Observer-tracked privacy display

A display apparatus comprising:

• a display device comprising:
• a spatial light modulator arranged to output spatially modulated light;
• a display polariser arranged on a side of the spatial light modulator, the display polariser being a linear polariser;
• and
• a view angle control arrangement comprising:
• an additional polariser arranged on the same side of the spatial light modulator as the display polariser, the additional polariser being a linear polariser;
• and
• at least one polar control retarder arranged between the display polariser and the additional polariser, wherein the at least one polar control retarder comprises a switchable liquid crystal retarder comprising a layer of liquid crystal material;
• two surface alignment layers disposed adjacent to the layer of liquid crystal material and on opposite sides thereof, the surface alignment layers each being arranged to provide homogenous alignment in the adjacent liquid crystal material, the liquid crystal material being provided with a twist;
• and
• first and second electrode arrangements disposed on opposite sides of the layer of liquid crystal material and arranged to provide an electric field perpendicular to the layer of liquid crystal material,
• wherein the display apparatus further comprises a control system arranged to control the spatial light modulator and to supply voltages to the first and second electrode arrangements for providing the electric field perpendicular to the layer of liquid crystal material, the control system being arranged to vary the voltages to the first and second electrode arrangements for controlling a direction of minimum light transmission of the view angle control arrangement.