Author Topic: Why some Incandescent lamps tend to yellow ?  (Read 612 times)
Jovan
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Why some Incandescent lamps tend to yellow ? « on: July 22, 2020, 08:33:53 AM » Author: Jovan
Hello to everyone.I saw on some new(2017-2019) Philips incandescent bulbs that they tend to yellow inside ?As someone told me it can be some getter inside the bulb.What you think about this phenomenon and what causes it ?
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Re: Why some Incandescent lamps tend to yellow ? « Reply #1 on: July 22, 2020, 08:52:06 AM » Author: Binarix128
Maybe some very little quantity amount of air leaked into the bulb when the bulb was manufatured, and when you runned the lamp based up the heat created some chemical reactions with the gas and the glass, or the yellow thing is tungsten oxide or other compounds.
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Re: Why some Incandescent lamps tend to yellow ? « Reply #2 on: July 22, 2020, 09:58:03 AM » Author: dor123
This problem occurs mainly with carbon, tantalum, squirted, sintered and drawn tungsten filament lamps, as they have often air gettering process which leaves yellow coating on the bulb.
This phenomenon is almost non exists in coiled filament lamps, as these have an inert gas and not vacuum, and uses air gettering processes that don't leaves yellow coating.
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Re: Why some Incandescent lamps tend to yellow ? « Reply #3 on: July 22, 2020, 10:41:31 AM » Author: Jovan
Maybe some very little quantity amount of air leaked into the bulb when the bulb was manufatured, and when you runned the lamp based up the heat created some chemical reactions with the gas and the glass, or the yellow thing is tungsten oxide or other compounds.
Maybe but I'm using these 2 bulbs from November 2019 so if air leaked tungsten would react and burn out.
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Re: Why some Incandescent lamps tend to yellow ? « Reply #4 on: July 22, 2020, 02:16:12 PM » Author: Ash
It may be a limited quantity of air that got trapped inside during manufacture, not a leak. But i dont think it is air since actual air leak tends to make a white-ish smokey appearance, not yellow

I think it might be sputtering of phosphor coating from the filament (in some GLS lamps the phosphor getter is applied directly on the filament instead of on the stem)
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Re: Why some Incandescent lamps tend to yellow ? « Reply #5 on: July 22, 2020, 11:19:37 PM » Author: Medved
Some getter materials do that. Many makers place them so the yellowing does not affect the outer surface, but with some lamp construction that wont be possible (getter needs to be heated to activate it, so many apply them onto the filament, so first lamp power up does that)
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Re: Why some Incandescent lamps tend to yellow ? « Reply #6 on: July 23, 2020, 05:28:37 AM » Author: Jovan
One former worker at Tesla factory told me that bulbs tend to yellow because phosphor is appliend on tungsten wire and it evaporates and coats bulb in yellow which removes and burns any impurities.
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Re: Why some Incandescent lamps tend to yellow ? « Reply #7 on: July 23, 2020, 07:25:24 AM » Author: dor123
Isn't modern gasfilled incandescent lamps used other gettering methods to bake impurities?
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Re: Why some Incandescent lamps tend to yellow ? « Reply #8 on: July 23, 2020, 10:37:33 AM » Author: Medved
Isn't modern gasfilled incandescent lamps used other gettering methods to bake impurities?

It is more of a techniques how to make the Phosphorus getter to not cause staining in the area where it is visible and affect the lamp performance, but direct it e.g. on the stem,...
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Re: Why some Incandescent lamps tend to yellow ? « Reply #9 on: July 27, 2020, 06:16:13 PM » Author: James
Indeed the ginger colour is from phosphorus pentanitrile getter.  In case the lamps are of average or poor cleanliness, the getter reacts with the impurities when flashing and no colour is seen.  But if the lamps are unusually pure then there is no residual gas or vapour for the getter to react with, and it condenses as a ginger film on the bulb wall.  So these lamps are actually very pure and should give excellent life.  But in severe cases the getter can start absorbing light.  The machine setter should always tweak the concentration of his getter so as to find the optimal balance for the weather conditions (humidity) at the time of production, but not all are equally good at maintaining a perfect balance.
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Re: Why some Incandescent lamps tend to yellow ? « Reply #10 on: July 27, 2020, 06:27:05 PM » Author: Jovan
Indeed the ginger colour is from phosphorus pentanitrile getter.  In case the lamps are of average or poor cleanliness, the getter reacts with the impurities when flashing and no colour is seen.  But if the lamps are unusually pure then there is no residual gas or vapour for the getter to react with, and it condenses as a ginger film on the bulb wall.  So these lamps are actually very pure and should give excellent life.  But in severe cases the getter can start absorbing light.  The machine setter should always tweak the concentration of his getter so as to find the optimal balance for the weather conditions (humidity) at the time of production, but not all are equally good at maintaining a perfect balance.
Thanks for reply.This 60W works from 08.11.2019. on dimmer switch.Hope that it will last.
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Re: Why some Incandescent lamps tend to yellow ? « Reply #11 on: July 28, 2020, 08:10:51 AM » Author: Medved
Thanks for reply.This 60W works from 08.11.2019. on dimmer switch.Hope that it will last.

Well, it could be of exceptionaly pure lamp, in theory.
But (more plausible) I see it as an indication of general problems to maintain the purity (and generally processing quality control) on that line, with just quick and dirty fix by just overdosing the getter, to fix the most severe reliability problem (water catalyzed tungsten migration). But all other quality problems will remain.
And this generally bad process control will very likely not yield any exceptionaly long life at all, even when on dimmer (dimmer prolongs the life only when tungsten evaporation is the limitting factor).
But with poor quality manufacture, there will be other problems, not related to evaporation, limitting the lamp life, so the dimmer wont help.
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Re: Why some Incandescent lamps tend to yellow ? « Reply #12 on: July 28, 2020, 09:02:50 AM » Author: Xytrell
The other getters I've seen were flashed from a ring internal to the lamp. Incandescent lamps don't have this feature though, so where is the getter flashed FROM? A ring in the vacuum system that is removed when the glass is pinched off perhaps?
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Re: Why some Incandescent lamps tend to yellow ? « Reply #13 on: July 28, 2020, 10:28:17 AM » Author: Medved
The other getters I've seen were flashed from a ring internal to the lamp. Incandescent lamps don't have this feature though, so where is the getter flashed FROM? A ring in the vacuum system that is removed when the glass is pinched off perhaps?

Painted drop onto the filament was one popular method (gets activated by the filament heat once the lamp is fired the first time).
Unlike the hard vacuum getters used in vacuum tubes (where it has to capture pretty everything), the incandescent getter is specifically targetted mainly to water vapor, but to not obscure the light (and be cheaper)...
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Re: Why some Incandescent lamps tend to yellow ? « Reply #14 on: July 31, 2020, 08:34:36 AM » Author: Jovan
Painted drop onto the filament was one popular method (gets activated by the filament heat once the lamp is fired the first time).
Unlike the hard vacuum getters used in vacuum tubes (where it has to capture pretty everything), the incandescent getter is specifically targetted mainly to water vapor, but to not obscure the light (and be cheaper)...
Yes.In Tesla that was common practice.
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