School-Safe Puzzle Games

Any Bright Ideas?

light bulb brain teaser with switch

OK, Get your thinking caps on- Here’s a great brain teaser Doug recently sent in:

There are 2 rooms that are completely isolated from each other. In 1 room, there are 3 light switches. In the other, 3 light bulbs.

How can you determine which light switch is connected to each light bulb if you can only be in each room ONCE?

40 Comments to “Any Bright Ideas?”

  1. charity | Guest

    ok i think i might have it…you go in the room and quickly turn on the lights and see which goes to the room your in….now there is two switches left, turn one on and leave it on for a few, now run to the next room and see if the light is warm, if so it goes to that room in not the switch goes to the other then the remaining light goes to the room you havent eliminated.

  2. xena | Guest

    Assuming you can touch the light bulbs…in switches room…
    Switch 1 -> Turn on
    Switch 2 -> Turn on and leave on for 5 minutes or so; then turn off
    Switch 3 -> Leave off

    Go into other room. The bulb that is on belongs to 1. The bulb that is off and warm belongs to 2. The bulb that is off and cool belongs to 3.

  3. Matthew | Guest

    You go into the room with the switches and turn two on. Wait, and then turn only one of the two off.

    You then enter the room with the bulbs. The bulb which is on is connected to the switch which you left one. Then there will be two bulbs off. One of them will feel a little warm because you turned it on for a while and turned it off. The other bulb will be cold as you never used the light switch

  4. Mick M | Guest

    In the light switch room turn one switch on and leave it on for a while then turn it off. Now turn a different switch on and leave it on. Now go to the light bulb room. You know the switch you turned on by the light being on, you can find the first light switch controlled light by feeling the other bulbs , the warm one will be the one, The last switch controlls the cold light bulb.

  5. jason | Guest

    turn on the left one first, for a couple of minutes, then turn it back off and turn on the right one and leave it on. Go to the other room and see what light is on(that would be the right one), then feel the other two and see which one is warm(that would be the left one then), and the only one not on, and not warm, would be to the middle switch.

  6. santhosh | Guest

    Let us assume Room A has 3 switches. Room B has 3 bulbs.
    I will enter Room A, Use Swich 1 and light ON. Use Switch 2 and light on for some time and switch off. Don’t use Switch 3.

    Enter Room B, whichever light ON, that will be related to Switch 1, if a light is bit warm(when we switch on any light for some time, it will be warm) that is related to Switch 2 and other light is related to Switch 3.

    Am I correct?

  7. Ted | Guest

    Well, I’d say, first go in the room with the switches, turn the first one on, wait 10 minutes, turn it off, then turn the second one on, wait 3-4 minutes, turn it off and finally go in the room with the light bulbs. The hottest one is turned on by the first switch, the second hottest, by the second (really?!?!?!?!) and the cold one… well, that one you’ll have to guess!

  8. Deejam | Guest

    Put on switch A for a minute and then turn it off.
    Put on switch B and then enter the bulb room.

    The one which glows is connected switch B.
    among rest, which is heat is connected to switch A.
    the other is connected to switch C.

  9. Slavco | Guest

    You turn one of the switches and leave it ON for a few minutes. Then you turn it OFF, turn ON the second switch and immediately go to the room where the bulbs are.

    The switch that you lastly turned ON is connected to the bulb that is now ON.

    There should be 2 OFF bulbs now. You touch them both, one of them should be HOT.

    The HOT OFF bulb is connected to the first switch you turned ON and OFF.

    The COLD OFF bulb is connected to the switch you never touched.

  10. Ian | Guest

    turn 2 on and wait for a while.
    turn one off.
    go into other room.
    one is on(the one you left on), 2 are off.
    one of the ones off will be warm(the one you turned on and then off after a while)
    the other will be cold(the one you never turned on)

    I heard this before

  11. Ari | Guest

    Throw one switch on, wait for say 10 seconds then turn the switch off.
    Throw one of the other switches on then go to the room with the lamps.
    Obviously one lamp should be on so you know which switch that one connects to.
    Next you try which one on the lamps that are off is warm. The warm one is
    connected to the first switch you turned on.
    The last lamp is of course connected to the remaining switch.

  12. Jay | Guest

    Turn on 2 switches, wait a minute, turn 1 off, go into 2nd room (make sure you note which switches were turned on and off before entering). 1 bulb should be lit. Now feel for the warm bulb and that should be the one for the switch you just turned off. The 3rd switch that wasn’t touched should obviously be the one that correlates to the cold bulb… Did that make sense?

  13. Renzo | Guest

    C= Use the third switch to burn out the third light bulb.

    Go to the second room and check witch one is burnt out. You have to switch the position of the light bulbs in order to find out.

  14. scott k | Guest

    send about a trillion volts into one light switch so the light blows up, then just turn one on and leave the other off

  15. Daniel | Guest

    I would:
    -enter the switch room
    -turn the first switch on
    -wait one year
    -turn the second switch on
    -go to the bulb room
    -one of the bulbs will be burned out, one will be on, and one will be off; this will tell me which is which. (a burned-out bulb can be differentiated from one that is merely turned off by close inspection.)

  16. anon | Guest

    remove the switches and install dimmers

  17. anon | Guest

    actually install one dimmer, put one switch on and keep the other switch off.

  18. Alex | Guest

    In the room with switches, turn on two switches and wait a few minutes, allowing the bulbs to warm up. Turn off one switch and immediately go to the second room with the bulbs. One light bulb will be on (switch left on), one will be warm (switch turned off), and the third will be cool (switch that was not manipulated at all)

  19. Sinata | Guest

    Turn on the light in one and let it be turn on a minute, and turn off the light and turn on a another light and go in other room, one light should be warm, one cold and one have the light turned on

  20. Levi | Guest

    Hah this is a good one absolutely; took me a minute and had to realize that you could turn all on (which is the same as turning all off in the sense that it wouldn’t do anything) or turn one or two on which would leave you with the same challenge of figuring out which of the two on (or off) belong to a specific switch. The answer:

    Turn one on for 5 mins or something and then turn it off. Turn a different one on and go to the other room. The one that is on is obviously connected to the switch that is on, but for the other two simply touch the bulbs. The hot bulb was the one that you turned on first.

  21. suineg | Guest

    one solution is this:
    in the room with the switches:
    1) turn on the first light switch for 10 min then turn it off
    2) turn the second light switch
    3) the third switch remain untouched
    now go to the room with the bulbs:
    1) the bulb that is off and is hot is the one conected to the first light switch
    2) the bulb that is on is conected to the second light switch
    3) the bul that is off is conected to the thid switch that is untouched.

  22. sorin | Guest

    Well.. heres what i think:

    I’d start off in the switch room. Id turn one on wait 10 minutes and then turn it off , then id turn another switch on and leave it, and i would leave that last one off:

    switch one: off
    switch two: on for 10 min, off
    switch three: on

    then id go into the bulb room,
    there, the bulb that is on is controlled by switch three, the bulb that is off but warm is controlled by switch two and the bulb thats off and cold is switch one.

    Bulb one: off and cold
    Bulb two: off and warm
    bulb three: on

  23. ngdses | Guest

    turn on two lights by flicking two switches, then wait a while then turn off one of the lights by flicking one of the already swithed-on switches. Go into the room with the light bulbs and the light bulb that is on corresponds to the switch that was only flicked once, the lightbulb that is hot or warm is corresponds to the switch that was flicked on then off, and the last lightbulb corresponds to the last, untouched switch.

  24. Shanelly | Guest

    Turn each switch on for different (but consecutive) amounts of time. Turn them all off.

    Go into the next room, and see which bulb is hottest/takes the longest to cool down…etc…

  25. James | Guest

    I would go by the heat of the bulbs. Flip one switch and leave it on for a while. Then flip a second for only a little bit, then turn them all off. Go into the other room and see what bulb is hottest, which is warm, and which is cold.

  26. Geert Jan | Guest

    (1) Switch switch 1, wait 10 minutes
    (2) switch the second one on and switch the first off
    (3) hurry to the other room

    when entering the second room one light is burning (the second switch). The other two lights are off. One is hot (the first switch) and one is cold (the third switch).

  27. Richard | Guest

    in the switches room, leave the first one switch off, leave second one on for 30mins then turn it off an leave the third one switched on as you go into the room with the bulbs. One bulb will be illuminated, and 2 won’t, but you will be able to tell which had recently been on by the heat coming off it, thus finding the second switch.

  28. Kevin from Bathurst | Guest

    The solution i came up with…
    Turn one switch on for 5 minutes
    Then turn a second switch on
    Change rooms

    The hottest globe is connected to the first switch you turn on
    The cooler globe is connected to the second switch
    And the third switch is the globe that is off

  29. Rupert Parson | Guest

    An old classic.

    We assume that the light bulbs are incandescent – i.e. get hot when they are switched on.


    In the switch room turn on one liight switch, and leave it on for 1 minute, then turn it off. Turn on one of the other switches.

    Go into the light bulb room:

    The bulb that is on is controlled by the switch that is on.
    The bulb that is off but warm is controlled by the switch that was on for 1 minute.
    The bulb that is off and cold is controlled byt he remaining switch.

  30. Rune | Guest

    Leave switch number one off.
    number two on
    let switch number three burn for a few minutes…

    In the other room:
    the bulb connected with switch one is identified as not producing light
    bulb two as producing light
    and bulb three is hot when you touch it but is not lit!

    First time I post on this site, found it a few weeks ago, and its great fun! So hi everybody:)

  31. Shawn | Guest

    send a friend into the light bulb room, then go into the switch room and flip each switch on from left to right.

  32. colin | Guest

    Flip on the first two switches. Leave them on for a while, and then flip the second switch off.

    Go into the other room and feel the two dark bulbs for which one is still hot. The hot one goes to your second switch. The cold one goes to the third switch and the glowing bulb goes to the first switch.

  33. RK | Profile

    Didn’t think many would get this one right!

    Hi Rune (& other new visitors :) we’re working on implementing more interactive type features on the site so you can more freely chat with each other, open up discussions, view profiles/answer & comment histories etc…

  34. Mike | Guest

    You actually only have to go into the room with the light bulbs. You don’t even need to go into the switch room. Just go into the the room with the light bulbs and remove them all. Then you can determine that none of the light bulbs are connected to the switches.

  35. Rune | Guest

    Haha, good one, Mike!

  36. johan | Guest

    You start at the switches room:

    Leave one on -> glows
    Leave one off -> dark
    Let one be on for a while then turn off -> dark, but hot

  37. Tommy | Guest

    It’s a shame that more efficient light bulbs might make this question almost impossible for future generations.

  38. evie_sleeve | Profile

    Personally I would have dimmer light switches installed so they all are a different brightness, easy peasy!

  39. Darkened_Shadow | Profile

    “There are 2 rooms that are completely isolated from each other. In 1 room, there are 3 light switches. In the other, 3 light bulbs.”

    Anyone who’s suggesting to turn the light bulbs on needs to re-read this.

    in one room there’s 3 switches, in the other there’s three light bulbs… So pick up the light bulbs and take them into the room with the switches, and put them in the sockets.

    That’s how you can tell which switch operates which light bulb

  40. clumsyninja | Profile

    *flip two light switches on.
    *let them stay on for 5 minutes.
    *flip one of the the two switches that has been
    on for the past 5 minutes off.
    *leave the room with the switches.
    *enter the room with the lightbulbs.
    *the light that is on in the room indicates
    it is connected to the switch that you left on
    in the other room.
    *now feel of the light bulbs that are off..
    the one that isnt warm will be connected to the switch in the
    other room that hasnt been touched. the one that is still warm
    will be the one that you turned of in the other room..
    *if you can remember which switches you turned on and off and left alone
    then you will have solved which switches are connected with which lightbulbs.

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