Five years of advanced satellite imagery show that there is more artificial light at night all over the world, and that night light becomes brighter. The growth rate is approximately two percent each year, both in the number of illuminated areas and in the glow of light.
An international team of scientists reported on Wednesday the results of a historical study of global light pollution and the increase of outdoor light-emitting diode (LED) light. The study, published today in the journal Science Advances, detects both light pollution and energy consumption by constantly illuminating a large part of the planet. The findings also challenge the badumption that increases in the energy efficiency of outdoor lighting technologies necessarily lead to a global decrease in overall energy consumption.
The team, led by Dr. Christopher Kyba of the GFZ German Research Center for Geosciences in Potsdam, Germany, badyzed five years of images from the Suomi National Polar-orbiting Partnership satellite, operated jointly by the National Aeronautics and Space Administration of the United States and the National Oceanic and Atmospheric Administration. The data shows gains of two percent per year in both the amount of Earth's surface that is artificially lit at night and the amount of light emitted by outdoor lighting. Increases were seen almost everywhere on the team, with some of the biggest gains in regions that previously did not light up.
"Light is growing faster in places that did not have much light to start with," Kyba said. "That means that the highest rates of increase are occurring in places that until now have not been very affected by light pollution."
The results reported today confirm suggestions in previous investigations based on data obtained with measurements of the meteorological satellite of the US Department of Defense to the 1970s However, the better sensitivity of the Suomi cameras to illuminate the night side of the Earth and the significantly improved ground resolution led to more robust conclusions about the changing illumination of the world at night.
The study is one of the first to examine the effects, seen from space, of the ongoing global transition to LED lighting. Kyba's team discovered that the energy-saving effects of LED lighting in national energy budgets are lower than expected because of the increased efficiency of LEDs compared to older lamps.
LED lighting requires much less electricity to produce the same amount of light as older lighting technologies. Advocates of LED lighting have argued that the high energy efficiency of LEDs would help to decelerate global energy demand, since outdoor lighting represents a significant fraction of the typical world city night-time energy budget.
The team tested this idea by comparing changes in night lighting seen from Earth orbit with changes in countries' gross domestic product, or GDP, a measure of their overall economic output, over the same period of time . They concluded that the financial savings from the improved energy efficiency of outdoor lighting seem to be invested in the deployment of more lights. As a consequence, the expected large reductions in overall energy consumption for outdoor lighting have not been realized.
Kyba expects the global upward trend in the use of outdoor lighting to continue, generating a series of negative environmental consequences. "There is a potential for the revolution of solid state lighting to save energy and reduce light pollution," he added, "but only if we do not spend the savings in new light."
IDA has campaigned for the past 30 years to draw attention to the known and suspected risks badociated with the use of artificial light at night. The IDA Executive Director, J. Scott Feierabend, noted the repercussions that include damage to wildlife, threats to human well-being and potentially compromised public safety. IDA drew the public's attention to the concerns related to the strong blue light emissions from LED lighting since 2010.
"Today's announcement validates the message that IDA has communicated for years," explained Feierabend. "We hope the results will sound the alarm about the many unintended consequences of the uncontrolled use of artificial light at night."
The VIIRS instrument used in this study is relatively insensitive to blue light. The white LED light is rich in blue colors, so it partially escapes detection by VIIRS. That can lead to an underestimation of the problem of light pollution.
Blue light is also more efficient at scattering in Earth's atmosphere than light from other colors, so Suomi can not see accurately the brightness of Earth's cities. The conversion of exterior lighting from older technologies to white LEDs can make cities seemingly darker over time, but Kyba cautions that this is not necessarily true.
"Many large cities that we observed showed a decrease in brightness in the center of the city, but increase in peripheral areas," observed Kyba. "These declines can often be attributed directly to the replacement of old lamps with LEDs." Kyba hopes that future Earth observation satellite missions will overcome this deficiency and lead to a better characterization of how our world uses artificial light at night.