T3D Cooling projection lamps

[Virtual Imaging <vidi@xxxxxxxxxxxxx>]

I use and specify a lot of projector style lamps in my "day job" for the high speed 
imaging products we design and manufacture.  I can't say for sure why someone would 
put that cooling restriction on the lamp (in all my discussions with the lamp 
manufacturers, they have NEVER mentioned NOT to cool the lamp to extend lamp life), 
but if I had to guess I'd say the person saying that may have been concerned with the 
differences in the coefficient of expansion of the reflector material and the lamp envelope 
where it is cemented to the reflector.  When a lamp fails due to thermal stress it is 
almost _always_ at the base where the two lamp pins pass through the "squished" glass 
on their way to the filament.  In this area you have metallic pins cooled by the socket, a 
glass envelope sealing the pins and molybdenum ribbons going to the tungsten filament, 
and the cement holding the reflector to the envelope.  I would think you would want the 
least amount of temperature differential with all this going on.  I have seen many lamps 
fail where the pins lead into the envelope by creating a gas leak.  These lamps have a 
silver/gray swirl pattern on the interior of the lamp envelope.

   BTW, we have several hundred system out in the field burning hundreds and hundreds 
of 50W and 75W projector style lamps with all kinds of cooling on them and I haven't 
been told of a lamp failure issue yet in the 5 years they've been out there (for what that's 
worth).


John Vala


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