bulb burnout


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Old 11-30-17, 02:28 PM
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bulb burnout

What would cause the phosphorous coating on the inside of a bulb to burn off. These bulbs were brought in by a customer. They were installed for about 3 days before burnout. These are appliance bulbs made for a refrigerator or a microwave. They are not from the same package and were purchased at different times. Also different brands.

I suggested it might be coincidence, and to try an ordinary incandescent bulb and see what happens. If it continues to happen, then measure the voltage at that socket. If voltage is within limits of 110v to 125v and bulbs continue to burnout then call an electrician.

Notice on one bulb the filament is still in tact, but will not light.


 
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Old 11-30-17, 02:47 PM
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The customer could take 2 more of the same bulbs, put one on a different circuit & one at a friends house. That might answer some of the questions.
 
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Old 11-30-17, 03:17 PM
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The hot bulbs got wet.
That same thing happens in outside fixtures that aren't watertight.
 
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Old 11-30-17, 06:29 PM
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Thanks, Pete. I believe that is the answer. Maybe it didn't get direct water on it but just outside moisture would be enough. A refrigerator usually is frost free or would have a moisture tight globe on it.
 
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Old 11-30-17, 06:30 PM
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Connections in the base of the bulb could fail causing the bulb to not work even when the filament looks intact.

The most likely place for such a failure is actually visible. A thin wire comes out where the metal base meets the glass and is bent over and welded on.
 
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Old 11-30-17, 06:35 PM
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That wire you refer to looks in tact on both bulbs.
 
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Old 11-30-17, 07:16 PM
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When I volunteered at the historical museum I would often change out bulbs that looked just like that. I determined the cause was a breaking of the airtight seal allowing air inside the bulb.

The bulbs we used were from traffic control lights and they were made to operate in a "sideways" configuration. When done so, or in a "base down" configuration they would last for years but in a "base up" configuration they often wouldn't last a month. It had to do with the heat of the bulb affecting the cement used in the base.
 
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Old 11-30-17, 07:25 PM
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base down" configuration they would last for years but in a "base up" configuration they often wouldn't last a month
Good point. If they stop in again I'll ask what direction the bulbs were in.

On further inspection, both bulbs may be the same brand (cheap, Philips vs SATCO) and that may be the cause. That coupled with the outdoor moisture problem. That may also explain why the one bulb has the filament still intact.

Side note..Many years ago I had a bare bulb burning as I was doing some work. A drop of water hit the top. No explosion or breaking. just a hole and the bulb went bright and out.
 
 

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