# Light Output Question For Front Projector

Discussion in 'Displays' started by James Edward, Aug 8, 2003.

1. ### James Edward

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A friend will be renting a FP for a party he is having. His intention is to project concert DVD's on an 8ft x 8ft screen outdoors.
He lives in upstate NY, so ambient light from homes, streetlights, etc., will not interfere. His choices are: 2000 lumen projector for \$200 or a 3000 lumen projector for \$300.
Should 2000 lumens( Panny TL-520) be sufficient, or should he spring for the brighter unit? Would a full moon make a difference as far as needed light output?
I'm not familiar with projectors, so any advice is appreciated. Thanks

2. ### Gabriel_Lam

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That's a BIG screen.

Let's start with just a tiny bit of theory. The projected image would be 6' x 8' (or 72" x 96"). This gives you a 120" diagonal screen. There are a total of 48 square feet on that screen.

We'll assume, for now that the screen has a 1.0 gain (the light shined at it is reflected with exactly the same intensity).

With a 2000 ANSI lumen projector, you'll probably need to account for at least 20% loss of brightness due to calibration. That's reasonably low, most projectors are higher than this. We're down to 1600 ANSI lumens.

Projectors will only do full brightness with a brand new bulb. As UHP, SHP, NSH, and P-VIP bulbs age, they drop pretty quickly down about 20-25% brightness, and stay about there until their death. Xenon bulbs fall rapidly to 20%, and then slowly down to 50% at their end of life. The Panny is not Xenon, and I'm guessing the other one isn't either. We're down to about 1280 lumens.

With a 48 sq foot screen, we're at about 26.7 ft-lamberts of illumination, which is not bad at all (THX recommends 16 +/- 2 ft-lamberts). This being said, if the moon is really bright, the picture may still wash out.

The way our eyes see "brightness" is not linear. A 3000 lumen projector will not seem 50% brighter than a 2000 lumen. At best, it'll seem about 10-15% brighter.

What kind of screen does he plan to use?

3. ### James Edward

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Thank you Gabriel. So it seems that this might work...

He cannot get to it at the moment, so I'll go with your calculation as 1.0. If it has any gain, that'll work to his advantage.

He checked his calendar, and the moon will be waning and less than 1/4 full. A good thing, as Martha would say.

He is planning on putting the screen under a tarp that will cover the top and sides. This should be a real Rube Goldberg setup. I have to bring my camera and take some pictures and post them...