Abstract:
The invention relates to a display device including a luminous element and a light guide which has coupling locations and decoupling locations and transports a light signal that is emitted by the luminous element. The inventive luminous element has a radiation characteristic, the solid angle of which can be controlled.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present application is a continuation of international application PCT/DE03/002064, filed Jun. 20, 2003, which designated the United States, and further claims priority to German patent application DE10234124.9, filed Jul. 26, 2002, the both of which are herein incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     The invention relates to a display device comprising a luminous element and a light guide having incoupling and outcoupling locations, the light guide being able to transport a light signal emerging from the luminous element.  
         [0003]     In the case of display devices of this type, signals are displayed on a projection surface by means of a differentiating optical signal transmitter via an optically conducting element. In the case of such displays, use has been made to date of a multiplicity of individual light-emitting elements, or of an electronic display. Examples of the application of such display devices are multistatus displays in tacographs or car radios that display a number of display states on a display field via a light guide and, for example, two LEDs. Another case of application is economy displays, arranged in the form of a ring or bar, mentioned in combination instruments of motor vehicles and utility vehicles that is implemented, for example, by means of 20 light-emitting diodes (LED) or by a liquid crystal display (LCD). The disadvantage of such a display is the high outlay on circuitry and the large number of discrete components that thereby entail high production costs and a low degree of design freedom.  
       SUMMARY OF THE INVENTION  
       [0004]     It is the object of the invention to propose a display unit of simpler and more cost-effective design.  
         [0005]     This object is achieved according to the invention by a display device of the type mentioned at the beginning and in the case of which the luminous element has an emission characteristic of controllable solid angle.  
         [0006]     The display unit therefore has a spatially differentiating light source that can be controlled by a controlling or regulating unit. It is thereby possible to supply various display surfaces with a light signal from a single luminous element. In one possible refinement of the invention, the display surfaces are the outcoupling locations of the light guide. In another design, projection surfaces are provided onto which light emerging from the light guide falls. In a compact design of the display device, the projection surfaces are connected directly to the light guide. They can, however, likewise be realized as separate components. The same holds for the light entrance surfaces of the light guide, which are adapted to the optogeometrical conditions of the light guide and are positioned in accordance with the light source.  
         [0007]     In an advantageous development of the invention, the light guide has light channels that direct the incoupled light onto the appropriate display or projection surfaces. Possible problems arising from signals that produce optical crosstalk are achieved in the simplest case by optical separation of the light channels, for example, by introducing a non-transmissive layer. However, additional optical channels made from glass or glass fibers and introduced into the light guide are also conceivable. They permit the light to be guided to the projection surface without interference.  
         [0008]     The luminous element is configured in such a way that it can change its spatial emission characteristic as a function of a control signal. In the simplest case, there is located above the light exit plane of the luminous element an aperture slot that varies its position in accordance with the desired light entrance window.  
         [0009]     A mechanically less complicated design in the sense of this invention is provided by using a light-emitting diode that can vary its emission characteristic in three dimensions. Consideration is given in this regard, for example, to an RC-LED (Resonance Cavity LED) that keeps down the outlay on mechanical design. With this type of luminous element, “Bragg” mirrors in a light-emitting diode chip ensure that the spatial light intensity distribution curve, the so-called Rousseau diagram, becomes large or small. Thin film LEDs, in particular, can advantageously be used.  
         [0010]     In an advantageous design of the invention, the temperature of the chip is controlled not only via the LED current, but also via an additional heating and/or cooling element that is fitted at the smallest possible spacing from a heat sink of the LED chip. A controlling unit ensures that the current parameters are acquired and processed, if appropriate with the aid of current and temperature comparison tables, stored on a computer, for the appropriate alignment of the light distribution curve.  
         [0011]     Luminous elements having a sufficiently short wavelength such as, for example, UV light sources, render it possible to use projection surfaces equipped with wavelength transmitters to provide the light signal with different colors. As a rule, light with a wavelength of 400-800 mm is denoted as UV light. Use is made as frequency converters of phosphor and other so-called luminous materials whose activator centers emit the energy radiated by the luminous element with the desired color. It is also conceivable to use so-called silicon nanocrystals that emit different light of defined wavelengths after irradiation with UV light. Use in a dial is particularly advantageous here. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0012]     The invention is explained in more detail below with the aid of exemplary embodiments. In the drawing:  
         [0013]      FIG. 1  shows a first design of an inventive display device with a rigid light guide,  
         [0014]      FIG. 2  shows a second design of a display device according to the invention with a moveable light guide,  
         [0015]      FIG. 3  shows a schematic of an LED luminous element of which the light direction can be controlled, and  
         [0016]      FIG. 4  shows a schematic of the arrangement of a luminous element having a control unit. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0017]      FIG. 1  illustrates a first design of a display device according to the invention. Provided at the beginning of a beam path is a luminous element  12  that, depending on how it is driven, can produce a spatially different distribution of light cones, that is to say a different emission characteristic. By way of example,  FIG. 1  shows two light cones  4  that, of course, cannot be produced simultaneously, but are illustrated jointly in  FIG. 1  merely for display. A first light cone, illustrated by points, is narrow and therefore strikes a light entrance region  2  of a light guide  14  such that only a portion of the light entrance region  2  is irradiated by the light cone  4 . Formed in the light guide  14  are two light channels  5  that are optically separated from one another, for example by a reflecting layer. Instead of a reflecting layer between the two light channels  5  of the light guide  14 , it is also conceivable to provide other non-transmissive or only partly transmissive layers, for example a layer that is entirely or partially light absorbing or reflecting. On the other hand, light channels can also be formed by having the light guide  14  comprise a number of bundled glass fibers. Suitable glass fibers for UV light can consist of silica glass or a material resembling silica glass.  
         [0018]     In the case of the narrow light cone that is shown, the light strikes only in the lower light channel such that at a light exit region  1  of the light guide  14  a light signal is also to be detected only in the region of the lower light channel. The upper light channel, which receives no light signal from the luminous element  12 , remains unilluminated.  
         [0019]     The other light cone  4  shown is substantially larger, and comprises both light channels  5  of the light entrance region  2 , and so a signal is also to be seen on the side of the light exit region  1  in the region of the two light channels  5 .  
         [0020]     Only two light channels are illustrated in  FIG. 1 , but it is obvious that the invention can also be extended to light guides having more than two light channels.  
         [0021]     Also shown in  FIG. 1  is a light-shaping element  11  that is arranged between the luminous element  12  and the light guide  14 . This light-shaping element  11  serves the purpose of influencing the shape of the light cones  14  and contributing to light entering the light guide  14  in an optimum way.  
         [0022]     Whereas the light guide  14  is immobile with respect to the luminous element  12  in the exemplary embodiment of  FIG. 1 , the light guide  14  is arranged moveably in the case of the display device illustrated in  FIG. 2 . A luminous element  12  emits light that is deflected by a light-shaping element  11  onto the light entrance region  2  of a light guide  14 . Provided inside the light guide  14  are a number of light-deflecting elements  9  that deflect light signals transported through the light guide  14 , doing so in a defined way. In the beam path, a light signal from a first light-deflecting element is reflected into a horizontal region of the light guide  14 . Provided there are two further light-deflecting elements  9 , which serve the purpose of reflecting light signals upward such that they leave the light guide  14  from light exit regions  10 .  
         [0023]     As in the case of the exemplary embodiment of  FIG. 1 , the light guide  14  itself can be divided into a number of light channels such that light that is irradiated into the light guide  14  in a specific part of the light entrance region  2  is guided inside a specific light channel. The light deflecting elements  9 , which reflect light signals in the direction of the light exit regions  10 , are specifically designed for individual light channels such that there is a fixed assignment between a specific light exit region  10  and a region of the light entrance region  2 .  
         [0024]     Another design is a homogeneous light guide which is, therefore, not divided into individual channels. In the case of such a light guide  14 , as well, light can be irradiated by the luminous element  12  such that it emerges again at a specific location of the light guide  14 . This is possible because the light does not traverse the light guide  14  rectilinearly as a rule, but is reflected multiply at the boundary layers to the surroundings of the light guide. It is thereby possible to use the angle of irradiation and the knowledge of the geometrical shape of the light guide  14  to determine at which location a light signal irradiated at a specific angle emerges again. The light-deflecting elements  9 , which reflect light signals in the direction of the light exit regions  10 , can once again be arranged such that only light signals irradiated at a specific angle emerge at a specific light exit region  10 .  
         [0025]     A cover unit  8  is provided above the light guide  14 . It has sections that are formed as absorption elements  7 , and regions that are formed as display elements  6 . The display elements  6  are provided for the purpose of visualizing light signals emerging through the light exit regions  10  of the light guide  14 . For this purpose, they are formed either as transmission elements, that is to say allow the light beams to pass unimpeded, or else they are formed as projection elements. In the latter case, the surface is, for example, roughened such that the light is scattered. The projection or transmission elements can be colored in order to give the visible light a specific color. The absorption elements  7  ensure that crosstalk is prevented between different transmission and projection elements.  
         [0026]     In the further development of the invention shown in  FIG. 2 , there is also provided an additional movement unit  13  which can be used to displace or rotate the light guide  14 . It is thereby possible to drive a multiplicity of display elements  6  with the aid of a single light guide  14 .  
         [0027]     A description is given with the aid of  FIG. 3  of how a luminous element having Bragg mirrors is constructed, and of how the emission characteristic can be controlled. The luminous element  12  has a light-emitting semiconductor chip  15  that is embedded in a reflector housing  17 . The semiconductor chip  15  has a cold supply and heat dissipation surface  16  that is connected to a heating element and/or cooling element  20 . It is thereby possible for the chip  15  to be kept at the desired operating temperature. The luminous element  12  has terminals  18  for the semiconductor chip  15 , and terminals  19  for the heating element  20 . The heating or cooling element  20  can be used to set the temperature of the luminous element accurately in order via the temperature to set the reflection or refraction properties of the Bragg mirror, and thus to maintain the desired emission characteristic.  
         [0028]     It is shown schematically in  FIG. 4  how it is possible to design the drive of a luminous element  12 . The luminous element  12  is supplied with current by a supply device  24 . The control or the regulation of the luminous element adapted to a display interior temperature is taken over by a control device  21 . This has an interface for the purpose of being driven by a vehicle bus system  23 . As a rule, there is connected to the vehicle bus system an onboard computer that can also in this way provide information, for example relating to temperature/current value tables. Known bus systems are, for example, the CAN bus or the networks for vehicles that are known as K-line and MOST.