Abstract:
A parabolic aluminized reflector (PAR) lighting fixture is provided with a faceted lens having many distinct lens elements. A plurality of first lens elements use light refraction to direct light from the collimated beam supplied from the fixture reflector to uniformly illuminate segments of a region of an adjacent wall surface. A plurality of second lens elements use internal reflection to direct light from the collimated beam to uniformly illuminate other, off-axis segments of the region. The resulting highly asymmetric beam distribution pattern provides wall wash or cyc capability with a widely available PAR fixture and eliminates the need for dedicated cyc or wall wash fixtures.

Description:
PRIORITY CLAIM AND REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. Provisional Application Ser. No. 61/069,259, filed Mar. 13, 2008, under 35 U.S.C. § 119 and 35 U.S.C. § 120. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to an improved wash lighting fixture, e.g., curtain, cyclorama (cyc), scrim, wall or other surface. 
       DESCRIPTION OF THE PRIOR ART 
       [0003]    In lighting applications such as stage and studio and architectural lighting, there is a need for lighting fixtures capable of washing a curtain, cyclorama (cyc), scrim, wall or other vertical surface with light. Preferably, the surface should be evenly illuminated over the lighted region, and vertical and horizontal gradations in intensity should be minimized. To avoid complexity, and to prevent obstruction when the fixtures are supported on or above a floor, the fixtures should be placed relatively close to the vertical surface to be illuminated. This exacerbates the problem of achieving uniform illumination, particularly in the vertical direction. 
         [0004]    PAR (parabolic aluminized reflector) lighting fixtures are widely used in theatres, studios and the like and are readily available for use in lighting applications. A PAR fixture includes a lamp supported in a housing with a parabolic reflector that directs light, often through a lens, to project a generally collimated, cylindrical (typically circular or oval) beam of light. U.S. Pat. Nos. 1,466,358 and 4,285,034 disclose examples of PAR fixtures with refraction lenses. Often a PAR fixture has a fixed lens that refracts light passing through the lens. Successful modern PAR fixtures may have a removable lens, and such fixtures have been provided with replaceable lenses having different refraction characteristics for different purposes. Lenses available for PAR fixtures include lenses with different fixed beam angles and zoom lenses for continuous variation of the light beam dispersion angle. None of the known types and variations of PAR fixtures is suited for cyc or wall wash applications. They are not capable of projecting highly asymmetrical, uniformly distributed light over a vertical region. As a result, dedicated cyc or wash fixtures are required. 
         [0005]    Conventional cyc or wall wash lighting fixtures are special purpose, dedicated fixtures not well suited for other purposes. Normally, this type of fixture includes one or more rectangular lighting units relying on reflectors of special design to spread and direct light over a nearby vertical region to be illuminated. U.S. Pat. No. 1,350,295 discloses an example of a special purpose wall wash fixture. A studio or stage or other venue typically must have cyc or wall wash fixtures in addition to the widely used PAR fixtures. 
       SUMMARY OF THE INVENTION 
       [0006]    A primary object of the invention is to provide a lighting fixture that can function as a PAR fixture or a cyc fixture simply by replacing the lens. Another object is to provide a lens for a PAR fixture that uses both refraction and total internal reflection (TIR) for projecting uniform light over a wall surface such as a wall, cyc, curtain or the like. 
         [0007]    In brief, in accordance with the present invention, there is provided a lighting fixture for illuminating a wall surface. The lighting fixture includes a housing having an axis and a light source in the housing. A reflector in the housing has a concave shape of a surface of revolution for directing light reflected from the light source in a generally collimated beam in the direction of the axis. A lens is supported by the housing in the path of the beam. The lens includes a plurality of lens elements transforming the collimated beam into an illumination pattern for generally uniformly illuminating a region of the wall surface. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The present invention together with the above and other objects and advantages may best be understood from the following detailed description of the preferred embodiments of the invention illustrated in the drawings, wherein: 
           [0009]      FIG. 1  is a simplified schematic diagram of an example lighting fixture constructed in accordance with the present invention; 
           [0010]      FIG. 2  is an elevational view of a wall surface and a floor mounted PAR fixture showing the light beam distribution produced by a typical prior art PAR fixture used in a wall wash or cyc application; 
           [0011]      FIG. 3  is a view like  FIG. 2  illustrating the light beam distribution produced by an example fixture of the present invention in the same application; 
           [0012]      FIG. 4  is a front elevational view of the lens of the fixture of  FIG. 3 . 
           [0013]      FIG. 5  is an enlarged, fragmentary cross sectional view taken along the line  5 - 5  of  FIG. 4  and showing selected lens elements of the lens of  FIG. 4 ; 
           [0014]      FIG. 6  is an elevational view illustrating light beam distributions produced by example fixtures of the present invention in different fixture positions; 
           [0015]      FIG. 7  is a perspective view of a stage having a wall surface illuminated by example fixtures of the present invention; 
           [0016]      FIG. 8  is a front view of a preferred embodiment lens of the invention; 
           [0017]      FIG. 9  illustrates a preferred facet arrangement for the lens of  FIG. 8 ; 
           [0018]      FIGS. 10A-10C  illustrate illumination patterns of the facets of  FIG. 9 ; 
           [0019]      FIGS. 11A-11C  show measured illumination patterns for respective bottom placed fixture, top placed fixture, and combined bottom and top placed example fixtures of the invention, respectively; 
           [0020]      FIG. 12A  illustrates an illumination pattern from the combination of a floor mounted fixture and ceiling (or support) mounted fixture of the invention;  FIG. 12B  illustrates an illumination pattern of an example floor mounted fixture and a typical reflector-based cyc light;  FIG. 12C  illustrates the combined illumination pattern from one reflector-based cyc light on the floor and a second reflector-based cyc light mounted on the ceiling; 
           [0021]      FIG. 13A  is the illumination pattern from an example fixture of the invention set 4 feet from a surface;  FIG. 13B  is the illumination pattern from 3 example fixtures of the invention set 4 feet from a surface and spaced apart by 7.5 feet;  FIG. 13C  is the illumination pattern from a typical reflector-based fixture set 4 feet from a surface;  FIG. 13D  is the illumination pattern from three typical reflector-based fixtures set 4 feet from a surface and spaced apart by 8.5 feet; and 
           [0022]      FIGS. 14A and 14B  are respective front and side views of a typical parabolic fixture retrofitted with a lens of  FIGS. 8 and 9  to form a preferred embodiment fixture of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0023]    Having reference now to the drawings, in  FIG. 1  there is illustrated in simplified, schematic fashion a lighting fixture generally designated as  10  and constructed in accordance with the principles of the present invention. The fixture  10  of the illustrated embodiment of the invention is a parabolic aluminized reflector (PAR) fixture. It includes a housing  22  that may be provided with a yoke  24  for mounting the fixture  10 . Contained within the housing  22  is a reflector  26 , e.g., a concave reflector that is typically in the shape of a conic surface of revolution, and specifically a parabola. 
         [0024]    A lamp  28  supported in the housing  22  provides a concentrated source  30  of light, for example a filament or filament array, located at the focus of the (e.g., parabolic) reflector. Light emitted from the source  30  is reflected from the reflector  26  in a collimated light beam in the form of a right circular cylinder. The light beam, the reflector  26  and the housing  22  share a central axis  32 . 
         [0025]    In accordance with the present invention the lighting fixture  10  is provided with a lens structure  34 . The lens structure  34  includes a circular peripheral frame  36  positioned at the front end of the housing  22 . The frame  36  supports a lens  38  that is specially constructed and arranged to convert the collimated circular light beam from the reflector  26  into an entirely different, highly asymmetrical beam distribution pattern that is optimized for washing a wall surface with light. The beam distribution pattern achieved with the lens  38  is able to provide highly uniform illumination of an extended region of a wall surface. 
         [0026]    Definition. The term “wall surface” is used here to mean a surface that is adjacent to a fixture used for illuminating that surface, and can be a wall, a backdrop, a cyc screen, a scrim, an element of stage or studio scenery or any similar surface to be illuminated by an adjacent lighting fixture. 
         [0027]    Except for the lens structure  34 , the fixture  10  may be identical to a known PAR fixture, such as the SOURCE FOUR™ lighting fixtures sold by Electronic Theatre Controls, Inc. of Middleton, Wis., U.S.A. Such known fixtures may be provided with removable and replaceable lens structures of various types such as refracting lens for various fixed beam angles and adjustable beam angles. However, known PAR fixtures and lenses are not suited for wall wash or cyc applications. 
         [0028]    For example,  FIG. 2  is an illustration of a known PAR fixture  40  used to illuminate a wall surface  42 . The fixture  40  is supported on a floor surface  44  perpendicular to the wall surface  42 , and is positioned adjacent to the wall surface  42 , typically about three to six feet from the wall surface  42 . The light beam axis of the fixture  40  is inclined from vertical and toward the wall surface  42  at an angle of about seventy degrees. The central axis of the light beam from the fixture  40  strikes the wall surface  42  at a point  46  about eight or nine feet above the floor surface  44 . The illumination of the wall surface  42  is not uniform. Rather, the illumination pattern  48  on the wall surface can be described as generally conical. This beam distribution pattern  48  is not suitable for wall wash or cyc applications where a more uniform illumination of a large and generally rectangular wall region is needed. 
         [0029]      FIG. 3  is a view similar to  FIG. 2  showing the fixture  10  of the present invention mounted on the floor surface  44  and illuminating the wall surface  42 . In place of the conical beam distribution pattern  48  of  FIG. 2 , the beam distribution pattern  50  produced by the fixture  10  is generally rectangular and is generally uniform in light intensity throughout the illuminated region of the wall surface  42 . This beam pattern  50  is optimized to be effective as a wall wash or cyc pattern. 
         [0030]      FIG. 4  is a front elevational view of the lens  38  of the example fixture  10 , with a zonal map overlaid thereon for purposes of clarity. In accordance with the invention it is a faceted array of many distinct lens elements. These lens elements include a plurality of first lens elements  52  and one or more, and preferably a plurality, of second lens elements  54 . The lens elements  52  and  54  convert the collimated, generally circular cylindrical light beam from the reflector  26  of the fixture  10  into the beam distribution pattern  50  seen in  FIG. 4 . 
         [0031]    An example first element  52  and an example second element  54  are seen in greatly enlarged cross section in  FIG. 5 . Element  52 , a refracting element, functions by refracting a light beam  56  passing through the lens  38 . Front lens surface  58  is disposed at an angle to the axial beam direction, and the light beam  56  is redirected by refraction at the lens surface  58  and leaves the lens  38  at an angle  60  to the axial direction. Changing the direction of the slope of the front surface  58  of element  52  will change the deflection angle  60  from positive (up) to negative (down) where needed. 
         [0032]    The refractive lens elements  52  are preferably not all identical to one another, but instead are constructed and arranged to uniformly wash and fill segments of the beam pattern  50  with light. In  FIG. 4 , the first lens elements are identified by reference numerals  2 ,  3 ,  4 ,  5 ,  7 ,  8 ,  9 ,  10  and  11  on the zonal map. In the beam distribution pattern  50  seen in  FIG. 3 , the same reference numerals designate the portions of the beam distribution pattern  50  illuminated by the corresponding first lens elements  52 . For example, the lens elements  52  designated as  2  refract light in the columnar beam from the reflector  26  in a direction and at an angle  60  in order to illuminate the regions  2  in the beam pattern  50  of  FIG. 3 . Similarly, the other first lens elements are configured to illuminate the corresponding regions of the beam distribution pattern  50 . 
         [0033]    The ability of lens refraction to efficiently redirect light decreases as the refraction angle  60  increases. For example, the first, refracting lens elements  52  are effective to transmit and refract light in directions along and relatively close to the beam axis. However, when the refraction angle is greater than a relatively small angle, e.g., when the refraction angle exceeds about forty degrees, the first, refracting lens elements  52  are not capable of redirecting light efficiently into the beam distribution pattern  50 . In accordance with embodiments of the invention, the second lens elements  54  are employed for highly off-axis illumination. Example second lens elements  54  transmit and reflect light in off-axis directions diverging at relatively large angles (e.g., greater than 40 degrees) from the beam axis. 
         [0034]    As seen in  FIG. 5 , the example second lens element  54 , which is an internally reflective element such as a total internal reflection (TIR) element, functions by internally reflecting a light beam  62  passing through the lens  38 . Reflective lens surface  64  is disposed at an angle to the axial beam direction, and intercepts the light beam  62  after it enters the lens  38 . The light beam is reflected at the lens surface  64  and leaves the lens  38  at an angle  66  to the axial direction. 
         [0035]    Reflection angles  66  well in excess of forty degrees can be achieved by the internally reflective second lens elements  54 , and these elements are useful for illuminating off-axis regions of the beam distribution pattern  50 . In  FIG. 4 , second lens elements  54  are designated by the reference numeral  6 . In the beam distribution pattern  50  shown in  FIG. 3 , the off-axis areas illuminated by the second lens elements  54  are designated by the corresponding reference numeral  6 . Refractive and reflective lens elements  52  and  54  of the faceted lens  38  are designed to uniformly illuminate the entire beam distribution pattern  50 . 
         [0036]      FIG. 6  is a drawing showing illumination of regions of a wall surface  68  by example fixtures  20 A,  20 B,  20 C and  20 D of the present invention. Fixture  20 A is supported on floor surface  70  and provides a beam distribution pattern  72  like the pattern  50  (iso-illuminance) seen in  FIG. 3 . Fixture  20 B is mounted overhead on a support frame  74  and provides a beam distribution pattern  76  that is like the pattern  72  but inverted. Thus, fixtures  20 A and  20 B provide example beam distribution patterns  72 ,  76  where the fixtures are mounted either on the floor surface  70  or an overhead support frame  74 , respectively. Fixtures  20 C and  20 D are mounted in alignment with one another on the floor  70  and frame  74 , respectively, and combine to produce a beam distribution pattern  78  that uniformly illuminates a region of the wall surface  68  of substantial height. The combination pattern  78  is useful for lighting wall surfaces of stages and studios (for example) that may be of substantial vertical extent. 
         [0037]      FIG. 7  is a perspective view of an exemplary installation of a number of lighting fixtures  20  for a theatrical lighting installation using wall or cyc lighting. The fixtures  20  are positioned to illuminate a wall surface  80  that may be, for example, a cyc screen, scrim, wall, backdrop or element of scenery. The fixtures  20  can be placed front stage (in front) of the wall surface  80 . If the wall surface  80  is translucent, the fixtures  20  can be positioned back stage (in back) of the wall surface  80 . The fixtures  20  can be offset from the wall surface  80  by, for example, four to eight feet. The example wall surface  80  has a height of up to about 40 feet, though the wall surface height can vary for particular fixtures or groups, environments applications, etc. 
         [0038]    Groups 82 of the fixtures  20  are mounted on floor surface  84 , e.g., a stage floor, and other groups  86  of the fixtures  20  are mounted on an overhead support frame  88 . Groups may include one to four fixtures  20 , though it is also possible to have more than four fixtures in a group. Each group  82  and  84  may include fixtures  20  providing white light and fixtures with gels for providing different colors (e.g., three colors, plus white). This array of fixtures in groups can be controlled to achieve a great variety of wall wash or cyc lighting effects. 
         [0039]    As will be apparent to artisans, preferred fixtures of the invention achieve generally uniform illumination patterns even when spaced close, e.g., 3 feet, to a surface being illuminated, and with a high angle of illumination, e.g., up to 70 degrees. This conserves high valuable space that is often wasted to place typical prior fixtures at sufficient distance away from a surface being illuminated to achieve a sufficient amount of uniformity. Combinations of fixtures of the invention produce high uniformity, as well. An advantage of certain embodiments of the present invention is that a fixture, such as but not limited to a PAR fixture, that may not otherwise be suitable for wall washing or cyc applications, can be made suitable by providing a lens structure according to example embodiments of the invention. Thus, in an example embodiment, a prior PAR fixture is fitted with a lens to produce a lighting fixture of the invention. 
         [0040]      FIGS. 8 and 9  show more particular features of a lens  90  for a parabolic fixture according to an embodiment of the present invention. The lens  90  includes a plurality of first elements  52 , including refractive facets, and a plurality of second elements  54 , which preferably are embodied in TIR elements. Individual facets of first elements  52  can be generally configured and classified according to X tilt, Y tilt, X curvature, and Y curvature parameters. Facets of individual second elements  54  can be generally configured and classified according to Y tilt, Y curvature, Z tilt, and Z curvature parameters. In the example facet arrangement for the lens  90  of  FIGS. 8 and 9 , different combinations of these parameters are illustrated by different shadings. 
         [0041]    As shown by the zonal map in  FIG. 9 , common numbers indicate groupings of similar facets. For example, the four facets making up both groups numbered  9  for the first elements  52  are similarly shaped (and symmetrical with respect to the vertical centerline in the zonal map). In the same way, the groups numbered  17  for the second elements  54  have a largely similar pattern from left to right in  FIG. 9  (also symmetrical with respect to the centerline). 
         [0042]    For a particular application, lenses in accordance with the principles embodied in the lenses  90  of  FIGS. 8 and 9  can be designed to creating a smooth light pattern by a multi-step process using optical design software. An example optical design software known in the art is Zemax. 
         [0043]    Each facet making up the individual first elements  52  has a spherical or aspheric shape defined by a group of parameters that may be varied. Similarly, each facet making up the individual second elements  54  has an aspheric shape defined by a group of parameters that may be varied. The prescription of the facets should be adjusted to achieve several goals: uniform illumination over an area (as a non-limiting example, an 8′ wide by 20′ high area), smooth blending for multiple fixtures, and maximum efficiency. This can be accomplished by an iterative process, known to practitioners of the art, of tracing a sufficient number of rays and evaluating the results of a simulated light pattern until the goals are met. In the finished design, the first elements  52  may be all identical, or some may have one prescription and others a different prescription, or all elements may have their own unique prescription. 
         [0044]      FIG. 10A  shows an example first illumination pattern  92  for the lens  90  shown in  FIGS. 8 and 9  that is caused by refractive facets in groups  5 ,  7 ,  9 ,  10 , and  11 , as well as TIR facets in group  17 . For example, the facets in group  10  in  FIGS. 8 and 9  create the portions of the illumination pattern  92  marked  10 . Similarly,  FIG. 10B  shows an example second illumination pattern  94  that is caused by refractive facets in groups  1 ,  8 ,  12 ,  13 , and  14 .  FIG. 10C  shows an example third illumination pattern  96  that is caused by refractive facets in groups  2 ,  3 ,  4 ,  6 ,  15 , and  16 . These illumination patterns  92 ,  94 ,  96  are merely examples, as such illumination patterns can vary based on the particular respective configuration of the first and second lens elements  52 ,  54 . 
         [0045]    The illumination patterns  92 ,  94 ,  96  combine to form a uniform wash, even when a fixture is close to a surface being illuminated.  FIG. 11A  shows a measured photometric pattern from an example lens according to the present invention (such as lens  90 ) fitted into a fixture placed at a bottom of a surface being illuminated.  FIG. 11B  shows a measured photometric pattern from an example lens fitted into a fixture placed at a top of a surface being illuminated.  FIG. 11C  shows a combined measured photometric pattern from example lenses fitted into fixtures placed at a bottom and a top of a surface being illuminated. As shown, the example lens provides a uniform wash from either the bottom or top of the surface to be illuminated, and the combination of bottom and top fixtures produces a uniform wash across the entire vertical surface. 
         [0046]    Given the determined lens facet layout, the lens  90  can be manufactured and fitted into a lighting fixture, including but not limited to a PAR fixture, for wall wash or cyc applications. PAR fixtures fitted with an example lens of the present invention (such as lens  90 ) are compared to a conventional reflector-based cyc light fixture in  FIGS. 12A-12C  and  13 A- 13 D.  FIG. 12A  shows the illuminance along the vertical centerline for dual parabolic fixtures (referred to in  FIG. 12A  as “par cyc lights”), where one is mounted to floor and one to ceiling, having lenses according to an embodiment of the present invention. In  FIG. 12A , the dashed line indicates illumination of individual fixtures, and the solid line shows the combined illumination.  FIG. 12B  illustrates an illumination pattern from a floor (solid line) mounted fixture compared to a typical reflector-based cyc light mounted in the same way.  FIG. 12C  shows an illumination pattern of dual reflector cyc lights that are floor-mounted and ceiling-mounted, where the dashed line indicates illumination of individual fixtures, and the solid line shows the combined illumination.  FIGS. 12A-12C  show that the parabolic fixtures fitted with lenses according to embodiments of the present invention provide significantly more uniform illumination along a vertical surface. 
         [0047]      FIGS. 13A-13D  show the illuminance along horizontal lines at various heights for PAR fixtures fitted with lenses (such as lens  90 ) according to embodiments of the present invention and groups of such fixtures, as well as illumination patterns of a conventional cyc light fixture and groups of such fixtures. Particularly,  FIG. 13A  shows illumination patterns for a PAR fixture fitted with an example lens of the present invention set four feet from a vertical flat surface, while  FIG. 13B  shows illumination patterns for three such fixtures set four feet back from the vertical flat surface and spaced 7.5 feet from each other. For comparison,  FIG. 13C  shows illumination patterns for a conventional reflector-based cyc fixture set four feet back from the vertical flat surface, and  FIG. 13D  shows illumination patterns for three conventional reflector-based cyc fixtures four feet back from the vertical flat surface and spaced at 8.5 feet from each other. As shown in  FIG. 13A-13D , PAR fixtures provided with lenses according to embodiments of the present invention provide significantly more uniform lighting across various heights along the vertical surface. 
         [0048]    As shown in  FIGS. 12A-12C  and  13 A- 13 D, an advantage of example embodiments of the present invention is that certain fixtures that heretofore were ineffective for wall wash or cyc applications can be made effective by providing a suitable lens as disclosed herein. For example,  FIGS. 14A and 14B  show front and side views, respectively, of an example PAR fixture  100  (e.g., a wash luminaire) that is fitted with a lens such as the lens  90  shown in  FIGS. 8 and 9 . The fixture  100  includes a housing  102 , preferably made of a metal such as aluminum, and is provided with a yoke  104  for mounting. A reflector  106  is contained within the housing  102  in the shape of a conic surface of revolution, and specifically a parabola. A lamp (not shown in  FIGS. 14A-14B ), for example a filament or filament array, supported in the housing  102  provides a concentrated source of light, located at the focus of the reflector  106 . A suitable electrical coupling  109  provides a power supply for the lamp. For controlling a temperature of the reflector  106 , a heat sink is preferably provided. A heat sink may also be provided for the lamp, for example at a lamp base. 
         [0049]    The lens  90 , preferably moulded borosilicate glass, may be supported by a lens structure  110  that is positioned at a front end of the housing  102  (e.g., the lens may be mounted in the lens structure). In some example embodiments a rotating ring  114 , preferably thermally insulated, is provided for rotating the lens  90 . 
         [0050]    While the present invention has been described with reference to details of the embodiment of the invention shown in the drawings, these details are not intended to limit the scope of the invention as claimed in the appended claims.