelessly with infrastructure and other vehicles to navigate the streets — may reduce the need for brightly illuminated streets.
"I hopefully see a future when lights in cities are dim but sufficient for the pedestrian and bikers," Fabio Falchi, a researcher at Italy's Light Pollution Science and Technology Institute, explains in an email. On the other hand, if humans continue shining more and more light on the darkness, he warns that "we'll completely destroy the night."