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Sci.Electronics.Basics -> Trivial question for electricians
There are 6 messages in this thread.
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Author: Trickynick1001Date: 15:09 03-04-08
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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
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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).
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Author: John O'FlahertyDate: 16:00 03-04-08
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On 03 Apr 2008 15:56:16 -0400, DJ Delorie <dj@delorie.com> wrote:
>
>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).
That's what I thought, except the cause being two segments of the
filament touching and welding themselves together.
--
John
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Author: Tom BiasiDate: 17:01 03-04-08
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"Trickynick1001" <stargoatee@gmail.com> wrote in message
news:178cfe47-e03a-45b1-bc63-f0b57721731c@q27g2000prf.googlegroups.com...
> 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
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
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Author: John FieldsDate: 18:25 03-04-08
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On Thu, 3 Apr 2008 12:09:14 -0700 (PDT), Trickynick1001
<stargoatee@gmail.com> wrote:
>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?
---
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
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Author: Paul E. SchoenDate: 02:57 04-04-08
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"John Fields" <jfields@austininstruments.com> wrote in message
news:6bmav39vvq892oeajov1f45nbcgd097k3j@4ax.com...
> On Thu, 3 Apr 2008 12:09:14 -0700 (PDT), Trickynick1001
> <stargoatee@gmail.com> wrote:
>
>>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?
>
> ---
> 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
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
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