[W9TR]

This is a math problem with a little windage thrown in for good measure.

SMPTE specs between 14 and 22 ft-lamberts as the desired luminance for movie theaters that are light controlled. There are a bunch of different SMPTE specs that don't agree, this the range.
Let's say 20 ft-lamberts because that makes the math easier.

To get ft-lamberts, take the lumen output of the projector and divide it by the screen area in square feet.

For example my 106" diagonal 16:9 screen is 92" x 52" .

Divide each by 12 to get feet, then multiply to get square feet.

7.66 ft x 4.33 ft = 33.2 square feet.



So a 1000 lumen projector would get me 1000/33.2=30 ft-lamberts on my screen.

Conversely, to get 20 ft-lamberts on my screen I would need a projector with an output of 664 lumens.

Now comes the windage. You need to find out what isf calibrators are getting out of the projector you are interested in buying. A lot of these guys hang out @ AVS. Or check with a local isf person. This is a must. Why?

Because the lumen output of most projectors is spec'd uncalibrated.

So you have to fully calibrate the projector. Gamut, greyscale, etc.

Most but not all HID lamp-based projector's light output will drop 50% when you do this.

So your 2000 lumen projector is now a 1000 lumen projector.

Also the bulbs deteriorate 25% over a about 1000 hours, so you have to take that into account.

Need 3D? - roughly double the ft-lamberts needed to account for the loss in the glasses.

So you can work the problem backwards to see how much screen you can handle knowing the calibrated lumen output of the projector you are interested in.

Hope this helps.

Tom