Abstract:
An airport light for generating and elliptical beam of light and a method for generating such a beam of light is disclosed. The airport light has within a housing a first module with first LEDs, generating a first beam of light and a second module with a second LEDs, generating a second beam of light. The modules are mounted under an angle against each other resulting in non-parallel and partially overlapping beams of light from the LEDs

Description:
PRIORITY CLAIM 
       [0001]    This application is a continuation of pending International Application No. PCT/EP2012/069968 filed on 9 Oct. 2012, which designates the United States and claims priority from European Application No. 11184491.6 filed on Oct. 10, 2011. The contents of both of these applications are incorporated by reference in their entireties. 
     
    
     BACKGROUND 
       [0002]    1. Field of the Invention 
         [0003]    The invention relates to LED airport lights, preferably used as approach center-line lights or crossbar lights. It also relates to a method for emulating an elliptical radiation pattern. 
         [0004]    2. Description of Relevant Art 
         [0005]    LED (light emitting diode) lighting systems offer significant advantages over traditional incandescent, HID and fluorescent lamps. LEDs are of smaller size, offer higher reliability, longer operational life and lower energy consumption. This is specifically important for airport lighting systems where high reliability and robustness is required. However, there are specific requirements when using LEDs. As increased operating temperature significantly reduces lifetime, cooling is of high importance. Furthermore, most LED chips are approximately isotropic light sources with a lambertian light distribution, which must be adapted to specific requirements of a lighting system. 
         [0006]    Most airport lights, specifically approach centerline lights or crossbar lights have tightly specified radiation patterns. In general these have to comply with the ICAO standards. 
         [0007]    In the US patent publication U.S. Pat. No. 6,932,496 B2 a LED-based elevated omnidirectional airfield light is disclosed. Light emitted by a centered LED is deflected radially by a mirror. 
         [0008]    In the US patent publication U.S. Pat. No. 7,988,345 B2 a projection module of an automobile headlight is disclosed. Light emitted by LEDs is collimated and focused by a plurality of cascaded lenses to form a specific radiation pattern. This system may be adapted to a plurality of radiation pattern. The drawback is the very high complexity and resulting thereof high manufacturing costs and low reliability. 
         [0009]    US patent application publication 2009/0016069 A1 discloses a high efficiency broad-beam light device. There, a plurality of individual LEDs are radially mounted to a circular printed circuit board. The light beam is guided through a circular lens forming an approximately circular light beam. 
       SUMMARY 
       [0010]    The embodiments are based on the object of providing a LED based airport light having a radiation pattern suitable for air-port lights, like approach centerline lights or crossbar lights, further having high optical power, high reliability and lifetime. Furthermore, the solution should be inexpensive and suitable for manufacturing in large volumes. A further problem to be solved is to provide an elliptical radiation pattern without complex lenses and mirrors. 
         [0011]    In an embodiment, an airport light has at least first and second LEDs forming at least two light beams. The first LEDs are mounted to a first module while the second LEDs are mounted to a second module. The first module and the second module are mounted in an angle against each other. The LEDs thus emit non-parallel light beams. The angle between the modules is selected such, that the light beams of first LEDs and second LEDs partially overlap and thereby approximate an elliptical radiation pattern. The preferred angle between the modules is in the range of 6° to 30°. In a preferred embodiment the angle between the modules is 8°. This is specifically preferred when using LEDs with an angle of +−6° (equals 12° total) for 50% decrease of luminosity. This allows a simple and in expensive arrangement without complex and expensive optical means like lenses or reflectors. Although the resulting elliptical pattern is not perfect, it meets the minimum luminosity requirements of airfield lighting specifications like these issued by ICAO. In general the first and second modules may be any type of electronic module holding LEDs. In a very simple embodiment they may be printed circuit boards. They may also be mechanically structures holding the LEDs, while the LEDs are electrically connected by discrete wires or a printed circuit board, preferably a flexible printed circuit board. In a preferred embodiment, there is only one type of electronic module required. It is only necessary to mount the second module under an angle and rotated at 180° against the first module. The first and second modules are contained within a housing which preferably is made of metal to achieve good thermal conductivity. It preferably has a transparent cover which preferably is made of glass. 
         [0012]    In another embodiment additional modules are provided. With further modules the luminosity can be increased. Furthermore the beam can be extended. For example it is possible to produce a comparatively broad and narrow ellipsis. Further modules may be arranged horizontally, vertically, or like a matrix. 
         [0013]    In a preferred embodiment at least one of the first and second LEDs comprise of a plurality of LEDs, most preferably of 3 LEDs. For an improved approximation of the elliptical radiation pattern it is preferred, if the individual LEDs within at least one of first and second LEDs have slightly divergent light beams related to each other. This is also applicable to further modules. 
         [0014]    In a further embodiment the housing has a module holder for holding the first of the second modules under the required angle. To adapt the radiation pattern to individual requirements only the module holder has to be changed. As the modules, or electronic modules have not to be changed, they can be manufactured in large quantities thus reducing manufacturing costs. 
         [0015]    Another embodiment relates to a method for emulating an elliptical radiation pattern by LEDs which typically have a circular radiation pattern. The method comprises arranging first LEDs and second LEDs under an angle to obtain a first beam of light from the first LEDs and a second beam of light from the second LEDs. The first beam of light and the second beam of light are under the angle and form at least partially overlapping radiation patterns. Preferably the angle between the first and second LEDS is in the range of 6° to 30°. 
         [0016]    In a preferred embodiment each of the LEDs is mounted at an individual module, and the modules are arranged under an angle relative to each other, defining the angle between the LEDs. 
         [0017]    In another embodiment additional modules are provided. With further modules the luminosity can be increased. Furthermore the beam can be extended. For example it is possible to produce a comparatively broad and narrow ellipsis. 
         [0018]    In a further embodiment, at least one of the first and second LEDs comprise of a plurality of LEDs, most preferably of 3 LEDs. For an improved approximation of the elliptical radiation pattern it is preferred, if the individual LEDs within at least one of first and second LEDs have slightly divergent light beams related to each other. This is also applicable to further modules. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    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. 
           [0020]      FIG. 1  shows a first embodiment. 
           [0021]      FIG. 2  shows a radiation pattern as required by standards. 
           [0022]      FIG. 3  shows the approximation of an elliptical radiation pattern by circular radiation patterns. 
           [0023]      FIG. 4  shows the light beams approximating an elliptical radiation pattern. 
           [0024]      FIG. 5  shows an exemplary arrangement of LEDs. 
       
    
    
       [0025]    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 
       [0026]      FIG. 1  shows a first embodiment. The airport light  10  comprises a housing  60  which preferably is made of metal like aluminum to provide a good thermal conductivity. The housing is closed by a transparent cover  61  which preferably is made of glass. Inside the housing are a first module  11  and a second module  12 . The first module  11  holds first LEDs  21 , while the second module  12  holds second LEDs  22 . There may be additional electronic components like resistors, diodes or LED drivers on the modules. The first module  11  and the second module  12  are mounted under an angle against each other. This results in a first angle  18  between the first module  11  and a center axis  70  different from 90°. Furthermore the second angle  19  between the second module  12  and the center axis  70  is also different from 90°. As shown herein both angles are smaller than 90°. The angles may also be larger than 90°. The deviation of the angles from 90° is preferably in a range from 3° to 15°, resulting in an angle between the boards in a range from 6° to 30°. Most preferably the deviation is between 5° and 10°. The angles of the modules define the radiation angles of the LEDs attached thereto with respect to the center axis  70 . The light beam  31  of first LEDs  21  result in first LEDs radiation pattern  41 . The light beam  32  of second LED  22  recited in second LEDs radiation pattern  42 . By superimposing the first and the second radiation pattern, the minimum required luminosity as shown by the elliptical radiation pattern  50  can be maintained. 
         [0027]    In  FIG. 2  a radiation pattern is shown as required by ICAO standards for approach centerline lights and for crossbar lights. The main beam  100  has an elliptical shape and is within a horizontal angular range of −10 degrees (left side) to +10 degrees (right side). The vertical range is from 2.5 degrees above ground (bottom) to 13.5 degrees. The luminosity of the main beam must not exceed 10000cd. There further a first outer beam  101  and a second outer beam  102 . The luminosity is decreasing from the main beam to the outer beams. 
         [0028]      FIG. 3  shows the approximation of the above elliptical radiation pattern by two groups of circular radiation patterns. The first group of circular radiation patterns comprises radiation patterns  111 ,  112  and  113  which are generated by first LEDs  21 . The second group of circular radiation patterns comprises radiation patterns  121 ,  122  and  1  to  3  which are generated by second LEDs  22 . By super-imposing the radiation of six LEDs a comparatively good approximation of the required elliptical radiation pattern can be achieved. For example in the center area of the main beam light of all six LEDs is superimposed, resulting in the highest luminosity. In the outer areas like in the area of second outer beam  102  there is light of the lower number of LEDs superimposed. For example at the right and the left side there is only light of one LED  112 - or  122 . 
         [0029]    In  FIG. 4  the light beams for the radiation pattern are shown. The light being emitted from the first LEDs  21  results in radiation patterns  111 ,  112  and  113 . The light being emitted from the second LEDs  22  recited radiation pattern  121 ,  122  and  123 . 
         [0030]    In  FIG. 5  an exemplary arrangement of LEDs is shown. Here first LEDs  21   a,    21   b  and  21   c  are arranged on first module  11 . Second LEDs  22   a,    22   b  and  22   c  are arranged on the second module  12 . Such an arrangement of LEDs may produce a radiation pattern as described above. 
         [0031]    In  FIG. 6  an arrangement of 3 LED modules is shown. Here first LEDs  21   a,    21   b  and  21   c  are arranged on first module  11 . Second LEDs  22   a,    22   b  and  22   c  are arranged on the second  20  circuit board  12 . Third LEDs  23   a,    23   b  and  23   c  are arranged on the third module  13 . Such an arrangement of LEDs may produce a broader radiation pattern as described above. 
         [0032]    It will be appreciated to those skilled in the art having the benefit of this disclosure that this invention is believed to provide LED airport lights. 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 
       [0033]      10  airport light 
         [0034]      11  first module 
         [0035]      12  second module 
         [0036]      13  third module 
         [0037]      18  first angle 
         [0038]      19  second angle 
         [0039]      21  first LEDs 
         [0040]      22  second LEDs 
         [0041]      23  third LEDs 
         [0042]      31  beam of light by first LEDs 
         [0043]      32  beam of light by second LEDs 
         [0044]      41  first LEDs radiation pattern 
         [0045]      42  second LEDs radiation pattern 
         [0046]      50  required elliptical radiation pattern 
         [0047]      60  housing 
         [0048]      61  transparent cover 
         [0049]      70  center axis 
         [0050]      100  main beam 
         [0051]      101  first outer beam 
         [0052]      102  second outer beam 
         [0053]      111 ,  112 ,  113  radiation patterns of first LEDs 
         [0054]      121 ,  122 ,  123  radiation patterns of second LEDs