How Ambient Light Rejection Works

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ALR screens, which in full stands for ambient light rejection screens, provide a better viewing experience than regular projectors. This is because even in settings with ambient light, they can produce clear, vibrant, and accurate images. Pairing a good ALR screen with the Wemax Nova can produce clear projections as large as 150 inches from about 19 inches away.

Regular screens reflect light uniformly in all directions instead of just one angle. On the other hand, ALR screens work by reflecting light in a controlled manner toward the viewers. This effect is achieved by placing the projector and screen in a way that directs the projector’s light toward the audience while reflecting all the other lights in the room in different directions.

The design of ALR screens also aids this phenomenon which features advanced optical technology. ALRs are made from an embedded lenticular screen with a black-grid structure. The black areas absorb ambient light while the white components reflect projected light straight to the audience.

ALR screens are designed for use with ultra-short throw projectors, like the Wemax Nova, that is placed near the screen and project upward onto this surface when placed below the screen.

While this technology does sound revolutionary, it’s not entirely new. In fact, ALR projection screen technology has existed for some time now. Regardless, there’s still uncertainty over the operation of ALR, which is partly fuelled by manufacturers making false claims or marketing non-ALR surfaces as an alternative.

All screens reflect light through either diffuse reflection or specular reflection.

Diffuse Reflection

Diffuse reflection occurs when light strikes a surface and is scattered from multiple angles. The majority of the light is reflected by “scattering centers” underneath the surface. Since all incoming light is reflected in different directions, diffusive surfaces don’t create excellent ambient light rejection screens.

Diffuse reflection is also affected by the color of the viewing surface. The amount of white light reflected, as well as the color of the light reflected, is affected by the color of the material. A surface having a red tint, for instance, will reflect mostly red light. A perfectly white screen will not absorb any light but will instead reflect as much of it to the viewer. In the case of a gray screen, not all the light is reflected, and some is absorbed. The deeper the shade of gray, the more light the material absorbs while reflecting.

Despite white screens reflecting back all the light they receive, they aren’t perfect diffusers. The level of diffusion depends on the texture of the surface and, for film formulations, what kind of elements were used in the formulation. If a surface is too smooth, it will have high gloss levels, which can lead to hot spotting. At the same time, a screen that’s too rough will negatively affect the image’s visual quality.

Specular Reflection

When light strikes a surface and is reflected from a single, opposite angle, this is known as specular reflection. This phenomenon forms the basis for ALR screen surfaces, which prevent light from sources other than the projector from reflecting light to the audience. As discussed earlier, ALR screens achieve this using specular reflective components. These components are able to deflect off-axis light in a different direction from the audience. An important measure of a surface’s ALR performance is the level of specular reflection. Dark gray is used to improve the ALR performance of a screen by reducing glare and boosting contrast.

There are compromises though. Increasing a surface’s specular reflection will decrease the optimal viewing cone. Nonetheless, adding specular reflective elements increases a surface’s gain, which would otherwise be low owing to the surface’s dark gray color.

Gray Tint on a Screen Doesn’t Necessarily Mean It’s ALR

Despite many gray screens possessing a mild gray tint, most of them are really just diffusive reflective surfaces. Well, gray does assist in diffuse reflection, but it only aids in absorbing stray ambient light and slightly increasing contrast, especially in mild ambient light settings. Still, this doesn’t make a grey screen qualify as an ALR screen surface. The majority of ALR surfaces are much darker than standard gray surfaces.

Not Just a Number

Typically, there are two ways to indicate ambient light rejection: by reporting the amount of ambient light that passes through and the amount that is rejected.

Choosing the appropriate ALR solution entails more than just considering a number. A decent level of ALR demands a delicate balance. Furthermore, surface color, texture, gloss, and gain affect the viewing experience. Other performance metrics, like viewing angle and picture quality, will be altered if material qualities are modified to reject more ambient light.

As such, when selecting the most suitable ALR screen for your needs, don’t just consider the degree of diffuse reflection. Also, factor in other specs and suggestions (or lack thereof) from the manufacturer. Take a look at the whole gain curve for each surface and see how rapidly it loses gain at broader viewing angles.

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