Hello!
So dark that it is difficult to see.
In the middle of the night, it can become so dark that it is impossible to see what is in front of you. Therefore, when something is black as night, that thing is so dark that it would be challenging to see if surrounded by it.
One may describe a setting as being black as night if he or she is having difficulty viewing his or her surroundings. Sometimes, people may also describe an item as being black as night to show how dark that thing is. It is another way of describing it as shadowy or black.
