How to calculate day and night in the dark?

Day and night are randomly generated. Whenever you enter the game, it is randomly generated. No chance, it's purely random, and so is the weather. Like the grassland in the first act, sometimes it rains and sometimes it doesn't. The plateau in the fifth act is the same, sometimes it is snowing, sometimes it is not.

You can see around clearly during the day, but at night you can only rely on the lighting range provided by your equipment.