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I'm kind of dim on this "projector brightness" thing w/r/t CRT's. Could we talk about a couple of things. Projectors are rated using lumens. I see mainly "peak white" in specs, although you guys talk about optimum "foot/lamberts which I believe uses "ansi lumens". I believe the formula for foot/lamberts involves your projector's rated ansi lumens , screen size and gain. Foot/lamberts has to do with the amount of light being reflected from the screen, is this correct?


I'm sure there has to be gizmo's that will give you accurate foot/lambert readings. What are they, do they cost a lot? Can you figure foot/lamberts using a light meter?


Thanks
 

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You can use a light meter or use a camera. I cant remember the site off hand, but if you search for something like "estimating light for orchids." It involves holding a peice of paper and checking which f stop the camera chooses.


A light meter is also valuable, though I don't think its worth it just as a tool to have for a crt.


In the end, its more of a "is it bright enough for you?"


(As an aside to this, in the digital world there is a product called "Smart III" which is a light meter and a spreadsheet which will measure red/green/blue outputs and give you a color temp graph. I found it worked really well with my pt-l300u, and I can't think of many reasons why it wont work on the electrohome 8111. I am waiting until I get a new green tube as at that point a full new setup will be in order, along with actually ceiling mounting the beast.)


Scot
 

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Many companies make direct reading Foot Lambert meters. The SMPTE claims 16ft lamberts is the ideal level, however, virtually no theatres actually achieve this and when they do, most people feel it's too bright. 12 ft/lamberts is more than enough for a great picture, but remember, the lower ft lamberts you run at, the longer your tubes will last. With most projectors (depending on screen size), to achieve 12 ft lamberts, you would need a high gain screen. A 1.0 gain screen will most likely never make it.
 

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Scot,


Any more information using a camera as a light meter? I've searched Google using the terms you outlined but I haven't found the site you mentioned. Thanks.


Gary
 

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You would have to know what the camera's scale reads out in or check it against a real ft lambert meter.
 

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Quote:
Originally posted by Scot Kight
I found it worked really well with my pt-l300u, and I can't think of many reasons why it wont work on the electrohome 8111. I am waiting until I get a new green tube as at that point a full new setup will be in order, along with actually ceiling mounting the beast.)


Scot
Say Scot


Get in touch with me before you hang the 8111; there are some small but important mods you can do to save much grief later.
 

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Quote:
Originally posted by techman707
Many companies make direct reading Foot Lambert meters. The SMPTE claims 16ft lamberts is the ideal level, however, virtually no theatres actually achieve this and when they do, most people feel it's too bright. 12 ft/lamberts is more than enough for a great picture, but remember, the lower ft lamberts you run at, the longer your tubes will last. With most projectors (depending on screen size), to achieve 12 ft lamberts, you would need a high gain screen. A 1.0 gain screen will most likely never make it.
Is the 12 ft/lamberts the reading in the whites, blacks, overall average, or something else? I assume this reading is a measure of what is reflected off the screen, correct?


Thanks


Deane
 

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The 12 ft lamberts would be (illuminnance) reflected off the screen. Not to be confused with luminance, which is different.
 

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Discussion Starter · #10 ·
I did find some meters that measure foot-lambert. A little pricey if you're just going to use it for your home theater.


I'm still a little confused. Foot-Lambert: "a former unit of luminance equal to the luminance of a surface emitting or reflecting 1 lumen per square foot. A completely reflecting surface illuminated by 1 foot-candle has a luminance of 1 foot-lambert."


So in our application we're measuring the luminance of a screen which is reflecting light from a projector. I'm still unclear about some of the variables. Depending on what the projector is "displaying", the brightness is going to be different. Do you use some kind of standard image, or test pattern? SMPTE says 16 ft/lamberts, how would they go about measuring this?


Thanks,

John
 

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With Film, it is measured with no film in the gate, just a white screen. For Video, it would be a 100 IRE white pattern.
 
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