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Trivial question for electricians

Just a quick question for any electicians or the like out there: In the summer I work construction, and I've noticed something odd. Before the ductwork goes up in a house (that's my job), the electricians put in temporary lightbulbs, so we can see in the basement. They just screw the fixture to a support beam. The bulbs are regular 60w incandescent bulbs, like you'd see in a household fixture. I've noticed that when I hammer on the beam that the bulbs are on, they will often get noticeably brighter after a couple hits, usually followed by blowing out. Anyone know why this is? My only idea is that maybe the filliament gets stretched somehow due to the vibration, and it glows brighter because there's more resistance created? I'm no electrician, so I don't know if that even makes sense. Any thoughts? ~Nick

Reply to
Trickynick1001
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My guess has always been that the filament gets caught on something, causing a short circuit - so you've got, say, 50% of the filament carrying all the current (which is now twice as much).

Reply to
DJ Delorie

That's what I thought, except the cause being two segments of the filament touching and welding themselves together.

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John
Reply to
John O'Flaherty

The resistance is actually going down as the tension on the filament draws the spring-like unit closer. When I was a kid I would do that on purpose, my Father didn't like it much.

Tom

Reply to
Tom Biasi 

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If its resistance were to increase it would get dimmer, so I think
what\'s happening is that the vibration and shock is causing turns to
be shorted together, making the resistance lower, allowing more
current to flow through the filament, causing it to glow brighter and
shortening its life

JF
Reply to
John Fields

The filaments in ordinary light bulbs are held in place in only a couple spots, and they can stretch and short out easily from shock and vibration when incandescent. Ruggedized lamps have more supports, and are more resistant to to such abuse as experienced in portable lighting (but are less efficient because more heat is drawn from the filament). But even better now are the more efficient fluorescent lamps (but there is still risk of breakage, with some mercury release), so the best technology at present is LEDs. They are remarkably rugged and also will work at wide temperature extremes that are not tolerated by fluorescents.

Paul

Reply to
Paul E. Schoen

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