Montreal Gazette - Rusty brain? Oil it with fish, blueberry juice

(Chemistry professor Joe Schwarcz's column in The Gazette): Now think about this: A room has three reading lamps with each one connected to a separate switch, all switches being outside the room. Your task is to identify which switch turns on which bulb. You can turn the switches off and on as many times as you like, and leave them in any position you like, but you can enter the room only once. How would you solve the problem?