Re: Cooling fans and projector lamps

[P3D Dr. George A. Themelis <DrT-3d@xxxxxxxxxxxxxxxxxxxxxxxxxxx>]

I am forwarding this contribution regarding projector fans and lamps:

>To: DrT-3d@xxxxxxxxxxxxxxxxxxxxxxxxxxx
>From: Ralph Wilhelms <ralphw3@xxxxxxxxxxxxx>
>Subject: Cooling fans and projector lamps
>Date: Thu, 24 Oct 96 22:41:19 +0000

Dr. T,

I saw a thread on the 3-D mailing #1631 and wanted to tell you about this
topic of running cooling fans after the lamps are turned off in a
projector. Please forgive me if this has already been mentioned. I am
hopelessly behind in reading my e-mail.

Actually, running the fans after turning off the lamps in a projector is
strongly not reccommended if the lamps are made of quartz like most modern
ones. The lamps that fit into old 3-D projectors have envelopes made of
glass, not quartz. The filements do not care one way or the other. It is the
envelopes of lamps that DO care.

The quartz cools too quickly if the fan is left on after the lamps have been
on a while. This causes small cracks to form. These are many times visible
to the eye. After a number of these fast heat-cool cycles, the envelope
springs a leak and oxygen enters the envelope. IT won't take long after that
for the lamp to burn out.

I known this for over 20 years. I used to run movie projectors years ago.
Many lamp manufactures have been saying this since the quartz envelope has
been invented.

As far as glass envelopes are concerned, it is best to cool them down with
the fans.

Hope this helps out on whether to leave the fans running or not.

Ralph


------------------------------