# Why do my light bulbs unscrew themselves? **URL:** \ **Category:** Factual Questions\ **Created:** [July 20, 2009, 1:36am UTC](https://boards.straightdope.com/t/why-do-my-light-bulbs-unscrew-themselves/503579 "2009-07-20T01:36:39Z")\ **Posts on this page:** 9\ **Page:** 2
**Author:** ![Ethilrist](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ethilrist/32/4604_2.png) [@Ethilrist](https://boards.straightdope.com/u/Ethilrist)\ **Post date:** [August 19, 2012, 7:26pm UTC](https://boards.straightdope.com/t/why-do-my-light-bulbs-unscrew-themselves/503579/21 "2012-08-19T19:26:52Z")
Well, if you’re in France, I’d say you can’t keep the bulbs in the sockets once they’ve seen Paris. ---
**Author:** ![Napier](https://avatars.discourse-cdn.com/v4/letter/n/ce73a5/32.png) [@Napier](https://boards.straightdope.com/u/Napier)\ **Post date:** [August 19, 2012, 10:36pm UTC](https://boards.straightdope.com/t/why-do-my-light-bulbs-unscrew-themselves/503579/22 "2012-08-19T22:36:12Z")
I have a small incandescent bulb night light in the bathroom, which screws straight down into the socket. It goes on and off every few seconds. I think there is an expansion issue that cycles with the lamp heating itself. I figure something about this cycling also adjusts the bulb in and out by turning in the threads to keep itself in just the right position to cycle. This behavior has been pretty steady for a couple of months now. When I have tightened it in the past, it has returned to this behavior within a few weeks. ---
**Author:** ![ralph124c](https://avatars.discourse-cdn.com/v4/letter/r/8797f3/32.png) [@ralph124c](https://boards.straightdope.com/u/ralph124c)\ **Post date:** [August 20, 2012, 12:06am UTC](https://boards.straightdope.com/t/why-do-my-light-bulbs-unscrew-themselves/503579/23 "2012-08-20T00:06:39Z")
This is why spring loaded posts are better contacts for lightbulbs. Unfortunately, bulbs made this way cost 3-5 times the price of screw base bulbs. BTW-why are people buying those old carbon filament bulbs now? Inefficient and wasteful. ---
**Author:** ![GreasyJack](https://avatars.discourse-cdn.com/v4/letter/g/df705f/32.png) [@GreasyJack](https://boards.straightdope.com/u/GreasyJack)\ **Post date:** [August 20, 2012, 12:10am UTC](https://boards.straightdope.com/t/why-do-my-light-bulbs-unscrew-themselves/503579/24 "2012-08-20T00:10:33Z")
Someone is clearly [gaslighting](http://en.wikipedia.org/wiki/Gaslighting) you, both figuratively and (with allowances for modern technology) literally. ---
**Author:** ![aceplace57](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/aceplace57/32/3500_2.png) [@aceplace57](https://boards.straightdope.com/u/aceplace57)\ **Post date:** [August 20, 2012, 12:43am UTC](https://boards.straightdope.com/t/why-do-my-light-bulbs-unscrew-themselves/503579/25 "2012-08-20T00:43:56Z")
i had one fixture in a hallway that had a bulb constant going out/ then back on. Went through the tightening and replacing cycle several times. I finally took it down and saw on the back side, that the wires were scorched and so was the socket. This fixture was rated as a double 40 W. My bedroom fixture’s are double 75 Watts. I probably screwed up one time and used 75 Watts in the hallway. Hey, shit happens. 😃 Also, the original fixture had a cheap ass plastic socket. The replacement fixture I bought has a ceramic socket. I briefly looked around for a replacement socket and couldn’t find anything that I knew for sure would fit back exact. So, found a similar fixture (new) on Ebay. ---
**Author:** ![BubbaDog](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bubbadog/32/333_2.png) [@BubbaDog](https://boards.straightdope.com/u/BubbaDog)\ **Post date:** [August 20, 2012, 1:26pm UTC](https://boards.straightdope.com/t/why-do-my-light-bulbs-unscrew-themselves/503579/26 "2012-08-20T13:26:51Z")
> [@Saint\_Cad](#): > > I doubt it. If you heat an annulus, the hole on the middle gets bigger, not smaller. Correct. But an annulus is not a threaded incline. Consider this. The bulb and base have threads on them so that there is increased surface area to each other. The friction between those surfaces is what holds them in place. And if their specifications are just right they stay in place. But some are still usable but slightly out of spec. Now consider each of those surfaces expanding from heat, but not necessarily in unison. And then contracting as they cool, and again, not necessarily in unison. Its very easy to assume that the surfaces may creep away from each other due to the tensile force on the metal. It won’t creep far but repeat that situation multiple times and the bulb will slowly unscrew itself. And this happens to be a personal SDMB record for me; defending a comment I made three years ago. ---
**Author:** ![AaronX](https://avatars.discourse-cdn.com/v4/letter/a/7bcc69/32.png) [@AaronX](https://boards.straightdope.com/u/AaronX)\ **Post date:** [August 20, 2012, 3:12pm UTC](https://boards.straightdope.com/t/why-do-my-light-bulbs-unscrew-themselves/503579/27 "2012-08-20T15:12:17Z")
How about making marks on the bulb and socket, and seeing if they move out of alignment? Also, all the bulbs mentioned are screw mount, not bayonet, right? > [@ralph124c](#): > > BTW-why are people buying those old carbon filament bulbs now? Inefficient and wasteful. Do they still use carbon? I thought all incandescents used tungsten. ---
**Author:** ![furdmort](https://avatars.discourse-cdn.com/v4/letter/f/e47774/32.png) [@furdmort](https://boards.straightdope.com/u/furdmort)\ **Post date:** [August 20, 2012, 3:32pm UTC](https://boards.straightdope.com/t/why-do-my-light-bulbs-unscrew-themselves/503579/28 "2012-08-20T15:32:12Z")
> [@ralph124c](#): > > This is why spring loaded posts are better contacts for lightbulbs. Unfortunately, bulbs made this way cost 3-5 times the price of screw base bulbs. > BTW-why are people buying those old carbon filament bulbs now? Inefficient and wasteful. Because the CFL replacements don’t produce enough light and the light they do produce is of an icky color. If I put a CFL in the light socket in my living room, I have to use an extra lamp to read when sitting on the couch. If I put a regular bulb in the same socket, I don’t need the extra lamp - the light from the main socket is enough to read by. On top of all that, using a CFL in our stairwell confuses the bats. When there’s a CFL in the stairwell light socket in my house, the bats wil routinely smack into the window. With a regular light bulb, the bats have no problems. ---
**Author:** ![furdmort](https://avatars.discourse-cdn.com/v4/letter/f/e47774/32.png) [@furdmort](https://boards.straightdope.com/u/furdmort)\ **Post date:** [August 20, 2012, 3:34pm UTC](https://boards.straightdope.com/t/why-do-my-light-bulbs-unscrew-themselves/503579/29 "2012-08-20T15:34:39Z")
> [@AaronX](#): > > How about making marks on the bulb and socket, and seeing if they move out of alignment? Also, all the bulbs mentioned are screw mount, not bayonet, right? > > Do they still use carbon? I thought all incandescents used tungsten. Yes, tungsten. [Previous page](https://boards.straightdope.com/t/why-do-my-light-bulbs-unscrew-themselves/503579.md?page=1)