You are standing outside the first floor entrance to a building.

Next to you is a bank of 3 light switches. One of the switches controls a light bulb in a stock room on the second floor. The other two switches don’t control anything. The only way you can check the light on the second floor stock room is to physically walk up the stairs, open the door to the stock room, and check the light. You can do anything to the switches that you want before you walk up the stairs, however you are allowed only one trip up the stairs to check the light.

Assuming the light is off to start with, how do you find out which light switch controls the light?