Flare

Every other light on this list sits in your hand and tells everyone where you are. A flare lands somewhere else. You throw it into a dark corridor, a tunnel or the yard outside your walls, and the light sits there while you stay in the shadow behind it.

Night defence is where it pays. You hear footsteps by your wall in the middle of the night, and leaning out with a flashlight would put a beam right on your head. Lob a flare out of a window instead, peek, then decide whether to shoot or sit tight. The same trick works before you push into a room nobody has cleared yet.

It is not free, though. Each one takes gun powder and metal fragments at a Level 1 workbench, and early in a wipe that powder could have been ammo. Keep a few for the nights that matter.