Abstract:
A display window is particularly suited for LED and/or LC displays. The display window includes a lighting device and a microstructure for illuminating the display window. The microstructure is disposed on the side of the display window facing the display.

Description:
BACKGROUND OF THE INVENTION 
   Field of the Invention 
   The invention relates to a display window, in particular for LED (light emitting diode) and LC (liquid crystal) displays, with a lighting device and a microstructure for illuminating the display window. 
   Known from DE 20 2004 001 911 U1 is an LED display with a light-guide plate disposed in front thereof. The light-guide plate which can be illuminated with a projection light source is hereby intended to provide a light screening effect for the LED display. To ensure that the light from the projection light source can be reflected and concentrated as completely as possible, a light-guiding configuration is provided. This configuration is disposed on the surface of the light-guide plate facing the viewer. Since the light-guide plate occludes the display from the exterior, the configuration is exposed to all external influences without protection. A further drawback hereby is the fact that the uneven surface of the light guide plate due to the configuration offers a good resting place for contaminants such as, for example, dust. The contaminants or even damage, such as scratches for example, can have a negative impact on or even entirely impede the light-guiding function of the configuration. 
   SUMMARY OF THE INVENTION 
   Therefore, the object underlying the invention is to provide a display window, in particular for LED and LC displays, which protects the displays and ensures consistently good foreground illumination for the displays with simultaneously good legibility of the display information. 
   This object is achieved by a display window, in particular for LED and LC displays, with a lighting device and a microstructure for illuminating the display window in which the microstructure is disposed on the side of the display window facing the display. 
   According to the invention, a differentiation is made between a front side and a rear side of the display window. The side of the display window facing the viewer hereby represents the front side and the side facing the display represents the rear side of the display window. Generally, the front side and rear side are disposed in parallel to one another. In deviation from this, a non-parallel disposition of the front side and rear side in relation to one another may be necessary for structural reasons depending upon the design of the display unit. 
   The microstructure ensures the decoupling of the light energy coupled into the display window by the lighting device, for example laterally coupled-in light energy on the front side of the display window. This enables the entire display window to be illuminated in a targeted way. Due to its disposition according to the invention on the rear side of the display window, the microstructure lies within the interior of the display unit. This disposition protects the microstructure from adverse external influences and in this way guarantees permanently good legibility of the display information. For example, in this way, no dust particles are able to settle on the microstructure. Other influences such as chemical cleaning agents or damage due to mechanical impacts—for example scratches—are unable to damage the microstructure and impair its function. 
   The microstructure therefore fulfils a dual function: on the one hand, it emits light, which is irradiated laterally into the display window, toward the front side of the display window and hence against the direction of view of the user and on the other, it enables a user to view the display in a direction perpendicular to the plane of the display window. For this, the microstructure can comprise surfaces which reflect the light coupled into the display window by the lighting device perpendicular to the surface or front side of the display window. Hereby, the surfaces can be disposed at angles and/or be flat, concave or convex. Hereby, the geometric shape of the surfaces can in principle be freely selected as long as it results in substantially perpendicular radiation. The perpendicular radiation of the coupled-in light produces the most intensive light impression for the viewer and consequently offers the most efficient use of the coupled-in light energy. 
   In order to meet both aforementioned functions of the microstructure, in a first embodiment, the surfaces can completely cover the display window and be only partially reflecting or translucent enough for the display information to remain identifiable through them. According to another embodiment, the surfaces can be embodied as completely reflecting but then they will not occupy the entire area of the display window. Instead, they have free intervals between each other through which the display information remains identifiable. The miniaturized design and the uniform distribution of the surfaces in the microstructure mean the user still receives a homogeneous impression. 
   The microstructure can also be embodied within the display window in the form of microparticles with reflecting surfaces with an alignment suitable for perpendicular light reflection. The alignment of the microparticles can, for example, take place by means of a magnetic field during the process of the production of the display window, wherein, for example, metal powder is added to the actual microparticles. A very fine distribution of the microparticles achieves a two-dimensional and homogeneous decoupling of the light energy. 
   According to the invention, a differentiation is made between lighting devices for illuminating the display window on the one hand and display LEDs or display LC cells for representing the display information on the other. 
   It is also possible to use LEDs as lighting devices. LEDs of this kind can in principle be all LEDs known to the person skilled in the art suitable for illuminating the display window. For example, it is possible to use SMD (surface mounted device) LEDs which are placed on the same board as that bearing the display LEDs. The display LEDs can also have an SMD design. The board can, for example, be a PCB (printed circuit board). 
   The lighting devices in the form of LEDs can, for example, be integrated in the display window, adjoin the side of the display window and/or also be disposed remotely from the display window. In particular with a disposition of the lighting devices remotely from the display window, according to a further advantageous embodiment of the invention, optical links can be disposed between the lighting devices and the display window. The optical links conduct the light energy from the lighting device to the visible area of the display window. The optical links can be part of the display window. They can be disposed in the plane of the display window or at an angle thereto. 
   According to the invention, the display window can comprise a film or an inscription. The film or inscription can preferably—protected against external influences—be disposed on the rear side of the display window and, to define regions of the of the display window, cover it partially or completely. This can involve both regions for representing display information and regions in which no display information is represented. In the case of opaque films or inscriptions, regions of the display window without display information can be covered so that they appear dark to the viewer. The regions with display information can then be embodied either with transparent film or without an inscription. This enables demarcation or better contrast with illuminated regions with display information. Alternatively, the display window can comprise a film or an inscription in some regions only. In this way, the light energy reflected by means of the microstructure can be made visible in the form of foreground illumination in precisely defined regions of the microstructure. 
   A further possibility for representing the display information is provided by a negative inscription or negative representation of the display information applied to the display window on a film or on the display window. Hereby, the display information—for example in the form of text and/or symbols—appears to be translucent to the viewer on illumination. The regions without display information can hereby be inscribed opaquely or covered with opaque film. 
   According to the invention, the film can be diffuse. A diffuse film causes display information represented by several individual LEDs to appear homogeneous to the viewers, since they are no longer able to perceive separate LEDs through the diffuse film. This effect can be assisted by a certain distance between the display LEDs and the display window. 
   The display window can be completely or partially colored so that regions of the display window appear to be differently colored. This can improve the assignment or recognition of certain regions for the viewer. For example, display information of a warning or alerting nature could be highlighted in red. 
   Particularly with regard to modern lighting design, depending upon the embodiment of the display window, colored displays can in particular achieve a high emotionality or impact on the viewer. The display window can therefore almost take on the function of a second display level. 
   According to the invention, a reflector box can be disposed between the display window and the board. This is used for the demarcation of different display information regions. Otherwise, in particular, when there are large distances between display LEDs and the display window, there could be a mutual negative influence of adjacent display information regions. For example, in the case of the above-described representation of the display information by means of a negative inscription, which can also be covered by a diffuse film, without a reflector box, a temporarily non-illuminated region with display information could also be illuminated in an undesirable way by the light energy of the LEDs in an adjacent illuminated region. 
   The reflector box can comprise a plurality of partitions which extend between the display LEDs and the display window and screen a luminous radiation from an adjacent region. A plurality of opaque partitions in the reflector box can form a lighting well, wherein the partitions represent the side walls of the lighting well. The partitions can also form a frame of which one side lies against the display window and the other against the board bearing the display LEDs. The frame of the reflector box can therefore determine the distance between the board or display LEDs and the display window and fix the location of the board or display LEDs relative to the display window. 
   In order to be able to position the reflector box accurately between the board bearing the display LEDs and the display window, the reflector box can comprise positioning elements. These elements can ensure the retention of a predefined position of the reflector box relative to the display window and/or the board. In the case of an elastic embodiment of the elements, these may, for example, be supported elastically on the board so that the reflector box fixes itself in a predetermined position relative to the display window when the latter is assembled. In addition, the elastic elements can compensate distance tolerances between the display window and the board. 
   Numerous variants of the display window can also be achieved by varying the film and/or inscription by geometrically different visual regions of the foreground illumination. For this, the microstructure can only cover regions of the display window. The reflector box can comprise a plurality of lighting wells separating regions of different display information or even regions with display information from others without display information. The side walls of the lighting wells can also be light-conducting. If they are also colored, the regions with display information demarcated by the lighting wells can be represented with optionally colored illuminated frames. 
   Advantageously, the display window according to the invention can also be combined with LC displays. The display window creates a foreground illumination for the LC cells of the LC displays. Therefore, even the low transmission of approximately 15 to 25% of transflective and transmissive LC cells can remain of no significance since the front side of the LC cells is illuminated. Compared to backlighting, foreground illumination also requires less light energy. In addition, the LC cells can be embodied reflectively in order to facilitate improved contrast properties, particularly with medium to bright ambient light. 
   The display window according to the invention can, for example, be used in domestic appliances. Domestic appliances are, for example: washing machines, driers, cookers, ovens, microwaves, dishwashers, refrigerators and steam cookers. However, the field of application of the present invention is not restricted to the examples given. 
   The principle of the invention is explained below in more detail by way of example with reference to diagrams which show: 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       FIG. 1  a schematic representation of an LED (light emitting diode) display with a display window as seen by a viewer; 
       FIG. 2  a sectional representation according to the line of intersection A-A shown in  FIG. 1 ; 
       FIG. 3  a schematic representation of the detail Z from  FIG. 2 ; 
       FIG. 4  a schematic representation of a display board with SMD (surface mounted device) LEDs; 
       FIG. 5  a schematic representation of a display board with SMD LEDs with a superposed reflector box; 
       FIG. 6  a schematic representation of a display board with SMD LEDs, superposed reflector box and a film and 
       FIG. 7  a schematic representation of a display board with SMD LEDs, superposed reflector box, film and display window. 
   

   DESCRIPTION OF THE INVENTION 
     FIG. 1  shows an LED display unit  10  with a display window  12  and a housing  14  as seen by a viewer. This shows a front side of the display window  12 . 
   The display window  12  is depicted with a rectangular flat front side. The housing  14  completely surrounds the display window  12  in the plane of projection. The front side of the display window  12  forms a flat surface with the housing  14 . The housing  14  has a recess with a shape corresponding to the area of the display window  12  visible to the viewer. 
     FIG. 2  shows the display unit  10  shown in  FIG. 1  in section along the line of intersection A-A. 
   The housing  14  and the display window  12  form a horizontal plane. A board  18  is disposed parallel to this plane and at a distance to the display window  12 . SMD LEDs  16  are attached in a marginal region of the board  18 . Optical links  20  extend adjacent to these SMD LEDs in their direction of radiation. The light guide paths  20  are embodied as a component of the display window  12  and protrude at right angles from its edge. A plurality of display LEDs  22  are disposed in the central region of the board  18  below the display window  12 . 
   There is also a reflector box  24  between the display window  12  and the board  18 . It comprises a plurality of lighting wells  28  which extend from above the display LEDs  22  in the direction of the display window  12 . They are adjoined by side walls  30  extending between the display window  12  and the board  18  perpendicularly to the front side of the display window  12 . 
   The display window  12  is illuminated by the SMD LEDs  16 . These SMD LEDs  16  are placed on the board  18  to the side of the display LEDs  22 . The light energy is relayed from the SMD LEDs  16  to the display window  12  by the optical links  20 . These directly adjoin the SMD LEDs  16  or are disposed adjacently to and/or at a distance from the SMD LEDs  16 . 
   The display LEDs  22 , which are also LEDs in SMD design, are also disposed on the board  18 . The display LEDs  22  reproduce the display information. They emit their light energy in the direction of the display window  12 . Hereby, the side walls  30  of the lighting wells  28  divide regions of different display information or regions with and without display information from each other. 
   The reflector box comprises a plurality of positioning elements  26  in a marginal region. They are embodied elastically so that any positional tolerances that occur, for example in relation to the distance between the board  18  and display window  12 , can be compensated. The elastic positioning elements  26  automatically ensure that the reflector box  24  is securely positioned relative to the board  18  and to the display window  12  during the assembly of the display unit  10 . 
   A film  32  is applied between the rear side of the display window  12  and the reflector box  24 . It is transparent and diffuse. This makes the display information appear more homogeneous to the viewer even if it is generated by a plurality of individual display LEDs  22 . 
     FIG. 3  shows a enlargement of the detail identified with Z in  FIG. 2 . 
   In this enlarged representation, a microstructure  36  comprising a plurality of surfaces  38  disposed on the rear side of the display window  12  can be identified. The surfaces  38  comprise a predefined inclination relative to the front side of the display window  12 . 
   The display LEDs  22  in a display information region disposed on the board  18  emit their light energy  34  through the lighting well  28  in the direction of the display window  12 . The display LEDs  22  are also embodied in an SMD design. The display information represented by the display LEDs  22 , for example text or symbols, appear through the diffuse film  32  to the viewer of the display window  12  as homogeneous continuous lines and not in the form of a plurality of individual, for example punctiform, light sources. 
   The surfaces  38  of microstructure  36  are aligned so that the light energy coupled into the display window  12  by the SMD LEDs  16  is reflected perpendicularly upward to the surface  40  of the display window  12 . 
   For a better elucidation of the design of the display unit  10 ,  FIGS. 4 to 7  show individual parts of the display unit  10  in a perspective view. The sequence of  FIGS. 4 to 7  can also be considered to be an assembly sequence for the display unit  10 . 
     FIG. 4  shows the board  18  with nine display LEDs  22  applied in a central region of the board  18 . These are used for the representation of display information. In a marginal region of the board  18 , three SMD LEDs  16  are disposed in each case to the right and left of the display LEDs  22 . They form the basis for the illumination of the display window  12  (not shown in  FIG. 4 ). Positioning aids  42  in the form of recesses are also introduced into the board  18  in order to enable the reflector box  24  to be securely positioned on the board  18 . 
     FIG. 5  shows the board  18  shown in  FIG. 4  with a superposed reflector box  24 . The reflector box  24  comprises projections  44  whose shape and position correspond to the positioning aids  42  of the board  18 . When the reflector box  24  is superposed on the board  18 , these projections  44  engage in the positioning aids  42  of the board  18  and in this way secure the position of the reflector box  24  relative to the board  18 . The necessary distance between the lower edge of the reflector box  24  and the display LEDs  22  or the board  18  is ensured by the positioning elements  26 . These are embodied elastically resulting in the automatic alignment and fixing of the reflector box  24  relative to the display window  12  and the board  18 . 
   The reflector box  24  comprises a plurality of lighting wells  28 , whose disposition, number, shape and size correspond to those of the display information regions. Disposed around the lighting wells  28 , there is a frame which ensures that the reflector box  24  lies securely on the display window  12 . 
     FIG. 6  differs from  FIG. 5  in that the film  32  is applied to the reflector box  24 . For secure positional fixing of the film  32  on the reflector box  24 , the film  32  has an adhesive layer, for example a glued layer. 
     FIG. 7  shows an assembled state of the display unit  10 , in which, additionally to the assembled state shown in  FIG. 6 , the display window  12  with the optical links  20  is superposed on the film  32 . 
   Finally, reference is made once again to the fact that the display unit  10  described in detail above is an exemplary embodiment which can be modified by the person skilled in the art in a wide variety of ways without leaving the scope of the invention. In particular, the specific embodiments of the housing  14  and the display window  12  can differ from the form described here. The reflector box  24  can also be of a different form if necessary for reasons of space or design. 
   For reasons of completeness, reference is also made to the fact that the use of the indefinite article “a” or “an” does not mean that the features in question cannot be pressure several times.
       10  Display unit     12  Display window     14  Housing     16  SMD-LED     18  Board     20  Optical link     22  Display LED     24  Reflector box     26  Positioning element     28  Lighting well     30  Side wall     32  Film     34  Light energy     36  Microstructure     38  Surface of the microstructure  36       40  Surface of the display window  12       42  Positioning aid     44  Projection