Film-Tech Forum ARCHIVE: Xenon off or on?

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Posted by Matthew Nock (Member # 1575) on 04-23-2003, 09:15 AM:

What is everyone's opinion on turning off their xenons between sessions? for example, if you have a 5 minute turn around, are you turning the lamps off? or leaving them on? how about 15 minutes? half an hour?

generally, at both theatres I am working at at present, we work on if its more than half an hour, the bulb is turned off, if not, then we leave it on.

Does continuously striking throughout the day shorten the life at all? obviously a better lamphouse (such as the nice ones on our Kinotons') will make the lamps last longer anyways...

Posted by Ray Bernardi (Member # 1615) on 04-23-2003, 09:33 AM:

For better or worse, we shut down at the end of every run. Even if we are setting up and going again right away.

Posted by John Hawkinson (Member # 1135) on 04-23-2003, 09:44 AM:

This has been discussed a fair bit on these forums...it would be worth doing a search and digging up some pointers to other threads and linking to them. I don't have time right this moment to do that, but I can offer:

Over in Spots developing on Osram bulbs I cited Osram's publication Technology and Applications: XBO Theatre Lamps, which is a very good reference on the subject.

In reference to Matthew's question of how long to turn off,
Osram has this to say, on page 27 under "Operating Duty Cycle":

quote:

The average life specification for high-wattage XBO lamps refer to a burning time of 90 minutes per switching operation, in accordance with typical operating times in modern theatres. If intervals are short (less than 20-30 minutes) it is advisable to leave the lamps burning, or to operate them in standby mode at the current control range minimum in cases where the lamp current can be adjusted. See the previous section for relevent information. This type of operation also has the advantage that the greater arc instability ni the first minutes of operation of a still cold lamp does not occur, and that there is no possibility of ignition pulse interference in the sound equipment.

So, Ray, re-striking with a 5-minute turnaround is definitely a bad idea. I think you'll find everyone here who runs 2k changeovers on this site leaves lamps hot for the whole show, but there's some variation with respect to 6k changeovers. That's what you'd expect for a time of 30min.

In regards to Matthew's question, "Does continuously striking throughout the day shorten the life at all?" the answer is definitely. It's also more difficult to strike a warm bulb, though it may less bad for the bulb. Osram says (same section):

quote:
XBO lamps have their higehst life expectancy if once switched on they are not switched off again. Every additional startup, especially from cold, shortens lamp life. This is beacuse in cold ignition--and in this context this means everything more than 5 to 10 seconds after switching off the lamp--the high startup current needed to set up and ignition path must be handled by the cathode in its cold state when its emission capability is very limited. This torture erodes the cathode tip (tungest particles can be split off) thus altering its robust surface, and sudden local overheating can cause depletion of the doping material added to the tungsten in teh cathode to improve its emission capability. At an impoverished cathode the arc wnders restlesly to and fro searchnig for the lpace where emission cnoditions are best, without ever finding it.

Hope this is useful.

--jhawk

Posted by Bill Gabel (Member # 1105) on 04-23-2003, 10:44 AM:

I leave them on for the whole show, I run 2K change-overs. The
only time they go off is if I have over 70 minutes between shows.
Or when we run video. I'm in a Studio Post-Production operations.
Some days they stay on from 9am to 10pm. We have tobe ready if a
client books time.

Posted by Mike Perju (Member # 1482) on 04-23-2003, 11:45 AM:

The rule of thumb is that every strike shaves about 20mins. off a bulb's life... so if your intermission is anything under 30mins, it's really not worth killing the bulb.

Posted by Sam Hunter (Member # 1119) on 04-23-2003, 11:53 AM:

So in my instance if I run a show at home and I using one projector with 6K reels then I would be better off closing the lamphouse dowser doing the new reel and starting up/ opening dowser. Guess I need to invest in a zipper so that my homemade automation will work.

Posted by Michael Schaffer (Member # 1204) on 04-23-2003, 12:48 PM:

I have thought for a long time that it might be a good idea to have the possibility to warm the cathode up before striking the lamp the first time every day or after a long break. But this would of course involve additional costs to the equipment - while it would probably save costs in the long perspective. And it would make operating it in a typical modern theater environment "more complicated" for those untrained freshly-in-from-the-street operators we have everywhere now.

Posted by Paul G. Thompson (Member # 655) on 04-23-2003, 02:23 PM:

It depends. Electrical cost savings vs. lamp life. Unless you have quick turn-arounds, turn it off.

Remember one thing.....at the end of the show, the projector shuts down and the CO douser will close. However, if you do not have a device to automatically close the hand douser, you run the risk of damaging the projector shutter or the CO douser blade.

If there is a knucklehead running your equipment, it is just better to have the lamp shut down at the end of the show.

Posted by Manny Knowles (Member # 1171) on 04-23-2003, 03:33 PM:

For safety reasons our systems are set up to extinguish the lamp when the dowser closes just before tailout or, in some cases, when the motor cuts out after tailout.

From where I sit, the days of professional projectionists are over. The money saved by hiring one youngster to run half-a-dozen screens makes the "shortened lifespan" a non-issue.

As Paul G. mentioned above -- despite our efforts to attract and train good staff -- we do occasionally end up with a knucklehead in the booth.

Posted by Dennis Udovich (Member # 1066) on 04-23-2003, 07:45 PM:

The rule of thumb is that every strike shaves about 20mins. off a bulb's life... so if your intermission is anything under 30mins, it's really not worth killing the bulb
Guess I'm doing this all wrong..... We have Strong lamphouses, burn mostly 2000w Osram lamps, shut down between all showings, and most of my lamps last OVER 3000 HOURS! I don't think we'll change anything.

Posted by Gordon McLeod (Member # 33) on 04-23-2003, 08:32 PM:

Actually it is probably closer to 1 hr per ignition
I always leave the lamps lit between reels

Posted by Matthew Peters (Member # 1495) on 04-24-2003, 06:09 AM:

At the theatre I work for, the lamps are struck in the mornings prior to the first show for each cinema. They are left on virtually all day, until closing time. The average time between sessions is fifteen minutes, sometimes longer.

Even when a show has been cancelled because of nil audience, the lamps are left on. My last no-show was a few weeks ago – Standing in the Shadows of Motown. So the lamp would have been left burning for 2½ hours. (15 min pre show intermission + 2 hour feature + 15 min pre show intermission ≈ 2:30).

Turning off the lamp even when there is a no-show would cause complications because striking sometimes causes air-conditioning units and the dimmer unit to stop responding.

Posted by Don Furr (Member # 1469) on 04-24-2003, 07:03 AM:

I operate a pair of Super Lume-X's at the Rialto in downtown Atlanta....special screenings, film festivals, etc. Both lamps go on at showtime 1pm and go off at midnight (approx). Can you imagine shutting down the lamps between every changeover?? Last show I run 57 reels of films....let's see....57 bulb strikes!!!!
Leave the bulbs ON!

Posted by Scott Norwood (Member # 30) on 04-24-2003, 08:06 AM:

I'll echo the other comments here.

For changeover shows with 2000' reels, I leave the bulbs on (except with Kinoton projectors where that's not possible in the standard configuration). I haven't run changeovers with 6000' reels for a while, but I usually turned the bulbs off between reels except for "important" shows.

For a single-screen house with platters, I'll leave the bulb on all day, too. I usually run this type of show manually, even if the theatre has some form of automation.

For a multiplex with platters, I let the automation turn off the bulbs at the end of each show. I'd rather lose some bulb life than melt a changeover blade or shutter because there was no operator to close the hand douser between shows. Also, having to close the hand douser between shows would make the use of start timers impossible.

Posted by Ray Bernardi (Member # 1615) on 04-24-2003, 08:07 AM:

My gear is old to begin with, and there's nothing automatic about the dowser. My fear is that, being the knucklehead I am, I'll damage the equipment if I don't shut the damn thing off. I think it's okay for me, I run a pretty light schedule being a one screen small town operation. The only days we have more than one show are Saturday and Sunday. The time between shows just depends on how long the movie is.

Posted by Manny Knowles (Member # 1171) on 04-24-2003, 05:44 PM:

Going with the rule of thumb that each strike kills off an hour of lamp life, what happens if I turn the lamp on for a 2hr movie and then shut the lamp off? Have I killed off two or three hours?

Posted by Erik Stevens (Member # 1497) on 04-25-2003, 06:53 AM:

If spoke to our Osram representative a couple of years ago, and was stressing the point that all elements of the bulb must be cold before restriking, otherwise you are doing the bulb damage. On average, a lamp will take half an hour to an hour to 'fully' cool down.

As we have good airflow through our lamphouses, I use a happy medium of 45 minutes. If the turn around time is less, I will leave the bulb struck, if longer, I will switch it off.

We have two types of projectors on our circuit - Kinoton & Cinemecannica. As they use exactly the same bulb, you can see the extended lamp life in the cinemecannica lamhouse, as the bulb can be left on continously. Unfortunately you can not continuously leave the bulb on with the Kinoton (without making modifications). Thus striking between sessions, and thus seeing shorter lamp life.

Ciao,

Erik

Posted by Manny Knowles (Member # 1171) on 04-25-2003, 06:40 PM:

This is interesting because after about 10-15 mins my 2kW lamps are cool to the touch. Maybe my cooling system is just that intense.

Posted by John Hawkinson (Member # 1135) on 04-25-2003, 10:54 PM:

Manny, are you being serious?

I assume you're not actually touching the lamp's quartz envelope with your bare hands.
One would expect the anode and the cathode to stay warm longer than the quartz envelope.
Generally you should allow about 30 minutes of cool-down time for a lamphouse before openning it.

Also, remember that it's quite possible to over-cool a xenon bulb; they require less cooling than carbon arcs do. Osram says (page 25), "Excessive cooling is not good because it too can bring about increased arc instability due to turbulence in the lamp bulb. If the lamp voltage with cooling falls by more than 1 volt compared with uncooled operation, this normally means that cooling excessive."
(I'm not sure how they expect you to measure uncooled operation, though, since it implies defeating the safety interlocks of your lamphouse.)

--jhawk

Posted by Manny Knowles (Member # 1171) on 04-25-2003, 11:03 PM:

Well actually, I only change lamps in the morning before opening.

My senior tech is the one who goes around testing Xenon lamps. And, no, he's not using his bare hands. He uses his tongue. [Wink]

As for cooling, I have to assume that everything is kosher because we get a lot of mileage out of our bulbs.

Posted by Bob Healey (Member # 1003) on 04-25-2003, 11:31 PM:

Running 6K changeovers here, the lamps are struck at 6:30 PM, left on for three shows, then turned off after the last reel on the projector has run. The booth gets nice and toasty, but running 3 nights a week gets 2-3 years/lamp. In addition, the lamp houses can be tempermental striking depending on what other equipment is powered up (lamp one only strikes nicely when 2 is lit, 2 only strikes nicely when 1 is off)