We take it for granted that we can see at all times of day...

We take it for granted that we can see at all times of day and night. But there was a time, not all that long ago, in the age before electricity, when night brought total darkness - and with it, a not-so-small amount of terror. We get a sense of this when we go camping or when there's a power outage, and our fear of the darkness is primal.