An overhead projector for use with a flat panel display assembly. The specialized overhead projector provides cooling for the LCD flat panel when used in an overhead projection configuration. The projector contains a rail on which the flat panel display is positioned for alignment and to provide air passage there through for cooling. A clamping mechanism is also described for securing the flat panel display to the projector. The flat panel display is a back-lit flat panel display subsystem for direct viewing as a monitor and also has overhead projection capability. The display subsystem contains a removable door assembly which provides for back-lighting for direct viewing. When the door assembly is removed, the active matrix LCD is semi-transparent and can be placed over the imaging screen of the overhead projector such that the LCD color image can be thus projected. The lamps that provide the back-lighting remain within the display subsystem when the door is removed and a unique optical coupling is provided between the lamps and a light pipe within the door. The display subsystem contains a sensor detecting door presence and simultaneously shuts off the lamps and reverses the display image upon door removal for overhead projection capability.