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This topic comprises 3 pages: 1 2 3
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Author
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Topic: heat waves?
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Josh Jones
Redhat
Posts: 1207
From: Plano, TX
Registered: Apr 2000
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posted 03-10-2002 10:04 PM
I noticed something else when I was at "We were soldiers" today. at the top of the screen during the movie ther were curls of distortion, only noticeable in light areas of the picture which were darker than the surrounding white image. is that the hot air around the bulb distorting the light in the lamphouse or what? I also saw it during the prescreen ads and also in another house at the same theater. Anyone know what this is?Josh ------------------
"Film is made of silver, video is made of rust"
'nuf said
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Mark Gulbrandsen
Resident Trollmaster
Posts: 16657
From: Music City
Registered: Jun 99
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posted 03-10-2002 10:32 PM
Josh,
Thats exactly what it is. The heat waves from the ceiing mounted vents that shoot air downward into the cone of light traveling to the screen. Its definately not the plasma inside the bulb or anything like that. I remember once an engineer fomr HAnovia telling me that the actual plasma itself has never been observed in an operating xenon lamp.Paul, Please put that weenie down will ya. There's weenie goop running out from all over my monitor screen! All it does is smear around, can't clean it off! Mark @ GTS
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Jerry Chase
Phenomenal Film Handler
Posts: 1068
From: Margate, FL, USA
Registered: Nov 2000
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posted 03-11-2002 12:11 AM
I'm gonna disagree with youse guys. I had this exact problem in the Strong X-15 vertical lamp lamphouses. They used two reflectors, with the front one being solid metal. I was always getting heat waves, whether the HVAC was on in heat, air conditioning, or turned off entirely. I put up with those damn things for years.This isn't plasma, which would theoretically only be within the arc itself, it is the hot gases "boiling" and transferring heat from the arc to the envelope. I've never seen this problem be as noticable with horizontal lamps or deep dish reflectors. The double reflector system somehow accentuates the visibility, perhaps because the light is shining through the gas to the front reflector, then back through the gas again, all the way through before being caught by the rear reflector. HVAC units can also cause problems, so I have no idea which problem Josh is seeing. The thing to ask would be whether the lamphouses have vertical lamps and double reflectors.
Paul, I hope you brought enough weenies for everyone. 
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Aaron Sisemore
Flaming Ribs beat Reeses Peanut Butter Cups any day!
Posts: 3061
From: Rockwall TX USA
Registered: Sep 1999
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posted 03-11-2002 12:44 AM
This one has been the subject of many an argument... Here's mine.Unless someone can give me evidence to the contrary, it is impossible for the heat 'convections' either in the bulb itself or inside the lamphouse to show up clearly on the screen with the lens in, as neither of them are anywhere close to the focal point of the lens. Which leads us to the next cause. EVERY time I have seen this phenomenon happen, the heaters were operating, and in nine out of ten cases there were HVAC registers within 5 feet from the screen. Turned off the heater, phenomenon went away. I have seen this happen to a lesser extent when A/C was operated in a warm auditorium as well, with similar curative actions (turning the system off) Lamps I have observed this phenomenon occur with include:
CFS consoles
Christie horizontal lamps
Xetron XHC-35 and XH2000 horizontal lamps
Strong X-16, Super Lumex and Super 80
Peerless Magnarc (so much for the 'gases in the bulb' theory!)  My bottom line here: its the HVAC system! -Aaron
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Pete Naples
Phenomenal Film Handler
Posts: 1565
From: Dunfermline, Scotland
Registered: Feb 2001
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posted 03-11-2002 02:44 AM
The Cameo in Edinburgh has suffered the 'waterfall effect' for as long as anyone can remember. Various experts told us it was gas convection in the bulb and/or lamphouse and there was little we could do. Changing from a Magnarc to a Super Lume-X made no difference. It looks really bad in there as the ventilation (extract, no AC) ducts are position dead on the centre line of the theatre, and when the fans aren't running, ie it's cold, then you get cold air falling down the vents from outside. These vents were installed a long time before anyone thought about electric dampers or such like. By trial and error I found that I could eliminate the effect by matching the speed of the enormous 3 phase extract fan (this thing is cast ally and is about the size of a small helicopter! Well ok I exagerate, but you get the idea, one fan pulls all the air from a 250 seat auditoreum). Must have looked kind of odd to anyone coming into the booth to find the projectionist looking out the port, adjusting the fan speed controller, looking out the port, adjusting the fan speed controller....
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