[Credit: NASA's Goddard Space Flight Center]

The holidays this time of year always seems to make night a little brighter. Now NASA and the NOAA have released evidence that during December, cities especially in the United States shine up to a whopping 50 percent brighter - a change best seen from space.

The relatively new satellite Suomi NPP, a joint NASA/NOAA mission, carries an instrument called the Visible Infrared Imaging Radiometer Suite (VIIRS) that is specifically designed for measuring the glow of lights on the dark side of Earth. The result of these observations was a series of maps called "Earth a Night," which helped illustrate how composites of monthly average light use can help us better understand cultural trends and electricity use across the globe.

Predictably, holidays tend to be one of the largest drivers of light use, whether it be stunning Christmas displays lighting up a street, or a "festival of lights," complete with floating lanterns on a summer evening.

A new analysis of holiday lights in particular made use of an advanced algorithm developed by NASA's Goddard Space Flight Center team. The algorithm filters out moonlight, clouds, and reflective airborne particles in order to isolate man-made light output across the globe on a day-to-day basis.

In the United States

Predictably, the researchers found that the United States sees the start of its brightest season just after Thanksgiving, growing progressively brighter into New Year's Day.

"It's a near ubiquitous signal. Despite being ethnically and religiously diverse, we found that the US experiences a holiday increase that is present across most urban communities," said Miguel Román, a member of the Suomi NPP Land Discipline Team, who co-led the research. "These lighting patterns are tracking a national shared tradition." (Scroll to read on...)

He added that in most suburbs and outskirts of major cities, light intensity increased by 30 to 50 percent. Lights in the central urban areas did not increase as much as in the suburbs, but still brightened by 20 to 30 percent.

This has a lot to do with the simple fact that most urban areas are already well lit year-round. Suburbs, on the other hand, make a stunning effort to light their otherwise dark lawns and houses this time of year, resulting in a huge spike in light.

This trend is noticeable in other countries with holidays that focus on lighting the night as well, such as the Chinese New Year.

Mystery In the Middle East

However, not every light spike was associated with a "light the night" holiday. During Ramadan, for instance, several cities in the Middle East like Cairo, Riyadh, and Jeddah saw a sudden surge in night light by nearly 60 to 100 percent, despite no known tradition of holiday decoration, fireworks, or lantern release. In fact, Ramadan is a holiday that centers around fasting, so what was going on there?

The researchers suspect that in large and bustling cities like Cairo, Muslims spend more of what could have been mealtime socializing and enjoying night life, which means shops stay open later, and more people, and more lights, are about. (Scroll to read on...)

However, this wasn't apparent in all Muslim cities.

"Even within majority Muslim populations, there are a lot of variations," said Eleanor Stokes, who co-led the study with Román. "What we've seen is that these lighting patterns track cultural variation within the Middle East."

However, as the time came for the Eid al-Fitr celebration that marks of the end of Ramadan, light use soared across all study groups, as all the neighborhoods appeared to join in the festivities.

This told the researchers that shared cultural customs will sometimes drive light usage across entire regions - a pattern that utility companies even in places like the Middle East must account for.

"What's really difficult to do is to try and track people's activity patterns and to understand how this shapes the demand for energy services," Román explained. "We can now see pieces of these patterns from space - when, where and how often we turn on the lights."

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