# So why can't you touch a halogen bulb?
**URL:** https://boards.straightdope.com/t/so-why-cant-you-touch-a-halogen-bulb/57492
**Category:** Factual Questions
**Created:** [March 11, 2001, 1:17am UTC](https://boards.straightdope.com/t/so-why-cant-you-touch-a-halogen-bulb/57492 "2001-03-11T01:17:48Z")
**Posts on this page:** 9
**Page:** 1
### Author:  [@Miss\_Gretchen](https://boards.straightdope.com/u/Miss_Gretchen)
#### Post date: [March 11, 2001, 1:17am UTC](https://boards.straightdope.com/t/so-why-cant-you-touch-a-halogen-bulb/57492/1 "2001-03-11T01:17:48Z")
This is one of those things that “Everyone knows”- that if you touch a halogen bulb with your bare hands, it won’t work. I’ve asked people who’ve told me this to elaborate and the answer is usually “Because. That’s why.”, or something to that effect.
However, I know that this crowd is a lot smarter than the people I come into contact with (OK, for the most part 🙂 ), So can someone please explain?
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### Author:  [@Sue\_Duhnym](https://boards.straightdope.com/u/Sue_Duhnym)
#### Post date: [March 11, 2001, 1:37am UTC](https://boards.straightdope.com/t/so-why-cant-you-touch-a-halogen-bulb/57492/2 "2001-03-11T01:37:05Z")
WAG ALERT!!!
I always thought it was because you left oil or dust from your fingers on the bulb.
Maybe it has something to do with…well, you know how you can put a pan of water on to boil and it will boil faster if there’s something in it that serves as a place for the bubbles to start…I figured it had something to do with that. Somehow the oil or dust caused a weakness at that spot on the bulb when it got hot, resulting in breakage.
Then again, I’m pretty much an idiot, so I’m sure I’m wrong.
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### Author:  [@Miss\_Gretchen](https://boards.straightdope.com/u/Miss_Gretchen)
#### Post date: [March 11, 2001, 1:44am UTC](https://boards.straightdope.com/t/so-why-cant-you-touch-a-halogen-bulb/57492/3 "2001-03-11T01:44:30Z")
Yeah, but you still have a much better explanation than anyone I’ve met so far.
People seem to be under the impression that if you touch it it will (POOF!) not work.
Hmmm.
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### Author:  [@Lsura](https://boards.straightdope.com/u/Lsura)
#### Post date: [March 11, 2001, 1:44am UTC](https://boards.straightdope.com/t/so-why-cant-you-touch-a-halogen-bulb/57492/4 "2001-03-11T01:44:58Z")
From [http://www.pa.msu.edu/sci\_theatre/ask\_st/022394.html](http://www.pa.msu.edu/sci_theatre/ask_st/022394.html)
> [@](#):
>
> \*Halogen bulbs burn much brighter and produce much more heat than standard incandescent bulbs.
>
> When you touch one of these bulbs (never touch a light bulb while it is on), oil from your skin leaves a residue on the glass shell to the bulb. When the bulb is turned on, it begins to get hot. Much of this heat is dumped into the air around the bulb and is carried away.
>
> However, when there is oil on the bulb, it begins to get heated as well. The heat is actually enough to cause the oil to boil and its temperature can reach near 1,100 degrees Fahrenheit.
>
> This “hot spot” puts a great deal of heat near the glass bulb and can cause the glass in the hot spot to warp and stretch. This causes a weak spot in the glass bulb which can break and thus shorten the life time\*
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### Author:  [@friedo](https://boards.straightdope.com/u/friedo)
#### Post date: [March 11, 2001, 1:49am UTC](https://boards.straightdope.com/t/so-why-cant-you-touch-a-halogen-bulb/57492/5 "2001-03-11T01:49:55Z")
I don’t know if consumer halogen bulbs get this hot, but in my stage and movie lighting days, we never touched new lamps with our fingers because the oil will boil and rupture the glass, causing the lamp to explode. (I’ve seen this happen, it makes a hell of a mess.)
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### Author:  [@Miss\_Gretchen](https://boards.straightdope.com/u/Miss_Gretchen)
#### Post date: [March 11, 2001, 3:32am UTC](https://boards.straightdope.com/t/so-why-cant-you-touch-a-halogen-bulb/57492/6 "2001-03-11T03:32:47Z")
Wow. Thanks!
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### Author:  [@Zenster](https://boards.straightdope.com/u/Zenster)
#### Post date: [March 11, 2001, 6:28am UTC](https://boards.straightdope.com/t/so-why-cant-you-touch-a-halogen-bulb/57492/7 "2001-03-11T06:28:20Z")
There is another more fundamental process at work as well.
The oils left in your fingerprint also contain body salts and a host of other chemicals. There is a substantial amount of energy departing a halogen filament that is in the infrared region of the spectrum.
I would venture that most halogen bulbs have a quartz envelope. Quartz is virtually transparent to infrared light. If you cause any part of the quartz to become opaque, (i.e., leave a fingerprint on it) it is no longer able to transmit the infrared component of the optical spectrum and that energy is absorbed by the “glass” of the bulb.
The concentration of heat promotes a process known as “vitrification”. This drives a cascading reaction in the envelope of the bulb that causes a non-uniform or localized build-up of heat in one area of the lamp’s globe. The thermal stress involved can eventually shatter the bulb.
This same exact mechanism manifests in large “bell jar” type epitaxial reactors used in the semiconductor industry.
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### Author:  [@handy](https://boards.straightdope.com/u/handy)
#### Post date: [March 11, 2001, 4:09pm UTC](https://boards.straightdope.com/t/so-why-cant-you-touch-a-halogen-bulb/57492/8 "2001-03-11T16:09:51Z")
[http://www.howstuffworks.com/question151.htm](http://www.howstuffworks.com/question151.htm) :
“A halogen lamp also uses a tungsten filament, but it is encased inside a much smaller quartz envelope. Because the envelope is so close to the filament it would melt if it were made from glass. The gas inside the envelope is also different - it consists of a gas from the halogen group. These gases have a very interesting property - they combine with tungsten vapor! If the temperature is high enough, the halogen gas will combine with tungsten atoms as they evaporate and redeposit them on the filament. This recycling process lets the filament last a lot longer. In addition, it is now possible to run the filament hotter, meaning you get more light per unit of energy. You still get a lot of heat, though… And because the quartz envelope is so close to the filament it is EXTREMELY hot compared to a normal light bulb.”
I always thought you don’t touch them cause they are really really hot!
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### Author:  [@lawoot](https://boards.straightdope.com/u/lawoot)
#### Post date: [March 11, 2001, 4:31pm UTC](https://boards.straightdope.com/t/so-why-cant-you-touch-a-halogen-bulb/57492/9 "2001-03-11T16:31:33Z")
I’ve seen the oil effect on a halogen lamp (BTW - the correct term for the fixture is ‘lamp’, not ‘bulb’, damned if I can remember why off the top of my head), and i’ve seen glass ‘blisters’ that were wider than the main body of the lamp, with the filament pulled into the blister. Oddly enough, these tyhings will continue to burn, but you get an inferior , smudgy light out of it (stage instruments are VERY dependent on lamps being in the correct position).