Film-Tech Forum ARCHIVE: Xenon bulb duty cycle

This is topic Xenon bulb duty cycle in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

To visit this topic, use this URL:
https://ft-forum.com/ft/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=1;t=009163

Posted by Daniel W. Skeen (Member # 4269) on 03-06-2008, 09:31 PM:

I have heard so many different stories on the "duty cycle" of the xenon bulbs. Is there a requirement that the bulbs have to stay off for a certain amount of time? I've heard 20 minutes off before re-lighting them. I've also heard it's better to leave them on. I have CXL-20's and 30's.

Posted by John Walsh (Member # 168) on 03-07-2008, 08:58 AM:

I think the general feeling is if the time between showings is an hour or less, it's better to leave them on.

Posted by Jeff Taylor (Member # 443) on 03-07-2008, 02:35 PM:

...based on the concept that the strike is more damaging to the tungsten electrodes than an hour of burn time, not necessarily because the lamps need a "rest".

Posted by Mike Renlund (Member # 4675) on 03-07-2008, 02:50 PM:

With my group moving more and more to Digital, and the warranty hours being usually smaller, at least with the Ushios, we turn them off...

On an Ushio 6K the warranty is 500 hours, I don't have to worry about how many times it is struck, all I care about is the hours. If one of those explodes, its about six thousand dollars for a new reflector/lamp tray.

So digital has changed my thinking on this.

Posted by Mark Gulbrandsen (Member # 72) on 03-07-2008, 03:32 PM:

Mike,

I think you need to take a serious look at the screens and lamps you are currently using. I know your largest screen at Gateway is matte white... a new gain screen would pay for itself in about two years time by lowering lamp cost... I know its hard to copnvince the suits though. Also consider trying the new CDXL45 in place of that regular 60. You should get the same light on screen and you will have a better warranty period, less BTU to get rid of and less load on the rectifier. The amount of luck one has with either Osram or Ushio short gaps SHOULD be the same since USHIO makes Osram's short gap lamps! The only difference being the metal ends.

Mark

Posted by Monte L Fullmer (Member # 2797) on 03-08-2008, 12:48 AM:

...esp, in that 500 plus seat, No.1 house!

Thatsa big house with a massive screen that needs that high gain screen to make the dig pict real good looking!

Posted by Mark Gulbrandsen (Member # 72) on 03-08-2008, 09:55 AM:

Monte,

The digital picture there does look really good... even on scope where I'm sure they are straining to get 14fl on the screen in scope. I see films in that auditorium all the time and I can vouch for how good it looks and sounds in there. The whole point is that with a gain screen they could go to a lower wattage short gap lamp and have alot better warranty life... and lower lamp cost. Some day logic will prevail!!
Mark

Posted by Mike Renlund (Member # 4675) on 03-08-2008, 10:50 AM:

Its about 56' on that screen, running the NEC at 96% on a Ushio 6K lamp I get 14.1 fl. Despite the cost of an Ushio 6K, I really love the light, and how even it is.

We've considered changing screens, and have decided for the time being to attempt to work primarily on lamp hours and and lamp costs. It has been a burden, changing so many screens to digital. The cost of running a lamp is just higher. We are actively working with bulb manufacturers to decrease cost, and increase warranty hours. If I get any good news or can share any helpful hints, I will post here and at digitalcinematics.com

Posted by Steve Guttag (Member # 268) on 03-09-2008, 08:51 AM:

So Mark, with a gain screen, you get a hot spot...in that you get the benefits of the gain in the screen only on those light rays that reflect back at an angle equal to the incidence angle to the screen (The screen is brighter in front of where ever you happen to be sitting but darker everwhere else.

Or is your suggestion for a gain screen to also properly curve it to keep the hot spotting to a minimum in the lateral plain (you will still get it in the vertical but it is less noticable since the screens are much wider than tall).

Most of the screens around here are between 1.0 and 1.3 gain and perhaps that contributes to why I find that even my film theatres/rooms have a very flat and uniform illumination. Those screens that I have installed as gain (1.5-1.8 gain typ...depending on the batch of screen...unless it is a Stewart), I have indeed curved using an old Mathematica program I wrote in college...that works too and I personally prefer curved screens. BUT there are lenses for film that will pincushion the image (Magnacoms, .52X "C" magnifiers) such that the distortion introduced by the curve are minimized...no such lenses exist for Digital yet and digital seems to have this silly aversion to digital keystone correction and other digital image manipulation at the theatre level...all one can do is crop the picture to fit the curve.

So, in short, I'm confused by your suggestion to install a gain screen...at best that is just a partial solution

Steve

Posted by Mark Gulbrandsen (Member # 72) on 03-09-2008, 10:37 AM:

Steve,

The frame is for the most part already curved to a point where a 1.4 gain screen would slap right in place and light would stay even. Its not curved enough for any higher gain than that. This is a screen where in scope(film) I once measured 6 foot lamberts with the PSA with a new 6kw lamp straining at max. in a Highlite 2/Simplex X-L. It ran this way for 4+ years... pathetic to say the least.

Personally I don't care much for the look of a matte white screen. They generally appear to have a more diffused look while a gain screen of 1.4 or so certainly presents more snap and is contrastier. No... I don't need to measure the contrast difference to know... it Its plainly visible to my eyes and many others. As you mention there are distortion producing magnacoms and such... but I certainly HOPE you are not using those... sure the distortion may correct for some of the distortion a curved screen introduces but Magna-Coms also lack any light baffles at all and have horrible light scattering which in turn lowers contrast alot.... nasty lenses! All modern lenses incorporate carefully engineered light baffles within to keep light scattering and reflection to a minnimum. I am not a big fan of going to 1.8 but we do have a customer that is and fortunately he allows us to do deep curves to keep the hot spot at bay. We just put the DP-100 and ZX's on his screens and light distribution was pretty darn good... but again they were curved properly for the situation.

In at least some locations you also need to keep daily operating expenses at bay and still put up a picture that meets stsndards... going with a gain screen to keep the lamp used with-in those that have longer life/warranty works well.

Mark

Posted by Steve Guttag (Member # 268) on 03-10-2008, 10:38 AM:

quote: Mark Gulbrandsen
No... I don't need to measure the contrast difference to know... it Its plainly visible to my eyes and many others.

And your eyes would be quite wrong too. Contrast is the black to white ratio, as you know. If white is 16fL then it is a matter of when one hits the lowest black level that sets the contrast ratio...screen gain can affect what it appears to be based on incidence/reflectance angle of the limiting black levels (be they source originated or parasitic light within the room itself).

What you are seeing that gives you that snap is that the light uniformity is not as good as a matte white and thus creates a sharp transition...however this is not contrast persay but a loss of darker detail...think of it as a gamma curve in that you are seeing mostly white or black and not the full spread...detail is what is lost.

I've seen people use the same arguements for liking silver screens...very saturated colors and VERY contrasty...though if 16fL is set for the white point, no more actual contrast. Now some will let their gain screens get up there to say 22fL and at that point yes you can get some more contrast but you are also not presenting the picture as it was made...film pictures are timed for 16fL open gate or 14fL for DCinema.

One of the edges Dolby 3D has over Real D is that Dolby gets their colors right by calibrating its color and white points to what was actually recorded...Real D, with a silver screen will not have that...the colors will be oversaturated and the illumination is inherently less uniform.

BTW, I'm not dismissing your preference to a higher gain screen looking more contrasty...you are not alone in that. In fact, I've had the discussion with others on lens manufacturers...Schneider is more contrasty...they are more blue too...however if you project resolution targets, ISCO, though appearing to have less contrast will resolve more detail. That said, there are those that absolutely love the Schneider look over the ISCO...and I respect that...but in terms of presenting the image as it was created, one needs to put aside one's personal preferences and just try to get that image (or sound) to be as exact a reproduction as they can. A gain screen rarely if ever achieves that and only when curved...which brings about other artifacts.

BTW...a Stewart Snomatte 100 is indeed a 1.0 gain matte white screen and it has a lot of pop to it...but it is way more expensive than the typical exhibitor will spend. I probably use more Ultramatte 130s (1.3 gain) than anything and it does seem to strike that balance between even light and a little more gain. I've measure some "matte-whites" that were not matte white at all and had a gain as much as 1.2.

Steve

Posted by Louis Bornwasser (Member # 3063) on 03-10-2008, 11:12 AM:

Mark: Osram bulbs are made in Germany and Christie bulbs (for the most part) are Ushio-Japan.

No XBO bulbs are made by Ushio/Christie. This has just been confirmed to me by both Osram-Germany and by 2 Osram sales people here in North America.

If what you say is true, there would be legal issues related to mislabeling country-of-origin with U S Customs. Louis

Posted by Mark Gulbrandsen (Member # 72) on 03-10-2008, 01:24 PM:

Steve... I agree 100% with what you say including the differences in lenses. IN fact there is a difference of lens to lens of the same focal lentgh and same manufacturer. What I see is not something that is really of much matter to the movie going patron... they are not going to be sitting there saying to each other...."My Bob... that gain screen has such poor light distribution, I'm not comming here again". Indeed, a gain screen of around 1.4 is just something I prefer... even if light distribution is a bit wobbly... The high gains are much prefered by just about everyone I do work for. However light distribution on a properly curved 1.4 gain screen is actually pretty good if done correctly. Definately though... nothing is going to beat the light distribution of a matte white. I totally agree on silver... horrible!

Louis,
Forst off its probably not something that many at OSRAM are privy too... and second Its just some of the short gap lamps... Just place them side by side as I have... The glass and electrodes are identical to USHIO... its hardly a coincidence! The metal ends are more than likely made by Osram and put on in Germany so they can say "Made In Germany" without creating legal issues. An item doesn't have to be 100% made somewhere to claim it. I got this from someone at Christie and I have personally had both lamps one in each hand at the same time. Also don't forget that Ushio is a large Corporation... thay could very well have a plant over in Germany.... I can check if you'd like.

Mark

Posted by Steve Guttag (Member # 268) on 03-10-2008, 02:11 PM:

Ah Mark...that dreaded Psycoptics thing again...I like 1.3 gains myself but that is pretty close to 1.4...but honestly, I have no problem with matte-white.

Now as to your statement

quote: Mark Gulbrandsen
"My Bob... that gain screen has such poor light distribution, I'm not comming here again".

Isn't some form of that used to justify any substandard system...picture or sound? Audiences sit and see scratched film and don't complain and seem to come back...about all that can keep people away are crappy stories.

BTW...whose 1.4 gain screen do you use? About all that boast their screen is 1.4 is Harkness with their Perlux 1.4 and MDI with the Northview 1.4 Hurley is 1.5-1.8, depending on the batch. Technikote isn't normally even uniform from on the same screen though I think their pearl is their best surface. Stewart is uniform and on the money but they tend to go to a 1.5 gain (Ultramatte 150) and I doubt many of your customers are in the market for a Stewart...so my guess is Harkness. The Northview has a rather steep fall off (down 40% in just 15-degrees).

Steve

Posted by Mark Gulbrandsen (Member # 72) on 03-10-2008, 03:56 PM:

We generally only use Harkness screens be what ever surface it is. Have had too much trouble with Hurley and Technikote isn't even in the running any more..were they ever?

Mark

Posted by Darryl Spicer (Member # 711) on 03-10-2008, 07:18 PM:

I believe we used to use Hurley screens back in the late 80's early 90's but they tended to show more seams in the screens. Now we use Harkness and I think they look damn good. We have a couple of 1.4 gain screens that are 46 feet wide and the hot spot issue is minimal at best using 4k Christie lamps in SLC consoles we get very even distribution with I believe right at 16 ftl center with a -2 ftl on the left and right. When you stand to the side you really don't have any brightness shift and the screen is not curved.

Before they took out the 1.4 gain 40 foot screen and replaced it with the silver screen I thought the Digital image looked damn good. I wish we didn't have to have that silver screen because of the severe hot spotting.

Edit for a spelling mistake.

[ 03-10-2008, 09:05 PM: Message edited by: Darryl Spicer ]

Posted by Mark Gulbrandsen (Member # 72) on 03-10-2008, 08:55 PM:

About three years ago we had this problem and since then we pretty much only sell Hurley if a customer demands it. We had 5 out of 8 at a plex look like this and this one at a distant theater in Montana. Hurley replaced the Montana screen only after constant phone calls and telling them how well Harkness stands behind their product...(They do!) Then they gave in and replaced it. I don't remember if the screens at the plex were replaced or not... they were not as bad as this one but I suspect they got replaced. This is not an enhanced photo... its right off the screen with a pocket Nikon.

Hopefully they have since rectified this problem... its the kind of problem that costs the dealer AND the manufacturer [Roll Eyes]

.
Mark

Posted by Gordon McLeod (Member # 33) on 03-10-2008, 09:43 PM:

I have found MDI and Lesna stand behind their screens very well and I am very happy with the mdi 1.4 gain screens

Posted by Steve Guttag (Member # 268) on 03-10-2008, 09:58 PM:

Harkness drops 40% of their light at about 20-degrees off-center on the Perlux 1.4 So your statement about only being 2fL down, Darryl, on the sides versus the center seems improbable unless you are VERY far away from the screen when you measure it.

Harkness can indeed have very good screens. I have lived through bad batches with "zebra" stripes. We've had good MDI, Hurley and Harkness. We've had less than steller ones from them too. Then again, I've had a couple bum Stewarts.

I have an installation coming up with Harkness Pearluxs...I will be using a PSA when measuring the systems...I'll make a careful note of what the eveness of the screen is.

Steve

Posted by Darryl Spicer (Member # 711) on 03-11-2008, 01:58 AM:

The left and right numbers could have been lower if measured closer to the screen. It was taken all the way back at the projector port. Our screens have a slight tilt back for some reason or another I don't know if that had anything to do with it or not. Next time my engineer comes in to do his PM I will get the meter from him and verify the light output on those screens again.

Posted by Mark Gulbrandsen (Member # 72) on 03-11-2008, 09:03 AM:

I will say though that plus or minus 2 is about what you should see with a properly curved frame with a 1.4 gain Harkness. Still no where as even as any matte white though which on dailies jobs I was able to get almost perfectly flat using a super-lumex.

Mark