Ambient Light Rejecting Screens and the Laws of Physics

Today, the hot topic in projection screens is ambient light rejection (ALR). An ALR screen is designed to provide brightness and picture quality rivaling other display technologies, while keeping the lights on in the room. It achieves this by managing light falling on the screen and controlling what is reflected to the eyes of the audience.

Surfaces typically reflect (diffuse) incoming light in evenly all directions. This means you can look at art on a wall, and from anywhere it looks virtually identical.  For projection screens, matte white is the “perfect” diffuser, reflecting incoming light at nearly 180°, for extremely wide viewing angles. The problem is that any ambient light present will also diffuse evenly, degrading contrast and color saturation. In higher ambient light situations, this can render the images unacceptable.

Another screen type is angular reflective. Incoming light is reflected along a single direction, where the angle of incidence equals the angle of reflection. Since this allows managing where incoming light is reflected to, ambient light can be directed away from the audience. These screens are typically higher gain, causing projector light to be focused back in a narrower viewing cone. The concept of controlling incoming light and reflecting it at predetermined angles is the basis for most ALR screens. By selectively reflecting ambient light, you can position the screen so that projector light is directed towards the audience, ambient light is slightly absorbed, and reflected away from the audience.

ALR screens use a combination of optical filters and dispersion to accomplish this.  They are uniquely multi-layered, consisting of a molecular layer that acts as an optical filter to eliminate indirect light, positioned below a contrast-enhancing layer. These microscopic filters actively reflect a projected image while diverting indirect light away from the audience.

In most ALR screens, there are specific horizontal and vertical viewing angles that are the “sweet spot” for the viewer. As with traditional gain screens, going beyond these angles will reduce the quality of the image on the screen. If ALR is used as designed, brightness, contrast, and color saturation are maintained or enhanced in the presence of higher ambient light.

All ALR screens are not equal. The new Stewart Filmscreen Phantom™ HALR™ is an example of the current state of the art. First, Phantom is flexible in sizes up to 40’ x 90’, can be placed in a fixed frame, or put in an electric screen enclosure. It is also available in perf configurations. Testing shows that it is inherently compatible with higher resolutions. 

Phantom is unity gain, where competitors are between 0.8 and 1.3 gain. This provides an even viewing cone, horizontal and vertical, where others tend to favor the horizontal over the vertical. In other words, it uniformly performs ambient light rejection across the full screen width and height.

Phantom is equal to the blackest screens available, leading with over 30:1 contrast for a 2,000-lumen projector and 20 foot-candles of ambient light (from several sources) hitting the screen surface at 40°.  In high ambient light conditions, with over 50 foot-candles of ambient light directly on the screen, Phantom meets ANSI industry standards. For the 3D fans out there, Phantom retains polarization for linear or circular 3D displays.

This translates into the ability to produce surfaces that limit ambient light from intruding on the image. As UHD and HDR become common, with 8K (and 16K) on the roadmap, ALR screens like the revolutionary new Phantom™ HALR™ from Stewart Filmscreen will further enhance your viewing pleasure on the big screen.

Read the full technical white paper on Ambient Light Rejecting Screens and the Laws of Physics HERE.