This is a mod for Fallout 4 that will make the nights in the Commonwealth darker. Now you can know when it is dark without having to check the time on your pip-boy. This is a great way to be more aware of your surroundings.

There are seven levels of darkness to choose from.

It provides an optional set of plugins which improves the ability of NPCs to detect you in low light conditions. There is a version "calibrated" to each of the seven levels of darkness but you may choose any one of them if you are not happy with the default.

It basically allows NPCs to become alert (enter caution) at about the same distance as in vanilla.