# What gas is in a halogen light bulb

**URL:** <https://boards.straightdope.com/t/what-gas-is-in-a-halogen-light-bulb/337872>\
**Category:** Factual Questions\
**Created:** [December 31, 2005, 6:31pm UTC](https://boards.straightdope.com/t/what-gas-is-in-a-halogen-light-bulb/337872 "2005-12-31T18:31:07Z")\
**Posts on this page:** 5\
**Page:** 2

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**Author:** ![Tevildo](https://avatars.discourse-cdn.com/v4/letter/t/b9bd4f/32.png) [@Tevildo](https://boards.straightdope.com/u/Tevildo)\
**Post date:** [January 1, 2006, 8:18pm UTC](https://boards.straightdope.com/t/what-gas-is-in-a-halogen-light-bulb/337872/21 "2006-01-01T20:18:20Z")

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> [@psychonaut](#):
>
> Because they get very, very hot.You can get severely burned.
> 
> 😃

This side of it, I am aware of. 🙂

I see that [doubts have been cast](http://boards.straightdope.com/sdmb/showthread.php?t=351998) on the thesis that touching a cold bulb will reduce its life. I’ll be very interested to see the results of any subsequent experiment.

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**Author:** ![Ruken](https://avatars.discourse-cdn.com/v4/letter/r/f475e1/32.png) [@Ruken](https://boards.straightdope.com/u/Ruken)\
**Post date:** [January 1, 2006, 11:11pm UTC](https://boards.straightdope.com/t/what-gas-is-in-a-halogen-light-bulb/337872/22 "2006-01-01T23:11:31Z")

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> [@Padeye](#):
>
> Ordinary incandescent lamps are typically filled with vacuum. That’s why household bulbs pop when broken.

The pressure may be less than atmospheric, but it’s definately not a vacuum. If you put the bulb into a vacuum chamber it will explode ;). Having some gas in there helps prevent evaporation of the filament.

I read once that the filament is initially coated with some substance that is supposed to react with any residual oxygen the first time it is turned on. I’m having trouble varifying that at the moment.

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**Author:** ![HMS\_Irruncible](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hms_irruncible/32/7394_2.png) [@HMS\_Irruncible](https://boards.straightdope.com/u/HMS_Irruncible)\
**Post date:** [January 2, 2006, 12:13am UTC](https://boards.straightdope.com/t/what-gas-is-in-a-halogen-light-bulb/337872/23 "2006-01-02T00:13:22Z")

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> [@Ruken](#):
>
> The pressure may be less than atmospheric, but it’s definately not a vacuum. If you put the bulb into a vacuum chamber it will explode ;). Having some gas in there helps prevent evaporation of the filament.

Correct sir. Bulbs are filled with argon, nitrogen, or a similar fill. At what pressure I don’t know. Personally I think part of the reason they go “pop” when they break is that’s what thin glass bulbs do.

> [@](#):
>
> I read once that the filament is initially coated with some substance that is supposed to react with any residual oxygen the first time it is turned on. I’m having trouble varifying that at the moment.

It is worth noting that the filament itself is made of material that will react with any residual oxygen the first time it is turned on. Can’t see why they’d need an extra coating, of course that doesn’t mean it’s impossible.

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**Author:** ![Ruken](https://avatars.discourse-cdn.com/v4/letter/r/f475e1/32.png) [@Ruken](https://boards.straightdope.com/u/Ruken)\
**Post date:** [January 2, 2006, 12:40am UTC](https://boards.straightdope.com/t/what-gas-is-in-a-halogen-light-bulb/337872/24 "2006-01-02T00:40:08Z")

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> [@Brain Wreck](#):
>
> It is worth noting that the filament itself is made of material that will react with any residual oxygen the first time it is turned on. Can’t see why they’d need an extra coating, of course that doesn’t mean it’s impossible.

My guess is that a cheaper coating burning up means a longer filament lifetime. They could also have less stringent purity restrictions on the filler gas if they can just use up the oxygen with the coating. This is all I’ve found:

> [@](#):
>
> Incidentally, the filament in many incandescent bulbs is treated with a small amount of a phosphorus-based “getter” that reacts with any residual oxygen that may be in the bulb the first time the filament becomes hot. That’s how the manufacturer ensures that there will be no oxygen in the bulb for the tungsten filament to react with.

[link](http://howthingswork.virginia.edu/search.php?searchs=light+bulbs&searchq=yes&searcha=yes)

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**Author:** ![danceswithcats](https://avatars.discourse-cdn.com/v4/letter/d/9e8a1a/32.png) [@danceswithcats](https://boards.straightdope.com/u/danceswithcats)\
**Post date:** [January 2, 2006, 12:52am UTC](https://boards.straightdope.com/t/what-gas-is-in-a-halogen-light-bulb/337872/25 "2006-01-02T00:52:51Z")

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[This site](http://www.electrical-online.com/howtoarticles/Lighting/Halogen.htm) claims krypton to be the elemental gas. The thick plottens. 😉

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