By: Draper Inc.
If there’s one constant in the AV industry, it is change. Technologies change, solutions evolve, new ideas take hold and force out old ways of thinking.
Projection screens have followed this same course of evolution and improvements. New materials have continually been in development to deal with changes in projection technology, room conditions, and usage requirements.
One of the most common areas we get questions on nowadays is ambient light rejection. Let’s face it: we’ve all been there when someone rolls down a white projection screen in a room full of bright lights and an underpowered projector. So now a screen’s ability to reject ambient light is something AV people like and want to know more about.
Obviously, white screens aren’t a good choice for rooms with ambient light conditions; they’re very diffusive and spread light in a very wide pattern. They do this with both projection light and room ambient light, so both types of light then compete at the viewer’s eyes.
The first question people usually ask when we talk ambient light rejection is, “Can I jack up the gain?” While that does reflect more light, we still have the same problem mentioned above—the screen is reflecting all light indiscriminately.
“So,” comes the next question, “I need a grey screen?” And the answer—perhaps surprisingly to some—is yes and no. Going grey doesn’t necessarily solve this problem because not all grey screens are ambient light rejecting materials. They do help with contrast, and with blacks, but some are also diffusive and reflective and don’t reject off-axis ambient light away from the audience. Traditional grey screens also tend to have very low gains, so they’ll eat up your projected light, forcing you into a brighter projector.
What you need is an ambient light rejecting (ALR) screen material.
ALR materials have a darker tint that absorbs even more light from a projector. Like standard grey screens, ALR materials improve contrast due to the darker tint; however, they also reject ambient light away from the audience. That’s because they are more angular reflective than diffusive. Reflective components in the vinyl surface reflect off-axis ambient light away at the same angle as it is hitting the surface, essentially bouncing it away from the audience. ALR surfaces with reflective components reject ambient light best.
ALR materials do eat up more projector light, however. So, you should use a projector that is 15%-18% brighter than one that would be used with a typical matte white material. This will bring image white levels up to an appropriate level, while the material helps produce better black levels.
One thing to remember with ALR materials, those with the most reflectivity have less off-axis performance. They also require longer lens/throw distance ratios so that you don’t get hot spotting.
The best choice is an ambient light rejecting material with a good balance of angular reflectance and diffusion for good ALR performance and wide off-axis performance.
If you’re interested in more information on how projection screens reject ambient light, let us know! We’d love to talk about how the projection screen industry continues to evolve and innovate to provide solutions to help keep two-piece projection relevant in a changing AV world!
By: Draper Inc.