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TOPIC: Screen Size/Brightness

Screen Size/Brightness 10 Nov 2003 20:21 #28953

  • Mudbrother
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Hi all,
How do you go about determining the ideal wattage for your bulb/lamphouse based on screen size and projector throw?

While we're at it, how do you determine your ideal screen size? I want to figure out a good screen size for a 30'x30' proscenium. I figure with a 29' wide screen, we would need about a 13' height?

Thanks for any information,
Rance Edwards
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Re: Screen Size/Brightness 10 Nov 2003 22:55 #28954

  • outaframe
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HELLO RANCE, and welcome to the "club"... Well, your first question here has no DEFINITIVE answer, but here are some things to consider... First, you can't buy a screen exactly the size you're considering: you will probably need to buy a 30' wide screen, which will probably be 18 to 20 feet high, and then mask it to fit the projected image size of you lens, at the throw you'll be using... Some manufacturers will claim their 1,000 watt Xenon lamp will light up to a 30' screen, but this is optimistic, and doesn't say at what aspect ratio... SMPTE specs call for a light intensity of 12 to 22 foot lamberts (lumens per square foot), with 16 foot lamberts on a matte white screen being a desireable standard... For a scope (2.35 to 1) aspect ratio that would mean about the 13' height you referred to... If this same 13' (fixed) height is what you want for "flat" (1.85 to 1) as well, the 1,000 watt lamp may skid by at the lower limit of the specs... However, if you ALSO want the "flat" picture to be 30' wide (16+' height), it will probably require a larger lamp... If you look at the aperture plate used for "scope" you will see that it's about the size of a postage stamp, and uses most of the round cone of light that's available from the lamphouse's optical system... But the "flat" aperture plate is only a bit more than 1/2 as high, and actually "wastes" most of the light that's available... The image height of the "flat" picture, and the optical efficiency of your lamphouse is what will determine how large a lamp you will need... At 13' height, your flat picture will be 24' wide (312 square feet), but at 16 1/4' height, the flat picture will be 30' wide (488 square feet), or about 1.56 the size of the 24' wide picture... Most lamphouse optics are somewhere between 10% and 15% efficient, when you deduct the lens and port glass light losses... Some may range up to 20%, but this is very optimistic... A 1,000 watt Xenon bulb has about 35,000 lumens gross output, so will have a net screen reading of 3,500 lumens (10% efficiency) up to a theoretical maximum of 7,000 lumens, AND this figure is then divided by the square footage of the image, to determine the lumens per square foot... A very efficient 1,000 watt lamp will light a 24' flat picture, but for a 30' flat picture, you will need a larger lamp... A 1,600 xenon bulb has a gross lumen output of about 55,000 lumens, and a 2,000 watt bulb has about 80,000 lumens gross output, so these are things you will need to consider... Most Xenon lamps are run at about 85% amperage when new, then gradually increased to an absolute maximum of 105% amperage as they age and darken... You can do the math, and make your selection based on how efficient your lamphouse is reported to be, but it's not an exact science...

[This message has been edited by outaframe (edited November 10, 2003).]
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Re: Screen Size/Brightness 11 Nov 2003 00:30 #28955

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Outtaframe, thanks for the speedy reply! I've been a 'lurker' of the forums for quite awhile. What kind of screen size would you recommend for the proscenium opening? I calculated that 13' would be the height of a scope image 29-30' wide, but it doesn't have to be. I figured it's usually easier to mask the sides rather than up/down. I had calculated a need of about 6,000 lumens for a 29'x13' screen with scope image (insert standard screen size here.) So if I can count on a 10%-15% efficiency rating from lamphouse optics.. that would mean I would need about a 60,000 lumen lamp. So, by what your saying, I should count on at least a 2000 watt lamp, right? (This theatre has a throw of 60-70'.) And of course this is assuming a 24'x13' flat image masked.
Thanks again for your help!
Rance Edwards
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Re: Screen Size/Brightness 11 Nov 2003 02:00 #28956

  • outaframe
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HELLO, AGAIN <> Actually you will have to mask BOTH width and height, and using fixed masking for the height leaves the option of either fixed or movable masking for the width... Of course, movable masking for the width gives a nice razor sharp edge to both scope and flat, but isn't absolutely necessary: you can just let your flat picture be centered in the area masked for scope... It's done both ways... You will need to check lens focal length/throw distances to select lenses that will fill a height of masking that is a (minor) compromise for both, and may need to do some aperture filing to one or the other aspect ratio to fill both ratios... You need a projected image that spills over onto the masking about 2" around the perimeter of the scope, and about 2" top and bottom for flat (IF you don't move the masking for flat)... Lens charts and/or calculators will be close, but you need to project an actual image (in focus) to get it exactly right... Sometimes the exact focal length lens you need isn't made, so you have to compromise a bit... Yes, a 29-30' scope picture, and a 24' flat picture will be approximately 13' high, and this is the easiest way to go... Because of the 30' width of your proscenium, that has to be the screen limit unless you want to do some major remodeling... So, 24x13 is 312 sq ft X 16 lumens = 4,992 lumens to light it... IF your lamphouse is 10% efficient, a 1,000 watt lamp would give you 3,500 lumens (not enough), but IF it's 15% efficient, that's 5,250 lumens (enought, with a little reserve)... A 1,600 watt lamp would yeild 5,500 to 8,250 lumens, depending on efficiency (more than plenty)... It's COMMON to overpower a bit, but the higher the wattage, the more the lamphouse, rectifier, and lamps will cost to buy, and OPERATE... Another thing to consider is the rated life of the bulb: all bulbs are NOT equal, and can even vary between manufacturers... Personally, I would try to find a high efficiency 1,000 watt setup for your location: over the long pull that will save you money over the average efficiency 1,600 watt lamp, and is somewhat less likely to cause some of the problems that are common to higher wattage lamps... But, as I said, many will overpower, and can offer their rationalization for doing so: there is no "cast in stone" answer...
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Re: Screen Size/Brightness 11 Nov 2003 02:16 #28957

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PS <> I guess I didn't make all this clear: Flat is the least efficient ratio because of the smaller aperture plate and the light waste it causes... IF you can light your flat screen with the lamp you choose, the larger aperture of the scope image will take care of the additional screen area (and width) of scope (as long as both aspect ratios are the same HEIGHT)... I assume you realize that scope is an anamorphic process, and that the image is "squeezed" (horizontally) when it is photographed, then expanded (opened back up to its original width) when it is projected by the scope lens, or anamorphic attachment... For any given screen height, the focal length of a scope lens will be considerably longer than the lens for a 1:85 to 1 flat picture of that same screen height...

[This message has been edited by outaframe (edited November 11, 2003).]
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Re: Screen Size/Brightness 11 Nov 2003 02:39 #28958

  • Large
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I run 2,000 watts on my 10' x 25' screens. They're nice and bright.

I run 3,000 watts on my 13' x 30' screen and there is good but not great light.

Also, some lamphouses are better than others.
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Re: Screen Size/Brightness 11 Nov 2003 07:47 #28959

  • Mudbrother
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Thanks for the great answers everyone. I think I have a good idea what I'm looking for now. I think a fixed upper/lower masking with moveable sides is the way I'd like to go. This theatre already has a couple of Strong Super Lumex 39000 lamphouses which I believe will support the 1.6k to 2k wattage bulbs (I'll need to double check that.) I'm not sure of the efficiency on this model, or on the working condition of these lamphouses (or their rectifiers for that matter
). I'm helping an historic downtown theatre in Southwest Virginia renovate, and I wanted to make sure I had the right advice regarding screen size and adequate screen illumination.
As for myself, I'm the General Manager of the historic Lyric Theatre in downtown Blacksburg, Virginia. We're a single screen 1930's movie palace. We renovated and reopened back in 1998 and have been running quite successfully since then.
Thanks, Outtaframe and Large for your advice!
Rance Edwards
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Re: Screen Size/Brightness 11 Nov 2003 08:25 #28960

  • John Pytlak
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A "rule of thumb" for a matte white (gain=1) screen is 5 watts of xenon power per square foot of "scope" screen area. If you use a properly curved "gain" screen, you can reduce the power proportionately (e.g., a screen with a 1.5 gain will need about 5/1.5 = 3.3 watts per square foot. But a gain screen MUST be properly curved per SMPTE Recommended Practice RP95, or you will not have uniform illumination. Also, a very high gain screen works best in a long, narrow auditorium that uses a moderate to long focal length lens.

Always size your screen to "care about composition":
http://www.kodak.com/US/en/motion/newsletters/pytlak/spring2001.shtml

Standard SMPTE 196M specifies the preferred viewing distance is between 2 and 4 times the height of the image, so most of your seats should be in this range.

John P. Pytlak, Senior Technical Specialist
Customer Technical Services
Entertainment Imaging
Research Labs, Building 69, Room 7525A
Eastman Kodak Company
Rochester, NY 14650-1922
Telephone: +1 585-477-5325 Cell: +1 585-781-4036 Fax: +1 585-722-7243
E-Mail: This e-mail address is being protected from spambots. You need JavaScript enabled to view it
Website: http://www.kodak.com/go/motion
John P. Pytlak, Senior Technical Specialist
Customer Technical Services
Entertainment Imaging
Research Labs, Building 69, Room 7525A
Eastman Kodak Company
Rochester, NY 14650-1922
Telephone: +1 585-477-5325 Fax: +1 585-722-7243
E-Mail: This e-mail address is being protected from spambots. You need JavaScript enabled to view it
Website: http://www.kodak.com/go/motion
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Re: Screen Size/Brightness 11 Nov 2003 11:08 #28961

  • muviebuf
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Screens may customed ordered in any size and any dimensions. Mine is 15 x 30 flat matte and was manufactured by Hurley in Maryland to the exact measurements and specifications that we provided. Install was by Walsh Systems out of the DC area.

As prints these days tend to be dark it is always a good idea to overlamp a bit. I use a 2500 with a Super Lumex lamphouse (80 foot throw to the screen) and the picture is bright and sharp. According the charts for my throw to the screen with my size I "ideally" needed 2,200 watts. By runnign the bulb at 90% of capacity you get extended life and a quality picture.
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Re: Screen Size/Brightness 11 Nov 2003 12:17 #28962

  • John Pytlak
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Remember, it's mostly the SIZE of the image and the GAIN of the screen that determine the power requirements.

The THROW factors in only as it determines the lenses that can be used (for example, a really long throw may require a very long focal length lens that may be limited to a larger f/number and be less efficient).

John P. Pytlak, Senior Technical Specialist
Customer Technical Services
Entertainment Imaging
Research Labs, Building 69, Room 7525A
Eastman Kodak Company
Rochester, NY 14650-1922
Telephone: +1 585-477-5325 Cell: +1 585-781-4036 Fax: +1 585-722-7243
E-Mail: This e-mail address is being protected from spambots. You need JavaScript enabled to view it
Website: http://www.kodak.com/go/motion

[This message has been edited by John Pytlak (edited November 11, 2003).]
John P. Pytlak, Senior Technical Specialist
Customer Technical Services
Entertainment Imaging
Research Labs, Building 69, Room 7525A
Eastman Kodak Company
Rochester, NY 14650-1922
Telephone: +1 585-477-5325 Fax: +1 585-722-7243
E-Mail: This e-mail address is being protected from spambots. You need JavaScript enabled to view it
Website: http://www.kodak.com/go/motion
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Re: Screen Size/Brightness 11 Nov 2003 14:50 #28963

  • outaframe
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RANCE <> You didn't mention that you already had lamps & rectifiers, but what you have should be ideal... The Strong setup is good quality & should accept a 2,000 watt lamp, which is one of the best for warranty/life/cost... If the optics are in good condition, it should easily light your proposed screen, and do so with a ton of reserve... Nobody has mentioned the allignment, but that's something that is often poorly done, and is a major factor regarding the light that reaches the screen... Poor allignment can waste half the available light, and cause dark areas in the picture... Also, you need optical glass in your ports, and to keep it, the lamp optics and your lenses squeaky clean: every little bit of light you can gain adds to the efficiency...
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Re: Screen Size/Brightness 11 Nov 2003 14:57 #28964

  • Mudbrother
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Sorry Outtaframe, I didn't mean to leave the lamphouses outta the equation.
They're actually sitting in a warehouse right now, and I'm not even certain whether they are in working condition. (They look ok, and I am assuming they will work ok for this theatre.) I worded my original question a little vaguely as I wanted to know the 'rules of thumb' that you guys have taught me rather than a specific answer.


Rance
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Re: Screen Size/Brightness 14 Nov 2003 12:52 #28965

Always start with more light than required it is easier to get rid of it than find it
The superlumex is rated up to 2.5K and with a pearlescent screen a 2K will be excellent
Also the 2K has the best warranty lifespan/cost ratio

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Re: Screen Size/Brightness 14 Nov 2003 13:37 #28966

  • John Pytlak
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For a 12 x 29 foot screen, a 2000 watt lamp would certainly be enough to light a matte white (gain=1) screen, and very nice (even better) with a properly curved moderate gain (pearlescent) screen. As Gordon notes, you can always trade excess light for another advantage (e.g., defocus the lamp slightly for even better uniformity).

John P. Pytlak, Senior Technical Specialist
Customer Technical Services
Entertainment Imaging
Research Labs, Building 69, Room 7525A
Eastman Kodak Company
Rochester, NY 14650-1922
Telephone: +1 585-477-5325 Cell: +1 585-781-4036 Fax: +1 585-722-7243
E-Mail: This e-mail address is being protected from spambots. You need JavaScript enabled to view it
Website: http://www.kodak.com/go/motion
John P. Pytlak, Senior Technical Specialist
Customer Technical Services
Entertainment Imaging
Research Labs, Building 69, Room 7525A
Eastman Kodak Company
Rochester, NY 14650-1922
Telephone: +1 585-477-5325 Fax: +1 585-722-7243
E-Mail: This e-mail address is being protected from spambots. You need JavaScript enabled to view it
Website: http://www.kodak.com/go/motion
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Re: Screen Size/Brightness 17 Oct 2005 12:32 #28967

Mr. Pytlak,

What is the proper curve of a gain screen as per SMPTE Recommended Practice RP95?

Where can I find information on SMPTE's recommmendations?
Since 1987
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