# Three light switch riddle, help. **URL:** \ **Category:** Factual Questions\ **Created:** [October 19, 2008, 1:19am UTC](https://boards.straightdope.com/t/three-light-switch-riddle-help/468589 "2008-10-19T01:19:14Z")\ **Posts on this page:** 17\ **Page:** 2
**Author:** ![Dervorin](https://avatars.discourse-cdn.com/v4/letter/d/eb8c5e/32.png) [@Dervorin](https://boards.straightdope.com/u/Dervorin)\ **Post date:** [October 19, 2008, 8:38am UTC](https://boards.straightdope.com/t/three-light-switch-riddle-help/468589/21 "2008-10-19T08:38:28Z")
> [@Q.E.D](#): > > Alternate solution for smartasses like me: Use your one trip upstairs to replace the bulb with a buzzer. Then, when you go back downstairs, flip the switches one by one until you hear your buzzer go off. This has the added benefit of working for any number of switches and is independent of the initial state of the bulb. Ah, but that only works for this version of the riddle. The version I know is that there are three bulbs and three switches, and you have to figure out which switch controls which bulb. Same solution as above, but with the advantage of being immune to this particular form of smart-assery. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [October 19, 2008, 8:44am UTC](https://boards.straightdope.com/t/three-light-switch-riddle-help/468589/22 "2008-10-19T08:44:56Z")
Alternate solution with no trips upstairs: find the electrician who wired the house and tell him “I’ll give you this nice barometer if you tell me which switch controls the attic light.” ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [October 19, 2008, 3:11pm UTC](https://boards.straightdope.com/t/three-light-switch-riddle-help/468589/23 "2008-10-19T15:11:22Z")
> [@Dervorin](#): > > Same solution as above, but with the advantage of being immune to this particular form of smart-assery. Yeah, but I’m an _inveterate_ smartass. Thus, I have three buzzers, each with a different tone. 😃 ---
**Author:** ![Rico](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rico/32/3582_2.png) [@Rico](https://boards.straightdope.com/u/Rico)\ **Post date:** [October 19, 2008, 5:51pm UTC](https://boards.straightdope.com/t/three-light-switch-riddle-help/468589/24 "2008-10-19T17:51:08Z")
> [@Indistinguishable](#): > > I wonder what the third switch does… “_Not the third switch! Don’t throw the third switch! AAAAAAAAAAAAAaaaaaaaaaa!_” ---
**Author:** ![Dervorin](https://avatars.discourse-cdn.com/v4/letter/d/eb8c5e/32.png) [@Dervorin](https://boards.straightdope.com/u/Dervorin)\ **Post date:** [October 20, 2008, 8:14am UTC](https://boards.straightdope.com/t/three-light-switch-riddle-help/468589/25 "2008-10-20T08:14:59Z")
> [@dtilque](#): > > Alternate solution with no trips upstairs: find the electrician who wired the house and tell him “I’ll give you this nice barometer if you tell me which switch controls the attic light.” Is that story from Feynman, or am I just imagining it? ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [October 20, 2008, 8:56am UTC](https://boards.straightdope.com/t/three-light-switch-riddle-help/468589/26 "2008-10-20T08:56:13Z")
> [@Dervorin](#): > > Is that story from Feynman, or am I just imagining it? It’s a parody of an alternate solution to the puzzle of how to find the height of a building using a barometer. Have no idea who came up with this alternate solution. ---
**Author:** ![muldoonthief](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/muldoonthief/32/3188_2.png) [@muldoonthief](https://boards.straightdope.com/u/muldoonthief)\ **Post date:** [October 20, 2008, 1:24pm UTC](https://boards.straightdope.com/t/three-light-switch-riddle-help/468589/27 "2008-10-20T13:24:55Z")
> [@dtilque](#): > > It’s a parody of an alternate solution to the puzzle of how to find the height of a building using a barometer. Have no idea who came up with this alternate solution. Yeah, this is a standard high school physics joke. Correct answer - measure pressure at street level and on roof, use the formula you’re currently learning that details how air pressure varies with altitude. Smart ass answer - drop barometer off roof, measure time it takes to fall, use the formula you learned back in the first week of class s = 1/2 at[sup]2[/sup]. Really smartass answer - Go to the basement, find the building super, and offer him a shiny new barometer if he’ll tell you how tall the building is. ---
**Author:** ![Enright3](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/enright3/32/2897_2.png) [@Enright3](https://boards.straightdope.com/u/Enright3)\ **Post date:** [October 20, 2008, 2:50pm UTC](https://boards.straightdope.com/t/three-light-switch-riddle-help/468589/28 "2008-10-20T14:50:06Z")
> [@Chronos](#): > > Of course, even the simplest inside-the-box solution as the OP has phrased it still gives you a 2 in 3 chance of guessing right, which is pretty good odds for winning a free house. Unless of course they were behind three doors, and after you picked one your host opened one of the two remaining doors and asked if you wanted to switch. ---
**Author:** ![Heller\_Highwater](https://avatars.discourse-cdn.com/v4/letter/h/278dde/32.png) [@Heller\_Highwater](https://boards.straightdope.com/u/Heller_Highwater)\ **Post date:** [October 20, 2008, 3:02pm UTC](https://boards.straightdope.com/t/three-light-switch-riddle-help/468589/29 "2008-10-20T15:02:06Z")
[Quote=Enright3] Unless of course they were behind three doors, and after you picked one your host opened one of the two remaining doors and asked if you wanted to switch. [/Quote] But I thought the switches were on the walls, not the doors. 😕 😃 For the record, I really like **Q.E.D.**'s answer. ---
**Author:** ![Mijin](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mijin/32/9369_2.png) [@Mijin](https://boards.straightdope.com/u/Mijin)\ **Post date:** [October 20, 2008, 3:31pm UTC](https://boards.straightdope.com/t/three-light-switch-riddle-help/468589/30 "2008-10-20T15:31:19Z")
> [@Heller\_Highwater](#): > > But I thought the switches were on the walls, not the doors. 😕 Ah, you’re obviously not familiar with the [Monty Hall Problem](http://en.wikipedia.org/wiki/Monty_Hall_problem). w.r.t. the OP. I didn’t get it, I’m useless at lateral thinking puzzles, but it’s at least partly because they often need you to make similar assumptions to the dude who originally thought of the puzzle. And yet, you still feel like kicking yourself when told the solution… ---
**Author:** ![Heller\_Highwater](https://avatars.discourse-cdn.com/v4/letter/h/278dde/32.png) [@Heller\_Highwater](https://boards.straightdope.com/u/Heller_Highwater)\ **Post date:** [October 20, 2008, 3:39pm UTC](https://boards.straightdope.com/t/three-light-switch-riddle-help/468589/31 "2008-10-20T15:39:45Z")
Oh, I’m all too familiar with the Monty Hall problem. I was making an (admittedly bad) pun about switching doors vs. switching lightbulbs. As a small hijack, how well does the solution to this riddle hold up in the face of new technology? For example, I don’t know how fast compact fluorescent bulbs build up or dissapate heat. Would that make a difference in the solution? (That is, if there isn’t enough heat remaining in the bulb when you walk into the room, the solution fails.) ---
**Author:** ![vetbridge](https://avatars.discourse-cdn.com/v4/letter/v/b5e925/32.png) [@vetbridge](https://boards.straightdope.com/u/vetbridge)\ **Post date:** [October 20, 2008, 3:43pm UTC](https://boards.straightdope.com/t/three-light-switch-riddle-help/468589/32 "2008-10-20T15:43:18Z")
I thought I had a way to do it, but the chicken would eat the grain. ---
**Author:** ![Defensive\_Indifference](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/defensive_indifference/32/6502_2.png) [@Defensive\_Indifference](https://boards.straightdope.com/u/Defensive_Indifference)\ **Post date:** [October 20, 2008, 3:46pm UTC](https://boards.straightdope.com/t/three-light-switch-riddle-help/468589/33 "2008-10-20T15:46:45Z")
> [@muldoonthief](#): > > Yeah, this is a standard high school physics joke. Correct answer - measure pressure at street level and on roof, use the formula you’re currently learning that details how air pressure varies with altitude. Smart ass answer - drop barometer off roof, measure time it takes to fall, use the formula you learned back in the first week of class s = 1/2 at[sup]2[/sup]. Really smartass answer - Go to the basement, find the building super, and offer him a shiny new barometer if he’ll tell you how tall the building is. I have an old book at home with a version of this written by a university Physics professor (a real guy), but he presents it as a true story that happened to him. His version is very elaborate. The student comes up with a litany of possible solutions, including: walking up the stairwell and marking off “barometer units” on the wall; lowering the barometer on a rope and measuring the rope; and making a pendulum of the barometer and measuring its something-or-other at each location (Physics was too long ago for me). He does end with the “I will give you this barometer…” punchline, and the professor relents, passing the sutdent. The story goes over several pages. I doubt the story is really true, but it’s an especially well-told version. ---
**Author:** ![yabob](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/yabob/32/2821_2.png) [@yabob](https://boards.straightdope.com/u/yabob)\ **Post date:** [October 20, 2008, 3:49pm UTC](https://boards.straightdope.com/t/three-light-switch-riddle-help/468589/34 "2008-10-20T15:49:01Z")
> [@Heller\_Highwater](#): > > Oh, I’m all too familiar with the Monty Hall problem. I was making an (admittedly bad) pun about switching doors vs. switching lightbulbs. > > As a small hijack, how well does the solution to this riddle hold up in the face of new technology? For example, I don’t know how fast compact fluorescent bulbs build up or dissapate heat. Would that make a difference in the solution? (That is, if there isn’t enough heat remaining in the bulb when you walk into the room, the solution fails.) I wondered about that. A small experiment with the CFL in my living room lamp shows that it warms up in a few minutes, and 1 minute after being shut off is still warm - not as much as an incandescent bulb, but still detectable. LED illumination may be another story, though. ---
**Author:** ![Annie-Xmas](https://avatars.discourse-cdn.com/v4/letter/a/ecc23a/32.png) [@Annie-Xmas](https://boards.straightdope.com/u/Annie-Xmas)\ **Post date:** [October 20, 2008, 3:49pm UTC](https://boards.straightdope.com/t/three-light-switch-riddle-help/468589/35 "2008-10-20T15:49:29Z")
Flick switch #1, go outside, see if attic light is on. If not, repeat with #2. If neither turn the light on, it’s switch #3. If you think I’m running up to the attic and back to see if the light is on, you’re crazy. ---
**Author:** ![Mijin](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mijin/32/9369_2.png) [@Mijin](https://boards.straightdope.com/u/Mijin)\ **Post date:** [October 20, 2008, 3:58pm UTC](https://boards.straightdope.com/t/three-light-switch-riddle-help/468589/36 "2008-10-20T15:58:24Z")
> [@Heller\_Highwater](#): > > Oh, I’m all too familiar with the Monty Hall problem. I was making an (admittedly bad) pun about switching doors vs. switching lightbulbs. So, I thought you’d been whooshed, but really it was me… > [@Annie-Xmas](#): > > If you think I’m running up to the attic and back to see if the light is on, you’re crazy. I’d rather run up and down the stairs twice than wait 5 to 10 minutes. It’s good exercise and I’m impatient. That’s why, for me, the premise that I can only go upstairs once makes me implicitly rule out ‘slow’ solutions – because they’re more hassle\ ---
**Author:** ![panache45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/panache45/32/64_2.png) [@panache45](https://boards.straightdope.com/u/panache45)\ **Post date:** [October 20, 2008, 7:58pm UTC](https://boards.straightdope.com/t/three-light-switch-riddle-help/468589/37 "2008-10-20T19:58:20Z")
> [@jtgain](#): > > I have owned a couple of old houses with “mystery” switches. They serve no purpose and/or their purpose is lost to time and known only to God. They control nothing and do nothing. I have a few of those myself. I also have a receptacle in the kitchen that’s on the same circuit as an upstairs bedroom ceiling light. And there was a receptacle in the dining room that was connected to standard lamp cord which went through a hole in the floor, and was plugged into a receptacle in the basement. The previous owner was very creative. [Previous page](https://boards.straightdope.com/t/three-light-switch-riddle-help/468589.md?page=1)