The darkness of night and the light of day are much more than changes that occur when the sun either sets or rises.
Conceptually, Darkness and Light manifest in many different aspects of our lives. We have good days and dark days.
We have times when everything seems to be going our way; when whatever we do works out, and whatever happens to us is right. When this happens, the Day never seems long enough.
But we also have times when everything goes the other way; when whatever we do goes wrong, and whatever happens to us is trouble. Then, the Night never seems to end.
In this, we are experiencing the process of Creation – and our own creation – over and over again.
Kramer, Chaim. Crossing the Narrow Bridge