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I've been unsuccessful in finding information discussing how to evaluate projector lumen ratings relative to viewing room light level, screen size, etc.How do I determine if projector requires complete darkness for good viewing? How does image brightness vary vs. screen size? How critical is screen material choice to image brightness/contrast? Are projectors impractical in a typical house environment without completely opaque window coverings?
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Da-lite recommends 20 ft lamberts as a minimum brightness off the screen. Yes, you need light control in almost all cases. You take the width of the screen times the length of the screen and then divide by 144 inches. For example a 52 by 92 inch screen is 4784 then divide by 144 inches which give you 33.222 square feet. Once you have that figure you divide the lumens by it. For example a projector with 700 lumens/33.2 would produce 21 foot lamberts off the screen if the screen had a gain of 1.0 which could be considered neutral. Some screens have higher gains or lower gains in which case you multiply by that number after you get the lumens/square feet number. For example the same 700 lumens projector would be be 37.8 foot lamberts with a screen with a gain or 1.8 or only 16.8 foot lamberts with a sceen with a negative gain of .8 like a Da-lite High Contrast. With say 38 foot lamberts, you need a lot less light control and can have light in the room. With 20 foot lamberts, I'd suggest a completely dark room. Hope this helps.
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