. . . and to rule during the day and during the night, and to make a distinction between light and darkness; and God saw that it was good. And there was evening and there was morning, the fourth day. — Genesis 1:18-19
Day means goodness and night evil, so in common parlance the good things people do are associated with the day, while the bad things they do are called deeds of the night.
Light means truth and darkness falsity, as the Lord says:
People loved darkness more than light. One who does the truth comes to the light. (John 3:19–21)
from Secrets of Heaven, Volume 1, Section 38