Photos of Calgary, Alberta, taken from the International Space Station on Dec. 23, 2010 (left) and Nov. 27, 2015. A change from orange sodium lamps to white LED ones can be seen in several neighborhoods. Photos: Earth Science and Remote Sensing Unit / NASA Johnson Space Center
Despite a global move to more efficient lighting and various efforts to lessen the impact of lighting on humans and the environment, scientists say both the brightness and the area of Earth lit at night continue to increase by 2.2% each year on average, per a study published in Science Advances this week. That's likely because people are using more lighting now that it is cheaper and more efficient.
Why this matters: Light pollution has been shown to negatively impact human health, environment and ecosystems, and astronomical research. While not surprised, the researchers say they are "very disappointed" with the results. They'd hoped as efficient LED-lighting technology became more available the amount of light emitted from artificial sources would decrease.
What they did: The international team attached a sensor (called VIIRS Day/Night Band) to a satellite to measure the change in light emissions from October 2012 to October 2016 by looking at the surface area of Earth lit above a certain threshold and by examining how the level of brightness changed in areas that already had light. The satellite – which will continue to run for decades – circles the earth between the two poles a little more than 14 times per day.
To minimize the effect of snow, clouds and moonlight reflecting off water, the researchers compared data from the month of October to yearly data and used data free from the effects of clouds and moonlight and averaged them into monthly composites, according to Kimberly Baugh, from the University of Colorado's Cooperative Institute for Research in Environmental Sciences.
What they found: Both the surface area and the level of brightness increased at a rate of roughly 2.2% per year. However, German Research Center for Geoscience's Christopher Kyba says there are two caveats to their study:
1. There are strong regional differences. The rate of growth in developing countries is much faster than developed areas, with the increase in light pollution corresponding to the growth in gross domestic product.
- The world's brightest nations, like the U.S. and Spain, remained stable but most nations in South America, Africa and Asia grew in brightness.
- Decreases in brightness were see in a few regions experiencing warfare, particularly Yemen and Syria.
2. The sensor doesn't measure "blue light" prevalent in LED white lights and seen with human eyes, so "in fact, that true increase that a human being would perceive is actually larger than what we report here," Kyba said. Blue light has been shown to have the most negative impact on humans and the environment.
- Travis Longcore, an urban ecologist at the University of Southern California who was not part of this study, says the research shows the "unsustainable" rate of global light pollution from the LED revolution but one limitation is the absence of data about blue light. He says others may fill that gap and that tiny satellites called CubeSats could be used to monitor the blue-light level of particular cities.
Impact of light pollution: Franz Hölker, an ecologist at the Leibniz-Institute of Freshwater Ecology and Inland Fisheries, says "artificial light is an environmental pollutant with ecological and evolutionary implications for many organisms from bacteria to mammals, including us humans." Light pollution has been shown to threaten 30% of nocturnal vertebrates and 60% of nocturnal invertebrates plus it affects plants and microorganisms. It can also impact critical ecosystem functions.
The American Medical Association last year said that white LED lights are increasingly suspected of impacting humans, estimating they have "five times greater impact on circadian sleep rhythms than conventional street lamps."
What can be done now:
- The first cost-effective LEDs for outdoor lighting were blue LEDs coated with phosphor, but these can be replaced with newer versions that have less blue and more red or green, like the PC Amber LED lights or filtered LED lights called FLED.
- People can control both the direction and the intensity of current LED lights. Controls systems can be added to dim lights by time or by motion rather than keeping lights on all of the time.
Background: Longcore said in the case of the U.S. it was "where the money got ahead of the technology." He said a lot of municipal street lights were replaced due to the Recovery Act, which gave a substantial amount of money to subsidize the transition to blue LEDs. "The DOE just didn't listen to scientists who wanted a different standard," he said. "DOE was really only interested in energy savings."