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Topic: GS 1200 XENON Reflector repair
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Matt McBride
Film Handler
Posts: 62
From: Starkville, MS USA
Registered: Oct 2012
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posted April 04, 2013 08:37 PM
The best way is to go by the rated hours. You may or may not have that handy. A lot of projectors that operate xenon bulbs have a lamp meter to count the hours. If this is a 35mm system or a theatrical 16mm, the lamp meter would be on the lamphouse or console. If you know the model number you may be able to look it up. As bulbs get older, they become harder to ignite and may not ignite on the first strike. Also as bulbs get older they start to cloud up, making the glass look gray to black, however this depends greatly on how often the bulb is run in duration. Most xenons, and guys correct me if I am wrong, 1000 watts and under should last for about 2000 hours before they should be changed, keep in mind this is just a rough guess. If you don't have a lamp meter on your machine you can take a guess on how many movies you have watched and multiply by 2, an average length of a movie, and that will get you in the ball park of the current hours.
As an example, let's say you watch a movie once a week, there are 52 weeks in a year so that is 52*2= 104 hours per year, let's round up to 110 hours, for various things, such as initial setup and alignment etc. Then 2000/110 = approx 18 yrs. If it were me in this example, after 12-15 yrs, I would probably change it, because the picture will be a lot dimmer, maybe even after 10 I'd change it. It's a personal preference. Though you can use this example to estimate where you current bulb life is based on how many movies you think you have watched since you've had it. Again knowing the bulbs rated hours is what is best.
Keep in mind though, the older and more used the bulb gets, the more unstable the bulb becomes and the more likely it can explode, so even more care should be taken when removing a spent bulb.
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Matt McBride
Film Handler
Posts: 62
From: Starkville, MS USA
Registered: Oct 2012
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posted April 05, 2013 12:37 AM
Well you can look for clouding in the bulb. The darker the glass the closer it is to its lifespan. Though this is not always failsafe. There is another thing you can look at, is to see how pitted the anode and cathode ends where the arc actually goes across. If they are pretty pitted out, then the bulb may be out the door. It seems like you have put a lot less than 400 hours on it just judging on your comment quote:
During these years I have screened a lot fewer films than a full-length per week.
And since you got this without knowing the hours, I would almost say if you can buy a new bulb and just change it now. In my opinion it's probably better to spend an extra few dollars now to replace that bulb new and start fresh so you can keep track of the hours, than have the headache of hearing the bulb explode and to find reflector damage.
Getting used bulbs is always an issue unless the seller knows how many hours are on it. Just as an example, my current 1000w bulb for my 35mm setup, I bought used, but I was told it had low hours on it. The seller didn't know exactly the hours, but once I reach 1000 hours on this bulb and once the bulb starts to struggle to ignite after this time, I'm getting a new one, just to be precautous. Though of course bulb not igniting on the first strike can be from other factors as well.
The point is I don't want to risk reflector damage as replacement/resilvering is a lot more expensive than the bulb. Unfortunately with these arc lamps there are a lot of factors that go into them, and there can be many things that happen when they reach the end of their life. There is a nice paper in the warehouse section under tips on film-tech.com called Analyzing xenon bulb failures. Here is the link: Xenon Bulb Failure Analysis This will give you a very good understanding of what can happen to these bulbs as they age.
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This of course is another plus point for film against Blu-Ray projection as audience participation in Xenon lamp explosion is a real crowd pleaser.
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