Here are some real world examples from our Race to Black series. Let’s use a room with an ambient light level of 30fc and the screen with 10fc of light on it. Using a typical projection screen, which has an ambient reflected value of 35%, the best black level possible would be 10 x .35 = 3.5fc. To get a 20:1 contrast ratio you would have to have a projector that would enable the white point to be 3.5x20 = 70fc. That is achievable, but very bright and uncomfortable to look at. Realistically, you would have to have a projector achieve 30fc and no more to be comfortable, and the max contrast would be 30 / 3.5 = 8.57:1. Viewable, but poor at best.
Using an optical screen with an ALR value of just 5% the same room would have a black level of 10 x 0.05 = 0.5. So, to hit a contrast level of 20:1 the projector would only need to be able to hit a white point of 0.5x20 = 10fc. Now that would be very easily done, but the white level should be between 75% and 150% of the room ambient with 1:1 being perfect. So if you were to use a projector that could hit just 30fc on screen, then it would be very comfortable and offer an outstanding contrast ratio of 30fc / 0.5fc = 60:1.
At the end of the day, it’s easy to see based on the example above that an optical screen can make a huge difference in image quality. The room was barely capable of supporting projection originally, but with an optical screen it was capable of achieving great contrast and image quality. So where prior a good designer would have only used a light emitting technology such as a flat panel or direct view LED, now a projection system could be used. Combine that with the fact that it really is a race to black, optical screens are a must have in every designer’s tool set.