Abstract:
A lamp, in particular a position lamp for a motor vehicle, has a housing in which at least one light source is arranged, with the housing having a light pane covering an opening of the housing, with the light source being structured as a plurality of light-emitting diodes. A light field formed by a plurality of similar first light-emitting diodes to produce a basic light-intensity distribution and at least one additional second light-emitting diode to produce a preferred light-intensity distribution is provided so that a predetermined total light-intensity distribution is obtained by superpositioning, or overlapping, of the basic light-intensity distribution and the preferred light-intensity distribution.

Description:
BACKGROUND OF THE INVENTION 
     This application claims a priority of German application 100 34 767.3, filed Jul. 18, 2000, and the contents of that application are incorporated herein by reference. 
     This invention relates to a lamp, in particular a position lamp for a motor vehicle, having a housing in which at least one light source is arranged and having a light pane covering an opening of the housing. 
     It is conventional to equip lamps with incandescent bulbs and a reflector to achieve, for example, a desired light-intensity distribution for a position lamp. In the case of motor vehicles, reflectors which produce a uniform emittance of light with a symmetrical light-intensity distribution are used. In the case of aircraft, it is known that when a position lamp is provided on a free end of a wing, for example, different light-intensity distributions in the vertical and horizontal directions are required. One disadvantage of such a known lamp is that the light intensity of the incandescent bulb must be relatively high, because in order to ensure the functionality of the night vision equipment used by pilots, light rays of a certain wavelength must be filtered out by an additional light-absorbing light filter mounted on the lamp. Due to the absorbing effect of the filters, there is self-heating of the incandescent bulb, which shortens the lifetime of the lamp. 
     It is therefore an object of this invention to improve upon a lamp for motor vehicles such that it is possible to assure that a predetermined light-intensity distribution will be achieved with economical operation and a relatively long lifetime. 
     SUMMARY OF THE INVENTION 
     According to principles of this invention, in a lamp, in particular a position lamp for a motor vehicle having a housing in which at least one light source is arranged and having a light pane that covers an opening of the housing, a light source is structured as a plurality of light-emitting diodes (LEDs) with an illumination field formed by a plurality of similar first light-emitting diodes provided to create a basic light-intensity distribution, and at least one additional second light-emitting diode provided to produce a preferred light-intensity distribution, so that by superimposing the basic light-intensity distribution on the preferred light-intensity distribution a predetermined total light-intensity distribution is produced. 
     A particular advantage of this invention is that due to the presence of light-emitting diodes of different luminous properties, it is possible to achieve a basic light-intensity distribution as well as a preferred light-intensity distribution, which can be superimposed to produce a predetermined total light-intensity distribution. A basic idea of this invention is to form an illumination field with a plurality of similarly structured light-emitting diodes with which the basic light-intensity distribution is achieved. A preferred light-intensity distribution can be produced in a certain spatial angle range by additional second light-emitting diodes, usually having a greater power, oriented in a certain preferred direction. By selecting the second light-emitting diodes of the certain light intensity or light-intensity distribution, it is possible to configure a specific total light-intensity distribution in an advantageous manner. A power consumption of the lamp can be reduced and its lifetime greatly increased by using light-emitting diodes. In particular, through the choice of light-emitting diodes, it is possible to achieve a spectrum which stays away from interfering with a wavelength range of night vision equipment. The filter glass is omitted and it is not necessary to use an additional night vision filter. 
     According to a particular embodiment of this invention, the first light-emitting diodes are combined in a separate basic light module which is a compact unit having a module housing with only two connecting pins. A plurality of first light-emitting diodes is connected together on a light-emitting diode carrier. The first light-emitting diodes may be mounted with a relatively high packing density. By combining the first light-emitting diodes on the light-emitting diode carrier, a separate mechanical and electrical coupling of the basic light module from the housing of the lamp can be created in an advantageous manner. The mounting of the basic light module is simplified because only two electric terminals are provided. By combining the first light-emitting diodes in the module housing, the first light-emitting diodes can be protected mechanically and also can be arranged within the housing of the lamp by the secure mechanical and electronic connection. 
     According to another embodiment of this invention, the first light-emitting diodes are arranged in a grid on a light-emitting diode carrier plate of the module housing so that a uniformly and broadly-radiated light-intensity distribution can be achieved. The first light-emitting diodes preferably each have a relatively low light intensity. By superimposing a plurality of such regularly arranged first light-emitting diodes, a basic light-intensity distribution having a relatively constant gradient over a spatial angle range can be achieved in an uncomplicated manner. 
     According to another embodiment of this invention, the basic light module is mounted on a first holding part, and the additional second light-emitting diodes are arranged on a second holding part of the housing, with the holding parts being arranged at an inclination to each other by a predetermined angle. In this way a maximum value of the basic light-intensity distribution on the one hand and the preferred light-intensity distribution on the other hand can be defined in space in an advantageous manner, so that a predetermined total light-intensity distribution is achieved. 
     According to another embodiment of this invention, the housing of the lamp is arranged on a free end of a wing of an aircraft, where the lamp serves as a position lamp. The second holding part extends perpendicular to the direction of flight, and the second light-emitting diodes mounted on the second holding part are oriented in the direction of flight. The first part extends at an acute angle rearwardly to the second holding part, so that the basic light is emitted substantially in a lateral direction to the longitudinal axis of the vehicle. 
     According to another embodiment of this invention, a reflector element is arranged at a borderline area between the first and second holding parts, so that beams of light emitted by the second light-emitting diodes are partially reflected by this reflector element. The reflector element thus serves to increase the light intensity emitted by the second light-emitting diodes in certain spatial angles. In addition, the reflector element also has an light-shield function. An edge of the reflector element facing way from the borderline area is oriented with respect to the basic light module so that an exact light-dark border image is achieved at a predetermined angle. By this means a blinding of pilots can be prevented. 
     According to another embodiment of this invention, the basic light module has a light-transmissive cover in the form of a cupola, or dome, which permits a homogeneous emission characteristic. 
     According to another embodiment of this invention, an infrared diode is positioned on a base plate oriented in the direction of flight. In this way it is possible to send optical identification patterns between members of a flight group for identification of friend vs. foe. Since the infrared diode projects laterally outward away from the base plate, there is a main direction of emittance perpendicular to the direction of flight, thus preventing a direct blinding of pilots. 
     According to another embodiment of this invention, the basic light module and the second light-emitting diodes are driven by a common control circuit. The basic light module on the one hand and the second light-emitting diodes on the other hand are connected in parallel, so that a total current, which is delivered as an impressed supply-current amperage from the control circuit to the consumer elements, is determined as a function of the prevailing component currents flowing in branches. The control circuit preferably has a step-down converter and at least one constant current source with which the consumer-dependent supply-current amperage is applied. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is described and explained in more detail below using an embodiment shown in the drawings. The described and drawn features can be used individually or in preferred combinations in other embodiments of the invention. The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention, as illustrated in the accompanying drawings in which reference characters refer to the same parts throughout. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating principles of the invention in a clear manner. 
     FIG. 1 is a perspective front view of a lamp of this invention, 
     FIG. 2 is a side view of the lamp of FIG. 1, 
     FIG. 3 is a top, or end view of the lamp of FIG. 1, 
     FIG. 4 is a front view of the lamp of FIG. 1, 
     FIG. 5 is a graph showing a plot of a horizontal total light-intensity distribution of a lamp of this invention, 
     FIG. 6 is a graph showing a plot of a vertical total light-intensity distribution of a lamp of this invention, 
     FIG. 7 is an enlarged side view of a basic light module used in a lamp of this invention, and 
     FIG. 8 is a block circuit diagram of a controller for a lamp of this invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A lamp of this invention is used as a position lamp for an aircraft, in particular planes or helicopters. To this end, the position lamp is arranged on a free end of a wing of an aircraft projecting perpendicular to a direction of flight. The lamp has a housing  1  on whose base side a cylindrical socket  2  is connected for engaging in an opening in an outer shell of the aircraft and being affixed there. The housing  1  is structured generally in the shape of an egg, tapering to a point in a direction opposite to flight  3 , so as to be aerodynamically advantageous. 
     In a front of the housing  1 , in the direction of flight  3 , there is a lamp compartment  4  in which a basic light module  6  of a plurality of first light-emitting diodes  5 , a plurality of second light-emitting diodes  7  and a reflector element  19  are arranged. The lamp compartment  4  is covered by a clear light pane  9 . 
     The basic light module  6  is arranged on a first plate-shaped (flat) holding part  10  and the second light-emitting diodes  7  are arranged on an adjacent, laterally-offset, second holding part  11  extending at an acute angle α to the first holding part  10 . A base plate  12 , which is usually arranged perpendicular to a longitudinal axis of an aircraft wing, is connected at a right angle to the second holding part  11 , along the direction of flight  3 . 
     The basic light module  6  forms a circular field of illumination  13  which creates a spherical basic light-intensity distribution GL according to FIG.  5 . The basic light-intensity distribution GL is illustrated in FIG. 5 in the horizontal direction. A maximum of the horizontal basic light-intensity distribution GL is at an angle of approx. 50 degrees; which angle corresponds to the angle of inclination α at which the first holding part  10  and the second holding part  11  are structured to be inclined to one another. 
     As illustrated better in FIG. 7, the basic light module  6  includes a module housing  14  in which is arranged an LED carrier  15  in the form of a substantially-flat board. A plurality of first light-emitting diodes  5  are arranged in a grid pattern on the LED carrier  15 . The individual first light-emitting diodes  5  have a relatively low light intensity. A light intensity corresponding to the light intensity of a single second light-emitting diode  7  can be achieved by super-positioning, or overlapping, the plurality of first light-emitting diodes  5  (see FIG.  5 ). The LED carrier  15  is closed by a light-transmissive dome-shaped cover  16  which allows light emitted by the first light-emitting diodes  5  to be radiated in a three-dimensional angle range of approximately 170 degrees. The first light-emitting diodes  5  are attached in rows and columns in a grid on the LED carrier  15 , so that the light-emitting diodes are always switched in rows, and in parallel with one another. The connections of the first light-emitting diodes run together on the LED carrier  15  and are electrically coupled through to two terminal pins  17  which project outward on the back side of the module housing  14 . This creates a separate and compact module, which produces a relatively constant light-intensity distribution over a large spatial angle range. As shown in FIG. 5, for example, this light distribution can be used to create a basic light-intensity distribution GL of the lamp. By positioning five of the second light-emitting diodes  7 , for example, on the second holding part  11 , this yields an offset arrangement of light-intensity distributions due to the offset positioning of the second light-emitting diodes  7  to one another. By superimposing these light-intensity distributions, a preferred light-intensity distribution VL is obtained, resulting in a relatively high maximum total light-intensity distribution R, which is composed of the basic light-intensity distribution GL and the preferred light-intensity distribution VL. Because of the arrangement of. five second light-emitting diodes  7 , a maximum total light-intensity distribution R is approximately five times greater than the maximum basic light-intensity distribution GL. In this way, a predetermined total light-intensity distribution R in horizontal and vertical directions can be produced in a controlled manner. 
     Because the basic light module  6  is inclined at an acute angle α to the direction of flight  3 , while the second light-emitting diodes  7  are oriented in the direction of flight  3 , the preferred light-intensity distribution VL of the second light-emitting diodes  7  contributes mainly to the total vertical light-intensity distribution R (see FIG.  6 ). The vertical total light-intensity distribution R is arranged symmetrically to a zero point. 
     To increase the light intensity of the basic light module  6 , the reflector element  19  is arranged at a borderline area  18  between the first and second holding parts  10  and  11 , which reflects a portion of the beams of light emitted by the basic light module  6 . In addition, the reflector element  19  is arranged relative to the basic light module  6  so that an edge  20  which is located on a side of the reflector element  19  facing away from the borderline area  18  precisely creates a light-dark boundary image for the basic light-intensity distribution GL. In this way, the light-dark boundary of the basic light-intensity distribution can be set at 0 degrees, for example (not shown in FIG.  5 ). So that pilots are not blinded by the light of the basic light module  6 , the modules are arranged to be offset relative to a front edge  21  of the base plate  12 , opposite to the direction of flight  3 . In this way the base plate  12  can serve as a shield for light emitted by the second light-emitting diodes  7 . 
     In addition, an infrared diode  22  may be mounted flush in the base plate  12  so that a flashing optical pattern can be generated for identification of friend or foe for members of a flight group. 
     The reflector element  19  and module housing  14  are mounted on the first holding part  10  by screw connections  23 . Opposite the direction of flight  3 , a cooling body  24  having a plurality of disc-shaped cooling ribs  25  is connected to the lamp compartment  4 , which serves to cool the lamp compartment  4  and the electronic components. The electronic components are coupled to the cooling ribs  25  by suitable heat conducting materials. 
     A control circuit  26  is provided for controlling the basic light module  6  on the one hand and the second light-emitting diodes  7  on the other hand, which control circuit  26  has a step-down converter  31  which converts an onboard d.c. voltage of 28 V into a lower d.c. voltage. A constant current source connected downstream from this step-down converter  31  applies a supply-current amperage  27  as a function of a current demand of consumer elements (basic light module  6 , second light-emitting diodes  7 ). Because the basic light module  6  in a first branch  28  and the series-connected second light-emitting diodes  7  in a second branch  29  are connected in parallel, a constant voltage is applied in branches  28 ,  29 . In the event of a failure of individual second light-emitting diodes  7  or a failure of the consumer elements of an entire branch, a constant supply current can be adapted which respects limit values. To this end, the current is returned through branches  28  and  29  through separate inputs E of the control circuit  26 . Another constant current source  30  is connected at the input of the second branch  29  which can have an appropriate influence on the converter  31  that delivers the supply amperage  27 . The current returned through the first branch  28  is processed further in a reference circuit  32 , which exercises a controlling function on the constant current source  30  and converter  31 . 
     A safety circuit  33  is preferably connected upstream from the control circuit  26  to shut down the power supply current  27  in the event of an over voltage of more than 48 V according to a hysteresis characteristic, and if the voltage drops below a predetermined voltage threshold this safety circuit makes it possible to again supply the required current amperage  28 . In addition, the safety circuit  33  may have a polarity reversal protection which guarantees that the power supply voltage will be switched through only when the contacting of the light-emitting diodes and/or the basic light module is correct. 
     According to an alternative embodiment, the lamp compartment  4  may also be structured to not have a reflector element. It is self-evident that the number of second light-emitting diodes  7  may be varied, depending on given requirements, or they may be arranged in rows or in a field in the manner of a grid.