It is unlikely, though, that an adult could die directly and exclusively from prolonged darkness. Most likely a person would become ill and die from a range of chronic diseases caused by lack of sunshine, such as diabetes, high blood pressure, and tuberculosis. So, yes, I would say that humans need sunlight to survive.

Can you die if you don't get sunlight?

But it's very unlikely an adult could die directly and exclusively from prolonged darkness. The most plausible deadly scenario is that a lack of sunlight could prevent the body from producing vitamin D, which, in turn, would inhibit calcium absorption.

How long would humans survive without sunlight?

A relatively simple calculation would show that the Earth's surface temperature would drop by a factor of two about every two months if the Sun were shut off. The current mean temperature of the Earth's surface is about 300 Kelvin (K). This means in two months the temperature would drop to 150K, and 75K in four months.