We live in a world of artificial lights. They have become so ubiquitous that we can hardly fathom life without them. Some live every day with hardly any exposure to the sun at all. They do not need it. And all is well, so long as the lights stay on.

But one day, the electricity will be cut, and it will not come back on. And then we will remember the horror of the dark, and why we always needed the sun.