# How does a three-way lamp switch work - or not? **URL:** \ **Category:** Factual Questions\ **Created:** [March 29, 2008, 8:47pm UTC](https://boards.straightdope.com/t/how-does-a-three-way-lamp-switch-work-or-not/443202 "2008-03-29T20:47:04Z")\ **Posts on this page:** 15\ **Page:** 1
**Author:** ![Frank](https://avatars.discourse-cdn.com/v4/letter/f/3d9bf3/32.png) [@Frank](https://boards.straightdope.com/u/Frank)\ **Post date:** [March 29, 2008, 8:47pm UTC](https://boards.straightdope.com/t/how-does-a-three-way-lamp-switch-work-or-not/443202/1 "2008-03-29T20:47:04Z")
I bought some cheap lamps on Monday. Five days later, the three-way switch in one has already broken. Instead of off-on-onner-onnest, I’ve got the old off-off-on-on. I’ve had other lamps do this, though not quite so quickly. What makes a three-way switch work? Why do they fail so easily? ---
**Author:** ![3waygeek](https://avatars.discourse-cdn.com/v4/letter/3/e95f7d/32.png) [@3waygeek](https://boards.straightdope.com/u/3waygeek)\ **Post date:** [March 29, 2008, 8:55pm UTC](https://boards.straightdope.com/t/how-does-a-three-way-lamp-switch-work-or-not/443202/2 "2008-03-29T20:55:59Z")
It’s probably the bulb, not the switch. Three-way lamps have two filaments; one of which is usually rated at a higher wattage than the other (e.g. 50W & 100W – when both are lit, you get 150W). The usual sequence of the switch is off-low wattage-high wattage-both – so since you’re seeing off-off-on-on, your low wattage filament is probably shot. A new bulb should fix the problem – if it doesn’t, then it’s probably the switch or a dirty contact; unplug the lamp & investigate further (e.g. clean the contacts in the socket with a pencil eraser or emery board, pry the contact points up very gently to improve contact, or just replace the damn socket). Do not do any of this with the lamp plugged in, or your lights may be turned out permanently. ---
**Author:** ![Frank](https://avatars.discourse-cdn.com/v4/letter/f/3d9bf3/32.png) [@Frank](https://boards.straightdope.com/u/Frank)\ **Post date:** [March 29, 2008, 9:00pm UTC](https://boards.straightdope.com/t/how-does-a-three-way-lamp-switch-work-or-not/443202/3 "2008-03-29T21:00:55Z")
[QUOTE=3waygeek] It’s probably the bulb, not the switch. [/QUOTE] I have to admit to looking at your username with some bemusement. 🙂 It’s not the bulb; I tried it in a lamp that still works. I’ll give a shot to your other suggestions. Thanks! ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [March 29, 2008, 10:07pm UTC](https://boards.straightdope.com/t/how-does-a-three-way-lamp-switch-work-or-not/443202/4 "2008-03-29T22:07:43Z")
If you look down into a three way socket, you’ll usually see a centered contact for the base of the light, and raised directly above that a ring or washer shaped contact for the second connection to the lamp, plus the metal screw in threads, which also act as a contact for the lamp. Sometimes the ring shaped contact gets bent down so that it touches the center contact. That’ll cause the switch to behave as a conventional on-off-on type switch. You can fix that problem by raising the contact ring slightly with a screwdriver or pliers. Be sure to unplug the lamp first. This doesn’t always fix the problem as it’s sometimes the result of wear in the internal contacts of the switch itself. Those are not designed to be fixable, so if that’s the cause of your troubles you’ll have to replace the whole socket. ---
**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:** [March 29, 2008, 10:30pm UTC](https://boards.straightdope.com/t/how-does-a-three-way-lamp-switch-work-or-not/443202/5 "2008-03-29T22:30:42Z")
[QUOTE=Squink] If you look down into a three way socket, you’ll usually see a centered contact for the base of the light, and raised directly above that a ring or washer shaped contact for the second connection to the lamp… [/QUOTE] I’ve never seen a three-way lamp socket as you describe. All of the ones I’ve encountered have been some variation of [this](http://img524.imageshack.us/my.php?image=threewayih1.jpg). I’ve marked the center contact with a blue arrow and the radial contact with a red one. This second contact makes connection with a concentric annular contact on the bulb base (perhaps this is what you were thinking of). ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [March 29, 2008, 10:46pm UTC](https://boards.straightdope.com/t/how-does-a-three-way-lamp-switch-work-or-not/443202/6 "2008-03-29T22:46:47Z")
[QUOTE=Q.E.D.] I’ve never seen a three-way lamp socket as you describe. [/QUOTE] All my three ways are relicts from the 30’s and 40’s. That’s how they were built. They still work with an occasional bit of fidgeting. The two inner contacts look pretty well isolated from each other on that new design. That means that Frank’s troubles probably lie within the switch itself. Replacement is the simplest option. ---
**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:** [March 29, 2008, 11:05pm UTC](https://boards.straightdope.com/t/how-does-a-three-way-lamp-switch-work-or-not/443202/7 "2008-03-29T23:05:21Z")
[QUOTE=Squink] All my three ways are relicts from the 30’s and 40’s. [/QUOTE] Any chance of getting some pics? I love old electrical stuff. ---
**Author:** ![Harmonious\_Discord](https://avatars.discourse-cdn.com/v4/letter/h/74df32/32.png) [@Harmonious\_Discord](https://boards.straightdope.com/u/Harmonious_Discord)\ **Post date:** [March 30, 2008, 12:29am UTC](https://boards.straightdope.com/t/how-does-a-three-way-lamp-switch-work-or-not/443202/8 "2008-03-30T00:29:32Z")
You can pick up a new three way socket to replace the one on the lamp. The first thing to try is unplug the lamp and pry the bottom prong up a little bit. [Guts only](http://electrical.hardwarestore.com/13-39-lamp-sockets/three-way-lamp-socket-interior-103190.aspx) [Whole socket](http://electrical.hardwarestore.com/13-39-lamp-sockets/three-way-brass-socket-234898.aspx) ---
**Author:** ![BJMoose](https://avatars.discourse-cdn.com/v4/letter/b/5fc32e/32.png) [@BJMoose](https://boards.straightdope.com/u/BJMoose)\ **Post date:** [March 30, 2008, 12:41am UTC](https://boards.straightdope.com/t/how-does-a-three-way-lamp-switch-work-or-not/443202/9 "2008-03-30T00:41:55Z")
Far be it from me to suggest to a Moderator that his light bulb isn’t screwed in tight, but . . . **Frank** , are you sure your light bulb was screwed in tight? Just the other day I replaced a three-way and discovered I hadn’t torqued it enough. ---
**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:** [March 30, 2008, 12:48am UTC](https://boards.straightdope.com/t/how-does-a-three-way-lamp-switch-work-or-not/443202/10 "2008-03-30T00:48:51Z")
You shouldn’t have to tighten a bulb all that much. If screwing it in finger tight (no jokes, please!) doesn’t make good contact, then there’s something wrong with the socket. ---
**Author:** ![Harmonious\_Discord](https://avatars.discourse-cdn.com/v4/letter/h/74df32/32.png) [@Harmonious\_Discord](https://boards.straightdope.com/u/Harmonious_Discord)\ **Post date:** [March 30, 2008, 1:44am UTC](https://boards.straightdope.com/t/how-does-a-three-way-lamp-switch-work-or-not/443202/11 "2008-03-30T01:44:46Z")
Maybe he needs to get ten monkeys to screw in the bulb, or get a gnu bulb. ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [March 30, 2008, 2:24am UTC](https://boards.straightdope.com/t/how-does-a-three-way-lamp-switch-work-or-not/443202/12 "2008-03-30T02:24:28Z")
[QUOTE=Q.E.D.] Any chance of getting some pics? [/QUOTE] I’ll see if I can get my camera to give me a decent shot tomorrow. It’s kinda tight in those things. [QUOTE=Harmonious Discord] Maybe he needs to get ten monkeys to screw in the bulb [/QUOTE] If he tries that, he will then need to [carve a potato into the right shape to remove the broken bulb.](http://boards.straightdope.com/sdmb/showthread.php?t=353356&highlight=potato+lightbulb) Even that [doesn’t always work.](http://boards.straightdope.com/sdmb/showthread.php?t=390372&highlight=potato) ---
**Author:** ![thirdname](https://avatars.discourse-cdn.com/v4/letter/t/d07c76/32.png) [@thirdname](https://boards.straightdope.com/u/thirdname)\ **Post date:** [March 30, 2008, 5:21am UTC](https://boards.straightdope.com/t/how-does-a-three-way-lamp-switch-work-or-not/443202/13 "2008-03-30T05:21:25Z")
You can also get a 3-way dimmer that works with a regular lamp. I think it works sort of like a switching power supply, turning on and off a certain fraction of the time. You can hear it buzz when it’s on a dimmed setting. ---
**Author:** ![Harmonious\_Discord](https://avatars.discourse-cdn.com/v4/letter/h/74df32/32.png) [@Harmonious\_Discord](https://boards.straightdope.com/u/Harmonious_Discord)\ **Post date:** [March 30, 2008, 11:05am UTC](https://boards.straightdope.com/t/how-does-a-three-way-lamp-switch-work-or-not/443202/14 "2008-03-30T11:05:03Z")
The thing with using a 3 way bulb is they have a higher output than single filament bulbs. ---
**Author:** ![Frank](https://avatars.discourse-cdn.com/v4/letter/f/3d9bf3/32.png) [@Frank](https://boards.straightdope.com/u/Frank)\ **Post date:** [March 30, 2008, 6:54pm UTC](https://boards.straightdope.com/t/how-does-a-three-way-lamp-switch-work-or-not/443202/15 "2008-03-30T18:54:28Z")
Lifting up the contact with my fingernail fixed it. Thanks all!