light bulb blowout
August 25, 2005 11:58 PM   Subscribe

How do I fix a light fixture which causes a bulb to blow out, but only after a month or so?

I have a light fixture, a ceiling chandelier, which takes six 60-watt light bulbs, ordinary screw-in bulbs. One of the lights keeps blowing out. Not immediately but after a few weeks or a month. Andd once or twice it happened when I flick on the switch. The other five light sockets seem to be fine. I can understand if I had an immediate short circuit that blew out the bulb as soon as I turn on the swtich. But what could be causing this problem of substantially shorter life?
posted by mono blanco to Home & Garden (6 answers total)
Strange. Is there a water issue? Is that socket warmer than the others? Does it wiggle? I can not see how something electrical would cause this. A short would blow the fuse, not the bulb, and a surge would likely affect all the bulbs, not to mention other devices on the same circuit. However, a temperature, or perhaps a physical shock could do it.
posted by caddis at 1:04 AM on August 26, 2005

One more thought, a bad contact in the socket could be causing that bulb to lose power, or at least partly so, temporarily and the changes could stress the filament leading to early death. Is there corrosion in the socket or is it somehow physically different than the others?
posted by caddis at 1:13 AM on August 26, 2005

I'm also stumped as to what could be going on, so treat this post with that in mind - this is totally a long-shot - adding to caddis point - bad contacts in the other sockets, or higher resistance in their wiring (such as if the fixture had been repaired in past, with one socket rewired using much better wire than the old original stuff) would lead to that one bulb running slightly brighter than the rest, which wouldn't be a problem since it's designed to run on the mains, but if the mains circuit was on the edge of spec, or beyond, (or the bulbs used are all sub-standand) that could produce the effect, but it seems an unlikely hypothesis - you would be almost certain to have some other lights somewhere that also burn out quickly.

If you're able to disconnect the fixture and take it down, using a multimeter to check the wiring resistance to each bulb could give insight, but disconnecting the fixture is probably a lot more work than it's worth.
posted by -harlequin- at 1:29 AM on August 26, 2005

I agree with caddis, absent any visible flickering or obviously brighter bulbs, I'd suspect thermal or mechanical stress. Does the design of the chandelier cause the bulb in the "special" socket to run much hotter than the others? Does an air vent cause the bulb in the special socket to be subject to vibration due to air currents? Does water drip on one of the bulbs?

If you can't figure it out a simple fix would be to install a bulb in the special socket that is more resistant to thermal or mechanical stress. For example, try a long life, vibration resistant, or garage door bulb. Another possibility would be to replace the bulb with a halogen bulb (such as Philips Halogena) since their "capsule inside a bulb" design and operating principles make them much less suscentable to temperature and vibration problems. However, because a halogen bulb has a different physical appearance you'd probably want to replace all five bulbs. As a bonus, using halogen bulbs has the additional advantages of having to climb up to replace the bulbs much less often and slightly better energy efficiency.
posted by RichardP at 3:26 AM on August 26, 2005

All good points, and I'd suspect vibration as well. An operating filament is much weaker than a cool one, shaking a hot lamp is a fast way to destroy it.

Easiest way to check if it is the lamp: Two lamps.

Take two two lamps, with the same size and make lightbulbs (Ideally, two fresh ones from the same pack). Plug one lamp on a very long extension cord to another circuit, leave the suspect lamp where it is, and bring the test lamp into the same room as the suspect lamp. Then, turn them on and compare the light. They won't be exactly the same, lightbulbs aren't built to put out a precise amount of light, but they should be close. Obviously, major differences in lampshades would cause problems, so remove the lampshade. It'll be easier to see differences if you put something large and white the same distance behind the bulbs, and use your hand to block the direct view of the lightbulb.

If one of them is significantly brighter than the other, turn off both, switch the lightbulbs and try again. If the bright one is now the other lamp, you've got a difference in bulbs. If the brighter one is the same lamp, then there is something up with that lamp, and repair/replace according to your preferences and skills.

(Actually, to be thorough, if they are the same, switch the lightbulbs anyway and test again, in case you put a dim lightbulb into a "bright" lamp. If so, when you switch, one lamp will be very bright, the other much dimmer.)
posted by eriko at 6:04 AM on August 26, 2005

At the bottom of the socket is a metal tab that the bottom of the bulb contacts. Turn off the electricity and pry that tab up so it's not flattened. A flattened tab is the biggest cause of short bulb life.
posted by Mack Twain at 11:02 AM on August 26, 2005

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