3 Bulbs & 3 Switches
You are outside a closed room. Three switches control three bulbs inside.
You may enter the room only once. Can you determine the full mapping?
Outside the room
Manipulate the switches before your one visit.
Elapsed heating time
0 min
Hint: the bulb gives you more information than just ON/OFF.
Bulb room
The door is closed. Bulb states are hidden.
0 / 1 visits
Make your deduction
Match each switch to the correct bulb.
The one-trip solution
- Turn Switch 1 ON and leave it on for several minutes.
- Turn Switch 1 OFF.
- Turn Switch 2 ON. Leave Switch 3 OFF.
- Enter the room once.
Now inspect the bulbs:
💡 Lit bulb → Switch 2
♨️ Dark but warm bulb → Switch 1
❄️ Dark and cold bulb → Switch 3
Key idea: residual heat stores information about the past.
That gives each bulb three useful observable states: lit, dark-but-warm, and dark-and-cold.