If all humans died, when would the last light go out?

We've spent more than 100 years illuminating the darkness with electricity. Over time, those electrical systems got bigger and more automatic. Randall Munroe's What If series received the question, "If all humans died, when would the last light go out?" To answer the question, Munroe completely ignored the theoretical scenario of our demise and got straight to the lights. It comes down to the power source, since some are more automatic than others. Those relying on fuel delivery will go out first, but some kind of artificial lights will last for way longer than you might think. And then we must consider what we mean by "artificial lights." Enriched nuclear fuel gives off a light even though we don't use that light for everyday (or every night) activities. Commenters brought up even more lights, like the Voyager space probes, which have manmade lights, although they are not on earth. There's also the burning coal seams like in Centralia, Pennsylvania, which are natural, but were ignited by human activity. They can burn for thousands of years, but whether you term them manmade lights is a matter of semantics.