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When consulting manuals, electricians, online sources, etc., they always instruct you to handle halogen light bulbs with gloves.

The "explanation" that usually accompanies this statement is that oils and salts from a bare hand can "react" with the surrounding glass/quartz, owing to the fact that halogen bulbs are much hotter than ordinary ones. These reactions would cause weak spots in the quartz (or in some versions of the story, the filament), decreasing the lifetime of the bulb.

Is there any merit to this explanation? What are then the precise mechanisms involved in the bulb's degradation when the bulb is touched by a dirty monkey finger?

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It is most likely not a chemical reaction, quartz is quite inert even at higher temperatures but dirt and burned substances can cause thermal gradients and stress in the glass. –  Alexander Aug 13 '12 at 13:13
    
That seems plausible, although I'd love to see some numbers backing this up –  Rody Oldenhuis Aug 13 '12 at 13:31
    
I've never seen them say "react", generally, the explanation is that the extra oil will interfere with the cooling of the lamp, plus it'll burn etc (and might thus affect the lm output of the bulb). –  cnst Feb 20 at 3:42
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Any oil from your fingers that resides on the outside of the halogen lamp will absorb some of the heat and light from the filament in operation, and cause the fingerprint area to be hotter than other parts of the bulb.

All it takes sometimes is a small differential in temperature for anything made of glass or quartz to develop a weak spot from the additional thermal / mechanical stress.

Wearing gloves or handling the bulb with something that won't leave fingerprints (I usually use a small piece of paper towel) is a very good idea.

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