DE102021108786B4 - Lighting device for a screen for a clear and a restricted view mode and use of such a lighting device - Google Patents

Abstract

Lighting device (1a) for a screen (1), which can be operated in at least two operating modes B1 for an unobstructed view mode and B2 for a restricted view mode, comprising- a planar extended backlight (2), in turn comprising- a planar radiator, which as second light guide (2a) is designed with second light sources (2b),- an optical component (2e) located in front of the planar radiator in the viewing direction of an observer (5) for light direction limitation, designed as a lamellar filter, the optical component (2e) along said preferred direction is divided into different areas (A1, A2, ...), with a separate reference direction being selectable for each area (A1, A2, ...), with all reference directions also being different in pairs and with a maximum tolerance of 10 degree in the direction of an observer (5), and in each such area (A1, A2, ...) the transmission maximum fu r the light penetrating the optical component (2e) is in the corresponding reference direction, with the lamellae of the optical component (2e) designed as a lamellar filter being inclined at an angle to the left or right edge of the background lighting (2), which creates moiré effects or other visible overlay effects with the screen (1) and/or other components in the lighting device (1a) are avoided, - so that the areally extended backlighting (2) emits light in a restricted angular range, with the backlighting (2) along a preferred direction is divided into different areas, and a separate reference direction can be selected for each area (A1, A2, ...), with all reference directions being different in pairs and pointing in the direction of an observer (5) with a maximum tolerance of 10 degrees, and the backlight (2) in each such area (A1, A2, ...) for da s light emitted there has the luminance maximum in the corresponding reference direction, - a plate-shaped light guide (3) located in front of the background lighting (2) in the viewing direction, which has decoupling elements (6) on at least one of the large areas and/or within its volume, wherein the light guide (3) is at least 50% transparent for the light emanating from the backlighting (2), - illuminants (4) arranged laterally on the narrow sides of the light guide (3), - the backlighting (2) being in operating mode B2, and the lighting means (4) are switched off, and wherein at least the lighting means (4) are switched on in operating mode B1.

Description

field of invention

In recent years, great advances have been made in widening the viewing angle of LCDs. However, there are often situations in which this very large viewing area of a screen can be a disadvantage. Information is also increasingly available on mobile devices such as notebooks and tablet PCs, such as bank details or other personal details and sensitive data. Accordingly, people need control over who can see this sensitive data; they must be able to choose between a wide viewing angle in order to share information on their display with others, e.g. when looking at holiday photos or for advertising purposes. On the other hand, they need a small viewing angle if they want to keep the image information confidential.

A similar problem arises in vehicle construction: the driver must not be distracted by image content such as digital entertainment programs when the engine is switched on, while the passenger would like to consume the same while driving. A screen is therefore required which can switch between the corresponding display modes.

State of the art

Additional films based on micro-lamellas have already been used for mobile displays in order to achieve visual data protection. However, these foils were not switchable, they always had to be applied by hand and then removed again. You also have to transport them separately to the display when you don't need them. A significant disadvantage of the use of such lamellar foils is also associated with the associated loss of light.

The U.S. 6,765,550 B2 describes such a privacy screen using micro-slats. The biggest disadvantage here is the mechanical removal or mechanical attachment of the filter and the loss of light in protected mode.

In the US 5,993,940A describes the use of a film that has small prism strips evenly arranged on its surface in order to achieve a privacy mode. Development and production are quite complex.

In the WO 2012/033583 A1 switching between free and restricted vision is generated by driving liquid crystals between so-called "chromonic" layers. This results in a loss of light and the effort is quite high.

The US 2012/0235891 A1 describes a very complex backlight in a screen. There come according to 1 and 15 not only several light guides are used, but also other complex optical elements such as microlens elements 40 and prism structures 50, which transform the light from the rear lighting on the way to the front lighting. This is expensive and complex to implement and also associated with light loss. According to the variant after 17 in the US 2012/0235891 A1 Both the light sources 4R and 18 produce light with a narrow illumination angle, and the light from the rear light source 18 is first converted into light with a large illumination angle with great effort. This complex conversion is - as already mentioned above - strongly reducing the brightness.

According to the JP 2007-155783 A special optical surfaces 19 that are complex to calculate and produce are used, which then deflect light into different narrow or wide areas depending on the angle of incidence of the light. These structures resemble Fresnel lenses. There are also interference edges that deflect light in undesirable directions. It therefore remains unclear whether sensible light distributions can actually be achieved.

In the U.S. 2013/0308185 A1 describes a special light guide designed with steps, which emits light over a large area in different directions, depending on the direction from which it is illuminated from a narrow side. In interaction with a transmissive image display device, for example an LC display, a screen that can be switched between free and restricted viewing modes can thus be produced. One of the disadvantages here is that the limited visual effect can be generated either only for left/right or for up/down, but not for left/right/up/down simultaneously, as is necessary for certain payment transactions. In addition, a residual light is still visible even in restricted viewing mode from blocked viewing angles.

The WO 2015/121398 A1 the applicant describes a screen with two modes of operation, in which scattering particles are present in the volume of the corresponding light guide, which is essential for switching between the modes of operation. However, the scattering particles selected there from a polymer usually have the disadvantage that light is decoupled from both large areas, which means that about half of the useful light is emitted in the wrong direction, namely towards the backlight, and not in the right direction due to the structure appropriate extent can be recycled. In addition, the scattering particles made of polymer distributed in the volume of the light guide can, under certain circumstances, particularly at higher concentrations, lead to scattering effects which reduce the visual protection effect in the protected operating mode.

In the WO 2017/089482 A1 the applicant discloses a screen that can be operated in at least two operating modes B1, a clear view mode, and B2, for a restricted view mode. A light guide is used, which is at the front from the viewer's point of view, which is transparent and contains means for light extraction, for example nanoparticles such as titanium dioxide, barium sulfate, etc., which are homogeneously distributed in the volume of the light guide. With this configuration, any residual light that may still be unintentionally present in the B2 operating mode can be superimposed or outshined in the angular areas that are actually protected from view in such a way that contrast is no longer perceptible and thus no image perception from the non-released angles is possible. The disadvantage here is that the light from the light guide itself that is superimposed on the residual light is in turn not desirable or permitted in all applications.

The DE 10 2006 003 134 A1 describes a planar light source with an anisotropically scattering surface for emitting anisotropically distributed light. With this, however, it is not possible to generate selectable light emission characteristics for an optionally free or restricted view.

The DE 10 2019 115 530 A1 relates to a method for gluing a transfer film onto a substrate, in particular for decorative cold embossing. Here, too, it is not possible to generate selectable light emission characteristics for an optionally free or restricted view.

In the DE 11 2010 004 660 T5 discloses a liquid crystal display device which allows switching between two light distribution curves by means of two light guides and other optical elements. The disadvantage here is that the light guide facing the viewer should produce a narrow light distribution. If, for example, a strong light restriction has to be achieved, which is necessary for applications in passenger cars, then this boundary condition for the design of the said light guide facing the viewer requires very high and expensive requirements in order to not let any residual light reach the driver, which would result in unauthorized visibility would.

The WO 2019/034557 A1 the applicant discloses a screen that can be operated in a free and a restricted view mode, with this switchability of the view modes being able to be reduced to a partial area. The disadvantage here is that it is not possible to achieve a large half-width of the luminance for the viewer without further optimization in the privacy mode.

In the U.S. 8,395,726 B2 a manufacturing process for a lamellar filter is described. Its slats are each inclined towards a specific point. However, such a lamellar filter can only permanently influence the direction of light, but not switching between optionally different light emission characteristics.

Finally revealed the WO 2018/225714 A1 a light filter, which has slanted slats in sections in order to optimize the light transmission to a specific area. Here, too, only a permanent influencing of the light direction can take place, but not a switchover between optionally different light emission characteristics.

The aforementioned methods and arrangements usually have the disadvantage in common that they significantly reduce the brightness of the basic screen and/or require an active, or at least a special, optical element for mode switching and/or require complex and expensive production and/or or reduce the resolution in free-to-view mode and/or the image quality in at least one mode.

Description of the invention

It is therefore the object of the invention to describe a lighting device which, in conjunction with a screen, can be used to reliably display information by means of a selectively restricted viewing angle, with a free view, if possible unrestricted in the viewing angle, being possible in a further operating mode. The invention should be able to be implemented as inexpensively as possible using simple means. The highest possible resolution, particularly preferably the native resolution of the screen used, should be visible in both operating modes. Furthermore, only the lowest possible light loss should be introduced by the solution and the restricted viewing angle should achieve the most comprehensive visual protection effect possible with the highest possible image quality.

• - eine flächenartig ausgedehnte Hintergrundbeleuchtung, die Licht in einen eingeschränkten Winkelbereich abstrahlt, wobei die Hintergrundbeleuchtung entlang einer Vorzugsrichtung in verschiedene Bereiche eingeteilt ist, und für jeden Bereich eine eigene Referenzrichtung wählbar ist, wobei alle Referenzrichtungen paarweise verschieden sind und bis auf eine Toleranz von maximal 10 Grad in Richtung eines Betrachters weisen, und wobei die Hintergrundbeleuchtung in jedem solchen Bereich für das dort abgestrahlte Licht jeweils in der entsprechenden Referenzrichtung das -bevorzugt einzige globale- Leuchtdichtemaximum aufweist, (die Leuchtdichteverteilung kann z.B. in einer die Vorzugsrichtung beinhaltenden Ebene senkrecht zur Hintergrundbeleuchtung gemessen werden)
• - einen in Betrachtungsrichtung vor der Hintergrundbeleuchtung gelegenen, plattenförmigen Lichtleiter, welcher auf mindestens einer der Großflächen und / oder innerhalb seines Volumens Auskoppelelemente aufweist, wobei der Lichtleiter für das von der Hintergrundbeleuchtung ausgehende Licht zu mindestens 50% transparent ist,
• - seitlich an Schmalseiten des Lichtleiters angeordnete Leuchtmittel,
• - wobei in der Betriebsart B2 die Hintergrundbeleuchtung ein- und die Leuchtmittel ausgeschaltet sind, und wobei in der Betriebsart B1 mindestens die Leuchtmittel eingeschaltet sind.

According to the invention, this object is achieved by an illumination device for a screen which operates in at least two operating modes B1 for a free view mode and B2 for a limited view mode can be operated, including

• - A flat, extended backlight that emits light in a limited angular range, with the backlight being divided into different areas along a preferred direction, and a separate reference direction being selectable for each area, with all reference directions being different in pairs and with a maximum tolerance of 10 degrees in the direction of an observer, and with the backlighting in each such area for the light emitted there having the -preferably single global- luminance maximum in the corresponding reference direction (the luminance distribution can be measured, for example, in a plane containing the preferred direction perpendicular to the backlighting )
• - a plate-shaped light guide located in front of the backlight in the viewing direction, which has decoupling elements on at least one of the large areas and/or within its volume, the light guide being at least 50% transparent for the light emanating from the backlight,
• - lamps arranged laterally on the narrow sides of the light guide,
• - Wherein the operating mode B2 the background lighting is switched on and the lamps are switched off, and where in the operating mode B1 at least the lamps are switched on.

The fact that the reference directions point in the direction of an observer can be realized in different ways. For example, it is conceivable to align all of the reference directions to the same point on the viewer, for example to the tip of the nose. However, it is also possible that the reference directions are aligned with body parts of the observer that are at least partially disjoint in pairs, i.e. some are aligned with the same body part (and therefore not necessarily with the same point) and others with a different body part.

In operating mode B2, the angle-dependent luminance distribution is adapted to the observer depending on his position in front of the display, so that he sees a more homogeneous image of higher quality - in conjunction with a screen - than if this adaptation does not take place. At the same time, switching to operating mode B1 ensures that, if necessary, several viewers can see an image displayed on the screen.

Because of this essential property of the invention, basically any area that is smaller than the half-space in front of the backlighting can inherently be considered as the restricted angular area; however, what is preferably meant here is, for example, an angular range of +/-20 or 30 degrees horizontally and/or vertically or as a cone around the surface normal or a selectable directional vector on the background lighting; small amounts of light from less than 1% to 5% maximum brightness can be ignored when defining the restricted angle range.

Furthermore, both the background lighting and the lighting means can be switched on for an operating mode B3. Here, too, the aforementioned adjustment supports the improvement in image quality, at least for the viewer to whom the reference directions point.

Of course, the aforementioned adjustment only applies to a specific viewer position or within a certain tolerance around such a selected viewer position.

• - einen flächigen Strahler, der als zweiter Lichtleiter mit zweiten Leuchtmitteln ausgebildet ist,
• - eine in Betrachtungsrichtung eines Betrachters vor dem flächigen Strahler gelegene optische Komponente zur Lichtrichtungsbeschränkung, welche entlang der besagten Vorzugsrichtung in verschiedene Bereiche eingeteilt ist, wobei für jeden Bereich eine eigene Referenzrichtung wählbar ist, wobei ferner alle Referenzrichtungen paarweise verschieden sind und bis auf eine Toleranz von maximal 10 Grad in Richtung eines Betrachters weisen, und wobei in jedem solchen Bereich das -in der Regel einzige globale- Transmissionsmaximum für das die optische Komponente durchdringende Licht jeweils in der entsprechenden Referenzrichtung liegt (die Transmission kann z.B. in einer die Vorzugsrichtung beinhaltenden Ebene senkrecht zur optischen Komponente gemessen werden).

Furthermore, the backlight includes at least

• - a flat radiator, which is designed as a second light guide with second light sources,
• - an optical component located in front of the planar radiator in the viewing direction of an observer to limit the light direction, which is divided into different areas along said preferred direction, with a separate reference direction being selectable for each area, with all reference directions also being different in pairs and with a tolerance of a maximum of 10 degrees in the direction of an observer, and where in each such area the -usually only global- transmission maximum for the light penetrating the optical component lies in the corresponding reference direction (the transmission can, for example, be in a plane containing the preferred direction perpendicular to the optical component are measured).

The optical component for restricting the direction of light includes a lamellar filter. This is preferably designed in such a way that at least some of the lamellae, but usually all of them, are inclined in such a way that the light penetrating the lamellar structure is transmitted in the above-described reference directions with a transmission maximum. Thus, the blades are all or in groups inclined at different angles, depending on the division of said areas and the choice of reference directions.

Such a lamellar filter and its production are, for example, in U.S. 8,395,726 B2 described.
The louvers are also tilted at an angle to the left or right edge of the backlight to avoid moiré or other visible interference effects with the screen and/or other components in the assembly.

In a further configuration, the lighting device comprises, in the viewing direction of an observer, in front of the flat radiator (which preferably comprises a second light guide with second light sources), a diffuser and/or at least one prismatic grid, which at least partially focuses or deflects the light emitted by its large surfaces.

For all the configurations described above, said preferred direction can be perpendicular to an edge of the light guide, preferably perpendicular to an edge which, from the point of view of an observer, corresponds to a narrow side on the left or right.

Furthermore, depending on the application, it is helpful if all reference directions mentioned point in the direction of an observer with a tolerance of only a maximum of 8 degrees, preferably even only 5 degrees.

In the event that in operating mode B2 with a camera which is aligned perpendicularly to the lighting arrangement at a distance of approximately three times the diagonal length of the light guide in front of its center, the measured luminance distribution over the entire light-emitting surface of the lighting device can advantageously have a minimum to maximum ratio of at least 0.3, preferably at least 0.4.
Further measurement regulations are conceivable analogous to the "Uniformity Measurement Standard for Displays V1.3" of the "German Automotive OEM Work Group Displays".

It is also advantageous for all of the aforementioned configurations of the lighting device if they also include a transmissive screen, preferably in the form of an LCD panel, which is arranged in front of the lighting device in the viewing direction of an observer and which, due to the lighting device, can be used in at least two operating modes B1 for a free view mode and B2 can be operated for a limited view mode.

The light guide, and if present also a second light guide, preferably consists of a transparent, thermoplastic or thermoelastic polymer, e.g. plastic, or of glass. For example, the light guide or its substrate can comprise at least 40 percent by weight polymethyl methacrylate, preferably at least 60 percent by weight polymethyl methacrylate, based on its weight. Alternatively, it can be polycarbonate (PC), for example.

The structure of the decoupling elements can be specified so that the effect of each decoupling element is at least approximately known and properties of the light guide or the light emerging from the light guide can be defined in a targeted manner by a definable distribution of the decoupling elements. The required properties for the decoupling elements that are essential for the invention in terms of their number per unit area, their shape and extent in three dimensions and their distribution on at least one of the large areas and / or within the volume of the light guide can be determined, for example, with optics simulation software such as "LightTools" from Synopsis or other providers and then physically implemented accordingly. It is possible that decoupling elements are attached to both large areas and optionally in the volume.
The decoupling elements for decoupling light on at least one of the large surfaces of the light guide preferably consist of microlenses and/or microprisms and/or diffractive structures and/or three-dimensional structural elements and/or scattering elements with a maximum expansion in their largest dimension that is less than 100 micrometers, preferably less than 50 microns. In the case of diffractive structures, it can be a hologram or a grating/diffraction grating, for example.

However, the outcoupling elements themselves can also have the external form of microlenses, microprisms, scattering elements and/or diffractive structures. They can then be designed in particular as cavities, which are then formed in the volume of the light guide. The cavities can be empty of air, but are preferably filled with a gaseous, liquid or solid material. The material has a refractive index which differs from that of the material used for the light guide; it is preferably lower. By filling with material and by the choice of material, you can influence the light conduction or decoupling. Alternatively or additionally, the haze value of the material also preferably deviates from that of the material used for the light guide, and is preferably higher. Advantages of these configurations are higher efficiency in light extraction.

Accordingly, the background lighting can basically be constructed like an LED backlight, for example as a so-called direct-lit LED backlight, edge LED backlight, OLED or as another surface emitter,

Means for reducing or controlling reflections, for example an anti-reflection coating, can be arranged on the upper side of the screen and/or on at least one of the large areas of the light guide as well as on at least one other optical component, if present.

A further useful embodiment of the lighting device extended by a screen is that in the viewing direction in front of the screen there is another light guide (eg made of glass or plastic) with means for coupling out light, which can be fed with light from the side of lamps. The means used here for decoupling are, for example, those described above, or those known in the prior art, such as nanoparticles such as titanium dioxide, barium sulfate, etc. in suitable sizes and quantities - such as in the WO 2015/121398 A1 and the WO 2017/089482 A1 described - which are homogeneously distributed in the volume of the light guide. With this configuration, any residual light that may still be unintentionally present in the B2 operating mode can be superimposed or outshined in the angular areas that are actually protected from view in such a way that contrast is no longer perceptible and thus no image perception from the non-released angles is possible.
The corresponding illuminants for the additional light guide are designed to emit colored or white light. The light sources can emit light in a color that does or does not appear in the image displayed by the transmissive screen.

The lighting device according to the invention with a screen is used particularly advantageously in a vehicle for selectively displaying image content only for the passenger in operating mode B2 or simultaneously for the driver and the passenger in operating mode B1. The former is useful, for example, when the passenger is watching entertainment content that could distract the driver.

A lighting device according to the invention with a screen as well as an image display device according to the invention can be used to enter or display confidential data, for example PIN numbers, e-mails, SMS or passwords, at ATMs, payment terminals or mobile devices.

In all of the aforementioned configurations, the lighting means mentioned can be LEDs or LED lines or laser diodes. Other variants are conceivable and are within the scope of the invention.

In principle, the performance of the invention is retained if the parameters described above are varied within certain limits.

It goes without saying that the features mentioned above and those still to be explained below can be used not only in the specified combinations, but also in other combinations or on their own, without departing from the scope of the present invention.

character list

• 1 eine Prinzipskizze zur Auskopplung von Licht, das seitlich in einen Lichtleiter eingekoppelt wird, aus der unteren Großfläche des Lichtleiters, auf welcher sich die Auskoppelemente befinden, wobei das Licht an der oberen Großfläche den Lichtleiter verlässt,
• 2 eine Prinzipskizze zur Auskopplung von Licht, das seitlich in einen Lichtleiter eingekoppelt wird, aus der oberen Großfläche des Lichtleiters, auf welcher sich die Auskoppelemente befinden, wobei das Licht an der oberen Großfläche den Lichtleiter verlässt,
• 3 eine Prinzipskizze einer Beleuchtungseinrichtung in einer ersten Ausgestaltung im Zusammenspiel mit einem Bildschirm im Modus B1 für einen freien Sichtmodus,
• 4 eine Prinzipskizze einer Beleuchtungseinrichtung in einer ersten Ausgestaltung im Zusammenspiel mit einem Bildschirm im Modus B2 für einen eingeschränkten Sichtmodus,
• 5 eine Prinzipskizze zu einer in einer Beleuchtungseinrichtung einsetzbaren Hintergrundbeleuchtung,
• 6 ein beispielhaftes Diagramm für mögliche normierte Leuchtdichteverteilung in verschiedenen Bereichen einer Hintergrundbeleuchtung, sowie
• 7 eine Prinzipskizze zur Erläuterung des beispielhaften Zusammenhangs zwischen Bereichen einer Hintergrundbeleuchtung, einer Vorzugsrichtung und Referenzrichtungen.

The invention is explained in more detail below with reference to drawings, which also show features that are essential to the invention. It shows

• 1 a schematic diagram for the decoupling of light, which is coupled into a light guide from the side, from the lower large surface of the light guide, on which the decoupling elements are located, with the light exiting the light guide on the upper large surface,
• 2 a schematic diagram for the decoupling of light, which is coupled into a light guide from the side, from the upper large surface of the light guide, on which the decoupling elements are located, with the light exiting the light guide on the upper large surface,
• 3 a schematic diagram of a lighting device in a first embodiment in combination with a screen in B1 mode for a clear view mode,
• 4 a schematic diagram of a lighting device in a first embodiment in combination with a screen in mode B2 for a limited view mode,
• 5 a basic sketch of a backlight that can be used in a lighting device,
• 6 an example diagram for possible normalized luminance distribution in different areas of a backlight, as well as
• 7 a schematic diagram to explain the exemplary relationship between areas of a backlight, a preferred direction and reference directions.

The drawings are not true to scale and merely provide schematic representations.

Detailed description of the drawings

In 1 1 is a schematic diagram for decoupling light, which is coupled into a light guide 3 from the side of lamps 4, on the lower large surface of the light guide 3, on which the decoupling elements 6 are located. However, the decoupled light leaves the light guide 3 from the upper large area. In the horizontal direction, the light is decoupled from the upper large surface of the light guide 3 at a wide angle (greater than 60°). The location of the decoupling elements 6 is indicated by the number 6, but the actual decoupling elements 6 are not shown here because they have to be microscopically small. Light from the lighting means 4, for example from LEDs, is thus coupled into the light guide 3 from the side. Due to total reflection, rays of the coupled light (rays drawn in bold) are thrown back into the light guide 3 on the outer wall until they finally (possibly repeatedly) hit a decoupling element 6 for the desired decoupling. The decoupling is stylized by the thin rays. The representation in 1 is strongly stylized for better recognition; in reality, a very large number of beam paths are implemented in the light guide 3 . In addition, light refractions at refractive index transition surfaces are not taken into account.

2 shows a schematic diagram for decoupling light, which is coupled into a light guide 3 from the side of lamps 4, from the upper large surface of the light guide 3, on which the decoupling elements 6 are located. The light also leaves the light guide 3 here through the upper large area. The statements on apply here mutatis mutandis 1 .

The only technical difference here is the position and, if necessary, the design of the decoupling elements 6, which are now on the upper side of the light guide 3 and thus decouple the light directly upwards, without it having to pass across the same again to leave the light guide 3. as opposed to in 1 shown.

For everyone in the 3 , 4 and 5 In the configurations of the lighting device 1a described in more detail below, a transmissive screen 1 is arranged in front of a viewer 5 in the viewing direction, preferably in the form of an LCD panel, which, due to the lighting device 1a, is operated in at least two operating modes B1 for a clear view mode and B2 for a restricted view mode can be.

Furthermore, the 3 is a schematic diagram of the lighting device in a first embodiment in conjunction with a screen in mode B1 for a free view mode, while the 4 correspondingly shows the same configuration in combination with a screen in mode B2 for a limited view mode.

• - eine flächenartig ausgedehnte Hintergrundbeleuchtung 2, die Licht in einen eingeschränkten Winkelbereich abstrahlt, wobei die Hintergrundbeleuchtung 2 entlang einer Vorzugsrichtung in verschiedene Bereiche (beispielhaft A1..A7 in 4) eingeteilt ist, und für jeden Bereich eine eigene Referenzrichtung (fette Pfeile in 4) wählbar ist, wobei alle Referenzrichtungen paarweise verschieden sind und bis auf eine Toleranz von maximal 10 Grad in Richtung eines Betrachters 5 weisen, und wobei die Hintergrundbeleuchtung 2 in jedem solchen Bereich A1..A7 für das dort abgestrahlte Licht jeweils in der entsprechenden Referenzrichtung das - bevorzugt einzige globale- Leuchtdichtemaximum aufweist, (die Leuchtdichteverteilung kann z.B. in einer die Vorzugsrichtung beinhaltenden Ebene senkrecht zur Hintergrundbeleuchtung 2 gemessen werden)
• - einen in Betrachtungsrichtung vor der Hintergrundbeleuchtung 2 gelegenen, plattenförmigen Lichtleiter 3, welcher auf mindestens einer der Großflächen und / oder innerhalb seines Volumens Auskoppelelemente 6 aufweist, wobei der Lichtleiter 3 für das von der Hintergrundbeleuchtung 2 ausgehende Licht zu mindestens 50% transparent ist,
• - seitlich an Schmalseiten des Lichtleiters 3 angeordnete Leuchtmittel 4,
• - wobei in der Betriebsart B2 (siehe 4) die Hintergrundbeleuchtung 2 ein- und die Leuchtmittel 4 ausgeschaltet sind, und wobei in der Betriebsart B1 (siehe 3) mindestens die Leuchtmittel 4 eingeschaltet sind.

In this case, an illumination device 1a for a screen 1, which can be operated in at least two operating modes B1 for a clear view mode and B2 for a restricted view mode,

• - A flat, extended backlight 2, which emits light in a limited angular range, with the backlight 2 along a preferred direction in different areas (example A1..A7 in 4 ) and each area has its own reference direction (bold arrows in 4 ). - preferably has a single global luminance maximum (the luminance distribution can be measured, for example, in a plane containing the preferred direction perpendicular to the background lighting 2)
• - a plate-shaped light guide 3 located in front of the backlight 2 in the viewing direction, which has decoupling elements 6 on at least one of the large areas and/or within its volume, the light guide 3 being at least 50% transparent for the light emanating from the backlight 2,
• - lamps 4 arranged laterally on the narrow sides of the light guide 3,
• - where in operating mode B2 (see 4 ) the background lighting 2 is switched on and the lamps 4 are switched off, and in the operating mode B1 (see 3 ) at least the lamps 4 are switched on.

The dashed arrows in 4 are intended to indicate that in each area A1..A7 outside of the reference directions, less light is emitted than in the actual reference direction. while here in 4 only seven such areas A1 .. A7 are shown for reasons of clarity, depending on the design, a large number of such areas A1 .

In operating mode B2, the angle-dependent luminance distribution is thus adapted to the viewer 5 depending on his position in front of the display, so that he—in conjunction with a screen 1—sees a more homogeneous image of higher quality than if this adaptation does not take place. At the same time, switching to operating mode B1 ensures that, if necessary, several viewers can also perceive an image displayed on screen 1.

Because of this essential property of the invention, basically any area that is smaller than the half-space in front of the backlighting can inherently be considered as the restricted angular area; however, what is preferably meant here is, for example, an angular range of +/-20 or 30 degrees horizontally and/or vertically or as a cone around the surface normal or a selectable directional vector on the background lighting; small amounts of light from less than 1% to 5% maximum brightness can be ignored when defining the restricted angle range.

• - einen flächigen Strahler, umfassend einen zweiten Lichtleiter 2a mit zweiten Leuchtmitteln 2b,
• - eine in Betrachtungsrichtung eines Betrachters 5 vor dem flächigen Strahler (d.h. dem Lichtleiter 2a) gelegene optische Komponente 2e zur Lichtrichtungsbeschränkung, welche entlang der besagten Vorzugsrichtung (welcher hier der horizontalen Richtung entspricht) in verschiedene Bereiche A1, A2, A3, ... eingeteilt ist, wobei für jeden Bereich A1, A2, A3, ... eine eigene Referenzrichtung (dargestellt durch die fetten Pfeile) wählbar ist, wobei ferner alle Referenzrichtungen paarweise verschieden sind und bis auf eine Toleranz von maximal 10 Grad in Richtung eines Betrachters 5 weisen, und wobei in jedem solchen Bereich das -in der Regel einzige globale- Transmissionsmaximum für das die optische Komponente durchdringende Licht jeweils in der entsprechenden Referenzrichtung liegt (die Transmission kann z.B. in einer die Vorzugsrichtung beinhaltenden Ebene senkrecht zur optischen Komponente gemessen werden).

Furthermore, the 5 a basic sketch of a backlight 2 that can be used in a lighting device 1a. Advantageously, such an exemplary backlight comprises 2 at least

• - a flat radiator, comprising a second light guide 2a with second light sources 2b,
• - An optical component 2e located in front of the flat radiator (ie the light guide 2a) in the viewing direction of an observer 5 for limiting the light direction, which is divided into different areas A1, A2, A3, ... along the said preferred direction (which corresponds here to the horizontal direction). is, with a separate reference direction (represented by the bold arrows) being selectable for each area A1, A2, A3, , and in each such area the -usually single global- transmission maximum for the light penetrating the optical component lies in the corresponding reference direction (the transmission can be measured, for example, in a plane containing the preferred direction perpendicular to the optical component).

For reasons of clarity, in 5 only five areas A1..A5 drawn, although according to the circumstances 5 would be ten areas, and in reality there are usually significantly more.

In the viewing direction of a viewer 5 are in the embodiment 5 in front of the flat radiator (here the second light guide 2a with second light sources 2b) a diffuser 2c and at least one prism grid 3d, which transmits the light emerging from the flat radiator (ie the second light guide 2a) over one of its large surfaces - here the upper one - at least partially focused or distracted.

Furthermore, the optical component 2e for restricting the light direction includes a lamellar filter, as in FIG 5 indicated in the sectional view. This is preferably designed in such a way that at least some of the slats, but usually all of them, are inclined in such a way that the light penetrating the slat structure in the above-described reference directions, which are chosen depending on the area A1, A2, A3, ..., with a Transmission maximum is transmitted. Thus, the slats are all inclined at the same time, or at least in groups of slats, at different angles, depending on the division of said areas A1, A2, A3, .... and the choice of reference directions.

Such a lamellar filter and its production are, for example, in U.S. 8,395,726 B2 or in the WO 2018/225714 A1 described.

For this shows 6 an exemplary diagram for a possible standardized luminance distribution in different areas A2, A3, A4 and A5 of a backlight 2 according to FIG 5 .

The luminance distribution was measured here in the preferred direction—that is, the horizontal direction—perpendicular to the background lighting 2 over various angles.

The point-point-dash curve in 6 corresponds approximately to the transmission behavior of the optical component 2e 5 in the area A5, therefore in summary the radiation behavior of the backlight 2 in the area A5. Analogously, the dot-dash curve corresponds to area A4, the dashed curve to area A3 and the solid curve to area A2.

It can also be seen that all curves each have a global maximum.

The slats are also inclined at an angle to the left or right edge of the backlight 2 to avoid moire effects or other visible interference effects with the screen 1 and/or other components in the structure.

Furthermore, the 7 a schematic diagram to explain the exemplary relationship between areas A1 to A4 of a backlight 2, a preferred direction V and reference directions R1 to R4.

Here said preferred direction V is perpendicular to the left and right edges of the background lighting 2, which correspond to a narrow side on the left or right from the point of view of an observer 5. Furthermore, the preferential direction is arranged in the center of the backlight 2 in the vertical direction. Perpendicular to the preferred direction V, the backlighting is divided into (only four here as an example) areas A1 to A4. Based on this, the respective reference directions R1 to R4 now point to an observer 5, indicated stylized by a point.

In the drawing, the reference directions R1 to R4 lie in the plane indicated by the dashed line, which is perpendicular to the backlight 2 and includes the preferred direction V and the center of the surface of the backlight 2 .

An angle α, which spans between the preferred direction V and a direction to be measured, for example a reference direction R4, is then preferably used for the measurements of luminance distributions over angles.

The reference directions R1 to R4 can be offset in parallel for all points of an area A1, A2, . . . apply. Alternatively, each point on the surface of an area A1, A2, .

The decoupling elements 6 for decoupling light on at least one of the large surfaces of the light guide 3 (or 2a or 3a) preferably consist of microlenses and/or microprisms and/or diffractive structures and/or three-dimensional structural elements and/or scattering elements with a maximum extent in their largest dimension that is less than 100 microns, preferably less than 50 microns. In the case of diffractive structures, it can be a hologram or a grating/diffraction grating, for example.

In all of the aforementioned configurations, said lighting means 4 or 2b or 3b can be LEDs or LED lines or laser diodes. Other variants are conceivable and are within the scope of the invention.

The lighting device according to the invention described above and the screen that can be implemented with it solve the task: Solutions that can be implemented easily in practice are permitted in order to implement a reliable display of information through an optionally restricted viewing angle, while in another operating mode a free view with unrestricted viewing angle is possible. The invention can be implemented inexpensively with simple means. The native resolution of the image display device used can be used in both operating modes. In addition, only a small light loss is introduced by the solution and the limited viewing angle achieves a comprehensive privacy protection effect with the highest possible image quality.

The invention described above can be used to advantage wherever confidential data is displayed and/or entered, such as when entering a PIN or displaying data at ATMs or payment terminals or for entering passwords or reading emails on mobile devices. As described above, the invention can also be used in passenger cars.

Claims (4)

Lighting device (1a) for a screen (1), which can be operated in at least two operating modes B1 for an unobstructed view mode and B2 for a restricted view mode, comprising - a flat, extended backlight (2), in turn comprising - a flat radiator, which as second light guide (2a) is designed with second lighting means (2b), - an optical component (2e) located in front of the planar radiator in the viewing direction of an observer (5) for restricting the light direction, designed as a lamellar filter, the optical component (2e) along said preferred direction is divided into different areas (A1, A2, ...), with a separate reference direction being selectable for each area (A1, A2, ...), with all reference directions also being different in pairs and with a maximum tolerance of 10 degrees pointing towards a viewer (5), and in each such area (A1, A2, ...) the transmission maximum for the light penetrating the optical component (2e) lies in the corresponding reference direction, with the lamellae of the optical component (2e) designed as a lamellar filter being inclined at an angle to the left or right edge of the background lighting (2), whereby moiré effects or other visible overlay effects with the screen (1) and/or other components in the lighting device (1a) are avoided, - so that the areally extended background lighting (2) emits light in a limited angular range, with the background lighting (2) being divided into different areas along a preferred direction, and a separate reference direction being selectable for each area (A1, A2, ...), with all reference directions being different in pairs and point in the direction of a viewer (5) with a maximum tolerance of 10 degrees, and wherein the background lighting (2) in each such area (A1, A2, ...) for the light emitted there is in the corresponding reference direction luminance maximum, - a plate-shaped light guide (3) located in front of the background lighting (2) in the viewing direction, which has decoupling elements (6) on at least one of the large areas and/or within its volume, the light guide (3) for that of the background lighting (2) outgoing light is at least 50% transparent - arranged laterally on the narrow sides of the light guide (3). e lamps (4), - the backlighting (2) being switched on and the lamps (4) being switched off in operating mode B2, and at least the lamps (4) being switched on in operating mode B1. Lighting device (1a) according to one of the preceding claims, further comprising a diffuser (2c) and/or at least one prism grid (2d) in front of the flat radiator in the viewing direction of an observer (5), which the light exiting from the flat radiator via one of its large surfaces at least partially focuses or distracts. Lighting device (1a) according to one of the preceding claims, further comprising a transmissive screen (1) arranged in front of the lighting device (1a) in the viewing direction of an observer (5), preferably in the form of an LCD panel, which, due to the lighting device (1a), has at least two operating modes B1 for a clear view mode and B2 for a restricted view mode can be operated. Use of a lighting device (1a) according to one of the aforementioned Claims 1 - 3 in a vehicle for the optional display of image content only for the front passenger in mode B2 and simultaneously for the driver and the front passenger in mode B1.

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