Most of this episode was shot in downtown Oregon City.
When Mabel lists her duties in the town, she ends with "Chancellor of the Exchequer." This is a direct reference to Gilbert and Sullivan's "The Mikado" and the character of Poo-Bah, whose comedy comes from the large number of positions he holds in the town of Titipu, one of which is Chancellor of the Exchequer.
When discussing how to bring the trapped townspeople back, Cassandra says that all the gas lamps need to be cleaned thoroughly. This could be a reference to Nikola Tesla's undiagnosed obsessive-compulsive disorder, as he refused to touch anything dirty and would have cleaned all his inventions vigorously.
Cassandra sends a message to the others in the form of a Morse code 'L' for Librarians, calling back to the moment in "And the Horns of a Dilemma" when Baird did the same thing.
The episode title is "the City of Light". " The City of Lights" is the nickname of Paris, France