EP3291214B1 - Display device with dynamic adaptation - Google Patents

Description

The invention relates to a display device for writing and images and a method for operating such a display device.

In recent years, screens or displays have been developed which are at least partially transparent, i. H. Light falling on the display from the back can at least partially pass through it, so that a user or viewer of the display not only sees the information shown on the display, in particular texts, characters or images, but also the background behind the display .

This is a desired or advantageous effect for various reasons. On the one hand, since transmission takes place in all directions, this means that the display can be read from both sides. Furthermore, by superimposing display images on the technical background, effects can also be achieved that are impossible with a non-transparent display, at least not without the help of an additional (video) camera. This is, for example, the superimposition of context information on people, items or objects visible in the background, which is also known as "augmented reality".

Such displays also open up the possibility of using them as head-up displays, in which information that is important for the viewer, for which it is advantageous if it is always in the field of vision and available, is shown. Head-up displays are originally known from military aircraft, but have recently also found their way into civilian aircraft and vehicles. A realization using a (semi-)transparent screen/display would be much simpler, cheaper and more space-saving than the previously known head-up displays.

The last advantage of transparent displays, which should be mentioned here, is the aesthetic effect that seemingly free-floating writing or image information creates for the viewer.

However, a major problem with such transparent displays is readability in front of the respective background. If this is to be guaranteed in any case, precautions must be taken in addition to the actual display, either to hide the background if necessary, or to adjust the brightness or the To increase the contrast of the display so that the information to be displayed is still recognizable.

Previously known techniques for transparent displays initially include TFT displays, which, however, only achieve a transmission of around 10%. This means that 90% of the light hitting the back does not reach the viewer. Furthermore, high-resolution, self-illuminating oLED displays are currently being developed that achieve transmission levels of 40-50%. However, the highest degrees of transmission that have been possible to date are obtained with TEL (transparent electroluminescence) displays, which have degrees of transmission of up to 80%.

Various proposals for solving the problem addressed are known in the prior art. This is what the European patent application specification discloses EP 3015915 A1 a display device provided with an energy-saving backlighting system, intended for mounting on a window pane, and in which light incident on the display from behind, if any, is shared with the display of the image. This allows the backlight of the display can be operated with low power, so that advantageously energy can be saved. Essential for this is the attachment of a so-called smart window, which represents a pane with variable transparency or transmission, via which the rear side of the display can be used to control the external light that is let through.

Furthermore, the patent application describes U.S. 2010/0177025 A1 an information display device having a light source, and a light guide plate by means of which light from a light source is uniformly dispersed for the purpose of backlighting the display in front of this plate. The light originating from the internal light source is introduced into the light guide plate from one end, while light originating from the outside is introduced from the other end. The light guide plate contains a light control mirror that can be switched electrically and can either transmit or reflect light. This allows the light intensity used for backlighting to be controlled.

The disadvantages of the aforementioned solution are that the readability, i.e. essentially contrast and brightness, of the display as a whole must be set by the user or viewer, and they do not automatically adapt to the lighting conditions in front of or behind the display.

The object of the present invention is therefore to find a display device and a method for operating the same that ensure automatic, rapid and precise adaptation of the readability to changing lighting conditions both on the viewer side and in the background.

The International Publication WO 2016/122571 A1 proposes a display device comprising a close-up display with which a virtual image can be displayed in front of a real background.

the U.S. Patent 5,773,845 discloses a liquid crystal display device having a plurality of redundant lines formed on a substrate and a signal line covering them, thereby reducing an aperture ratio. In some of the embodiments presented there, the redundancy lines are higher than they are wide.

As a solution, the present invention proposes a display device according to claim 1.

An essential element of the display device is the pane, which can be regulated in terms of its transparency and transmissivity, the two light sensors and the control unit, which uses the light intensity values measured by the light sensors and the desired brightness and contrast values set by the viewer to determine the transparency and transmissivity of the pane as well as the brightness and contrast of the Displays are regulated in such a way that an average image brightness as the sum of a light component generated by the display panel and a light component transmitted through the pane and a contrast between the displayed information and the background behind the pane corresponds to a preset value or a value that can be selected by the viewer, which means that the displayed information can be read information should be guaranteed.

The set transparency is dependent on the one hand on the measured brightness behind the pane, referred to here as background brightness, and on the brightness prevailing on the observer's side, referred to here as ambient brightness. Furthermore, the brightness and contrast values set by the viewer are decisive. In general, the transparency decreases with the background brightness and the desired contrast, but increases with the ambient brightness and the desired (image) brightness.

The present invention proposes a proportional, ie linear, quadratic or logarithmic dependency. The latter has the advantage of being adapted to the natural adaptation of the human eye. For the subjective perception of brightness, a change in the objective light intensity by a certain factor over several orders of magnitude of the ambient brightness is only associated with a gradual change in the subjective brightness. This would be taken into account by a logarithmic dependency of the transparency.

Attachment to a pane of a room and/or a vehicle is intended as a reference use of the display device according to the present invention, so that a clear distinction can be made between light conditions in front of and behind the pane, i.e. inside and outside. The possible lighting conditions combinations and the transparency or contrast settings to be carried out by the control unit according to the method according to the invention are to be described here on the basis of a subdivision into three rough stages.

berechnet, wobei $T_{\mathit{abs}}^{\mathit{max}}$

und $T_{\mathit{abs}}^{\mathit{min}}$

die maximale respektive minimale absolute Transmissivität bezeichnen. Die absolute Transmissivität gibt den absoluten Anteil des transmittierten Lichtes an, üblicherweise bezogen auf das Spektrum der Sonne.A distinction must first be made as to whether visibility of the background is desired or not. In the latter case, the pane would simply always be switched to opaque/reflective, with the possible exception of the case where the outside brightness is very low. Contrast and brightness could then be adjusted solely according to interior/ambient brightness and user preferences. An exception to this is the case where the pane can be switched/controlled not only in its transparency but also in its transmissivity. 0% (relative) transparency and 100% (relative) transmissivity mean that although there is complete but also completely diffuse light transmission, so that only an even brightness can be seen, but no clear image can be seen. Intermediate stages when varying these two parameters, which are regarded as fundamentally independent, result from interpolation. Relative transparency or transmissivity here means the transparency or transmissivity relative to the maximum possible values of the respective pane material. Using the example of the transmissivity T, this means that the relative transmissivity T _rel can be calculated from the absolute T _abs according to the formula $$T_{\mathit{rel}}\left[\mathit{in}\%\right]=100\frac{T_{\mathit{Section}}-T_{\mathit{Section}}^{\mathit{at\; least}}}{T_{\mathit{Section}}^{\mathit{Max}}-T_{\mathit{Section}}^{\mathit{at\; least}}}$$

calculated where $T_{\mathit{Section}}^{\mathit{Max}}$

and $T_{\mathit{Section}}^{\mathit{at\; least}}$

designate the maximum and minimum absolute transmissivity. The absolute transmittance indicates the absolute proportion of the transmitted light, usually related to the spectrum of the sun.

Two electrically switchable pane materials known from the prior art will serve as an example and illustration of this. On the one hand, so-called pdLC (polymer dispersed liquid crystal) discs are known, the absolute transparency of which can be switched from almost 0% to about 85% by applying a voltage. A voltage of about 60-120VAC is required to achieve maximum transparency and the switching process takes about 100 ms.

The situation is different with the so-called SPD (suspended particle device) disks. In this case, suspended particles are aligned parallel to one another by an applied voltage, thus changing the transmission and transparency properties. Without an applied voltage, the particles are randomly distributed and thereby absorb incident light. From a voltage of approx. 60VAC, all particles are aligned and the relative transmission reaches 100%, but with a low transparency value. With voltage values in between, relative transmission values between 0 and 100% can be achieved.

Ideal would be pane materials in which both transparency and transmission can be controlled independently by means. Alternatively, the present invention proposes to achieve this by combining two disks of different types, such as a pdLC and SPD disk. It is also conceivable to integrate layers of both materials into one pane, ie for example a pdLC layer between a first and a second electrode and an SPD layer between the second and a third electrode. By means of the two voltages between the first and second as well as the second and third electrode, transmission and transmission could then be controlled independently of one another within certain limits.

If the viewer looks from a bright interior to a bright exterior, the pane behind the display is switched to almost no transparency by the control unit, and a high brightness and high contrast of the display is selected, which corresponds to the brightness and contrast settings desired by the viewer scale. This means that the control unit assumes that high or very high contrast and brightness are necessary for clear readability, but this can be ignored by the viewer through his settings.

We will now describe the regulation of a display device according to the invention in nine different situations, assuming that a background visibility is desired since, as explained above, this is the more essential and interesting case.

If the viewer's gaze moves from a bright interior to a moderately bright exterior, the pane is switched to semi-transparent, and the brightness and contrast of the display must also be set high with regard to the value selected by the viewer.

If the outside space or the background is only moderately bright, a semi-transparent to largely transparent setting should be selected. The basic brightness of the display should continue to be high, the contrast can be selected from high to normal, since the background brightness washes out less than in the first case.

If the light intensity on the viewer's side is high but low behind the display, the pane can be switched to full transparency, the brightness remains high, but a high contrast setting is not absolutely necessary, since there is hardly any additional, den Contrast-reducing backlighting takes place.

If the viewer's gaze goes through the display from a moderately bright interior to a bright exterior, the pane should be switched to semi-transparent and medium brightness, but high contrast selected.

If the view goes from a moderately bright interior to a moderately bright exterior, the pane should also be semi-transparent. Contrast and brightness should then both be set to medium high relative to the desired value selected by the viewer.

If the interior is moderately bright, but the exterior behind the display device is dark, the pane can be set to be completely transparent, the brightness setting of the display should be medium/normal and the contrast too.

If the interior is dark but the exterior is bright, the pane should be set to almost opaque and the brightness of the display should be selected rather low, but the contrast should be normal or low. However, if the outside brightness is only moderate, a semi-transparent setting for the pane can be selected, but the control unit would set the brightness and contrast as in the previous case. A dark interior and a dark exterior are considered as the last case. In this case, the pane is or can be completely transparent in order to ensure that no light sources are overlooked. Brightness and contrast should be chosen rather low.

The above control behavior of the control unit of the display device according to the invention applies in the event that an essentially clear view of the background is desired, so that the information displayed is visible together with the objects located in the background. A pane with switchable transparency is required for this. However, if the light from the back is only to be used for additional backlighting, a diffuse pane with switchable transmission is required. However, the control behavior described above could remain largely unchanged.

The advantages of the display device according to the invention are, on the one hand, the automatic and rapid adaptation of the readability to the lighting conditions and the wishes of the viewer. It is essential here that this is able to react much more quickly than manual readjustment by an observer and is obviously also much more comfortable. In addition, the IR radiation can be reduced as required, which means that excessive heating of the interior can be avoided.

Equipping the display device with a pane that can be switched in terms of its transparency and transmission, which can also be a window pane, results in a versatile usability of the display device according to the invention. On the one hand it is possible to use it as a simple window with complete transparency switching and the display switched off. Furthermore, also when the display is switched off or if no information is displayed on it, the display device according to the invention represents a window whose permeability can be switched, so that the heating of a room or vehicle can be reduced in strong sunlight, for example, by relative transparency is reduced to a value below 100%. On the one hand, this benefits the comfort of the people in the room or vehicle, but at the same time it also has the important technical advantage of reducing the thermal load on devices, including the display device according to the invention itself, which reduces their service life and MTBF (mean time between failures). advantageously increased. If it is possible for the pane to be completely opaque or impermeable, a room can be sealed off from light, for example as a replacement for roller shutters or window shutters. The diffusely transmitting panes, in which the degree of transmission can be switched, allow an opaque closure that ensures privacy and in which the incidence of light can be regulated.

Further embodiments, which can be implemented individually or in combination, unless they are obviously mutually exclusive, are to be explained below.

Ideally, the pane used in the display device according to the invention would be controllable from about 0-100% both in its absolute transmission and in its absolute transparency. However, no realization of such a pane is known in the prior art. With the SPD panes mentioned above, it is mainly the transmission that can be switched, but the transparency also changes in such a way that diffuse transmission takes place with relative transmissivity of 0 and 100%, i.e. the pane is opaque, but with transmission values in between it is certain transparency is given, so the pane is at least transparent to a certain degree. The pdLC discs that are also known can be switched from opaque to transparent by applying a voltage.

Since they do not simply absorb incident light when they are opaque (like e.g. SPD panes), but mostly reflects it back, albeit diffusively, they are suitable as electrically controllable transflectors for the backlighting of TFT displays. The combination of both pane types, i.e. placing one on top of the other, results in a pane which is controllable in both its transmissivity and transparency as claimed in claim 1, but at the cost of increased complexity, higher cost and lower absolute transmission and Transparency.

In a preferred embodiment, two discs of the same type (e.g. two SPD or two pdLC discs) are arranged on different sides of the display and, usually parallel to it and either spaced apart or attached directly to it, the present invention recommends a double-sided reading or viewable display panel to use. On the one hand, TFT displays can be used for this purpose. These usually consist of a large number of pixels arranged in a grid-like manner, each of which is made up of a red, blue and green liquid crystal cell (LCD) in the case of a color display. Each LCD cell is controlled by a thin-film transistor and switched to more or less translucent. The thin design of the transistors ensures transparency, although the maximum possible absolute transmittance is only around 50%. A TFT display does not have a preferred viewing direction, so it can naturally be read from both sides if there is appropriate backlighting.

The advantage of TFT displays is that they represent a very well mastered, mature technology and enable very high information densities of currently up to approx. 400ppi (pixels per inch, pixels per inch). For each pixel it is individually possible to determine the relative Change transparency from 0 to 100%. A TFT matrix would therefore also be suitable as a switchable disc, but would be significantly more complex to manufacture and control.

If very high absolute transmittance is desired and high information density is of secondary importance, an EL display that can be read from both sides is conceivable (EL = electroluminescence). It consists of a sandwich of two conductive layers which enclose a layer of electroluminescent material between them. If a current flows from one conductive layer to the other, the electroluminescent material in between lights up. If both conductive layers are made of a transparent material, the result is an EL display that can be read from both sides, also referred to as TEL for short, or transparent electroluminescent display. Transmission grades that can be achieved here are up to 80%.

However, the most brilliantly colored images with a resolution that corresponds to that of TFT displays can be achieved with so-called transparent oLED (organic LED) displays. They consist of pixels arranged in a grid or matrix-like manner, with each pixel being assigned at least one light-emitting diode for one of the three primary colors red, green and blue. These light-emitting diodes are made of an organic material, which gives the display its name, and is placed on a substrate that also contains the electrical leads to each pixel. If this substrate is transparent, an at least partially transparent display is obtained. Transmissivity or transparency of such an oLED display is reduced by the substrate and the control lines of the oLEDs present therein. In current models, it achieves between 40-50% of the light applied. The advantage of OLED displays is that they provide very even illumination and high brilliance can be achieved since the pixel is self-illuminating and does not depend on backlighting via a TFT display. Achievable pixel sizes are in the range of a few 10 microns, and the information density therefore roughly corresponds to that of a TFT display.

Instead of a transparent substrate, it would also be conceivable to use a non-transparent substrate with a bore introduced below the LED. In order to match the viewing angle on the rear side to that on the front side, it would be advantageous to position a diverging lens on the exit side of the bore. This basic structure can be used with oLEDs and pLEDs, but also with conventional inorganic LEDs mounted on a printed circuit board.

With TFT and oLED, and often also with EL displays, the pixels are generally arranged in a grid or matrix-like manner so that, with a sufficiently high resolution, general characters, texts or images can be displayed either statically or in motion. For special applications, however, it is also conceivable that the pixels are not arranged in a grid or matrix-like manner but in some other way. For example, ready-made lettering and/or characters can already be present on the display, so that the display's display capability is limited to a limited set of shapes or characters. This is e.g. This is the case, for example, with so-called 7-segment displays of digital clocks. In principle, such non-raster-like displays can be realized with all display types mentioned above. However, since this principle is only practical for low information densities, EL and LED displays are particularly suitable for this.

In a preferred embodiment, the present invention further proposes that the disk has sectors that can be switched separately. These sectors can be distributed over the surface of the pane in a matrix-like manner or also irregularly, but they should fill the pane surface completely. Each sector requires at least two electrical leads to control the transparency and transmissivity. According to the present invention, these should preferably be designed, at least for the sectors not adjoining the edge of the pane, in such a way that the cross section of the supply line has a significantly greater extent parallel to a main viewing direction than perpendicularly.

The pane of the present invention can be a separate element or a possibly existing electrically switchable window pane of a room and/or vehicle. In the first case, a display device that can be used in a mobile manner is obtained, while in the latter case, the additional provision of a pane that can be switched in terms of transparency and transmissivity is saved.

The light sensors and the control unit of the display device according to the invention can be designed in various ways. One possibility is that both functions are performed by physically separate facilities. This means that sensors are installed on the edge or at a point inside the surface of the pane and have signal lines via which the measured values are passed on in digital or analog form to the control unit, which is preferably located outside the pane surface, e.g. B. is arranged on one of the disc faces, or on a face of the display.

However, it is also possible and useful for the light sensors to be integrated into the control unit.

This minimizes the signal paths and all the electronics required for control can be attached to the pane and display in one installation step. In this case, the control unit would preferably be designed in such a way that a light sensor is mounted on two opposite end faces, which measures the light intensity coming from the respective hemisphere.

According to another preferred embodiment of the present invention, per viewable page and. There is at least one light sensor in the main viewing direction of the display and for each switchable sector of the pane. This is permanently assigned to the respective sector and the direction of view and forwards a measurement signal related to the sector to the associated control unit. This can be a central control unit for evaluating all light measurement signals of the display device according to the invention, or it can be a control unit that is also assigned to a sector and main viewing direction. In the latter case, several existing control units would have the advantage that sector-related control of the contrast and brightness setting of the display would also be easier to carry out if the switchable sectors on the pane are also assigned separately controllable sectors of the display.

In further embodiments, the pane is permanently connected to the display panel. This is preferably done using the optical contact bonding method, ie without adhesive and only by intermolecular forces between the contact surfaces of the slide and display, which are shaped in a complementary manner up to the highest tolerances. This further improves the achievable contrast.

In further embodiments, the display device according to the invention has backlighting sources that are attached to one or more end faces of the pane, for example to opposite end faces. This backlighting is particularly preferably a narrow LED light source (so-called "edge light LED").

The primary viewing direction(s) of a display should be understood herein as the relative directions from which a viewer sees the clearest, brightest, and highest contrast image. Displays are usually constructed in such a way that this direction is essentially perpendicular to the display plane. In the case of a display that can be read from both sides, the main viewing directions would usually be both possible surface perpendiculars.

In the method according to the invention for operating a display device presented here, a viewer first selects a main viewing direction, i.e. the viewer selects one of the maximum two possible sides that can be viewed as the 'active' side. This can be done either by actuating a corresponding control element or also automatically by evaluating images from an assigned camera and forwarding the corresponding information to the device according to the invention. Furthermore, the viewer selects a brightness and contrast setting that preferably applies to the entire display, i.e. does not have to be set individually for each sector.

The method according to the invention is characterized in that the light sensor first measures a local brightness and forwards it to the control unit, the control unit controls transparency and/or transmission for each sector in such a way that the intensity is below one permissible maximum value and furthermore the control unit adjusts the brightness and contrast of the display panel in such a way that, seen from the selected viewing direction, they correspond to a value dependent on the measured light intensity and the settings selected by the viewer, and then the information to be provided is shown on the display.

It is preferred here that these three steps are repeated at regular or irregular intervals, for example within the response time of the pane and/or the display. This should be done especially when the user changes the desired contrast and brightness settings.

The maximum value used to control the transmissivity and the transparency of the pane of the display device according to the invention results from the brightness and contrast settings desired by the user, which can be communicated to the control unit via corresponding input means. It is preferred that this maximum value increases in proportion to the brightness setting selected by the user and decreases in proportion to the contrast setting selected by the user. This ensures that the background brightness let through by the pane does not outshine the image to be displayed or that the contrast and the level desired by the user are not reduced.

Furthermore, it is preferred by the invention that, in the method according to the invention, the light sensors on the selected viewing direction at the front measure a sector-dependent ambient brightness and the light sensors at the rear in the viewing direction measure a sector-dependent background brightness and at least the sector-dependent brightness to regulate the transparency

Backlighting and for controlling the brightness and / or contrast setting at least the ambient brightness is used. The present invention proposes reducing the pane transparency as the background brightness increases, with the transparency being inversely proportional to the measured background brightness in one possible embodiment.

It is also proposed to increase the brightness and contrast settings as the ambient brightness increases, for example with a linear dependency.

Furthermore, it is preferred that the regulation and contrast and/or brightness setting of the display also takes place as a function of the sector. According to the invention, the pane of the display device according to the invention can be switched both in terms of transparency and transmissivity. The present invention proposes, if visibility of the background is not desired or necessary, to use the light incident on the display device from the rear side from the viewing direction for display backlighting.

A distinction must be made here between different display types. In any case, an LCD or TFT display is dependent on backlighting, usually by a light element from a fluorescent lamp or an LED bar. The energy consumption of this additional lighting could be reduced here by reducing the relative transparency of the pane to a small value and adjusting the transmissivity in such a way that the additional energy required for backlighting is minimized.

This should preferably be made dependent on the difference or the quotient of the background and the ambient brightness. If the difference/high quotient between the background and the environment (of the observer) is high, a low transmissivity should be selected. Correspond to if the two brightnesses are approximately the same, then a medium transmissivity is preferred. A high negative difference or a small quotient means that only little light is available for additional backlighting relative to the requirement. Thus, at least the essential image brightness is necessary due to the artificial backlighting by means of the lighting element. In order to improve its effectiveness, it is advantageous to switch the pane to non-transparent if this is equivalent to high reflectivity, as is the case with a pdLC pane, for example.

If a self-illuminating display is installed, for example an oLED, EL or LED display, backlighting is usually not required. A diffuse-transmitting pane can still be used in certain situations. For example, if text or other characters are to be displayed on a white background, this can be formed by the disc that is diffusely illuminated by the background brightness. The active generation of white light by the pixels of the display belonging to the image background is no longer necessary, which helps to save energy.

It is further proposed that, if transparent TFTs are used, the information display is switched over automatically from one main viewing direction to another on the basis of external parameters, such as the operating parameters of a vehicle carrying the display device. If the display device according to the invention is used, for example, as a display that can be viewed from inside and outside in a train window, the switchover from the main viewing direction "inside the vehicle" to "outside the vehicle" can take place on the basis of the speed and/or position of the train, with the information from the inside and below it is readable from the outside.

On the one hand, legibility relates to the appropriate choice of contrast and brightness settings, as explained above, and, on the other hand, to the mirror-symmetrically correct display of the image content, which is essential for the legibility of text information, for example. Not only can the already displayed content be reversed or mirrored, but additional or different information can also be displayed. Continuing with the example, information such as train speed, distance to the nearest train station, visible sights, and the like could be displayed to the passengers during the journey. When entering a station, detected based on position and speed, the display device can then switch to an external display of information such as train number, train destination, car number, seat occupancy, etc.

Further details, features and advantages of the present invention result from the exemplary embodiment explained below with reference to the figure. These only serve to explain the idea of the invention and are not intended to restrict it in any way.

Figur 1:

Schematischer Aufbau zweier einseitig betrachtbarer Ausführungsformen der Anzeigevorrichtung, welche nicht alle Merkmale von Anspruch 1 aufweist.

Figur 2:

Beidseitig betrachtbare Ausführungsformen der Anzeigevorrichtung, von denen die der Teilfigur B nicht alle Merkmale von Anspruch 1 aufweist.

Figur 3:

In vier Teilfiguren das Regelungsprinzips der transparenten Scheibe sowie des Displays vorliegender Erfindung für die Ausführungsform aus Figur 2A für nicht Anspruch 1 gemäße, nur in der Transmissivität schaltbare Scheiben.

Figur 4:

Für die Ausführungsform aus Figur 2 die Ansteuerung im Fall der Betrachtung von beiden Seiten gleichzeitig.

Figur 5:

Perspektivische Ansicht des Aufbaus einer beidseitig betrachtbaren Anzeigevorrichtung mit mehreren schaltbaren Sektoren.

Figur 6:

In vier Teilfiguren die Ansteuerungsprinzipien für die schaltbaren Scheiben sowie das Display einer beidseitig betrachtbaren Anzeigevorrichtung ähnlich der in Figur 5.

Figur 7:

Querschnitt eines Bildpunktes einer beidseitig ablesbaren LED Displays.

They show in detail:

Figure 1:

Schematic structure of two one-sided view embodiments of the display device, which does not have all the features of claim 1.

Figure 2:

Two-way viewable embodiments of the display device, of which that of sub-figure B does not have all the features of claim 1.

Figure 3:

In four partial figures, the control principle of the transparent pane and the display of the present invention for the embodiment Figure 2A for panes which are not according to claim 1 and can only be switched in terms of transmissivity.

Figure 4:

For the embodiment off figure 2 the control in the case of viewing from both sides at the same time.

Figure 5:

Perspective view of the structure of a display device that can be viewed from both sides with several switchable sectors.

Figure 6:

In four partial figures, the control principles for the switchable discs and the display of a display device that can be viewed from both sides, similar to that in figure 5 .

Figure 7:

Cross-section of a pixel of an LED display that can be read from both sides.

figure 1 shows, in two partial figures, schematic cross sections of two embodiments of display devices that can be viewed from one side, but which do not have all the features of claim 1. Located behind the display panel 10 as seen from the main viewing direction B1 and aligned parallel to it is one (partial figure A) or two (partial figure B) transparent panes 11 whose transparency or transmissivity can be switched. Light sensor 12 is shown here between pane and display, but can also be positioned behind the pane(s) when viewed from the direction of view. In any case, it measures an incident light intensity from a subspace angle of the rear hemisphere. The output signal of the light sensor 12 is forwarded to a control unit 13, which controls the unit of the signal and the desired contrast and brightness settings of the display 10 and pane 11 that are fixed or can be selected by a user.

Different cases can be distinguished here. On the one hand, the already mentioned positioning of the light sensor. If this is arranged behind the pane from the viewing direction, the exposure to light does not change as a result of any activation of the

Disk 11 by the control unit 13, i.e. in this case there is a control and not a regulation in the actual sense. If the control unit's response curve simply has a proportional or substantially proportional relationship between the input (light intensity) and the output (drive voltage for the electrically switchable disc), a simple and robust drive of the disc transmissivity is possible, but correct functioning depends on a precise calibration dependent on the target control. This is not the case if the light sensor is located behind the pane, as shown here. The amount of light reaching the light sensor from the background is then reduced as the transmissivity of the pane decreases, so real control must take place in which the control unit 13 adjusts the actual value of the amount of light let through to a target value. In order to avoid unwanted feedback/oscillation in the manipulated variable due to the delayed response of the disc, however, suitable damping of the control must be provided.

A further distinction is necessary between a pane which can be switched in terms of its transmissivity, its transparency or both. Regulation of the transmissivity means that a certain proportion of a light intensity applied to one side is measured on the other side. Transparency, on the other hand, relates to the deflection of the light particles that hit the pane. If these are allowed to pass through without deflection, there is 100% transparency, whereas with a 100% diffuse pane the direction of propagation of incident light particles/rays is completely randomized, so that the direction of exiting particles/rays is in no way related to the direction of the originally in the Disc entering beam can be closed. This However, this does not rule out the possibility that all of the light that originally hit the pane can exit again on the other side, i.e. there is 100% transmissivity. As a rule, however, the direction of propagation is randomized in the entire solid angle, ie a ray impinging on the diffuse pane is re-emitted in any direction (if it is not absorbed). In this case, with a transparency of 0%, in principle only an absolute transmission of a maximum of 50% can be achieved, since on average half of the light is emitted back into the half-space from which it originally hit the pane.

A pane whose transparency can be switched is suitable for the applications mentioned at the outset, such as augmented reality or as a head-up display, but not for the energy-saving use of the amount of light applied to the display from behind as additional background lighting. It is therefore particularly suitable for combining with self-illuminating displays such as oLED, EL or LED displays. The situation is different with panes that can be switched in terms of their transmissivity, i.e. the degree of transmission, with the diffusivity or transparency remaining either almost constant or at least very high even with minimal transmission. An example of this are the so-called SPD panes. They are suitable for providing additional backlighting that is useful for saving energy, but not if the information shown on the display is to be displayed in changing light conditions in front of a background that is in principle clearly visible but can be switched in terms of its apparent brightness. Depending on the application, one or the other display can be selected.

It is also proposed by the present invention that the two different disc types are combined in order to achieve both goals. this is in Figure 1B shown. Here, in viewing direction B1, behind the display 10 are two panes of different types oriented parallel to the display, for example a pdLC and SPD pane. Furthermore, the control unit 13 controls the intensity information received from the light sensor 12 and the desired contrast and brightness settings entered by the viewer. This combination of the two pane types advantageously makes it possible for graphics and text to be displayed in front of a clearly visible background, but also for the background brightness to be used as additional background lighting. In the first case, disc 11' would be switched to 100% (relative) transparency, and the brightness of the visible background would be adjusted to the light conditions with the aid of disc 11 by setting or regulating the relative transmissivity.

figure 2 shows two schematic cross-sectional drawings of embodiments of the display device according to the invention that can be viewed from both sides, but the one shown in sub-figure B does not have all the features of claim 1 . The two possible viewing directions B1, B2 are two identical panes or two pairs of identical panes 11, 11' each arranged on different sides of the display 10. These are controlled by the control unit 13 using the light intensities recorded by light sensors 12 and incident from the respective viewing direction. It is essential here which is the active viewing direction, ie the viewing direction used by the viewer. After this has been determined, the front pane 11 or panes 11, 11' from the active direction is switched to full transparency and transmission. The control/regulation of the discs 11, 11' behind the display panel 10 takes place as in the embodiment in FIG figure 1 described.

figure 3 illustrates in four partial figures the control of the embodiment that can be viewed from both sides Figure 2A , In which the disc 11 can be switched to transmissivity and thus does not have all the features of claim 1 and the display 10 is self-illuminating. Full transmissivity, semi-transmissivity, and impermeability are symbolized by horizontal, oblique, and double hatching, respectively. The size of the circles in the display 10 stands for the (basic) brightness setting and the contrast between the left and right halves for the contrast setting.

Subfigure 3A shows the case of a bright exterior/background, symbolized by a stylized sun, and a bright interior/environment, symbolized by a lamp pictogram. In this case, the rear pane 11 is set to low transmissivity and the display 10 is set to high brightness and high contrast.

Subfigure 3B shows the case of a bright exterior/background and a moderately bright interior/environment. In this case, the rear pane 11 is set to medium transmissivity and the display 10 is set to normal brightness and normal to high contrast.

Partial figure 3C shows the case of a dark exterior space/background, symbolized by a crescent moon, and a less bright interior space/environment. In this case, the method according to the invention provides for the rear pane 11 to be set to high transmissivity and the display 10 to be set to low brightness and low to normal contrast.

Partial figure 3D shows the case of a dark exterior space/background and a light interior space/environment. In this last case illustrated here, the disc 11 lying at the rear is open a high transmissivity and to set the display 10 to normal-high brightness and normal contrast.

Since the same viewing direction B applies to all figures, the front pane 11 seen from this direction must always be kept at 100% relative transmission.

The two partial figures A and B of figure 4 illustrate two possible cases in which, despite unequal lighting conditions on both sides, simultaneous reading from both sides of an embodiment of the display device according to the invention Figure 2A can be realized, as symbolized by the two directional arrows for the main viewing directions B1 and B2.

The discs 11 can be switched to transmissivity here. The display 11 is either self-illuminating (oLED, LED, EL) or passive (TFT). Part A shows daytime operation with a bright exterior and moderately bright interior. In contrast to the in Figure 3A The situation shown are switched to very high transmissivity in order to enable simultaneous readability, both discs 11. Display brightness and contrast should be high in daytime operation. However, in order not to dazzle the viewer on the darker side, the pane there must be adjusted to a lower but still high transmissivity.

Subfigure B illustrates nighttime operation. The main difference is that the general light level is lower, and therefore the display brightness can be set lower. A normal value is necessary because the observer needs a certain minimum brightness on the light inner side (the side with the lamp pictogram). In order not to jeopardize the adaptation of the eyes of the outside observer to the dark surroundings, pane 11 is set to medium transmissivity on this side.

figure 5 shows another embodiment of the display device according to the present invention that can be viewed from both sides, in which the panes 11 are divided into sectors, each of which has its own brightness sensor 12 permanently assigned to the sector. The sensors forward a sector and side-related measurement signal to the control unit 13, which then regulates the transparency and transmissivity of the panes according to the settings of the viewer(s). The principles on which this is done are the same as set out above. The advantage of this embodiment lies in the fact that sector-dependent regulation is possible, as a result of which, for example, shading or selective incidence of light can be compensated for. In order to avoid unsightly sector borders, a fairly high number of sufficiently small sectors is necessary. It makes sense for such a display device to use an LCD or TFT matrix as a switchable disk. The complexity of production and control can be reduced by using larger pixels than is usual for a screen display.

Examples of such a sector-dependent regulation are in figure 6 four cases are shown in which the transmissivity of the pane 11 and the brightness and contrast of the display 10 are set individually for each sector in accordance with the lighting conditions prevailing there.

Sub-figures A and B illustrate the daytime sub-figures C and D the night-time operation. Subfigure A shows the case of shading when looking from a moderately bright environment into a bright exterior space or onto a bright background.

In sub-figure B, the viewing direction is reversed and an annoying light spot on the less bright side has to be compensated for. This happens in that only in the affected sector(s) the transmissivity is regulated down to a corresponding level.

Subfigure C shows how a backlit interfering light source S2 relating to a sector can be masked out in the dark outside space by darkening, i.e. switching the corresponding sector to non-transmissive. In contrast, the interfering light source S1 shining from the bright interior onto another sector of the front side in the viewing direction B1 is compensated for by increasing the brightness and possibly also the contrast setting of the corresponding sector of the display 10 .

Subfigure D shows the case from subfigure C when viewed from the opposite direction. The sector irradiated by the stray light source S1 now remains completely transmitting, whereas the pane 11 lying behind the display 10 from the direction B2 is basically switched to semi-transmitting with the exception of the sector that is irradiated by the stray light source S2. In order to soften this light source, this is set to an even lower transmission. If the interior is not to be visible from the outside, but its brightness is to be used for backlighting (LCD-TFT display) or for providing a basic brightness, then, as already explained for the general case, the transparency must also be reduced to correspondingly low values .

figure 7 shows a cross section through a pixel 20 of an LED display. LED 201 is mounted on circuit board 200 and emits light in at least two solid angle areas, here up and down. The light emitted downward can pass through the circuit board 200 through the hole 2001 . In order to match the viewing angle on the back of the display (here: below) to that on the front (here: above), diverging lens 202 is attached to the underside of circuit board 200 concentrically with hole 2001.

reference list

1

display device

10

display panel

11

Smart Window

12

light sensor

13

control unit

B1

first main perspective

B2

second main perspective

S1

stray light source 1

S2

stray light source 2

20

LED display

200

circuit board

2001

drilling

201

LEDs

202

diverging lens

Claims (13)

1. Display device comprising

   - a display having a front and a rear side, wherein information displayed on the display, in particular a text, character or image, can be viewed from at least one main viewing direction (B1, B2), in particular from a front side, and wherein the display is configured in such a way that a viewer can look through the display onto a background lying behind it,

   - at least one pane (11) with switchable, in particular electrically switchable transparency and transmissivity, the pane (11) being arranged behind the display (10) as seen from the main viewing direction (B1, B2), here transmissivity designates that portion of a light intensity incident on one side, which arrives at the other side, while transparency, on the other hand, refers to the deflection of the light rays incident on the pane (11), whereby, if these are transmitted without deflection, transparency is 100%, whereas, in the case of a 100% diffuse pane, from the direction of an exiting light ray the direction of the light ray originally entering the pane (11) cannot be inferred in any way, and

   - a control unit (13) which controls the transparency and the transmissivity of the pane (11) as well as a contrast setting and a brightness setting of the display,

   - wherein the display is a display panel (10), and

   - two light sensors (12) are present, one light sensor (12) measuring a background brightness, i.e. a light intensity coming from the half-space behind the pane, and the other light sensor (12) measuring an ambient brightness, i.e. a light intensity coming from the half-space in front of the display panel (10), and

   - the control unit (13) controls the transparency and transmissivity of the pane (11) and the brightness and contrast setting of the display panel (10) on the basis of the background and ambient brightness measured by the light sensors (12) in such a way, that an average image brightness as a sum of a light component generated by the display panel (10) and a light component transmitted through the pane (11) and a contrast between the displayed information and the background lying behind the pane (11) each corresponds to a preset or viewer-selectable brightness or contrast value.
2. The display device according to claim 1, wherein the pane (11) has a plurality of sectors which are separately switchable in their transparency and transmissivity.
3. The display device of claim 2, wherein the sectors are arranged in a grid-like manner.
4. The display device according to claim 3, wherein, provided that there are sectors not adjacent to the edge of the pane (11), the control lines associated therewith have a cross-section which has a substantially greater extension parallel to a main viewing direction (B1, B2) than perpendicular to this viewing direction.
5. The display device according to any one of the preceding claims, wherein there are two panes (11) arranged on opposite sides of the display panel (10) so that the display device is viewable from two opposite main viewing directions (B1, B2).
6. The display device according to any one of the preceding claims, wherein the display panel (10) consists either of pixels or light elements arranged in a grid-like manner or of pixels or light elements not arranged in a grid-like manner..
7. The display device according to any one of the preceding claims, wherein the display panel (10) is a transparent LCD, TFT, EL, oLED , pLED or LED display.
8. The Display device according to any one of the preceding claims, wherein the light sensors (12) are integrated into the control unit (13).
9. The Display device according to claim 5, wherein one light sensor (12) is provided per switchable sector of the pane (11) and per main viewing direction (B1, B2) of the dis-play panel (10).
10. A Method for operating a display device according to one of claims 2-9, wherein

    - the brightness value and the contrast value and, if appropriate, the main viewing direction (B1, B2) are selected by an observer, and

    - the light sensors (12) measure the ambient brightness and the background brightness in each case in a sector-related manner and pass these on to the control unit (13), and

    - the control unit (13) adjusts the brightness and contrast settings of the display panel (10) so that, for all sectors of the pane (11), they correspond to the measured light intensities and the preset or viewer-selectable brightness and contrast values, and

    - information to be displayed is shown on the display, and

    wherein the control unit (13) controls the transmissivity for all sectors of the screen (11) such that a transmitted light intensity is below an allowable maximum value, the maximum value of the transmitted intensity being proportional to the brightness setting selected by the viewer.
11. The method according to the preceding claim for operating a display device according to claim 9, wherein at least the background brightness is used in controlling the transparency and at least the ambient brightness is used in controlling the brightness and the contrast of the display panel (10).
12. The method according to the preceding claim, wherein the control of the contrast and the brightness settings of the display panel (10) is performed separately for each sector of the front side in the selected viewing direction.
13. The method according to any one of claims 10-12 wherein, if visibility of the background is not desired by the viewer, the transmissivity of the pane (11) is reduced, wherein the transmissivity is adjusted according to the background brightness measured by the light sensor (12) on the rear side and the preset or viewer-selectable brightness value, wherein the transmissivity is reduced with increasing background brightness and decreasing brightness value, and conversely is increased for lower background brightness and higher brightness values.

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