Subject: Pressure in a tungsten halogen bulb

From: [email-masked] (Stephen J Hart)
Date: Thu, 2 Nov 1995 04:12:24 GMT

Hi folks

I'm working on a new special purpose illuminator for holographic
display. I need to label it properly as regards UL-122 and 1950 and CE.
To do so I need to know if the bulb I've selected is considered "high
pressure" or not. The standards tell me how to calculate this, but to
do so I need to know the bulb pressure in atmospheres at 50 degrees
centigrade.

The specific lamp is an Osram (Sylvania) HLX-64655 24V 250W tungsten
halogen (Xenophot).

Does anybody out there know what the internal pressure in this lamp
would be? Or where I could go for an answer? The manufacturers seem
unable to give me a definitive answer!

Stephen J Hart                      fax              +1 (714) 348-8665
Director of R&D                     e-mail            [email-masked]
                                    WWW URL       http:/www.voxel.com/

VOXEL, 26081 Merit Circle, #117,    The opinions and "facts" expressed
Laguna Hills, CA 92653-7017, USA    herein are not necessarily correct

---

From: "Barry D. Besmanoff" <[email-masked]>
Date: Thu, 02 Nov 95 23:54:25 PDT

Contact the Osram/Sylvania engineering dep't in Danvers, Mass. This should be 
a readily available figure if you can get to the right engineer's desk!

---

From: [email-masked] (Perry West)
Date: Thu, 2 Nov 1995 20:47:26 GMT

To the best of my recollection, the halogen lamp envelopes must operate 
at a temperature around 700 degrees Farenheit (approx 390 degrees 
Celsius), not 50 degrees!  I also seem to recall the interal operating 
pressure being 2 to 3 atmospheres.

I am not certain about these nubers, but do know that the envelopes must 
run very hot for the halogen cycle to work, and that the pressure is high 
enough for explosion to be a possibility if the bulb is damaged.

Regards,
Perry

---

From: [email-masked] (Stephen J Hart)
Date: Mon, 6 Nov 1995 17:39:07 GMT

> pressure being 2 to 3 atmospheres.

Yes, that's right. But apparently the safety spec is written in terms
of the internal pressure at 50 degrees C (with a mandated formula to
convert for other temperatures). I don't know why!

> enough for explosion to be a possibility if the bulb is damaged.

We've designed the bulb into an enclosure where any explosion would be
contained safely. But to label it correctly we still have to know if
the bulb is "high pressure" or not according to the standard's formula.

---

From: [email-masked] (Loren Wilton)
Date: 7 Nov 1995 08:53:00 GMT

>do so I need to know the bulb pressure in atmospheres at 50 degrees

I do not know what the regulators consider "high pressure".  However,
theatrical experience with these sorts of lamps would indicate that they
are "low pressure".  I have never seen one explode, even as badly as a
normal incandescent would do when operating.  Mostly they fail by melting
a hole in the side of the bulb, if they suffer envelope failure at all.
I believe that they are at a significantly lower than atmospheric pressure
at normal temperatures, and probably only run a few atmospheres when hot.

Zenon arc lamps *ARE* high pressure instruments.  They require special
lamp houses, interlocks, and elaborate transport cases for new and used
lamps and elaborate procedures for safe relamping.  The cases the lamps
come in are *plastered* with warning stickers.  I would suggest a lack of
such warning stickers on normal halogen lamps is a good indication that
they are not classified as high pressure instruments.

	Loren