Abstract:
A door frame hingeably mounted to a lensed fluorescent troffer lighting fixture and carrying a prismatic lens cover, the door frame also integrally provides a light trap function. Structural components of the door frame have fastening elements formed integrally therewith for attachment of said components together without the use of separate fastening elements. The door frame includes low profile latching structure which allows ready opening of the door frame for relamping or other maintenance functions, hinge elements acting not only to hold the door frame to the light fixture but also to hold the door frame in a fully open position. The door frame further acts to impart rigidity to the lighting fixture when in a closed position.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates generally to lensed fluorescent troffer lighting fixtures and particularly to a combination door frame and light trap which mounts the lens cover to the fixture, the door frame being readily opened to gain access into the interior of the fixture. 
     2. Description of the Prior Art 
     Fluorescent lighting has long been commonly employed in commercial, institution and industrial applications due primarily to energy efficiencies inherent in the operation of fluorescent fixtures and the relatively low fixture cost associated with the need for large numbers of such fixtures in such applications. Fluorescent lighting fixtures suitable for such applications must also be of pleasing appearance and must provide a desired quality of light including adequate light for task lighting applications inter alia. Fluorescent lighting in the form of lensed fluorescent troffer lighting fixtures have long provided acceptable lighting solutions in office environments and the like, such applications requiring literally thousands of such lighting fixtures mounted by suspended ceiling grid arrangements and the like to provide desirable lighting performance and desirable aesthetics. Lensed fluorescent troffer lighting fixtures can also be surface mounted in those applications requiring such mounting and can provide excellent performance in such applications. In recessed applications, however, the space within which lighting fixtures are to be mounted has become increasingly smaller, these applications typically being referred to as reduced plenum installations, it being necessary to provide a fluorescent troffer lighting fixture of reduced volume and particularly of reduced depth to allow ready mounting within reduced plenums while retaining desirable performance characteristics such as minimal lamp image with desirable light outputs. Within this context, the need to provide fixtures which can be manufactured at minimum cost and high performance has increased. Such fixtures must be capable of manufacture with low material costs, low labor costs and must be capable of shipment to a job site with cost efficiencies. Once at a job site, such low-cost, high performance fixtures must be capable of rapid installation while continuing to provide ever-increasing energy efficiencies. Lensed fluorescent troffer lighting fixtures must therefore provide a marriage of aesthetic and performance considerations at minimum manufacturing and shipping costs. When in use, both grid-type and specification premium lensed fluorescent troffer lighting fixtures are seen by occupants of a space being illuminated primarily as prismatic lens covers surrounded by a reveal which in essence comprises portions of a door frame which mounts the lens cover in a desired relationship to lamping contained within the fixtures. As is commonly practiced in the industry, the door frame is structured to provide a minimum reveal consistent with appropriate mounting of the door frame to remaining portions of a fixture. Due to aesthetic considerations, latching structure which allows the door frame to be opened and thus to gain access into the interior of the fixture must be unobtrusive and preferably be of a low profile which is not perceived by an occupant of the space being illuminated. Lensed fluorescent troffer lighting fixtures also must be designed to obscure lamp images, such obscuration being a function not only of a prismatic lens cover but also of the fixture itself. Use of T8 lamping and relatively low profile electronic ballasts facilitate the design of lensed troffers of lesser height dimensions and which are capable of mounting within reduced plenum situations. Fixtures of this type must be provided with door frames of relatively low profile and which are configured to avoid the use of separate fastening elements in the manufacture of the door frame. Further, light leaks about interfaces between the housings of lensed troffer fixtures and door frames must be prevented in order to provide a desirable appearance. A door frame for a lensed troffer fixture must also be readily openable by manipulation of latches which are available for manual manipulation from beneath the fixture while being visually unobtrusive. On opening of a door frame for a lensed troffer fixture, it is further desirable for the door frame carrying the lens cover to remain in place and attached to remaining portions of the fixture during the time when access to the interior of the fixture is necessary such as for relamping or other maintenance. 
     An example of a lensed fluorescent troffer lighting fixture is seen in U.S. Pat. No. 3,045,577 to Lazerson. Lazerson describes a door frame which carries a lens cover. Lazerson does not provide structural components comprising a door frame which can be assembled together by means of fastening elements integrally formed with the structural components. In U.S. Pat. No. 3,988,609, Lewin describes lensed troffer lighting fixture including a lighting panel or prismatic lens cover described as exhibiting substantial efficiencies, the fixture itself apart from the lens cover not being improved relative to the prior art. 
     In U.S. Pat. No. 5,823,663, Bell et al describe a fluorescent troffer lighting fixture and particularly a parabolic troffer formed of a housing assembly comprising structural components capable of snap-fit assembly. Kaiser et al, in U.S. Pat. No. 5,806,972, describe a light trap and louver mounting arrangement useful with the housing assembly disclosed in the Bell et al patent. The parabolic troffers disclosed by Bell et al and Kaiser et al relate to the present lensed fluorescent troffers only in the similar concept of providing structure capable of snap-fit assembly without the need for separate fasteners, the particular structures of the present lensed troffers including the present door frame and light trap combination differing from corresponding structures as disclosed in the Kaiser et al and Bell et al patents. 
     The invention thus provides a door frame for a lensed fluorescent troffer lighting fixture wherein the door frame is capable of snap-fit assembly of structural body elements without the need for separate fasteners. The structural body elements of the invention which form the present door frame and light trap combination are provided with fastening elements which are integral with the body elements, thereby yielding savings in material costs as well as in assembly costs while providing a door frame and light trap combination having excellent mechanical performance as well as being aesthetically pleasing and which can be mounted to fixture housing assemblies of varying description including housing assemblies of lensed troffer lighting fixtures formed with a minimum depth to allow installation in reduced plenum environments while retaining desirable performance characteristics including reduction of lamp image and production of desired illumination levels. The door frame of the invention provides necessary functions such as the mounting of a prismatic lens cover to a housing assembly of a lensed troffer fixture while also providing a light trap function, the present door frame being readily manufactured at low cost while being capable of pleasing appearance when in use. 
     SUMMARY OF THE INVENTION 
     The present invention provides a door frame and light trap combination comprising a portion of a lensed troffer lighting fixture, the door frame being capable of assembly from component parts amenable to automated fabrication. The component parts of the door frame and light trap combination are assembled together without the use of separate fasteners, the resulting assembly being characterized by simplicity and economy of construction. The door frame further imparts rigidity to a lensed troffer fixture when in an assembled relationship with a housing assembly of a lensed troffer according to the invention. The rigidity of the lensed troffer fixture having the present door frame and light trap combination mounted thereto allows excellent lighting performance due to retention of component parts of the fixture in place relative to each other. The ability of the component parts of the door frame and light trap combination to retain a precise fitting of said parts allows rough handling of the structure during installation and retains necessary performance after installation. 
     The door frame and light trap combination of the invention mounts a lens cover such as a prismatic light panel in place relative to remaining portions of a lensed troffer fixture, component parts of the door frame including cooperating fastening elements formed integrally with the component parts being capable of inordinately rapid and ready assembly of said component parts to form the door frame and light trap combination. The integral fastening elements formed on said component parts are configured to allow snap-fastening of the component parts together in a manner which assures a locking together of the component parts which is reliable and precise. The door frame and light trap combination configured according to the invention is therefore capable of rapid and easy assembly without the use of separate fastening elements. The door frame and light trap combination of the invention is further provided with latching elements which allow opening and closure of the door frame by simple manipulation of the latch elements and particularly through simple finger pressure on a visible portion of the latch elements. Release of the door frame by the latch elements allows pivoting of the door frame and light trap combination about one edge thereof due to the provision of hinging elements which releaseably connect the door frame and lens cover carried thereby to remaining portions of the fixture, the hinge elements further allowing continued attachment of the door frame to the fixture at full pivoting extension of the door frame relative to remaining portions of the fixture without the need for manual intervention of a user to maintain the door frame and lens cover carried thereby in place when access to the interior of the fixture is necessary such as for relamping or other maintenance. 
     Accordingly, it is an object of the invention to provide a door frame and light trap combination for a lighting fixture such as a lensed troffer lighting fixture and which is capable of superior mechanical efficiency even though being rapidly assembled from component parts which can be fabricated using standard automated fabrication techniques. 
     It is a further object of the invention to provide a door frame and light trap combination for a lighting fixture and particularly a lensed fluorescent troffer lighting fixture which can be assembled through the expedient of fastening elements formed integrally with component parts of the door frame, the door frame thus being capable of rapid and economical assembly from component parts which can be fabricated using standard automated fabrication techniques. 
     It is a further object of the invention to provide a door frame and light trap combination particularly intended for use as a part of a lensed fluorescent troffer lighting fixture and wherein the door frame can be rapidly and efficiently assembled without the need for separate fasteners. 
     Further objects and advantages of the invention will become more readily apparent in light of the following detailed description of the preferred embodiments. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view from above and to one end of a lighting fixture provided with a door frame and light trap assembly configured according to the invention; 
     FIG. 2 is a perspective view of the lighting fixture of FIG. 1 taken from the other side thereof; 
     FIG. 3 is a detail perspective view of one corner of the lighting fixture of FIG. 2; 
     FIG. 4 is a detail perspective view of a corner of the lighting fixture as seen in FIG. 1; 
     FIG. 5 is a perspective view of the lighting fixture of FIG. 2 taken from beneath and to one side of the fixture; 
     FIG. 6 is a bottom view of the lighting fixture of FIGS. 1 through 5; 
     FIG. 7 is an exploded assembly view of the lighting fixture of FIGS. 1 through 6 with a lens cover being removed for ease of illustration; 
     FIG. 8 is an exploded assembly view of the door frame and light trap assembly configured according to the invention and being shown in spaced relation to a lens cover; 
     FIG. 9 is an elevational view of the lighting fixture of FIG. 1 with an end plate removed in order to view internal portions of the fixture; 
     FIGS. 10A through 10F are perspective, end elevational and detail perspective views of side structural bars configured according to the invention; 
     FIGS. 11A through 11D are perspective, side elevational and end elevational views of end structural bars configured according to the invention; 
     FIG. 12 is a perspective view of a corner connection element or “biscuit” configured according to the invention; 
     FIGS. 13,  14  and  15  are perspective views illustrating assembly of the structural bars of the invention together in combination with the biscuit of FIG. 12; 
     FIGS. 16A through 16E are related perspective and detail views of a latching element which allows rapid latching and unlatching of the door frame and light trap assembly to remaining portions of a lensed troffer lighting fixture; 
     FIGS. 17A through 17E are perspective views illustrating assembly of the latching element to one of the side structural bars; 
     FIG. 18 is a detail perspective view of a corner of a lighting fixture configured according to the invention and illustrating operation of the latching element; 
     FIG. 19 is a perspective view of the lighting fixture of the invention showing the door frame and light trap assembly being fully unlatched from the remaining portions of the fixture; 
     FIGS. 20A through 20C are perspective views of a hinge element configured according to the invention; 
     FIG. 21 is a detail perspective view of the hinge element mounted to one of the side structural bars; 
     FIG. 22 is a perspective view illustrating the door frame and light trap assembly in a fully open position relative to remaining portions of a lighting fixture; 
     FIGS. 23A through 23D are related perspective and detail views of a lens cover retaining element; and, 
     FIGS. 24A through 24E are related perspective and detail views of an alternative latch element. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference is made to copending U.S. patent application Ser. No. 09/358,376, entitled “Lensed Troffer Lighting Fixture”, assigned to the present assignee and filed of even date, the disclosure of said patent application being incorporated hereinto by reference. Reference is also made to copending U.S. patent application Ser. No. 09/298,298, entitled “Inverted Apex Prismatic Lens”, assigned to the present assignee and filed Apr. 23, 1999, the disclosure of said patent application being incorporated hereinto by reference. 
     Referring now to the drawings and particularly to FIGS. 1 through 9, a lighting fixture configured according to the invention is seen generally at  10 , the fixture  10  as shown being a lensed fluorescent troffer lighting fixture intended to mount elongated fluorescent lamps as will be described herein. The fixture  10  comprises a housing assembly  12  and a door frame and light trap assembly  14 , referred to hereinafter as the door frame  14 , the housing assembly  12  being described in detail in copending U.S. patent application Ser. No. 09/358,376, entitled “Lensed Troffer Lighting Fixture” mentioned above. The door frame  14  carries prismatic lens cover  16  and maintains said lens cover  16  in an appropriate spatial relationship relative to lamping carried within the housing assembly  12 . The housing assembly  12  comprises inter alia a housing channel  18  and end plates  20  respectively connected to each end of the housing channel  18  and mounted thereto by fastening elements integrally formed on said housing channel  18  and on said end plates  20 , the end plates  20  being connected securely to the housing channel  18  without the need for separate fastening elements as is described in the aforesaid copending patent application Ser. No. 09/358,376. 
     As particularly seen in FIGS. 2 and 3, the door frame  14  is mounted to the housing assembly  12  with portions of one each of the latching elements  96  extending from shaped slots  88  formed in the housing assembly  12 . In FIG. 3, each of the latching elements  96  is seen to be located at one of the respective ends of the fixture  10 . FIG. 16 provides more detailed views of the latch  96 . While a portion of a side structural bar  21  can be seen in FIG.  3  through the slot  88 , the remaining portions of the door frame  14  cannot be seen in FIGS. 2 and 3 since the housing assembly  12  hides the door frame  14  in these figures. As will be described hereinafter, a portion of the latching element  96  intended to be manually manipulated to release the door frame  14  from the housing assembly  12  extends outwardly of the fixture  10  through a lower portion of the slot  88  so as to be accessible for its intended use. 
     FIGS. 1 and 4 show the fixture  10  from the other side thereof, the other side of the fixture  10  being that side which is hinged by means of hinge elements  94  which are connected to side structural bar  23  as will be described hereinafter. As is best seen in FIG. 4, a portion of the hinge element  94  extends through a slot  88  formed in the housing assembly  12 . In essence, the door frame  14  is not visible in FIGS. 1 and 4. The slots  88  formed in the housing channel  18  on the side thereof on which the hinge elements  94  are mounted are essentially identical with the slots  88  formed along the opposite side edge of the channel  18  for mounting the latching elements  96 , one each of the slots  88  being located near each end of the housing assembly  12  along each side thereof. 
     FIGS. 5 and 6 illustrate an assembly of the door frame  14  to the housing assembly  12  from a position beneath the fixture, the prismatic lens cover  16  being visible and shown to be carried by the door frame  14 . The door frame  14  is seen to fit flushly within a peripheral recess  25  defined by structural portions of the housing channel  18  and of the end plates  20  as is described herein. The ledges  72  and  74  disposed along each side edge of the housing channel  18  and flanges  148  and  152  of each of the ends plates  20  as seen in copending Ser. No. 09/358,376, filed of even date, define the recess  25 , the recess  25  being dimensioned to receive the door frame  14  flushly thereinto. Receipt of the door frame  14  into the recess  25  coupled with structure to be described hereinafter which is integral with the side structural bars  21 ,  23  and end structural bars  27 ,  29  and in combination with the light trap elements  174  effectively block light from leaking through the interface between the door frame  14  and the housing assembly  12  thus causing a light trap to be formed. The hinge elements  94  are located along the edge of the fixture  10  along which the side structural bar  23  is disposed. However, the hinge elements  94  are not visible in FIGS. 5 and 6. Structure specifically described in detail in copending patent application Ser. No. 09/358,376, filed of even date as aforesaid and as identified above is also to be seen in FIGS. 5 and 6 to form a border about visible peripheral portions of the door frame  14 , this structure being identified in said copending patent application and herein as flanges  76  formed integrally with the housing channel  18  and flanges  152  formed integrally one each with each one of the end plates  20 . Lowermost surfaces of the flanges  76 ,  152  can be seen from below the fixture  10  in an installed situation. The flanges  76  and  152  are disposed about the periphery of the recess  25  into which the door frame  14  is flushly received. As is seen in FIGS. 5 and 6, the door frame  14  and the lens cover  16  carried thereby form an aesthetically pleasing interface with the housing assembly  12  by virtue of flushly fitting within the recess  25  as aforesaid and having borders defined by the flanges  76 ,  152  respectively formed integrally with the housing channel  18  and the end plates  20 . 
     FIGS. 7 and 8 provide exploded assembly views, the illustration of FIG. 7 providing an assembly view of the entire lighting fixture  10  with the exception of the lens cover  16 . FIG. 8 provides an exploded assembly view of the door frame  14  with the inclusion of the lens cover  16 . Various structural elements of the fixture  10  and particularly of the housing assembly  12  are seen with reference to numerals which are employed in copending patent application Ser. No. 09/358,376, filed of even date and referred to hereinabove. This numbering of structural elements not necessarily described explicitly in this patent application is intended for ease of reconciling the disclosure of this patent application in view of the disclosure of the aforesaid copending patent application, thereby to facilitate understanding of both applications. As seen in FIGS. 7 and 8, the side structural bars  21 ,  23  connect to the end structural bars  27 ,  29  to form a frame within which the lens cover  16  is securely carried, the details of the assembly of the bars to each other being provided hereinafter. 
     Referring now to FIG. 9, the fixture  10  is seen from an end elevational view with one of the end plates  20  being removed so that it is possible to see interior structure of the housing assembly  12 , such as the sockets  50  which mount lamps such as the lamp  52  which is seen in FIG.  7 . For ease of illustration, the lamping is typically not shown in the various figures so that the structure of the fixture  10  can be better understood. It is to be understood as is described in the copending patent application referred to hereinabove that the fixture  10  is intended to utilize T 8  fluorescent lamps of the elongated tubular type, these lamps such as the lamp  52  being mounted conventionally by the sockets  50 . 
     Referring now to FIGS. 10A through 10F, the structures of the side structural bars  21  and  23  are shown, the structures of said bars  21 ,  23  being essentially identical except for the provision of certain openings formed therein. In the side structural bar  21 , a rectangular opening  31  is formed near each end of the bar  21  for receiving one each of the latching elements  96  as will be described hereinafter. In the side structural bar  23 , a single circular aperture  33  is formed one each near each end of the bar  23  in order to mount one each of the hinge elements  94 . Openings  139  are formed one each above the apertures  33  in flanges  37  of the bars  23 . The remaining structure of the bars  21 ,  23  is identical and description of one will suffice for a description of the other. Considering the side structural bar  21  with particular reference to FIG. 10C, an elongated central body  35  is substantially planar in conformation and is the portion of the bar  21  having at least a portion of the rectangular openings  31  formed therein. In a similar manner, the elongated central body  35  of the bar  23  has the circular apertures  33  formed therein. The flanges  37  are elongately formed along one side edge of the central body  35  of each of the bars  21 ,  33 , the flanges  37  being substantially planar and being bent at right angles to said bodies  35 . The rectangular openings  31  extend into that bend in the bar  21  between the body  35  and the flange  37 . The flange  37  extends essentially the full length of the edge of the body  35  of the bars  21 ,  33  and terminates at ends  39  thereof Along the opposite side edge of the central body  35  of each of the bars  21 ,  23 , a U-shaped flange  41  is formed with a first leg  43  taking the form of an elongated, planar piece of material lying in a plane which is substantially parallel to the plane of the flange  37 . Yoke  45  of the U-shaped flange  41  recurves to join with second leg  47  of said flange  41 , the second leg  47  extending outwardly of the plane within which the central body  35  lies and recurving outwardly thereof to form a U-shaped outer flange  51 . The U-shaped outer flange  51  has a first leg  53  which is an extension of the second leg  47  of the U-shaped flange  41 , yoke  55  of the U-shaped outer flange  51  recurving inwardly to form a second leg  57  which, like the other legs  43 ,  47  and  53 , comprise elongated planar structural elements. It is to be understood that the side structural bars  21  and  23  can be formed from a single piece of material by conventional operations. It is further to be understood that wall surfaces of the leg  43  and the leg  47  interiorly of the U-shaped flange  41  are spaced apart as are wall surfaces of the legs  53  and  57  of the U-shaped outer flange  51 . Each end of the structural bars  21 ,  23  are essentially identical in structure to the other, the flanges  41  and  51  being cut off at each end of said bars at a mitered angle essentially identical to the angle of the mitered end  39  of the flange  37 . Each end of the central body  35  of each of the bars  21 ,  23  terminates in a substantially rectangular tab  59 . An elongated slot (not shown) formed substantially centrally of the juncture between the end of the body  35  and an inward side edge of the tab  59  can be formed in the bars  21 ,  23  to facilitate bending of the tab  59  relative to each of the bodies  35 . 
     Referring now to FIGS. 1A through 1D, the end structural bar  27  is shown. Since the end structural bar  29  is identical to the structure of the end structural bar  27 , only the bar  27  will be described herein. The bar  27  is formed of an elongated central body  63  which is planar in conformation and which bends along one side edge thereof at right angles to form an elongated flange  65  which extends essentially the full length of the side edge of the body  63 , ends of the flange  65  being mitered at  67 . At the other side edge of the body  63 , a U-shaped flange  69  extends therefrom and terminates at the outward end of leg  71  of said flange  69  in a U-shaped outer flange  73 , the cross-sectional shape of the end structural bars  27  and  29  being essentially identical to the cross-sectional shape of the side structural bars  21  and  23 . The ends of the U-shaped flanges  69  and  73  are also mitered as is the flange  65  as aforesaid. A locking tab  75  extends from each end of the body  63  and slots  61  are formed substantially centrally of the juncture between the end of the body  63  and the inward side edge of the tab  75 . The slots  61  facilitate bending of the tabs  75  and receive the tabs  59  for connection of the bars  27 ,  29  to the bars  21 ,  23 . 
     As is seen in FIG. 12, a corner reinforcement plate  77  is seen to comprise a planar body portion  79  of chevron shape, the plate  77  having a substantially  90 ° point at  81  with lateral legs  83  formed on each side of the plate  77 . The legs  83  are rounded at  85 . Punched-out apertures  78  formed in each leg  83  each retain pressure plates  89  bent within said apertures  78 . Free ends of the plates  89  extend outwardly of the apertures  78 . The plate  77  functions substantially in the manner of a “biscuit” such as is employed in woodworking. Essentially, the plate  77  acts to reinforce corner joints between the respective side structural bars  21 ,  23  and the end structural bars  27 ,  29 . 
     As is seen in FIGS. 13 through 15, assembly of the bars  21 ,  23  and  27 ,  29  together is shown in sequential steps to form the door frame  14  with a corner joint being shown at the corner seen in the figures. Each corner of the door frame  14  is so formed. In assembly, one of the lateral legs  83  of the corner reinforcement plate  77  is inserted into that space defined by inner wall surfaces of the flanges  41 ,  51  of the bar  21  or of the flanges  69 ,  73  of the bar  27  according to choice, the locking tab  75  of the side structural bar  21  (or  23 ) then being inserted into the slot  61  of the end structural bar  27  (or  29 ) with the other leg  83  of the corner reinforcement plate  77  then being received into the other of the yokes of said bars  21 ,  23  or of the bars  27 ,  29 . This assembly is seen in FIG. 14 to illustrate assembly of the plate  77  to the bars  21 ,  23  and the bars  27 ,  29 , thereby to form a strong corner joint  285 . Mitered portions of the bars  21 ,  23  and mitered ends  39  of the bars  27 ,  29  fit together as seen in the drawings. Assembly is completed by the bending of the locking tab  75  at right angles against an outer surface of the central body  35  of one of said bars  27 ,  29  and the bending of the tab  76  against outer surfaces of the central body  63  of each the bars  21 ,  23 . Each of the corner joints  285  are thus completed to substantially complete the door frame  14  with the exception of the assembly of the hinge elements  94  and the latching elements  96  thereto. 
     Referring now to FIGS. 16A through 16E, one of the latching elements  96  is shown in detail. Since the latching elements  96  are substantially identical to each other, a description of one of the latching elements  96  will suffice for a description of both. The latching element  96  is formed of a body member  289  which takes the form of a planar, rectangular plate from which lance  91  is stamped, the lance  91  extending from an outward face of the latching element  96 . The lance  91  is substantially triangular in conformation and provides a ramping function relative to portions of the channel  18  on assembly of the door frame  14  to said channel  18 , the lance  91  resting against opposing portions of the channel  18  on assembly of said door frame  14  thereto. The body member  89  bends at  93  to form an arcuate section which terminates in a U-shaped element  95  comprised of respective legs  97  and  99  which are spaced apart and angled relative to each other and which are further joined together by means of yoke  101 . As will be seen from description given hereinafter, the U-shaped element  95  is inserted into an appropriate opening in a portion of the door frame  14  with the yoke  101  being first inserted, the ability of the legs  97 ,  99  to be compressed and then spring apart facilitating attachment of the latching element  96  to the door frame  14 . The leg  99  terminates in a lip  121 . A lance  103  punched out of the leg  97  has a free end which “faces” toward the door frame  14  during assembly, a lance  105  formed in the leg  99  facing the opposite direction from the lance  103 . In essence, the lance  103  prevents the latching element from rotating in place. When properly connected to the door frame  14 , the lance  103  does not actually abut structure on the door frame  14 . The lance  105 , sloping “backwardly” from the door frame  14  when assembled as will be described hereinafter, acts to prevent the U-shaped element  95  from being pulled from its connection with the door frame  14  as will be described hereinafter. 
     At the opposite end of the body member  89 , the latching element  96  angles outwardly to form an extension element  123  which is dimensioned and formed simply to extend the lower portion of the latching element  96  from portions of the door frame  14  to allow clearance. The extension element  123  terminates in a plate  125  which extends at an angle from said plate  125  and substantially vertically when in use, the plate  127  doubling back upon itself at  127  and then angling inwardly to form actuation plate  129  which terminates with a lip  131 . As will be described hereinafter, the actuation plate  129  is visible to a user of the fixture  10  in a use environment whereby the actuation plate  129  can be engaged manually such as by a finger to exert pressure on the latching element  96  in order to unlatch said element  96  from engagement with the housing assembly  12  of the fixture  10 , thereby to open the door frame  14  so that the frame  14  can pivot about the hinge elements  94  located on the side structural bar  23  of the door frame  14  to allow access to the interior of the fixture  10 . It is to be understood that the latching element  96  is preferably formed of a metal such as stainless steel configured with an appropriate thickness to produce a spring-like function. In essence, the body member  89  and the arcuate portion of the latching element  96  connecting the body member  89  with the U-shaped element  95  as is shown at  93  functions to act in a spring-like manner, this spring-like portion of the latching element  96 , that is, the body member  89  essentially, extending through one of the slots  88  formed in the housing channel  18  as aforesaid. Accordingly, the latching element  96  can be manipulated in order to disconnect an upper surface of the actuation plate  129  from a notch formed in the U-shaped outer flange  51  of the side structural bar  21 , thereby to disengage the door frame  14  along one side of the fixture  10 . 
     As is seen in FIGS. 17A through 17E, the U-shaped element  95  is received into the opening  31  formed in the bar  21  at each end of said bar  21 , the U-shaped element  95  being compressed to allow receipt of substantially all of the U-shaped element  95  into said opening  31 . As is best seen in Figure lD, the lance  103  formed in the leg  97  of the U-shaped element  95  remains outwardly of the opening  31  due to extension of the opening throughout that curved portion of the bar  21  connecting angled body portions of said bar  21 . As indicated previously, the free end of the lance  103  does not abut edge portions of the opening  31  under normal circumstances but does function to prevent rotation of the latching element  96 . As the U-shaped element  95  is inserted into the opening  31  as indicated above, the actuation plate  129  fits beneath the flange  51  of the bar  21  while portions of the element  123  and the plate  125  are positioned immediately outwardly of notch  133  formed in the flange  51  of the bar  21 . The terminal lip  131  functions as a guide to prevent binding of any portion of the actuation plate  129  against edges of the notch  133 . On full assembly of the latching element  96  with the bar  21  as is seen in FIG. 17E, the lance  105  formed in the leg  99  functions to prevent the latching element  96  from being pulled outwardly from or disengaged from the opening  31 . It is to be noted that the lance  105  cannot be seen in FIG.  17 E. When fully assembled, it is to be seen that pressure exerted on the actuation plate  129  causes portions of the extension element  123  and of the plate  125  to move into the notch  133 , thereby unlatching the door frame  14  from the housing assembly  12 . It is noted that the lance  91  engages the channel  18 . 
     FIGS. 18 and 19 illustrate disengagement of the latching element  96  from the slot  88  formed in the housing assembly  12 . The latching elements  96  are seen to be completely disengaged from the housing assembly  12  so that the edge of the door frame  14  along which the bar  21  lies can be displaced downwardly to the position shown and can further be displaced through its full range of motion to the position shown in FIG. 22 wherein the hinge elements  94  retain the door frame  14  on the fixture  10  for access into the interior of the fixture  10  such as for relamping or other maintenance. Once maintenance is completed, the door frame and lens cover  16  retained by the door frame can then simply be pivoted back into position with the latching elements  96  releasably locking said door frame  14  to the housing assembly  12  by a simple fitting together of the component parts of said door frame  14  and of the housing assembly  12  as provided by the latching elements  96 . FIGS. 18 and 19 show the first stages of the pivoting of the door frame  14  from engagement with the housing assembly  12 , a full pivoting movement of the door frame  14  relative to the housing assembly  12  as contemplated by the invention resulting in the configuration seen in FIG.  22 . In FIG. 21 inter alia, it can further be seen that the U-shaped outer flanges  51  and  73  formed as integral portions of the side bars  21 ,  23 , and the end bars  27 ,  29  respectively extend over horizontal ledges  72  along each edge of the housing channel  18  and lateral flanges  152  of the end plates  20  respectively to form a light trapping function which function is substantially provided by integrally formed elements of the door frame  14  as aforesaid. 
     Referring now to FIGS. 20A through 20C, one of the hinge elements  94  is seen. Since the hinge elements  94  are substantially identical, a description of one of the elements will suffice for a description of both. The hinge element  94  is comprised of a base plate  107  which engages the central body  35  of the side structural bar  23 , the base plate  107  having an aperture  109  formed therein for receiving a rivet (not shown) or the like therethrough, the aperture  109  aligning with one of the apertures  33  formed at each end of the side structural bar  23  so that the rivet is received through both the aperture  109  and the aperture  33  to hold the base plate  107  to the bar  23 . The base plate  107  is further provided with depending legs  113  at either lateral end thereof, the legs  113  engaging inner wall surfaces of the flange  51  in order to provide increased stability. When only one rivet is utilized, the legs  113  act to prevent the base plate  107  from turning in place. A tongue element  115  extends from a lower edge of the base plate  107  outwardly of the bar  23 , the tongue element  115  being slightly bent at its juncture with the base plate  107  and having an arcuate distal end  117  which curves away from the plane of the tongue element  115  in a direction away from the base plate  107  to terminate in an elongated tab  119  which is rounded at both ends  121 . The length of the elongated tab  119  is dimensioned to fit within an enlarged rectangular portion  90  of the slot  88  so that the hinge element  94  can be connected to the housing assembly  12 , the width of the tongue element  115  fitting within a lower rectangular portion  92  of lesser length formed in the housing assembly  12  such that the tongue element  115  can be movably received within the rectangular portion  92  of the slot  88  but wherein the elongated tab  119 , having a length greater than the length of the rectangular portion  92  of the slot  88 , cannot be displaced therefrom, thereby allowing the hinge elements  94  to effectively serve a hinging function and to maintain the door frame  14  in place as is seen in FIG. 22 when the door fame  14  is pivoted to a maximum degree relative to the housing assembly  12  to allow access into the interior of the lighting fixture  10 . Centrally of the upper edge of the base plate  107  is formed a fastening element  135  having a U-shaped body portion terminating in a tab  137 . 
     Now considering FIG. 21, the hinge element  94  is seen to be mounted to the central body  35  of the side structural bar  23  and thus to be configured for insertion of the elongated tab  119  into a portion of the slot  88  as aforesaid configured to receive said elongated tab  119 , the hinge element  94  then being displaced within the slot  88  to cause the elongated tab  119  to be held by a portion of the slot  88  as aforesaid which is dimensioned to retain said tab  119  within the slot  88 . The tab  137  is received within the opening  139  and is positioned to engage the underside of the body portion  39  of the bar  23 , the U-shaped body portion of the fastening element  135  extending from the base plate  107  and through the opening  139  on assembly of the base plate  107  to the bar  23 . 
     FIG. 22 provides illustration indicated previously relative to full opening of the door frame  14  relative to the housing assembly  12 . FIG. 22 also illustrates a fixture  198  configured essentially identically to the fixture  10  previously illustrated with the exception that the housing assembly of the fixture  198  is of a reduced length. In particular, the fixture  198  of FIG. 22 illustrates a fixture which is substantially square in conformation with that side of the fixture  198  defined by the length of a housing channel being identical to the length of the end plate  20 . Illustration of the fixture  198  is provided simply to show that the invention can be configured other than in the form of a single fixture having one particular set of dimensions. 
     Considering now FIGS. 23A through 23D in concert with other figures such as FIG. 9, a lens cover retainer  200  is seen to function in a manner which positively holds the lens cover  16  in place within the door frame  14 . The retainer  200  comprises a base plate  201  having legs  203 ,  205  extending from opposite sides thereof, the legs being elongated and extending from the base plate  201  at angles. A locking tab  207  terminates a U-shaped element  209 , a portion of the element  209  joining to the base plate  201 . A disc-like projection  211  extends from an upper face of the base plate  201  to engage a circular opening (not shown) which is formed in a wall portion of the bars  27 ,  29  so that the retainer  200  can be conveniently held in place. The locking tab  207  in a similar sense can be received into a slot (not shown) formed in the bars  27 ,  29  or other portions of the door frame  14 , receipt of the tab  207  into a slot such as described acting to lock the retainer  200  in place. It is to be understood that it is not necessary to provide both the locking tab  207  and the projection  211  simultaneously. The angled or “splayed” legs  203 ,  205  of the retainer  200  extend outwardly from the base plate  201  to engage the lens cover  16  when the retainer  200  is joined to the door frame  14  as aforesaid. Engagement of distal end portions of the legs  203 ,  205  with the lens cover  16  functions to hold the lens cover  16  in place. In the event that the plastic forming the lens cover  16  is wavy, it is sometimes necessary to provide conventional clips (not shown) along sides of the lens cover  16  in order to prevent bowing of the lens cover  16 . 
     Referring now to FIGS. 24A through 24E, an alternative latching element  301  is seen, the latching element  301  being particularly configured so that it may be formed of a polymeric or “plastic” material. The latching element  301  has similarities to the latching element  96  including a substantially similar body member  303  which corresponds to the body member  89  of the latching element  96  as particularly seen in FIG. 16. A ramp  305  is formed within the body member  303  and corresponds functionally to the lance  91  described relative to the latching element  96 . Since the latching element  301  would be molded from a “plastic” material, the ramp  305  would be molded rather than stamped as is the case with the lance  91 . The body member  303  terminates at its upper end with a plate  307  from which an upper leg  309  of a U-shaped element extends, lower leg  313  being free to be displaced toward and away from the upper leg  309  since the lower leg  313  is not connected to the plate  307 . Notches  315  are formed in the plate  307  on either side of the body member  303  at the juncture of the body member  303  with the plate  307 . The body member  303  further terminates at its upper end in a centrally disposed connecting element  317  having a base  319  which is effectively formed integrally with a portion of the upper leg  309 , the connecting element  317  having a free end  321  which is discontinuous with the leg  309  to form a channel  323  between the free end  321  of the connecting element  317  and a facing surface of the leg  309 . The U-shaped element  311  is compressed and is capable of receipt within one of the openings  301  in the bar  21  in a manner similar to that described for the latching element  96 . However, portions of the body portion of the bar  21  adjacent an upper edge of the opening  31  would be received within the channel  323  to provide stability to the mounting of the latching element  301  to the bar  21 . 
     At the opposite end of the body member  303 , an extension element  325  and a plate  327  function similarly to the extension element  123  in the plate  125  of the latching element  96  as aforesaid. The plate  327  has molded thereto an actuation plate  329  which functions in a manner essentially identically to the function of the actuation plate  129  of the latching element  96  as described hereinabove. The latching element  301  can be employed in those situations where a plastic latching element would appear to be preferable. 
     The door frame  14  in assembled relationship with the housing assembly  12  acts to block light leakage from any reasonable line of sight at the juncture of the door frame  14  and the housing assembly  12 . The door frame  14  of the invention thereby exhibits multiple connection functions while also providing the function of a light trap per se. The element  174  described in the copending patent application filed of even date described hereinabove also facilitates the light trapping function. 
     It is to be understood that the invention can be configured other than as is described explicitly herein. Accordingly, while the invention has been described explicitly in reference to a preferred embodiment thereof, it is to be understood that the invention can be practiced other than as described with the scope of the invention being limited only by the scope of the appended claims.