Abstract:
A lighting device for streets, paths, and the like, includes a lighting unit containing a lighting element and a lens arranged in front of the lighting element in the main emission direction to produce a specified light distribution characteristic. The lens includes a light entrance surface on a light entrance side facing the lighting element and a light exit surface on a light exit side facing away from the lighting element, at which surfaces the light is refracted. The light entrance surface and/or the light exit surface of the lens is shaped in a direction transverse to the optical axis of the lighting element in such a way that the luminous intensity of the coupled out light, starting from a center plane that intersects with the optical axis, rises with an increasing emission angle from the optical axis at least partially according to a tangent function.

Description:
PRIORITY CLAIM 
       [0001]    The present application is a continuation of a currently pending International Patent Application No. PCT/EP2010/056453 filed on May 11, 2010, which designates the United States and claims priority from and benefit of the German Patent Application No. 10 2009 021 182.9 filed on 13 May 2009. The present application claims priority from and benefit of the aforementioned International Patent Application and, through this International Patent Application, a priority from and benefit of the above mentioned German Patent Application. Disclosure of each of the above-mentioned patent applications is incorporated herein by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention relates to a lighting device for streets, pathways and the like, with a lamp unit including a light source and, positioned in front of the light source in the main emission direction, a lens configured to generate a predefined light distribution pattern. 
         [0004]    2. Description of Relevant Art 
         [0005]    DE 103 30 261 A1 describes a vehicular lighting device which, in addition to a light source and a reflector, is equipped with a lens positioned in front of the light source in the emission direction. The lens is rotationally symmetrical relative to the optical axis of the light source and on the side facing away from the light source it features a total-reflection surface, reflecting the light impinging on it in a direction perpendicular to the main emission and onto a light-exit perimeter. The light is thus deflected sideways toward the reflector surface, with the lens essentially serving as a means for redirecting light toward the lateral reflector surface and not only for generating a predefined light distribution pattern. 
         [0006]    EP 1 916 468 A1 describes a lighting device with a lamp unit for streets, pathways and the like, including a light source and, positioned in front of the light source in the main emission direction, a lens serving to generate a predefined light distribution pattern. The lens is dome-shaped and centrically symmetric relative to points on an optical axis of the light source, and features on a light-exit side of the lens facing away from the light source several segmented free-form areas. A light-entrance surface positioned on a light-entrance side facing the light source is spherically shaped. Depending on the curvature of the light-entrance surface of the lens, larger or smaller rectangular light distribution patterns can be generated. However, the lamp units can only serve to illuminate a partial area of a street section that is to be lit. To fully illuminate the entire object street section it is necessary to combine lamp units with variously contoured or shaped lenses. 
       SUMMARY OF THE INVENTION 
       [0007]    The embodiments are based on the object of developing further the design of a lighting device in a manner whereby, in a simple fashion and as needed, a predefined light distribution is achieved for the homogeneous illumination of an area. 
         [0008]    In an embodiment a lighting device for streets, pathways and the like, with a lamp unit that includes a light source and, positioned in front of the light source in the direction of the main emission, a lens configured for generating a predefined light distribution characteristic. The lens has a light-entrance surface at a light-entrance side facing the light source for coupling in light from the light source. It furthermore has a light-exit surface at a light-exit side facing away from the light source for coupling out light from the lens. Furthermore the light-entrance surface and/or the light-exit surface of the lens is configured in a direction extending transversely relative to the optical axis of the light source in a manner whereby, starting from a central plane that intersects the optical axis, the light intensity of the coupled out light rises at an increasing emission angle relative to the optical axis at least in part along a tangent function. 
         [0009]    The particular advantage stems from the fact that, by conforming the lens to the emission characteristic of the light source, a light beam can be emitted whose light intensity rises at an increasing emission angle relative to the optical axis corresponding to a tangent function. Advantageously, therefore, a preferably rectangular area, especially a street, can be evenly illuminated. 
         [0010]    In one preferred embodiment, a light-entrance surface and/or light-exit surface of the lens is configured in a manner whereby the light intensity increases according to a tangent function in the longitudinal direction up to a first characteristic angle and in the transverse direction up to a second characteristic angle, with the first characteristic angle being larger than the second characteristic angle. The first characteristic angle may be in an angular range between 55° and 75°. In an LED light source with a Lambert emission characteristic the characteristic angle is about 55°. The first characteristic angle and the second characteristic angle are emission angles relative to the optical axis at which the light intensity reaches its maximum in the longitudinal and, respectively, in the transverse direction. At emission angles exceeding the characteristic angles the light intensity decreases again, with the decrease from the maximum light intensity preferably following a cosine curve. Advantageously, a homogeneous illumination of a rectangular area is possible while at the same time it avoids blinding persons at a distance. The assumption is that the optical axis of the lamp unit extends in a direction perpendicular to the street surface to be illuminated, so that persons who are farther away and sees the lighting device at a relatively flat angle will not be blinded. 
         [0011]    In a further embodiment the lens is of a conchiform design with two opposing longitudinal side sections that are connected by a central section. Each side section features a marginal surface from which a partial light beam, coupled at a relatively large emission angle in relation to the optical axis, is totally reflected in the direction of the light-exit side. These side sections extend along both sides of the longitudinal central plane, whereby the converging deviation of the partial light beam through the side section results in a smaller beam width in the transverse direction and thus, in simple fashion, in a rectangular illumination of the street. 
         [0012]    In a preferred embodiment, the lens features longitudinal sections, each having an ascending lateral wing and a descending lateral wing. The ascending lateral wing has a lateral surface which totally reflects part of the incident light beam in a manner whereby, in the direction of the optical axis and longitudinal central plane and intersecting these, the light beam is coupled out. The descending lateral wing is merely provided with surface areas by which the incident light beam is refracted in the direction of the longitudinal central axis without intersecting the longitudinal central axis. Advantageously, this may result in a lamp unit which in its transverse direction exhibits a relatively strong asymmetry while preferably permitting an extended lighting range. Since in the descending lateral wing the light is merely coupled out through refraction, the material cost can be reduced. 
         [0013]    In a further embodiment, the longitudinal side sections of the lens can extend symmetrically or asymmetrically relative to the longitudinal central axis. Advantageously, a symmetric configuration of the longitudinal side sections will illuminate a rectangular area with the lamp unit essentially centered above the street. An asymmetric configuration of the longitudinal side sections will illuminate a rectangular area with the lamp unit positioned at a distance from the center. 
         [0014]    In a first variation, lateral surfaces and a front surface of a first longitudinal side section may be so configured that the incident light beam is coupled out at an acute deflection angle. The result is a uniform light flux, which enhances the generation of a homogeneous light distribution. 
         [0015]    In a further embodiment, the lateral surface and a front surface of a second longitudinal side section are so configured that the light beam coupled into the second longitudinal side section will be coupled out, intersecting the optical axis, at a relatively large deflection angle. Together with an opposite first longitudinal side section this permits the generation of an asymmetric light distribution, so that the lamp unit can be positioned for instance at the edge of a street that is to be illuminated. It also lends itself well to linear illumination. 
         [0016]    In a further embodiment, a front surface of the central section, facing away from the light source, is oval-shaped while a light-entrance surface facing the light source is bell-shaped. In contrast to a circular exit surface, the oval exit surface (front surface of the central section) offers the advantage whereby the maximum emission angle is determined by marginal areas of the longitudinal side section. Advantageously, this permits positioning the lens closer to other components of the lighting device without shadows effects in the light distribution. 
         [0017]    In a further embodiment, the light source is a LED light source, preferably with a beam angle greater than 70°. If the beam angle of the light source were smaller, the total-reflection surfaces of the lateral surface sections would be ineffective. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    In the following, the invention will be described by way of example, without limitation of the general inventive concept, on examples of embodiment and with reference to the drawings. 
           [0019]      FIG. 1  is a top view of the lens of a lamp unit; 
           [0020]      FIG. 2  is a longitudinal section view of a lamp unit in a first embodiment; 
           [0021]      FIG. 3  is a cross section view of the lamp unit in its first embodiment; 
           [0022]      FIG. 4  is a light intensity distribution curve of the lamp unit in its first exemplified embodiment; 
           [0023]      FIG. 5  is a schematic vertical section view of the lamp unit, for use as a street lamp, in its first embodiment for the symmetric illumination of a street area; 
           [0024]      FIG. 6  is a diagrammatic top view of the street to be illuminated, with the first-embodiment lamp unit positioned in the center of the illumination area; 
           [0025]      FIG. 7  is a cross section view of a lamp unit according to a second embodiment; 
           [0026]      FIG. 8  shows the light intensity distribution of the lamp unit in its second embodiment; 
           [0027]      FIG. 9  is a schematic vertical section view of the lamp unit, for use as a street lamp, in its second embodiment for the asymmetric illumination of a street area; 
           [0028]      FIG. 10  is a diagrammatic top view of the street to be illuminated, with the second-embodiment lamp unit positioned off-center relative to the illumination area; 
           [0029]      FIG. 11  is a perspective illustration of a lens in another embodiment; 
           [0030]      FIG. 12  is a cross section view of a lamp unit with a lens according to  FIG. 11 ; and 
           [0031]      FIG. 13  shows the light intensity distribution of the lamp unit per  FIG. 12  in its transverse direction. 
       
    
    
       [0032]    While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the present invention as defined by the appended claims. 
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0033]    A lighting device for streets, pathways and the like may incorporate for instance a frame-shaped housing, not illustrated, which may be flange-mounted on a pole. The housing may integrally contain at least one light-source module so that, when the lighting device is switched on, it can illuminate a surface or spatial area of the street. The housing of the lighting device may be positioned at a predefined distance from the street surface, with at least one light module extending parallel to the street surface. 
         [0034]    The light modules preferably are of a linear or elongated form and extend on the same, common plane of installation. For example, the light modules may be arranged in a manner whereby the lighting device is of a frame-, line-, star- or cross-shaped configuration. In a first embodiment the light modules feature a number of lamp units  1  row-mounted on a common support in a recess of the housing. The support and the array of lamp units  1  of a light module (for instance eight light modules) are closed off by a common transparent cover pane. 
         [0035]    The lamp unit  1  essentially includes a light source  2  in the form of an LED chip and, positioned in the direction and in front of the main emission  3 , a lens  4 . 
         [0036]    Lens  4  preferably is conchiform or has a batwing-shaped cross section and features two longitudinal side sections  5  in opposing positions relative to the longitudinal central plane M L , as well as a central section  6  connecting the longitudinal side sections  5 . In an embodiment, lamp unit  1  depicted in  FIGS. 1 to 6  has identically shaped longitudinal side sections  5 , so that lens  4  is symmetrical not only relative to the longitudinal central plane M L  but also relative to a transverse central plane M Q . 
         [0037]    As shown in  FIG. 2 , the LED light source  2  is positioned on a light-entrance side  7  of lens  4  in a cavity  8  at a distance from a bell-shaped light-entrance surface  9  of lens  4 . The bell-shaped light-entrance surface  9  is preferably rotationally symmetric in relation to an optical axis  10  of light source  2  and lens  4 . 
         [0038]    On a light-exit side  11  of lens  4 , facing away from light source  2 , at least the central section  6  is provided with a longitudinally oval light-exit surface  12 . 
         [0039]    Accordingly, in the longitudinal direction L of lens  4 , the light-entrance surface  9 , serving as the entrance optic, and the light-exit surface  12  of lens  4 , serving as the exit optic, are so shaped that a light intensity distribution curve K 1  (light distribution characteristic) is generated whose light intensity increases in the longitudinal direction, starting from an emission angle Θ whose value in the optical axis  10  is zero, along a tangent function as shown below. 
         [0000]    
       
         
           
             
               I 
                
               
                 ( 
                 θ 
                 ) 
               
             
             = 
             
               
                 I 
                 max 
               
               · 
               
                 
                   tan 
                    
                   
                     ( 
                     0 
                     ) 
                   
                 
                 
                   tan 
                    
                   
                     ( 
                     
                       θ 
                       
                         I 
                          
                         max 
                       
                     
                     ) 
                   
                 
               
             
           
         
       
     
         [0000]    I(Θ): Light intensity in the direction of angle Θ
 
I max : Maximum light intensity generated
 
Θ Imax : Angle at which maximum light intensity is generated
 
         [0040]    As can be seen in  FIG. 4 , the light intensity distribution K 1  reaches its maximum at emission angle Θ KL =70°, then drops back down to emission angle Θ=90° toward zero. The light intensity gradient is steepest in the range between 50° and 80°. For a better understanding,  FIG. 4  additionally shows a light intensity distribution J of LED light source  2  that is configured as a Lambertian emitter. Due to the geometry of light-entrance surface  9  and light-exit surface  12  in the longitudinal direction L the light rays  13  are refracted at the boundary surfaces of lens  4  from optical axis  10  and the transverse central plane M Q  in a manner whereby the maxima are generated in the range of the first characteristic angles Θ KL , Θ KL . The drop in the light intensity distribution above the stated characteristic angles Θ KL  takes place along a cosine curve. 
         [0041]    The geometry of lens  4  in the longitudinal direction L predefines a length l of an illuminated street area  14 . The geometry of lens  4  in the transverse direction Q predefines a width b of the illuminated street area  14 , as is illustrated in  FIG. 6 . The lamp unit  1  is positioned in a central location, i.e. at center Z of the rectangular illumination area  14 . 
         [0042]    To make the emission angle characteristic of lamp unit  1  smaller in the transverse direction Q than in the longitudinal direction L, the longitudinal side sections  5  are provided with a peripheral lateral surface  15  and a front surface  16  on the light-exit side  11 , so that a partial light beam  17 , coupled-in at a relatively large angle in relation to optical axis  10 , will be totally reflected at lateral surface  15  and emitted on the front surface  16  more steeply than a corresponding partial light beam  17 ′ of lens  4  coupled in the longitudinal direction L. The longitudinal side sections  5  thus perform a comparatively collimating function for the light rays coupled at a relatively large angle in relation to the optical axis  10  in the transverse direction Q as compared to the light rays  17 ′ coupled at a large angle relative to optical axis  10  in the longitudinal direction L. Maximum light intensity is thus already attained at a second characteristic angle Θ KQ1 =60°, as in  FIG. 8 , which is smaller than Θ KL =70°. 
         [0043]    In reference to the longitudinal central plane ML and to the transverse central plane MQ the light intensity distribution shown for the first embodiment is symmetric. 
         [0044]    The central section  6  of lens  4  preferably has a scattering effect, with that scattering effect in the longitudinal direction L also extended to the marginal areas as shown in  FIG. 2 . 
         [0045]    In a second embodiment of a lamp unit  21  as shown in  FIGS. 7 to 10 , differing from lamp unit  1  according to the first embodiment, a lens  22  is configured asymmetrically in the transverse direction Q as depicted in  FIG. 7 . In the longitudinal direction L, lens  22  is essentially symmetrical relative to the trans-verse central axis M Q . 
         [0046]    Lens  22  features a first longitudinal side section  5  that is identical to longitudinal side section  5  of lens  4 , as well as, in an opposite location, a second longitudinal side section  23  whose cross section is bulgier than that of the first longitudinal side section  5 . 
         [0047]    The bulgy second longitudinal side section  23  has an arched lateral surface  24  which totally reflects, at a relatively large deflection angle, the partial light beam  17 ″ coupled-in at a relatively steep emission angle and, refracted at a front surface  26  of the second longitudinal side section  23  and intersecting optical axis  10  or the longitudinal central plane M L , is emitted. 
         [0048]    A light beam  18  emitted by the light source  2  transversely relative to the longitudinal central plane M L  is deviated at a larger deflection angle β 1  than a corresponding light beam  19  that impinges on the first longitudinal side section  5  and is deviated at an acute deflection angle α 1 . Another light beam  18 ′ is deviated at the lateral surface  24  and the front surface  26  at an obtuse angle β 2  toward optical axis  10 . This results in an asymmetric light distribution in the trans-verse direction as shown in  FIG. 8 , in that the relative maximum of a light distribution K 2  generated by the second longitudinal side section  23  is smaller than the maximum generated by the first longitudinal side section and occurs at a second characteristic angle Θ KQ2 =−40°. This allows rectangular illumination of the street area  14  even though the lamp unit  21  is not positioned in the center Z of the street area  14  but is laterally offset from the latter. By increasing the bulginess of the second longitudinal side section  23  the asymmetric effect of lamp unit  21  can be further augmented, thus permitting the lamp unit  21  to be positioned for instance at the edge  27  of street area  14 . This embodiment will be employed for illuminating a street from one side, with the lighting device positioned for instance in a transitional area between the street and a sidewalk. 
         [0049]    Another embodiment, shown in  FIGS. 11 to 13 , employs a lamp unit  31  which, like lamp unit  21  in the second embodiment, features longitudinal side sections  33 ,  34  asymmetrically configured in the transverse direction Q. The first longitudinal side section  33  is shaped as an ascending lateral wing that is essentially positioned on a first side of a longitudinal central plane M L  of lens  32 . A second longitudinal side section  34  is in the form of a descending lateral wing positioned on the opposite side of the longitudinal central plane M L . 
         [0050]    The ascending lateral wing  33  and the descending lateral wing  34  are connected via a central section  35  which extends essentially in an area near the longitudinal central plane ML. 
         [0051]    The ascending lateral wing  33  features an outward-arched lightentrance surface  36  which refracts light rays  37  emitted by the light source  2  essentially in the direction of a steeply extending lateral surface  38  which totally reflects them in a manner whereby the light rays  37  are coupled out on a front surface  39  of the ascending lateral wing  33 . The front surface  39  is arched from a forward edge of lateral surface  38 ; the light-entrance surface  36  is arched from a rearward edge of the lateral surface  38 , both toward each other up to the central section  35 . A forward section, in particular, of the lateral surface  38  extends at a relatively steep angle, meaning that the forward section of the lateral surface  38  extends at a relatively small acute angle toward the longitudinal central plane ML, whereby a proportion of light greater than in the second embodiment is reflected past the longitudinal central plane M L  and to the opposite side in relation to the longitudinal central plane M L  and is coupled out via the front surface  39 . 
         [0052]    On its side facing the light source  2 , the descending lateral wing  34  features an arched entrance surface  40  as well as a front surface  41  and a lateral surface  42  descending against the main emission direction. Due to the shape especially of the lateral surface  42  the light rays  43  coupled into the descending lateral wing  34  are merely refracted in the direction of the longitudinal central axis M L  of lens  32 . 
         [0053]    The central section  35  features a light-exit surface, whereby incident light rays  44  are refracted toward both sides of the longitudinal central plane M L . 
         [0054]    In the transverse direction Q, as depicted in  FIG. 13 , a light intensity distribution K′ 2  is generated which, compared to the light intensity distribution K 2  of the second embodiment in  FIG. 8 , exhibits a stronger asymmetry. A first relative maximum Imax 1 ′ is reached at a first characteristic angle Θ KQ1′ =65° as compared to I max1  in the second embodiment at Θ KQ1 =60°. This allows for a comparative increase in range with lens  32 . A second relative maximum Imax 2 ′ is reached at Θ KQ2 ′=30°. I max2 ′ is 0.38, so that a quotient from the second relative maximum I max2 ′ to I max2 ′ is the first relative maximum I max1 ′ less than 0.5. That quotient is thus smaller than the corresponding quotient from Imax 2  and Imax 1  in the second embodiment as in  FIG. 8 . In total, in the transverse direction, the light intensity distribution of the lamp unit  31  covers an angular range of −40° to +75°. Compared to the preceding embodiment, the result, in particular, is a greater light component in the angular range between 50° and 70° in the transverse direction, allowing for an extended range of coverage. 
         [0055]    The light sources preferably employed are LED chips with a beam angle greater than 70°. In the longitudinal direction the lenses  4 ,  22  are so contoured that the tangential increase of the light intensity distribution K 1 , K 2  is in an angular emission range between 0 and 75°. When the LED light source is in the form of a Lambert-type emitter, the tangential increase of the emission angles Θ will be in a range from 0 to 55°. 
         [0056]    Identical components and component functions of the embodiments described bear identical reference numbers. 
         [0057]    In an alternative embodiment, not illustrated, the emission angles Θ may only extend in sub-ranges according to the tangent function; especially in a range near the optical axis  10  the gradient may be steeper or flatter. 
         [0058]    The lighting device lends itself to being used for street lighting but also for interior spaces such as kitchen or living-room furnishings. 
         [0059]    It will be appreciated to those skilled in the art having the benefit of this disclosure that this invention is believed to provide street lighting devices and lamps, such as LED-lamps. Further modifications and alternative embodiments of various aspects of the invention will be apparent to those skilled in the art in view of this description. Accordingly, this description is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the general manner of carrying out the invention. It is to be understood that the forms of the invention shown and described herein are to be taken as the presently preferred embodiments. Elements and materials may be substituted for those illustrated and described herein, parts and processes may be reversed, and certain features of the invention may be utilized independently, all as would be apparent to one skilled in the art after having the benefit of this description of the invention. Changes may be made in the elements described herein without departing from the spirit and scope of the invention as described in the following claims. 
       LIST OF REFERENCE NUMERALS 
       [0000]    
       
           1  lamp unit 
           2  light source 
           3  main emission direction 
           4  lens 
           5  longitudinal side section 
           6  central section 
           7  light-entrance side ( 4 ) 
           8  cavity 
           9  light-entrance surface 
           10  optical axis 
           11  light-exit side ( 4 ) 
           12  light-exit surface 
           13  light rays 
           14  street area 
           15  lateral surface 
           16  front surface 
           17 ,  17 ′ partial light beam 
           18  light beam 
           19  light beam 
           20  light beam 
           21  lamp unit 
           22  lens 
           23  second longitudinal side section 
           24  lateral surface 
           26  front surface 
           27  edge 
         b width 
         J light intensity 
         K 1 , K 2 , K′ 2  light intensity distribution 
         L longitudinal direction 
         l length 
         M L  longitudinal central plane 
         M Q  transverse central plane 
         Q transverse direction 
         Z center 
         α 1  deflection angle 
         ⊕ 1 , β 2  deflection angle 
         Θ emission angle 
         Θ KL  first characteristic angle 
         Θ KQ , Θ KQ ″ second characteristic angle 
           31  lamp unit 
           32  lens 
           33  longitudinal side section 
           34  longitudinal side section 
           35  central section 
           36  light-entrance surface 
           37  light rays 
           38  lateral surface 
           39  front surface 
           40  light-entrance surface 
           41  front surface 
           42  lateral surface 
           43  light rays 
           44  light rays 
         I max ′, I max1 ′ relative maximum 
         I max2 , I max2 ′ relative maximum