Ambient Light Rejecting (ALR) screens differ from a regular screens
in several ways.
The most common screen surfaces reflect the incoming light uniformly
in all directions.
These screen surfaces are referred
to as diffuse reflectors.
The light is reflected back in many angles, rather than just at one angle.
Surfaces that reflect back at only one angle are referred to specular reflectors - they reflect light at an angle
precisely opposite the one at which that light arrived, such as a mirror.
Some projector screens may not be purely diffuse reflectors in the
sense that they may reflect light back in one direction more than other
directions. This is often done to increase the brightness of the reflected
image (gain) within a certain area (viewing angle).
An ALR screen works by selectively reflecting light back to the
audience. This effect is achieved by positioning the projector and screen in
such a way that the projector's light is bounced towards the audience, while
the other light in the room is reflected back in some other direction.
Some ALR screens work due to a principal referred to as Angular
Reflectivity. This means that your projected image will reflect back to the
audience at the mirror-opposite angle to the projector hitting the screen. I.e.
if the projector is angled down at a 15 degree angle, the audience will get the
brightest image while viewing the screen looking up at 15 degrees.
Other
ALR screens negate ambient light by using optics.
Optical ALR screens are usually composed of multiple layers with each layer
having different absorption and reflectivity properties with lens-like elements.
This is often referred to as a lenticular structure.
Whichever
the ALR technology that your surface is using, there will still be some ambient
light that cannot be negated. ALR screens only work if the ambient lighting is
NOT hitting the screen from the same direction the projector. I.E. if you have
your projector positioned at the back of the room near other light sources that
are also aiming towards your screen, the ALR surface will not do anything to
negate that other lighting.
The
ambient light source must be coming from a different direction/angle than your projector
such as reflections off of white walls, overhead or recessed lighting or from
windows on the side of your room in order to get the benefit of an ALR screen.
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