When you purchase a projection screen, you want a good idea of what to expect. After all, you want to be sure that it meet the needs of your project. That’s why Draper tests nearly 30 different characteristics of our projection screen surfaces. Most of these attributes are well-known measures of a screen’s performance. Gain, viewing angle, half angle, and percentage of ambient light rejected are all measured and published by most screen manufacturers.
We also take the time test many other attributes, including color shift color temperature, flame resistance, and plasticizer migration.
Here are three things Draper tests on all projection screen lots that don’t seem to get much attention. But all of these are important to the overall performance of the screen.
Gloss is the perceived shine on a screen surface. Or, as the ASTM D 523 Standard Test Method for Specular Gloss states, “Gloss is associated with the capacity of a surface to reflect more light in directions close to the specular than in others.” Too much gloss can cause hotspotting. Too little gloss and the screen’s gain may be too low. Gloss can also have an impact on color accuracy. We measure gloss using a BYK Micro-Gloss 60 Gloss meter, making sure the amount of gloss is within tight tolerances that guarantee there’s no negative impact on performance.
Many projection screen viewing surfaces have a slight embossment or a raised pattern. This can affect image quality, especially as pixel density increases with higher resolutions, such as 4K. In the past, it has been thought that the embossing helps direct projected light from the screen. Some manufacturers have also claimed that the patterns affect color. Whatever role embossment plays, too much is definitely a bad thing. If it is even slightly visible under projection, it can be a distraction. For higher resolutions, such as 4K and above, the surface needs to be as smooth and as flat as possible.
Draper tests for embossment up to 10x magnification using a Mitutoyo series 183 Pocket Comparator.
Uniformity is a description of performance at different points on a viewing surface. Draper tests projection screen uniformity in three attributes: brightness, color, and thickness.
For brightness and color, we want to be sure that every viewing in the room is seeing the same high-quality image, and that their eyes are perceiving the same level of brightness and the same colors. We use a Christie HD6K-M Projector and a Photo Research PR-655 SpectraScan Spectoradiometer. If readings over several points throughout the entire sample vary by more than 5%, that material is rejected.
We also keep track of the uniformity of screen thickness. This may not seem as important as other screen characteristics. However, having the flattest viewing surface possible is very important, as is having a surface devoid of flaws. We test every 30 cm across the width of the surface using a Mitutoyo Absolute ID-S 1012 Digimatic Indicator thickness gauge. If actual measurements vary from the stated thickness by more than 0.02mm the material is rejected.
Although we don’t publish all of the nearly 30 attributes we measure, we do put the most important ones out there. To see those measurements, click here to locate technical data sheets for every Draper projection screen viewing surface.
Source: Blog Posts