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From: bhoughto@cmdnfs.intel.com (Blair P. Houghton)
Newsgroups: sci.electronics
Subject: Re: Do Halogen lamps need ballasts?
Message-ID: <1205@inews.intel.com>
Date: 2 Dec 90 22:48:58 GMT
References: <1147@inews.intel.com> <1197@inews.intel.com> <153447.28605@timbuk.cray.com>
Sender: news@inews.intel.com
Distribution: sci.electronics
Organization: Intel Corp, Chandler, AZ
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In article <153447.28605@timbuk.cray.com> kilian@cray.com (Alan Kilian) writes:
>
>Coefficient of thermal expansion 5.5 X 10^-7 cm/cm/degree C From 20 to 320 C
>   (That's way low)

Not low enough.

>Tensile strength 7,000 PSI Compressive strength > 160,000 PSI
>   (That's very strong)

Not strong enough.

>Softening point (Approx) 1665 Degrees C (1938 degrees K)
>   (That's way up there)

Lower than I thought, but higher than any spot of
carbonization will stick around to reach.

>So, If I place some oil on the quartz with the lamp off and let the 
>temperatures equalize and then turn on the lamp WHY does the quartz
>break (If it really does as so many have said).

Halogen lamps in these pole-lamp assemblies come with
expensive-looking protective gear to keep the shards of
quartz envelope from splattering all over your living room.

They break.

The skin oil keeps heat in the quartz that is escaping
elsewhere on the envelope.  The temperature difference
causes localized stresses.  Poof.

				--Blair
				  "Poof."


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