Rear projection screens (or RP screens as they are often called) are used when the viewer and the projector are located on opposite sides of the screen surface. The projector is mounted behind the screen and beams light through the screen at the viewer. The screen choice is very important for rear projection because it will dictate how the light is transmited through the surface. The surface can provide a bright, crisp image with a tight viewing cone or a softer image with an wide, even viewing cone depending on the screen. Rear projection is often used where people or objects need to be right up against the screen without casting a shadow or when high ambient light is required as most rear projection screens are either dark grey or black, which also allows them to easily disappear into the background when not in use.