I recall a small scene (near the end likely) of a group of young people (kids to 20s/30s) that are living in a bunker. They are questioning and yet waiting for the sun to rise.
The planet has been in darkness for so long that the idea of a sunrise is skeptical. But it rises and everyone welcomes it with awe and surprise.
I know this is at least a 70s film if not older, because it was a late night movie that I only saw the end of because I woke up before it ended. I saw it between '78-82, which is why I give it a 70s to possibly 60s timeframe.
The feeling that I recall was that darkness lasted lifetimes or at least decades and was why a sunrise was not believed.