Abstract:
A lighting assembly for illuminating a vehicle interior has an elongated housing which supports a printed circuit board that has an electrically conductive pattern. A plurality of electrical terminals are connected to the electrically conductive pattern for coupling the lighting assembly to a source of electricity. A plurality of light emitting diodes are arranged in a plurality of rows on the printed circuit board. The light emitting diodes in each row being electrically connected in series between two of the electrical terminals. The light emitting diodes are so connected that application of electricity to selected ones of the electrical terminals causes illumination of different combinations of the rows of light emitting diodes which results in the lighting assembly producing different light intensity levels in the vehicle interior.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
         [0001]    Not Applicable  
         STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
         [0002]    Not Applicable  
         BACKGROUND OF THE INVENTION  
         [0003]    1. Field of the Invention  
           [0004]    The present invention relates to semiconductor lighting systems and more particularly to interior lighting of a vehicle using dimmable assemblies of light emitting diodes.  
           [0005]    2. Description of the Related Art  
           [0006]    The interior cabins of vehicles, such as automobiles, trains and especially aircraft, currently are illuminated by fluorescent or incandescent lighting systems. The disadvantages of those types of systems include short life of the light emitter or bulb, significant weight, generation of radio frequency interference, heat generation, maintenance costs and fragility.  
           [0007]    One solution used to counter the problems identified above has been to use a light emitting diode (LED), either singularly or in groups. U. S. Pat. No. 6,158,882 describes a vehicle lighting system which employs a plurality of LED&#39;s mounted in a linear array to form a lighting strip. Such a strip can be used to wash a wall or ceiling of the vehicle with light. This device is particularly useful to illuminate the cabin of an aircraft. The DC voltage required to illuminate the LED&#39;s is furnished from a power supply that includes a mechanism for varying the DC voltage to control the intensity of the illumination provided by the lighting strip. Specifically a variable voltage regulator is provided in the system described in the aforementioned patent. This enables the illumination of the vehicle&#39;s interior to be adjusted depending upon the outside light level. For example, in daylight the LED lighting strip typically is driven at a voltage level which provides maximum illumination. At nighttime, that maximum illumination level may interfere with the ability of occupants to see through the vehicle windows. Therefore, a lower interior illumination level is preferred at night.  
           [0008]    Electromagnetic interference (EMI), especially in the radio frequency spectrum (RFI) is especially troublesome in aircraft, as such can interfere with navigation and communication systems. Thus variable power supplies often require special filtering and insulating elements to avoid or minimize EMI and RFI. That in turn adds weight and consumes space, both of which are a premium in an aircraft.  
           [0009]    Weight always is a major consideration in the construction of aircraft and manufacturers go to great lengths to reduce weight of components where ever possible. Thus it is desirable to reduce the weight of circuits for dimming aircraft cabin lighting.  
         SUMMARY OF THE INVENTION  
         [0010]    A lighting assembly for illuminating a vehicle interior has an elongated housing adapted to be mounted in the vehicle interior and has a plurality of electrical terminals for connection to a source of electricity.  
           [0011]    A plurality of light emitters, preferably light emitting diodes, is supported by the housing and arranged in a plurality of rows. The light emitters in each row are electrically connected together and to ones of the plurality of electrical terminals wherein application of electricity to selected ones of the plurality of electrical terminals causes illumination of different combinations of the plurality of rows of light emitters. Such selective application of electricity results in the lighting assembly producing different light intensity levels in the vehicle interior.  
           [0012]    In the preferred embodiment in which the light emitters are light emitting diodes, each of the rows is divided into groups of light emitting diodes electrically connected in series with the groups for a given row electrically connected in parallel. When the lighting assembly is powered by alternating current, a first set of the groups of light emitting diodes in a given row are connected in an inverse parallel manner to a second set of groups in the given row. Thus each set will illuminate during opposite half-cycles of the alternating current. In another embodiment for use with alternating current, a full-wave rectifier is provided to power the light emitting diodes and the full-wave rectifier may employ some of the light emitting diodes to rectify the alternating current.  
           [0013]    In one version of the present lighting system there are first, second and third rows of light emitters with the first and third rows electrically connected in parallel. A switching device is attached to the rows of the lighting assembly. The switching device has a first state in which electricity is applied to only the second row of light emitters, a second state in which electricity is applied to only the first and third rows of light emitters, and a third state in which electricity is applied to every row of light emitters.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    [0014]FIG. 1 is an isometric view of an LED lighting strip according to the present invention;  
         [0015]    [0015]FIG. 2 is a top view of a printed circuit board of the LED lighting strip;  
         [0016]    [0016]FIG. 3 is a schematic diagram of the LED lighting strip connected by external switches to a source of direct current;  
         [0017]    [0017]FIG. 4 is a schematic diagram of an alternative embodiment of the LED lighting strip connected by switches to a source of alternating current; and  
         [0018]    [0018]FIG. 5 is a schematic diagram of another embodiment of the LED lighting strip for use with alternating current. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0019]    With initial reference to FIG. 1, a strip-type lighting assembly  10  includes a housing  12  in the form of a U-shaped channel which supports longitudinal edges of a printed circuit board  14 . The circuit board  14  has three longitudinally extending rows  15 ,  16  and  17  of light emitting diodes (LED&#39;s)  18 . In order to provide a relatively compact lighting assembly  10 , the LED&#39;s  18  in the outer two rows  15  and  17  are located side by side along the length of the lighting assembly, as seen in FIG. 2. The adjacent LED&#39;s in each of the outer rows  15  and  17  are spaced apart so that an LED of the second, or middle, row  16  nest longitudinally between those adjacent LED&#39;s in the outer rows  15  and  17 . Thus, the printed circuit board has only two LED&#39;s abreast of each other, making the lighting assembly  10  relatively thin.  
         [0020]    A first electrical connector  20  is coupled by a cable  22  to a conductive pattern at one end of the circuit board  14  and a second electrical connector  24  is coupled by another electrical cable  26  to the conductive pattern at the other end of the printed circuit board. The two connectors  20  and  24  are of opposite gender so that a plurality of lighting assemblies  10  can be connected together in a daisy chain manner. That is, the first connector  20  of another lighting assembly  10  can be connected to the second connector  24  of the assembly shown in FIG. 1. Thus a plurality of lighting assemblies  10  may be wired end to end along the interior of an aircraft cabin, for example.  
         [0021]    With reference to the electrical schematic diagram of FIG. 3, the LED&#39;s in each row  15 - 17  are connected to the conductive pattern on the printed circuit board  14  wherein each row forms a separate circuit branch so that each LED row is individually controllable. The LED&#39;s  18  in each row are further divided into three groups, each forming a separate sub-branch of the respective row circuit branch, for example sub-branches  31 ,  32  and  33  of the first row  15 . Each sub-branch  31 - 33  comprises an equal number of LED&#39;s  18  connected in series with a current limiting resistor  28 . The sub-branches  31 - 33  for the first row  15  are connected in parallel between a first terminal  34  of the first connector  20  and a ground terminal  36  of that connector. The LED&#39;s in the second, or middle, row  16  are grouped into sub-branches having a similar electrical configuration and those groups, or sub-branches, are connected in parallel between a second terminal  35  of the first connector  20  and the ground terminal  36 . Similarly, the sub-branches of the third row  17  are connected in parallel between a third terminal  37  of the first connector  20  and the ground terminal  36 .  
         [0022]    The second connector  24  has four terminals  41 ,  42 ,  43  and  44  which are directly connected to the four terminals  34 ,  35 ,  36  and  37 , respectively, of the first connector  20 . Therefore, when a plurality of light assemblies  10  are connected in a daisy chain manner, each light assembly is connected in parallel to the source of DC voltage, as will be described.  
         [0023]    The lighting assembly  10  is illustrated, in FIG. 3, connected to a control circuit  40  which governs which of the rows  15 - 17  of LED&#39;s are illuminated at any given time. Although the control circuit  40  is shown connected to the first connector  20 , it alternatively could be connected to the second connector  24 . Terminals  34  and  37  for the outer two rows  15  and  17  of LED&#39;s  18  are connected together to one contact of a first switch  46  that has another contact connected to a source of positive voltage V+. A second electrical switch  48  couples the source of positive voltage V+ to the second terminal  35  of the second row  16  of LED&#39;s within lighting assembly  10 . The ground terminal  36  is connected to the ground connection for the vehicle or for the power supply that furnishes the positive voltage V+.  
         [0024]    This interconnection of the rows of LED&#39;s enables the lighting assembly  10  to produce three different light intensities for illuminating the interior of a vehicle. For the maximum illumination, both switches  46  and  48  are closed to apply electric current to all three rows  15 - 17  so that all of the LED&#39;s are illuminated. A second intensity level of 66% of the maximum illumination intensity can be achieved by closing only the first electrical switch  46  and opening the second electrical switch  48 . In this case, electrical current is applied to only the outer first and third rows  15  and  17 , so that the LED&#39;s in only two rows are energized. A third still dimmer illumination level can be accomplished by closing only the second switch  48  and opening the first switch  46 , which applies electric current to only the middle second row  16  of LED&#39;s. In this latter mode, only one of the three rows of LED&#39;s  18  is active thus producing illumination at 33% of the maximum illumination intensity. Obviously, by opening both switches  46  and  48 , the entire light assembly  10  can be turned off.  
         [0025]    A greater number of illumination levels can be made available by providing addition rows of light emitting diodes in the lighting assembly. In that case, the control circuit  40  would have more switches to enable selection of a larger number of combinations of active and inactive rows. For example, adding a fourth row to the lighting assembly provides four different illumination levels.  
         [0026]    The lighting assembly  10  can have substantially the same number of LED&#39;s in order to produce the same maximum light level as previous LED strips which were controlled by a dimming power supply. Because dimming is accomplished by using only a pair of switches, the weight and space of the control circuit  40  is considerably less than that of prior dimmable regulated power supplies. Thus, there is a significant advantage of the present lighting assembly in vehicles, such as aircraft, where weight and space are a significant concern.  
         [0027]    There is a current trend in aircraft electrical systems away from the use of direct current toward alternating current. For example, more recently developed aircraft utilize 400 Hz alternating current for cabin lighting. FIG. 4 illustrates the connection of the rows of LED&#39;s in a lighting assembly  50  which can be utilized in such alternating current systems. The LED&#39;s in each row  51 ,  52  and  53  are grouped into an even number of sub-branches, such as the pair of sub-branches  58  and  59  for the first row  15 . The sub-branches, or groups,  58  and  59  are connected in parallel between a first terminal  54  and a common terminal  57 . Half of the sub-branches in the first row have LED&#39;s poled in one direction between terminals  54  and  57 , and the LED&#39;s in the other half of the sub-branches in the first row  15  are poled in the opposite direction. In other words half of the sub-branches are poled in an inverse parallel manner to the other half of the sub-branches in a given row. Thus, when alternating current is applied across terminals  54  and  57 , half of the LED&#39;s in the first row  15  conduct, and thus illuminate, during each half cycle of the alternating current. The same is true with respect to the second and third rows  52  and  53 . The sub-branches of the second row  16  are connected in parallel between a second electrical terminal  55  and the common terminal  57 , while the sub-branches for the third row  17  are connected in parallel between the third electrical terminal  56  and the common terminal  57 .  
         [0028]    The second connector  24  of a lighting assembly has terminals  61 ,  62 ,  63  and  64  which are respectively directly connected to terminals  54 ,  55 ,  56  and  57  of the first connector  20 .  
         [0029]    This lighting assembly  50  is coupled to a control circuit  60  which is similar to the control circuit  40  in FIG. 3. Specifically, the first and third terminals  54  and  56  for the outer, first and third rows  51  and  53  of LED&#39;s are connected to one contact of a first electrical switch  66  which has another contact connected to a first power terminal  65 . The second terminal  55  for the second row of LED&#39;s  52  is coupled by a second electrical switch  68  to the first power terminal  65 . The common terminal  57  for the light assembly  50  is connected to a second power terminal  67 .  
         [0030]    In operation alternating current from a source is applied across the first and second power terminals  65  and  67 . By closing both electrical switches  66  and  68 , alternating current is applied to all three rows  51 - 53  and the lighting assembly  50  is illuminated to its full intensity. Because of the relatively high frequency (e.g. 400 Hz) employed in aircraft lighting systems, occupants of the cabin will not perceive any flicker in the light from the LED&#39;s produced by the alternating current, even though only half of the LED&#39;s are illuminated at any given instant because of the alternating current. The reduced illumination can be compensated for by increasing the number of LED&#39;s per inch in the lighting assembly or utilizing LED&#39;s with greater light output.  
         [0031]    To dim the lighting assembly  50 , the first switch  66  is closed to activate only the first and third rows  51  and  53  of LED&#39;s, thus producing illumination at a level equal to 66% of the full illumination level. A lower light level, i.e. 33% of full illumination, only the second electrical switch  68  is closed which applied electricity to only the LED&#39;s in the second row  52 .  
         [0032]    [0032]FIG. 5 illustrates another lighting assembly  70  for use with an alternating current source. This lighting assembly has terminals  54 ,  55 ,  56  and  57  which correspond to the like numbered terminals in FIG. 4 for connection to the control circuit  60 . However, the lighting assembly  70  incorporates full-wave rectifier bridges which enable all the LED&#39;s in an activated row to illuminate during both half cycles of the alternating current. The lighting assembly comprises three LED rows  71 ,  72  and  73 . Each row comprises a plurality of sub-branches, such as sub-branches  74 ,  75  and  76  for the first row  71 . The first row  71  has a full-wave bridge rectifier  80  formed by diodes  81 ,  82 ,  83  and  84  and having a pair of nodes connected to the first terminal  54  and the common terminal  57 . The bridge  80  has another pair of nodes across which the three sub-branches  74 - 76  are connected and parallel. The other two rows  72  and  73  have similar circuit configurations with additional full-wave bridge rectifiers  86  and  88 . Alternatively, some of the light emitting diodes of a row may be utilized in the bridge rectifiers.  
         [0033]    The foregoing description was primarily directed to a preferred embodiment of the invention. Although some attention was given to various alternatives within the scope of the invention, it is anticipated that one skilled in the art will likely realize additional alternatives that are now apparent from disclosure of embodiments of the invention. For example, although light emitting diodes are used in the preferred embodiment other types of light emitters could be used. Accordingly, the scope of the invention should be determined from the following claims and not limited by the above disclosure.