snopes.com  

Go Back   snopes.com > Urban Legends > Science

Reply
 
Thread Tools Display Modes
  #1  
Old 14 April 2009, 10:02 PM
snopes's Avatar
snopes snopes is offline
 
Join Date: 18 February 2000
Location: California
Posts: 107,977
Glasses Don't touch light bulbs

Comment: I have been told for years that it shortens the lifespan of some
lightbulbs if you touch it with your fingers. Apparently the oils of your
fingers can somehow cause the filament to burn out earlier. Some quartz
lamps come with instructions to avoid touching the bulb and a piece of
foam to handle them with.
I have always been skeptical of this and cannot imagine how it could
damage the metal element, which is 1/4" or more away from the glass tube.
Reply With Quote
  #2  
Old 14 April 2009, 10:06 PM
chillas's Avatar
chillas chillas is offline
 
Join Date: 09 September 2002
Location: Columbus, OH
Posts: 11,147
Default

It doesn't do anything to the filament, but the oils combined with the heat from the bulb once turned on can damage the glass. That damage can be enough to cause the bulb to break.
Reply With Quote
  #3  
Old 14 April 2009, 10:13 PM
jimmy101_again jimmy101_again is offline
 
Join Date: 29 December 2005
Location: Greenwood, IN
Posts: 4,882
Default

I'm not sure about the direct affect of fingerprints on the life of the filament. I do know that with certain types of bulbs the life of the glass shell can be significantly shortened if it is handled with damp/oily hands. The thin film of oil left on the glass changes the thermal characteristics of the glass. When the bulb is turned on the glass undergoes pretty significant thermal stress as it heats up. A patch of the glass with an oily finger print on it heats up slower since the oil has to be vaporized or burned off. That creates a large amount of thermal stress in the glass. It doesn't take much stress to shatter the glass or create a hairline crack.

A cracked bulb won't last long since the inert atmosphere that it is supposed to be in the bulb escapes and is replaced by air. A light bulb filament will only last a second or two in air if power is applied.

Usually the admonition to touching the glass of the bulb is for high power lamps like quartz bulbs or the bulbs used in projectors. Those high power lamps generate a lot of heat, and therefore a lot of thermal stress in their envelopes, when they are on.
Reply With Quote
  #4  
Old 14 April 2009, 11:46 PM
Latiam's Avatar
Latiam Latiam is offline
 
Join Date: 19 June 2005
Location: Ontario, Canada
Posts: 3,881
Default

Both halogen bulbs and the bulbs in light projectors say not to touch the bulb. And theatre lights that are touched grow grossly mutated and then break, so the same goes for them. (At least, that's what I was told when I was crew for a few plays).
Reply With Quote
  #5  
Old 15 April 2009, 06:38 AM
Troberg Troberg is offline
 
 
Join Date: 04 November 2005
Location: Borlänge, Sweden
Posts: 11,368
Default

Quote:
Originally Posted by chillas View Post
It doesn't do anything to the filament, but the oils combined with the heat from the bulb once turned on can damage the glass. That damage can be enough to cause the bulb to break.
Exactly, but it's only an issue for high performance bulbs, like headlights or projectors. For ordinary light bulbs, it's not a problem.
Reply With Quote
  #6  
Old 15 April 2009, 12:51 PM
chillas's Avatar
chillas chillas is offline
 
Join Date: 09 September 2002
Location: Columbus, OH
Posts: 11,147
Default

Quote:
Originally Posted by Troberg View Post
Exactly, but it's only an issue for high performance bulbs, like headlights or projectors. For ordinary light bulbs, it's not a problem.
Yes, exactly. I meant to mention that in my post but forgot.
Reply With Quote
  #7  
Old 15 April 2009, 12:57 PM
A Cat Named Easter's Avatar
A Cat Named Easter A Cat Named Easter is offline
 
Join Date: 19 August 2005
Location: Frederick, MD
Posts: 541
Default

I think it's worth mentioning that this also applies to car headlamp bulbs. Vinyl or latex gloves work well if you need to change those.
Reply With Quote
  #8  
Old 15 April 2009, 04:18 PM
jimmy101_again jimmy101_again is offline
 
Join Date: 29 December 2005
Location: Greenwood, IN
Posts: 4,882
Default

Quote:
Originally Posted by A Cat Named Easter View Post
I think it's worth mentioning that this also applies to car headlamp bulbs. Vinyl or latex gloves work well if you need to change those.
Actually, it only applies to the modern type headlights where the bulb is separate from the reflector and front lense. With the more traditional headlight design, the "sealed headlight", you can handle the "bulb" with your bare hands all you want. Once installed the bulb is going to be subjected to rain, snow, road spray, salt etc. anyway so a few grungy fingerprints isn't going to make and difference.
Reply With Quote
  #9  
Old 16 April 2009, 06:06 AM
Troberg Troberg is offline
 
 
Join Date: 04 November 2005
Location: Borlänge, Sweden
Posts: 11,368
Default

Quote:
Originally Posted by jimmy101_again View Post
Actually, it only applies to the modern type headlights where the bulb is separate from the reflector and front lense. With the more traditional headlight design, the "sealed headlight", you can handle the "bulb" with your bare hands all you want. Once installed the bulb is going to be subjected to rain, snow, road spray, salt etc. anyway so a few grungy fingerprints isn't going to make and difference.
How old is the "traditional" design? I've never seen it on any of my cars, and the oldest has been a 1979 model.
Reply With Quote
  #10  
Old 16 April 2009, 06:10 AM
me, no really's Avatar
me, no really me, no really is offline
 
Join Date: 02 June 2005
Location: Brisbane, Australia
Posts: 2,298
Default

Quote:
Originally Posted by Troberg View Post
How old is the "traditional" design? I've never seen it on any of my cars, and the oldest has been a 1979 model.
I had a 1971 Corolla that had sealed beam headlights.

me
Reply With Quote
  #11  
Old 15 July 2009, 07:29 PM
Debunker's Avatar
Debunker Debunker is offline
 
Join Date: 29 September 2003
Location: Yorba Linda, CA
Posts: 417
Default

Many years ago I worked on Navy display equipment. One of these was a large screen projector that used a xenon arc lamp (used today on IMAX projectors, among others). We were experiencing a larger than expected amount of catastrophic lamp failures. Analysis showed oils from fingers would create hot spots on the glass that caused the glass to crack so that there was no vacuum inside. I don't think they exploded, per se, just died. We had to change the replacement instructions to include a caution about avoiding touching the lamps with bare fingers. Once that was in place, the failure rate was reduced significantly.

Last edited by Debunker; 15 July 2009 at 07:30 PM. Reason: Fix typo
Reply With Quote
  #12  
Old 15 July 2009, 07:45 PM
htonl's Avatar
htonl htonl is offline
 
Join Date: 19 July 2006
Location: Cape Town, South Africa
Posts: 1,527
Default

Some of the compact flourescent bulbs in my cupboard also have labels with pictorial instructions that tell you to screw them in holding the "base" part and not the tubes. Is this for the same reason? Or is it just the possibility that someone might grip the tubes too hard and break them?
Reply With Quote
  #13  
Old 15 July 2009, 08:05 PM
Alchemy Alchemy is offline
 
Join Date: 05 March 2001
Location: Plymouth, MI
Posts: 4,267
Default

Quote:
Originally Posted by htonl View Post
Or is it just the possibility that someone might grip the tubes too hard and break them?
Probably that. CF bulbs operate much cooler than incandescent bulbs.
Reply With Quote
  #14  
Old 15 July 2009, 08:35 PM
Eddylizard's Avatar
Eddylizard Eddylizard is offline
 
Join Date: 15 June 2006
Location: Tonbridge, Kent, UK
Posts: 17,861
Default

I think the advice only applies to halogen lamps, which AFAIK are only fitted in car headlamps. They run pretty hot - I can feel the heat from mine if I put my hand a foot away from the headlamp.

I don't think there is any damage one can cause by handling a bog standard incandescent lamp with bare fingers.
Reply With Quote
  #15  
Old 15 July 2009, 08:55 PM
Arriah's Avatar
Arriah Arriah is offline
 
Join Date: 15 August 2005
Location: Everett, WA
Posts: 3,380
Default

You can get halogens for regular lamps too but they're for halogen lamps that take nothing else. I've had them before and the packages for the bulbs had the warning about not touching them directly. They do get pretty darn hot though and they suck power like there's no tomorrow so we don't use those lamps anymore. CFLs all the way!

ETA: They did have the advantage of being pretty inexpensive dimmable floor lamps though, they were way cool, just really hot and power sucking.
Reply With Quote
  #16  
Old 16 July 2009, 02:23 AM
Singing in the Drizzle Singing in the Drizzle is offline
 
Join Date: 24 November 2005
Location: Bellingham, WA
Posts: 4,196
Default

I have only seen the warning on light that are very hot like the halogens. The oil from you finger will create a hot spot relative to the rest of the crystal tube. This can cause stress in the tube will cause it to crack and shorten its life.

If you do happen to touch it bulb, cleaning it with alcohol and clean cloth will fix the problem.
Reply With Quote
  #17  
Old 16 July 2009, 03:03 AM
FullMetal FullMetal is offline
 
Join Date: 19 December 2005
Location: Edmonton, AB
Posts: 1,228
Default

i think it's only applicable to high temp lamps. like halogens or projector bulbs,

as for sealed beam headlights? my dad's 91 Mazda Pickup had them. also as late as 95 the Chev S-10 (GMC Sonoma, and their Blazer/jimmy Counterparts) had them,

Also most automobile halogen bulbs are inserted from behind, negating the need to touch the bulb at all.
Reply With Quote
  #18  
Old 16 July 2009, 04:24 AM
Roadsterboy's Avatar
Roadsterboy Roadsterboy is offline
 
Join Date: 13 September 2007
Location: Illinois
Posts: 3,803
Default

Quote:
Originally Posted by Troberg View Post
How old is the "traditional" design? I've never seen it on any of my cars, and the oldest has been a 1979 model.
Sealed beams are far more common on U.S. market cars, and were required here until 1983, at which point replaceable bulb headlights were allowed. For instance, many older British cars used the Lucas "tripod" lights in European markets, but sealed beams here (there's a bit of a market for kits to replace the sealed beams with tripods). They were still fairly common though-my '96 Miata uses sealed beams (the traditional round ones, same as my '71 MG).

-RB
Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On

Forum Jump


All times are GMT. The time now is 09:45 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.