EP3291214A2 - Display device with dynamic adaptation - Google Patents

Abstract

Display device, comprising a display panel (10) with front and back, wherein a displayed information, in particular a text, characters or an image, at least from the front is her viewable, at least one disc (11) with switchable, in particular electrically switchable transparency and / Transmissivity, wherein the disc is arranged on one side of the display panel (10), at least one light sensor (12) for measuring a light intensity, and a control unit (13), the transparency and / or the transmissivity of the disc (11) and Settings of the display panel (10) controls, wherein the control unit (13) the transparency and / or transmissivity of the disc (11) and a brightness and / or contrast adjustment of the display panel (10) so regulated that a mean image brightness as the sum of the display panel ( 10) and a proportion of light transmitted through the disc (12), and a contrast value between the displayed one Information and a background substantially corresponds to a preset or by a viewer selectable value.

Description

The invention relates to a display device for fonts and images according to the preamble of claim 1 and a method for operating such a display device.

In recent years, screens have been developed which are at least partially transparent, that is, transparent. H. From the back of the display falling light this can happen at least partially, so that a user or viewer of the display sees not only displayed on the display information, especially text, characters or images, but also the background behind the display.

This is a desired or advantageous effect for various reasons. On the one hand, this means that since transmission takes place in all directions, the display can be read on both sides. Furthermore, the superimposition of display images on the technical background can also achieve effects that are impossible with a non-transparent display, at least not without the help of an additional (video) camera. These are, for example, the superimposition of context information on persons, objects 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 important information for the observer, in which it is advantageous if they are always available in the field of view and available quickly, is displayed. Head-up displays are originally known from military aircraft, but have recently found their way into civilian aircraft and vehicles. A realization by means of (semi) transparent screen / display However, would be much easier, 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 creates a seemingly free-floating font or image information in the viewer.

An essential problem of such transparent displays, however, is the readability against the respective background. Should this be guaranteed in any case, then in addition to the actual display, still precautions must be taken, either hide the background if necessary, or the brightness or the Contrast of the display to increase so far that the information to be displayed is still recognizable.

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

In the prior art, various proposals are known to solve the problem addressed. Thus, the European patent application publication EP 3015915 A1 a display device provided with a power-saving backlighting system which is intended to be mounted on a window pane and in which light acted upon from behind on the display, if present, is shared for displaying the image. This can cause the backlight of the display are operated at low power, so that advantageously energy can be saved. Essential for this is the attachment of a so-called Smart Windows, which represents a variable in its transparency or transmission disc over which the back of the display transmitted external light is controllable.

Furthermore, the patent application describes US 2010/0177025 A1 an information display device with a light source, and a light guide plate by means of which light is uniformly dispersed by a light source for the purpose of backlighting the display located in front of this plate. In contrast, the light originating from the internal light source is introduced from the other light originating from the outside into the light guide plate from the other end face. The light guide plate contains a light control mirror, which is electrically switchable and can either transmit or reflect light. As a result, the light intensity used for the backlighting can be controlled.

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

Object of the present invention is therefore to find a display device and a method for operating the same, which ensure automatic, rapid and accurate adjustment to the readability to changing lighting conditions both on the viewer side and in the background.

As a solution, the present invention proposes a display device according to claim 1, which is operated according to the method described in claim 14.

An essential element of the display device here are the controllable in its transparency disc, the light sensors and the control unit, which on the basis of the measured light intensity values and set by the viewer, desired brightness and contrast transparency transparency of the disc and brightness and contrast of the display so controls that a readability of the displayed information is guaranteed.
The set transparency value is dependent on the measured brightness behind the screen, here called background brightness, as well as on the brightness prevailing on the viewer side, here referred to as ambient brightness. Furthermore, the brightness and contrast values set by the viewer are decisive. In general, the transparency should decrease with the background brightness and the desired contrast, but should increase with the ambient brightness and the desired (image) brightness.

As the simplest realization, the present invention proposes a proportional, ie linear dependence. However, other mathematical relationships are also conceivable, such as a quadratic or logarithmic dependence. 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 is associated with a gradual change in the subjective brightness over several orders of magnitude of the ambient brightness. This would be taken into account by a logarithmic dependence of transparency.

As a reference use of the display device according to the present invention, the attachment to a pane of a room and / or a vehicle is contemplated, so that clearly between light conditions in front of and behind the pane, i. can be distinguished in the interior and exterior. On the basis of a subdivision into three rough stages, the possible combinations of light conditions and the transparency or contrast settings to be carried out by the control unit thereupon according to the method according to the invention are described here.

berechnet, wobei ${\mathit{T}}_{\mathit{abs}}^{\mathit{max}}$

und ${\mathit{T}}_{\mathit{abs}}^{\mathit{min}}$

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.It must first be distinguished whether a visibility of the background is desired or not. In the latter case, the disc would simply always be switched to intransparent / reflective, with the possible exception of the case where the external brightness is very low. Contrast and brightness could then be done alone according to the interior / ambient brightness and user settings. An exception to this is the case that the disc is not only controllable in its transparency but also in its transmissivity. 0% (relative) transparency and 100% (relative) transmissivity mean that, although complete but also completely diffuse light transmission takes place, so that only a uniform brightness, but no clear picture is more visible. Intermediate stages in the case of variation of these two parameters, which are generally regarded as independent, result from interpolation.
Relative transparency or transmissivity here means the transparency or transmissivity relative to the maximum possible values of the respective disc material. Using the example of transmissivity T, this means that the relative transmissivity T _{rel is} derived from the absolute T _abs according to the formula $$T_{\mathit{rel}}\left[\mathit{in}\%\right]=100\frac{T_{\mathit{Section}}-{\mathit{T}}_{\mathit{Section}}^{\mathit{min}}}{{\mathit{T}}_{\mathit{Section}}^{\mathit{Max}}-{\mathit{T}}_{\mathit{Section}}^{\mathit{min}}}$$

calculated, where ${\mathit{T}}_{\mathit{Section}}^{\mathit{Max}}$

and ${\mathit{T}}_{\mathit{Section}}^{\mathit{min}}$

denote the maximum and minimum absolute transmissivity. The absolute transmissivity indicates the absolute part of the transmitted light, usually related to the spectrum of the sun.

By way of example and illustration, two electrically switchable disc materials known from the prior art are to be used. On the one hand, so-called pdLC (polymer dispersed liquid crystal) disks are known, which can be switched from almost 0% to about 85% by applying a voltage in their absolute transparency. To achieve the maximum transparency, a voltage of about 60-120VAC is required and the switching process takes about 100 ms.
The situation is different with the so-called SPD (suspended particle device) disks. In this case, dispersed particles are aligned parallel to each other by an applied voltage and thus the transmission and transparency properties are changed. Without 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 disc materials in which both transparency and transmission are 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. Also conceivable is the integration of layers of both materials in a disk, 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 and the second and third electrodes, transmission and transmission would then be independently controllable within certain limits.

If the viewer looks from a bright interior to a bright outdoor space, the control unit will switch the pane behind the display to barely transparent, as well as choose a high brightness and a high contrast of the display, which will match the brightness and contrast settings desired by the viewer scale. This means that the control unit assumes that basically high or highest contrast and brightness are required for clear readability, but this can be ignored by the viewer through his settings.

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

If the viewer's gaze goes from a bright interior to a moderately bright outside space, the window is switched to semi-transparent, and the brightness and contrast of the display are also set high with regard to the value selected by the viewer. If the outside space or the background is only moderately light, a semi-transparent to largely transparent setting must be selected. The basic brightness of the display should still be high, the contrast can be selected to be high to normal, since the leaching by the background brightness is lower than in the first case.

If the light intensity on the viewer side is high, but behind the display is low, the lens can be switched to full transparency, the brightness is still high, but a high contrast setting is not absolutely necessary, because of the back of the display hardly an additional Contrast-reducing backlighting takes place.
If the viewer's gaze goes from a moderately bright interior to a bright exterior through the display, then the pane should be switched to semi-transparent, and medium brightness but high contrast selected.
If the view from a moderately bright interior to a moderately bright exterior is also semitransparent to the pane, contrast and brightness are then set to be medium high relative to the desired value chosen by the viewer.
However, if the interior is moderately bright but the outside space behind the display is dark, the screen can be set to be completely transparent, the brightness setting of the display is medium / normal and the contrast is also good.
If the interior is dark, but the exterior is bright, the lens should be set to almost non-transparent, and the screen's brightness should be low, but the contrast should be normal or low.
However, if the external brightness is only moderate, a semitransparent adjustment of the pane can be selected, but brightness and contrast would be adjusted by the control unit as in the previous case.
The last case considered is a dark interior and a dark exterior. In this case, the pane can be completely transparent to ensure that no light sources are overlooked. Brightness and contrast are rather low.

The above control behavior of the control unit of the display device according to the invention applies to the case that a substantially clear view of the background is desired, so that the displayed information is visible together with the objects located in the background. For a switchable in its transparency disc is needed. If the light applied from the rear side is to be used only for additional backlighting, however, a diffuse disk which can be switched in its transmission is necessary. However, the above-described control behavior 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 beholder. It is essential that this is able to react much faster than a manual readjustment by a viewer and obviously also much more comfortable. In addition, as required, the IR radiation can be reduced, whereby excessive heating of the interior can be avoided.

By equipping the display device with a switchable in its transparency and / or transmission disc, which may also be a window, results in a versatility 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, likewise when the display is switched off or when no information is displayed thereon, the display device according to the invention represents a window which can be switched in its permeability, so that the heating of a room or vehicle can be reduced, for example in the case of strong solar radiation, by the Relative transparency is reduced to a value below 100%. On the one hand, this benefits the comfort of the persons or people in the room, 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, thereby reducing their service life and MTBF (mean time between failure). advantageously increased. If a complete lack of transparency or impermeability of the pane is possible, then the light-tight closure of a room, for example, as a replacement for shutters or shutters is possible. The diffusely transmissive discs with which the transmittance is switchable, allow an opaque closure that ensures privacy and in which the light is adjustable.

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

Ideally, the disk used in the display device according to the invention would be controllable both in its absolute transmission and in its absolute transparency in each case from about 0-100%. The prior art, however, no realization of such a disc is known. In the case of the above-mentioned SPD disks, the transmission is mainly switchable, but the transparency also changes in such a way that a diffuse transmission takes place both at relative transmissivity of 0 and 100%, ie the disk is opaque, but with transmission values therebetween certain transparency is given, the disc is so transparent, at least to a degree.
The still known pdLC disks can be switched from opaque to transparent by applying a voltage.

Since they do not simply absorb incident light in the opaque state (such as SPD disks), but throw it back largely, albeit diffusely, they are suitable as an electrically controllable transflector for the backlighting of TFT displays. The combination of both types of discs, i. Attaching one over the other would result in an element that is both transmissive and controllable in transparency but at the cost of increased complexity, higher cost and lower absolute transmission and transparency.

In a preferred embodiment, two similar slices (eg two SPD or two pdLC slices) are placed on different sides of the display and, usually parallel to it and either spaced or directly attached to it, the present invention recommends that a two-sided reading be made. or viewable display panel to use. For this purpose, on the one hand TFT displays in question. Usually, these consist of a plurality of grid-like arranged pixels, each of which, in a color display, each of a red, blue and green liquid crystal cell (LCD) is constructed. 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 maximum possible absolute transmittances are only about 50%. A TFT display does not have a preferred viewing direction, so it is naturally readable from both sides if there is appropriate backlighting.
The advantage of TFT displays is that they represent a very well-controlled, mature technology and enable very high information densities of currently up to about 400ppi (pixels per inch, pixels per inch). For each pixel, it is individually possible, the relative To change transparency from 0 to 100%. Thus, a TFT matrix would also be suitable as a switchable disk, but would be much more complex in the production and control.

If very high absolute transmittances are desired and a high information density is of secondary importance, a double-sided readable EL display is conceivable (EL = electro-luminous license). It consists of a sandwich of two conductive layers which enclose between them a layer of an electroluminescent material. If a current flows from one to the other conductive layer, the intermediate electroluminescent material illuminates under. If both conductive layers are made of a transparent material, this results in a double-sided readable EL display, also referred to as TEL for short, or transparent electroluminescent display. Achievable transmittances are up to 80%.

However, the most brilliantly colored images with a resolution similar to that of TFT displays can be achieved with so-called transparent oLED (organic LED) displays. They consist of raster-like or maxtrixartig angeordenten pixels, each pixel is assigned at least one LED each 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 deposited on a substrate which 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 reaches between 40-50% of the applied light. The advantage of OLED displays is that a very uniform illumination and high brilliance can be achieved because the pixel is self-luminous and does not rely on a TFT display backlighting. Achievable pixel sizes are in the range of a few 10 micrometers, and thus the information density is about the same as a TFT display.

Instead of a transparent substrate, it would also be conceivable to use an intransparent substrate with a bore introduced underneath the LED. In order to match the viewing angle on the rear side with that on the front side, it would be advantageous to position a diverging lens on the output 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, so that, if the resolution is sufficiently high, general characters, texts or images can be displayed statically or in motion. For special applications, however, it is also conceivable that the pixels are not arranged in a grid or matrix manner but otherwise. For example, pre-written lettering and / or characters may be present on the display so that the display capability of the display is limited to a limited set of shapes or characters. This is z. As in so-called 7-segment displays of digital watches the case. Such non-grid-like displays can be realized in principle with all the above-mentioned display types. However, since this principle is only practicable for low information densities, in particular EL and LED displays are suitable for this purpose.

The present invention also proposes, in a preferred embodiment, that the disc has separately switchable sectors. These sectors may be distributed in a matrix-like or irregular manner over the surface of the disk, but should completely fill the disk surface. Each sector requires at least two electrical leads to control transparency and / or transmissivity. These should preferably be designed according to the present invention, at least for the not adjacent to the edge of the disc sectors so that the cross section of the lead parallel to a main viewing direction has a substantially greater extent than perpendicular.

The pane of the present invention may be a separate element, or any existing electrically switchable window pane of a room and / or vehicle. In the former case, one obtains a mobile usable display device, in the latter case, however, saves the additional provision of a switchable in transparency and / or transmissivity disc.

The sensor and the control purity of the display device according to the invention can be configured in various ways. One possibility is that both functions are performed by physically separate devices. That is sensors are installed at the edge or at a point inside the surface of the disc and have signal lines through which the measurements are passed in digital or analog form to the control unit, which preferably outside the disc surface, for. B. on one of the disc end faces, or disposed on an end face of the display.
But it is also possible, and useful, especially if only one sensor is present, that this is integrated into the control unit.

As a result, the signal propagation paths are minimized and the entire 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 configured in such a way that a light sensor is mounted on each of two opposite end faces and measures a light intensity coming from the respective half-space.

In accordance with another preferred embodiment of the present invention, more than one light sensor is present. In particular, it is advantageous if at least one light sensor is present per viewable side or main viewing direction of the display and / or per switchable sector of the pane. This is permanently assigned to the respective sector and / or the viewing direction and forwards a measurement signal related to the sector to the associated control unit. This can be a central control unit for evaluating all the light measuring signals of the display device according to the invention, or it is in each case also a control unit which is likewise assigned to a sector and / or main viewing direction. In the latter case, several existing control units would have the advantage that a sector-related control of the contrast and brightness adjustment of the display would be easier to perform, if the switchable sector on the disc are also assigned separately controllable sectors of the display.

In further embodiments, the disc is firmly connected to the display panel. This is preferably done in the optical contact bonding method, ie adhesive and only by intermolecular forces between the up to the highest tolerances complementarily shaped contact surfaces of sliding and display. As a result, the achievable contrast is further improved.

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

The main viewing direction (s) of a display should be understood here as the relative directions from which a viewer sees the clearest, brightest and most contrasting image. Typically, displays are designed so that this direction is substantially perpendicular to the display plane. For a two-sidedly readable display, 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, ie the viewer selects one of the maximum two possible viewable pages as the 'active' page. This can be done either by actuation of a corresponding operating element or else automatically by evaluating images of an associated camera and forwarding the corresponding information to the device according to the invention. Furthermore, the viewer selects a brightness and contrast setting which preferably applies to the entire display, ie does not have to be set individually for each sector.
The inventive method is characterized in that first the light sensor measures a local brightness and forwards it to the control unit, control unit for each sector transparency and / or transmission controls so that here the intensity below a permissible maximum value and furthermore adjusts the control unit brightness and contrast of the display panel so that they are seen from the selected viewing direction, one dependent on the measured light intensity and the settings selected by the viewer value, and then the information to be displayed on the display.

It is hereby preferred that these three steps are repeated at regular or irregular intervals from the example within the response time of the disc and / or the display. This should especially happen when the user changes the desired contrast and brightness settings.

The maximum value used for regulating the transmissivity or 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 increase in proportion to the user-selected brightness setting as well as decrease in proportion to the user-selected contrast setting. This ensures that the background brightness transmitted through the pane does not overshadow the image to be displayed, or that the contrast and the level desired by the user are reduced.

Furthermore, it is preferred by the invention that in the method according to the invention the light sensors measure a sector-dependent ambient brightness on the selected viewing direction front side and the light sensors located on the rear side in the viewing direction measure a sector-dependent background brightness and at least the sector-dependent one for controlling the transparency Backlighting and to control the brightness and / or contrast setting at least the ambient brightness is used.

The present invention proposes to reduce the transparency of the disc with increasing background brightness, wherein in one possible embodiment the transparency is inversely proportional to the measured background brightness.
It is also proposed to increase the brightness and contrast settings with increasing ambient brightness, for example with linear dependency.

Furthermore, it is preferred that the regulation and contrast and / or brightness adjustment of the display also be sector-dependent. If the pane of the display device according to the invention can be switched both in 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.
Here you can differentiate between different display types. In any case, an LCD or TFT display is dependent on backlighting, usually by a fluorescent lamp element or an LED rail. Here, the energy consumption of this auxiliary lighting could be reduced by reducing the relative transparency of the pane to a small value and adjusting the transmissivity so as to minimize the additional energy required for backlighting.
This is preferably dependent on the difference or quotient of background and ambient brightness. With high difference / high quotient background to environment (of the observer) a low transmissivity is to be selected. Correspond If the two brightnesses are approximately equal, an average transmissivity is preferred. A high negative difference or a small quotient mean that, relative to the requirement, only a small amount of light is available for additional backlighting. Thus, at least the essential image brightness due to the artificial backlighting by means of the luminous element is necessary. In order to improve its effectiveness, it is advantageous to switch the disk to intransparent, provided that this is equivalent to high reflectivity, as in the case of a pdLC disk.
If a self-illuminating display is installed, such as an oLED, EL or LED display, a backlight is usually not needed. A diffuse-transmitting disk can nevertheless be used meaningfully in certain situations. If, for example, text or other characters are to be displayed on a white background, this can be formed by the disk diffusely illuminated by the background brightness. The active generation of white light by the pixels belonging to the image background of the display is unnecessary, which helps save energy.

It is further proposed that, if transparent TFTs are used, the switching of the information display from one to another main viewing direction is done automatically based on 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 window which can be viewed from the inside and outside, the switchover from the main viewing direction "vehicle interior" to "vehicle exterior" can be effected on the basis of the speed and / or position of the train, wherein above a threshold value the information from inside and is displayed readable from the outside.

On the one hand, readability concerns the appropriate choice of the contrast and brightness settings as explained above, and on the other hand the mirror-symmetrically correct display of the image contents, which is essential for the readability of text information, for example. In this case, not only the already displayed content can be reversed or mirrored, but also other or other information can be displayed. To stick with the example, passengers might find information such as train speed, distance to the nearest train station sights, etc. during the journey. Like. Displayed. When entering a station, detected by position and speed, the display device can then switch to an external display of information formats such as train number, train destination, car number, seat occupancy, etc.

Further details, features and advantages of the present invention will become apparent from the following with reference to the figure of the illustrated embodiment. These serve only to explain the idea of the invention and are not intended to limit it in any way.

Figur 1:

Schematischer Aufbau zweier einseitig betrachtbarer Ausführungsformen der erfindungsgemäßen Anzeigevorrichtung.

Figur 2:

Beidseitig betrachtbare Ausführungsformen der Anzeigevorrichtung.

Figur 3:

In vier Teilfiguren das Regelungsprinzips der transparenten Scheibe sowie des Displays vorliegender Erfindung für die Ausführungsform aus Figur 2A.

Figur 4:

Für die Ausführungsform aus Figur 2 die Anstauung 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:

FIG. 1:

Schematic structure of two unilaterally viewable embodiments of the display device according to the invention.

FIG. 2:

Double-sided viewable embodiments of the display device.

FIG. 3:

In four sub-figures, the control principle of the transparent pane and the display of the present invention for the embodiment of FIG. 2A ,

FIG. 4:

For the embodiment of FIG. 2 the congestion in the case of viewing from both sides simultaneously.

FIG. 5:

Perspective view of the structure of a double-viewable display device with multiple switchable sectors.

FIG. 6:

In four sub-figures the driving principles for the switchable discs and the display of a double-viewable display device similar to in FIG. 5 ,

FIG. 7:

Cross-section of a pixel of a double-sided readable LED display.

FIG. 1 shows in two sub-figures schematic cross-sections of two embodiments of unilaterally viewable display devices according to the present invention. Seen from the main viewing direction B1 located behind the Displaypaneel 10 and aligned parallel to this is a (part of A) or two (part B) transparent and transparent in their transparency or transmissivity switchable disc 11 is arranged. Light sensor 12 is shown here between the disk and the display, but can also be positioned behind the disk / disks when viewed from the viewing direction. In each case, it measures a light intensity incident from a subspace angle of the rear half space. The output of the light sensor 12 is passed to a control unit 13, the unit of the signal and fixed or set by a user selectable desired contrast and brightness settings display 10 and disc 11 drives.

There are different cases to distinguish. On the one hand the already mentioned positioning of the light sensor. If this is arranged from the viewing direction behind the pane, the exposure to light does not change as a result of possible activation of the light Disc 11 through the control unit 13, ie in this case is a control and no regulation in the true sense. If the response curve of the control unit simply has a proportional or substantially proportional relationship between the input quantity (light intensity) and the output quantity (drive voltage for the electrically switchable disk), a simple and robust control of the wafer transmissivity is possible, but correct functioning on a precise calibration instructed the disk drive. This is not the case if the light sensor, as shown here, is located behind the pane. Then, the amount of light reaching from the background to the light sensor reduces with decreasing transmissivity of the disk, so it must be a real control, in which the control unit 13 adjusts the actual value of the transmitted amount of light to a target value. To avoid unwanted feedback / oscillation in the manipulated variable due to the delayed response of the disc, however, a suitable damping of the control is provided.

A further distinction is necessary between a disc which is switchable in its transmissivity, its transparency or both. In this case, regulation of the transmissivity means that a certain amount of light applied to one side is measured on the other side. Transparency, on the other hand, concerns the deflection of the light particles that appear on the glass. If these are transmitted without deflection, then there is 100% transparency, whereas with a 100% diffuse disk, the direction of propagation of incident light particles / rays are completely randomized, so that the direction of the exiting particles / rays in no way on the direction of the original in the Disc entering beam can be closed. This However, it does not rule out that the entire light, which originally hit the glass, can also escape on the other side, ie 100% transmissivity is present. In general, however, the randomization of the direction of propagation takes place in the total solid angle, ie a beam incident on the diffuse disk 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 impinged on the disk.

A disk which is switchable in its transparency is suitable here 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 light quantity acted upon from behind onto the display as additional backlighting. It is therefore particularly suitable for combination with self-illuminating displays, such as oLED, EL or LED displays. The situation is different with discs which are switchable in their transmissivity, ie the transmittance, but the diffusivity or transparency remains either very constant or very high, at least even with minimal transmission. An example of this are the so-called SPD disks. They are suitable for providing additional backlighting useful for energy saving, but not if the information displayed on the display is to be displayed in changing light conditions in front of a background which in principle is clearly and clearly visible but switchable in its apparent brightness. Depending on the application, one or the other display can be selected.

It is also proposed by the present invention that in order to achieve both objectives, the two different disc types are combined. This is in FIG. 1B shown. This is located in the direction B1 behind the display 10 two parallel to the display oriented discs of different types, such as a pdLC and SPD disc. Furthermore, the control unit 13 uses the intensity information obtained by the light sensor 12 as well as the desired contrast and brightness settings entered by the viewer. By this combination of the two types of disks, it is advantageously possible that both the representation of graphics and text against a clearly visible background, but also a use of the background brightness as additional backlighting is possible. In the first case, slice 11 'would be switched to 100% (relative) transparency, and the brightness of the visible background would be adjusted to the light conditions by means of slice 11 by adjusting or controlling the relative transmissivity.

FIG. 2 shows two schematic cross-sectional drawings of both sides viewable embodiments of the display device according to the invention. The two possible viewing directions B1, B2 are two identical or two pairs of similar, each arranged on different sides of the display 10 discs 11, 11 'can be seen. These are regulated by the control unit 13 on the basis of the light intensities recorded by light sensors 12 and incident from the respective viewing direction. It is essential, which is the active, that is the viewing direction used by the viewer. Once this has been determined, the disk 11 or 11 'lying in front of the active direction is switched to complete transparency and transmission. The control / regulation the behind the Displaypaneel 10 lying discs 11, 11 'takes place as in the embodiment in FIG. 1 described.

FIG. 3 illustrated in four sub-figures, the control of both sides viewable embodiment FIG. 2A in which the disk 11 is transmissibly switchable and the display 10 is self-luminous. Full transmissivity, semi-transmissivity or impermeability are symbolized by horizontal, oblique or double hatching. The size of the circles in the display 10 represents the (basic) brightness setting and the contrast between the left and right half for the contrast setting.
In sub-figure 3A, the case of a bright exterior / background, symbolized by a stylized sun, and a bright interior / environment, symbolized by a lamp icon, shown. In this case, the rear pane 11 is set to low transmissivity and the display 10 to high brightness and high contrast.
In Part 3B, the case of a bright outdoor space / background, and a moderately light interior / environment is shown. In this case, the rear panel 11 is set to a medium transmissivity and the display 10 to normal brightness and normal to high contrast.
Part 3C shows the case of a dark outer space / background, symbolized by a crescent moon, and a little light interior / environment. In this case, the method according to the invention provides for adjusting the rear pane 11 to a high transmissivity and the display 10 to low brightness and low to normal contrast.
Partial 3D shows the case of a dark exterior / background and a bright interior / environment. In this last case illustrated here, the rear disk 11 is on a high transmissivity and the display 10 to adjust to normal high brightness and normal contrast.
Since the same viewing direction B applies to all figures, the disk 11, seen from this direction, is always to be kept at 100% relative transmission.

The two subfigures A and B of FIG. 4 illustrate two possible cases in which, despite uneven lighting conditions on both sides of a simultaneous readability on both sides of an embodiment of the display device according to the invention after FIG. 2A is feasible, as symbolized by the two directional arrows for the main viewing directions B1 and B2.
The discs 11 are here in transmissivity switchable. The display 11 is either self-luminous (oLED, LED, EL) or passive (TFT). Part A shows a daytime operation with a bright exterior and a moderately bright interior. Unlike the in FIG. 3A In order to allow simultaneous readability, both discs 11 are switched to very high transmissivity. Display brightness and contrast are to be selected high during daytime operation. However, in order not to dazzle the viewer on the darker side, the slice there is to lower to a lower, but still high transmissivity.
Sub-part B illustrates the night mode. The main difference is that the general level of light is lower and therefore the display brightness can be set lower. A normal value is necessary because for the viewer on the bright inside (the side with the lamp pictogram) a certain minimum brightness is necessary. In order not to endanger the adaptation of the eyes of the external observer to the dark environment, the disc 11 is set on this side to an average transmissivity.

FIG. 5 shows another bilaterally viewable embodiment of the display device according to the present invention, in which the discs 11 are divided into sectors, each of which has its own, permanently assigned to the sector brightness sensor 12. The sensors transmit a sector-related and page-related measurement signal to the control unit 13, which then regulates the transparency and / or transmissivity of the panes according to the settings of the viewer or viewers. The principles according to which this is done correspond to those set out above. The advantage of this embodiment is that it is possible to regulate sector-dependent, as a result of which, for example, shadowing or punctual incidence of light can be compensated. In order to avoid unsightly sector borders, a rather high number of sufficiently small sectors is necessary. It is suitable for such a display device to use an LCD or TFT matrix as a switchable disc. The complexity in production and control can be reduced by the fact that larger pixels than usual for a screen display are used.

Exemplary of such a sector-dependent regulation are in FIG. 6 shown four cases in which transmissivity of the disc 11 and brightness and contrast of the display 10 for each sector is set individually according to the prevailing light conditions there. Sub-figures A and B illustrate the day sub-figures C and D night operation. Part A shows the case of shading in the case of viewing from a moderately bright environment in a bright outdoor space or looking at a bright background.
In sub-figure B, the viewing direction is reversed, and a perturbation of the light spot on the less bright side must be compensated. This is done by reducing the transmissivity to an appropriate level only in the affected sector (s).

Subfigure C shows how a backlighting spurious light source S2 relating to a sector can be masked out in the dark outer space by shading, ie inverse switching of the corresponding sector. By contrast, the stray light source S1 shining out of 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.
In sub-figure D, the case of sub-figure C is shown in the reverse viewing direction. The sector irradiated by the disturbing light source S1 now remains completely transmissive, whereas the disc 11 lying behind the display 10 from the direction B2 is fundamentally switched to semi-transmissive with the exception of the sector which is irradiated by interfering light source S2. This is, in order to mitigate this light source, set to an even lower transmission. If the interior is not visible from the outside, but its brightness is still used for backlighting (LCD TFT display) or provide a basic brightness, then, as already explained for the general case, in addition to reduce transparency to correspondingly low values ,

FIG. 7 shows a cross section through a pixel 20 of an LED display. LED 201 is mounted on circuit board 200 and emits light at least in two solid angle areas, here above and below. The downwardly emitted light may pass through the circuit board 200 through bore 2001. In order to match the by the viewing angle on the back of the display (here: below) on the front (here: above), diverging lens 202 is mounted on the underside of the circuit board 200 concentric with the bore 2001.

LIST OF REFERENCE NUMBERS

1

display device

10

Display panel

11

Smart Window

12

light sensor

13

control unit

B1

first main viewing direction

B2

second main view direction

S1

Störlichtquelle 1

S2

Fault light source 2

20

LED display

200

circuit board

2001

drilling

201

LED

202

diverging lens

Claims (21)

Display device comprising a display panel (10) with front and back side, wherein displayed information, in particular a text, characters or an image, is viewable at least from the front, - At least one disc (11) with switchable, in particular electrically switchable transparency and / or transmissivity, wherein the disc (11) is arranged on one side of the display panel (10), at least one light sensor (12) for measuring a light intensity, and a control unit (13) which regulates the transparency and / or the transmissivity of the pane (11) and settings of the display panel (10), characterized in that - The control unit (13) controls the transparency and / or transmissivity of the disc (11) and a brightness and / or contrast adjustment of the display panel (10) so that a mean image brightness as a sum of the Displaypaneel (10) generated light component and by the disc (12) transmitted light component, and a contrast value between the displayed information and a background essentially corresponds to a preset or selectable by a viewer value. A display device according to claim 1, characterized in that the disc (11) over several, separated from each other in their Transparency and / or Transmissivity switchable sectors. Display device according to claim 2, characterized in that the sectors are arranged like a grid. Display device according to claim 3, characterized in that, at least for sectors not adjacent to the edge of the disc (11), associated control lines have a cross-section which has a substantially greater extent parallel to a main viewing direction (B1, B2) than perpendicular to this viewing direction. Display device according to one of the preceding claims,
characterized in that more than one disc (11) is present, wherein either at least one disc (11) before and a disc (11) of the same type behind the display, or two discs (11) of different types are arranged on the same side , Display device according to one of the preceding claims,
characterized in that the display panel (10) is readable from at least two main viewing directions (B1, B2). Display device according to one of the preceding claims,
characterized in that the display panel (10) consists either of grid-like arranged pixels or luminous elements or non-grid-like arranged pixels or luminous elements. Display device according to one of the preceding claims,
characterized in that the display panel (10) is an LCD, TFT, EL, oLED, pLED or LED display. Display device according to one of the preceding claims,
characterized in that the sensor (12) between the display (10) and the disc (11), or seen from the main viewing direction (B1) behind the disc (11) is arranged. Display device according to one of the preceding claims,
characterized in that the sensor (12) and in the control unit (13) is integrated. Display device according to one of the preceding claims,
characterized in that more than one sensor (12), in particular at least one sensor per switchable sector of the disc (11) and / or per Hauptbetrachtungsrichtung (B1, B2) of the display panel (10) is present. Display device according to the preceding claim,
characterized in that each sensor (12) is associated with a sector and a main viewing direction (B1, B2). Display device according to one of the preceding claims,
characterized in that at least one of the sensors (12) measures a brightness value only within a certain solid angle. Display device according to one of the preceding claims, characterized in that - Display panel (10) and disc (11) are interconnected by means of optical contact bonding, and / or - Slice (11 ") on one of its end faces a backlight, in particular an LED light source. A method of operating a display device according to any one of claims 1-14, wherein a viewer selects a main viewing direction (B1, B2) and a brightness and / or contrast setting,
characterized in that i. each light sensor (12) measures a sector-related brightness value and forwards it to the control unit (13), ii. by the control unit (13) for all sectors of the disc (11) - the transmissivity is controlled so that a transmitted light intensity is below a maximum permissible value, and a brightness and / or contrast setting of the display panel (10) is adapted to correspond to the measured light intensity and the settings selected by the viewer for all sectors of the pane (11), and iii. information to be displayed on the display. Method according to the preceding claim, characterized in that the maximum value of the transmitted intensity is proportional to the brightness setting selected by the viewer. Method according to one of the two preceding claims for operating a display device according to one of claims 11-13, characterized in that light sensors (12) on the front side in the selected viewing direction, a sector-related ambient brightness and light sensors on the rear side in the selected viewing direction measure a sector-related background brightness and at least the background brightness is used to control the transparency and at least the ambient brightness is used to control the brightness and / or contrast values of the display panel (10). Method according to the preceding claim, characterized in that the regulation of the contrast and / or brightness settings of the display panel (10) for each sector of the separately in the selected viewing direction front side. A method according to claim 15, characterized in that the steps 3 to 5 at regular or irregular intervals, in particular within a response time of the disc (11) and / or the display (10), for example about once every 20 to 100 msec repeated. Method according to one of claims 15-19 for operating a display device according to any one of claims 1-13, wherein the disc 11 of the display device 1 is also switchable in its transparency, characterized in that , if the observer visibility of the background is not necessarily desired reduces the transparency of the disk 13, adjusting the transmissivity of the background brightness measured by backside light sensors 12 and the adjusted or viewer-desired image brightness, which reduces transmissivity with increasing background brightness and image brightness, and vice versa for lower background and background brightness higher desired image brightness is increased. Method according to one of claims 15-20, characterized in that switching of the displayed information takes place from one to another main viewing direction based on operating parameters of a vehicle carrying the display device.

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