Film-Tech Forum ARCHIVE: Cooling Xenon Bulbs

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Posted by Joe Redifer (Member # 3) on 06-02-2003, 02:11 AM:

We have extremely poweful OSRAM 1600watt and 2500watt xenons inside extremely powerful ORC lamphouses running our large giant screens. How long, given these details, would you say it would be safe to leave the xenon off before firing it up again for the next show vs letting it stay on all day for a theater with very little intermission times? 10 minutes? 20 minutes? 3 days? This is all assuming that our ventilation is adequate. And how much would you say striking a xenon detracts from its life if not cooled enough before restriking? Worth worrying about?

Posted by Michael Rourke (Member # 1142) on 06-02-2003, 02:28 AM:

I usually would let a bulb cool down between shows, even with a water cooled trap, an almost constant blasting of intense heat to the trap area would eventually damage the film. I've left a bulb running between the last show and a preview and understand that every time a bulb is struck it is weakened, but I wouldn't recommend leaving a bulb on all day long. I feel 10 minutes is enough time for a bulb to cool down before being restruck, so I usually don't keep a bulb running if I can get a 10 minute cool down in.

Posted by Leo Enticknap (Member # 534) on 06-02-2003, 02:40 AM:

I was told that under normal circumstances, each ignition knocks out 30 minutes of a lamp's life.

So I usually worked on the 30-minute rule, i.e. any longer than that between shows and the lamp went off, otherwise it stayed lit. With adequate ventilation I never had any problems leaving the lamp on all day. If they can operate for two hours at a constant temperature then there's no reason why they can't run for 12.

The only circumstances in which I would switch the lamp off for a shorter period is if the weather was very warm and the projection box was getting like a greenhouse, in order to give the air conditioning a chance to bring the overall temperature in the box down a bit.

If the lamphouse ventilation and douser are doing their job the projector mechanism itself shouldn't suffer a progressive build-up of heat over a long-time period: it should heat up to a set point and stay there until the lamp is switched off and the source of heat is removed. If the gate area is significanly hotter after 12 hours than after 2, then the cooling system is either inadequate or not working properly.

Posted by Stan Gunn (Member # 554) on 06-02-2003, 02:44 AM:

It is general rule that every time a lamp is ignited it reduces the life by around 30 mins.
Most cinemas I have worked leave the lamp on all day, and get 2000 + hours.

My method would be to leave it on unless there is a break of over 30 mins. [beer]

Posted by Adam Martin (Member # 641) on 06-02-2003, 02:08 PM:

The anode and cathode tips are mildly damaged every time an arc is struck between the two. Over time, the electrodes will become blackened and/or pitted, resulting in increasingly difficult strikes and an increased likelihood of arc wandering later in life.

Additionally, the rest of the lamp parts are stressed every time the lamp is allowed to cool between uses. The quartz and seals weaken through the life of the lamp as it heats up and cools down repeatedly.

Posted by Ken McFall (Member # 845) on 06-02-2003, 03:41 PM:

Ok....
leaving a lamp running all the time is fine in a single screen where there is always an operator beside the machine.

However, if you are running single manning and cannot be there then the lamp HAS to be turned off by the automation, no automation I know of closes the dowser.... only the shutter. The shutter is only intended for change overs or short blanking of the picture for lens changes etc. Let's not go down the dowser/shutter road.... PLEASE.

In general I find turning off the lamp has little real impact on lamp life. I would have thought leaving a lamp running at full current with a dowser closed would only make the lamphouse environment even hotter than normal. I'm not a fan of running lamps way over their life expectancy. Is it really worth risking a show if a lamp fails in the middle of a show?

Yes by all means run it 25% over its rated life, even a little more if you really must. But anything more is really a false saving. Factor in the cost of a mirror, lost revenue and good will and it just don't add up.

Guaranteed lamp life is just another cost factor of single manning and has to be accepted as such.

The biggest contribution to lamp life is good ventilation and serviceing of the rectifier and its control gear. Look after all of that and you should get the life from your lamps that you are entitled to expect.... GUARANTEED LIFE and nothing more. The rest is at your own risk!

Posted by Gordon McLeod (Member # 33) on 06-02-2003, 05:11 PM:

Most manufacturers offer a motorized dowser option that the automation can control and many also offer standbye mode on the rectifier that is tied into the dowser so when it closes it drops to 1/2 power

Posted by Stan Gunn (Member # 554) on 06-02-2003, 06:03 PM:

At our local cinema, That I used to service, I saw lamps that had done over 5000 hours, and to look at them there would only be mild darkening of the quartz with the electrodes noticeably worn. [Big Grin]

The reason for removal was unsteady light. [Cool]

Posted by Mark J. Marshall (Member # 1409) on 06-02-2003, 07:58 PM:

I've never heard of anyone bringing the bulbs down to half power except IMAX, which isn't to say that it doesn't happen. Is that feasible or recommended on smaller bulbs?

Posted by John Pytlak (Member # 331) on 06-02-2003, 08:36 PM:

Standby at low current can work, if the lamp envelope remains hot enough to keep the tungsten deposits from subliming on the quartz. Too cool, and the lamp will blacken quickly.

Posted by Stephen Jones (Member # 16) on 06-02-2003, 09:16 PM:

If there is a gap between sessions ie an hour I turn the lamp off if its only 40 to 45 min break I leave it on,other than that the lamps are turned on at the start of the day usually 30 min before the first session of the day in that particular theatre they then are on for the whole day usually about 14 hrs a day.The heat isnt a problem as the exhaust system copes well and there is no effects on the projector head. We run lamps from 7k down to 2k with no probs.The hours we are getting from the lamps by leaving them on are about average .We get about 3500 hrs from a 2k and 2000 fom a 7 k and over 4000hrs from our 4k lamps.They are changed usually because they are starting to flicker at that stage of thier lives and they are starting to darken.
We are useing Kinoton FP50Ds with Kinoton consol's which have excellent ventilation.
Steve [Wink]

Posted by Travis Hubrig (Member # 1745) on 06-02-2003, 10:12 PM:

I work at a 7-plex and we don't have the staffing to keep anyone in the booth at all times. Because we would need to close the dowser each time to keep the bulb on, we only leave the bulb on if we are experiencing problems with ignition. I have breaks of less than 20 minutes sometimes and I have had bulbs last 2000 all the way up to 5000 hours. I say let them turn off and cool, the biggest difference on lamp life is actually how clean the overall system is and well maintained... My theatre is 25+ years old and very dusty, keeping everything clean in the booth makes a noticeable difference

Posted by Gordon McLeod (Member # 33) on 06-03-2003, 11:39 PM:

The original horizontal xenon system were from Xebex of Japan with Sanrex rectifiers and standbye mode was standard on them (christie built there lamphouses under license of them)
LP associates and ORC also had it as an option