What might cause a lightbulb to explode while turned off?

Factual Questions
1

Scenario: the fixture is a ceiling fan with four tiltable track light style cans. The bulbs are GE soft white 45 watt floodlight bulbs. The fixture has a kitchen table underneath, not directly but offset from center so that the bulbs are just over the far side of the table. The near side of the table is two feet or so from the wall. The center of the fan is about five feet from the wall.

Two days ago I changed the dead bulb closest to the wall. This evening, I left just before 7. The fan lights in question had been on just before I left, but had been turned off. I returned around 11:30, and found the new lightbulb shattered on the floor next to the wall. The base of the bulb was still in the socket, and when I unthinkingly turned that light on, the bare filament smoked itself away.

Facts: There was no broken glass on the table or the chairs around it. If the bulb had managed to drop straight down, hit the table and not break until it landed on the tile floor, the fragments would not have been grouped several feet away along the wall. It is unlikely the bulb dropped straight down to the table, but was propelled out of its fixture towards the wall.

The fragments of glass were not directly in front of the fixture as if the bulb had been shot straight out of its can, but were about 2 feet to one side.

When I removed the base of the broken bulb from the fixture, the break was very clean all the way around the base. Very little glass protrudes above the metal.

It is certain that the bulb broke AFTER the switch had been turned off, because the filament was not burned up until I turned it back on.

The bulb did not break just as I turned the switch off, because the fragments happened to end up under the switch itself, and I would have been hit.

Turning off the light in question was one of the last things I did before I left the house. I heard nothing before closing the door.

There are no pets and were no other people in the house.

Anyone have any ideas as to how this happened? Could this just have been a defective bulb, or, given that I had just changed a burned out bulb, might it be worth checking out the fixture for problems?

2

Sounds like a defective bulb to me. Something in the factory probably grips it around the base and scored it by accident. After you left some little vibration in the house caused it to drop from the fixture, land on the table and as improbable as it seems, not break but roll off the table and hit the floor where it finally broke. I know it seems odd, but I just can’t fathom any way where the bulb could propel itself from the socket. For starters it’s under a vacuum so there’s no pressure in there for it to launch itself and without the metal and the extra glass inside it’s not going to weigh much. I could see it not breaking if it landed just right.

3

An exploding light bulb is a tungsten halogen or high-intensity discharge lamp, which ruptures explosively. Because these lamps operate with high pressure inside a high-temperature envelope, explosion can result in small pieces of hot glass ejected at high speed
1 Causes of bulb explosion
2 Hazards
3 Incidents
4 See also
5 Reference
[edit]Causes of bulb explosion

If the protective outer shell of a halogen lamp is broken, the inner hot bulb may explode due to contact with moisture. Touching the glass of a light bulb with one’s fingers leaves oils on the surface, which causes increased stress in the glass due to uneven temperature. This can lead to rupture of the glass, causing bulb explosion.Light bulb explosions are highly unpredictable. These explosions happen in both cold nonoperative and hot operative condition.

4

Maybe the wiring is not grounded well. Was there a lightning storm that day/night?

5

there likely was a stress that caused a crack to grow and the weight of the globe caused it to fracture and fall. those bulbs have thick glass and curved surfaces, they will sometimes bounce once.

6

This is my theory too. I was once replacing a bulb in a bathroom vanity. I accidentally dropped the bulb, which bounced off the laminate countertop and onto the linoleum floor. The glass did not break on either leg of the fall.

As for the cause of it dropping loose - some lightbulbs are simply glued to the metal part that screws in, and I have seen cases where the glass separated when I was trying to screw it in for the first time.

7

I wouldn’t be surprised if lightning cause a bulb to explode, but I would be surprised if it left the filament intact. The filament didn’t burn out until the OP turned the light back on.

8

Hi - I had the same thing happen to me - 4 bulb light fixture too. Lights had been off for a while as we went to bed at around 11pm and at 4am were awakened by the sound of shattered glass. My boyfriend woke up to check the house and found the light bulb had exploded.

Actually it seems more like it fell off and broke when it hit the dining room table beneath it because there was powder on the table from glass breaking when it hit it and the pieces of glass were large. Also the filament was intact - and didn’t burn out even after we turned on the lights. The metal part was still in the fixture.

It’s weird because we thought maybe the glass part came unglued from the metal but there was still glass attached to it - pretty close to the metal - not a lot of it left but still.

The lights had been off for hours already - freaked me out a little as it was 4am and I though someone was trying to break in when I heard the sound of glass shattering lol