Display device and driving method

Abstract

A display device has a light blocking arrangement for selectively blocking light which has or would be emitted at large lateral angles. The display can be configured so that light reaching these elements is either allowed to reach the viewer or is blocked from reaching the viewer. This means that a public viewing mode can be chosen or a private viewing mode. The light blocking elements are controlled optically in order to simplify the construction and control.

Claims

1. A display device having a privacy mode and a public mode, comprising: a display panel; a backlight arrangement, wherein the backlight arrangement is arranged to illuminate the display panel; and a light blocking arrangement, wherein the light blocking arrangement is arranged to selectively block light, wherein the light is directed in a lateral output direction from the display panel, wherein the display blocks the laterally directed light using the light blocking arrangement in the privacy mode, wherein the display does not block the laterally directed light in the public mode, wherein the light blocking arrangement comprises elements formed from a photochromic material, wherein the blocking function of the photochromic material is dependent on a light stimulus of a particular wavelength incident on the light blocking arrangement, wherein the backlight arrangement has a first, non-visible, light output which is the light stimulus for inducing switching of the light blocking elements to an opaque state, wherein the backlight arrangement has a second, visible, light output, wherein the backlight arrangement has a third output for inducing switching of the light blocking elements to a transparent state wherein the first, non-visible output is a UV light output, wherein the third output is an IR light output.

2. The display device as claimed in claim 1, further comprising a UV filter at the display panel output.

3. The display device as claimed in claim 1, further comprising an IR filter at the display panel output.

4. The display device as claimed in claim 1, wherein the backlight arrangement comprises a single waveguide, wherein the single waveguide comprises scattering elements, wherein the scattering elements are arranged to provide out-coupling of a first light from the waveguide, wherein the backlight arrangement comprises UV, visible and IR light LEDs, UV, visible and IR light LEDS provide a second light into the waveguide.

5. The display device as claimed in claim 1, wherein the light blocking arrangement comprises a photochromic material, the photochromic material comprising a mixture of a solvent, resin or polymer with a photochromic dye.

6. The display device as claimed in claim 1, further comprising: an array of lenses, wherein the array of lenses is arranged in front of the display panel, wherein the light blocking arrangement selectively blocks light which is directed between the lenses, wherein the light blocking arrangement comprises elements disposed between adjacent lens locations, wherein the light blocking arrangement blocks the light which is directed between the lenses in the privacy mode, wherein the light blocking arrangement does not block the light which is directed between the lenses in the public mode.

7. The display device as claimed in claim 2, wherein the third output is an IR light output.

8. The display device as claimed in claim 7, further comprising an IR filter at the display panel output.

9. The display device as claimed in 7, wherein the backlight arrangement comprises a single waveguide, wherein the single waveguide comprises scattering elements, wherein the scattering elements are arranged to provide out-coupling of a first light from the waveguide, wherein the backlight arrangement comprises UV, visible and IR light LEDs, UV, visible and IR light LEDS provide a second light into the waveguide.

10. The display device as claimed in claim 1, further comprising an IR filter at the display panel output.

11. The display device as claimed in 3, wherein the backlight arrangement comprises a single waveguide, wherein the single waveguide comprises scattering elements, wherein the scattering elements are arranged to provide out-coupling of a first light from the waveguide, wherein the backlight arrangement comprises UV, visible and IR light LEDs, UV, visible and IR light LEDS provide a second light into the waveguide.

12. The display device as claimed in 8, wherein the backlight arrangement comprises a single waveguide, wherein the single waveguide comprises scattering elements, wherein the scattering elements are arranged to provide out-coupling of a first light from the waveguide, wherein the backlight arrangement comprises UV, visible and IR light LEDs, UV, visible and IR light LEDS provide a second light into the waveguide.

13. The display device as claimed in 10, wherein the backlight arrangement comprises a single waveguide, wherein the single waveguide comprises scattering elements, wherein the scattering elements are arranged to provide out-coupling of a first light from the waveguide, wherein the backlight arrangement comprises UV, visible and IR light LEDs, UV, visible and IR light LEDS provide a second light into the waveguide.

14. A method of operating a display device having a privacy mode and a public mode, wherein the display device comprises a display panel, a backlight arrangement, wherein the backlight arrangement is arranged to illuminate the display panel and a light blocking arrangement arranged to selectively block the light which is directed in a lateral output direction from the display panel, wherein the light blocking arrangement is formed from a photochromic material, wherein the blocking function of the photochromic material is dependent on a light stimulus of a particular wavelength incident on the light blocking arrangement, the method comprising: configuring the display in one of the privacy mode and the public mode, wherein the configuring depends on the spectrum of light incident on the light blocking arrangement; using the backlight arrangement to provide a first, non-visible, light output, wherein the light output is the light stimulus for inducing switching of the light blocking elements towards an opaque state to implement the privacy mode, wherein the light blocking arrangement blocks the laterally directed light; using the backlight arrangement to provide a second visible light output; removing the light stimulus from the light blocking arrangement; and using the backlight arrangement to provide a third output for inducing switching of the light blocking elements to a transparent state, wherein the transparent state implements the public mode, wherein the light blocking arrangement does not block the laterally directed light wherein the first, non-visible output is a UV light output and the third output is an IR light output.

15. The method as claimed in claim 14, wherein the display device further comprises an array of lenses arranged in front of the display panel, wherein the light blocking arrangement is arranged to selectively block the light, wherein the light is directed between the lenses, wherein the light blocking arrangement comprises elements disposed between adjacent lens locations, wherein the light blocking arrangement blocks the light which is directed between the lenses in the privacy mode, wherein the light blocking arrangement does not block the light which is directed between the lenses in the public mode.

16. The method as claimed in claim 14, wherein the display device comprises a UV filter at the display panel output.

17. The method as claimed in claim 14, wherein the display device comprises an IR filter at the display panel output.

18. The method as claimed in claim 14, wherein the backlight arrangement comprises a single waveguide, wherein the single waveguide comprises scattering elements, wherein the scattering elements are arranged to provide out-coupling of a first light from the waveguide, wherein the backlight arrangement comprises UV, visible and IR light LEDs, UV, visible and IR light LEDS provide a second light into the waveguide.

19. The method as claimed in claim 14, wherein the light blocking arrangement comprises a photochromic material, the photochromic material comprising a mixture of a solvent, resin or polymer with a photochromic dye.

20. A display device having a privacy mode and a public mode, comprising: a display panel; a backlight arrangement, wherein the backlight arrangement is arranged to illuminate the display panel; and a light blocking arrangement, wherein the light blocking arrangement is arranged to selectively block light, wherein the light is directed in a lateral output direction from the display panel, wherein the display blocks the laterally directed light using the light blocking arrangement in the privacy mode, wherein the display does not block the laterally directed light in the public mode, wherein the light blocking arrangement comprises elements formed from a photochromic material, wherein the blocking function of the photochromic material is dependent on a light stimulus of a particular wavelength incident on the light blocking arrangement, wherein the backlight arrangement has a first, non-visible, light output which is the light stimulus for inducing switching of the light blocking elements to an opaque state, wherein the backlight arrangement has a second, visible, light output, wherein the backlight arrangement has a third output for inducing switching of the light blocking elements to a transparent state wherein the third output is an IR light output.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) An embodiment of the invention will now be described, purely by way of example, with reference to the accompanying drawings, in which:

(2) FIG. 1 is a schematic perspective view of a known autostereoscopic display device;

(3) FIG. 2 shows how a lenticular array provides different views to different spatial locations;

(4) FIG. 3 shows a cross-section of the layout of a multi-view auto-stereoscopic display;

(5) FIG. 4 is a close-up of FIG. 3;

(6) FIG. 5 shows a 9-view system in which the views produced in each of the sets of cones are equal;

(7) FIG. 6 shows an example of display device as disclosed in WO2013/179190;

(8) FIG. 7 shows a first example of display device of the invention;

(9) FIG. 8 shows a second example of display device of the invention; and

(10) FIG. 9 shows how the intensity of views within a viewing cone may be adapted to improve the cutoff in the private viewing mode.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(11) The invention provides a display device that has a light blocking arrangement for selectively blocking light which has or would be emitted at large lateral angles. The display can be configured so that light reaching these elements is either allowed to reach the viewer or is blocked from reaching the viewer. This means that a public viewing mode can be chosen or a private viewing mode. The light blocking elements are controlled optically in order to simplify the construction and control.

(12) The invention will be described with reference to an autostereoscopic display device, but it can be used generally to provide a private and a public viewing mode.

(13) FIG. 1 is a schematic perspective view of a known direct view autostereoscopic display device 1. The known device 1 comprises a liquid crystal display panel 3 of the active matrix type that acts as a spatial light modulator to produce the display.

(14) The display panel 3 has an orthogonal array of display sub-pixels 5 arranged in rows and columns. For the sake of clarity, only a small number of display sub-pixels 5 are shown in the Figure. In practice, the display panel 3 might comprise about one thousand rows and several thousand columns of display sub-pixels 5. In a black and white display panel a sub-pixel in fact constitutes a full pixel. In a color display a sub-pixel is one color component of a full color pixel. The full color pixel, according to general terminology comprises all sub-pixels necessary for creating all colors of a smallest image part displayed.

(15) A full color pixel may have red (R) green (G) and blue (B) sub-pixels possibly augmented with a white sub-pixel or with one or more other elementary colored sub-pixels. For example, an RGB (red, green, blue) sub-pixel array is well known, although other sub-pixel configurations are known such as RGBW (red, green, blue, white) or RGBY (red, green, blue, yellow).

(16) The structure of the liquid crystal display panel 3 is entirely conventional. In particular, the panel 3 comprises a pair of spaced transparent glass substrates, between which an aligned twisted nematic or other liquid crystal material is provided. The substrates carry patterns of transparent indium tin oxide (ITO) electrodes on their facing surfaces. Polarizing layers are also provided on the outer surfaces of the substrates.

(17) Each display sub-pixel 5 comprises opposing electrodes on the substrates, with the intervening liquid crystal material therebetween. The shape and layout of the display sub-pixels 5 are determined by the shape and layout of the electrodes. The display sub-pixels 5 are regularly spaced from one another by gaps.

(18) Each display sub-pixel 5 is associated with a switching element, such as a thin film transistor (TFT) or thin film diode (TFD). The display sub-pixels are operated to produce the display by providing addressing signals to the switching elements, and suitable addressing schemes will be known to those skilled in the art.

(19) The display panel 3 is illuminated by a light source 7 comprising, in this case, a planar backlight extending over the area of the display sub-pixel array. Light from the light source 7 is directed through the display panel 3, with the individual display sub-pixels 5 being driven to modulate the light and produce the display.

(20) The display device 1 also comprises a lenticular sheet 9, arranged over the display side of the display panel 3, which performs a view forming function. The lenticular sheet 9 comprises a row of lenticular elements 11 extending parallel to one another, of which only one is shown with exaggerated dimensions for the sake of clarity.

(21) The lenticular elements 11 are in the form of convex cylindrical lenses, and they act as a light output directing means to provide different images, or views, from the display panel 3 to the eyes of a user positioned in front of the display device 1.

(22) The device has a controller 13 which controls the backlight and the display panel.

(23) The autostereoscopic display device 1 shown in FIG. 1 is capable of providing several different perspective views in different directions. In particular, each lenticular element 11 overlies a small group of display sub-pixels 5 in each row. The lenticular element 11 projects each display sub-pixel 5 of a group in a different direction, so as to form the several different views. As the user's head moves from left to right, his/her eyes will receive different ones of the several views, in turn.

(24) The skilled person will appreciate that a light polarizing means must be used in conjunction with the above described array, since the liquid crystal material is birefringent, with the refractive index switching only applying to light of a particular polarization. The light polarizing means may be provided as part of the display panel or the imaging arrangement of the device.

(25) FIG. 2 shows the principle of operation of a lenticular type imaging arrangement as described above and shows the backlight 20, display device 24 such as an LCD and the lenticular array 28 of lenses 27. FIG. 2 shows how the lenticular arrangement 28 directs different pixel outputs to three different spatial locations.

(26) When applied to an autostereoscopic display, the invention relates to view repetition in such displays, which is explained below.

(27) FIG. 3 shows a cross-section of the layout of a multi-view auto-stereoscopic display. Each sub-pixel 31.sup.I to 31.sup.VII underneath a certain lenticular lens 27 will contribute to a specific view 32.sup.I to 32.sup.VII. All sub-pixels underneath this lens will together contribute to a cone of views. The width of this cone (between lines 37 and 37) is determined by the combination of several parameters: it depends on the distance 34 (D) from the pixel plane to the plane of the lenticular lenses. It also depends on the lens pitch 35 (P.sub.L).

(28) FIG. 4 is a close-up of FIG. 3, and shows that the light emitted (or modulated) by a pixel of the display 24 is collected by the lenticular lens 27 closest to the pixel but also by neighboring lenses 27 and 27 of the lenticular arrangement 28. This is the origin of the occurrence of repeated cones of views. Pixel 31.sup.IV for example contributes to viewing cones 29, 29 and 29 as shown.

(29) The corresponding views produced in each of the cones are equal. This effect is schematically shown in FIG. 5 for a 9-view system (i.e. 9 views in each cone).

(30) For an acceptable compromise between 3D effect and resolution penalty, the total number of views is limited to typically 9 or 15. These views have an angular width of typically 1 to 2 degrees. The views and the cones have the property that they are periodic.

(31) FIG. 6 shows one example arrangement of WO 2013/179190 in which light blocking elements 62 are provided between the lenses. The arrangement as a whole (not necessarily the parts between the lenses) can be switched to a light transmitting or blocking mode. In this way, light from a pixel that would leave the display from a neighboring lens can be blocked while the primary viewing cone is unaltered. The system can be implemented as optical elements between the lenticules and additional layers which provide the control of the light entering/leaving the lenticular lenses so that the light blocking function is enabled or disabled.

(32) Examples of possible light blocking arrangement disclosed in WO2013/179191 are:

(33) (i) The light blocking structure is a polarizer, and the optical path includes at least one retarder.

(34) (ii) The light blocking structure is a retarder and the optical path includes a polarizer.

(35) (iii) The light blocking structure is an electrophoretic cell.

(36) FIG. 6 is based on the use of a polarizer as the light blocking element. A first polarizer 60 is provided between the display panel 24 and the lenticular array 28. An arrangement of second polarizers 62 is provided between the lens elements. An optical retarder 64 is provided between the polarizers 60, 62.

(37) The lenticular sheet can be manufactured by embossing the lenticular sheet and filling it with material that, when dry, has a polarizing function. An alternative is to produce lenticular and polarizing strips separately and then glue them together to form a lenticular sheet. That sheet can then be placed on top of the other display layers.

(38) The retarder 64 can for example be a single liquid crystal cell covered on both sides with a single transparent (for example ITO) electrode, such that the retarder as a whole can be switched between polarity states. Alternatively the retarder 64 can be patterned such that an LC cell covers a single sub-pixel, pixel or set of pixels. In that case cells can be switched independently. This allows for content, task or application privacy modes such that sensitive information on the display (for example mail) is only visible in a small viewing cone, while insensitive information is not.

(39) The structures disclosed require electrically controlled layers or stripes with their associated electrode arrangements, and this increased the complexity of the design of the lenticular structure.

(40) An alternative has been proposed in WO2013/048847 in which barriers are formed from electrochromic material, so that the barrier transmittance is electrically controllable by application of an electric field. This again requires a control electrode arrangement as part of the lenticular structure.

(41) This invention makes use of optically controlled light blocking elements. The design thus makes use of photochromic materials.

(42) FIG. 7 shows an example.

(43) The light blocking elements 70 are formed from a photochromic material. They have an optical absorptance which is dependent on a light stimulus.

(44) A photochromic material is selected that can be switched in a relatively short time, e.g. seconds or tens of seconds, but preferably less than a minute, or less than 30 seconds. Preferably, the switching time is less than 10 seconds.

(45) A photochromic material is generally a mixture of a solvent, resin or polymer with a photochromic dye. There are many photochromic molecules that may be used. For example, photochromic molecules can belong to various classes: triarylmethanes, stilbenes, azastilbenes, nitrones, fulgides, spiropyrans, naphthopyrans, spiro-oxazines, quinones and others.

(46) One well known use of photochromic materials is in light reacting sunglasses. A typical photochromic material used in light reacting sunglasses is based on a solution with silver chloride or silver halide. The molecules are transparent to visible light in the absence of UV light, which is normal for artificial lighting. When exposed to UV rays, as in direct sunlight, the molecules undergo a chemical process that causes a shape change. The new molecular structure absorbs portions of the visible light, causing the lenses to darken. The number of molecules that change shape varies with the intensity of the UV light.

(47) A subsequent absence of UV radiation causes the molecules to return to their original shape, resulting in the loss of their light absorbing properties.

(48) The switching speed of photochromic dyes is typically higher in solution than when trapped in a polymerized matrix. However, there are known solutions which add a chemical component to a photochromic dye to improve the switching speed for a polymerized matrix. An example is disclosed in R. A. Evans et al., The generic enhancement of photochromic dye switching speeds in a rigid polymer matrix, Nature Materials, volume 4, pp. 249-253, 2005.

(49) Another approach for increasing the switching speed is disclosed in WO 2013/132123 which discloses a photochromic-material based on oil core capsules.

(50) The photochromic dye may have any desired color. Silver chloride or halide is silver/grey, but other materials may be selected to provide other colors if desired.

(51) In order to provide the light stimulus, the backlight 72 is designed to provide a switchable UV output. For example, the backlight 72 may comprise an LED backlight comprising an array of LEDs. In one example, the backlight arrangement comprises a single waveguide with scattering dots to provide out-coupling of light from the waveguide, and multiple LEDs or LED packages including both UV and visible light LEDs providing light into the waveguide. This provides an edge-lit waveguide backlight design with multiple light wavelengths provided to the waveguide. The scattering dots (or other light out-coupling structures such as raised or indented profiles) are selected to be sufficiently wavelength independent to provide out-coupling of all required light.

(52) The use of a photochromic material means that electrodes are not needed to switch between the public and private modes.

(53) When the UV LEDs are turned off, the display (gradually) returns to public mode. FIG. 7 also shows a UV-filter 76 in front of the blocking elements 70 (i.e. on the display output side) to prevent the display from switching to the private mode in the presence of sunlight, and also to prevent the user from prolonged UV radiance.

(54) A high intensity UV light output may be used when switching to the private mode to enable fast switching, and a lower intensity UV light may be used to maintain the private mode. Thus, the second backlight unit may have a variable output intensity, with the intensity controlled during transition between the two modes of operation.

(55) Switching to the public mode is made more rapid by implementing heating, for example using Infrared (IR) LEDs, because the return to a transparent state when the UV LEDs are turned off makes use of a heat-based process. The IR LEDs function as a heat source, and they are thermally coupled to the light blocking elements to transform the generated IR light into heat.

(56) Some alternatives to the single waveguide approach outlined above will now be presented.

(57) A first alternative is to provide only UV LEDs, and incorporate a patterned layer of phosphors, or a patterned layer of a mixture of quantum dots, in order to obtain narrow red, green and blue peaks in the visible spectrum, and also an IR peak. In this way, it is possible to generate visible light and also IR radiation from UV light sources.

(58) Another alternative is to provide a filter layer between the backlight unit and the photochromic elements 70 that absorbs or reflects a narrow band of UV frequency. This could be implemented as a Bragg reflector, and this is used to generate heat along the entire backlight and thus at each of the light blocking elements. Another UV band may then be transmitted through the filter for implementing the switching function. In this case there could be two or three different sets of UV LEDs for all functions. It is again also possible to generate a second UV band from a first UV band using a quantum dot layer or phosphor layer.

(59) In principle, there are many other general backlight configurations which may be used to provide a UV (or generally a non-visible) light output and a visible light output. Examples include:

(60) a visible light edge-lit waveguide with a directly illuminating UV LED array on top which is substantially transparent (to visible light);

(61) a visible light edge-lit waveguide with an edge-lit UV waveguide on top which is substantially transparent (to visible light);

(62) a UV edge-lit waveguide with a visible edge-lit waveguide on top which is substantially transparent (to UV);

(63) a UV edge-lit waveguide with a directly illuminating visible LED array on top which is substantially transparent (to UV);

(64) a directly illuminating LED array with a substantially transparent UV directly illuminating LED array on top;

(65) a directly illuminating visible LED array with an edge-lit UV backlight on top; and

(66) interspersed direct light UV and visible LEDs on a single support panel.

(67) Diffusers may be used to spread the UV and visible light output (and also IR if used).

(68) Different intensities for the UV light and the visible light may be selected. A larger UV intensity, for example implemented by UV LEDs occupying a larger proportion of a shared backlight area, will increase switching speed but might reduce display uniformity. Different light sources (UV, RGB, IR) may be provided on different sides of an edge lit backlight.

(69) IR LEDs may be integrated into the backlight in the same way (and as well as) as UV LEDs in any of the manners as explained above. In this case, the filter 76 comprises a band-pass filter which blocks both UV and IR light. The system then makes use of two wavelengths, and the chemical processes in the photochromic layer react to those wavelengths to switch transparency and thereby between private and public modes.

(70) The light blocking elements may be positioned at any position between the backlight and the viewer. In the example above, they are between the lens elements and therefore over the display panel. However, they may be between the backlight and the display panel. This arrangement may reduce moir effects.

(71) The example above is actively switchable between the private and public modes.

(72) A UV-filter between the viewer and the light blocking elements may be used to prevent the sunlight from switching the display. The display thus can be in public or private mode in any ambient light situation.

(73) The lens array according to FIG. 7 can be made by molding and curing a polymer to form the lenses. The photochromic material (polymer and dye) is then provided between the lenses and the photochromic polymer is also cured.

(74) The example above shows the curved faces of the lenticulars of the lenticular array 28 facing away from the display panel 24. An alternative design, which has better performance over wide viewing angles, is described in detail in WO 2009/147588. The application of this type of design is shown in FIG. 8.

(75) A glue 80 (typically a polymer) has a refractive index that is different from that of the lenticular lens array 28. A glass or polycarbonate slab 82 has a refractive index similar to the glue 80 and is used to create enough distance for the lenticular lens to focus on the display panel 24. The curved face of the lenticulars of the lenticular array 28 then faces toward the display panel 24.

(76) The slab 82 incorporates the light blocking elements 70.

(77) FIG. 8 is more straightforward to manufacture because the light blocking elements are in the spacer and the lenticular lens is on top. Thus, they can be made separately. The photochromic material could be a solvent and dye to enable a fast response, in which case the two substrates have to be sealed. Alternatively, a polymerized matrix design may be used to avoid the need for sealing.

(78) It can be seen from the examples above that the light blocking elements are integrated into the structure of the display panel, so they are between the display output surface (for example the lenticular lenses) and the display backlight, i.e. beneath the display output surface and above the backlight output surface. They may be:

(79) between the individual lenses of a lenticular array (FIG. 7);

(80) between the lenticular array layer and the display panel (FIG. 8); or

(81) between the backlight and the display panel.

(82) As explained above, the backlight preferably makes use of LEDs such as white LEDs. This give good energy efficiency and they can be turned on and off quickly and thereby allow frame-based local dimming in order to improve the black level and power efficiency. Another step is to use RGB LEDs instead of white LEDs with the benefit that the color gamut can be increased. The LEDs can be placed behind the display panel or on the sides of a patterned waveguide to produce a side-lit display.

(83) However, a cold cathode fluorescent lamp (CCFL) backlight may instead by used, which typically comprises a row of CCFL lamps placed in a cavity lined with a white and diffuse (Lambertian) back. The light from the CCFL lamps either directly or via the back lining passes through a diffuser to hide the lamps and ensure sufficiently uniform screen intensity.

(84) Organic light emitting diodes (OLED), organic light emitting transistors (OLET) and quantum dot LEDs (QLED) may also be used to create backlights as the techniques allow to create a uniformly emitting surface. This removes the need for diffusers and waveguides and thus can reduce the number of components and make the display even thinner. However, to use the full potential of these techniques, the pixels themselves could be emitters to improve the efficiency.

(85) A backlight can then be dispensed with for the generation of the image to be displayed if a direct emitting display technology is used. For the controllable implementation above, only a UV lighting arrangement is then needed to implement control of the light blocking elements.

(86) The invention can be applied to all of these types of display.

(87) The examples above show non-switchable autostereoscopic displays.

(88) By making the lens of a multi-view display switchable, it becomes possible to have a high 2D resolution mode in combination with a 3D mode. Other uses of switchable lenses are to increase the number of views time-sequentially (WO 2007/072330) and to allow multiple 3D modes (WO 2007/072289). Known methods to produce a 2D/3D switchable display replace the lenticular lens by:

(89) (i) A lens shaped cavity filled with liquid crystal material of which the lens function is turned on/off by electrodes that control the orientation of LC molecules or is turned on/off by changing the polarization of the light (through a switchable retarder).

(90) (ii) A box shaped cavity filled with liquid crystal where electrodes control the orientation of LC molecules to create a gradient-index lens (see for instance WO 2007/072330).

(91) (iii) An electro wetting lens of droplets of which the shape is controlled by an electric field.

(92) (iv) A lens-shaped cavity filled with transparent electrophoretic particles in a fluid of different refractive index (WO 2008/032248).

(93) This invention can be applied to switchable autostereoscopic displays, for example of the types outlined above.

(94) The examples above make use UV illumination to control the switching of the full display. The UV light source may be controllable locally as a pixelated light source, to enable a locally set switchable privacy mode. In this case, the device can operate such that the privacy mode is set locally in a way that is clear and convenient to the user.

(95) The examples above show the use of the invention in an autostereoscopic display. The invention may however be used for a 2D display, to provide private and public viewing modes.

(96) When applied to an autostereoscopic display, the light blocking elements may be placed at different positions in the stack (e.g. in front or behind the lens array or between the backlight and the display panel). The function of the light blocking elements are essentially to provide collimation of light. To preserve the collimation, there should be no strongly diffusing elements in front of the privacy filter because the benefit would be lost.

(97) As explained above, the photochromic arrangement does not do not interfere with the 3D function of a 3D lenticular display, especially when the light blocking elements are optimized to pass the primary cone, and reduce secondary viewing cones.

(98) An important benefit that is specific to 3D lenticular displays is that the fall off in the primary cone of the intensity caused by the light blocking elements (at least in private mode) can be partially compensated for by setting a correcting intensity profile along the views.

(99) This approach is shown in FIG. 9. FIG. 9(a) shows the intensity (y-axis) as function of angle (x-axis) in the public mode. The primary cone 90 has a width of around 15 degrees each side of the normal. FIG. 9(b) shows the intensity (y-axis) as function of angle (x-axis) in the private mode without any compensation.

(100) FIG. 9(c) shows the intensity (y-axis) as function of angle (x-axis) to represent the compensation function applied in the private mode. The resulting intensity (y-axis) as function of angle (x-axis) in the private mode without this compensation in shown in FIG. 9(d).

(101) The center views within the primary cone 90 (and indeed within each cone) are adapted to have a lower intensity than the outer views. Due to cone repetition, the falloff to the secondary cone will be sharper as shown in FIG. 9(d).

(102) Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word comprising does not exclude other elements or steps, and the indefinite article a or an does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.