Screen Brightness - How Bright is Too Bright? - AVS Forum
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post #1 of 6 Old 11-30-2001, 07:11 AM - Thread Starter
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I posted this question in another thread before I realized it wasn't relevant to the original post that started the thread.

Nevertheless, I have a rather odd situation that makes my pending Theater setup very challenging. In calculating my screen brightness I'm very confused as to what my target should be. Through research, I've seen 25-30 ft-Lamberts. I've also seen a minimum of 8. That's all fine and dandy, but here's the calculations for my future setup:

***800 ANSI Lumen XGA (NEC LT150) projected on a 64"x48" Da-Lite High Power Model B Pulldown
***Extremely high ambient light, white furniture, white built-ins, beige carpet. Note: 90% of viewing will occur at night eliminating the ambient light problem, but the light furnishings remain.

Screen Brightness =(800/((64*48)/144)) * 2.8 => 105 ft Lamberts

Is this too high for my potential setup? Should I adjust the gain until I obtain a brightness value closer to 25 ft Lamberts?

25 = (800/((64*48)/144)) * Gain => 0.67

Should I be looking at a different screen material(Gain = 0.67) for this small of a screen size or should I aim for the brightest(105 ft Lamberts) possible image?

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post #2 of 6 Old 12-01-2001, 08:40 PM
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Too bright is usually not an issue, although with all the white furniture, it coulc create an interesting situation. Regardless, can't you reduce the brightness output in the event that the image is 'too bright'?

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post #3 of 6 Old 12-02-2001, 09:06 AM
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Remember this is my experience. For lights off this is too bright but for what may be a small sum in the big picture( pun intended) one could get a larger grey screen that will inprove blacks and give a larger image. Since light goes by 1/D squared then a little larger screen will reduce the light reflected rather quickly.
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post #4 of 6 Old 12-02-2001, 10:27 AM
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At 800 lumens, that LT150 would be brighter than a double stack of new G90s. Hmmm.
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post #5 of 6 Old 12-03-2001, 05:04 PM
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Matt,

I don't think you are going to be quite that high.

Out of the box the LT150 puts out about 650 lumens. After a few hundred hours it will be at 500. Now if you do any color correction, you might be at 400.

Now, the Da-Lite bright but is more like 2.3 - 2.5 peak and if you are viewing slightly off-center or using the projector in a ceiling mount you can be at 2.0 easily.

Now your equation winds up with about 40ft-L which should be fine.

100 would be too much IMO, but not completely out of whack.

Your eye is pretty good at making your projector's peak white look like white no matter if that is 10ft-L or 100ft-L.

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post #6 of 6 Old 12-04-2001, 08:19 AM - Thread Starter
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I really appreciate the replies I got.

I had a notion that the more conservative numbers Mr. Wigs spoke of would validate this screen choice. I'm very eager to get this equipment ordered and set up to see for myself.

Thanks again!

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