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Author Topic: What the heck is a lampere???? Eliza Plumlee Film Handler Posts: 6 From: portland, or usa Registered: Mar 2007 posted 04-01-2007 04:58 AM                     I have a psychotic director who wants to do a screening at my theater and demands to know how many lamperes (lampheres???) my projector has or is, or something. I don't know how it is spelled, but cannot find out what it is anywhere. an ideas? perhaps a measurement of light or energy? how do you find out how many you have? I work on a dual projection system. Century projectors. thanks.  |  IP: Logged Monte L Fullmer Film God Posts: 8367 From: Nampa, Idaho, USA Registered: Nov 2004 posted 04-01-2007 05:03 AM                     the term is footlampberts - fl .. measures of brightness from a projector measured on a screen by a light meter. (courtesy of this famous link ..lots of info is obtained here). I'm sure that the director there wants the recommended 16fl measured on that screen for his film was probably produced with this light requirement. Anything different would make his film look terrible good luck - Monte  |  IP: Logged Frank Angel Film God Posts: 5305 From: Brooklyn NY USA Registered: Dec 1999 posted 04-01-2007 07:39 AM                        Find out what size lamp is in your lamphouse and then tell this genius director that your projector puts out a whopping 2000, 4000 (whatever it is) of pure white voltamps of energy. Then ask him what kelvolumens his film was shot at.  |  IP: Logged Richard Fowler Film God Posts: 2392 From: Ft. Lauderdale, FL, USA Registered: Jun 2001 posted 04-01-2007 09:43 AM                     He is probably talking about lumen output of projector which can be converted to foot lamberts or candela after striking a screen surface, factoring screen fabric gain in the measurement.  |  IP: Logged Tim Reed Better Projection Pays Posts: 5246 From: Northampton, PA Registered: Sep 1999 posted 04-01-2007 07:31 PM                       Sounds to me like he's confusing LUMENS with AMPERES.  |  IP: Logged John Hawkinson Film God Posts: 2273 From: Cambridge, MA, USA Registered: Feb 2002 posted 04-01-2007 09:05 PM                     Hi, Eliza. Everybody's told you true, but let's try to put it on context. If this guy really knows his stuff, he'd want to know how bright your screen is. And we measure that in foot-lamberts reflected off the screen. Unfortunately, if he really knew his stuff, he'd know that almost no projectionists actually know how bright their theatres are in foot-lamberts, because the proper tool to measure it (a spot photometer) is really expensive and specialized. Ideally your theatre technician has one, but probably that doesn't help you. He might just be asking how bright your lamphouse is, to get an idea of how bright your screen might be. That would be the type of lamp you have, like 2K (2 kilowatt), 4k, etc. etc. That you should know (or be able to easily check; hopefully it's written on the bulb maintenance card for your lamphouse, but you can check the current and voltage to determine it). There are a lot of factors that affect how bright your screen will be for a given lamp wattage (size and gain of screen, type of lens, type of shutter, quality of lamphouse reflector, etc., etc.) but absent all other things, wattage of the lamp gives a general indication. He might also be asking about lumens (lm), which is a measure of light output (luminous flux). It's typically used when talking about video projectors, and generally not used when talking about film projectors. Lumens are usually measured at the output of a video projector (but not including a screen), and are generally numbers from a manufacturer's datasheet. If he's asking for lumens, well, remind him this is not a video projector. You could check the spec sheet for your lamp (e.g. for an OSRAM XBO 2000W/H OFR, it is 80,000 lumens). But it's not a meaningful number because of projector/lamphouse differences (as well as screen and lens differences). It's possible he's asking about amperes, but it seems unlikely. The ampere is a measure of current, and it is mostly dictated by bulb size. You should be able to check the ammeter on your lamphouse to see what it is. For each bulb size there's a range, for instance, a 2k bulb has a nominal current of 70A, but an acceptable current range of 50A-85A, for varying the brightness. It's also possible he's asking about an obscure unit like the candela, the measure of luminous intensity. Again, you can look that up from your lamp's spec sheet (7500cd for a 2KW lamp), but it's not meaninful. Frank was joking when he mentioned "kelvolumens," of course. A "volt-amp" is almost the same as a watt, but not quite--usually volt-amps are measured on the input side of a device, and watts on the output, the difference being in the efficiency of the device. Hope this is helpful. --jhawk  |  IP: Logged Eliza Plumlee Film Handler Posts: 6 From: portland, or usa Registered: Mar 2007 posted 04-02-2007 02:27 AM                     Hey there film Gods, you all have been very helpful. I am now sure that he was asking about foot lamberts. I have since found out that my projectors produce 16 foot-lamberts, just like they are supposed to! However, I am soooooo tempted to ask him about his kelvolumens! I offered to project a trailer for him, so that he could see the quality for himself, but I guess that he was too busy for something so practical. Our projectors generally run @ 75 amperes, but i didn't think that was what he was referring to. Anywho, thanks a lot. You guys are radddddd!!!!!!!  |  IP: Logged Randy Stankey Film God Posts: 6539 From: Erie, Pennsylvania Registered: Jun 99 posted 04-02-2007 01:10 PM                     Tell him that you had to adjust the fratistat almost three full turns before you could get the recommended 16 Kelvolumens out of your projector!  |  IP: Logged Mike Blakesley Film God Posts: 12767 From: Forsyth, Montana Registered: Jun 99 posted 04-02-2007 01:22 PM                        And then tell him you're going to maintain this bourdon hold until you receive portal magnus clearance from Melnix.* (* courtesy of Dean Martin, in the original "Airport")  |  IP: Logged Will Kutler Phenomenal Film Handler Posts: 1506 From: Tucson, AZ, USA Registered: Feb 2001 posted 04-04-2007 01:15 AM                     What should you do? Open up a book like the Machinist's Ready Reference that has a huge section on scientific conversion values. Convert his requirements and mangle it up with the most ridiculus-odd-obscure measurement units you can find, and then let the genius unravel it!!  |  IP: Logged John Pytlak Film God Posts: 9987 From: Rochester, NY 14650-1922 Registered: Jan 2000 posted 04-04-2007 09:47 AM                        Standard SMPTE 196M-2003 specifies the viewing conditions. The aim is indeed 16 footlamberts: http://store.smpte.org/product-p/smpte%20196m-2003.htm quote: Motion -Picture Film -Indoor Theater and Review Room Projection - Screen Luminance and Viewing Conditions quote: 5.2 Theater nominal luminance Theater screen luminance shall be nominally 55 cd/m2 (16 fL) measured at the screen center. The luminance of the screen sides and corners shall be measured at a distance of 5% of the screen width from the screen edges. The readings shall be taken from each location specified in 5.1. 5.3 Theater luminance limits Theater screen luminance at the screen center shall be between 41 cd/m2 (12 fL) and 75 cd/m2 (22 fL). Luminance at the screen sides shall be 75% to 90% of the screen center luminance, but not less than 34 cd/m2 (10 fL).  |  IP: Logged

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