Abstract:
Prismatic structures having at least certain conventionally linear surfaces thereof configured in a non-linear fashion to control the direction of light exiting said structures, the invention functions to reduce light losses in a luminaire or the like while facilitating the emanation of light from the luminaire at an acceptable viewing angle and with a reduction in glare. Prisms, particularly splitter prisms, configured according to the invention are formed with at least portions of conventionally linear surfaces as arcuate, curvilinear or generally curving segmented surfaces so as to direct light out of the luminaire for useful illumination rather than in a wasteful direction back into the luminaire. Prisms configured according to several embodiments of the invention function to increase light efficiencies either upwardly or downwardly depending on illumination requirements.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates generally to prismatic structures configured to maximize light control and particularly to splitting prisms having conventionally non-linear surfaces capable of directing light incident thereon away from impingement on adjacent prisms and therefore out of a light-transmissive luminaire body or the like such that the directed light is available for illumination. 
     2. Description of the Prior Art 
     Prismatic structures, or prisms, have been known for centuries to be useful in a variety of applications including incorporation into light transmissive “globes” and the like for use in luminaires of varying description. U.S. Pat. No. 563,836 issued in 1896 to Blondel et al discloses “globes, shades, reflectors, and other envelops” useful in luminaires and having prisms molded or otherwise formed on such globes for the purpose of reflecting, refracting and directing light rays in a desired manner. For purposes of background and elucidation of the scope and nature of the present invention, U.S. Pat. No. 563,836 is incorporated hereinto by reference. It is to be understood that literally thousands of issued United States patents and literally millions of light transmissive objects manufactured by mankind have existed and exist, many of these objects having prisms of varying character incorporated thereinto, Franck, in U.S. Pat. Nos. 2,818,500 and 2,887,568 discloses prisms generally useful in luminaire structures. Franck describes a variety of prisms, flutes and light-directing structures typically formed of glass and intended to efficiently illuminate areas in the vicinity of such luminaires. In U.S. Pat. No. 2,887,568, splitting prisms are mentioned as being useful for light direction in the illumination of an elongated environmental space such as a hallway. In U.S. Pat. No. 2,818,500, Franck describes the shaping of portions of prisms at apices and at valleys between adjacent prisms for reduction of light loss. Barnes et al, in U.S. Pat. Nos. 4,839,781 and 5,444,606, generally describe the use of prisms in globes used in luminaires and particularly in globes formed of “plastic” materials such as acrylic materials, these materials having come in more recent times to be used along with “glass” materials of varying description for the formation of globes used in luminaires. In U.S. Pat. No. 4,839,781, Barnes et al disclose a luminaire globe having differing kinds of prisms formed in differing zones to reflect and/or refract light for selective variation of light distribution depending on location of a light source within the luminaire. Barnes et al particularly describe vertical prisms of refractive or reflective characteristics, or both, as being useful in luminaire structures such as are disclosed with the choice of such prisms being dependent upon the location of a light source within a luminaire so configured. 
     Osteen, in U.S. Pat. Nos. 4,118,763 and 5,036,445, respectively describes globe members used within a luminaire and disposed about a light source, such globe members being constructed of light transmissive material having a variety of prismatic surfaces formed thereon which act in combination and in confluence with the shape of the globe member to produce light output in desirable directions. In U.S. Pat. No. 5,036,445, Osteen discloses a reflector structure having prisms capable of total internal reflection so that light exiting from the top of a globe member can be limited. Pearce, in U.S. Pat. No. 5,416,684, discloses the use of prisms formed on differing portions of a globe member for accomplishing desired light direction such as for increasing downward output of light from a luminaire. In U.S. Pat. No. 3,329,812, Harling discloses a particular refractor structure useful in a luminaire for light control through direction of light emanating from a light source to illuminate locations externally of the luminaire. Fouke, in U.S. Pat. No. 6,027,231, inter alia, describes globe members particularly useful in luminaires and formed of glass, acrylic materials and the like, for direction of light from a luminaire for efficient illumination. Kelly et al, in U.S. Pat. No. 5,434,765, describe a globe member having reflector and refractor sections and having prisms formed on surfaces of said sections for direction of light in a downward manner. 
     The United States patents mentioned above are only representative of a very substantial body of art that encompasses light transmissive reflector/refractor structures used in luminaires or the like wherein light output from a luminaire is controlled for direction into desired locations in the vicinity of such luminaires. Globe members used in such luminaires are light-transmissive members exhibiting either refractive, reflective or a combination of refractive and reflective properties, these properties occurring by virtue of the nature of prismatic and similar structures incorporated into such globe members. In this general area of lighting technology, light from a luminaire may be intended to directed upwardly, downwardly or both from a luminaire with the preponderance of light emanating from such a luminaire being intended as “uplight” or as “downlight”. Judicious selection of prismatic structures incorporated into such luminaire globe members permits light control and direction of light in a desired manner as has long been understood in the art. 
     Need often arises in the illumination arts for directing light into space located about a luminaire at an acceptable viewing angle with a minimum of glare. Various products manufactured and marketed by Acuity Brands, Inc. of Atlanta, Ga., formerly Holophane Corporation, under the trademark PRISMGLO utilize a particular kind of prism known as a splitter prism or splitting prism such as is shown in  FIG. 5  of U.S. Pat. No. 563,836 to Blondel et al as referred to above. In the PRISMGLO luminaires, splitter prisms are used in order to take advantage of both total internal reflection and refraction to control light direction. Splitter prisms such as are used on PRISMGLO luminaires utilize linear or “straight line” sides or “flat” prismatic surfaces. Luminaire globe members of certain configurations with which splitter prisms can advantageously be employed have been found to be subject to light losses when splitter prisms having linear or straight sides or flat surfaces are utilized. Accordingly, the present invention intends the configuration of a splitter prism in particular that accomplishes light redirection more efficiently than is possible with splitter prisms configured according to the prior art. Prior art splitter prisms disposed on luminaire globe, members of certain shapes and with light incident thereon at certain angles of incidence unavoidably function to direct light onto an immediately adjacent prism. Light rays incident on the immediately adjacent prisms in such situations are redirected into the interior of the luminaire globe member or in some other direction such that the light is lost and the efficiency of the luminaire is thereby reduced. Splitter prisms configured according to the present invention and particularly functioning within particular environments as disclosed herein are formed so that light incident thereon is redirected in a manner so as to avoid incidence on immediately adjacent prisms, thereby allowing more light to enter a space being illuminated and thereby causing the luminaire to be more efficient. It is to be understood that the concept embodied by the several embodiments of the present invention can be applied to prisms of differing kind and not only to prisms such as could be referred to as “splitter prisms” or the like. 
     SUMMARY OF THE INVENTION 
     The invention provides in several embodiments prismatic structures or prisms having at least certain surfaces configured in a curvilinear manner in order to better control light incident on said surfaces. The prismatic structures of the invention are of varying kind and character and can be configured according to the teachings of the invention. In preferred embodiments, however, prisms typically referred to as splitter prisms or splitting prisms formed particularly in refractor portions of luminaires can be configured according to the teachings of the invention in order to increase the efficiency of such luminaires. A prism, such as a splitter prism, is conventionally configured with linear “sides” or surfaces that appear to be linear when such a prism is viewed in section. Typically, splitter prisms have been used in luminaire structures as at least a portion of the prisms provided on a refractor section for refracting light both upwardly and downwardly, such prisms functioning both by total internal reflection and refraction to control light direction. Globe members of conventional luminaires can be shaped in a manner such that immediately adjacent prisms of “straight-sided” splitter prisms can intercept light exiting one of said splitter prisms and redirect light other than as is intended such as back into the luminaire globe member. Light can therefore be lost and luminaire efficiency reduced. It should be understood that those light rays misdirected in this manner are typically those rays incident on the straight side or flat surface of such a prism near a “valley” where adjacent prisms meet. Those light rays incident more toward the apex of a given prism would typically not be redirected to be incident on an adjacent prism but would be redirected outwardly of the luminaire to provide appropriate and desired illumination, According to the invention, at least one straight side or flat surface of a prism, such as a splitter prism, can be formed in a curvilinear manner so that light rays incident thereon from interiorly of a luminaire globe member or the like is redirected in a manner such that an immediately adjacent prism does not intercept the light ray and direct said ray either back into the luminaire globe member or in an undesired direction. The invention contemplates prism surfaces formed inter alia in a non-linear manner such as in a curved manner, in a partially curved manner or in a series of straight segments having a generally arcuate character. In essence, a prism surface configured according to the invention is at least partially curved and particularly over that portion thereof in proximity to an anterior portion of the prism as opposed to a distal portion or apex of said prism. Prisms configured according to the invention are preferably utilized as refracting prisms although prisms having reflecting capabilities or both refracting and reflecting capabilities can also be configured according to the invention. It is also to be understood that prisms configured according to the invention can have both “sides” or “surfaces” configured according to the invention, that is, either “upper” or “lower” surfaces so configured depending upon the direction in which light is to be directed. Essentially, linear sides or flat surfaces of conventional prisms are configured according to the invention to at least have a portion of otherwise conventionally linear sides or flat surfaces formed in a non-linear fashion in order to produce the advantages accruing to a practice of the invention. 
     It is further to be understood that prisms configured according to the invention can be provided on a refractor section of a luminaire globe member with a cooperating reflector section being capable of formation from materials that differ from the material used to form said refractor section. In particular, a reflector section of a luminaire globe member could be formed of metal, glass, plastic materials such as acrylic, etc. while the refractor sections on which prisms configured according to the invention are incorporated can be formed of light transmissive materials such as glass, acrylic, etc. It is also to be understood that prisms configured according to the invention can be used to refractively redirect high angle lamp light into useful downwardly directed rays, upwardly directed rays or both in order to increase the percentage of light directed from a luminaire globe member, thereby to reduce light loss and increase lighting performance. Particular lighting applications wherein prisms configured according to the invention can most effectively be used is within an environmental space wherein light directed from a refractor section of a luminaire globe member must be available to a viewer at an acceptable viewing angle with a minimum of glare. The usefulness of prisms configured according to the invention within such use environments depends primarily upon the angle of incidence of light from a light source within a luminaire onto said prisms and particularly coupled with the shape of the luminaire globe member. 
     It is therefore an object of the invention to provide prismatic structures having shaped surfaces over at least portions of elongated surfaces thereof for the purpose of controlling the direction of light exiting from said prismatic structures. 
     It is another object of the invention to provide prisms of differing kind having surfaces configured in an arcuate or curvilinear manner at least at portions thereof and especially such portions near anterior ends or edges of said prismatic structures. 
     It is a further object of the invention to provide luminaire globe members having prisms formed thereon and configured such that normally straight sided or flat-surfaced portions of said prisms are configured at least partially in a non-linear manner such as in a smoothly curvilinear or segmented curvilinear manner so that light is directed from the luminaire globe member for efficient use rather than back into the globe member or in a direction that is wasteful of light. 
     Further objects and advantages of the invention will become more readily apparent in light of the following detailed description of the preferred embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic idealized representation of a luminaire globe member having prisms formed thereon and configured according to the invention; 
         FIG. 2  is a schematic idealized representation illustrating a sectional view of a conventional prism having “straight” sides or “flat” surfaces; 
         FIG. 3  is a schematic idealized representation of a portion of a luminaire globe member having at least certain prisms formed thereon and configured according to the invention; 
         FIG. 4  is a detailed schematic idealized representation of prisms configured according to a first embodiment of the invention; 
         FIG. 5  is a schematic idealized representation comparing in overlaid relation the prisms of the invention as shown in  FIG. 4  to prior art prisms such as are shown in  FIG. 2 ; 
         FIG. 6  is a schematic idealized representation illustrating conventional prisms usable on a luminaire globe member in association with prisms configured according to the invention; 
         FIG. 7  is a schematic idealized representation illustrating prisms configured according to the invention of an arcuate curvature and of a particular radius; 
         FIG. 8  is a detailed schematic idealized representation illustrating another embodiment of prisms configured according to the invention; 
         FIG. 9  is a detailed schematic idealized representation of prisms configured to yet another embodiment of the invention; 
         FIG. 10  is a detailed schematic idealized representation of prisms configured according to a further embodiment of the invention; 
         FIG. 11  is a detailed schematic idealized representation of prisms configured according to a still further embodiment of the invention; 
         FIG. 12  is a detailed schematic idealized representation of prisms configured according to further teachings of the invention; 
         FIG. 13  is a detailed schematic idealized representation of prisms configured according to still further teachings of the invention; 
         FIG. 14  is a detailed schematic idealized representation of prisms configured according to yet another embodiment of the invention; and, 
         FIG. 15  is an idealized schematic representation of a portion of a reflector section of a luminaire having prisms configured according to an embodiment of the invention and illustrating light rays passing through said refractor section at different portions thereof. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference is hereby made to U.S. patent application Ser. No. 10/280,281, entitled “Reflector/Refractor Light Control Luminaire”, filed of even date and assigned to the present assignee and also to U.S. patent application Ser. No. 10/280,280, entitled “Luminaire Globe having Low Glare Bandless Seam”, filed of even date and assigned to the present assignee, these applications being incorporated hereinto by reference. 
     Referring now to the drawings and particularly to  FIG. 1 , a globe member of a luminaire is shown representationally at  10  to be formed of a separate reflector  12  and refractor  14 , a light source being represented at  16  to be located internally of the globe member  10 . The globe member  10  is further seen to be provided with a door  18  intended to permit access into the interior of said globe member  10  for purposes of relamping and the like. The globe member  10  is understood to be conventional in the sense that similar structures have long been employed for use in luminaires of varying description including the PRISMGLO products of Acuity Brands, Inc. as referred to hereinabove. In luminaires of this kind, the reflector  12 , the refractor  14  and the door  18  are conventionally formed of glass or other light transmissive material such as plastics including acrylics and the like. The light source  16  in such conventional luminaire structures can take essentially any form but typically takes the form of a gaseous discharge lamp such as a high intensity discharge (HID) lamp. The reflector  12  and the refractor  14  are mounted together such as by structure (not shown) and/or through use of bonding material and the like inter alia. The door  18  can be mounted to the refractor  14  in a conventional manner, the door  18  typically having thread-like elements which allow the door  18  to be fitted into positive engagement with the refractor  14 . It is further to be understood that the reflector  12  could be formed of a material such as metal or any other material providing the capability of reflecting light from the light source  16  in a desired fashion. 
     When the reflector  12  is configured essentially as shown in  FIG. 1 , a plurality of refractive prisms  20  are formed on inner surfaces of the reflector  12 , the prisms  20  also being shown in  FIG. 6  to reflect light incident thereon back into the interior of the globe member  10  and toward any of a plurality of either splitter prisms  22  or refractive prisms  24  formed on the refractor  14 . As seen in  FIG. 6 , an incident ray shown at  26  is refracted by one of the prisms  20  and is then incident on one of a plurality of prisms  28  for reflection back toward one of the prisms  20  whereby reflected ray  30  is then again refracted by the prism  20  and directed toward the refractor  14  for further direction by one of the splitter prisms  22  or one of the refractive prisms  24  on the refractor  14  externally of the refractor  14  for illumination purposes. The structure and function of the prisms  20  and  28  of  FIGS. 1 and 6  can be conventional in nature and are described herein for purposes of illustration of a particular environment within which prisms configured according to the invention can be used. It is further to be understood that the prisms  28  are represented as shown since, in the essentially sectional representation of  FIGS. 1 and 6 , the prisms  28  would be seen in a longitudinal sense rather than in the sense of concentricity as the prisms  20  are seen. 
     The prisms  24  formed as component portions of the refractor  14  are essentially conventional prisms intended to be refractive in nature. Reference is made to disclosure present in copending U.S. patent application Ser. No. 10/280,281, entitled “Reflector/Refractor light Control Luminaire” referred to hereinabove and incorporated hereinto by reference for a description of preferred refractive structures useable as the prisms  24 . Prisms utilized in the environment shown could also have reflective capabilities as well as refractive capabilities as is conventional in the art. It is also to be understood that prismatic structures could optionally be formed on interior walls of the refractor  14  such as is represented at  32  in a conventional manner for conventional functions well known in the art. Light emanating from the light source  16  as well as light directed from the reflector  12  can be incident on the prisms  24  and be redirected externally of the globe member  10  by said prisms  24  in a conventional manner. 
     Given the shape of the refractor  14 , that is, the curvature of the refractor  14  downwardly from the loci of mating between the reflector  12  and the reflector  14  toward lowermost portions of the globe member  10  as direction is referenced in  FIG. 1  and considering also the angle of incidence of certain light rays incident on those prisms located near the juncture of the reflector  12  and the refractor  14 , it is to be seen that the construction of the prisms  22  as splitter prisms or splitting prisms configured according to the invention is necessary for greatest light efficiency. The prisms  22  are chosen to be splitter prisms due to the fact that light incident upon said prisms  22  and which is to be most efficiently refracted thereby has an incidence angle of approximately 15° or such incidence angles are within a similar range of incidence angles. In order for light incident on the section of the refractor  14  having the splitter prisms  22  formed thereon, the prisms  22  are preferably formed with non-linear, that is, preferably curvilinear, surfaces over upper faces of said prisms  22  as can be seen clearly in  FIGS. 3 and 4  inter alia. As particularly seen in  FIGS. 3 and 4 , a light ray  36  incident generally at  38  on anterior portions of the surface  34  is redirected such that the exiting ray  40  is not incident upon an immediately adjacent prism  22  due to internal reflection from the non-linear surface  34  of each one of said splitter prisms  22 . 
     As seen in  FIG. 2 , a light ray as seen at  27  is refracted into incidence onto adjacent conventional splitter prisms  21  when incident on at least anterior surfaces of any one of the conventional splitter prisms  22  as shown, the conventional prisms  21  having straight sides or flat surfaces  44 . Refracted light ray  42  as shown in  FIG. 2  is wasted. 
     Referring again to  FIGS. 3 and 4 , the “top” surface of each of the prisms  22 , that is, the surface  34  of each of said prisms  22 , is preferably curved in order to internally reflect the incident light ray  36  in a fashion such that the exiting ray  40  is not incident on the adjacent prism  22  directly below the prism  22  upon which the light ray  36  is initially incident. 
     As is seen at  42  in  FIG. 5 , the light ray  36  incident on a linear surface of any one of the prisms  22  if configured according to the structure of  FIG. 2  (as shown in dotted lines in  FIG. 5 ) would be reflected into incidence with the immediately adjacent prism  22  below said prism  22  and light would then be refracted essentially inwardly of the refractor  14  and would thus be lost. It is to be understood that light rays incident more distally of any one of the splitter prisms  22  would be more likely to be redirected externally of the refractor  14 . In essence, light rays incident more distally of any one of the prisms  22  would more likely be redirected outwardly of the refractor  14  even if a surface corresponding to the surface  34  at a distal portion thereof is formed in a linear fashion. For this reason, more distal surface portions of any one of the splitter prisms  22  can be formed linearly as will be described in more detail hereinafter. The shaping of a surface of one of the prisms  22  other than as shown by the shape of the surface  34  can be accomplished according to other embodiments of the invention as will also be described in more detail hereinafter. It is further to be understood that lower surfaces of at least some of the prisms  22  are formed such as in the shape of the surface  34  on “upper” surfaces of said prisms  22  since light incident thereon, such as the light ray  36 , if light is intended to be directed upwardly. In such situations where light needs to be directed upwardly, that surface lowermost of the prisms  22  would be shaped in order to efficiently redirect light upwardly of the globe member  10  as will be described in more detail hereinafter. 
     Referring once again to  FIG. 5 , the splitter prisms  22  are seen to be formed with the non-linear surfaces  34  referred to hereinabove, a representation of the prisms  22  being seen to have superimposed thereon a straight side or flat surface at  44  shown in dashed lines in order to differentiate clearly between a conventional prism as would be represented by the straight surface  44  and the prisms  22  of the invention having the non-linear surface  34  as previously discussed. As seen in the superimposed representations, the light ray  36  incident on the surfaces  34  and  44  at locations near valley  46  at the juncture of adjacent prisms  22  would be internally reflected in a different manner, the exiting ray  40  exiting the prism  22  having the nonlinear surface  34  being outwardly directed so as to miss the immediately adjacent prism  22  while the exiting ray  42  exiting a prism having a linear or straight-sided surface  44  at locations on said surface  44  in proximity to the valley  46  would be redirected as  42  to be incident on the immediately adjacent prism as aforesaid and therefore wasted or lost by being redirected either toward the interior of the optical structure or in a direction such that the ray  42  is not effectively and efficiently utilized for illumination purposes. It is to be noted that light rays incident on either of the surfaces  34  or  44  toward a distal end or apex  48  of one of the prisms  22  would typically be appropriately directed outwardly of the prisms  22  for effective utilization for illumination purposes. 
     Referring now to  FIG. 7 , one of the prisms  22  is shown in detail in order to illustrate typical dimensions. The effective dimensional length of the prism  22  is between 0.2 and 0.3 inch both for prior art straight-sided prisms and for the splitter prism  22 , particular prism dimensions being subject to cosmetic considerations. It is possible to dimension the prism  22  in a range such as between 0.1 to 0.5 inch in practical applications. However, smaller prisms lead to a higher proportion of light leakage through the apices and valleys of the prisms. Prisms of a larger size produce a rougher appearance, the range of 0.2 to 0.3 inch being a compromise that provides effective function and desirable appearance. While the curvature of the nonlinear surface  34  can be taken to be a circular arc or other curvilinear shape, a suitable shape is taken to be a circular arc of one inch radius. 
     Referring now to  FIG. 8 , prisms such as prism  50  is seen to be configured according to another embodiment of the invention to be formed with an arcuate anterior surface at  52  and a straight-sided surface at  54  distally of the prism  50  toward apex  56  of said prism  50 . In essence, the arcuate surface  52  is formed in proximity to valley  58  at the juncture of adjacent prisms  50  at anterior portions of prism surfaces while distal portions of said surfaces are essentially linear. The shaping shown in  FIG. 8  functions appropriately in view of the fact that light rays incident on anterior surface portions of the prism  50  needs to be redirected in a manner according to the invention while light rays incident more distally of prism surfaces in proximity to the apex  56  are redirected without the necessity for shaping according to the invention. The respective lengths of the arcuate surface  52  and the straight surface  54  can preferably be taken to be equal. 
     Referring now to  FIG. 9 , a prism  60  configured according to the invention is seen to be provided with a surface  62  that is segmented along its full length in a manner approximating a curve or arc, segments  64  forming the surface  62  being of the same or even differing lengthwise dimensions. In  FIG. 10 , a similar prism  66  is illustrated to be segmented anteriorly of the prism  66  at  68  but with a straight-sided surface at  70  distally of the prism  66 . 
     Referring now to  FIG. 11 , a prism  72  configured according to a further embodiment of the invention is seen to be formed with a curved “upper” surface  74  and a straight-sided lower surface  76 , the lower surface  76  being longer than the upper surface  74 . The respective lengths of the surfaces  74  and  76  can vary depending on location of a light source such as the light source  16  within a globe member such as a globe member  10 . In situations where the light source  16  is disposed at essentially the same elevation as the set of splitter prisms  22  as seen in  FIG. 1  inter alia, the upper and lower surfaces of prisms configured according to the invention, as described above relative to the prisms  22 , are similar in length. Disposition of the light source  16  at a different elevation causes the lengths of the surfaces  74  and  76  to diverge. As shown in  FIG. 11 , formation of the lower surface  76  to have a length greater than the length of the upper surface  74  is occasioned by a lowering of the light source  16  within the globe member  10  when compared to placement of the light source  16  within said member  10  as shown in  FIG. 1 . 
     Referring now to  FIG. 12 , a prism  78  is configured according to a further embodiment of the invention by formation of lower surface  80  in a curved, arcuate or non-linear manner such as described hereinabove while upper surface  82  is straight-sided. The prism  78  so configured functions to improve uplight from a globe member such as a globe member  10  when a prism such as the prism  78  is formed with said member  10  as a component part thereof to function for desirable light redirection. 
     As is seen in  FIG. 13 , a prism  84  is seen to have both upper and lower surfaces  86  and  88  respectively formed in a non-linear fashion according to any of the several teachings referred to hereinabove, the prism  84  therefor functioning to improve the efficiency of light redirection both downwardly and upwardly relative to a globe member oriented such as the globe member  10  is oriented in  FIG. 1  as an example. 
     Referring now to  FIG. 14 , a prism  90  configured according to yet another embodiment of the invention has an upper surface  92  formed in the shape of a curve that is other than a circular arc, the surface  92  being of substantially the same length as straight-sided lower surface  94 . It is understood that the prism  90  could be variously configured with a non-circular arcuate portion configured in a manner similar to the configuration of those prisms referred to hereinabove as being shaped according to the teachings of the invention. 
     Referring now to  FIG. 15 , a portion of the refractor  14  is representationally seen in order to illustrate the paths of light rays passing through at least portions of the refractor  14 . Light ray  95  incident on an upper portion of the refractor  14  and emanating from a central portion of the light source  16  at a high angle is redirected by the prism  22  upwardly of the globe member  10 , thereby providing at least some degree of uplight. As noted above, light rays such as the light ray  36  are redirected downwardly and out of the globe member  10  by the agency of non-linear surfaces of the prisms  22  to produce the light ray  40 . Light rays emanating from the light source  16  downwardly thereof pass through refractive prisms  98  formed on the door  18 . Light rays emanating from the light source and incident on portions of the refractor  14  having the refractive prisms  24  thereon are refracted outwardly and downwardly of the globe member  10  to illuminate that space in the vicinity of the globe member  10 . 
     While the invention has been particularly described as being useful on particular kinds of prisms, it is to be understood that other kinds of prisms could be configured according to the teachings of the invention without departing from the intended scope thereof. Still further, it is to be understood that prisms configured according to the inventions can be utilized in environments other than the luminaire environments particularly referred to herein without departing from the intended scope of the invention. Accordingly, it is to be understood that the invention can be embodied other than as explicitly described herein without departing from the scope of the invention, the inventive scope being provided by the definition of the appended claims.