Every theatre leaves a light burning on the empty stage. Ask why and you will get two answers, usually from the same person and usually in the same breath.
The practical one
A dark stage is a hole. The thrust is 0.9 m above the stalls floor, the vomitories are unlit, and the get-out happens at midnight by people who have been working since six. Somebody walks into the void, once, and after that the building has a ghost light.
The other one
The other answer is that it is for the ghosts — so they can put on their own plays and leave the living alone. Nobody in this building believes that and nobody in this building would ever be the one to switch it off.
Ours
The lamp on our stand is a 40 W pearl on a wire cage, on a stand welded in the workshop in 1974 out of what is almost certainly scaffold tube. Ellis Greaves keeps one spare bulb for it in a drawer in the electrics store and has never had to use it, because it burns at a fraction of its rating and never gets switched off, which is what filaments actually want.