A display screen which can be operated in at least two operating modes, an operating mode B1 for a free viewing mode and an operating mode B2 for a limited viewing mode in which light is emitted in a viewing angle range that is limited for a viewer relative to the free viewing mode, comprising:
- an image reproduction device;
- and
- an optical film which is arranged in front of the image reproduction device in a viewing direction and which has a liquid crystal layer which is switchable between at least two states,
- wherein the liquid crystal layer is in the first switching state in operating mode B2, and wherein the liquid crystal layer is in the second switching state in the operating mode B1,
- the optical film comprising a first polarization layer with a first absorption axis which forms an angle from 0° to 30°, inclusive, with a surface normal of the optical film, at least one phase-shifting compensation layer for improving the limiting of the viewing angle range, and a second polarization layer with a second absorption axis which is oriented parallel to the surface of the optical film, wherein
- i. in a first alternative, a first B* compensation layer which is formed to be spatially homogeneous and comprises a first biaxially birefringent material with two optical axes and three principal refractive axes is arranged between the first polarization layer and the second polarization layer,
- wherein a refractive index nx, ny, nz is uniquely associated with each of the principal refractive axes,
- wherein either the principal refractive axis to which the lowest refractive index corresponds or the principal refractive axis to which the highest refractive index corresponds lies parallel to the first absorption axis, and
- wherein a condition
- Δ
-
- p
-
- h
- =
- 2
-
- π
- λ
-
- d
- ·
- ❘
- "\[LeftBracketingBar]"
- n
- x
- -
- n
- y
- ❘
- "\[RightBracketingBar]"
- <
- 2
-
- π
- is met for the first B* compensation layer, where d is a thickness of the first B* compensation layer, Δph is the phase shift, and λ is a given wavelength, and
- ii. in a second alternative, at least two compensation layers comprising uniaxially birefringent materials are arranged between the first polarization layer and the second polarization layer, wherein:
- a first, spatially homogeneous A* compensation layer comprises a first uniaxially birefringent material with a first optical axis and two first principal refractive axes differing from one another, wherein the first optical axis lies perpendicular to or parallel to the first absorption axis of the first polarization layer, and, behind this viewed from the direction of a viewer, is arranged;
- and
- a second, spatially homogeneous A* compensation layer which comprises a second uniaxially birefringent material with a second optical axis and two second principal refractive axes, wherein the second optical axis lies perpendicular to the first optical axis,
- wherein a condition
- Δ
-
- p
-
- h
- =
- 2
-
- π
- λ
-
- d
- ·
- ❘
- "\[LeftBracketingBar]"
- n
- e
- -
- n
- o
- ❘
- "\[RightBracketingBar]"
- <
- 2
-
- π
- ,
- where d is a thickness of a compensation layer, ne is an extraordinary refractive index, no is an ordinary refractive index, Δph a phase shift, and Δ is a given wavelength, is met for each of the compensation layers,
- wherein, in both alternatives i. and ii., the materials and thicknesses d of the compensation layers are specified such that, measured in a spherical coordinate system having an origin on the surface of the film and in the plane of the surface of the film, the luminance is minimal exclusively in a specified solid angle range R which comprises azimuthal angles φ for which |φ| and |180°−φ| are less than an amount of a predetermined limiting azimuthal angle φlim measured with reference to a preferential direction in the plane of the surface of the film, and a polar angle θ of a greater magnitude than a predetermined limiting polar angle θlim measured with reference to the surface normal or, if the first absorption axis does not lie parallel to the surface normal, measured with reference to the first absorption axis and in a plane which is defined by the surface normal and the first absorption axis,
- and wherein:
- either a liquid crystal layer which is switchable between at least two states and which is formed such that light transmitted by the second polarization layer is transmitted by the liquid crystal layer with unchanged polarization or with polarization rotated by 90° in a first switching state and with circular or elliptical or linear polarization in a second switching state is arranged between the second polarization layer and the compensation layer arranged closest to the second polarization layer;
- or the liquid crystal layer which is switchable between the at least two states and which is formed such that light transmitted by the first polarization layer is transmitted by the liquid crystal layer with unchanged polarization or with polarization rotated by 90° in a first switching state and with circular or elliptical or linear polarization in a second switching state is arranged between the first polarization layer and the compensation layer arranged closest to the first polarization layer.