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Rear projection screen

In lecture theatres elsewhere where forward projection is used, video and data projectors are often suspended from the ceiling, at a set distance from the screen. Being 15-20 feet from the floor they are costly to maintain or adjust. Another feature of forward projection is that the areas of the image which need to be portrayed as black, can only ever be as black as allowed by the ambient light levels of the room. (In every lecture situation, a certain amount of ambient light is unavoidable.) This light reflects on the white surface of the screen reducing the contrast range, and therefore the quality of the image.

With rear projection facilities, this is reduced considerably by blacking the walls in the projection room, ensuring that all the lighting on the back of the screen is provided by the projector. This allows more ambient light in the lecture room without causing the same reduction in the image contrast range, ensuring that the lecturer can be more comfortably and intimately lit, without relying on unflattering under-lighting from the lectern light. In each theatre there are spotlights on the lecturer which are shuttered to stop light spilling over onto the screens. Adequate light can also be provided for the audience to take notes without difficulty. Providing an integrated set of services is much easier to achieve with rear projection. It also means that much of the technology can be hidden in the projection/support room out of sight of the audience.

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