The most common type of screen surface works by reflecting the incoming light in a uniform manner in all directions. They’re known as diffusive reflectors because they diffuse the light all over in equal instead of chaotically uneven portions, resulting in a brighter projection image or lighting.
Surfaces that reflect back at only a single angle are instead known as specular reflectors. With that in mind, let’s talk about ALR screens. What is an ALR screen?
What is an Ambient Light Rejecting Screen?
Ambient Light Rejecting (ALR) screens obviously work by rejecting ambient light while letting projector light shine through. It’s a specular reflector that reflects light at an angle precisely opposite the one where the light arrived, like a mirror or a billiard’s ball ricocheting at a 90-degree angle.
Some projector screens might not be diffuse reflectors in that they might reflect light back in one direction instead of other directions. They favor a certain direction more than others, allowing the screen to increase the brightness or gain of a reflected image at a certain viewing angle or area.
It’s through these technologies and quirks that an ALR screen successfully filters out ambient light while focusing in on projector light as though you’re viewing a backlit HDTV instead of a faded projection.
How Does an ALR Screen Work?
The ALR screen works by selective reflection of light back to the viewers. Some light, preferably ambient light that robs your projector light of brightness, is rejected while the rest is reflected back to the people watching your projected movie or playing your projected videogame.
The effect is achieved through projector and screen positioning. Angle the screen and projector at the right throw distance so that the projector’s light is seen by them while any ambient light from the ceiling or outside like daylight is rejected from other angles.
It’s an effective light filtration method that allows you to maximize your projector lumens without investing in high-lumen outdoorsy projectors (which are more expensive than lower lumen displays).
What is Angular Reflectivity?
Ordinarily, an ALR works by reflecting ambient light in some other direction away from the audience while all they see is the light and projection coming from the projector.
Naturally, if the audience member were to move from their seats or view the screen from another angle, the effect isn’t as pronounced. As for angular reflectivity, it’s a principle used by some ALR screens to achieve this ambient light rejection effect.
It works by reflecting the projected image back to the viewers at a mirror-opposite angle to the projector that’s projecting the image to the screen. If the projector is angled down on a 15-degree angle, the audience will see the brightest imagery when viewing the screen at 15 degrees.
What is Optics and Lenticular Structure?
Other ALR screens work by optics. They negate ambient light by having a screen surface composed of multiple layers. Every layer has different absorption and reflectivity level with lens-like elements. Long story short, this “lenticular structure” or multi-layered surface rejects non-lens ambient light.
At the same time, light focused on a lens like with a projector is reflected to the audience at peak brightness while ambient light is deflected so as to maximize that brightness without it being robbed of its shine altogether.
The obvious advantage of this particular ALR tech is that you won’t have to finagle or manipulate viewing angles as much with this projector screen type compared to ALRs that use angular reflectivity.
Can an ALR Screen Reject All Ambient Light?
Regardless if you’re using lenticular structure or angular reflectivity, there will always be a bit of ambient light that cannot be negated. Therefore, sometimes it’s best to instead invest in blackout curtains in order to control or minimize the appearance of this brightness-robbing light.
Furthermore, all ALR screens work best when the ambient light isn’t hitting the screen directly from the same direction as the projector. If the daylight or lamp light is moving along with the projector light, this will lead to the image looking more faded as the brighter light outshines it.
Therefore, avoid positioning your projector at the back of the room near other light sources like open or transparent windows with daylight flooding in or nearby lamps and bulbs.
What Light Can’t the ALR Screen Negate?
The lights that the ALR Screen can’t negate is any light traveling at the same angle as the projector light or lights directly aimed at the screen. The surface can’t deflect all light or else it will also deflect the projector light (which defeats the purpose of its creation).
You should make sure that the ambient light source is angled or originating at a different angle from your projector light so that your ALR screen can properly isolate the projection rays alone while deflecting or rejecting all other lights elsewhere like a shield or a filter of some sort.
Whitewall reflections, overhead lighting, or windows on the side of the room instead of along with your projector are candidates for ALR screen deflection and filtration. It’s all about the angles and light sources in the end.
What Happens to Projector Brightness When Ambient Light is Present?
Your living room, gaming room, movie-screening home theater, recreational room, conference room, office, or convention area requires high brightness or ALR screens in order to deliver the brightest projector image without being robbed of its light by ambient light.
All other light sources collectively or by themselves can rob the brightness of your projector image by their very presence the same way a brighter star in the sky can make duller stars disappear by their brightness. Light pollution at night also keeps whole constellations from being viewable.
A Few More Items to Consider
To sum things up, ALRs or Ambient Light Rejection screens made for projectors work by somehow rejecting ambient light while reflecting back to the audience the projector light or a rather vivid projector image.
It works by angular reflectivity or angling your screen in a way that the projector image is directly bouncing back to the audience while in all other angles, ambient light is bounced back everywhere else away. The lenticular structure meanwhile uses multiple screen layers that isolate lens light.
References:
- “Ambient Light Rejecting Screens Explained“, ProjectorScreen.com Blog, January 22, 2016