Film-Tech Forum ARCHIVE: Rotating Bulbs - 1/4 or 1/2 turn -Does It Matter?

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Posted by Jonathan M. Crist (Member # 413) on 06-12-2001, 10:47 AM:

Several years ago the manufacturer's advice was to rotate xenon bulbs 1/2 turn at the warranted half life of the bulb. Now I understand the recommendation is 1/4 turn at 1/4 of the warranted life (although the instructions in my Osram package still say 1/2).

Is the 1/4 turn now the standard? Which is better 1/2 0r 1/4? Does one way or the other really effect the life of the bulbs that dramatically? What do you do?

Posted by Antonio Marcheselli (Member # 373) on 06-12-2001, 11:10 AM:

Jonathan,

We talked about rotating bulb few time ago. Search the forum and you will find everything. However, rotating a bulb will not increase the life of the bulb but will mantain a constant and better light during the life of the bulb. If only one side of the bulb will be dark, you'll have to misalign the lamphouse to compensate.

Most people think that rotate a bulb 1/4 a time is a goog tecnique but the time that you take to rotate all bulbs every few hours can be spent better in a booth. It is better to, say, rotate the bulbs 1/2 turn a time and have more time to clean projectors better...

Bye
Antonio

Posted by John Pytlak (Member # 331) on 06-18-2001, 08:31 AM:

AFAIK, rotating horizontally-mounted xenon lamps is recommended to even out the wear on the electrodes and even out the blackening of the lamp envelope. Some also felt that the red hot electrodes would "sag" over time, and rotating the lamp helped keep them in line.

Best to follow the particular lamp manufacturer's recommendations. If they say to rotate, and you have the correct spacer, then rotate on the schedule they suggest. After rotating, don't forget to check lamp focus and alignment to assure correct screen luminance and uniformity!

------------------
John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Eastman Kodak Company
Research Labs, Building 69, Room 7419
Rochester, New York, 14650-1922 USA
Tel: 716-477-5325 Cell: 716-781-4036 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com
Web site: http://www.kodak.com/go/motion

Posted by Paul G. Thompson (Member # 655) on 06-18-2001, 01:20 PM:

There used to be a thick washer that came with a new HTP lamp from several manufacturers. The thickness of that washer was equivilant to one-half turn. When I installed a new HTP lamp, I used the washer. At lamp half-life, I removed the washer and threw it in the 20-year box. If I needed it again, I simply fished it out of the 20 year box.

Posted by John Walsh (Member # 168) on 06-18-2001, 06:48 PM:

While there are a lot of different opinions (with good reasons) here is my humble take on this issue:

Look at how dark the bulb gets. The darker it gets over time, the more likely you should rotate it. For example, at the place I work we just don't rotate them at all. Even after 4000 hours, there is very little blackening on the bulb. Having a good cooling / fan system helps a lot, I think.

I don't have a "grey-scale" chart to show what would indicate exactly how "dark" is "too dark"; it's just one of those things you have to see for yourself. But, except for bulb darkening, I don't see any advantage to rotating.

I think the reason manufacturers suggest rotating is they know most lamphouses only provide adequate- not great air flow.

Posted by Rick Long (Member # 213) on 06-18-2001, 07:25 PM:

Perhaps, years ago, when we installed the Kniesley xenon conversions in the housings of those old Mighty 90's and 135's we should kept the rotating mechanism. Mind you, woulda needed a fairly long bulb lead.

Posted by Gordon McLeod (Member # 33) on 06-19-2001, 09:55 AM:

Rick that has a bit of truth to it Ashcraft attempted to build a Xenon lamphouse that had a rotating mechanism in it. Needless to say it didn't fly