Americans love Christmas lights. So much so that many large US cities are 20 to 50 percent brighter at night during the holiday season than they are during the rest of the year.
Researchers affiliated with NASA took a look at holiday lighting with the Suomi NPP satellite and generated these maps. The green bits are areas where the urban lighting is brighter between Thanksgiving and New Year's than it is during the rest of the year:
Holiday lights on the US East Coast
The researchers, Miguel Román and Eleanor Stokes, looked at 70 major cities using an algorithm to filter out moonlight, clouds, and pollution (they had to exclude any cities with lots of snow, because snow reflects so much light that it skewed the data). This helped them focus just on changes in lighting during the holidays. And they found a striking change.
Many cities brightened by about 20 to 30 percent during the holidays. In suburban areas, where displays are often even bigger and brighter (due to bigger houses and lawns), light intensity went up by 30 to 50 percent.
Holiday lights in the San Francisco Bay Area
Apart from generating neat maps, the research could be useful for figuring out how much electricity the United States actually uses for holiday lighting.
Currently, it's a bit hard to figure out how much electricity all that holiday lighting uses. Stringing up 10 strands of efficient LED lights on a house and leaving them on for 12 hours a day all through December would use around 20 kWh of electricity, which would only cost an extra $2 to $3. But, of course, some houses have much bigger displays — moving reindeer, light-up snowmen, the works.
Nighttime lighting during Ramadan in the Middle East
The researchers also took a look at how the Middle East lit up during Ramadan. By analyzing data over three years between 2012 and 2014, they found a noticeable increase in nighttime lighting during the holidays. These aren't necessarily holiday lights per se — it's because Muslims are fasting during the day and pushing meals, family gatherings, and other activities into the nighttime hours.
But there were big variations here: In Saudi Arabian cities like Riyadh and Jeddah, lighting increased by about 60 to 100 percent through the month of Ramadan. But Turkish cities didn't do as much to celebrate. And Syria and Iraq saw little increase in lighting, NASA noted, likely "due to unstable electrical grids or conflict in the region."