3 Switches And 1 Light Bulb

You are standing outside a closed door. On the other side of the door is a room that has a light bulbs in it. The room is completely sealed off from the outside. It has no windows and nothing can get in or out except through the door. On the outside of the room there are three light switches that controlling light bulb on the other side of the door.

Your assignment is to determine which light switch controls that light bulb. You are allowed to enter the room only once and once you come out, you must be able to state with 100% certainty which light switch controls which light bulb.

Which controls bulb?

What should you do? 

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