The person turning off the lights finishes a day that others have already left.

Every shared day has a tail that most people never see. The room empties, the noise stops, and one person is still there doing the last twenty minutes: locking, checking, switching off, putting right what got left. Their day ends later than everyone else’s by definition, and because nobody is present for it, it rarely appears in anyone’s account of who did what. Closing is work, even though it looks like absence.

Find out who does it where you are, and thank them specifically rather than generally. If it is always the same person, ask whether the rota could be shared, since staying last should not be a permanent appointment.