EMILY: So are you living together?
LORELAI: Mom, get out the interrogation lamp, why don’t you.
Lorelai refers to the trope in 1950s police and detective TV shows/movies where the police or detective shines a bright lamp into a suspect’s face to make him confess. It was parodied in Get Smart, earlier mentioned, and these days is usually used humorously, if at all.
The Annotated Gilmore Girls 