This is topic How Much Can I Turn Down Xenon Current? in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.


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Posted by Jim Cassedy (Member # 4115) on 04-23-2010, 03:02 PM:
 
I had to install a 4K lamphouse for "Clash of Titans" in
Technicolor 3D system.

This week I'm going back to 2D projection for the next month.
The 4K is far too bright on that screen in 2D.

How much can I 'back off" on the current to burn the bulb at
a lower wattage before it does harm to the bulb?

Can I burn the bulb as low as 3500Watts, for example?

Or would it be better for me to stick somwhere around 3800W?

Thanks!
 
Posted by Robert D Hall (Member # 5674) on 04-23-2010, 03:47 PM:
 
You can run a 4k as low as 2700 watts. Around 100-105 amps should give you 2700
 
Posted by Ian Parfrey (Member # 5122) on 04-23-2010, 04:20 PM:
 
Hi Jim.

Using Osram XBO 4000 HS OFR as an example, the operating current range is 80-150 amps.

Also according to the manufacturers information, there is little to gain and much to lose by running any xenon lamp at it's minimum current range for extended periods of time.

Quote from "XBO Theatre Lamps". p 26 Current Control Range

"...It is not advisable to operate lamps continuously at MINIMUM CURRENT. The expected increase in lamp life often does not take place as the arc is constricted at the cathode end, makes a small area hotter and so offsets possible gains in lamp life with increased blackening. If a lamp is operated at minimum wattage because it is too bright, it is usually advised to use a lamp of the next lower wattage."

From personal experience, I can vouch for the increrase in wandering of the arc and a more rapid degeneration of the lamp in general - in both Osram and Ushio xenon 4000W lamps.

Whatever the reason for wanting to run any xenon at a low current setting, the end results will be the same.

With this at hand, and with the increase in power usage, shortened lamp life, increase in striking difficulty and wandering arc streams, I would personally advise to purchase a smaller lamp and to run that higher into it's operating current range than risk permenantly damaging an expensive 4K lamp.

Keep us informed, Jim, on what is decided on.

Cheers
Ian
 
Posted by Jeremy Weigel (Member # 4208) on 04-23-2010, 05:03 PM:
 
How about just de-focusing the bulb a bit to bring down the brightness without changing your present amperage setting and then re-focus it for your next 3D feature?
 
Posted by Robert Throop (Member # 61) on 04-23-2010, 05:08 PM:
 
quote: Jeremy Weigel
How about just de-focusing the bulb a bit to bring down the brightness without changing your present amperage setting and then re-focus it for your next 3D feature?
Better yet, stop down the lenses for increased depth of focus.
Bob
 
Posted by Steve Guttag (Member # 268) on 04-23-2010, 05:32 PM:
 
There is definitely a sweet spot on a xenon lamp range. However, what Osram states about operating the lamp towards the bottom end of the range not extending the lamp life is false. It is only true once you go below the bottom end of the range. There I've seen the arc wander to the point that the image looks like it is shaking.

However, operating the lamp in the lower portion of its range will often GREATLY extend its life as well as its light output during its life. As once increases the current the amount of lumen decay over time progressively increases. It is almost always a bad idea to plan on a system where the lamp operates at the top-end of its range for all but the last portion of its life.

I'll admit, I've done less study on Osram lamps than some others in the area of decay but there is more than a passing trend at what operating a lamp at the upper end of its range does, regardless of manufacturer.

My recommendation, if your system will allow for it, is to change the lamp to a smaller lamp for 2D presentations. This will save you money on lamp costs as well as electricity. However, your lamphouse/console must be able to accommodate the smaller lamp as well as your rectifier.

Steve
 
Posted by Brian Huk (Member # 5690) on 05-02-2010, 09:04 PM:
 
Sweet topic, this is almost exactly what I was looking for.

Slight derail. My booth has recently changed out 5 bulbs, with hours ranging between 2590 and 4010. They're ASLs and I was wondering how to get the max life out of them. Something more like the 4010 (which was still preforming fine, I think it was replaced out of fear of explosion).

We've been installing them right at their rated amperage. For those recommending lower settings, what do you do? 80% 90%... play it by ear (sight) on what's on screen? Also, if we do end up installing them at lower settings, are we supposed to raise the current in small bumps until near the end of the bulb's life it's at its rated current?

Also as far as I know the 2590hr bulb (replaced because of flickering) and the 4010hr bulb both stayed at their rated currents the entire time. Any ideas on the massive difference?

Info would be greatly appreciated as management won't buy a goldberg show shipper for budget reasons... and I seriously want one.
 
Posted by Tony Bandiera Jr (Member # 2365) on 05-02-2010, 11:48 PM:
 
Hi Brian,

First off welcome to F-T. You'll find lots of great info and really cool (and funny) people on here.

To answer your question about the difference in bulb life, there are many factors such as

I'm sure some of our other experts will point out other factors that I missed.
And some manufacturer's bulbs work better (or worse) in a given brand of lamphouse.
Nothing wrong with your procedure of running at the beginning at rated current, the life you've gotten from those bulbs is actually quite good.

As for the show shipper issue, welcome to the world of exhibition. [Roll Eyes]

Owners are notorious for spending NO money on the booth but they don't seem to mind spending thousands on neon and fake plants for the lobby.
 
Posted by Mark Gulbrandsen (Member # 72) on 05-03-2010, 08:56 AM:
 
Removing and replacing largish lamps of any brand is not necessarily a good thing. Christie outright does not recommend it on lamps 4kw and up, especially on short gap lamps. So leave the lamp in place and get yourself a Rosco neutral density gel and put it over the port. They are optically perfect and won't cause any image degradation and they are thin enough not to add any diffraction. They also only cost about 8 bucks. I do this for locations that I don't want touching the lamp in digital projectors.

Mark
 
Posted by Louis Bornwasser (Member # 3063) on 05-03-2010, 11:00 AM:
 
I see that too-much-light is a problem (?) now that Technicolor has trained people how to properly align lamphouses. Too bad we didn't do this years ago! lol.

If all is well, I have found 50-60 ft/lamberts to be flicker free and brilliantly lit. Yes, I know about the standards. Just try to reduce this brightness in a cinema that once had almost no light. Louis
 




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