Imagine the Earth at night—the vast and curving darkness, splotched with rivulets of light. It is a gorgeous sight, and a familiar one. Today, this image often plays as a beautiful cliché, a pre-metabolized testament to human invention and connectedness, as likely to appear in Koyannisqatsi as in a Kia commercial. For economists, though, this spectacle is more than a symbol: It is a powerful data set.
For the last few decades, and almost since astronauts first captured images of the nocturnal Earth, researchers have recognized that “night lights” data indirectly indexes the wealth of people producing the light. This econometric power seems to work across the planet: Not only do cities glow brighter than farmland, but American cities outshine Indian cities; and as a country’s GDP increases, so does its nighttime luminosity. Two years ago, a Stanford professor even used night lights data to show that North Korean leaders were passing the costs of international economic sanctions down to farmers and villagers. As foreign governments imposed sanctions, Pyongyang became brighter and light from the hinterlands waned.
Night lights, therefore, appear to be an incredible resource. So much so that in countries with poor economic statistics, they can serve as a proxy for a regional wealth survey—except no one has to go house to house, running through a questionnaire. Yet research has also shown this not-a-survey will remain inexact: To a satellite at night, a few well-lit mansions and a dense but poorly lit shantytown can look nearly the same.