P3D Re: Project-or-View bulbquestion

[Bob Wier <wier@xxxxxxxxxxxxxxxxx>]

>The purpose of a silver or opaque coating on the top of a projection
>bulb is to prevent the filament from radiating through the top of the
>lamp, and thus reduces light spill from any cooling vents atop the
>projector, nothing more.  A coating of some sort is most likely more
>cost-effective than a metal stamping, but such a heat-resistant coating
>is probably also a more recent technology.  I'd guess you had quite an
>old lamp there.

That's possible, or it might be a "ruggedized" version. In vacuum
tubes there were military versions which were electrically similar,
but had much stouter construction, including heavier gauge metal,
and so forth - it's just a guess, though.

-BW

              Bob Wier
     mailto:wier@xxxxxxxxxxxxxxxxx
   1:09 PM Wednesday, February 2, 2000
        Unix/Internet Administrator
   Rocky Mountain College, Billings MT.
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