Patent Publication Number: US-8523382-B1

Title: Fluorescent lamp fixture and method of dissipating heat from same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not Applicable. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a fluorescent lamp fixture for mounting a ballast and at least one fluorescent lamp. Fluorescent lamp fixtures are used in a variety of settings including residential, commercial, and industrial buildings. The fluorescent lamps mounted in such fixtures provide light in an energy efficient manner. In general, fluorescent lamps are gas-discharged lamps that use electricity to excite mercury atoms in a gas-filled tube. The excited mercury atoms emit short-wave ultraviolet light, which in turn causes a phosphor coating on the lamp to fluoresce thereby producing visible light. Fluorescent lamp fixtures often initially cost more than incandescent lamp fixtures because fluorescent lamp fixtures require a ballast. The ballast is used to regulate the current flowing through the lamp. Without a ballast to control the current, the fluorescent lamp will blow out. The ballast can also provide the striking voltage required to light the lamp. The life of a ballast is affected by heat. If the ballast is exposed to high temperatures for an extended period of time, it will degrade. Some fluorescent light fixtures known in the art provide a shield or other insulating material to isolate the ballast away from the heat emitted from the fluorescent lamp. Ballasts are typically rated for use at a maximum case temperature of 85° C.-90° C. 
     At one time it was standard practice to construct a fluorescent lamp fixture housing out of metal. It was also known that heat dissipation was promoted by connecting the ballast directly to the metal housing. In recent years, housings molded from a resinous material have become popular and offer cost advantages, weight savings, and durability. The practice of mounting the ballast directly to the housing was discontinued with the molded housings because the heat from the ballast could deform the resinous material and jeopardize the integrity of the connection between the ballast and the housing. Instead, the standard practice with molded housings has been to mount the ballast spaced from the housing so that there is an air space between the two. Surprisingly, with the present invention the use of a metal strip inserted into a groove in the housing and used to mount the ballast to the housing has been found to offer several advantages. 
     First, by mounting the ballast directly to the metal strip, heat dissipation is promoted—resulting in a lower temperature within the housing when compared to the prior art construction where the ballast is mounted spaced from the housing. 
     Second, the metal strip, which is sandwiched between the ballast and the housing, precludes damage to the molded housing from the heat of the ballast. 
     Third, use of the metal strip provides a secure attachment point for the ballast so that in the event of excessive heat, such as upon ballast failure, the connector for the ballast remains structurally intact and precludes failure at the attachment point, which would not be the case if the ballast was affixed directly to the molded housing. 
     Fourth, the use of the metal strip facilitates attachment of the ballast without t drilling holes in the housing which is labor intensive and could negatively impact the structural integrity of the housing. 
     Fifth, the utilization of the metal strip provides for an unlimited number of positions along the length of the housing where the ballast may be mounted, which is not possible when holes are drilled in the housing or predrilled holes are utilized. 
     BRIEF SUMMARY OF THE INVENTION 
     The fixture of the invention comprises a molded housing having a top and sides and is designed for use with a ballast and a fluorescent lamp. The top of the housing defines a groove that extends along a major portion of the length of the housing. The groove presents three sides and an opening. The fluorescent lamp fixture also comprises a hat-shaped metal strip having a protrusion and two flanges. The protrusion has three surfaces, each of which is in contact with a side of the groove. The flanges extend outside of the groove and contact the top of the housing. The metal strip secures the ballast in direct contact with the flange, whereby heat from the ballast is transferred to the metal strip and dissipated from the housing during use. 
     In a preferred embodiment, the strip protrusion comprises an outer wall and a pair of inner walls. The inner walls are positioned relative to the outer wall so as to define a chamber within the protrusion. In this embodiment, a fastener is slidably held by the inner walls of the metal strip such that a portion of the fastener is retained within the chamber and the fastener can slide along the length of the strip. 
     Additional aspects of the invention, together with the advantages and novel features appurtenant thereto, will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned from the practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of the preferred embodiment of the fluorescent lamp fixture when viewed from the top. 
         FIG. 2  is a perspective view of the preferred embodiment of the fluorescent lamp fixture when viewed from the bottom. 
         FIG. 3  is a perspective view of the housing of the preferred embodiment of the fluorescent lamp fixture when viewed from the bottom. 
         FIG. 4  is a detailed bottom view of the housing of the preferred embodiment of the fluorescent lamp fixture. 
         FIG. 5  is a cross-sectional view of the preferred embodiment of the fluorescent lamp fixture taken along line  5  as shown in  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENT 
     With reference to  FIG. 1 , the fluorescent lamp fixture  10  is shown. Fixture  10  comprises a housing  12  molded from a resinous material and having a top  14  and sides  16 . Housing  12  is coupled with lens  18  using clamps  20  mounted on housing sides  16 . Clamp  20  is shown in  FIG. 1  and similar clamps (not shown) are provided at intervals around housing  12 . Housing  12  also includes a number of tabs  22 , which are used to hold brackets (not shown) that mount fixture  10  to a surface such as a ceiling. With reference to  FIG. 2 , lens  18  is shown coupled with housing  12 . Lens  18  is made from a transparent or translucent material through which visible light from a fluorescent lamp may pass. Lens  18  has been removed in  FIG. 3  to show additional details of housing  12 . 
     As shown in  FIGS. 1 and 3 , housing top  14  includes a raised portion defining a groove  24 . In the preferred embodiment, groove  24  has three sides at approximately right angles to one another. Groove  24  extends above the top surface of housing top  14  and along a major portion of the length of housing top  14 . As the term is used throughout the specification and claims, “major portion” means more than 50% of the total length of housing top  14 . A hat-shaped metal strip  26  fits partially within groove  24  as shown in  FIG. 3 . Strip  26  is made of a heat conductive material, which is preferably metal and most preferably aluminum. With reference to  FIG. 3 , a ballast  28  is shown mounted to strip  26  using a fastener  30 . A second fastener  30  (not shown) secures the opposite end of ballast  28 . 
     With reference to  FIG. 4 , a detailed view of the bottom of housing  12  is shown. As previously explained, strip  26  is hat shaped; it has a protrusion  37  and two flanges  36   a  and  36   b . Protrusion  37  (shown in  FIG. 5  and described below) is secured within groove  24 . Flanges  36   a  and  36   b  extend outside of groove  24  and are in contact with housing top  14 . Ballast  28  is mounted directly to flanges  36   a  and  36   b  using fasteners  30 . In this position, at least one surface of ballast  28  is in direct contact with at least one surface of strip  26 . 
     With reference to  FIG. 5 , a cross-section of housing  12  and metal strip  26  is shown. Protrusion  37  extends at a right angle relative to flanges  36   a  and  36   b  and presents three flat surfaces at right angles to one another such that each of the three surfaces is in contact with a side of groove  24 . Flanges  36   a  and  36   b  extend outside and on either side of groove  24 . As shown in  FIG. 5 , strip  26  is fixed to the sides of groove  24  and housing top  14  using an adhesive  38 . In the preferred embodiment, metal strip  26  has an outer wall  32  and a pair of inner walls  34   a  and  34   b . As described above, outer wall  32  is in contact with the sides of groove  24 . Inner walls  34   a  and  34   b  are positioned relative to outer wall  32  such that outer wall  32  and inner walls  34   a  and  34   b  define a chamber  40  within protrusion  37 . Inner walls  34   a  and  34   b  form rails over which fastener  30  rides while a portion of fastener  30  is retained in chamber  40 . In the preferred embodiment, fastener  30  is a carriage bolt having a head with a width that is greater than the space between inner walls  34   a  and  34   b . In this manner, fastener  30  can slide along the length of strip  26  to accommodate ballasts having varying lengths and mount ballasts in various positions along strip  26 . As shown in  FIGS. 4 and 5 , ballast  28  is mounted in direct contact with flanges  36   a  and  36   b  using fasteners  30 . 
     During use, ballast  28  generates heat. The heat generated by the ballast, in combination with heat generated by the fluorescent lamps mounted in the fixture, creates an environment where the life of ballast  28  is adversely affected. Thus, dissipation of heat is of utmost importance. In the present invention, heat is conducted away from ballast  28  by metal strip  26  due to the direct contact between ballast  28  and metal strip  26 . The surfaces of metal strip  26  in contact with housing top  14  then allow heat to dissipate out of housing  12 . By dissipating the heat from the fluorescent lamp fixture in this manner, the life of ballast  28  is extended. 
     The utilization of metal strip  26  for mounting ballast  28  provides a secure attachment structure that is not jeopardized in the event of a sharp rise in temperature, which may result from ballast failure. Even if sufficient heat is generated to soften the resinous material from which the housing is molded, the metal strip spreads the weight of the ballast over a relatively large area, and there is metal-to-metal contact at the point of connection. The configuration of strip  26  also offers the advantage of being able to mount the ballast anywhere along the length of the strip by simply sliding fasteners  30  to the desired location. This is accomplished without the need for drilling or molding holes into the housing. Moreover, the hat-shaped metal strip increases the surface area from which the heat from the ballast can dissipate by having protrusion  37  in contact with more than one side of groove  24 . This construction is highly effective in dissipating heat from the fixture. 
     The term “hat shaped” used in this application is intended to encompass all of the above and any other configurations where there are at least two sides in contact with the sides of a corresponding shaped groove and at least one flange extending away from the groove and in contact with the top of the housing. Although a hat-shaped strip having a three-sided protrusion as shown in  FIG. 5  is preferred, protrusion  37  may (in cross section) alternatively have two surfaces and be triangle shaped, have more than three surfaces and be polyhedron shaped, or have a curved surface such that it is round or oblong shaped. A serpentine configuration will provide additional surface area and may also be used. In these alternative embodiments, a housing having a groove presenting a shape that corresponds with the shape of the protrusion and permits contact between the surfaces of the protrusion and the sides of the groove is used to maximize the surface area from which heat may dissipate. In addition, although strip  26  having two continuous flanges is preferred as it maximizes the direct contact with the ballast, strip  26  may have a single flange or a segmented flange. A strip having either of these alternative constructions would require less material than a strip with two continuous flanges, which may result in cost or weight savings. 
     Although only a single ballast is shown in  FIG. 3 , multiple ballasts may be used within a single fluorescent lamp fixture. Strip  26  can accommodate any number fasteners used to secure the desired number of ballasts. In the preferred embodiment shown in  FIG. 4 , additional fasteners may be added to the fixture by inserting the head of the fastener into groove  24  and sliding it towards strip  26  until the fastener head engages inner walls  34   a  and  34   b  within protrusion  37 . Other fasteners known in the art, including hooks, clamps, and screws may alternatively be used to secure each ballast to strip  26 . 
     While specific embodiments have been shown and discussed, various modifications may of course be made, and the invention is not limited to the specific forms or arrangement of parts and steps described herein, except insofar as such limitations are included in the following claims. Further, it will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims.