Choosing the colour of a projection screen
There are numerous trends, fads and ‘flavours of the month’ when it comes to AV technologies and the world of projection screens is no exception to the rule.
But, do you really need just one type of projection material for any home theatre or commercial presentation? Does one size really fit all?
With all of the assumptions that a projection screen is merely a low-tech piece of cloth, it is surprising to see just how much engineering actually goes into creating a good material that will suit the endless variations of projectors and lighting.
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To begin with, the answer to the title question is this: matte white is the most commonly used solution in projection screens, but it can come up lacking in cases of ambient light or projectors that don’t pack a punch in brightness or contrast.
In order to follow the rest of this discussion, you must first understand the meaning of a projection screen’s brightness or gain, which is based upon a common white control element. The control element used to determine the whiteness of the material is magnesium carbonate.
With a brightness or gain of 1.0, it is the universal comparison used against all other projection screen materials.
So I suppose the next question is this: what are all these different screen ‘colours’ for? I’m glad you asked.
Matte white
As stated before, matte white is the most common choice because it is the most versatile. Its wide diffusion uniformity (wide viewing angle) makes it a favourite for large group presentations while its colour neutrality makes it a good fit with most projectors, so long as the lighting is favourable.
Matte white usually has a gain of 0.95 to 1.2 and it comes in many forms from front to rear projection, non-tensioned, tensioned and acoustically transparent.
Non-tensioned material is a composite of one or more material layers coated with a white optical paint. It is primarily for manual and electrical roll-up projection screens. Non-tensioned material tends to be an excellent low-cost solution, but the varied chemical layers react at slightly different temperatures. This reaction leads to slight curling at the edges which is unsightly to some.
Tensioned material is used in fixed-frame screens and cord-reinforced, roll-up models. It presents a much flatter surface but is generally more expensive to produce than the non-tensioned materials.
The final variant of matte white is the acoustically transparent material. ‘AT’ material, as it is commonly called, is specially woven to present a solid projection surface that allows sound to breathe through it with a minimal amount of attenuation. But the porous characteristics of a cheaper AT material can overlap with the pixilated image of a digital projector, creating a visual artifact known as moiré.
The moiré effect is when the projected image has a grainy effect similar to watching something through a double-layer of screen mesh. The problem is rectified by creating an ultra-fine weave and cutting it in a certain angle. Although the AT material works well over in-wall speakers, the thin characteristics of the fabric can also allow light to bleed through, decreasing the brightness (gain) of the projected image.
Grey screens
Grey projection screen material is quite possibly the most misunderstood. Grey material is used to enhance black levels for greater contrast.
This is especially useful when paired up with digital projectors that have somewhat lacklustre contrast performance.
The drawback is that it sacrifices brightness in order to enhance black levels.
A huge myth about a matte grey projection screens is that they are ideal for ambient light. In reality, the low gain of a matte grey screen is not suitable at all for ambient light. The origin of this myth is that there is another ‘grey projection screen’ that is really a high performance (up to 8.0 gain) material that is coated in grey contrast layers. The high gain layers concentrate the brightly reflected image directly to the viewer while its contrast layers filter out ambient light.
High gain and 3D
High gain projection screens are the perfect solution for environments with limited light control. They achieve their brightness by focusing light into a narrower reflective cone. This means that the image is bright when a viewer is directly in front of it but leaves much to be desired for those viewing from off to the side.
This type of reflectivity is either retro-reflective (reflects straight back to the light source), commonly found in tabletop projectors; or angular (reflects at an angle opposite to the angle of the light source), usually seen in ceiling-mounted projectors. They appear in a variety of shades from silver-ish to grey with brightness levels varying from .8 to 8.0 gain.
The mirror variant of this material has a niche purpose for use in ambient light but can easily overpower the presentation when the lights are out. The layered material however, has found prominent use in both residential and commercial applications with stunning picture clarity.
3D materials fit into this category on account of their ability to produce superior contrast in addition to higher reflectivity.
This article just touches the tip of the proverbial iceberg on the subject. The increasing sophistication present in even the most affordable digital projectors has dramatically reduced the need for many other materials that were not even mentioned here. Still, as long as there is more than one type of projection environment, there will continue to be more than one type of projection screen material.
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