Abstract:
A warehouse dock light includes a lamp assembly which is provided with a plurality of LEDs arranged in such a fashion as to collectively provide sufficient light for illumination of an area. The LEDs are arranged in two columns with each column having both LEDs with narrow angle and wide angle lens, and with each column being angled so as to project outwardly from a central axis. Heat from the LEDs is dissipated through bi-metal boards to an extruded aluminum heat sink, and air is blown through the ribs of the heat sink by a fan. A heat sensor is provided with electronic circuitry to responsively turn on the fan and/or turn off the LEDs at predetermined temperature thresholds.

Description:
TECHNICAL FIELD 
     The present invention relates to a dock light and, more particularly, to a dock light with a plurality of LEDs for cooperatively projecting light into the interior of a truck. 
     BACKGROUND OF THE INVENTION 
     The use of dock lights on the loading platform of a warehouse for the purpose of illuminating the interior of a truck backed up to the loading platform is well known. Typically, the base of the light is mounted to a wall on the inside of the warehouse to protect the dock light from the elements when not in use, but it includes an extendible linkage for extending the light through the door of a truck so that it can illuminate the interior of the truck. 
     Such an extendible dock light is disclosed in U.S. Pat. No. 5,709,458 wherein a single halogen lamp is included for obtaining the desired illumination. One disadvantage to the use of halogen lamps is that they are relatively sensitive to damage from impact and can be made inoperable if the surrounding lamp assembly is hit by a door, for example. Further, because of the relative large size of the halogen lamp, the profile of the lamp assembly is relatively large and therefore more likely to be hit by an object. 
     Another disadvantage to the use of halogen lamps is that, although they use less energy than an incandescent light, they still use a considerable amount of energy to light them. Further, their life is relatively short (i.e. in the range of 2,000 to 5,000 hours). 
     SUMMARY OF THE INVENTION 
     In accordance with one aspect of the invention, a dock light is provided with a plurality of LEDs which, in combination, provide the desired illumination when projected into the interior of a truck. 
     In accordance with another aspect of the invention, the LEDs are mounted in two columns to cooperatively provide a mix of desired projection angles. 
     By yet another aspect of the invention, the two columns are each angled at an angle of 5° outwardly from a central axis to provide the desired divergence of light. 
     By another aspect of the invention, each column includes a plurality of high output LEDs with selective lenses, with one LED having a narrow angle lens and the remaining LEDs having a relatively wide angle lens. 
     In accordance with another aspect of the invention, each of the columns is mounted on a circuit board with the LEDs being connected in series to thereby maintain constant current, and with each having a zener diode connected thereacross to allow continued operation of the remaining LEDs if one should burn out. 
     In accordance with another aspect of the invention, a heat sensor is mounted on one board and has two set points one to turn on the fan and another to turn off the LEDs. 
     In the drawings as hereinafter described, a preferred embodiment is depicted; however, various other modifications and alternate constructions can be made thereto without departing from the spirit and scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a dock light assembly in accordance with the present invention. 
         FIG. 2  is a perspective view of the lamp assembly portion thereof. 
         FIG. 3  is an exploded view thereof. 
         FIG. 4  is an end view of the lamp assembly. 
         FIG. 5  is a schematic illustration of the electrical circuitry in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The dock light is shown in  FIG. 1  to include a housing  11  with an interconnected tube  12  leading to a lamp assembly  13 . The housing  11  includes flanges  14  for attachment to the inner wall of a warehouse in such a position that the flexible tube  12  can be extended through a warehouse door opening and into the rear door of a truck which is backed up to the dock for loading or unloading. The lamp assembly  13  is intended for illuminating the inside of the truck during the loading/unloading process. 
     The housing  11  includes electrical circuitry for connection to a power source. It also includes a fan for drawing air in through the louvers  16 , with the airflow then passing down through the flexible tube  12  to the lamp assembly  13  for purposes of cooling the lamp assembly  13 . The structure and function of both the housing  11  and the flexible tube  12  is substantially the same as that described in U.S. Pat. No. 5,709,458, assigned to the assignee of the present invention and incorporated herein by reference. 
     Referring now to  FIG. 2 , the lamp assembly  13  is shown to include a reducer  17  having at its one end a small cylinder  18  for attachment to the tube  12  and at its other end a larger cylinder  19  for attachment to a heat sink  21  which is formed in a partial cylinder as shown. Mounted within the heat sink  21  are two columns  22  and  23  of light emitting diodes (LEDs)  24 . An end plate  26  is secured at the other end of the lamp assembly  13 . 
     The details of the various components of the lamp assembly  13  can be better seen by reference to  FIGS. 3 and 4 . As will be seen, the reducer  17 , the heat sink  21  and the end plate  26  are interconnected by way of a core member  27  which includes a shaft  28  and a transversely extending side connector  29  fastened at its upper end. The side connector  29  has upstanding side flanges  31  and  32  which are secured to the reducer  17  by rivets  33 . The shaft  28  extends downwardly through a core opening  34  of the heat sink  21 , through an opening  36  in the end plate  26 , with the assembly then being fastened in place by a fastener  37  threadably engaging the lower end of the shaft  28 . 
     The heat sink  21  is a unitary member formed by way of an aluminum extrusion. It includes an outer member  38 , a cross member  39  and a plurality of ribs  41  interconnecting the outer member to the cross member as shown. Extending from the interconnection of the outer member  38  and the cross member  39  are a pair of arms  42  and  43  with respective slots  44  and  46  for frictionally receiving the edges of a flexible, polycarbonate cover  47  therein. The cover  47  allows the light to pass therethrough but protects the LEDs  24  from exposure to the elements. The cover  47  may have an anti-reflective coating and can be flexed into place so the light will pass through the cover at close to right angles to minimize reflections. 
     The two columns  22  and  23  of LEDs are mounted on metal core boards with a dielectric layer (aluminum and ceramic)  48  and  49  by conventional techniques and methods. The bi-metal boards  48  and  49  are, in turn, mounted to the side surfaces  51  and  52  of the cross member  39 . The interface between the boards  48  and  49  and the side surfaces  51  and  52 , respectively, need to be such that the heat transfer characteristics of the interface are maximized. One approach is to use a double sided, heat transfer thermal tape as the interface. Another approach is to use a heat curing epoxy as the interface. Still another approach would to be use a mechanical fastening means with a heat transfer compound being applied between the boards  48  and  49  and their respective side surfaces  51  and  52 . 
     It will be seen that the structure of the cross member  39  is such that the side surfaces  51  and  52  are angled at an angle Θ from the plane P as shown by the dashed lines. The installed boards  48  and  49  and their attached LED columns  22  and  23  are, of course, also angled in the same manner, such that their projections are at an angle Θ from a central axis C/L. The purpose is to widen the overall illumination effect such that the entire width of the trailer, including the side opposite the dock light assembly, is properly illuminated. Although a wider lens may be applied to each of the LEDs to obtain a wider spread illumination, the resulting diffusion and loss of light will not bring about satisfactory results. 
     The angle of the diversion between the side surfaces  51  and  52  can be selected to bring about the desired results for any particular application. However, the applicants have found that an angle Θ in the range of 4-6°, or 5°, in particular, has been to be found quite suitable. 
     The particular type of LED can also be selected to meet the needs of a particular application. A type of LED that the applicants have found to be suitable for each of the fourteen LEDs in columns  22  and  23  is a Cree kit XREWHT-LI-0000-007E4 to XREWHT-LI-0000-008F5 or XREWHT-LI-0000-008E4 with a minimum output of 83 lumens at 0.350 mA. Color is BINS  4 A to  4 D 4300 to 4750° K. Although the fourteen LEDs are all identical, there respective lens have been varied to obtain the desired illumination within the trailer. That is, in each of the columns, the top three and the bottom three LEDs have a relatively wide angle lens (lens ledil CR square medium order code CRS-M+/−14°). The middle LED in each column, however, is a relatively narrow angle lens (lens ledil CR square smooth spot order code CRS-SS+7°). The respective 14° and 7° designations are actually half angles meaning that, a designated 14° divergence means that the light is diverted 14° on each side of the axial direction. 
     Considering now the electrical circuitry, reference is made to  FIG. 5 . 
     The two circuit boards  48  and  49  are shown within the dotted lines and include the respective LED columns  22  and  23 . Each of the LEDs  24  in those two columns is connected in series with the other LEDs in that column and includes a zener diode  54  connected in parallel therewith. In this way, if one LED goes open, then the rest of the LEDs will not go out because the diode will jump the open condition. In this regard, the LEDs are connected in series so as to obtain a constant current therethrough, a condition which would not exist if they were connected in parallel. 
     The circuit boards  48  and  49  are individually powered by respective power sources  56  and  57 , which are 25 watt supplies with a constant current at 700 milliamps. The output voltage is 18-36 volts DC. Power from the power source  56  flows first to the receptacle  58 , then to the receptacle  59  to the header  61  of the circuit board  48 . Power to the circuit board  49  passes from the power source  57  to the receptacle  58  and then to the header  62  of the circuit board  49 . 
     Power is provided to the fan  63  through a series-connected circuit breaker  64  and relay contacts  66 . The relay contacts close when the relay coil  67  is energized byway of receptacle  58  in a manner to be described more fully hereinafter. 
     It is recognized that the LEDs  24  generate a reasonable amount of heat which must be dissipated in order to ensure proper operation. The providing of the heat sink  21  to conduct the flow of heat away from the LEDs by way of the bi-metal boards  48  and  49  is one feature that assists in the cooling of the LEDs  24 . Other features which are included for this purpose are referred to as the thermal management apparatus as shown at  68  in  FIG. 5 . It is included on only one of the circuit boards  48  and  49  since it assumed that the conditions surrounding the circuit board column  22  is substantially the same as those conditions surrounding the LED column  23 . 
     Within the thermal management apparatus  68  is included a temperature sensor  69  which senses the temperature of the circuit board  49 . As the temperature of the circuit board  49  rises, there are two temperature thresholds that can be progressively reached, triggering first the turning on of the fan  63  and secondly the turning off of the LEDs. The operations which occur during these steps will now be described. 
     The two thresholds are set by the three resistors  71 ,  72  and  73 , and comparators  74  and  76  are used to implement the response when the thresholds are reached. 
     If the comparator  76  determines that the heat sink temperature rises above a first threshold set by resistors  72  and  73  and the voltage reference  77 , then the comparator output goes high to turn on the transistor  78 , which in turn turns on the PNP transistor  79 , which in turn turns on the NPN transistor  81  to thereby activate the relay, close the relay switch  66  and turn on the fan  63 . If the temperature then drops below the first threshold level, the operation is reversed and the fan is turned off. 
     If the comparator  74  determines that the circuit board temperature is above a second threshold level it will turn on the transistor  82  which, in turn, will turn off the mosfet  83  to thereby remove power from the LED columns  22  and  23 . Again, if the temperature of the circuit board  49  drops below the second threshold level, then the mosfet  83  will again be turned on and power will be resumed to the LEDs. 
     While the present invention has been particularly shown and described with reference to the preferred mode as illustrated in the drawing, it will be understood by one skilled in the art that various changes in detail may be effected therein without departing from the spirit and scope of the invention as defined by the claims. For example, although the LEDs have been shown to be square shaped, they could be round as well.