Door frame for lensed troffer

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.

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.

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 T8 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.degree. 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. 17E. 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.