A switchable privacy display device comprising: a backlight arranged to output light; a transmissive spatial light modulator arranged to receive output light from the backlight; a display polariser arranged on a side of the spatial light modulator; an additional polariser arranged on the same side of the spatial light modulator as the display polariser; and plural retarders arranged between the additional polariser and the display polariser; wherein the plural retarders comprise: a switchable liquid crystal retarder comprising: a layer of liquid crystal material having a positive dielectric anisotropy and having a retardance for light of a wavelength of 550nm in a range from 500nm to 1000nm, two surface alignment layers (431, 433) disposed adjacent to the layer of liquid crystal material and on opposite sides thereof, each of the surface alignment layers (431, 433) being arranged to provide homogeneous alignment in the adjacent liquid crystal material and each of the surface alignment layers (431, 433) having a pretilt having a pretilt direction with a component in the plane of the liquid crystal layer that is parallel or anti-parallel or orthogonal to the electric vector transmission direction of the display polariser; and at least one passive compensation retarder that comprises either: a passive retarder having its optical axis perpendicular to the plane of the retarder and having a retardance for light of a wavelength of 550nm in a range from -300nm to -700nm; or a pair of passive retarders (330A, 330B) having optical axes in the plane of the retarders (330A, 330B) that are crossed and each having a retardance for light of a wavelength of 550nm in a range from 300nm to 800nm. a backlight arranged to output light; a transmissive spatial light modulator arranged to receive output light from the backlight; a display polariser arranged on a side of the spatial light modulator; an additional polariser arranged on the same side of the spatial light modulator as the display polariser; and plural retarders arranged between the additional polariser and the display polariser; wherein the plural retarders comprise: a switchable liquid crystal retarder comprising: a layer of liquid crystal material having a positive dielectric anisotropy and having a retardance for light of a wavelength of 550nm in a range from 500nm to 1000nm, two surface alignment layers (431, 433) disposed adjacent to the layer of liquid crystal material and on opposite sides thereof, each of the surface alignment layers (431, 433) being arranged to provide homogeneous alignment in the adjacent liquid crystal material and each of the surface alignment layers (431, 433) having a pretilt having a pretilt direction with a component in the plane of the liquid crystal layer that is parallel or anti-parallel or orthogonal to the electric vector transmission direction of the display polariser; and at least one passive compensation retarder that comprises either: a passive retarder having its optical axis perpendicular to the plane of the retarder and having a retardance for light of a wavelength of 550nm in a range from -300nm to -700nm; or a pair of passive retarders (330A, 330B) having optical axes in the plane of the retarders (330A, 330B) that are crossed and each having a retardance for light of a wavelength of 550nm in a range from 300nm to 800nm. a switchable liquid crystal retarder comprising: a layer of liquid crystal material having a positive dielectric anisotropy and having a retardance for light of a wavelength of 550nm in a range from 500nm to 1000nm, two surface alignment layers (431, 433) disposed adjacent to the layer of liquid crystal material and on opposite sides thereof, each of the surface alignment layers (431, 433) being arranged to provide homogeneous alignment in the adjacent liquid crystal material and each of the surface alignment layers (431, 433) having a pretilt having a pretilt direction with a component in the plane of the liquid crystal layer that is parallel or anti-parallel or orthogonal to the electric vector transmission direction of the display polariser; and at least one passive compensation retarder that comprises either: a passive retarder having its optical axis perpendicular to the plane of the retarder and having a retardance for light of a wavelength of 550nm in a range from -300nm to -700nm; or a pair of passive retarders (330A, 330B) having optical axes in the plane of the retarders (330A, 330B) that are crossed and each having a retardance for light of a wavelength of 550nm in a range from 300nm to 800nm. a passive retarder having its optical axis perpendicular to the plane of the retarder and having a retardance for light of a wavelength of 550nm in a range from -300nm to -700nm; or a pair of passive retarders (330A, 330B) having optical axes in the plane of the retarders (330A, 330B) that are crossed and each having a retardance for light of a wavelength of 550nm in a range from 300nm to 800nm.