Abstract:
An elongated indirect lighting fixture having a upwardly directed shallow concave sheet element suspended at its ends with spars interconnected along the outer marginal edges of the reflector element. The spars are preformed in an upward and inward direction to resist sagging both in a downward direction and an outward direction so that the lighting fixture, as represented by the sheet element, is substantially linear.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to lighting and more specifically to linear indirect lighting fixtures. 
     2. Description of the Related Art 
     Linear indirect lighting has been used for many years to illuminate industrial and commercial buildings by providing a light source adjacent the ceiling of a room and projecting rays onto the ceiling to provide a more uniform lighting for the interior space. Such linear indirect lighting assemblies generally are suspended or supported at the ends thereof. This is to minimize the number of shadows that are thrown onto the ceiling by the supports leading up to the ceiling. The basic aesthetic component (that is the observable portion of the fixture) of the indirect lighting fixture is an elongated sheet-like element, usually formed from metal. The sheet-like element is shaped in various cross-section configuration so that a concave side faces the ceiling, although it is possible under some circumstances to have it face downward. In typical commercial fixtures, the concavity of the sheet has to be relatively flat. In addition to the function of a reflector element, the sheet-like element may provide a support for a separate reflector, as well as a mounting and support for electrical wiring, ballast and other usual components of such a lighting fixture. This shallow concavity presents a problem when the indirect lighting fixtures are provided in substantial lengths, usually from eight to twelve feet. With a length of this type, there is a significant portion of the midsection not supported by any external structure. Consequently, the sheet metal may be subjected to bends and distortion from the stress generated by the weight of the sheet element itself. This becomes a particular problem because the sheet element, in addition to providing other functions for the fixture, also provides an aesthetic component since its exterior is the observable portion of the fixture. Visual observation by a person can detect distortions of as little as one thousands of an inch so it is imperative that the geometry of the semi-circular sheet-like element be maintained uniformly. 
     What is needed in the art is a reinforcement for light fixtures of this type that maintains a uniform geometry and is simple and effective. 
     SUMMARY OF THE INVENTION 
     In one form, the invention is a supporting structure for an elongated lighting fixture including an elongated sheet element of the fixture having a generally uniform cross-section with a shallow concave face and at least one elongated spar interconnected with the elongated sheet element at least at several locations along the length of the spar and sheet element. The spar is preformed into a curved form relative to its longitudinal axis prior to interconnection with the sheet element so that the supporting structure is substantially linear and resists sagging. 
     In another form, the invention is an elongated light fixture which includes at least a pair of electrical and structural mountings for an elongated lighting element. An elongated sheet element is connected to and extends between the mountings, the sheet element having a generally uniform cross-section with a shallow concave face. At least one elongated spar is interconnected with the elongated sheet element at least at several locations along the length of the spar and the sheet element. The spar is preformed into a curved form relative to the longitudinal axis thereof prior to interconnection with the sheet element so that the light fixture is substantially linear and resists sagging. 
     In yet another form, the invention is a method of reinforcing an elongated lighting fixture including the steps of forming an elongated sheet element of the fixture into a form having a generally uniform cross-section with a shallow concave face. An elongated spar is formed into a curved form relative to its longitudinal axis. The elongated spar and the sheet element are interconnected at least at several locations along the length of the spar and the sheet element so that the resultant fixture is substantially linear and resists sagging. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a side view of a linear indirect lighting fixture embodying the present invention; 
         FIG. 2  is a plan view of  FIG. 1  taken on lines  2 - 2  of  FIG. 1 ; 
         FIG. 3  is a side view of a spar used in the lighting fixture of  FIG. 1 ; 
         FIG. 4  is a top view of a spar used with the wetting fixture of  FIG. 1 ; and 
         FIG. 5  is an enlarged cross-section view of the lighting fixture of  FIG. 1  taken on lines  5 - 5  of  FIG. 1 . 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrates one embodiments of the invention and such exemplification is not to be construed as limiting the scope of the invention in any manner. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings and more particularly to  FIGS. 1 ,  2  and  5 , there is shown a linear indirect lighting fixture  10  having supports  12  and  14  for a plurality of elongated lighting elements  16 , herein illustrated as fluorescent tubes. The tubes  16  come in standard lengths up to twelve feet long, with the usual length for commercial and industrial fixtures being 8 to 12 feet. The support elements  12  and  14  are typically suspended from a ceiling by cables  18  and  20 , or other appropriate means of suspension. An element  22  is employed that extends between structural elements  12  and  14 . Element  22  is in sheet form, usually from steel and has a thickness from 20 to 22 gauge. Sheet element has a generally uniform cross section with a shallow concave face facing upward as shown in  FIG. 1 . As shown particularly in  FIG. 5 , the element  22  has a semi-circular cross section with a shallow concavity. It should be apparent, however that other cross-sectional shapes may be employed to span the distance between the supports  12  and  14 . Sheet element  22  may function as shown to be a reflector curved to disperse the light over a greater portion of a ceiling for indirect lighting. Some reflectors  22  are provided with no direct down light so that they are essentially opaque. Other elements may have one or more openings to direct a portion of the light from the fluorescent tube  16  directly downward, as well as upward. In still other instances, a separate reflector may be carried by sheet element  22 , as well as various electrical components. 
     In either case, the requirement that the lighting fixture  10  be suspended from its ends, for example by cables  18  and  20 , means that all the inherent weight of the sheet element  22  is only supported by its end portions. As a result, the element  22  has a tendency to sag downward to a dashed line indicated at  24  in  FIG. 1 . This line is exaggerated for purposes of illustration but in practice the sagging is enough so that it can be observed as an irregular structure. In addition to the downward sagging illustrated by dash line  24  in  FIG. 1 , the element  22  exhibits a characteristic referred to as canoeing where the sides additionally expand to dash lines  26  shown in FIG.  2 ., further exaggerating the deviation from a uniform, linear structure. 
     In accordance with the present invention, a spar  28 , shown in  FIGS. 3 and 4  is employed to minimize, if not eliminate the deficiencies described above. Spar  28 , as particularly shown in  FIG. 5 , has a generally U-shaped cross-section with a first longer leg  30  and a second shorter leg  32  positioned outboard of the longer leg  30 . Legs  30  and  32  are inter-connected by an integral section  34 . As shown in  FIG. 3 , spar  28  is formed to a curved form that deviates from a linear longitudinal axis A in a direction, when installed that is towards the ceiling to which the lighting fixture  10  is attached. As shown in  FIG. 4 , the spar  28  is also formed to a curve that departs from a linear axis A for the spar inward towards the center of the lighting fixture  10 . This multidimensional curve is a result of the different lengths of the legs  30  and  32  forming the generally U-shaped cross-section. The spar  28  is sized so that it fits under bent over marginal edges  36  and  38 , integral with element  22 . As shown in  FIG. 5 , the spar  28  is affixed to the element  22  by rivets  40  extending through element  38  at a plurality of locations along the length of the element  22  and the spars  28 . It should be apparent, however, that means other than rivets may be employed to affix the portions together, including spot welding, adhesives and even forming an additional marginal edge of element  22  to capture spars  28 . 
     The curvature of each spar  28  is selected so that when it is inserted in-between the elements  36  and  38 , it exhibits a force opposite to the gravity forces that cause the sagging exhibited by dashed lines  24  and  26  in  FIGS. 1 and 2 . The resulting structure exhibits substantially a linear shape when installed and suspended by its ends, for example through cables  18  and  20 . This ensures that the aesthetic portion contributed by the element  22  is maximized by having a form that is substantially linear to the observer. 
     While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.