Keep increasing the lumens in the first calculation until you get the ft-L measurement that is right for your space. The general consensus is that if you have a little ambient lighting, 40 ft-L will work for you, but if you have high ambient light that you cannot control or that needs to be on during projection, then 60 ft-L would be better for your needs. This will provide a foot-Lambert measurement. (2) With the screen size information in hand, calculate the square footage, then divide the number of lumens you think you might need by the square footage and multiply by the screen gain (start with 1.0). A simple calculation of dividing by 1.78 (for 16:9 aspect ratio) or 1.33 (for 4:3 aspect ratio) can provide the height. There are a couple different methods to accomplish this, but I follow the one that is based on furthest viewing seat away from the screen (measured in feet), then divide by 8, which gives us the screen width (divide by 5 for home theaters).
(1) First, figure out what size image you need for your space. So, what do you need to know about projector-stacking before deciding if it's right for your environment or attempting to do it yourself? Many of these are accomplished using both stacking and blending in order to provide the bright, vibrant images that amaze audiences. You may have seen videos over the last few years of impressive architectural projection displays using projection-mapping. Stacked projectors can sometimes be placed directly on top of one another, but various rigging and racking systems for aerial mounting are widely available. Differences in color, brightness, processing, etc., can lead to a lot of trouble when trying to match projectors. However, best practice is to ensure that you have matching projectors whenever possible. If that does not provide you with enough options, there are many third party companies that also provide solutions, which can be helpful if you have projectors from different manufacturers. Some high-end manufacturers provide camera-based alignment to help make the process even easier, and most better commercial projectors will provide geometric correction, warping, and other blending tools built right into the menu system to help you navigate what is still a somewhat complex operation.
Most manufacturers even provide their own proprietary software or systems to help the installer or end user accomplish this task. What has changed, though-along with the increased brightness of today's digital projectors-is that the ease of setting up a successful projector stack has gotten much, much easier. The idea of stacking multiple projectors is not a new one, having been around since the days of low-brightness, three-gun CRT projectors. In some 3D configurations, four projectors may be used to provide enough brightness while also providing the necessary stereo image, using two stacks of two projectors. With some 3D systems, for example, two projectors are required to provide a true stereo image. This is a clear example of how budget can be a factor when determining a projection solution however, sometimes the purpose of the projection system can be the most important factor. This is because the premium associated with projectors at 10,000 lumens and above remains high, while the cost of those below that brightness continues to drop. Fortunately, by stacking two 7,000-lumen HD laser projectors, we could get them where they needed to be without breaking the bank.
However, a 14,000-lumen, high-definition laser projector was outside the price range of the client. As an example, I was recently working on a proposal for a church and they needed 14,000 lumens of intensity to provide an acceptable image on the size screen they are using.