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Author Topic: How Many Lumens? Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 08-03-2003 10:47 AM                     Frank...a couple things here As to light...lumens is lumens...foot-lamberts is foot-lamberts...there is nothing hokey going on here. foot-lamberts is reflected light so one must know what the screen material and square footage is in order to calculate...how could a projector manufacturer state an fL figure? They only can state what their projector is putting out, not what screen material and what size screen you are using. If you look at John's (and mine) math you will see that both the screen reflectivity and square footage is given (matte white screen) As to light output...there is wizardry going on there. How to get more light is always an issue. However one thing is constant...a point source form of light is more efficient than a larger source. So, if I can get the arc (or any source of light smaller) I can have a more efficient system. One thing xenon manufacturers and users have discovered is that more watts (an electrical expression) does not mean more light output. The current crop of 6KW xenons are generally brighter than last decade's 7KW xenons. The big reason? They 6KW has a smaller arc and can be more efficient (the electrodes are also smaller so the shadow they create is diminished). One trend you will see with video projectors is the imagers are going to get smaller (as technology allows). This will increase efficientcy. As the imager (DLP, LCD or what have you) gets smaller, the light source must also get smaller (smaller arc) and we get closer to the theoretical limits of light efficientcy. Remember, with film we are constrained to established aperture sizes...not so with the vidiots. In fact, those people really don't have to think about it...all lenses are expressed in "throw-ratios" that already take into account the size of imager. You will also see that future generation of "Dcinema" projectors will go away from film-style lamphouses since they will crave efficientcy. Right now, with the current DLPs you nead nearly 50% more "watts" for the DLP as compared to a film projector. That is, if your film projector has 16fL with a 4KW lamp...plan on 6KW for a DLP. Remember, for DCinema, they have to "deal" with 1.85 and 2.39 and not the easy-pezy sqaure stuff we abandoned in 1953. Next thing going for video projectors in the light efficientcy wars...their apertures...at the moment...are almost all either 4:3 or 5:4. Compare that to a film aperture. They are not wasting a good portion of their light going through "light shields" and then smacking on an aperture plate. While not square, a 5:4 imager is only 1.25:1. Wanna see the difference in your film projector? Measure your brightness...take off the anamorphic attachment to your scope lens and measure again...see how bright your system is with just a small square picture. As to ratios...the Video people are correct on that one. 4:3 is an exact expression. 1.33 is an approximation. Likewise for 16:9 versus 1.78. Anyone that knows how to use a slide rule understands carrying exact ratios is the way to go. Lets face it film's facination with decimal equivalents has taken on the absurd...we use film expressed in millimeters but all other aspects are in inch form...even the expression of "footage" (regardless of country you are in) ensures some conversion. Our aperture sizes are such that .446 x .825 is for flat...what is with a number like .446?. Heck even the "Academy" aperture is .602" tall...couldn't leave well enough alone at .600? Or lens diameters...in metric they are 70.6mm in diameter...yeah, yeah but they started out in English measure...fine 2-25/32" (2.78125)...where the heck did that come from? 2.5, 2.75, 3" wouldn't one of them suficed? At least when the 50's rolled around they went to a solid 4" diameter barrel! The aperture was a nice rosey .715 x .910 too...yeah for CinemaScope! However that just wouldn't do so we went to a mag/opt and turned a nice easy aperture that was .715 x .838 or some such nonsense that has been played with ever since until it settled in a more civilized .690 x .825. So don't give me any more of you white zone Bull sh#$%....er I mean decimal equivalent is better than an exact ratio. Lets face it, 1.85 is going to stick...it seems nice and finished...1.78 wouldn't stand a chance...it LOOKS like an equivalent....why do think there is all the fuss with scope? 2.39 doesn't have near the finsihed sound of 2.35. Respectfully submitted.... Steve  |  IP: Logged John T. Hendrickson, Jr Jedi Master Film Handler Posts: 889 From: Freehold, NJ, USA Registered: Apr 2001 posted 08-03-2003 11:57 AM                     Bravo, Steve!  |  IP: Logged Randy Stankey Film God Posts: 6539 From: Erie, Pennsylvania Registered: Jun 99 posted 08-03-2003 01:13 PM                     According to the story I heard, George Eastman is responsible for a fair bit of it. The way it was told to me, when he was developing the first film that we call "35mm", he used panes of glass taken straight from the windows of his house. He progressively cut the pieces of glass in half until he came up with a strip that was "about right". Logically speaking, all of the 35mm film in the world has the dimension(s) it does because of the size of the windows in the Easman house! And, by extension... Since John P. works for Eastman's company... IT'S ALL HIS FAULT! J.K.  |  IP: Logged Frank Angel Film God Posts: 5305 From: Brooklyn NY USA Registered: Dec 1999 posted 08-03-2003 03:06 PM                        Leave it to Steve to clear up the sweet mysteries of life. I say, round everything off to the nearest whole number and be done with it. So do 35mm projector manufactures ever use lumens in their specifications when they are describing their console/head systems? Seems like film people and video people could get on the same page with this. Plus, I do understand the difference between lumens and foot-lamberts but I still don't see why video manufacturers can't use the standard benchmarks that will tell you with some certainty how their projector will compare to film or even other video projectors when being used in real-life. I have a hard time seeing how useful lumen claims can be if a projector that claims to put out 11,000 lumens won't produce an image as bright as one that claims to put out 3500, all other things being equal. Shouldn't a projector manufacturer be able to say, my projector will be able to produce 16 foot-lamberts on an matte white with an image size of x? Then any idiot, be he film or video, can look at the numbers and say, this one is the one I need in my theatre. As for that difference in light efficency between passing light through a film aperture and the DLP nano-mirrors struck me when I first heard about the SMPTE demo. They said they were projecting on a 40ft screen and using a 7000w lamp. I wondered how come no one pointed out that you don't need a 7000w lamp to adaquately light a 40ft screen when using a 35mm system. Seemed like just in terms of energy cost for an exhibitor, that was a BIG difference, but I didn't hear anyone making much of a point about it. I also wondered how aiming that much energy at a stationary object will effect it over a long period of time. What happens to those little mirrors after a year or two....but I digress. As for scope, I hear guys refusing to call it 2.39 and they say the SMPTE can't make them. They are calling it 2.4:1, period. And as for the curse of the "light shields," as many have said over and over, cropped wide screen was a stupid idea right out of the starting gate -- never shoulda happened. The only thing that ever made any sense is to use the appropriate anamorphic to get whatever size wide screen you settle on. You want 1.85 (yup, it's a nice number), then do it full-frame -- use all the film geography and the appropriate anamorphosis -- you waste no light and you let ISCO and Schnieder start up a new lens line -- time to develope a quality variable anamorphic attachment that will work for old scope and new wide screen. Then after everyone gets used to the new wide screen numbers, you go back to the SMPTE and say you need to reduce the aperture height to cover up negative flashes, and you get even newer numbers. Frank  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 08-03-2003 03:45 PM                     Frank... I believe you will find that you will be able to predict video projector brightness with the Lumens spec better than film projector brightness with a wattage spec. If one projector states that it puts out 5000 ANSI lumens and another states it puts out 11000 ANSI lumens then I'd be willing to wager the 11,000 one will look about twice as bright on the same screen with the same size image as the 5000 one. It is the film industry that mucked that up. Why, oh why, do we express our light output in WATTS? Watts is an electrical measure...Volts * Amps = Watts. While there is often a corellation between wattage and light output within the same lamp time (xenon short arc, for instance) you can equate watts between lamp types nor draw any real conclusions on actual light output of the projection system. A lamphouse manufacturer can't really tell you what size you need to get 16fL give a particular size screen and material...they would would have to know the projector AND the lens you are using too (presuming no projection port glass since that will take away some as well). Different lamphouse manufacturer's use different reflector designs with understandably different efficientcies. You have projectors with conical shutters, flat shutters, barrel shutters, single blade, two blade, three blade...large, small ...etc...the efficientcy of the systems are all over the place. The lamphouse manufacturer also has to think about you changing the lamp...some designes need contortionists to change those lamps there is so little room infront of the reflector, even with a pivoting lamp table! So which projector does a lamphouse designer design to? Certainly the "house brand" of projector seems like a good idea, if one exists but that might limit your sales to those that buy the package. Then there is the lenses...who makes the best lens? Define best? Can everyone afford that? Does the brightest lens offer the sharpest picture? I'm sure if we went to f1.0 lenses the picture will get brighter but the focus will zip away too. Remember too, film has pulsates when it is heated up so the film projection lens MUST have an adequate depth of focus that the video lens does not.... The video lens and hence the projection system, is designed with a specific projector in mind (or a new projector is designed for an existing lens) so once again a video system can more easily state their lumen output since everything is known. When lamphouse manufacturers were stating how big a screen their products would light...they were using non realistic f/1.7 lenses on pearescent screens with 12fL...kinda like boasing a 36" TV only to find it is 36" on the diagonal. The closest anyone could get to the Lumen output are those manufacturers that offer complete systems (Christie, Strong, Kinoton, Cinemeccanica....etc) but then they would have to qualify that with a particular lens (manufacturer, size and model) and that could be construed as an endorsement...and I'm sure the most efficient size/model lens for their particular projection system would be used that may not tell you what you want to know if they use a 90mm ISCO and you have a 50mm Schneider (again, those are THE only two companies to consider in film projection lenses). Steve  |  IP: Logged Robert Throop Master Film Handler Posts: 412 From: Vernon, NY USA Registered: Jun 99 posted 08-05-2003 10:06 AM                     Years ago, National Carbon and some lamp manufacturers published lumen ratings for carbon arc lamps. They would specify the lamphouse characteristics (carbon combination, mirror size and current), the lens speed and focal length, and the aperture size. They would also state that no port glass, heat filter, lens attachment or shutter was used. Why can't the same thing be done with xenon?  |  IP: Logged John Pytlak Film God Posts: 9987 From: Rochester, NY 14650-1922 Registered: Jan 2000 posted 08-05-2003 10:30 AM                        The lumen output for carbon arc lamps was published in the National Projection Carbon Bulletins, Issue #3, December 1957, pages 4-7. It's in the Film-Tech "Manuals" section: http://www.film-tech.com/manuals/CARBONBULLETINS.pdf For a 35mm scope image, the larger rotating carbon lamps could produce between 30,000 and 40,000 lumens depending on the trim and current, with the "record" being 42,000 lumens for an experimental 11mm "Ultrex" carbon at 195 amperes and 80 volts. That trim was consumed at 45 inches per hour! The lumens were measured with a lens matching the f/number of the optical system, and no shutter.  |  IP: Logged Tim Reed Better Projection Pays Posts: 5246 From: Northampton, PA Registered: Sep 1999 posted 08-05-2003 10:38 AM                       I remember some manufacturers also used to give the intensity in candellas.  |  IP: Logged

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