easy Brainteasers

Light Bulb Switch

A release-checked easy problem for training Brainteasers.

Question

There is a lightbulb in a room, and $4$ switches outside of the room, just around the corner. None of the switches are on, and only one of them controls the lightbulb. You may flip any combination of switches on or off any number of times, and you may touch and look at the lightbulbs upon entering the room. How many times do you need to enter the room to determine which switch controls the light?

Practice focus

This Brainteasers problem is tagged Brainteasers. State the random variables and conditioning information explicitly, then check the result against boundary cases before opening hints or a solution.