Abstract:
A lamp that can be used in a refrigerated or cold environment where an overall light output measured on a target plane is not significantly reduced due to condensation or fog includes a housing including a translucent cover, an LED disposed in the housing, and an anti-fog film. The LED is disposed in the housing with relation to the translucent cover such that light from the LED passes through the cover. The anti-fog film is disposed on at least one of the surfaces of the translucent cover.

Description:
BACKGROUND 
   Commercial refrigerated display cases are typically illuminated using lamps located inside the display case. When a consumer opens a door of the refrigerated display case, warmer more humid air located outside the display case flows into the display case, which contains cooler less humid air. Condensation and fog can accumulate on the lens or translucent cover of the lamp as the warmer more humid air cools inside the display case. Until the condensation evaporates from the lens, a reduction in the overall light output measured on the products displayed in the refrigerated display case results. 
   At present, most commercial refrigerated display cases are illuminated using fluorescent lamps. Fluorescent tubes radiate heat as power is delivered to the lamp to illuminate the lamp. Since the fluorescent tubes are cylindrical, the heat radiates in all directions around the tube. The heat that is radiated toward the lens of the fluorescent lamp warms the lens. The warm lens can prevent fog or condensation from forming on the lens because the moisture quickly dissipates into the air of the refrigerated display case. 
   More recently, light emitting diode (LED) lamps have been employed to illuminate the inside of refrigerated display cases. LED lamps are preferred because they consume less power (watts) than their fluorescent counterparts, which results in an energy savings. Since less power is being delivered to the LED lamp, as compared to a fluorescent lamp, there is less heat generated by the lamp to warm the lens (or translucent cover) that covers the LEDs. Moreover, as more efficient LEDs have been developed and the systems have been improved to direct the light toward more useful areas of the display case, the amount of power that is delivered to the LED lamp is further reduced. 
   In addition to consuming less power, lamps that employ LEDs do not dissipate very much heat via radiation. Instead, LED lamps found in refrigerated display cases conduct heat from the non-light emitting side of the LED into a heat sink, a large portion of which is spaced from the lens or translucent cover. Accordingly, it is difficult to use the heat generated by the LEDs to dissipate any fog or condensation that forms on the lens or translucent cover of the LED lamp. 
   Additionally, LED lamps that are used to illuminate refrigerated display cases are also only moderately sealed. In other words, the housing of the lamp assembly allows for the ingress of air and water into the housing, which can result in condensation forming on the inner (light entering) surface of the lens or translucent cover for the LED lamp. 
   BRIEF DESCRIPTION 
   To overcome the fogging and condensation problems associated with LED lamps in cool environments, a lamp that can be used in a cool environment where an overall light output measured on a target plane is not significantly reduced due to condensation or fog includes anti-fog material disposed on at least one of the surfaces of the translucent cover of the lamp. 
   For example, a refrigerated display case includes a refrigerated enclosure, a door, and a lamp assembly. The enclosure includes a door opening, and the door attaches to the enclosure and covers the door opening for providing access to inside the enclosure. The lamp assembly connects to the enclosure for illuminating products stored within the enclosure. The lamp assembly includes a plurality of LEDs, a heat sink in thermal communication with the LEDs, a cover connected to the heat sink, and an anti-fog material in or on the cover. The plurality of LEDs conduct heat into the heat sink. The cover is disposed in relation to the LEDs so that light emitted from the LEDs passes through the cover. Providing the anti-fog material lessens the likelihood of fog or condensation forming on the translucent cover, which would lessen the overall light output measured on the products stored in the enclosure. 
   A method for manufacturing a lamp for use in a refrigerated environment includes placing an LED in a housing and attaching a cover made from sheet stock to the housing at a location so that light emitted from the LED passes through the cover. The sheet stock in this example has already been coated with an anti-fog material. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a front elevation view of a refrigerated display case that can be illuminated by the lamp disclosed in  FIGS. 2 and 3 . 
       FIG. 2  is a cross-sectional view of a lamp. 
       FIG. 3  is a perspective view of the lamp. 
   

   DETAILED DESCRIPTION 
   With reference to  FIG. 1 , a typical refrigerated case  2  has doors  4  mounted to a front portion of the case each covering a door opening. The doors mount to the frame members via hinges  6 . The doors include glass panels so that products inside the case are easily viewed without having to open the door. Mullions  8  provide door stops and points of attachment for the doors and hinges. The refrigerated enclosure  2  described can be a free-standing enclosure or a built-in enclosure. Furthermore, other refrigerated enclosures may include a different configuration, for example a refrigerated enclosure may not even include doors. The lighting systems described below can also be used with those types of refrigerated enclosures, as well as in a multitude of other cool applications. 
   With reference to  FIG. 2 , a lamp  10  for use in a cool environment, for example a refrigerated enclosure, includes a housing  12  and an LED  14  disposed in the housing. The housing includes a translucent cover  16 , which can also be a lens. In the depicted embodiment, the translucent cover  16  attaches to a heat sink  18  which also forms a part of the housing. The LED  14  is disposed in the housing with relation to the translucent cover  16  such that light from the LED passes through the cover onto products that are displayed in a refrigerated display case. The light may or may not be reflected by an optic or reflector prior to passing through the cover  16 . In the embodiment shown in the figures an optic is provided; however, an optic is not required. 
   The lamp  10  is generally elongated and paralleliped in configuration. The lamp without the anti-fog material is more fully described in U.S. application No. 60/889,458, which is incorporated by reference in its entirety herein. 
   In addition to the housing  12  and the LEDs  14 , the lamp  10  also includes a printed circuit board (“PCB”)  22  and the optic  24 , mentioned above. The LEDs  14  mount to the PCB  22  and the PCB is in electrical communication with a power source (not shown) for supplying power to the LEDs. The PCB is an FR4 two-sided printed circuit board having thermal vias. Circuitry is provided on the PCB in a manner that is known in the art. Alternatively, the PCB can be made from other materials such as metal clad or a metal core PCB. 
   The LEDs  14  are staggered on opposite sides of a central axis of the PCB  22  moving along the PCB and the direction parallel to the central axis. The LEDs  14  are driven by an external power supply that is connected to the PCB  22  in a known manner. The PCB  22  is held against the heat sink  18  by the optic  24 . The PCB  22  is held in a channel  26  formed in the heat sink  18 . From the LEDs  14  is heat conducted through the non-emitting side (lower) side of the LED  14  into the PCB  22 , which conducts the heat into the heat sink  18 . Very little heat is transmitted toward the translucent cover  16 , especially as compared to a fluorescent lamp. 
   The lamp  10  can be easily altered so as not to include a PCB. For example, electricity can be delivered to the LEDs via a flex circuit, wires, a circuit ribbon or another known carrier of electricity. In such an instance and where the lamp includes a heat sink, the LEDs can be in thermal communication with the heat sink. 
   The translucent cover  16  is made from polyethylene tetraphthlate glycol (PETG) or polycarbonate (PC) flat sheet stock. The PETG or PC sheet stock is flatter and clearer than existing extruded lenses that are made to include the curve that is shown in  FIG. 1 . The extruded curved lenses are being used presently on LED lamps in cool environments. A clearer sheet stock translucent cover allows more light to escape the lamp  10  as compared to the extruded curved lens. Nevertheless, the translucent cover  16  can be molded, sheet stock, extruded or produced by another manufacturing process that is common to produce translucent covers and/or lenses. As such, the translucent cover can be made to have lensing capabilities. 
   Because the translucent cover  16  is made of a flat sheet stock material, the flat sheet stock is bent prior to insertion into retaining grooves  32  that are formed in the heat sink  18 . Contact between the translucent cover  16  and the heat sink  18  is limited to the longitudinal edges of the translucent cover  16  that are retained in the channels  32  formed in the heat sink. A majority of the heat sink  18  is spaced from the translucent cover  16 . As such, a void  34  is formed in the housing  12  generally between the translucent cover  16  and the heat sink  18 . The air in the void insulates the heat in the heat sink from the central part of the lens, which can allow for the buildup of condensation and/or fog. Since a majority of the heat generated by the LED  14  is conducted into the heat sink  18 , and more particularly into a lower base  36  (the horizontal section in  FIG. 2 , which includes portion in contact with PCB  22 ) of the heat sink  18 , the translucent cover  16  is generally cooler and typically nearer the temperature of the air inside the refrigerated display case. When a consumer opens a door of the refrigerated display case, warmer more humid air located outside the display case flows into the display case and can collect on the cover  16 . 
   An anti-fog film, which can also be referred to as an anti-film coating, can be disposed on at least one of the surfaces of the translucent cover  16 . In the depicted embodiment, the anti-fog film is disposed on a light receiving surface  42  and a light emitting surface  44  of the translucent cover. The anti-fog film can be a two-sided polycarbonate film such as Lexan™ HP92AF film available from the General Electric Co. Other types of anti-fog films can also be used, for example the super hydrophilic coatings described in U.S. Published Patent Application No. 2007/0104922 A1, which is incorporated by reference in its entirety herein. Anti-fog films that exhibit similar properties to those shown in the table below can be good candidates for the anti-fog film. 
   
     
       
             
           
         
             
                 
             
           
           
             
               
                 
                           
                   
                       
                       
                   
                 
               
             
             
                 
             
           
        
       
     
   
   In the depicted embodiment, both the light receiving surface  42  and the light emitting surface  44  are coated with the anti-fog film. The anti-fog coating, or anti-fog film, can be applied using a typical spray coating process or a typical die coating process, each of which are well known in the art. This is the case because the housing  12  is only moderately sealed. The housing includes end covers  46  (only one shown) that attach to the ends of both the translucent cover  16  and the heat sink  18 . The connections between the end pieces, the cover and the heat sink allow for the ingress of air and water into the void  34 . Accordingly, condensation can form on the light receiving surface  42  of the translucent cover  16 . 
   A lamp that is useful for illuminating products found in a refrigerated display case has been described with particularity. The lamp is also useful in other cool environments. The lamp  10  can take many other configurations other than the specific embodiment disclosed. For example, the lamp can include a circular shaped or another shaped heat sink. The translucent cover can also take another configuration. The invention is not to be limited to only the embodiments that are described above. Instead, the invention is broadly defined by the appended claims and the equivalents thereof.