I ask because I have been having tons of problems with my bulbs since I stopped rotating, plus we switched from Osram to ORC (not happy), and I have had problems with bulbs fusing to the negative end clamp on my Christie SLC's.

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It might be a good idea to inspect that area perodically to make sure they are tight.

If the bulbs are turning black, I would rotate them at half-warrenty life.

I was told not to overtighten the socket head allen on the clamp or the bulb would fuse, but then when I took my reoccuring problem to Christie they told me to really wrench down on that screw.

Anytime a bulb is changed, the critical parts should be examined for evidence of pitting or overheating. If this condition exists, you can tighten things down until you are blue in the face, only to find later that the situation has gotten worse.

The parts that show overheating and pitting should be replaced. If the parts are not available, at least clean them up if at all possible. Lousy mechanical connections will probably void the warrenty.

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Electrical contacts need to be tight. Any resistance at the contact will cause a voltage drop and heating, and may "weld" the contact.

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John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Research Labs, Building 69, Room 7525A
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Tel: +1 585 477 5325 Cell: +1 585 781 4036 Fax: +1 585 722 7243
E-Mail: john.pytlak@kodak.com
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The theory of rotation and why to do it is fine and logical. But I hear a lot of reports about unstable arcs and increased arc waver after rotation, especially when that's done at half-life. Supposedly you can run the lamp at a higher current, near its maximum for a few hours, and the arc will generally settle down. I've seen instances where that does work and others where it doesn't.

I like the quarter-turn at quarter-life idea a little better. I like rotating the lamp if there is obvious darkening of the quartz on the top-half of the envelope a little better than that.

The best for me is if: a) the lamp arc is not wavering, and b) the quartz is clear, then don't fix what isn't broken. The lamp is "happy", let it run.

I think Mark's statement about the capability of the booth staff to do this and monitoring the results is probably the most important factor.

I agree with your concerns. But if electrode wear/sag has progressed to the point where simply rotating the lamp compromises performance, it's obvious that the wear is uneven. Perhaps the solution would be rotating on a more frequent schedule?

Hard to argue with the point that many theatres today do not have anyone on staff that have the knowledge and skill to properly and safely rotate a lamp, and then readjust the alignment for optimum light output.

BTW, are lamp mount shims available to allow a 90-degree rotation? Are they normally supplied by the lamphouse manufacturer, or the lamp manufacturer?

Yes Osram always supply a washer to enable a 90 degree rotation.

I don't know if I could keep up with all that bulb maintennance with 11 screens, especially since 4 of those screens weren't being run by projectionists for 7 years and need a lot of work.

I was taught to have the "tit", "nipple" whatever at 3:00 or 9:00, and then rotate at half life. I was told NEVER to have the "tit" at 12:00, and I was never told about increasing the wattage after rotation. Like Brad, I am just running as close to 100% of the bulb wattage from start up to finish, but I think the ORC bulb aren't fans of this method and have yet to wow me with prolonged performance.

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