In a theater or auditorium, the ambient-light things. Sometimes they're fluorescent
-- and take a while to get going; in this case, they just go off. Otherwise, the stage manager
will (at the start of a play) call out "House to half, *pause* house out" -- this dims the house lights, and then turns them out, signalling the audience
that the show's gonna start.
They also come up at intermission
and at the end of the play
, signalling everyone that it is, in fact, over.This writeup is a part of the (as-of-yet-nonexistant) theater metanode.