Light pollution is real, and the source is your holiday light display. According to NASA, data gathered by NOAA/NASA Suomi National Polar-orbiting Partnership (Suomi NPP) satellite reveals that nighttime light intensity over cities in the United States increases during Christmas and New Year’s—by as much as 20 to 50 percent! 

The Sumoi NPP uses an instrument called the Visual Infrared Imaging Radiometer Suite (VIRS) to observe the dark side of the plant and detect light emanating from cities across the globe. Scientists at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, developed an algorithm for filtering moonlight, clouds, and airborne particles out of the images. 

So, the results! A team led by Miguel Román, a research physicist scientist at NASA Goddard and member of the Suomi NPP Land Discipline Team, found that lights in the United States started to shine brighter on Black Friday and continued through New Year’s Day. The greatest increase in light intensity—30 to 50 percent—is found in suburban areas (where light-up Santas and snowflake house lights are more plentiful) rather than cities, where lights brightened by 20 to 30 percent. 

“What we were seeing is this shift in location of activity, where people are staying in their homes and their celebrating, or they’re traveling to the rural areas and celebrating, and they’re turning on the lights," Román says. "Whereas in the urban centers, people are turning off the lights because they’re going out for the holidays.”

"It's a near ubiquitous signal,” Román says. “Despite being ethnically and religiously diverse, we found that the U.S. experiences a holiday increase that is present across most urban communities.”

Since snow reflects so much light, therefore disrupting the images’ accuracy, NASA only examined snow-free cities, focusing on the West Coast, cities South of Washington D.C., and Puerto Rico. Even without taking Northern cities into account, the trend is clear.

As Román says, “These lighting patterns are tracking a national shared tradition.”