Abstract:
A signaling device includes a light source and a Fresnel optical system. Constructed in the form of ellipses on its rear side, the Fresnel optical system has defocusing lenses that form elongated focal areas in the focal plane. Despite the use of a light source of small lateral extent, the signaling device has a radiation characteristic with a large aperture angle.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    This application is a continuation of copending International Application No. PCT/DE01/01334, filed Apr. 5, 2001, which designated the United States and was not published in English. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The invention relates to a signaling device for traffic signals having a light source and an assigned collimator that has contiguously disposed scattering elements on a surface facing the light source.  
           [0004]    Signaling devices, in general, are known to the person skilled in the art. In particular, signaling devices exist in which a light source emits signaling light that is collimated by a Fresnel optical system. Spherical defocusing lenses are constructed on a side of the Fresnel plate facing the light source. Due to the defocusing lenses, mutually parallel light beams falling onto the Fresnel optical system are imaged in the focal plane not at punctiform foci, but on areally extended focal areas.  
           [0005]    Signaling devices for traffic signals must have a prescribed radiation characteristic. On the other hand, the light sources used for conventional signaling devices do not have the sufficiently great extent, required for the purpose, in a direction transverse to the optical axis. This means that the aperture angle of the beam emerging from the Fresnel optical system is small. Consequently, it is generally necessary also to provide an additional scattering lens that expands the beam.  
           [0006]    Another possibility is to configure the light-emitting diodes on a printing circuit board in the focal plane of the Fresnel optical system in accordance with the required radiation characteristic. However, in such a case, there exists a problem of having the printed circuit board be rendered correspondingly large.  
         SUMMARY OF THE INVENTION  
         [0007]    It is accordingly an object of the invention to provide a signaling device for traffic signals that overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and that creates a signaling device for traffic signals that produces a beam of large aperture angle despite a compact light source.  
           [0008]    With the foregoing and other objects in view, there is provided, in accordance with the invention, signaling device for traffic signals, including a light source and a collimator associated with the light source, the collimator having a surface facing the light source, the surface having contiguously disposed scattering elements formed as prominences elongated in a direction along the surface.  
           [0009]    According to the invention, the scattering elements are elongated prominences in a direction along the surface.  
           [0010]    Because elongated prominences are disposed contiguously on the surface facing the light source, parallel light beams falling onto the collimator are imaged in the focal plane of the collimator not at foci, but on areally extended focal areas. It suffices, when one point of light from the light source is located in the focal area associated with a direction of emission, to permit light to emerge from the signaling device in the relevant direction. A small number of points of light in a focal area are sufficient at the edge regions of the light source because, by contrast with the emission in the direction of the optical axis, only a very low luminous intensity is required at the edges of the radiation characteristic.  
           [0011]    In accordance with another feature of the invention, the collimator is a Fresnel optical system, in particular, a Fresnel lens or a Fresnel plate.  
           [0012]    In accordance with a further feature of the invention, the Fresnel optical system has a rear side; and the prominences are disposed on the rear side.  
           [0013]    In accordance with an added feature of the invention, the prominences have elliptical base areas on the surface of the collimator.  
           [0014]    In accordance with an additional feature of the invention, the prominences are formed by or are segments of ellipsoids.  
           [0015]    In accordance with yet another feature of the invention, the collimator has a focal plane and the light source is disposed at or in the focal plane of the collimator.  
           [0016]    In accordance with yet a further feature of the invention, the light source has a field with light-emitting diodes.  
           [0017]    With the objects of the invention in view, in a signaling device having a light source, there is also provided a focusing device, including a collimator associated with the light source, the collimator having a surface facing the light source, the surface having contiguously disposed scattering elements formed as prominences elongated in a direction along the surface.  
           [0018]    Other features that are considered as characteristic for the invention are set forth in the appended claims.  
           [0019]    Although the invention is illustrated and described herein as embodied in a signaling device for traffic signals, it is, nevertheless, not intended to be limited to the details shown because various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.  
           [0020]    The construction and method of operation of the invention, however, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]    [0021]FIG. 1A is a fragmentary, cross-sectional view through a signaling device according to the invention having a flat Fresnel plate;  
         [0022]    [0022]FIG. 1B is an enlarged, fragmentary, cross-sectional view of a portion of the signaling device of FIG. 1A;  
         [0023]    [0023]FIG. 2A is a fragmentary, cross-sectional view through an alternative embodiment of the signaling device according to the invention with a Fresnel lens;  
         [0024]    [0024]FIG. 2B is an enlarged, fragmentary, cross-sectional view of a portion of the signaling device of FIG. 2A;  
         [0025]    [0025]FIG. 3 is a side view of a ray-tracing diagram illustrating imaging without defocusing lenses;  
         [0026]    [0026]FIG. 4 is a perspective view of a ray-tracing diagram illustrating imaging with the Fresnel optical system according to the invention with spherical defocusing lenses; and  
         [0027]    [0027]FIG. 5 is a perspective view of a ray-tracing diagram illustrating imaging with the Fresnel optical system according to the invention with elliptical defocusing lenses. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0028]    Referring now to the figures of the drawings in detail and first, particularly to FIGS. 1A and 1B thereof, there is shown a cross-section through a signaling device  1  that has a light source  3  disposed in the focal plane of a Fresnel plate  2 . The  
         [0029]    Fresnel plate  2  has defocusing lenses  5  of short focal length on the rear side  4 , facing the light source  3 , of the Fresnel plate  2 . Consequently, focal planes  6  that lie between the light source  3  and the Fresnel optical system  2  are associated with the defocusing lenses  5 .  
         [0030]    Without the defocusing lenses  5 , the Fresnel plate  2  aligns light beams emanating from a central region  7  of the light source  3  in a fashion parallel to an optical axis  8 . Beams emanating from edge region  9  of the light source  3  are guided by a Fresnel plate  2  without defocusing lenses  5  in a direction that assumes an angle to the optical axis  8 .  
         [0031]    Illustrated in FIGS. 2A and 2B is a modified embodiment of the signaling device  1  in which the Fresnel plate  2  is replaced by a Fresnel lens  10 . The use of the Fresnel lens  10  has the advantage that, by comparison with the configuration of FIG. 1, the light beams emanating from the light source  3  impinge on the rear side  4  of the Fresnel lens  10  at a smaller angle, which results in larger transmission coefficients and a better efficiency of the optical system.  
         [0032]    For the sake of clarity, a side view of the signaling device  1  of FIG. 1 is illustrated, once again, in FIG. 3. It is clear from FIG. 3 that light beams  11  emanating from the central region  7  are combined to form a light beam aligned parallel to the optical axis  8 . By contrast, light beams  12  emanating from edge regions  9  are combined to form light bundles running along a minor optical axis  13 .  
         [0033]    [0033]FIG. 4 shows a perspective view that illustrates the action of the defocusing lenses  5  on the rear side  4  of the Fresnel plate  2  or the Fresnel lens  10 . Due to the action of the defocusing lenses  5 , light beams  12  incident along the minor optical axis  13  in the focal plane  6  are imaged not at a focal point, but on an areally extended focal area  14 . Conversely, it holds that light is emitted in the direction of the minor optical axis  13  whenever at least one point of light of the light source  3  is situated inside the focal area  14 .  
         [0034]    In the case of the example illustrated in FIG. 4, the focal area  14  is situated on the edge of a luminous area  15  of the light source  3 . Because the focal area  14  is not situated entirely on the luminous area  15 , less light is emitted by comparison with the case in which the focal area is situated entirely on the luminous area  15 . However, this can be taken for granted because only small luminosities are described for large aperture angles α. Due to the configuration of the defocusing lenses  5  on the rear side  4  of the Fresnel plate  2  or the Fresnel lens  10 , it is, therefore, possible to produce ray bundles with large aperture angles α with the aid of a small light source  3 .  
         [0035]    Such an effect can be further amplified when, as illustrated in FIG. 5, elongated defocusing lenses  5  are used instead of the spherical defocusing lenses. Such defocusing lenses  5  have an elliptical base area, for example, on the rear side  4  of the Fresnel plate  2  or the Fresnel lens  10 . The defocusing lenses  5  can also be segments of ellipsoids.  
         [0036]    Consequently, an elongated focal area  16  also results in the focal plane  6 . It suffices, when the focal area  16  comes to be situated partly on the luminous area  15 , to emit light beams  18  in the direction of an associated minor optical axis  13 . A radiation characteristic with a larger aperture angle α′, therefore, results in the case of the use of elongated defocusing lenses  5  in conjunction with the same extent of the light source  3 .  
         [0037]    The aperture angle α is usually to be approximately 60° in the horizontal direction and approximately 30° in the vertical direction. Consequently, the ellipsoidal defocusing lenses  5  situated next to one another on the rear side  4  must be disposed such that the long half axis is aligned vertically.  
         [0038]    In the case of a modified exemplary embodiment, the Fresnel optical system is replaced by a parabolic mirror in whose focal plane the light source  3  is disposed.