The point in a conversation at which a particularly dense person finally comprehends something: "I asked Debbie and Rick if I could come along, too, and they were all, like 'We kinda got plans,' and stuff. Then I was all, 'Light dawns over Marblehead! Hel-LO!' They wanna be alone together!" At least, that's what Laura Mitchell says. Kathy Palmacci says the expression is actually "light dawns ON Mahblehead:" "I've lived in Somerville my entire life, and we've always said that," she says.
Possibly the most incongruous use of the phrase, eva, was in the movie "Cocktail," when a City College of New York professor yells it at Tom Cruise.