Night exterior
Simulator
Night is read from the ratio between a cold edge and a warm source, not from how dark the picture is.
Dark enough, visible enough
A night exterior has to be dark enough to read as night and bright enough that an audience can follow a face. The answer is never a level, it is the ratio between a cold edge, a warm source and almost nothing else.
Moonlight is a convention
Real moonlight is roughly the colour of sunlight and far too dim to shoot. The cold blue backlight everyone calls moonlight is a language the audience learned from films, and it works because they learned it.
Backlight first
The single most useful unit on a night exterior is behind the subject, not in front. An edge on the shoulders and hair separates them from the dark and tells you the shape of the scene.
Motivate the warm
A practical, a window, a fire, a street lamp. One warm source in or near frame gives the eye a reason for the light and a colour to contrast the cold against. Without it, blue everywhere just looks like a mistake.
Ambient is the trap
A little lifts the blacks enough to see into; too much and the frame becomes an evenly lit grey scene with a blue cast. The moment you can see everything, it has stopped being night.
Eyes need something
At night levels, eye sockets go black and the performance disappears. A tiny unit near the lens, far too dim to light anything else, puts the catchlight back.
Expose for the face, not the frame
Meter the face and let everything else fall where it falls. A night exterior is mostly underexposed by design; the one thing that must not be is the person you are following.