Isaac Fellman beat me to some, but not all of it: “But what [Salieri’s] really doing, by railroading [Mozart] into a place of lonely illness, is forcing him to see only Salieri and recognize the million-watt intensity of his fandom. They haven’t invented the lamp yet that could be a good metaphor for Salieri’s fandom. He can only express it in candles, which must be frustrating.”
Amadeus (and this scene in particular) is one of my all-time favorites. This made my day!