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.