what's the deal with touching a bulb?

[leon2245]

I remember reading here about if you touch your flashlights bulb there will be a problem from oil & dirt on your fingers etc. I was replacing my broken pocket clip, and when I went to put the head back on, the disc that holds the bulb inside fell entirely out. I think it's still O.K. (not broken), so I just put it back in there, but haven't turned it on yet.

What's the deal with that, do I have to buy a new bulb, or is it O.K. to just use now? Maybe that warning was just for a specific type of flashlight (this one is a S.F. Aviator).

 

[R@ndom]

Reduce performance and bulb life. Will still run. Clean with alcohol.

 

[abvidledUK]

Only really appertains to halogen bulbs, AFAIK.

In domestic fittings and security lights.

 

[Grox]

What it boils down to is that finger oils and dirt make the glass expand at a different rate, possibly causing a crack in the envelope.

Wipe the glass with pure alcohol and allow it to dry and it should be fine.

As abvidled alluded to this is only really a concern for incandescant lamp assemblies.

I've had quite a few A2 lamps and they've all been good for me.

 

[leon2245]

Allright thanks guys, I'll wipe it & go.

 

[Gunner12]

With smaller bulbs it shouldn't be a big problem. With the high pressure bulbs though, the oil will cause the glass to heat up un-evenly and can cause the bulb to explode.

If you are worried, as said before, alcohol should be good at cleaning things off.

 

[mudman cj]

According to a professor of ceramic engineering I had in college, the fracture is caused by differences in thermal expansion between the affected glass and the unaffected glass. The salts present on our fingers serve as seed crystals for the devitrification of the quartz glass into cristobalite. That's just fancy talk for the glass crystallizes into a new form. The new crystalline phase has a different thermal expansion coefficient than the glass, and therefore when it goes through a large temperature change, significant stresses can develop.

 

[GreyShark]

I blew up an 1185 that way because I didn't know any better. After that I wiped an 1166 bulb with my shirt and it's been running fine for several hours.

 

[chmsam]

Any high temp, high pressure lamp can have that happen. Usually halogen but also HID. Good practice to wipe down any bulb with an alcohol swab after coming anywhere near it.

I used to work with halogen lamps in AV/library equipment and even though I used cotton gloves to install or work on the lamps I'd wipe them down with alcohol. Forgot to do that once and the bulb must have been touched by the manufacturer or the seller. Watching one pop is exciting but not for the usual, fun reasons. The glass gets very hot, very quickly. After only a minute or so the bulb got hot enough so that when the glass popped it glued itself to the surfaces it hit. There's a reason those machines have a safety interlock -- the lamp cannot come on until the housing tray is inserted into the projector/reader.

And just for a frame of reference, that piece of equipment had a transformer that stepped down line current to a smokin' 12 volts. The smell of the hot glass was distinctive. Makes one remember that "poof" and "poop" are only one letter different if you catch my drift.