Three light bulbs in a closed room belong to three switches outside. Switch off and on freely, enter the room once to identify the switch-bulb pairs.
The Puzzle
You have three light switches beside a closed door of a room. Each switch controls a bulb in the closed room that you cannot see into. You can manipulate the switches however you like, but you can enter the other room only once. How can you know which switch controls which bulb?
Recommended time to solve: 10 minutes.
Hint: Remember what happens when a light bulb is switched on.
Solution to The Three Light Switches Puzzle
Stage 1: First breakthrough to find the Often Ignored Unknown. Think Inventive.
Begin thinking simple.
With two switches and two bulbs, you'll switch on any one and ensure that the other switch is off. Enter the room. The bulb glowing has its switch on and the other switch is for the second lamp. Easy. Not a puzzle.
Even from such a simple experiment, you can draw a conclusion you can use later on:
A glowing lamp is connected with the switch in ON position.
But, here is a third switch to complicate things. Use your logical reasoning now:
It won't be possible to crack open this tricky puzzle only by a lamp glowing.
This is when kicks in the natural tendency to think in any which way, randomly, in circles that never can reach the solution.
Think. What is the crucial thing about a lamp that differentiate between a switched ON and switched OFF lamp? Answer is obvious, it is the glow of a lamp. By the property of the GLOW of a lamp you can differentiate between a switched off and switched ON lamp.
Now the situation is getting clearer.
Only the Glow property is not enough here. You need a new additional property of a lamp to solve the puzzle.
What can it be?
This is the first leap into the ignored area of ignored properties of a lamp.
Ever tried to replace a low power lamp which was switched on by a high power bulb? Didn't you first switch off the lamp? Why? Because it would have felt hot. That's why. There you have your ignored, forgotten second property:
When a light bulb, LED or incandescent old type, is switched on for a while and switched off, it still will feel warm on touch.
Stage 2: How to Use the New Property of Warmth of a Just Switched Off Bulb
Start from the end. You are sure now that only one switch should be ON and the connected bulb glowing inside the closed room.
The problem is simpler now: You need to differentiate between two remaining bulb and switch pairs.
How?
Must be by using the new property of warmth of a just switched off bulb.
Solution is now just a step away.
Three Light Switches Puzzle Solved
Path is clear now.
Step 1: Switch ON any of the three. Mark it as A. Keep it ON.
Step 2: Switch ON one of the other two switches. Mark it as B. Keep it ON for a few minutes for the connected bulb inside the closed room to get warm. Switch off this switch. Two switches are now OFF, One ON.
Final step: Enter the room. The lamp glowing belongs to the switch you left ON. Feel each of the other two bulbs. The bulb that feels warm must belong to the switch B, and the remaining bulb to the third switch.
End Note (don't miss reading it)
If you are clever and experienced in solving such out-of-the-box inventive thinking puzzles, you might solve the puzzle in three minute flat.
But I have not assumed anything, started with a no-bias mind. This is Zero based thinking.
If you start solving a problem with biased knowledge, chances are, your assumptions may lead you the wrong way. Instead, if you start with zero based thinking, you would be able to evaluate each piece of new fact and knowledge using your logical reasoning and problem solving techniques with freedom with greater chances of success.
In my work-life, this approach resulted in near 100% assurance in solving tough problems.
Nevertheless, while solving this puzzle, I went forward asking crucial questions and finding answers. This is Question, analysis problem solving technique or QAA technique in short. This is an ability anyone can acquire.
But, I could reach the crucial breakthrough by searching for and finding a new ignored property of a modest light bulb I forgot to consider at first—its warmth when switched on. This is the crux of the inventive Property Change Analysis Technique—searching for an ignored property of the most important element (the bulb here), that can be changed for inventive solution.
All the while, I have used logical reasoning, never going the wrong way, never missing a step. That was the thread woven through. This is the advantage of logical step by step thinking.
And I made no assumptions.
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