Why do my light bulbs unscrew themselves?

The other day my wife called me to change a light bulb in one of our closets. The light bulb was good, it had simply loosened up enough that it wasn’t making contact in the socket.

Friday night I went to replace the light bulb on our lamp outsiode. Again the light bulb was loose.

Today the one of the lights in the master bath burned out – oops, no. It was loose, as were the others in the fixture.

Incandescent or CFL, standard or decorative, inside and outside, standing up, pointing down and horizontal – all my light bulbs seem to be unscrewing themselves. What gives?

Maybe you didn’t get enough people to screw them in. What’s your occupation? :slight_smile:

Expansion caused by the heat and contraction caused by cooling results in the bulbs’ slowly creepingly unscrewing?

Personal guess would be vibration of some sort, though the expansion/contraction idea sounds pretty good as well. You could try putting the bulb in the refrigerator for a while before screwing it in and see if that allows it to squeeze itself in to an unslippable position.

ETA: Though I’m not sure whether the temperature difference would make too much difference on a lightbulb since they contain a vacuum, which should be keeping it pretty constant, I would think. Not to mention that very few people report unscrewing lightbulbs in locations with wide temperature differences.

I was thinking of the metal base.

As a serious point, I’m inclined to think vibration – which could be heavy traffic nearby, micro movements of house stricture owing to heating/cooling, settling, or other causes, or simply microquakes if the OP is anywhere subject to them.


How many people does it take to screw in a light bulb? Two – but they have to be very small and agile people.


What condition is your heating/cooling system in?

I thought the base was part of the main chamber. Though I suppose it makes more sense to have two wires running out of the glass bulb rather than trying to perfectly bond a metal cup to an open hole.

Anyone know? I can’t tell from the diagrams I can google.

Sage Rat: The glass envelope is fused fully closed during manufacture, with the wires embedded in the glass & extending out through the bottom. The wires are then soldered to the contacts in the metal base & then the base is glued to the glass.

OP: Lots of people screw lightblbs in very loosely, afraid they’ll get stuck over time. So it only take a little loosening to make them intermittent, then appear burnt out. If your place is new, or for some other reason most all the bulbs are the same age and installed by the same person, then they could all be loosening more or less at the same rate.

I have a 3-way lamp that does this. Every time I go to turn it on, it goes to “bright” on the first click, “brighter” on the second click, and stays at “brighter” on the third click. It’s not until I screw the lightbulb in tighter that it goes to the third step, “brightest.” I have to do this every time I turn on the lamp.

I think that it’s thermal expansion.

But not expansion of the light bulb or its metal base. It’s the expansion of the lamp’s socket that causes it to slowly push the light bulb out of the socket.

Do you know the difference between a light bulb and a pregnant blonde?

The light bulb can be unscrewed.

You may want to review Godfather II. It sounds to me like someone wants it to be dark when they shoot you. They haven’t thus far because they are “screwing up the courage”.

  1. I’ve seen it happen due to vibrations on a fan light fixture.

  2. I’ve seen it happen due to expansion and contraction. The bulb and socket were always a different metal. One being aluminum and the other being whatever the current brass colored metal is.

The thermal expansion/contraction theory sounds very reasonable, but if it is the real and main cause, why does it not happen to everybody’s light bulbs all the time? I do not get this problem, or at least, not often enough for me to have noticed. It might be part of the explanation, but it can’t be the whole story.

How many zombies does it take to screw in a light bulb?

I bumped this because every month or so I have to tighten nearly all the bulbs on our two faux-antique lamps, which have those cute little flame-shaped bulbs…but to njtt’s point, lots of our other bulbs stay seated. Why is that? Maybe tighter seating on some lamps makes it happen more quickly?

zombie or no

the center contact is often a bent metal that has spring effect, if it has springiness the bulb is tight then it might hold. if the center contact is a button or bent metal that has lost its springiness then the bulb may loosen quicker. also bulbs that are base up might loosen quicker due to gravity and friction (i.e. when they move away they do so loosening and stay that way).

if the center contact is a spring then you can give it more life. unplug the lamp or turn off the wall switch (put a piece of tape on it in the off position). sandpaper lightly the base and contacts to get shiny metal. with a needle nose pliers or small flat tip screwdriver bent the center contact up gently and ever so slightly. tighten bulb til snug without cranking it in.

I will occasionaly have to tighten the bulb in my lamp next to the bed, Also the ceiling light less frequently in my computer room. These are the two lights that go off and on most frequently.

I doubt it. If you heat an annulus, the hole on the middle gets bigger, not smaller.

The obvious answer, which no one has mentioned and is non Einsteinian, is invisible entities who are pulling your chain.