Originally Posted by yenal
Isn't this how light behaves normally when it hits a flat surface? Are they simply super flat materials?
Non ALR fabrics, matte fabrics, diffuse light at ~160 degrees angle.
Angular type ALR are like a mirror, the light will hit the surface at one angle and send it back at the same angle, in the opposite way. The user must be in the way of that reflected light beam. If they are not and they look at the screen, the image will seem dimmer.
Which is why some angular ALR's have a lower viewing angle.
The same happens with ambient light, if light comes from above, it gets reflected towards the ground. If it's from the right, it gets send to the left.
If the light is the projector beam in front of the screen, it gets sent back at the same angle.
If there is another light from the same direction as the projector, that will be send back towards the area of the projector/viewer as well.
The projector must be placed in such a way that the reflected beam of light reaches the viewer's position.
It cannot be too close, or the angle that the light will reflect will be too high.