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#### Christopher Calder

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Could someone please post the formula for calculating the screen brightness for a given size and projector. I misplaced my copy.

Christopher Calder

#### Art Sonneborn

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Christopher,

ANSI lumens of PJ X screen gain / screen size in square feet = reflected light in foot Lamberts.

Art

#### Christopher Calder

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Thanks. I remembered it being more complex than that.

Anyway, as a comparison, how many foot lamberts would a average 50" rear projection television be? A movie theater is about 20, right?

Christopher Calder

#### Art Sonneborn

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Christopher,

I don't know the answer to that but theaters aren't usually 20fL but closer to 10 to 15 range. Also remember the RPs use the high gain ( extremely directive ) Fresnel lenticular screens. This allows a ton of light in one narrow viewing area both horizontally and vertically but it falls off very rapidly off axis. Go over to the rear projection forum and I'll bet an answer would come in seconds.

Art

#### Drew Eckhardt

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Quote:
 Originally posted by Art Sonneborn Christopher, ANSI lumens of PJ X screen gain / screen size in square feet = reflected light in foot Lamberts. Art
Only when your projector and screen aspect ratios match.

If your screen is wider than your projector, you need to multiply lumens by the ratio between projector and screen aspect ratios.

For example: (4/3)/(16/9) = .75; so a hypothetical 200 ANSI lumen 4:3 projector would only output 150 lumens on a 16:9 screen.

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