Screen Gain + Projector Lumens - AVS Forum
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post #1 of 7 Old 05-14-2003, 12:32 PM - Thread Starter
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What is the equivalence between screen gain and a projector with greater output of lumens? For example, does a screen with a gain of 1.0 and a projector with 2000 lumens produce the same light output as a screen with a gain of 2.0 and a projector with 1000 lumens?

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post #2 of 7 Old 05-14-2003, 01:55 PM
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Correct. The perceived brightness of the thrown image is proportional to:

[Lumen Output of Projector] x [Screen Gain] / [Screen Area]

(screen area is, of course, proportional to the square of diagonal screen size)
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post #3 of 7 Old 05-15-2003, 12:17 PM - Thread Starter
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One of the other threads mentioned a problem that some high-gain screen's have in shedding ambient light. How do you determine the optimal amount of gain in a screen under different lighting conditions for a given projector, for example one with an output of 1000 lumens ?

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post #4 of 7 Old 05-15-2003, 02:21 PM
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I think there is no universal formula to determine the "optimal" gain in various situations. It heavily depends on your own preferences, too -- for instance, some people prefer a dimmer, understated image, while others like a brighter, vivid image.

However, many people (including myself) seem to be convinced that retro-reflective screens, such as the Da-Lite High Power, have a superior ability to shed ambient light, by throwing the ambient light back to the direction of its source, rather than to your eyes (assuming that the ambient light is not coming from right behind you).
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post #5 of 7 Old 05-15-2003, 03:00 PM
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Keep in mind that the ANSI ratings aren't very dependable, and your actual output will also vary depending on the projector aspect ratio and display mode.

Regards,

Matt
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post #6 of 7 Old 06-06-2003, 07:42 PM
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Sushi:

Actually, there are recommendations for screen brightness. Following is the excerpt from a FAQ I wrote during the formative stages of my home theater project. The numbers in the projector lumens requirement bake in the screen area calculation automatically.

- According to the American Academy of Motion Pictures, the recommended screen brightness is 12 to 22 footlamberts. The nominal value is 16 footlamberts. A footlambert is a luminance measurement unit. Use the following formula to determine your required projector lumens output corresponding to 16 footlambert screen brightness, and assuming you use a 30 degree viewing angle and a 16:9 formatted screen:

- Projector Lumens = (2.5847 * Distance (in feet)^2) / Screen Reflectivity (Gain)
- Example: at 15 feet from screen, Projector Lumens = (2.5847 * 15^2) / 1.0 = 582 Lumens
- Example: at 20 feet from screen, Projector Lumens = (2.5847 * 20^2) / 1.0 = 1034 Lumens
- The Screen Reflectivity, or gain, can increase or decrease your projector brightness requirement significantly. A Stewart Filmscreen Firehawk screen has a gain of 1.35. If you recalculate the lumens requirement at 20 feet, you get 766 lumens rather than 1034 lumens!
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post #7 of 7 Old 06-08-2003, 03:41 AM
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HTBuilder,

I am aware of those recommended luminance specs. However, my understanding is that these numbers are set intentionally low in order to prevent the audience from seeing the 24fps film flicker (human eyes becomes much more sensitive to flicker when overall brightness increases). So, yes, if one wishes to "simulate" the image of typical commercial theater, those specs are very useful. But I also propose that, equipped with the virtually flicker-free digital projectors, there are very little compelling reasons for us to follow these commercial specs.

After all, many people (including myself) very much enjoy brighter, more vivid images. That is why those high-gain screens such as the High Power and Silverstar are very popular in this forum.
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