Over-the-top lighting displays have become as much a part of the holidays as Santa Claus -- many so bright they can be seen from space.
NASA scientists, analyzing data from the NOAA/NASA Suomi National Polar-orbiting Partnership (Suomi NPP) satellite, have found that nighttime lights around major cities shine 20 to 50 percent brighter in many parts of the United States during Christmas and New Year's than the rest of the year.
"We all thought the nighttime lights were stable," said Miguel Román, a research physical scientist at NASA Goddard and member of the Suomi NPP Land Discipline Team, who co-led this research.
"What is happening during the holidays is that our patterns are changing," he told the American Geophysical Union meeting in San Francisco. "We are becoming this weird species. We are eating more turkey and we are going out to Macy's and buying stuff. We are changing our patterns of behavior."
Román said his research found that the holidays have also prompted a shift in energy use from the cities to the suburbs, where neighbors -- their houses covered in lights with towering Santa or other Christmas characters out front -- often compete to see who can put on the most ostentatious displays.
The biggest, like Mission Inn in Riverside, California, may feature millions of lights and as many as 400 animatronic characters, according to The Associated Press.
"What's really interesting about the United States is that pattern and behavior is effecting location and demand for energy services," Román said. "What does that mean? If you look at city of Atlanta ... it's creating this donut hole where you have this lighting output increase in predominantly residential regions. People are leaving work for the holiday and turning on the lights. People are demanding more energy services."
To analyze all these holiday lights, Román used an advanced algorithm developed at NASA'S Goddard Space Flight Center, which filters out moonlight, clouds and airborne particles. That allows researchers to isolate city lights on a daily basis and track when and how brightly people light up the night sky.
He and his colleagues examined the light output in 2012 and 2013 in 70 U.S. cities, as a first step in determining patterns in urban energy use, a key factor in greenhouse gas emissions. In most suburbs and outskirts of major cities, light intensity increased by 30 to 50 percent during the holiday season. Lights in the central urban areas did not increase as much as in the suburbs, but still brightened by 20 to 30 percent.
Because snow reflects so much light, the researchers could only analyze snow-free cities. That is why countrywide images show huge swaths of darkness across the Northeast. They focused on the U.S. West Coast from San Francisco and Los Angeles, and cities south of a rough imaginary line from St. Louis to Washington, D.C.
"Overall, we see less light increases in the dense urban centers, compared to the suburbs and small towns where you have more yard space and single-family homes," said Eleanor Stokes, a NASA Jenkins Graduate Fellow and Ph.D. candidate at Yale University's School of Forestry and Environmental Studies, New Haven, Connecticut, who co-led the study with Román.
The researchers found this holiday trend also was global, with similar lighting trends seen during the Muslim holy month of Ramadan when families gather at night to break their fast. In some Middle Eastern cities, nighttime lights shine more than 50 percent brighter during Ramadan -- up to 100 percent brighter in parts of Saudi Arabia -- compared to the rest of the year.