Abstract:
In order to provide an illumination device comprising at least one light source ( 1 ) and at least one diffusing element ( 2 ), which has a simple design and is economical to manufacture, the invention provides that the diffusing element ( 2 ) is composed of at least one diffusing plastic element ( 2 ) in which transparent diffusing bodies ( 3 ) are embedded in a transparent plastic mass ( 2 ), and the diffusing element ( 2 ) extends over at least one or more light sources ( 1 ) and is designed as an external housing part ( 2 ) of the illumination device.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is the National Phase Application under 35 USC §371 of International Application No. PCT/EP2006/000967, filed Feb. 3, 2006, which claims priority to German Patent Application 10 2005 004 931.1, filed Feb. 3, 2005. 
     BACKGROUND 
     A. Technical Field 
     The present invention relates to a lighting device comprising at least one light source and at least one diffusing element. 
     B. Background of the Invention 
     Such lighting devices are widely used. For example, such lighting devices are used in motor vehicles, where they may assume the form of a tail light or headlight. At least the backup light and, for example, the brake light are generally located in the tail light or headlight. Recently there has been a design trend to also integrate the directional signal light, for example, into the tail light together with the backup light and the brake light, and/or to integrate the directional signal light, for example, into the headlight. 
     In one type of conventional lighting device having multiple light sources, a clear glass lens, for example, allows an unrestricted view of all components behind the lens. However, designers of vehicle lights such as headlights, directional signal lights, and/or tail lights, for example, must frequently meet the requirement for a uniform external appearance of these vehicle lights. Thus, with respect to the differently colored lights to be integrated into the headlight, for example a yellow directional signal light and a colorless low-beam light, it is undesirable for this color difference to be externally visible when neither of the lights is switched on. In order to provide lights having multiple light sources, for example lights for general illumination, headlights, directional signal lights, and/or tail lights for vehicles, or other lights for which it is not possible to see all the components behind same, for quite some time lights with headlight covers have been used which have a prismatic design or the like on the exit or incident surface. As a result of the prismatic surface, directional light beams are refracted and/or reflected in various directions from each light source, depending on the particular location on the surface at which the light beam strikes the headlight cover. In this manner the directional light beam is converted to predominantly diffuse light radiation. As a result, the components located behind the headlight cover are not visible, and during operation the light sources essentially have the external appearance of a single homogeneous light source. In contrast, when prismatic headlight covers are used it is disadvantageous that their manufacture is complex, since a specific surface structure must be impressed during casting. Furthermore, in many cases a prismatic headlight cover is not desirable from a design standpoint because, for example, a uniform appearance of the headlights and body is preferred. 
     An improved form of a generic lighting device is disclosed in DE 198 18 009 C2. The cited document describes a multilayer cover for multifunctional tail lights for onroad vehicles. The cover is composed essentially of a three-dimensionally deformed plastic film and at least one reinforcement layer made of plastic which has been extrusion molded onto the three-dimensionally deformed plastic film. One characteristic of these known covers is that the plastic film is designed as a light diffusion plate. In this manner the complex manufacture of light-diffusing optical elements integrally molded in one piece to the interior of conventional light covers is avoided. According to the disclosure, the light diffusion plate may be made of polycarbonate, for example, in which spheres or hemispheres in the form of homogeneously dispersed diffusing pigments are embedded. In this respect, the cover disclosed in the cited document is an improvement over the prismatic headlight covers described in the preceding paragraph above. However, one disadvantage of the device disclosed in the cited document is that once again the manufacture of the proposed multilayer design is complicated, since it requires a method for producing multilayered structures. Since according to Claim  4  of the cited document it is proposed that the layer of the plastic film provided as a light diffusion plate has a thickness of 50 to 700 μm, it is disadvantageous that a reinforcement layer must necessarily be applied for achieving the structural strength required for the headlight cover. 
     SUMMARY OF THE INVENTION 
     The object of the present invention, therefore, is to provide a lighting device, comprising at least one light source and at least one diffusing element, which has a simple design and is economical to manufacture. 
     The object is achieved by means of a lighting device comprising at least one light source and at least one diffusing element, whereby the diffusing element is composed of at least one diffusing plastic element in which transparent diffusing bodies are embedded in a transparent plastic mass, and the diffusing element extends over at least one or more light sources and is designed as an external housing part of the lighting device. 
     The advantage of this approach is that the transparent plastic mass has the function of the reinforcement layer as well as the function of the light diffusion plate. In this manner, by using only one component which is composed of the transparent plastic mass containing embedded transparent diffusing bodies, it is advantageously possible to design, for example, a light for general illumination, a headlight, directional signal light, and/or tail light for vehicles, for example, or some other light, the outer housing part of which intrinsically provides the function of light diffusion. The number of light sources may be advantageously reduced when a lighting device designed according to the invention is used. For example, the lighting device according to the invention may be used for lights for general illumination or in headlights, directional signal lights, and/or tail lights for vehicles, for industrial lights, lighted billboards, or deep-drawn lights such as square panels provided with neon lights, for example, such as those used in railway stations, for elongated lighting fixtures or other lights illuminated by a plurality of light-emitting diodes or a plurality of other light sources, which use a lower number of light-emitting diodes or other light sources than do conventional lights, since the intrinsic diffusion characteristics of the housing part convert the initial directionally emitted light from the light-emitting diodes or other light sources to essentially diffuse light radiation. From a design standpoint, this has the advantage that the light for general illumination, for headlights, directional signal lights, and/or tail lights for vehicles or any other lighting device according to the invention appears to be homogeneously illuminated without the multiple light sources being separately visible. In applications in which differently colored light sources are present within the lighting device, for example in integrated directional signal lights and tail lights and/or headlights, use of the lighting device according to the invention has the further advantage that the color difference is not visible in daylight in the shut-off state. This advantageously results in the uniform appearance of the lighting device frequently desired by designers. 
     In one particularly advantageous embodiment of the lighting device according to the invention, the transparent plastic mass is selected from the group comprising polycarbonates. Polycarbonates have the advantage that they possess particularly favorable material properties. The impact strength at low temperatures as well as resistance to high temperatures are particularly advantageous. In addition, the processing temperature of polycarbonates is particularly well suited for injection molding processes. The use of polycarbonates as a replacement for glass materials in the lighting devices according to the invention has the particular advantage of significant weight reduction. This results from the fact that the density of polycarbonate is less than half that of glass. Furthermore, in most cases polycarbonate is more economical than glass. Fireproof polycarbonates as well as high-temperature polycarbonates are also particularly suitable. 
     When polycarbonates are used as the transparent plastic mass, it has proven to be particularly advantageous for the diffusion characteristics when the weight fraction of the embedded transparent diffusion bodies is 0.0001 to 10%, preferably 1%, and the diffusion bodies preferably have a size of approximately 0.1 μm to 5 μm, preferably 2.5 μm. In addition, for achieving optimal homogenization of the light with regard to the transmission angle it is advantageous when the size of the diffusion bodies has a narrow Gaussian distribution composed of different sizes. Bi- and multimodal narrow Gaussian distributions have proven to be particularly suitable. Particularly good diffusion characteristics are also obtained when the inclusions have an essentially spherical shape. When the diffusion bodies are admixed with the polycarbonate, it has surprisingly been shown that in particular the desired mechanical properties of the polycarbonate are maintained. Thus, it is advantageous that the mechanical properties of the polycarbonate are not adversely affected by admixture of the diffusion bodies. The use of polycarbonate together with the embedded diffusion bodies as described above according to the invention has the further advantage that in daylight, for example, a dark appearance considered to be particularly esthetic by designers is obtained when the light sources are not switched on. The polycarbonate may also be colored as desired, so that any given number of design color requirements may be met. 
     According to one specialized embodiment of the lighting device according to the invention, the lighting device is designed for general illumination. In contrast to conventional lights for general illumination, which are usually made of glass, the lighting device according to the invention has the advantage of having approximately half the mass. A light designed according to the invention for general illumination also has advantages with regard to operational safety, since there is no risk of glass splinters resulting from, for example, external impacts or from breakage of the light caused by bursting of the light bulb. In addition, the light designed according to the invention for general illumination may advantageously be manufactured more economically than conventional lights, which often are made of glass. The design of the lighting device according to the invention as a light for general illumination is also very advantageous because, for example, when polycarbonate is used as the plastic element the superior deformability of this material allows manufacture of virtually any given shape of lights for general illumination. Thus, optimal use may advantageously be made of current commercial design trends for general illumination. 
     According to another advantageous embodiment of the lighting device according to the invention, the lighting device is designed as a directional signal light, in particular a directional signal light for vehicles, especially motor vehicles. In contrast to conventional prismatic or glass directional signal lights, such a directional signal light according to the invention is advantageous due to the weight savings compared to lights made of PMMA or glass. In addition, these directional signal lights may be manufactured more economically than conventional prismatic and/or PMMA or glass directional signal lights. In particular, this may advantageously be coordinated with the trend observed in the automobile industry toward increasingly smaller directional signal lights, while at the same time meeting automotive regulatory requirements for good visibility of the directional signal lights from the widest possible viewing angle. 
     When according to one refinement of the invention the lighting device is designed as a multifunctional rear light and/or front light for vehicles, in particular motor vehicles, a directional signal light, for example, may advantageously be integrated into the headlight. It is thus possible, for example, to selectively provide only the segment of the multifunctional light with diffusive material which, for example, covers the directional signal light, in order to expand same without simultaneously expanding the light from the headlight, for example. When differently colored plastics are used in different segments of the multifunctional light according to the invention, prevailing design requirements may be easily and advantageously met. 
     According to a further advantageous embodiment variant according to the present invention, the lighting device is designed as a tail light for vehicles, in particular motor vehicles. In this case, integration of multiple lights, for example the directional signal light, backup light, and brake light, inside a lamp housing reduces the number of components needed for homogenization of light radiation emitted by light-emitting diodes or filament bulbs, for example, with benefits for the manufacturing costs. A further advantage of using polycarbonates is that this material is already widely used in particular in the automobile industry for fabrication of lamp covers. Therefore, a separate authorization procedure for this material for use as a headlight cover may be omitted for the most part. Therefore, in this sector the lighting device according to the invention may be rapidly employed to great advantage. The mechanical and thermal resistance of polycarbonates is particularly advantageous when the material is used for housing parts for ground vehicles, watercraft, and aircraft. 
     According to another embodiment of the invention, the lighting device is designed as a headlight for vehicles, in particular motor vehicles. In particular when the directional signal light is also integrated into the headlight, especially for motor vehicles, this has the advantage that the light source for producing the light for the directional signal, which is usually small relative to the headlight, is converted by diffusion into diffuse light having a large surface area. The visibility of the directional signal light is thus significantly improved, to great advantage. Producing diffuse light radiation for the directional signal light has the further advantage that the directional signal light is visible essentially from all important viewing angles. In particular, visibility from the side of the vehicle is especially advantageous for pedestrians, or for traffic on either side, is advantageous for traffic safety. In addition, as a result of the headlight cover simultaneously having the characteristics of a headlight housing and of a diffusion plate it is not possible to see the internal components of the headlight, in particular the lenses inside the headlight. This has the advantage of providing less appeal for vandalism. 
     In one refinement of the lighting device according to the invention, the lighting device is designed as a billboard. The advantage is that the uniformly homogeneous illumination desired for billboards is ensured, and at the same time the number of light sources used for illumination is reduced. Particularly for cases in which billboards are illuminated using a matrix of light-emitting diodes, the number of light pixels may be reduced with great cost savings due to the diffusive characteristics of the housing material according to the invention. Integration of the diffusive function directly into the housing part advantageously results in a very simple design of the billboard. Weight reduction is advantageously achieved when a billboard according to the invention is used to replace a conventional billboard made of PMMA or a similar material. Furthermore, in the event of breakage of the billboard, by vandalism, for example, there is a much lower safety risk since polycarbonate does not shatter. 
     According to one refinement of the invention, the lighting device according to the invention is designed as an indoor light. In this manner the requirement to achieve diffuse illumination of a room using the fewest possible light sources, frequently imposed in particular by interior designers, may be advantageously met in a particularly economical manner. The fact that diffuse light is intrinsically produced within the housing of the indoor light eliminates the need for additional optical devices within the indoor light, thereby significantly reducing the complexity of manufacture. Since the number of light sources, in particular filament bulbs or light-emitting diodes, may be reduced by the homogeneous distribution of the light radiation emitted by the light sources, this results in the additional advantage that the operating costs of an indoor light according to the invention are particularly low. 
     In a further variant of the invention, the lighting device is designed as interior lighting for vehicles, in particular motor vehicles. By the fact that the interior lighting according to the invention produces essentially diffuse light as a result of its diffusive characteristics, an interior light is advantageously provided which largely eliminates an undesirable blinding effect for the driver, which frequently occurs for interior lights having a directional light beam. Since the light diffusion is ensured by the intrinsic optical properties of the housing of an interior light for vehicles designed according to this variant of the invention, a prismatic or similar plastic surface structuring, which is complicated from a manufacturing standpoint and often undesirable for optical design reasons, may be omitted, thus advantageously reducing the manufacturing costs. This variant of the invention is also well suited for use as ambient lighting in interior spaces or in the passenger cabin of aircraft. 
     In another embodiment of the invention the lighting device is designed as an emergency switch light. Since the plastic material may be deformed in practically any given shape, according to the invention the lighting device may advantageously be used for many different types of emergency switches, the emergency switches being lighted in such a way that such switches fulfill both a signal function and a lighting function. Thus, emergency switches according to the invention may be used to great advantage, for example, for marking emergency exits in buildings, in industrial facilities, and on ships or aircraft. It is particularly advantageous that as a result of the diffuse light the illumination is visible from a wide viewing angle, thereby enhancing safety. In particular for emergency switches it is also very important that no glass be used, which due to breakage in a hazardous event, for example, could introduce an additional hazard source. 
     The object of the invention is further achieved in a particularly effective manner by use of a plastic having an embedded light diffusing element, in which polycarbonate-acrylonitrile-butadiene-styrene (PC-ABS) is selected as the plastic. 
     With regard to achieving the object of the invention, this material has the advantageous property that it may be electroplated, and also has an intense light-diffusing characteristic. Due to the capability for electroplating, assurance is provided that an adherent metal coating, such as chrome plating, may be applied on the surface of the material according to the appropriate known processes. As a result of embedding ABS, the material unexpectedly acquires enhanced transmission due to the increased light diffusion. This is all the more surprising since butadiene as such is known for its powerful light-absorbing properties. The invention is described in one preferred embodiment, with reference to a drawing by way of example. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawing specifically shows the following: 
         FIG. 1 : shows a schematic illustration of a light according to the invention for general illumination; 
         FIG. 2  shows a schematic illustration of another light according to the invention for general illumination; 
         FIG. 3 : shows a schematic illustration of a multifunctional tail light according to the invention; 
         FIG. 4  shows a schematic illustration of the configuration of directional signal lights according to the invention in a motor vehicle; and 
         FIG. 5  shows a schematic illustration of a tail light according to the invention, having multiple light-emitting diodes as light sources. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  schematically illustrates an oblong light for general illumination  11 . The light source  13  is located in the interior space  12  of the light for general illumination  11 . The lamp cover  14  of the light for general illumination  11  has a parallelepiped shape, and is produced from polycarbonate mixed with spherical diffusing elements. As a result of the superior deformability of polycarbonate, the mechanical properties of which are not influenced by admixture of the diffusing elements, within the scope of the invention practically any other shape is possible besides the parallelepiped shape shown by way of example. At the upper side  15  the parallelepiped lamp cover  14  is divided into three segments  16 ,  17 ,  18 . Each segment is composed of polycarbonate of a different color. The light source  13  emits essentially a concentrated light beam  5 . The concentrated light beam  5  is converted to diffuse light radiation  8  in the lamp cover  14  composed of polycarbonate with embedded diffusing elements. In this manner a light which may have practically any given shape is provided for general illumination  14 , by means of which the essentially directional light  8  from the light source  13  is converted to homogeneous, diffuse light radiation  8 . In addition, the white light from the light source  13  is emitted in a color which may be different depending on the segment. 
       FIG. 2  schematically shows another light for general illumination  11 , having a light source  13  located in the lamp cover  14 . The light  11  is illustrated in a partial sectional view. The lamp cover  14  annularly encloses the light source  13  on the sides in the form of a lateral cylindrical surface, and also surrounds the light source on the top and bottom sides in the manner of a cap. The lamp cover  14  is also produced from polycarbonate mixed with spherical diffusing elements  3 . Once again the light source  13  emits essentially a concentrated light beam  5 . The concentrated light beam  5  is multiply diffused inside the lamp cover  14  by the diffusing elements  3 , and in this manner is converted to diffuse light radiation  8 . In addition, as a result of the light guide effect the lamp cover composed of polycarbonate mixed with diffusing elements  3  diffusely emits the light over the entire exterior surface  19  of the lamp cover  14 . 
       FIG. 3  schematically illustrates the exterior of a multifunctional tail light for motor vehicles. The light cover  14  is divided into segments  16 ,  17 ,  18 , and is composed of polycarbonate mixed with spherical diffusing elements. Segment  16  is produced from red-colored polycarbonate, segment  17 , from yellow-colored polycarbonate, and segment  18 , from transparent colorless polycarbonate. Inside the housing  4  for the multifunctional tail light are located three light-emitting diodes  1 , each associated with one of segments  16 ,  17 ,  18 . Each light-emitting diode  1  emits concentrated light beams  5 . The concentrated light beams are multiply diffused by the diffusing elements which are mixed through the entire volume of the housing  4 , and emerge from the light cover  14  in segments  16 ,  17 ,  18  as diffuse light radiation  8 . 
     This specialized embodiment according to the invention provides a multifunctional tail light in which the red-colored segment  16  has the function of a tail light, the yellow-colored segment  17  has the function of a directional signal light, and the colorless segment  18  has the function of a backup light during backward travel. The multiple diffusion of the light inside the light cover  14  ensures that the light is easily visible from different viewing angles, and also that the surface area of each segment  16 ,  17 ,  18  is illuminated. 
       FIG. 4  schematically shows the configuration of directional signal lights  20  on a motor vehicle. The directional signal lights  20 , produced from polycarbonate with embedded diffusing elements, emit diffuse light radiation  8 . The diffuse light radiation  8  emitted by each directional signal light  20  is easily seen by observer  21  as well as by observer  22 , although observers  21 ,  22  observe the directional signal light  20  from very different viewing angles. 
       FIG. 5  shows a brake light containing three light-emitting diodes  1 . The light-emitting diodes  1  are located inside a cover plate  2  for the brake light. The cover plate  2  is produced from polycarbonate mixed with spherical diffusing elements  3 . At the same time the cover plate  2  forms the housing  4  for the tail light. 
     When the tail light is operating, each of the light-emitting diodes  1  emits essentially a concentrated light beam  5 . The concentrated light beam  5  from each of the light-emitting diodes  1  strikes the interior  6  of the cover plate  2 . The concentrated light beam  5  does not strike the unlighted area section  9  of the interior  6  of the cover plate  2 . Inside the cover plate  2  for the tail light the concentrated light beams  5  are multiply diffused by the diffusing elements  3  embedded in the polycarbonate. Diffuse light radiation emerges at the exterior  7  of the cover plate  2 . Thus, diffuse light radiation  8  is emitted from the cover plate  2  over the entire surface of the exterior  7 . In addition, the area sections  10  on the exterior  7  of the cover plate  2 , opposite from the unlighted area sections  9  in the interior  6 , emit diffuse light radiation  8 . Thus, by means of a tail light composed of surprisingly few components, diffuse light radiation  8  may be emitted from the entire exterior  7  of the cover plate  2 , although the concentrated light beams  5  from the light-emitting diodes  1  do not illuminate the area sections  9  on the interior  6  of the cover plate  2 . 
     LIST OF REFERENCE NUMERALS 
     
         
           1  Light-emitting diode 
           2  Cover plate 
           3  Diffusing element 
           4  Housing 
           5  Concentrated light beam 
           6  Interior 
           7  Exterior 
           8  Diffuse light radiation 
           9  Area section 
           10  Area section 
           11  Light for general illumination 
           12  Interior space 
           13  Light source 
           14  Lamp cover 
           15  Upper side 
           16  Segment 
           17  Segment 
           18  Segment 
           19  Exterior surface 
           20  Directional signal light 
           21  Observer 
           22  Observer