One bulb and 3 switches puzzle - Logical Interview Puzzle

Interview puzzles are critical-thinking and logical reasoning problems that make candidates use their problem-solving and analytical skills to find a solution. Interviewers prefer to ask these puzzles because it helps them understand your thought process, and your ability to solve complex problems using strategies, and high-order thinking. Usually, candidates applying for software development, data science, or engineering roles may encounter such puzzles. 

Here is an Interview puzzle that is frequently asked in Job Interviews.

Puzzle Details

There are 3 switches in a room, and one of them is assigned to a bulb in the next room. You can’t see whether the bulb is on or off until you leave the room. Find the minimum number of times you have to go into the room to identify which switch corresponds to the bulb in the other room.


This question has been asked several times during different analytics-based interviews. 

The person has to initially turn on the first switch and keep it on for 2-3 minutes. Next, turn off the first switch and turn on the second one. Rush to the other room as soon as you turn on the second switch.

If the bulb is glowing, the second switch corresponds to the light bulb; however, if the bulb doesn’t glow, but touching it feels warm, the first switch is the one that turns the bulb on. If it’s neither lit nor warm, then the third switch is the desired switch. So, a person must go only once to the other room to find out the accurate switch.

Watch The Below Video For a Detailed Explanation

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