Screen Size, Type, and Projector Output
How to make sure your setup looks as good as the best movie theaters according to CEDIA/CTA CEB23
You need to reach a certain amount of brightness with your particular screen with your particular projector to see a “reference level” image in your theater. This is a separate topic (though they interact) from how large the image should look from your seating position, which is also very important.
Combine the measured gain number of your intended screen, its size, the throw distance, and the projector model you plan to use, into this calculator:
Projection Calculator Pro - Projector to Screen Distance
To use that calculator, you need to know the real (not manufacturer’s marketing claim) gain of your screen. The most comprehensive study of (acoustically transparent) screen materials can be found here:
31 Acoustically Transparent Screens Compared
And while a bit out of date, the most comprehensive study of non acoustically transparent screens with gain ratings is here: Accucal Projection Screen Report^
Use the Projector Central calculator estimate for the "real world" performance of your projector, which is more realistic than what the manufacturer claims. This is the max output you will get, when new, at highest power.
Then see where you land (details):
DCI D-Cinema SDR (which is what CEDIA recommends as well for SDR)
Peak Brightness: 48 cd/m2 (48 nits) 14 fL
Dolby Cinema
Peak Brightness: 108 cd/m2 (108 nits) 32 fL
IMAX Laser
Peak Brightness: 75 cd/m2 (75 nits) 22 fL
I would shoot for Dolby Cinema levels, ie, 30fL, minimum for good HDR. Some people with video processors are able to get by with less. But ideally you’ll have even more headroom, ie, 45fL or 150 nits. And if you want to chase the DCI HDR standard, you’ll need to reach 300 nits off your screen (and have the right video processing to adapt HDR content to that level).
All of that is great for planning. What about confirming the end result?
So, without buying an expensive light meter and learning how to use calibration software, how can you measure your screen / image peak brightness?
Buy a "cheap" LUX meter from a place like Amazon.
Put a 100% white image up on your projector. (Okay, some projectors do interesting things with smaller windows of test images, ie, a 100% white image in the center of the screen surrounded by black, eg, JVC's light recycling, so you may want to use a slightly different image with them for some situations.)
Position your LUX meter at the center of the screen, facing the projector.
Take a reading.
Then, do some math:
Nits = lux * screen gain/3.14 (pi)
Now, when is your screen gain? You cannot rely on the manufacturer to be honest, unfortunately. But there are some third party measurements. Acoustically Transparent, Solid.
And then you can convert nits to ftl if you like (about 3.43 hits per ftl).
Footnotes
^Another link for the Accucal report: https://web.archive.org/web/20220327084419/https://www.accucalav.com/wp-content/uploads/accucal_front_projection_screen_report.pdf or
Accucal Front Projection Screen Report 2016 409KB Download and unzip to read the original PDF ∙ CBZ file