Pupillated illumination apparatus

A switchable backlight for a switchable privacy display apparatus comprises a collimated waveguide, first and second light sources and an optical turning film comprising elongate prismatic elements with facet orientations that pupillate the output of the waveguide in two orthogonal directions for each of first and second light sources. High luminance uniformity is achieved for a head-on user in privacy and public viewing modes and high uniformity of security factor is achieved for off-axis snoopers, with increased speed of privacy switch-on in privacy mode.