Ciao Telecom interview questions

The technical question was: Suppose you are outside of a building with 3 switches outside and 3 lightbulbs inside; each of the switches correspond to a lightbulb, albeit not necessarily in order. There is a window on the outside of the building but it is so tall that it can only reveal to you whether or not the room is being lit (aka, a lightbulb is on). Devise a procedure such that you can determine which switch corresponds to which lightbulb with only one visit into the room.