If the beam enters the sample perpendicular to the surface, then the electrons come out symmetrically about the axis of the beam. As the angle of incidence increases, the interaction volume from which they cone increases and the "escape" distance from one side of the beam decreases, resulting in more secondary electrons being emitted from the sample. Thus steep surfaces and edges tend to be brighter than flat surfaces, which results in images with a well-defined, three-dimensional appearance that is similar to a reflected light image.

Backscattered electrons