From the comments by the fallers that the stairs need to be better lit, I am guessing that a lot of the fallers are going up in the dark. Someone at BWW says that they were there when John Simon got injured, and he got up in the dark in the middle of the show.
I think the theater could make an announcement that if you need to get up while the lights are down, don’t forget there are stairs, but they can’t shine more light on the stairs during the performance without that being a distraction to those sitting nearby.