Lighting for Night Exteriors

Frame from Morgan's Fall Night-for-night shooting involves simulating a dark scene by using low key lighting, not by decreasing the intensity of the key light.
The key light, based on an apparent source such as moonlight or a streetlight, may actually be a back light. Fill light may be a different colour, reflecting the diversity of apparent sources in a night scene.

Remember that a blue gel reduces the intensity of a light by two stops, so the size of the area you can light is much smaller. For a large scene, use pools of light from more than one source.

Frame enlargement from Morgan's Fall.

Exercise caution when using extension cords at night. Use a Ground Fault protector in wet conditions.

Frame from Memento Day-for-night can be effective for a scene which does not include light sources in the frame (such as streetlights, flashlights or car headlights).
Steps to shooting day-for-night:

Shoot on a sunny day.
Underexpose about two stops.
White balance on yellow, to create a blue tint.
Use the sun as a backlight to simulate moonlight.
Avoid showing the sky.

Frame enlargement from Memento.

Frame from Somebody Cares Dusk-for-night is shot during the brief period when light sources such as streetlights and car headlights are on, but there is still enough blue fill light from the sky to provide some exposure. This is often ideal for establishing shots -- closer shots can then be done night-for-night (see above).
Frame enlargement from Somebody Cares.