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

Allan poses this question: "How long would it take for the last artificial light source to go out if all humans somehow just vanished from the face of the Earth?" Let's start with the obvious: most lights wouldn't last very long because the major power grids would go down relatively quickly without people. However, our refrigerators, air conditioners, and lava lamps would still be running fossil fuel plants, which provide the vast majority of the world's electricity. These plants require a steady supply of fuel, and their supply chains do involve human activity. As a result, other power sources would be burdened with the additional load.

Such a scenario is challenging to manage, even with human assistance, and the outcome would be a swift succession of domino failures that shut down all of the main power grids. Naturally, nuclear reactors don't need a constant supply of fuel; in fact, one reactor operator I spoke with stated that if their core entered low power mode, it could run almost endlessly. A cube of uranium contains roughly 6 million times the stored energy of a cube of coal of the same size. Nevertheless, even with plenty of fuel, most nuclear reactors wouldn't run for very long because the core would automatically shut down as soon as something went wrong.

It would quickly shut down if it did that. Many isolated communities, such as those on distant islands, rely on diesel generators for their electricity. These generators can run until their fuel tanks run out, which in most cases can be anywhere from days to months. Off-grid generating stations that don't need a human provided fuel supply would be in better shape. However, plenty of light comes from sources not tied to the major power grids. Let's look at a few of those and when each one might turn off. According to the, geothermal plants can operate without human intervention for a considerable amount of time.

The Fangi Island Geothermal Planet Iceland is scheduled for maintenance every six months. Without the assistance of humans, the operators must perform maintenance procedures such as changing the gearbox oil and regreasing all electric motors and couplings. Lights that run on wind power would last a little longer because wind turbines are made to require less maintenance because there are many of them and they are difficult to climb. The GSE wind turbine in Denmark was installed in the late 1950s, and it produced electricity for 11 years without maintenance. Modern turbines are usually rated to run for three years without servicing and there are no maintenance requirements.

An operator at the Hoover Dam once stated that if everyone left, the facility would continue to run on autopilot for several years, though if the power grid is down all that electricity would have nowhere to go in the end the dam would probably succumb to clogged intakes or the same kind of mechanical failure that hit the geothermal plants. The status LED in it somewhere eventually would cause the majority of the wind turbines to be stopped by the same thing that would destroy the geothermal plants their gear boxes would seize up generators that convert falling water into electricity will also keep working

solar power is likely the most promising option; there are many off-grid solar-powered buildings, weather stations, and other remote infrastructure around the world; emergency call boxes are frequently found along the side of the road in remote locations where they're hard to surfice. Last longer than others, but even batteries advertisers having long shelf lives typically only hold their charge for a decade or two