# Don't touch the Bulb! **URL:** \ **Category:** Factual Questions\ **Created:** [July 1, 2008, 10:09am UTC](https://boards.straightdope.com/t/dont-touch-the-bulb/454877 "2008-07-01T10:09:44Z")\ **Posts on this page:** 19\ **Page:** 2
**Author:** ![Daren66](https://avatars.discourse-cdn.com/v4/letter/d/3d9bf3/32.png) [@Daren66](https://boards.straightdope.com/u/Daren66)\ **Post date:** [May 17, 2016, 2:41am UTC](https://boards.straightdope.com/t/dont-touch-the-bulb/454877/21 "2016-05-17T02:41:54Z")
Okay. I used to work at Osram Sylvania where all halogen headlamps are made; in Hillsboro, NH for a number of years. Having worked there with the “burners” A.K.A. lamp portion of the headlights, I can maybe shed a little light: 1) the glass used in MFG of them is ~ .100 thick wall; 2) is annealed at ~ 1630 F gradually up to that and back down to room temperature - simplified version - during part of its process before becoming what you see from a tube of Corning glass; 3) contains quartz. BUT the burner should never be touched by a bare set of fingers. Why? The fingers WILL leave oils, salts, etc. behind which will shorten the life of the lamp. The HBR gas mixture inside is at 8 ATMS +/- .4 and excites the tungsten filament to an extremely high temperature around it. Any oils left behind from a fingerprint will cause a local hot spot outside, and due to the transference laws of thermodynamics LOL, inside. The life of the burner is heavily dependent on the filament maintaining a temperature (insert material science nerd speak here) hence why a very hard, brittle material like tungsten does a fine job - too hot = shorter life of the filament…in a nutshell. ---
**Author:** ![Isilder](https://avatars.discourse-cdn.com/v4/letter/i/cc9497/32.png) [@Isilder](https://boards.straightdope.com/u/Isilder)\ **Post date:** [May 17, 2016, 3:53am UTC](https://boards.straightdope.com/t/dont-touch-the-bulb/454877/22 "2016-05-17T03:53:10Z")
> [@CalMeacham](#): > > , but I HAVE seen my fingerprints neatly etched into the sides of quartz crucibles (that I thought had been cleaned) that I used for growing alkali halide crystals. These were taken to much higher temperatures – around 700-800 degrees C. And, even so, they didn’t compromise the integrity of the crucible. I have to assume that the bulb manufacturers are just being extra cautious. See, the very thin glass of the single glass halogen lamp is going to break when the fingerprint collects more heat , OR the fingerprint etches the glass… So the glass is affected by differences in expansion , due to different termperatures, and by the etching weakening it… Note that if the halogen gas bulb is enclosed with a larger cover, the larger cover is at a lower temperature… That is, the halogen lamps in incandescent standard sizes/sockets are actually a smaller halogen lamp inside a larger case… the high temperature is at the small bulb inside… ---
**Author:** ![Czarcasm](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/czarcasm/32/4050_2.png) [@Czarcasm](https://boards.straightdope.com/u/Czarcasm)\ **Post date:** [May 17, 2016, 6:46am UTC](https://boards.straightdope.com/t/dont-touch-the-bulb/454877/23 "2016-05-17T06:46:33Z")
> [@Daren66](#): > > Okay. I used to work at Osram Sylvania where all halogen headlamps are made; in Hillsboro, NH for a number of years. Having worked there with the “burners” A.K.A. lamp portion of the headlights, I can maybe shed a little light: 1) the glass used in MFG of them is ~ .100 thick wall; 2) is annealed at ~ 1630 F gradually up to that and back down to room temperature - simplified version - during part of its process before becoming what you see from a tube of Corning glass; 3) contains quartz. BUT the burner should never be touched by a bare set of fingers. Why? The fingers WILL leave oils, salts, etc. behind which will shorten the life of the lamp. The HBR gas mixture inside is at 8 ATMS +/- .4 and excites the tungsten filament to an extremely high temperature around it. Any oils left behind from a fingerprint will cause a local hot spot outside, and due to the transference laws of thermodynamics LOL, inside. The life of the burner is heavily dependent on the filament maintaining a temperature (insert material science nerd speak here) hence why a very hard, brittle material like tungsten does a fine job - too hot = shorter life of the filament…in a nutshell. Welcome to the SDMB, and thank you for shedding light on the situation. I found your post illuminating. ---
**Author:** ![Robot\_Arm](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/robot_arm/32/18280_2.png) [@Robot\_Arm](https://boards.straightdope.com/u/Robot_Arm)\ **Post date:** [May 17, 2016, 7:56am UTC](https://boards.straightdope.com/t/dont-touch-the-bulb/454877/24 "2016-05-17T07:56:14Z")
> [@Czarcasm](#): > > Welcome to the SDMB, and thank you for shedding light on the situation. I found your post illuminating. Got any more bright ideas? ---
**Author:** ![ticker](https://avatars.discourse-cdn.com/v4/letter/t/d07c76/32.png) [@ticker](https://boards.straightdope.com/u/ticker)\ **Post date:** [May 17, 2016, 8:51am UTC](https://boards.straightdope.com/t/dont-touch-the-bulb/454877/25 "2016-05-17T08:51:42Z")
Normal bulbs use a glass which has sodium added to it, as does regular glass used for windows, bottles etc. The sodium ions lower the melting point of the glass and also makes the melt less viscous and easy to work. Unfortunately this also increases its thermal expansion and vulnerable to breakage due to thermal shock. Halogen bulbs run much hotter than regular bulbs so normal glass will not work. Consequently they use a much purer silica glass, often referred to as quartz glass, because of its superior thermal properties. If you allow your sweat to contact the glass some of the sodium ions from the salt will leach into the glass so that you have regions in the structure with a higher thermal expansion coefficient than the rest, leading to cracking and failure. ---
**Author:** ![Fridgemagnet](https://avatars.discourse-cdn.com/v4/letter/f/22d042/32.png) [@Fridgemagnet](https://boards.straightdope.com/u/Fridgemagnet)\ **Post date:** [May 17, 2016, 11:03am UTC](https://boards.straightdope.com/t/dont-touch-the-bulb/454877/26 "2016-05-17T11:03:15Z")
> [@ticker](#): > > Normal bulbs use a glass which has sodium added to it, as does regular glass used for windows, bottles etc. The sodium ions lower the melting point of the glass and also makes the melt less viscous and easy to work. Unfortunately this also increases its thermal expansion and vulnerable to breakage due to thermal shock. > > Halogen bulbs run much hotter than regular bulbs so normal glass will not work. Consequently they use a much purer silica glass, often referred to as quartz glass, because of its superior thermal properties. If you allow your sweat to contact the glass some of the sodium ions from the salt will leach into the glass so that you have regions in the structure with a higher thermal expansion coefficient than the rest, leading to cracking and failure. An optical physicist colleague once told me about the sodium ion migration thing, though I did misinterpret his statement and for a while I believed that the sodium ions migrated all the way through the envelope and interfered with the halogen cycle. Local sodium contamination of the glass sounds much more plausible though. This is one of those little snippets of information where my google-fu fails me, and I have found it very difficult to find a reputable cite for the effects of sodium ions on halogen bulbs, so it’s nice to have my colleague’s information corroborated; cheers **ticker**. ---
**Author:** ![lance\_strongarm](https://avatars.discourse-cdn.com/v4/letter/l/87869e/32.png) [@lance\_strongarm](https://boards.straightdope.com/u/lance_strongarm)\ **Post date:** [May 17, 2016, 3:36pm UTC](https://boards.straightdope.com/t/dont-touch-the-bulb/454877/27 "2016-05-17T15:36:42Z")
> [@Mangetout](#): > > In some cases, grease residues from your fingers can cause the glass to heat unevenly and melt or crack - usually, this advice applies to bright halogen lamps, That’s what I’ve heard too. ---
**Author:** ![Tim\_T-Bonham.net](https://avatars.discourse-cdn.com/v4/letter/t/46a35a/32.png) [@Tim\_T-Bonham.net](https://boards.straightdope.com/u/Tim_T-Bonham.net)\ **Post date:** [May 17, 2016, 4:20pm UTC](https://boards.straightdope.com/t/dont-touch-the-bulb/454877/28 "2016-05-17T16:20:23Z")
> [@gazpacho](#): > > When I did high school theater we we told not to touch the bulbs because the oils would cause the bulbs to fail. There were a few bulbs we kept around because they had a spot on the side which had softened and the pressure from the hot interior had caused the bulb to expand there. It looked like the bulb was preparing to spawn another bulb asexually. I was told the same thing, in high school & college theatre. I think the “don’t touch” applies to any bulb that normally runs very hot. That includes theatre lighting equipment, but halogens are probably the only normal household lamps where this would apply. ---
**Author:** ![Chefguy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chefguy/32/138_2.png) [@Chefguy](https://boards.straightdope.com/u/Chefguy)\ **Post date:** [May 17, 2016, 4:27pm UTC](https://boards.straightdope.com/t/dont-touch-the-bulb/454877/29 "2016-05-17T16:27:53Z")
After eight years, has anyone figured out if this applies to halogen bulbs? ---
**Author:** ![RealityChuck](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/realitychuck/32/195_2.png) [@RealityChuck](https://boards.straightdope.com/u/RealityChuck)\ **Post date:** [May 17, 2016, 5:17pm UTC](https://boards.straightdope.com/t/dont-touch-the-bulb/454877/30 "2016-05-17T17:17:24Z")
The jury is still out. Someone may come by and shed light on the matter, if he’s fairly bright. ---
**Author:** ![bump](https://avatars.discourse-cdn.com/v4/letter/b/7c8e57/32.png) [@bump](https://boards.straightdope.com/u/bump)\ **Post date:** [May 17, 2016, 5:34pm UTC](https://boards.straightdope.com/t/dont-touch-the-bulb/454877/31 "2016-05-17T17:34:49Z")
Yes- halogen bulbs, in the sense of the [little tubular jobs](http://www.amazon.com/GE-Lighting-19379-300-Watt-Double-Ended/dp/B00006IBF4/ref=pd_bxgy_60_img_2?ie=UTF8&refRID=1DVG05SBK2A05WB450NZ)that were all the rage in [mid-1990s light fixtures](http://www.amazon.com/ORE-International-3030BK-Halogen-Torchiere/dp/B002S6CF0M). Not so much in the sense of [the halogen bulbs that look like a classic light bulb](http://www.amazon.com/TCP-Standard-Household-Equivalent--442243B4CLV/dp/B00T6RZWBA/ref=sr_1_5?s=hi&ie=UTF8&qid=1463506443&sr=1-5&keywords=halogen+60watt+bulb). Those are basically one of the little tubular jobs inside of a light-bulb shaped outer shell, so getting fingerprints on the outer shell doesn’t do any harm. (you can actually see how it’s laid out in the link) ---
**Author:** ![Chefguy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chefguy/32/138_2.png) [@Chefguy](https://boards.straightdope.com/u/Chefguy)\ **Post date:** [May 17, 2016, 6:35pm UTC](https://boards.straightdope.com/t/dont-touch-the-bulb/454877/32 "2016-05-17T18:35:19Z")
> [@bump](#): > > Yes- halogen bulbs, in the sense of the [little tubular jobs](http://www.amazon.com/GE-Lighting-19379-300-Watt-Double-Ended/dp/B00006IBF4/ref=pd_bxgy_60_img_2?ie=UTF8&refRID=1DVG05SBK2A05WB450NZ)that were all the rage in [mid-1990s light fixtures](http://www.amazon.com/ORE-International-3030BK-Halogen-Torchiere/dp/B002S6CF0M). > > Not so much in the sense of [the halogen bulbs that look like a classic light bulb](http://www.amazon.com/TCP-Standard-Household-Equivalent--442243B4CLV/dp/B00T6RZWBA/ref=sr_1_5?s=hi&ie=UTF8&qid=1463506443&sr=1-5&keywords=halogen+60watt+bulb). Those are basically one of the little tubular jobs inside of a light-bulb shaped outer shell, so getting fingerprints on the outer shell doesn’t do any harm. (you can actually see how it’s laid out in the link) Bit of a whoosh, I’m afraid, sir. ---
**Author:** ![wolfman](https://avatars.discourse-cdn.com/v4/letter/w/a8b319/32.png) [@wolfman](https://boards.straightdope.com/u/wolfman)\ **Post date:** [May 17, 2016, 8:02pm UTC](https://boards.straightdope.com/t/dont-touch-the-bulb/454877/33 "2016-05-17T20:02:05Z")
I have found the reverse interaction to be the more critical to remember when touching the bulb, ie fuck the integrity of the bulb, it’s the integrity of my finger as it singes and blisters touching a halogen gbulb that was just on. ---
**Author:** ![Senegoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/senegoid/32/6606_2.png) [@Senegoid](https://boards.straightdope.com/u/Senegoid)\ **Post date:** [May 17, 2016, 8:19pm UTC](https://boards.straightdope.com/t/dont-touch-the-bulb/454877/34 "2016-05-17T20:19:50Z")
> [@kunilou](#): > > You forgot . . . Also the Doper who chimes in to tell us it’s all [current President’s or Stupid Republicans’] fault, and another rebuke from moderator for political jabs while changing light bulbs. ---
**Author:** ![Snnipe\_70E](https://avatars.discourse-cdn.com/v4/letter/s/b5a626/32.png) [@Snnipe\_70E](https://boards.straightdope.com/u/Snnipe_70E)\ **Post date:** [May 18, 2016, 5:09am UTC](https://boards.straightdope.com/t/dont-touch-the-bulb/454877/35 "2016-05-18T05:09:00Z")
> [@Colophon](#): > > I have never heard this advice for regular incandescent light bulbs, but it is common advice with halogen bulbs, e.g. car headlamps. > > There is no “flow of gas” in a regular bulb - the gas is purely an inert atmosphere to stop the filament from oxidising. > > However, [Wikipedia](http://en.wikipedia.org/wiki/Halogen_lamp#Handling_precautions) says that fingerprints can cause the glass to weaken, but this relates only to high-temperature halogen bulbs I think. Agree with this. ---
**Author:** ![Ranger\_Jeff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ranger_jeff/32/2065_2.png) [@Ranger\_Jeff](https://boards.straightdope.com/u/Ranger_Jeff)\ **Post date:** [May 18, 2016, 7:15am UTC](https://boards.straightdope.com/t/dont-touch-the-bulb/454877/36 "2016-05-18T07:15:00Z")
I think not touching with bare fingers applies to all light bulbs that normally operate at a high temperature. I recall stickers warning not to touch the lamps in film projectors and also in theatrical lighting fixtures and follow spots. And in lighthouses also. ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [May 19, 2016, 12:00am UTC](https://boards.straightdope.com/t/dont-touch-the-bulb/454877/37 "2016-05-19T00:00:31Z")
> [@Colophon](#): > > There is no “flow of gas” in a regular bulb - the gas is purely an inert atmosphere to stop the filament from oxidising. The gas in a light bulb _does_ flow in circular paths due to convection. These convection currents carry heat away from the filament, and thus decrease the efficiency of the bulb. Double helix filaments, a.k.a. “coiled coil” filaments, were invented to help reduce the amount of heat transferred from the filament to the gas, thereby increasing its efficiency. ---
**Author:** ![Jumpbass](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jumpbass/32/147_2.png) [@Jumpbass](https://boards.straightdope.com/u/Jumpbass)\ **Post date:** [May 19, 2016, 3:47pm UTC](https://boards.straightdope.com/t/dont-touch-the-bulb/454877/38 "2016-05-19T15:47:35Z")
> [@Mathochist](#): > > Five > > One to answer the question > One to point out the hidden assumptions > One to answer the question given the new assumptions > One to cite Unca Cece’s answer in the column > One to say the first four are all idiots and get the thread Pitted. One to link to an XKCD strip. ---
**Author:** ![Accidental\_Martyr](https://avatars.discourse-cdn.com/v4/letter/a/ce7236/32.png) [@Accidental\_Martyr](https://boards.straightdope.com/u/Accidental_Martyr)\ **Post date:** [May 19, 2016, 7:23pm UTC](https://boards.straightdope.com/t/dont-touch-the-bulb/454877/39 "2016-05-19T19:23:35Z")
> [@Senegoid](#): > > Also the Doper who chimes in to tell us it’s all [current President’s or Stupid Republicans’] fault, and another rebuke from moderator for political jabs while changing light bulbs. Have we heard from anyone who makes their own light bulbs cheaper and better at home? [Previous page](https://boards.straightdope.com/t/dont-touch-the-bulb/454877.md?page=1)