An apparatus for illuminating a document includes an optical element formed of a light-transmissive material of a predetermined refractory index that defines a curved entry surface and an exit surface opposite the entry surface in which light enters the optical element via the entry surface and light exits the optical element via exit surface. A first substantially parabolic surface is defined between a first edge of the entry surface and first edge of the exit surface and a second substantially parabolic surface is defined between a second edge of the entry surface and a second edge of the exit surface such that the first and second substantially parabolic surface are spaced apart more at the exit surface than at the entry surface.