Backlight for switchable directional display

An illumination apparatus comprising:

• a waveguide extending across a plane and comprising:
• first and second opposed light guiding surfaces arranged to guide light along the waveguide, the second light guiding surface being arranged to guide light by total internal reflection, and
• an input end arranged between the first and second light guiding surfaces and extending in a lateral direction between the first and second light guiding surfaces;
• at least one light source arranged to input light into the waveguide through the input end,
• wherein the waveguide is arranged to cause light from the light sources to exit from the waveguide through the second light guiding surface by breaking total internal reflection;
• and
• an optical turning film component comprising:
• an input surface arranged to receive the light exiting from the waveguide, the input surface extending across the plane;
• and
• an output surface facing the input surface,
• wherein the input surface comprises:
• a first array of prismatic elements each comprising a pair of facets defining a ridge therebetween, the ridges extending along a first array of lines across the plane in which the input surface extends;
• and
• a second array of prismatic elements each comprising a pair of facets defining a ridge therebetween, the ridges extending along a second array of lines across the plane in which the input surface extends, the first array of lines and the second array of lines extending at different angles projected on to the plane so that the first array of prismatic elements and the second array of prismatic elements deflect the light exiting from the waveguide into different lobes.