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From: bhoughto@cmdnfs.intel.com (Blair P. Houghton)
Newsgroups: sci.electronics
Subject: Re: Do Halogen lamps need ballasts?
Message-ID: <1197@inews.intel.com>
Date: 1 Dec 90 21:25:34 GMT
References: <714@skipper.dfrf.nasa.gov> <1147@inews.intel.com> <1990Dec1.032426@envy.bellcore.com>
Sender: news@inews.intel.com
Distribution: sci.electronics
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In article <1990Dec1.032426@envy.bellcore.com> karn@thumper.bellcore.com writes:
>In article <1147@inews.intel.com>, bhoughto@cmdnfs.intel.com (Blair P.
>Houghton) writes:
[...deformation ==> rupture...]
>|> The oil doesn't "weaken the structure."  You can
>|> wipe it off.
>
>I don't think that's quite right. Quartz is used precisely
>because of its very low temperature expansion coefficient.

Very low != nonexistant.  Also, quartz is very brittle.
Any deformation causes catastrophic displacement
(cleaving).  When there's a uniformity of heat
distribution, things expand normally.  When there isn't,
they don't.

>I think the problem is that the heat will decompose the oil, producing
>elemental carbon which will then absorb the light hitting it from the
>filament.  This causes a hot spot on the surface of the envelope which
>could well cause it to soften and fail.

Take a halogen lamp.  Turn it on.  Allow a drop of water to
fall on it.  Run like hell.

You don't need any chemistry.  Temperature differences
are all you need to cause one of these to blow.

I don't think you can "soften" quartz without _extreme_
temperatures (thousands and thousands of K).

				--Blair
				  "Billions and billions of Big Macs..."


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