Film-Tech Forum ARCHIVE: Xenon gas, visible onscreen?

This is topic Xenon gas, visible onscreen? in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Max Eldright (Member # 2076) on 12-14-2003, 08:46 PM:

A couple nights ago I started noticing what looked like heat rays rising across the screen during a particularly bright portion of a film. At first glance it looked like smoke, but then I realized it was in the projection. It was quite "trippy" to watch, as I was not the only one to notice it all the way across the midsection of the screen. I've never noticed this before, and the bulb for that screen is only about 1,000 hours in.

Is this coming directly from the bulb? Or should I run for a fire extinguisher? heh...

And, how could I reduce this? I think it's hypnotizing our patrons.

Posted by Gordon McLeod (Member # 33) on 12-14-2003, 08:48 PM:

This has been discussed before
It can be heat patterns in the lamp or heat from a ceiling air vent in the theatre interferring with the beam of light

Posted by Jack Ondracek (Member # 1466) on 12-14-2003, 09:51 PM:

Gordon's probably right... and I'd bet it's more likely the heating system in your auditorium.

If you're really that interested & can do it, you could always turn the heat off or down to confirm it's your HVAC.

In any case, I'm wondering if you noticed this during your first show of the day. It happens at my place... especially if I cut my HVAC start time too close to my first show. After the room stabilizes, it's not so noticeable.

Posted by Sam D. Chavez (Member # 1841) on 12-14-2003, 10:04 PM:

I first saw this artifact many years ago with a Strong Futura arc lamp (who remembers those)and I traced it down to a heating register near the top of the screen.

Posted by David Stambaugh (Member # 1102) on 12-14-2003, 11:19 PM:

The one time I saw this during a movie it freaked me out. I was expecting a fire to break out in the booth or something. [Eek!]

It was probably HVAC though.

Posted by Steve Guttag (Member # 268) on 12-15-2003, 12:36 AM:

Every time I've documented it, it was the heat currents of the HVAC system.

As to the Futura...Just the Futura II for me...11mm or 13.6mm trims and never had flame-out problems either.

Steve

Posted by Jeff Taylor (Member # 443) on 12-15-2003, 12:40 PM:

Somewhat off topic, but I'm sure you've had the experience of pulling the lens out and seeing the "boiling" effect of the gas around the bullseye. From what you describe, though, my money's with the HVAC distribution.

Posted by Jesse Skeen (Member # 586) on 12-15-2003, 01:42 PM:

I first noticed this during the summer (Jurassic Park), so I don't think the heat was on then.

Posted by Floyd Justin Newton (Member # 1316) on 12-15-2003, 02:58 PM:

It's my understanding that xenon gas has no odor... is
invisible and relatively non-toxic and inert.

fjn

Posted by John Pytlak (Member # 331) on 12-15-2003, 04:08 PM:

Xenon is an inert gas. Unless the lamp explodes or has a seal failure, the xenon gas is completely contained within the lamp. Lamphouse odors may be due to ozone gas (produced from oxygen by either ultraviolet energy, or high voltage discharge during ignition), or heating of plastics and contaminants (e.g., lubricants) within the lamphouse. Ozone gas can be harmful to your health.

Posted by Paul G. Thompson (Member # 655) on 12-15-2003, 06:27 PM:

I agree. If there is a lens in a projector, the heat waves are more than likely from the HVAC louvers and/or diffusers in the ceiling of the auditorium.

Posted by Aaron Sisemore (Member # 145) on 12-15-2003, 09:31 PM:

quote:
I first noticed this during the summer (Jurassic Park), so I don't think the heat was on then.

It also can happen when the A/C is run in a hot auditorium. It is related to the optical 'distortion' effect caused by hot gases escaping in a cooler enviornment (such as a gas stove being used outdoors).

The 'Schurlien Effect' of the gases boiling around inside the bulb, while clearly visible on screen when there is NO LENS in the projector is not the cause as it would be impossible for them to have been magnified, focused, and projected onto the screen at the same time as the film was (they are in radically differeng focal planes from each other), and the effect would also be inverted (the swirling would be at the BOTTOM of the screen) if it were to happen, and I too have seen the aforementioned effect on a few occasions with carbon arc booths where there is no xenon bulb to have gases swirling about.

Here is another post about this phenomenon.

-Aaron