What I noticed about that window, the neon lights flashing, was that the fire escape was no longer visible. You know, the one Chad climbed thru to come see Abby.
In the movie BIG, with Tom Hanks, when he is BIG suddenly overnight, but still only 12 or 13, he had taken money from his dad's pants pocket or something, before he left the house so his parents would not see him. And that night he rented a room in a rather sleazy place, is in there, sitting on the bed in the dark, all sad and lonely, despondent, and those neon lights are flashing on and off like that, in the window.
That is what they are for, in my opinion. Ben is despondent, sad, worried, unhappy, feeling alone. At least, that is the feeling I think they are going for. And when he snaps, the lights inside the apt. are never turned on. Which they were when Ben first comes back, and Will is there, throwing the crumpled paper balls into the waste basket.