At the hardware store recently I noticed spray cans of White Knight "Reflect-All light reflective paint" and thought it might be suitable for spraying on a walls to make a high efficiency screen for projector. I tried it out in a typical tutorial room at the ANU. To avoid damaging the walls I sprayed the paint onto a piece of transparent plastic and dark blue cardboard and attached these to the wall and projected onto them. I compared this with flat very light blue wall paint, a whiteboard and a projection screen.
The reflective paint worked as expected. However, working as a retro-reflector, the image only reflected a narrow cone of about ten degrees either side of the projector. This makes it impractical to use for a projection screen in a typical classroom.
The paint may still be of use in some difficult applications, such as in very bright lighting conditions, with a very dim projector, or one in a very large auditorium. The paint did not have the problems I was expecting with stray reflections and so there could be a very bright light source beside the screen without washing out the image.
The paint may have other uses. Because the light is reflected back strongly in the direction of the source, a camera at that point will show the subject in silhouette. This can be used to electronically extract the subject from the background. The subject can then be transmitted to a remote location and inserted into a scene. This effect is commonly created against a black background, reflective grey cloth or a specially coloured surface (chroma key). But the reflective paint would have the advantage of being able to be applied to any coloured surface. The wall of a meeting room or classroom could be painted without interfering with normal use of the room.
For educational or video videoconferencing use, a presenter could be videoed live in the room next to a projected presentation. The wall behind the presenter would act as a screen for the projected image seen by those in the room. The wall would also act as a reflector for the video image. The camera recording the presenter would be able to see them, but not the projected image. As a result just the image of the person could be recorded, or transmitted. Their presentation could be digitally inserted into the same video image, or transmitted separately in a separate video stream. This would provide a much higher quality image (and use less bandwidth) than attempting to record the presentation slides with a camera.