P3D Re: Project-or-View bulb question

["Greg Wageman" <gjw@xxxxxxxxxx>]

From: Robert Cruickshank <robcruic@xxxxxxxxxxxx>


>One of the bulbs that came with my project-or-view was wearing a little
>metal cap. The bulb itself had none of the usual black or blue coating
on
>its top, the other bulb, which had the black coating, had no metal cap.
Am
>I correct in assuming that the metal thingy came with the bulb, (which
was
>dead) and not the projector?  Is this something that is needed to keep
>the projector from exploding in a ball of flame, or merely part of an
old
>style bulb?


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.

     -Greg W. (gjw@xxxxxxxxxx)