Abstract:
An improved lensed fluorescent troffer lighting fixture intended for ceiling mounting and particularly for recessed mounting to a suspended ceiling grid within a shallow plenum, the embodiments of the fixture having dimensions, particularly depth-wise dimensions, which allow installation within the confines of reduced plenums while maintaining fixture quality and retaining desirable characteristics such as minimal lamp image. The present lensed troffers can be manufactured at a high assembly rate due to the ability to snap together on an assembly line the various components of the fixture without the use of separate fasteners. The lensed troffers of the invention are particularly configured for use with T 8  fluorescent lamping and low profile electronic ballast. The configurations of the several embodiments of the present lensed troffer are chosen to fit within a shipping box shaped in a manner to allow maximum stacking efficiency and to maximize the number of fixtures which can be shipped within conventional volumes encountered in available transport vehicles.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates generally to lensed fluorescent troffer lighting fixtures and particularly to a fixture housing having a reduced profile to allow installation within the reduced volume of shallow plenums commonly encountered in ceiling structures, the housing further being capable of rapid manufacture due to the secure fitting together of components of the housing without the need for separate fasteners. 
     2. Description of the Prior Art 
     Lensed fluorescent lighting fixtures are commonly employed in commercial, institutional and industrial applications due primarily to the energy efficiency of fluorescent fixtures generally coupled with relatively low fixture cost even in specification premium installations. Fluorescent lighting in the form of lensed fluorescent troffer lighting fixtures provides acceptable lighting solutions in office environments as well as in other task lighting applications. In such applications as in a commercial office building, literally thousands of fluorescent troffer lighting fixtures are mounted by suspended ceiling grid arrangements and provide desirable lighting performance and pleasing appearance. Lensed fluorescent troffer lighting fixtures can also be surface mounted while providing similar performance. 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 and yet retain desirable performance characteristics such as minimal lamp image with desirable light outputs. Within this context, the need has further increased in the industry to provide fixtures which can be manufactured at minimum cost yet exhibit exceptionally high performance. Such fixtures must be capable of manufacture with low material cost, low labor cost and must be shipped to a job site with maximum volumetric shipping efficiency. Once at a job site, such low-cost, high performance fixtures must be capable of rapid installation and also provide ever-increasing energy efficiencies while producing desired illumination levels. Lensed fluorescent troffer lighting fixtures must therefore provide a marriage of aesthetic and performance considerations at minimum manufacturing and shipping costs. Grid-type lensed fluorescent troffer lighting fixtures in the present marketplace must be as shallow as possible while still enabling lamping of the fixture while using a minimum of material and retaining the capability of being mounted within conventional grid arrangements including plenums of reduced volume and height. Specification premium lensed fluorescent troffer lighting fixtures such as are produced according to the present invention typically have a greater depth in order to retain desirable lamp image characteristics and are further provided with reflective internal structure capable of preventing light from being trapped behind lamping, thereby to provide maximum illumination efficiencies. In the several embodiments of the invention, deficiencies of the prior art are eliminated in part by use of fluorescent lamping having smaller diameter tubular elements, such as T 8  lamping, and relatively low profile electronic ballasts rather than more bulky conventional magnetic ballasts. Economies in manufacture occur according to the present invention through the use of smaller components to form smaller lighting fixtures which retain dimensions necessary for mounting to conventional suspended ceiling grid arrangements, etc. Still further, the structure of those components forming fixture body assemblies as an example is configured to avoid the use of separate fastening elements in the manufacture of such assemblies. Structural portions of present fixture body assemblies are provided with integral fastening elements which allow snap-fit assembly without the need for screws or the like which must be procured separately and separately brought to the assembly location. Fasteners such as screws and the like are also difficult to work with in assembly situations due to small size and the usual necessity for manual placement and manipulation of the fastener. In such situations, a tool is ordinarily required to secure the fastener to the structural elements of the fixture which must be joined together quickly and with precision. 
     An example of a lensed fluorescent troffer lighting fixture is seen in U.S. Pat. No. 3,045,577 to Lazerson. The Lazerson structure requires use of separate fasteners which limit production in an assembly line environment. The Lazerson structure is also not shaped to allow rapid and efficient mounting in reduced plenum environments and for maximization of fixture stacking once packaged which leads to maximizing of the number of fixtures which can be shipped in conventional transport vehicles. Lewin, in U.S. Pat. No. 3,988,609, describes a lensed troffer lighting fixture intended to be improved by greater efficiencies in a lighting panel or prismatic lens cover provided for the fixture, the fixture itself not being improved relative to the prior art. 
     Bell et al, in U.S. Pat. No. 5,823,663, describe a fluorescent troffer lighting fixture and particularly a parabolic troffer formed of a housing assembly 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 differing from corresponding structures as disclosed in the Kaiser et al and Bell et al patents. 
     The invention thus provides a lensed fluorescent troffer lighting fixture and particularly a lighting fixture housing assembly wherein the housing assembly 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 housing assembly 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 fixture housing assembly having excellent mechanical performance and which contributes to overall fixture lighting performance. The housing assembly of the present lensed troffer lighting fixture further enables production of a fixture having 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. These performance characteristics are obtained even though preferred lamping for the present fixtures comprises T 8  fluorescent lamps which have smaller diameters than commonly employed T 12  lamping. The advantages of the invention occur with the retention of traditional and necessary functions such as efficient mounting of a door frame carrying a prismatic lens cover and the like. 
     SUMMARY OF THE INVENTION 
     The present invention provides a lensed fluorescent troffer lighting fixture and particularly a fixture housing assembly capable of assembly from a minimum of component parts, assembly being particularly suited according to the structure of the component parts to automated fabrication. The housing assembly of the invention is not only structurally simple and readily fabricated on a conventional assembly line, the housing assembly is economical in use of materials and in the labor required for manufacture while being sized to efficiently fit within reduced plenums available in common ceiling structures. While sized to fit in conventional suspended ceiling grid arrangements and the like, the present fixture housing assembly has a substantially reduced depth-wise dimension which retains desirable characteristics such as minimum lamp image and efficient light output. The rugged construction of the present fixture housing assembly permits maintenance of desired body contours during handling and use after assembly, the ability of the housing assembly to assume and retain body contours including internal parabolic contours causing the lensed troffer fixture itself to exhibit excellent lighting performance. The strength of the housing assembly is occasioned by a rugged yet precise configuration of structural components which integrally carry fastening structure enabling the snap-fitting together of the structural components substantially without the use of separate fasteners. The fitting together of the structural components forming the present lensed troffer lighting fixture eliminates light leaks while minimizing shadows and bright spots. 
     The integral fastening elements provided according to the invention on the several structural components of the fixture housing assembly include cooperating fastening elements which permit inordinately rapid and ready assembly of the structural components to form the present housing assembly. The integral fastening elements of the present structural components are configured to allow snap-fastening of the structural components together in a manner which assures a locking together of said components which is reliable and precise, the operations involved in assembly of the fixture being amenable to automated fabrication. The very substantial structural integrity of the present housing assembly virtually eliminates accidental or inadvertent loss of structural integrity in an installation. The rugged structural integrity of the present housing assembly not only provides for safety in use of the lighting fixture but also provides economies of fabrication and assembly without sacrifice of fixture performance. 
     The housing assembly of the invention is configured to maximize the number of fixtures which can be stacked in shaped boxes, the dimensions thereof being chosen for facilitating shipping of a maximum number of fixtures within a given volume present in a transport vehicle. 
     Lighting performance, particularly for specification premium lensed fluorescent troffer fixtures according to the invention, is improved by use of high performance, diffusive paints coated onto reflective surfaces of the housing assembly. Further, rib-like elements can be provided between lamping and the paint-coated reflective surfaces to prevent light from being trapped behind lamping, various configurations being employed depending upon whether a given lighting fixture utilizes two, three or four lamps. 
     Lamping preferably used according to the invention takes the form of elongated fluorescent bulbs having a diameter of approximately one inch, such bulbs being generally referred to as T 8  fluorescent lamps. Such T 8  lamps are preferably used with electronic ballasts and particularly low profile electronic ballasts in order to facilitate reduction of fixture depth. In specification premium embodiments of the invention, the distance of lowermost portions of the lamping to upper surfaces of a prismatic cover using T 8  lamping as preferred according to the invention is the same distance as in prior art fixtures utilizing T 12  lamping. Fixtures so configured according to the invention retain desired perceptions of product quality while exhibiting necessary reductions of lamp image and producing desirable illumination levels. 
     Accordingly, it is an object of the invention to provide a lensed fluorescent troffer lighting fixture which is capable of high levels of lighting efficiency and which is characterized by superior mechanical construction even though the fixture is simply and ruggedly constructed using standard automated fabrication techniques. 
     It is another object of the invention to provide a lensed fluorescent troffer lighting fixture which can be assembled through the expedient of fastening elements formed integrally with structural components of a fixture housing assembly, the housing assembly thus being capable of rapid and economical assembly from structural components, the present fixture being capable of fabrication using standard automated fabrication techniques. 
     It is yet another object of the invention to provide a lensed fluorescent troffer lighting fixture sized to be mounted by suspended ceiling grid arrangements of conventional design and which have depth-wise dimensions which allow installation in reduced plenums. 
     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 
     FIGS. 1A and B are perspective views of the lighting fixture of the invention taken from a location above and toward ends thereof; 
     FIG. 2 is a perspective view of the lighting fixture of the invention taken from below and toward one end of the lighting fixture; 
     FIG. 3 is an elevational view taken from below the lighting fixture; 
     FIG. 4 is a plan view of the lighting fixture; 
     FIG. 5 is an exploded assembly view of the lighting fixture of FIGS. 1 through 4 with a prismatic lens cover removed in order to show the primary structural components of the fixture in a scale which is as large as possible; 
     FIG. 6 is an exploded assembly view of one end of the lighting fixture of the invention; 
     FIG. 7 is an end elevational view of the lighting fixture of the invention with an end plate removed so that interior portions of the fixture can be seen; 
     FIGS. 8A through 8F are perspective, plan, side elevational, end elevational and detail views of a housing channel forming a portion of a housing assembly of the invention; 
     FIGS. 9A through 9E are exterior perspective, interior perspective, plan, side elevational and end elevational views respectively of an end plate forming a portion of a housing assembly of the invention; 
     FIGS. 10A, B and C are detail perspective views illustrating the assembly of an end plate to a channel to form a housing assembly according to the invention; 
     FIG. 11 is a detail perspective view of a corner portion of one end of the lighting fixture of the invention; 
     FIG. 12 is a detail perspective view of a corner portion of an end of the invention taken from the other side of the lighting fixture relative to that side seen in FIG. 11; 
     FIG. 13 is a perspective view of a lighting fixture having differing length-wise dimensions relative to the lighting fixture of FIGS. 1 through 4 inter alia, the lighting fixture of FIG. 13 illustrating a door frame unlatched from a housing assembly of the invention, a prismatic lens cover normally carried by the door frame being removed for convenience of illustration; 
     FIG. 14 is a detail perspective view of the lighting fixture illustrating the door frame in an unlatched configuration relative to the housing assembly; 
     FIGS. 15A through 15D are side elevational, plan, perspective and end elevational views of a socket plate; 
     FIG. 16 is a perspective view of a housing assembly forming a part of the lighting fixture of FIG. 13 illustrating a cover channel in exploded relation to remaining portions of a housing assembly configured according to the invention; 
     FIG. 17 is a perspective view of the housing assembly of FIG. 13 illustrating the channel cover of FIG. 16 in place within the housing assembly; 
     FIG. 18 is a schematic illustrating the function of an indentation formed in the housing channel above one of the lamps; and, 
     FIGS. 19A through 19D are perspective, end elevational, side elevational and plan views of a light trap element mountable to corners of each end plate to minimize light leakage from the fixture. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Copending U.S. patent application Ser. No., 09/358,378, for “Door Frame for Lensed Troffer”, filed of even date and assigned to the present assignee, and copending U.S. patent application Ser. No. 09/298,298, entitled “Inverted Apex Prismatic Lens”, filed Apr. 23, 1999 and assigned to the present assignee, contain disclosures which are incorporated hereinto by reference. 
     Referring now to the drawings and particularly to FIGS. 1 through 4, a lensed fluorescent troffer lighting fixture is seen at  10  to be comprised of a housing assembly  12  and a door frame  14  which carries a prismatic lens cover  16 . The door frame  14  is hinged to the housing assembly  12  in a manner referred to hereinafter and described in detail in copending U.S. patent application Ser. No. 09/358,378, entitled “Door Frame for Lensed Troffer”, filed of even date and assigned to the present assignee, the disclosure of which is incorporated hereinto by reference as aforesaid. Further, the door frame  14  is latched to the housing assembly  12  in a manner referred to hereinafter and described in detail in said copending patent application. The lens cover  16  can take a variety of forms including conventional A- 12  and A- 19  patterns as well as the particular lens structures disclosed and claimed in copending U.S. patent application Ser. No. 09/298,298, entitled “Inverted Apex Prismatic Lens”, filed Apr. 23, 1999 and assigned to the present assignee, the disclosure of this patent application being incorporated hereinto by reference. 
     As can be seen in FIGS. 1 and 2 as well as FIGS. 5 and 6 inter alia, the housing assembly  12  is primarily formed of a housing channel  18  which is shown in detail in FIGS. 8A through 8D and two end plates  20 , one of which is shown in detail in FIGS. 9A through 9E. The housing channel  18  and the end plates  20  are also shown in FIGS. 5 and 6 inter alia. The manner in which the end plates  20  are connected to each end of the housing channel  18  will be described in detail hereinafter. 
     Referring first to FIGS. 8A through 8D, the housing channel  18  is seen to be preferably formed of a unitary piece of material, typically  22  gauge steel which is shaped and provided with cutouts to yield the housing channel  18 . The respective ends of the housing channel  18  are essentially identical to each other as are the respective sides and side edges of said housing channel  18 . The profile in section of the housing channel  18  is essentially identical throughout most of its length as is seen in FIG.  8 D. Various projections, cutouts and indentations inter alia alter the profile or cross-section of the channel  18  slightly from one end to the other. The housing channel  18  comprises a substantially planar upper body portion  22  which essentially forms the “top” of the lighting fixture  10 . Indentations  24  are formed at three spaced locations of the body portion  22  and extend along the length of the channel  18  to provide a strengthening effect as well as to function as reflectors to prevent light from being trapped above the lamp  52  as best illustrated in FIG.  18 . Depending on lamping, more or fewer of the indentations can be used. An access opening  26  is formed in the body portion  22  near one end of the channel  18 , this opening  26  allowing access into the interior of the lighting fixture  10  once installed. The opening  26  can be covered with a cover plate (not shown) as desired. Knockouts  28  are provided in the event that a wiring access or the like is necessary. Crimps  30  punched from the body portion  22  mount a ballast  32  in a conventional manner as can best be seen in FIG.  16 . The ballast  32  is conventionally mounted through the use of two of the crimps  30  and by the use of a single screw (not shown) received into one of the holes  34  formed in the body portion  22  and in alignment with the opening  26 , the knockouts  28  and the crimps  30 , these elements formed in the body portion  22  being covered by means of a generally U-shaped channel cover  36  as also seen in FIG.  16  and as seen in the fully covering position in FIG.  17 . The channel cover  36  is provided with tabs  38  which fit into spaced apart slots or hooded bosses  40  formed in the body portion  22 . 
     The upper body portion  22  of the housing channel  18  is further provided at each end with three shaped cutouts  42  spaced apart along each end of the channel  18 . The cutouts  42  have trapezoidally shaped inner portions which act as lead-ins for structure mating therewith and formed on the end plates  20 . Immediately inwardly of each of the cutouts  42  as seen in FIGS. 8 and 10 is formed a trapezoidally shaped indentation  44  each having a plate  45  formed therewith. The indentations  44  are stamped into the material forming the upper body portion  22 . Immediately inwardly of the outermost pair of the indentations  44  at each end of the channel  18  are formed slots  46  disposed transversely of the channel  18 , the cutouts  42 , the indentations  44  and the plates  45  facilitating mounting of one of the end plates  20  to each end of the channel  18  as will be described hereinafter relative to FIG.  10 A. 
     Each side portion of the housing channel  18  is essentially identical to the opposite side portion and thus description of one will suffice for description of both. The side portions of the housing channel  18  are essentially formed from the same planar piece of material as forms the upper body portion  22 , the planar piece of material so formed being shaped by conventional apparatus to form side sections  54 , each side section  54  being formed of three elongated planar portions  56 ,  58  and  60 . The planar portions  56 ,  58  and  60  are angled relative to each other in order to effectively provide the reflective equivalent of a parabolic curve in each of the side sections  54 . At the juncture of the planar portion  56  with the upper body portion  22  at each end of the channel  18 , a longitudinal slot  62  is formed, a total of four of the slots  62  being provided for a purpose to be described hereinafter. Substantially centrally of each end of the planar portion  58 , a shoulder  64  is notched into said planar portion  58 , thereby reducing the effective length of the planar portion  58  along lower portions thereof as well as the length of remaining portions of the planar portion  60 . A side ledge  66  is formed immediately outwardly of the planar portion  60 , each of the side ledges  66  having a longitudinal notch  68  formed at either end of the channel  18  for receiving one of wings  178  of light trap element  174  to hold said element  174  in place. The side ledge  66  essentially comprises a planar body element which substantially lies in a plane parallel to the plane of the upper body portion  22 . The side ledge  66  bends along its outer edge at essentially a 90° angle to form vertical ledge  70 , the ledge  70  then bending along its outer edge at an angle of substantially 90° to form an intermediate, substantially horizontal ledge  72  which also extends essentially the full length of the housing channel  18  with the exception of the widths of the shoulders  64 . At an outer edge of the ledge  72 , the structure is bent downwardly at an angle of substantially 90° to form intermediate vertical ledge  74 , the ledge  74  then bending outwardly at 90° to form terminal edge flange  76  which is preferably reversely bent over at its outer edge at  78  to strengthen the outer edge of the flange  76 . The ledges  72  and  74  from a portion of a recess into which the door frame  14  fits. The vertical ledge  70  has a shaped aperture  80  formed near each end thereof, the aperture  80  having a substantially vertical portion at  82  at the lowermost edge of the ledge  70 , the vertical portion  82  intersecting with an angled slot-like portion  84  which is rounded at its upwardly terminal end at  86 . The aperture  80  can best be seen in FIG.  8 E. Spaced inwardly from the shaped apertures  80  are slots  88  which are also formed in the vertical ledge  70 , the slots  88  being compound slots having an upper enlarged rectangular portion  90  and a lower rectangular portion  92  which communicates with the portion  90  substantially medially of one side of said portion  90  to form each one of the slots  88 . The slots  88  are best seen in FIG.  8 E. The slots  88  on one side of the housing assembly  12  receive hinge elements  94  which are seen in FIG. 5 as comprising portions of the door frame  14 , the hinge elements  94  being receivable within the two slots  88  formed along one side portion of the housing channel  18 . The other pair of slots  88  located on the opposite side portion of the housing channel  88  receive for operation therein latching elements  96  which are also seen in FIG. 5 to comprise portions of the door frame  14 . The hinge elements  94  and the latching elements  96  are described in detail as to structure and function in copending U.S. patent application Ser. No. 09/358,378 entitled “Door Frame for Lensed Troffer” as referred to hereinabove. The “bent over” portion  78  of each of the flanges  76  is discontinuous immediately opposite each of the slots  88  for a distance substantially equal to the length of the rectangular portion  90  of each slot  88 , this structure facilitating operation of the hinge elements  94  and of the latching elements  96  as described in the aforesaid copending patent application which describes the door frame  14  in use with the housing assembly  12  of the present lighting fixture  10 . The structure of the housing channel  18  is thus shown and described in detail, the utility thereof when not readily apparent as described hereinabove being elucidated by reference to cooperating structural components of the housing assembly  12  as will be described hereinafter. 
     The angular relationship of the side sections  54  of the housing channel  18  relative to the upper body portion  22  lends strength and rigidity to the housing assembly  12  and allows in part the formation of the housing assembly  12  with a depth-wise dimension which is desirable in installation of the lighting fixture  10  in reduced plenum installation situations. Interior surfaces of the housing channel  18  comprise reflective surfaces which are improved by a coating of highly reflective paint, particularly paint having diffuse characteristics, thereby to improve light output as well as to facilitate reduction of lamp image when a paint having diffuse characteristics is utilized. 
     Referring now to FIGS. 9A through 9E, one of the end plates  20  is seen in detail. Only one of the end plates  20  will be described herein since a description of one suffices for a description of both as the end plates  20  are essentially identical to each other and are interchangeable for use at either end of the housing channel  18 . The end plate  20  is substantially trapezoidal in conformation by virtue of the shape of plate body  100  formed of upper and lower plate body portions  102  and  104 . Each of the body portions  102  and  104  are substantially trapezoidal in shape, the portions  102  and  104  being joined at edges thereof through the exigency of a bend  106  in the material forming the plate body  100 , the bend  106  causing the upper plate body portion  102  to extend outwardly of the housing assembly  12  relative to the lower plate body portion  104 . It is to be understood that each of the end plates  20  is formed from a single sheet of material such as  22  gauge steel. The top edge of the plate body  100  takes the form of an upper flange  108  which is bent back inwardly of the plate body  100  along its full upper edge, the upper flange  108  taking the form of an elongated rectangle having notches  110  formed at outer corners thereof, the material at the innermost corner of the notch  110  being rounded at  112 . Three friction tabs  116  having upturned free ends  118  are formed in the flange  108 , one of the friction tabs  116  being centrally disposed along the flange  108  with the other two friction tabs being located essentially the same distance from the central friction tab  116  and toward the respective ends of the flange  108  at locations outwardly of the indentation  24 . The friction tabs  116  are punched from the body of the flange  108  and each surmounts an opening  120  formed when the material comprising each one of the tabs  108  is punched from the body of the flange  108 . 
     Lateral flanges  122  which are identical in conformation are formed at each end of the end plate  20  and are bent inwardly in the same direction as the upper flange  108  from the sheet of material forming the end plate  20 , each of the lateral flanges  122  being essentially planar and generally rectangular in conformation and extending along a full side of the upper plate body portion  102  and a portion of the length of the lower plate body portion  104 . A tab  126  having an aperture  128  extends at an angle from each of the lateral flanges  122  near the uppermost end of said flange  122 . The tabs  126  are bent outwardly and support wiring or other material is tied through the aperture  128  to hang the lighting fixture  10  in certain installation situations. A hanger element  130  extends from the free elongated edge of the flange  122 , the hanger elements  130  being shaped in the manner of a hook and in a conventional manner, the hanger elements  130  remaining in the plane of the flange  122  unless pushed outwardly to mount to a suspended ceiling structure such as a T-bar grid (not shown) of conventional design. The hanger elements  130  remain connected to the flanges  122  only through the agency of respective neck portions  132 , the neck portions  132  each having a slot  136  formed therein to facilitate bending of the hanger element  130 . The hanger elements  130  can be readily bent at the base of the neck portions  132  to position said hanger elements  130  for accomplishment of a conventional function. Notches  134  are formed on either side of the neck portion  132  to facilitate bending of each hanger element  130 . The lower plate body portion  104  is rounded off at  140  below the flange  122  to form vertical edge  142  at each end of the end plate, the vertical edges  142  intersecting the lower edge  144  of the body portion  104 , the edges  142  being essentially vertically oriented at the intersection with said body portion  104  at each end thereof. The lower edge  144  of the lower plate body portion  104  bends inwardly to form an elongated interior flange  146  which extends the full length of the lower edge  144  of said body portion  104 . The flange  146  bends inwardly to form a connecting flange  148  which extends virtually the full length of the flange  146  except for notches  150  formed at each end thereof essentially at the juncture of the connecting flange  148  and lateral flange  152  which extends essentially the full length of the flange  146  and terminates in a shaped tab  154  having an arcuate free end which extends inwardly of the free edge of the flange  152 . The flanges  148  and  152  cooperate to form a recess which communicates with a recess formed by the ledges  72  and  74  of the housing channel  18 , the door frame  14  fitting into said recess. 
     The end plate  20  is further provided with a series of knockouts  158  provided in the upper plate body portion  102  at regular spacings thereof, the knockouts  158  being useful in the event that electrical wiring (not shown) or other structures are to be inserted into the interior of the lighting fixture  10  through the end plate  20 . The end plate  20  can further be provided with a series of slots (not shown) formed either in the body portions  102 ,  104  or both, such slots functioning to ventilate the interior of the lighting fixture  10  and thus to remove heat. It is to be understood that such slots can be provided in patterns particularly intended for efficient heat removal. It is further to be understood that essentially circular apertures can be formed near corners of the plate body  100  to mount clips (not shown) which are required by code in areas having earthquake activity. Apertures (not shown) can also be formed in the plate body  100  to function as mountings for damper structure (not shown) used in some installations to damp air flow. Two pairs of tabs  160  and  172  are punched out of the upper plate body portion  102  near the top of the plate body  100 . Each of the tabs  160  are located at one end of the plate body  100  and spaced essentially the same distance from the top edge of the body  100 . The tabs  172  are formed inwardly of the tabs  160  and are located closer to the top edge of the body  100  than are the tabs  160 . The pairs of tabs  160  and  172  facilitate mounting of socket plates of differing height as will be described hereinafter. 
     Referring now to FIGS. 10A,  10 B and  10 C, illustration is provided for the process of mounting the end plates  20  to the ends of the housing channel  18 . Each of the end plates  20  are mounted in an identical fashion to the housing channel  18 . Accordingly, description of the mounting of one of the end plates  20  to said channel  18  suffices for a description of both. As is seen in FIG. 10A, the shaped tab  154  at each lower end of each one of the end plates  20  is inserted into the shaped aperture  80  formed at each end of the housing channel  18  and on each side thereof, the shaped tabs  154  being inserted from inwardly of the housing channel  18  to extend outwardly thereof through each of the shaped apertures  80 . On full receipt of the shaped tabs  154  into said shaped apertures  80 , the body of the end plate  20  is rotated upwardly toward upper portions of the housing channel  18 , the tabs  154  pivoting within the shaped aperture  80  from positions initially aligning with the angled slot-like portions  84  of said apertures  80 , the portion  84  being of a greater length than the dimensions of the vertical portion  82  of the aperture  80 , the shaped tab  154  thus being longer than the dimensions of the vertical portion  82  of said aperture  80 , thereby to hold the tabs  154  within a lowermost portion, that is, the vertical portion  82  of the shaped aperture  80 . As the tabs  154  are locking into the apertures  80 , the upper flange  108  is fitting beneath edge portions of the ends of the upper body portions  22  of the housing channel  18 , each of the friction tabs  116  fitting into and through one each of the cutouts  42  to engage upper surfaces of the channel  18 . The upturned free ends  118  of the friction tabs  116  facilitate movement of the end plate  20  into location by preventing binding of ends of the friction tabs  116  against structure such as opposing edges of the cutouts  42 . The free ends  118  of the tabs  116  on assembly of the end plate  20  to the channel  18  then bias againt upper surfaces of the channel  18  to prevent rising up of the channel  18  relative to the end plate  20 . The friction tabs  116  therefore fit frictionally in position relative to the channel  18  when the end plate  20  is fully received onto the end of the housing channel  18 . Free ends of the plates  45  angle downwardly to be received into the openings  120  wherein said free ends can engage front edges  119  of said openings  120 . In this fully assembled position, the lateral flanges  122  fit over end portions of the side sections  54 . As is seen in FIG. 10, the end plate  20  is shown to be assembled to the end of the housing channel  18 . The simple integral fastening elements formed on the housing channel  18  and the end plates  20  act to effectively lock the housing channel  18  and the end plates  20  together to the degree that it is difficult to separate the end plates  20  from the housing channel  18  once assembled together. Free ends of the downwardly angles plates  45  abut front edges  119  of openings  120 . Extension of the upper flange  108  beneath the end of the upper body portion  22  of the housing channel  18  coupled with the surmounting relationships of the lateral flanges  122  relative to ends of the side sections  54  contribute to the locking together of the end plates  20  to the housing channel  18  with the resulting difficulty of separating said plates  20  from said channel  18 . Tension provided by the housing channel  18  itself, that is, the natural tendency of the side sections  54  of the housing channel  18  to bow outwardly can further act to hold the shaped tabs  154  within the apertures  80 . 
     FIG. 11 illustrates the appearance of corner portions of the assembled housing channel  18  and one of the end plates  20  with the door frame  14  further being assembled thereto to effectively form a complete lighting fixture  10 , the door frame  14  only being visible by virtue of the appearance of portions of one of the latching elements  96  as it extends through one of the slots  88 , minor portions of the door frame  14  being visible through the slot  88 . Similarly, FIG. 12 illustrates a corner of the fixture  10  showing full assembly of one of the end plates  20  to the housing channel  18  and wherein the door frame  14  is mounted to the housing assembly  12  thus formed. One of the hinge elements  94  mounted to the door frame  14  extends through one of the slots  88  on the opposite side edge of the fixture  10  from that side edge shown in FIG.  11 . Essentially, the door frame  14  is not seen in FIG. 12 except through the slots  88  although the hinge element  94  also forms a part of the door frame  14 . 
     Referring now to FIG. 13, the door frame  14  is shown as assembled to the housing assembly  12  but with the latching elements  96  disengaged from the slots  88  formed along one edge of the housing assembly  12 . It is to be understood that the door frame  14  can be rotated downwardly from the position shown in FIG. 13 with the hinge elements  94  (not shown) acting to create a line along the opposite side edge of the housing assembly  12  about which the door frame  14  pivots to open up the interior of the lighting fixture  10  from beneath said fixture  10  for maintenance or the like including relamping, etc. The lens cover  16  can be easily removed for maintenance. In FIG. 14, a detail view is seen of a corner of the fixture  10  as shown in FIG. 13, the door frame  14  carrying the lens cover  16  as seen in FIG. 14. A complete description of the structure and function of the door frame  14  including the structure and function of the hinge elements  94  and the latching elements  96  is provided in copending U.S. patent application Ser. No. 09/358,378, entitled “Door Frame for Lens Troffer”, filed of even date and assigned to the present assignee as aforesaid. 
     Referring now to FIGS. 15A through 15D as well as FIG. 11 inter alia, the socket plate  48  is seen to comprise a body portion  49  having an edge within which shaped cutouts  162  are formed, the cutouts  162  allowing mounting of one each of the sockets  50  in a conventional fashion. The sockets  50  extend upwardly from the plane of the body portion  49  and receive lamping such as the lamp  52  of FIG.  5 . The opposite edge of the body portion  49  has an angled flange  164  extending therefrom, the flange  164  having tabs  166  extending from an outer edge thereof, the tabs  166  being receivable one each within each one of the slots  46  formed in the upper body portion  22  of the housing channel  18 . As seen in FIG. 11 inter alia, the tabs  166  extend outwardly of the housing channel  18  through said slots  46 . Depending upon the size of the socket plate  48 , either the pair of the tabs  160  or the pair of the tabs  172  formed in the upper plate body portion  102  of each of the end plates  20  extend inwardly of the housing assembly  12  to bias against the socket plate  48 , thereby facilitating secure assembly of the socket plate  48  at each end of the housing assembly  12 . In essence, the socket plates  48  and the sockets  50  mounted thereby are conventional in the art. The sockets  50  mount T 8  lamping such as the lamps  52  referred to above. In a specification premium embodiment of the lighting fixture  10 , the distance between lower portions of the lamps  52  and an upper face of the lens cover  16  is identical to the distance between lower portions of T 12  lamping and an upper face of a lens cover in similar lensed troffer lighting fixtures utilizing T 12  lamping, this distance being desirable for maintenance of an adequate obscuration of lamp image. Typically, the lighting fixtures  10  formed according to the invention have a height of approximately 3.65 inches in a specification premium embodiment and approximately 3.14 inches in a non-specification troffer embodiment. FIG. 7 essentially illustrates the positions within the interior of the lighting fixture  10  at which the lamps  52  (not shown in the Figure) would be located as mounted by the sockets  50 . The distance from lower portions of the lamps to an upper face of the lens cover  16  would be that straight line distance downwardly from the sockets  50  to the lens cover  16 . 
     The exploded views of FIGS. 5 and 6 illustrate the assembly arrangement of the various structural components of the lighting fixture  10  and provide additional showings of the manner in which the various structural components of the lighting fixture  10  come together into assembled relationships. 
     A lighting fixture  168  as seen in FIGS. 16 and 17 is seen to be identical to the lighting fixture  10  with the exception that the lighting fixture  168  is formed as a two foot by two foot square while the lighting fixture  10  has effective dimensions of two feet by four feet. The lighting fixture  168  is shown to illustrate a differing dimensional conformation of a lighting fixture configured according to the invention as well as to show in assembly relationship the channel cover  36  to remaining portions of housing assembly  170  and in an assembled relationship thereto in FIG.  17 . It is to be understood that channel covers such as the channel cover  36  are conventional in the art and need not be described in detail herein. It is further to be understood that previous reference has been made herein to the channel cover  36  and its function in covering the ballast  32  as well as other structure aligned with the ballast  32  and the access opening  26  inter alia. The different dimensional embodiments of the invention can typically be formed with two, three and four lamps, it being necessary to utilize a socket plate such as the plate  48  configured for the particular number of lamps employed in a given fixture. 
     FIG. 18 diagrammatically illustrates the function of the indentations  24  formed in the upper body portion  22  of the channel  18 , light emanating upwardly from the lamp  52  reflecting from angled surfaces  25  of each of the indentations  24  and being thus directed at angles which allow the reflected light to move through the lens cover  16  and out of the fixture  10 . Light output is thus increased. 
     Referring now to FIGS. 19A through 19D, a light trap element  174  is seen to be comprised of a U-shaped body member  176  having projecting arcuate wings  178  extending outwardly of each of the leg portions of the body member. The light trap element  174  is assembled to the junction of the end plates  20  and the channel  18  after assembly of the end plate  20  to the housing channel  18  to prevent light leakage from the shaped apertures  80  and from the junction of the end plates  20  and the channel  18 . As aforesaid, one of the wings  178  fits into the notch  68  formed in the channel  18 . The other wing  178  fits into the channel formed by the elements  104 ,  146  and  148  of the end plate  20  at each end thereof, the elements  104 ,  146  and  148  being best seen in FIG.  9 E. The free end of this other wing  178  contacts inner wall surfaces of the element  146  and biases thereagainst. The wings  178  are arcuate in order to provide compression. While only one of the wings  178  needs to be arcuate, both are arcuately formed so that either of the wings  178  can be placed into the channel formed by the elements  104 ,  146  and  148 . 
     It is to be understood that the lighting fixtures  10  and  168  can be configured other than as explicitly shown and described herein without departing from the scope of the invention as defined by the appended claims.