Abstract:
A generally plano rectangular louvers are capable of being ganged in a stacked tiltable array to enhance light re-direction when titled to follow the solar elevation. Combinations of features and optical characteristic avoid optical artifacts and enhance efficiency of light utilization and manufacturing. Different louvers can be combined in alternative ways in such arrays.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims the benefit of priority the US provisional patent application of the same title that was filed on May 21, 2015, having application No. 62/164,834, and is incorporated herein by reference. 
     
    
     BACKGROUND OF INVENTION 
       [0002]    The field of invention is light re-directing structure suitable for use with exterior glazing to selectively enhance the penetration of exterior light within an interior space. 
         [0003]    Such light directing structures are well known and rely primarily on total internal reflection (TIR) of solar radiation, which has the highest angle of incidence on the glazing surfaces near noon time. A planar transparent member (which can either form a glazing surface or is mounted parallel to a glazing surface) can re-direct light that would otherwise only reach the floor closest to the glazing. High angle incident light, rather than being transmitted directly toward the floor close to a window, is re-directed upward toward the ceiling so that it then scatters distal from the window, resulting in a farther penetration of natural light into the interior rooms of the structure. 
         [0004]    It should be readily appreciated that controlling the re-directed angle allows for greater penetration of re-directed light, as the light incident at high angle near noon time, would be directed toward the ceiling rather than the floor, where it would be scattered to provide natural diffuse light from above, rather than glare from a polished or specular floor surface or absorbed by the floor (where it would not contribute to the illumination of work surfaces), and hence permit the minimization of the use of artificial lighting, as well as increase the productivity and well being of the additional inhabitants that enjoy natural light 
         [0005]    However, such light re-directing structures while generally effective have limitation and trade-offs between desirable benefits and undesirable effects. Further, the utility of current light redirecting structure are limited to particular daylight hours. 
         [0006]    Hence, it is a general objective of the invention to increase the efficiency of light re-direction while simultaneously greatly reducing the undesirable effects that may have been unappreciated or poorly understood in the prior art. 
         [0007]    The above and other objects, effects, features, and advantages of the present invention will become more apparent from the following description of the embodiments thereof taken in conjunction with the accompanying drawings 
       SUMMARY OF INVENTION 
       [0008]    In the present invention, the first object is achieved by providing a louver, comprising a generally rectangular planar support member having, an upper surface and a lower surface opposite the upper surface, an elongated front side on a side orthogonal to the plane of the upper surface, and an elongated back side opposed to and parallel with the front side, a right side on another side that is orthogonal to both the upper surface and the front side, and a left side opposite the front side that is parallel to the right side, a light redirecting structure that is at least one of attached to and disposed within the planar support member, the light redirecting structure comprising a plurality of spaced apart light reflective surfaces that terminate at corners, wherein the light reflecting surface thereof extend across the planar support member from the front side to the back side in which each light reflective surface faces the front or back side, wherein the light reflective surface is operative to increase the width of a main specular re-directed beam of incident light by at least about ±1°, but more preferably at least about ±2° and most preferably by at least about ±4°. 
         [0009]    A second aspect of the invention is characterized by the louver wherein the light reflective surfaces have a portion that is parallel to the opposing surface of each optical element and a portion that deviates in angle by up to at least about 2°. 
         [0010]    Another aspect of the invention is characterized by the louver wherein a portion of the reflective surfaces are tilted with respect to the front and back edge to provide the increase in width of a main specular reflected beam of incident light by at least about ±4°. 
         [0011]    Another aspect of the invention is characterized in by the louver wherein the spaced apart light reflective surfaces are formed by a series of stacked transparent optical elements. 
         [0012]    In the present invention, the first object is achieved by providing a louver, comprising a generally rectangular planar support member having; an upper surface and a lower surface opposite the upper surface, an elongated front side on a side orthogonal to the plane of the upper surface, and an elongated back side opposed to and parallel with the front side, a right side on another side that is orthogonal to both the upper surface and the front side, and a left side opposite the front side that is parallel to the right side, a light redirecting structure that is at least one of attached to and disposed within the planar support member, the light redirecting structure comprising a plurality of spaced apart light reflective surfaces that terminate at corners, wherein the light reflecting surface thereof extend across the planar support member from the front side to the back side in which each light reflective surface faces the front or back side, wherein the light reflective surfaces is operative to increase the width of a main specular reflected beam of incident light by at least about ±4°. 
         [0013]    A second aspect of the invention is characterized by the louver wherein the light reflective surfaces have a portion that is parallel to the opposing surface of each optical element and a portion that deviates in angle by up to at least about 2°. 
         [0014]    Another aspect of the invention is characterized by any such louver wherein a portion of the reflective surfaces are tilted with respect to the front and back edge to provide the increase in width of a main specular reflected beam of incident light by at least about ±4°. 
         [0015]    Another aspect of the invention is characterized by any such louver wherein the spaced apart light reflective surfaces are formed by a series of stacked transparent optical elements. 
         [0016]    Another aspect of the invention is characterized by any such louver wherein the spaced apart light reflective surfaces have a portion have a planar portion and a non-planar portion. 
         [0017]    Another aspect of the invention is characterized by any such louver wherein the spaced apart light reflective surfaces have a diffusing portion. 
         [0018]    Another aspect of the invention is characterized by any such louver wherein the non-planar portion has a sinusoidal variation in one of the slope, height and wavelength. 
         [0019]    Another aspect of the invention is characterized by any such louver wherein the sinusoidal variation in one of the slope, height and wavelength is at least partially random. 
         [0020]    Another aspect of the invention is characterized by any such louver further comprising a pattern of light attenuating elements disposed on one of the upper surface and the lower surface. 
         [0021]    Another aspect of the invention is characterized by any such louver wherein the light attenuating elements are disposed on one of the upper surface and the lower surface to provide an internal attenuation of incident light of about 10% to about 40%. 
         [0022]    Another aspect of the invention is characterized by any such louver wherein the light attenuating elements are round dots disposed in columnar arrays with an offset of adjacent columns. 
         [0023]    Another aspect of the invention is characterized by any such louver wherein the round dots have a diameter of between about 0.5 to 3 mm. 
         [0024]    Another aspect of the invention is characterized by any such louver wherein the light attenuating elements have a grey appearance. 
         [0025]    Another aspect of the invention is characterized by any such louver wherein the light attenuating elements are opaque and non-scattering. 
         [0026]    Another aspect of the invention is characterized by any such louver further comprising a pattern light diffusing elements disposed on one of the upper surface and the lower surface. 
         [0027]    Another aspect of the invention is a light re-directing louver assembly comprising a plurality of louvers that are operatively coupled to be tilted, each louver comprising a generally rectangular planar support member having; an upper surface and a lower surface opposite the upper surface, an elongated front side on a side orthogonal to the plane of the upper surface, and an elongated back side opposed to and parallel with the front side, a right side on another side that is orthogonal to both the upper surface and the front side, and a left side opposite the front side that is parallel to the right side, a light redirecting structure that is at least one of attached to and disposed within the planar support member, the light redirecting structure comprising a plurality of spaced apart light reflective surfaces that terminate at corners, wherein the light reflecting surface thereof extend across the planar support member from the front side to the back side in which each light reflective surface faces the front or back side, wherein the light reflective surfaces are operative to increase the width of a main specular re-directed beam of incident light by at least an angular deviation that arise between adjacent louvers in the louver assembly. 
         [0028]    The above and other objects, effects, features, and advantages of the present invention will become more apparent from the following description of the embodiments thereof taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0029]      FIG. 1A  is a cross-sectional elevation view of the desired effect of light re-directing structures toward noon time when light is incident at high angles on vertical glazing surfaces, whereas  FIG. 1B  is a similar elevation view showing the actual effect of the configuration of  FIG. 1A  earlier in the morning or later in the day. 
           [0030]      FIG. 2  is a cross-sectional elevation of a light redirecting structure that deploys an assembly of optical elements having planar orthogonal surfaces. 
           [0031]      FIG. 3A-D  are cross-sectional elevations of a ganged louver assemblies formed from light redirecting structure, in which  FIG. 3A  corresponds to the orientation in the lighting conditions of  FIG. 1A , and  FIG. 3B  corresponds to lighting conditions of  FIG. 1B , and in which  FIG. 3C  is an optional orientation for the louvers in the assembly.  FIG. 3D  is a perspective view of an embodiment of the invention in the form of a louver panel of the assembly. 
           [0032]      FIG. 4  is a photograph showing an example of the projected pattern of louvers on a interior wall 
           [0033]      FIG. 5A  is a schematic cross-sectional elevation of a portion of a louver assembly modeled in  FIG. 6  and  FIG. 7  with ray tracings, and  FIG. 5B  shows the ray tracings in  FIG. 5A  in a plan view. 
           [0034]      FIG. 6  is a ray tracing diagram corresponding to  FIG. 5A  showing potential deviation from a single louver. 
           [0035]      FIG. 7  is a ray tracing diagram corresponding to  FIG. 5A  showing potential deviation from light incident on the entire louver assembly. 
           [0036]      FIG. 8A  is a schematic cross-sectional elevation with ray tracings to illustrate the operation of a first embodiment of the invention, whereas  FIG. 8B  similarly illustrates a related embodiment. 
           [0037]      FIG. 9  is a schematic cross-sectional elevation with ray tracings to illustrate the operation of another embodiment of the invention. 
           [0038]      FIG. 10  is a schematic cross-sectional elevation with ray tracings to illustrate the operation of another embodiment of the invention. 
           [0039]      FIG. 11  is a schematic cross-sectional elevation with ray tracings to illustrate the operation of another embodiment of the invention. 
           [0040]      FIG. 12  is a schematic cross-sectional elevation with ray tracings to illustrate the operation of another embodiment of the invention. 
           [0041]      FIG. 13  is a schematic cross-sectional elevation with ray tracings to illustrate the operation of another embodiment of the invention. 
           [0042]      FIG. 14A-C  illustrate steps in a first process of forming an optical element in a louver assembly having the attributes of the embodiment of  FIG. 11   
           [0043]      FIGS. 15A and 15B  illustrate another process of forming an optical element in a louver assembly having the attributes of the embodiment of  FIG. 11   
           [0044]      FIG. 16A-C  illustrate alternative embodiments for forming various embodiment by a molding process that produces a spacer member. 
           [0045]      FIG. 17A-C  illustrate alternative embodiments for forming various embodiment by a molding process that produces a spacer member on a different surface. 
           [0046]      FIG. 18A-C  illustrate alternative embodiments for forming various embodiment by a molding process in which the spacer element is a diffuse blackening element coated on the upper surface. 
           [0047]      FIG. 19  is a cross-sectional elevation of a portion of a preferred embodiment of ganged louver assembly formed from light redirecting structure. 
           [0048]      FIG. 20  is an exploded view of another embodiment of the invention in which a light re-directing film is adhered to glazing with an adhesive and the light re-directing film has an exterior pattern of light absorbing and or diffusing members. 
           [0049]      FIG. 21A  is a cross-sectional elevation view of the light re-directing film of  FIG. 20  after application to the glazing, whereas  FIG. 21B  is a rear elevation of the glazing showing the pattern of absorbing and/or diffusing members. 
           [0050]      FIG. 22  is a top plan view of a planar sheet shaped substrate used for forming optical elements in various embodiment of the invention. 
           [0051]      FIG. 23A  is a cross-sectional elevation of an embodiment of the invention, whereas  FIG. 23B  is cross-sectional elevation of an alternative related embodiment of the invention fabricated using the sheet shown in  FIG. 22 . 
           [0052]      FIG. 24  shows a ray tracing of  FIG. 23B  in a top plan view. 
           [0053]      FIGS. 25A and 25B  are alternative embodiments of  FIG. 21A . 
           [0054]      FIG. 26A  is an alternative embodiment to  FIGS. 21A, 25A and 25B , whereas  FIGS. 26B  and C are elevation views of representative optical element arrays shown in section view in  FIGS. 21A, 25A, 25B and 26A . 
       
    
    
     DETAILED DESCRIPTION 
       [0055]    Referring to  FIGS. 1A through 26C , wherein like reference numerals refer to like components in the various views, there is illustrated therein a new and improved Louvered Light Re-Directing Structure, generally denominated  1000  herein. 
         [0056]    In accordance with the present invention the Louvered Light Re-Directing Structure  1000  comprises a plurality of elongated narrow and thin slats or louvers  600  (see perspective view in  FIG. 3D ) which individually or collectively have specific constructions described in details below. Other aspects of the invention include deploying slats  600  with different constructions, and that are separately adjustable. 
         [0057]    A slat or individual louver  600  should be understood to be a generally rectangular planar support member having an upper surface and a lower surface opposite the upper surface, an elongated front edge on a side orthogonal to the plane of the upper surface, and an elongated back edge opposed to and parallel with the front edge, a right side on another side that is orthogonal to both the upper surface and the front edge, and a left side opposite the front side that is parallel to the front side, and a light redirecting structure either attached to or disposed within the planar support member. The light re-directing structure would comprise a plurality of spaced apart light reflective surfaces  110   a  and/or  110   a ′ that terminate at corners, wherein the light reflecting surface thereof extend across the planar support member from the front edge to the back edge; so that each reflective surface is orthogonal to the planes of the left and right side sides of the planar support member. 
         [0058]    In some preferred embodiments described more fully below, the light reflective surfaces preferably have a periodic pitch of more than about 0.5 mm. 
         [0059]    In other embodiments of the light re-directing structure  1000 , different slat or louvers  600  are combined in a stack, in which the louvers are tiltable, but each louver need not have the same light redirecting properties as the other louvers in the structure. 
         [0060]      FIG. 1A  illustrates the preferred use of a day light re-directing structure or louver array  1000  deployed to direct at least some portion of light rays  10  incident at high angles from the sun  2  on glazing  15  away from the path  11 , which it would otherwise take in a room toward the floor  5 , and re-direct it back upward towards the ceiling  20  as ray  12 . Thus, incident sunlight is re-directed to the ceiling  20 , as ray  12 , where it will be scattered off the ceiling  20 , providing occupant  2 , whom is farther from a window glazing  15  than occupant  1 , with diffused natural light  13 . In  FIG. 1B , the sun  2  is at a slightly lower elevation, some rays  10 ′ would also be re-directed, as rays  12 ′, though deeper in the room, where it is scattered off the sealing as diffused natural light  13 ′. 
         [0061]    Hence, conventional light re-directing film applied on the entire window surface would not be able to provide the benefit of  FIG. 1A , and also alleviate the annoying direct light in  FIG. 1B . Further, although diffuse coating on a side of the convention light directing film can reduce glare, it also limits see through visibility. Hence, in uses where visibility is critical, the application of convention light re-directing films would be limited to the clerestory portion of the window  15   a  and the lower portion  15   b  of the window or glazing  15  would be covered with conventional shades or blinds. 
         [0062]      FIG. 3A-D  generally illustrates the various embodiments of the invention  1000 , as a ganged assembly of slats  600  in which the slat are tiltable. 
         [0063]    In  FIG. 3C , the light re-directing optical structure  1000 , is an assembly of louver or slat elements  600  (as shown in  FIG. 3D  among others), with each slat or louver element  600  being an independent light re-directing optical structure, which in at least a portion of the assembly are capable of rotation via a coupling or cable  620  to accommodate the variation in sun angle over the day. Thus, the tilting of the louvers or slat  600  permits a more efficient re-direction of incident sunlight, which scatters off the ceiling as, rays  13 , over a larger portion of the day. 
         [0064]    Each louver or slat  600  is a transparent rigid planar support surface in a rectangular shape having opposing faces, and a set of orthogonal front and rear faces and left and right side edges, in which the faces are longer than the edges. 
         [0065]    The louvers  600  are preferably constructed of generally elongated optical elements  110  that are assembled by a stacking process, and are preferably held together between front and rear surface  120 ′ and  120  respectively, as shown in  FIG. 3D , with  FIG. 2  showing an enlarged portion of a louver or slat  600  in which faces  120 ′ and  120  are horizontally disposed. Adhesive layer  130  and  130 ′ may be deployed to attach the plurality of optical elements  110  to the respective front and rear surfaces  120 ′ and  120 . 
         [0066]      FIG. 2  also illustrates that the optical elements  110  may deploy a light absorbing coating or covering  110   c  on surface  110   a ′ of each optical element  110 . The light absorbing layer precludes the re-direction of light that impinges on layer  120 ′ from below the horizon, as may occur at night from headlamps and street lighting when device  1000  is used in building floors above street level. Such discrete light sources would produce annoying light re-directed downward from the louver assembly, as well as preclude a room from staying dark when this is desired. The absorbing surface  110   c  also provides the benefit that light incident at high azimuthal angles, as shown in  FIG. 5B , rather than undergoing a double reflection, off both surface  110   a ′ and  110   a , and heading toward the floor would be absorbed at layer  110   c.    
         [0067]    As shown by the photograph in  FIG. 4 , an actual louvered device  1000  with slats or louvers  600  optimized for light re-direction can project a discrete image ( 401 ) of each slat  600  on both vertical (floor and ceiling) and horizontal walls. It would be more desirable if the slat assembly  1000  did not produce discrete images of each slat  600 , but more uniformly redirected light into the structure. These strong discrete projected images are now understood to be from a combination of tilt errors, which throws light out of one area, leaving a dark spot ( 403 ) while placing the light over a neighbor&#39;s light. Thus some areas ( 402 ) have double or triple the light intensity of a single neighboring slat. The waviness along the light (bottom left to upper right) is caused by wavy log like elongated optical elements  110 . 
         [0068]    It has now been discovered that the discrete images of each slat are caused by multiple factors. One such cause is the physical gap between each pair of slats, which is tilt dependent. Even if the slat  600  are tilted by the identical angle in the assembly  1000 , slight defects in structure produce noticeable effects, which are accentuated by deviation in tilt. Deviations from identical tilt can occur from slack or hysteresis in the mechanical drive system  620 , and possibly wear of mechanical components, as well as assembly and component tolerances. 
         [0069]    Small deviations greatly accentuate the image of the gaps, in that some bright areas will overlap, doubling the intensity ( 402 ), while intervening areas ( 403 ) will be darker. Thermal or other distortion of each slat  600  or slight deviations in mounting can also occur and contribute to the projection of slat image on the ceiling, walls or floor. 
         [0070]    Accordingly, the various embodiment of the invention disclosed below are intended to produce and assemble macro-optical elements  110  into slats  600  with intervening TIR surfaces in a manner where the angular distribution of reflected light has a pre-determined distribution with respect to the slat dimensions. The distribution is intended to eliminate the projection of discrete slat images. The most preferred embodiments are also intended to eliminate the projection of slat images without unduly degrading the efficiency of light reflection or introducing glare, that is, bright spots, bars, beams, rings or halos when the slat area is viewed directly. 
         [0071]    It is also desirable to achieve the pre-determined angular distribution of light from each slat without unduly degrading see through visibility. In other words, a room occupant, when looking at the window, should not have a distorted or defocused view of the exterior, nor should they see annoying bright regions, or glare. 
         [0072]    Since macro optical elements  110 , with width greater than about 0.5 mm, are needed to minimize glare by minimizing diffraction, there is now a need to spread light evenly across the interior ceiling, since re-directed sun light is highly collimated. The various embodiments of the invention and methods of fabricating such embodiment provide a viable construction for making the re-directed light sufficiently less collimated to account for construction and use deviations, while preferably maintaining a see-through function. 
         [0073]    Several embodiments deploy preferred embodiment of the stacked optical elements  110 , while other deploy specific constructions of the slats  600 . 
         [0074]    Other embodiments of the invention are directed to method of fabricating such optical elements  110  and/or slats  600 . 
         [0075]      FIGS. 5A and 5B  illustrates the ray tracings of a rectangular optical element  110  in the louver slat  600 . For simplicity, the rays are traced only through the portion of the slat  600  having TIR at surface  110   a ′. Each optical element  110  has a width of about 2 mm and a height of about 1 mm for a 2:1 aspect ratio. Light incident at 42° from normal is refracted to 27° inside the optical element, and after undergoing TIR on surface  110   a  exits rear surface  110   b ′ at 42°. It has been discovered that this element size and aspect ratio is optimal for medium angle sun, in which the azimuthal angle is high in the morning and afternoon and the elevation angle, α, is between about 30 to 65°. 
         [0076]    As illustrated in  FIGS. 5A and 5B , when the sun elevation decreases, there is an increase in azimuthal angle (ψ) of incidence on glazing surface  15  and optical element  110 , which has reflective upper and lower surface  110   a  and  110   a ′. Hence, the light incident on any optical structure used for light re-direction will have a greater path length as shown in the plan view in  FIG. 5B , in which ray segment  10   a  within the optical structure is longer as the azimuthal angle increases. Thus, some of these rays as shown in elevation view in  FIG. 5A , entering the optical element  110  as ray  10 , will undergo a first reflection at the lower surface  110   a ′, and then be directed upward and in the room direction and exits as ray  12 . However, others rays will actually undergo  2  reflections, the second on the upper reflective surface  110   a , and continue to the exit face of the optical element  110  but directed downward. Thus, optical re-directing structure will lose efficiency during the day as the suns position changes unless the angle of slat assembly  600  is fixed. As shown in plan view in  FIG. 5B , the high azimuthal angle increase the path length  10   a  in element  110 , so that the shorter width of TIR surface  110   a ′ minimizes the amount of light that is lost or not utilized from double reflections, which would be directed to the floor and not the room interior. In such cases, it is actually preferred that light that would undergo a second reflection is absorbed by an optional layer  110   c  deposited on what would otherwise be a TIR surface  110   a.    
         [0077]      FIGS. 6 and 7  illustrate the projection geometry of the louvers  600  on the ceiling  20  or room  40  to explain the theory of operation of the various embodiments now illustrated in  FIG. 8-24 . Room  40  is 10 feet high and 30 feet deep. Louver assembly  1000  is 2 feet high and starts 1 foot from the ceiling  20 . 
         [0078]    It has been observed that depending on the mounting and rotary means for the slats  600 , the lateral displacement of the slats  600  can vary by as much as 2 mm for a 50 mm (2 inch) high slat. Hence, the tilt angle between these slat is about tan (2/50) or about 2 degrees. A ±2° deviation in orientation from each slat will result in a 4° deviation in the projected image of each slat. It is preferred that each slat diffuses light beyond the pure collimated image by at least the amount of deviation from all sources. To spread the light beyond this range requires some fraction of the TIR surface to deliberately deviate over a similar range, for this 4 degree deviation, some portion of the TIR surface should have 2 degrees of slope deviation in the TIR reflection surface from the nominal orientation. 
         [0079]      FIG. 6  illustrate the bundle rays  12  as multiple parallel lines that exit the center of the surface of each slat  600  in an array that illuminate the ceiling  20  of room  40 . Ray  12 * results from a 2 degree deviation in tilt from the center of the center slat in the array. The array of slats spread light over the ceiling in region  1241 ′. 
         [0080]      FIG. 7  compares the ray  12 ′ from single slat  600  adjacent the deviant slat that produces rays  12 *. The tilt error of 2 degrees in a slat, represented by ray  12 *, has moved the center of that beam from position  1241  to  1241 *, approximately 57 inches on the ceiling  20 , at this re-direction angle. This 57 inch movement corresponds to observations of variance that arise from assembly deviations as well as slat deviations and thermal distortion. 
         [0081]    If a given slat  600  is not parallel to the adjacent neighboring slat within 2 degrees, the re-direction error will be twice that amount, or 4 degrees. If the light from each slat  600  can be spread over the same 4 degrees of deviation then slat images will overlap, removing the gaps between them and the patterns these deviations cause. However, it should be noted that it is possible for two slats next to each other to have a rotational deviation in opposite directions, which increase the ray deviation to about 8 degrees still providing non-uniform illumination on the ceiling, which the preferred embodiments are intended to minimize. According, the following means for overcoming this angular deviation is not limited to solutions for 2° deviation, as it will be apparent to one of ordinary skill in the art that teachings of the invention can be applied to other deviations that arise between adjacent or more distal slats  600  in a louver assembly  1000 . 
         [0082]      FIG. 8A  is a schematic cross-sectional elevation with ray tracings to illustrate the operation of a first embodiment of the invention. Optical element  110  has surface  110   b  covered by a diffusing rear surface  801 . The diffusing surface  801  would spread each ray that undergoes TIR in optical element  110  by about 2 degrees in each direction from the central beam, and more preferably 4 degrees. However, a uniform diffuse coating would degrade see through visibility of the louver assembly  1000 . A more preferred variation on this embossment is illustrated in  FIG. 8B  in which the diffuse coating  801 ′ is applied as a pattern. Since the preferred optical elements  110  have a height of about 1 mm in the vertical direction, it would be more preferable if each part of the pattern formed by elements  801 ′ is less than this height, and more preferably about a ¼ to a third the element height, that is about 0.25 to 0.33 mm. Such a pattern would not destroy see through visibility. The area of the patterned elements  801 ′ can be reduced by increasing the scattering power, that is have a more diffusing coating in the element  801  that cover the entire rear surface of the slat  600 . The total area of the patterned elements is perhaps about 1 to 5% of the covered glazing surface or surface of vertical louvers  600 , which preferably have dimensions of circa 2 to 7 mm, and more preferably 5 mm×5 mm, with a spacing of preferably about 10 to 30 mm, but more preferably about 23 mm. 
         [0083]    In another embodiment of the invention, the diffuse dots/squares, lines and like shown in  FIGS. 8B, 20, 21 and 21B  are alternatively non-diffuse, opaque regions that are optionally neutral or colored to provide a pattern that aids in masking the lone and isolated optical defects that would otherwise standout as cosmetic imperfections. The provisional of such opaque pattern regions in a repeating or non-repeating pattern of dots, squares or any geometric array at a low coverage percentage of circa 0.1 to 10%, and more preferably 1 to 5%, decreases the perception of such defects to the human eye. Hence, it would also minimize the appearance of seams that might be required in large panels or slat arrays that are not practical to make in a seamless fabrication. 
         [0084]      FIG. 9  is a schematic cross-sectional elevation of optical elements  110  in a slat  600  with ray tracings to illustrate the operation of another embodiment of the invention. A portion  901  of the TIR surface  110   a ′ is not planar and orthogonal to surface  110   b  and  110   b ′, but rather has adjacent titled facets  902  separated by vertical steps  903 . The facets  902  increase in tilt angle away from the plane of surface  110   a . The maximum tilt angle is preferably about 2° from planar portion  095 , which is parallel to surface  110   a.    
         [0085]      FIG. 10  is a schematic cross-sectional elevation with ray tracings to illustrate the operation of another embodiment of the invention in which a portion  1001  of the TIR surface  110   a ′ is not planar and orthogonal to surface  110   b  and  110   b ′, but rather gradually increases in curvature as it approaches surface  110   b ′, in essence forming a curved bottom near the corner of each optical element  110 . 
         [0086]      FIG. 11  is a schematic cross-sectional elevation with ray tracings to illustrate the operation of another more preferred embodiment of the invention in which the TIR surface  110   a  is non-planar but has a gradually sinusoidal variation in height, to provide an equivalent variation in slope. The variation need not be perfectly sinusoidal, but is preferably gradual to provide at least a maximum slope variation on ±2°. A 2 degree slope means that a line tangent to a portion of the TIR surface deviates from planar shape of the surface by 2 degrees. Hence in a preferred embodiment of the invention each slat  600  will re-direct incident light that is directed downward and upward as a main transmitted beam, while also spreading some light about the main transmitted or re-directed beam  12  by at least about ±1° from the angle of incidence, but even more preferably at least about ±2° from the angle of incidence, and most preferably at least about ±4° from the angle of incidence. Higher spreading of the light from the main beam  12  is also useful in projecting light deeper into a room. 
         [0087]    The desired circa 1-2 degree slope deviation is preferably provided by a generally sinusoidal oscillation in the surface shape. The tangents at the peaks and valleys of the surface will have a zero slope, being parallel to the macro-surfaces  110   a ′ as well as the opposing upper surface  110   a  of each optical element  110 . The surface tangents to the portions between the peaks and valleys will gradually vary in slope between zero and about 2 degrees. 
         [0088]      FIG. 12  is a schematic cross-sectional elevation with ray tracings to illustrate the operation of another more preferred embodiment of the invention in which surface  110   a  has a light absorbing coating  110   c  and TIR surface  110   a  is non-planar but has this preferred generally sinusoidal variation in slope. When the sinusoidal variation extends entirely across surface  110   a ′, the variation can be two-dimensional, that is each adjacent cross-section have the same shape, or 3 dimensional as well. 
         [0089]      FIG. 13  is a schematic cross-sectional elevation to illustrate another embodiment of the invention in which only portion  1301  of TIR surface  110   a  is non-planar but has a generally sinusoidal variation in slope, with a central portion  1302  being planar and parallel to surface  110   a . Such a general sinusoidal variation in slope is meant to embrace a randomly sinusoidal variation in slopes of between 0 and ±2° and optionally also that the period or wavelength is somewhat random in length. 
         [0090]      FIGS. 14A-C  and  15 A-B illustrate steps in alternative processes of forming an optical element  110  in a louver or slat  600  having the light re-directing attributes of the embodiment of  FIG. 11-13 . 
         [0091]    In the step shown in  FIG. 14  a transparent fluid, which is preferably a UV curable fluid,  1401  is printed on the surface of the sheet material  1400  used to form elongated optical elements  110 . The printing is in a predetermined pattern of a desired spacing and height, which optionally may include a random spacing. The printed coating when cured preferably has an identical refractive index to the underlying generally planar optical substrate material  1400 .  FIG. 14B  shows the fluid  1401  cured to a solid  1402  after a second step of covering with a second fluid coating  1403 , which is also preferably curable with UV light to form a solid coating  1404  having an identical refractive index to the underlying optical substrate material  1400 . 
         [0092]    The viscosity and thickness of layer  1403  will determine the level of shape conformity to the first solid pattern  1402 . When layer  1403  is thin relative to the thickness of the solid coating  1402  the degree of wetting from the relative surface tension will provide a wavy sinusoidal variation in shape to provide the desired surface  110   a ′ of  FIGS. 11-13 and 23A -B. The patterns and thickness of the solid pattern  1403  is selected to provide the wave spacing and height, and hence the degree of surface slope on the solid layer  1404 . The printed and coating in this process can be continuous across the entirety of the sheet  1400 , or patterned as shown in  FIG. 22  to provide the limited portions  1301  of surface shape modulation. This embodiment can provide a 2-dimensional variation in slope when the solid pattern is lines that extend on the long direction of each optical element  110 , or 3-dimensions when the pattern is discrete circles, squares, rectangles, polygons, dashed and continuous lines that optionally form a 2-dimensional array on the surface of sheet  1400 . 
         [0093]      FIGS. 15A and 15B  illustrate another process of forming an optical element  110  in a louver assembly having the attributes of the embodiment of  FIGS. 11-13 and 23A -B in which the substrate  1400  is coated with a curable fluid  1501  having dispersed filler particles  1502  that are comparable in size to the thickness of the fluid to form a wavy surface pattern. The pattern will not be perfectly periodic, however, as long as the mean repeat distance is much smaller than the width of the TIR surface and the surface slope is between about 2-4°, the anticipated optical benefits should also be achieved. The filler particles  1502  are preferably transparent and non-scattering internally, as well as at the interface with the cured or solid coating, having the same index of refraction. This embodiment has the advantage that a single layer of fluid, such as semi-gloss paint or finish can be applied to the sheet  1400 . The aforementioned process can provide regions of the wavy surface pattern that are continuous across the entirety of the sheet  1400 , or patterned as shown in  FIG. 22  to provide the limited portions  1301  of surface shape modulation. The surface variation will be 3-dimensional in this embodiment. It should be noted that the wavy surface pattern regions that are angle with respect to the sheet  1400  edges can be continuous or discontinuous, be applied in other or multiples directions as well as have other fill factors. 
         [0094]    In the embodiments of  FIGS. 14A-C  and  15 A-B, the opposite side of the sheet  1400  can be coated with a black or absorbing coating that forms layers  110   c  in each optical element. In either case, the sheet  1400  is then cut into long optical elements  110 , as described with respect to  FIG. 22 . 
         [0095]      FIG. 16A-C  illustrates alternative embodiments of the optical elements  110  with various partially angulated TIR surfaces  110   a ′ formed on optical element  110  by a molding process. Spacers  1601  and  1601  are molded on surface  110   a  at the same time as the deviation from planarity in surface  110   a ′. More specifically, the optical element  110  in  FIG. 16A  has the generally sinusoidal variation in surface slope of  FIG. 11-13 . The optical elements  110  in  FIG. 16B , has the faceted portions  901  of  FIG. 9 , and the optical elements  110  has the curved portion  1001  of  FIG. 10 . Spacers  1601  and  1602  preclude the optical elements surface  110   a  and  110   a ′ from making contact during stacking and attachment to outer covers  120  and  120 ′ of  FIG. 3D . 
         [0096]      FIG. 17A  illustrates an alternative embodiment of the optical elements  110  with spacers  1601  and  1601 ′ are molded on surface  110   a ′, opposite planar surface  110   a .  FIG. 17B-C  illustrates alternative embodiments in which the optical elements  110  have various partially angulated TIR surfaces  110   a ′ formed on optical elements  110  by a molding process. Spacers  1601  and  1601  are molded on surface  110   a ′ along with the variation in shape to spread light that under goes TIR on surface  110   a ′. These configurations facilitate the blackening of the upper or opposing surface  110   a  from the TIR surface  110   a ′, to provides the light absorbing upper surface  110   c , as shown in  FIG. 17C . The surface  110   a  that is intended to receive the black absorbing layer  110   c  is initially planar thus easier to uniformly coat at the same time, such as by spray, roller or curtain coating and the like processes. Although the elements  110  are molded separately the coating of layer  110   c  can occur while they are attached to a common mold runner or ganged together on a common support, such as a vacuum chuck from below. 
         [0097]      FIG. 18A-C  illustrate alternative embodiment of a molding process in which the spacer element  100   c  is a diffuse blackening element coated on the upper surface  110   a . The blackening coating or paint can have dispersed colorant, such as carbon black, as well as other pigment or fillers that create uneven rough surface on curing or drying. 
         [0098]      FIG. 19  illustrates a preferred embodiment of a ganged louvered structure in which the spreading of light is accomplished by mounting each louver  600  to have an approximately 1° relative tilt to the adjacent louver  600 ′. Accordingly, louver  600 ″ is mounted with approximately 2° relative tilt with respect to louver  600 , and so on along the louvered light re-directing structure  1000 . This embodiment can deploy any of the optical elements  110  described with respect to the other embodiments of the slats  600 . The louvers  600  can optionally deploy the light diffusing or partially angulated TIR surface disclosed in other embodiments. This example only illustrates 1° relative tilts, but is not limited to this increment. 
         [0099]    More particularly, in the context of a light re-directing louver assembly comprising a plurality of louvers that are operatively coupled to be tilted, as in a ganged assembly for disposing the louver array opposite glazing each louver is preferably operative to provide a predetermined angular deviation of a main specular re-directed beam of incident light from other louvers in the array, and more preferably from the immediately adjacent louver. 
         [0100]    In low diffraction, highly collimated optical assemblies of select embodiments of the instant invention, it is desirable to provide daylight across the ceiling extent and not just one tight location. When we lessen diffraction with macro optics, that is spacing apart the internal reflective surfaces or TIR surface by at least about 0.5 mm, we make the re-directed light beam tightly directional, which is improved by various embodiments of the invention. 
         [0101]    A predetermined deviation by tilt deviation of optical design, for example, helps to meld together, or smoothes, the light distribution on a ceiling that looks choppy from small angular errors in louver manufacturing that make the ceiling light look non-uniform. In a more preferred aspect it can also spread the light across the extent of the interior ceiling to fill the room with daylight from front to back. When spreading the light across the entire depth of the room ceiling, it is also desirable that each louver spreads the light a sufficient amount to avoid the choppy appearance on the ceiling and overlap with the light distribution of the adjacent louver. 
         [0102]    Hence, it is additionally preferred that light reflective surfaces of each louver are operative to increase the width of the main specular re-directed beam of incident light by at least any predetermined angular deviation of the main re-directed beam associated with each adjacent louver. 
         [0103]    It should be appreciated that a preferred degree of increase in the width of the main specular re-directed beam of incident light by a predetermined angular deviation is dependent on room dimensions, and that such deviation should increase in proportion to the depth of the room orthogonal to the glazing surface. 
         [0104]    In the case of a louver assembly that is ˜2 feet high and placed perhaps 1 foot below a 10 foot ceiling height. The angular deviation, which can be accomplished by the tilt of the louver, to re-direct the light to the center of the ceiling in a 20 feet deep room, is 12 degrees. If the lowest louver is operative to provide the deepest penetration, which is 20 feet, the re-direction angle is 9 degrees. If we make the top louver re-direct a symmetric +3 degrees, we then cover most of the ceiling. Here the light is re-directed within a range of 9 degrees to 15 degrees. 
         [0105]    Alternatively, one could deploy the top louver to re-direct the main beam at 18 degrees to provide a re-direction range 9 to 18 degrees, which is plus and minus 4.5 degrees, which would require only a +/−2.25 degree deviation in slope of the TIR surfaces within or between the upper and lower louver in the array. 
         [0106]    When a room is 30 feet deep, the preferred deviation of the main specular re-directed beam of incident light is 6 degrees for the top louver and between about 11 degrees or 12 degrees for the bottom louvers, which is a range of 6 degrees, which is +/−3 degrees, and a corresponding slope range of +/−1.5 degrees for the reflective or TIR surfaces in the louvers. 
         [0107]    However, to the extent the louver assembly is taller; the deviation of the main specular re-directed beam of incident light from the top and bottom louver can be reduced to cover the depth of the room. For example now with a 20 feet deep room and a louver assembly that is 3 feet tall, instead of 2 feet tall. The preferred re-direction angle of the top louver to the ceiling center is 14 degrees. The preferred re-direction angle of the bottom louver angle to the back of the ceiling is 11 degrees. 
         [0108]    It is generally preferred to provide a light re-directing louver assembly comprising a plurality of louvers that are operatively coupled to be tilted, each louver comprising a generally rectangular planar support member having, an upper surface and a lower surface opposite the upper surface, an elongated front side on a side orthogonal to the plane of the upper surface, and an elongated back side opposed to and parallel with the front side, a right side on another side that is orthogonal to both the upper surface and the front side, and a left side opposite the front side that is parallel to the right side, a light redirecting structure that is at least one of attached to and disposed within the planar support member, the light redirecting structure comprising a plurality of spaced apart light reflective surfaces that terminate at corners, wherein the light reflecting surface thereof extend across the planar support member from the front side to the back side in which each light reflective surface faces the front or back side, wherein each louver is operative to provide a predetermined angular deviation of a main specular re-directed beam of incident light from that of the immediately adjacent louver. It is preferred to further that the light reflective surfaces of each louver are operative to increase the width of the main specular re-directed beam of incident light by at least said predetermined angular deviation. It is more predetermined that the angular deviation from an upper louver to a lower louver in the array is at least about 1 degree. It is additionally predetermined that the angular deviation is at least is at least about 2 degrees. It is most preferred that the predetermined that the predetermined angular deviation is at least about 4 degrees. In another aspect it is generally preferred that the light reflective surfaces of each louver are operative to increase the width of a main specular re-directed beam of incident light by at least the predetermined angular deviation that occurs between adjacent louvers. In another aspect it is more generally preferred that the light reflective surfaces of each louver are operative to increase the width of a main specular re-directed beam of incident light by at least twice the predetermined angular deviation that occurs between adjacent louvers. 
         [0109]      FIG. 20-21B  illustrate another variant of the invention in which the patterned diffuser in  FIG. 8B  is applied to the exterior side of a light re-directing optical film or sheet  2100  that is monolithic or multi-layered (such as, without limitation, a UV cured resin layer with a texture on a monolithic substrate) and is applied to glazing surface  15  with an optical adhesive  2030 . Optical film or sheet  2100 , which has grooves  2105  that provide TIR surfaces on face  2100   b ′, is adhered to glazing  15  on interior surface  15   b ′ with optical adhesive  2030 . The optical film or sheet  2100  may have grooves spaced apart by less than 0.5 mm, but more preferably less that about 0.25 mm to form a flexible film, or about equal to or greater than about 0.5 mm to reduce columnar glare and be less flexible, having a greater total thickness generally increasing in proportion to an increased groove spacing. The spaced apart grooves can be multifaceted, curves or slightly offset in angle with respect to adjacent groves in the film or sheet as disclosed in any of the other embodiment to provide the desired spreading of the specular re-directed light beam to accommodate deviations of louver tilt in the assembly  1000 . Such spreading of the specular redirected light beam will also reduce columnar glare when the grooves are spaced apart by less than about 0.5 mm. Patterned elements  801 ′ are disposed on the side  2100   b  of the optical film  2100  that is opposite the grooves  2105 . As non-limiting examples, each patterned element  801 ′ is optionally a 5 mm×5 mm and the spacing is about 20-25 mm in both directions, as shown in the elevation view in  FIG. 21B . The pattern is intended to avoid a distracting appearance of minor defects in manufacturing and installation, without precluding see-through visibility. Note that the patterned elements  801 ′ can be diffuse as well as transmit light and are optionally opaque or partially transparent and of any color. They can also have various shapes, such as circles, squares, rectangle, discrete polygons, or lines, which can be continuous or dashed. 
         [0110]    It has also been discovered with respect to the illustration of  FIGS. 21A and 21B  that internal room ambiance can be improved when the patterned element  801 ′ are provided to reduce contrast in directly lit work surfaces, where light leaks through the optical elements  2100  to produce very bright area, so that the effect of daylighting produces a more pleasing generally diffuse light effect, but without overhead lights. These benefits are achieved over preferred configurations of such elements  801 ′ that do not adversely impair see through visibility for interior room occupants and provide an internal attenuation of incident light of about 10% to about 40%. Internal attenuation should be understood to mean the reduction in light transmission excluding the Fresnel reflection losses of circa 4-5% that occur at the front and rear external surfaces of louver  600  or other light redirecting structure. Such attenuation levels are preferably achieved when elements  801 ′ are round dots disposed in columnar arrays with an offset of adjacent columns, such as in hexagonal array and having a diameter of between about 0.5 to 3 mm, but more preferably about 1 to 2 mm. Such elements  801 ′ are preferably opaque to avoid creating and enhancing columnar glare from residual transmission at curved edges, but can have some transmission if they can be applied as a flat pattern. It has further been discovered that silk screen printing of such elements can provide the desirable flatness within the preferred size ranges of the printed element  801 ′. 
         [0111]    It has been discovered that the grey to black colored elements  801 ′ least interfere with the ability of building inhabitants to see outside at night, in contrast to white colored elements that overpower a dark background at night. The grey to black color of elements  801 ′ are also preferred as they do not change the external appearance of windows during the daytime. 
         [0112]    Such partially transmissive elements  801 ′ when printed very thin with a black ink composition have a grey appearance to internal viewers. This grey appearance can also be achieved using grey inks and printing opaque elements. As grey inks tend to be more transmissive and scattering than black inks, if grey inks are deployed, then elements  801 ′ should have an optical density of at least about 1.3, but more preferably at least 1.5, and most preferably at least about 2.0. The most preferred embodiment of the elements appear grey to the internal and external viewer but are opaque without any transmissive scatter. 
         [0113]    In such hexagonal arrays of elements  801 ′ it is anticipated that the preferred round dots are spaced apart by about 1-10 mm, but more preferably about 2-8 mm, and most preferably about 3-7 mm. Non-limiting examples of such arrays are illustrated in elevation view in  FIGS. 26B and 26C . 
         [0114]    It should be appreciated that the optical elements  801 ′ can also be applied regular and irregular patterns or flows, and provide the desired degree of attenuation with constant array dimensions or constant feature size. 
         [0115]    Preferably, the optical elements  801 ′ are opaque, with no transmissive scatter component. The scatter is undesirable as it increases glare in the window. We have found that inkjet printing optical element  801 ′ is not optimal as the droplets form lenslets which scatter. Inkjet deposit of optical elements also suffers from low throughput, is high in cost and can also cause deleterious heating of the optical film  2100 . Hence, optical elements  801 ′ are preferably deposited on the optical film  2100  or glazing  15  by screen printing using UV-cured inks, as this results in the outstanding quality level ink deposit which is key to minimizing scatter (both transmissive and reflective) yet at high production throughput speeds. Further, screen printing can achieve the desired results in one printing step, as opposed to multiple passes/colors. 
         [0116]      FIG. 25A  shows elements  801 ′ applied to the portion of the light re-directing film  2100  having the grooves  2105 , with optical adhesive  2030  attaching the optical film  2100  to the interior surface  15   b ′ of the glazing  15 . 
         [0117]      FIG. 25B  shows elements  801 ′ applied to the portion of the glazing  15  on interior surface  15   b ′. The optical adhesive  2030  is applied over the elements  801 ′ and the intervening portion of the glazing interior surface  15   b ′ for attaching the optical film  2100  to the interior surface  15   b ′ of the glazing  15 . 
         [0118]      FIG. 26A  shows the use of adhesive dots as opaque or high optical density optical elements  801 ′. The elements  801 ′ are an adhesive material that both attaches the film  2100  to the interior surface  15   b ′ of the glazing  15 , performing the function of the optical adhesive  2030  in other embodiments. It should also be noted that as these adhesive optical elements  801 ′ are disposed on the side of the grooves  2105  that provide TIR surfaces on face  2100   b′   
         [0119]    It should be appreciated that the embodiment of  FIGS. 25A , B and  26 A enclose the optical elements  801 ′ between the glazing  15  and the film  2100 , to prevent optical elements  801 ′ from being damaged or worn off in window cleaning or other potential source of contact or abrasion to the window interior. 
         [0120]    It should also be appreciated that any of the embodiments of  FIG. 20-21B  and  FIG. 25A-26C  can cover a portion of a plano glazing surface of window, or form louvers or slats  600 . 
         [0121]      FIGS. 22, 23A and 23B  illustrate an alternative method of forming the optical elements  110  of an embodiment in which only a portion  1302  of the TIR surface  110   a ′ is planar, such as generally described in  FIG. 13  in which regions  1301  and  1301 ′ deviate from the planarity of an intervening portion  1302 . 
         [0122]      FIG. 22  shows an optical sheet  1400  in a plan view after printing a predetermined pattern of narrow diagonal stripes  2202  on an upper surface. The diagonal bias is with respect to the direction of cuts (shown by broken lines  2201 ) that are made to form the elongated optical elements  110 . The optical sheet  1400  is intended to be formed into a plurality of the optical elements  110  shown stacked in  FIGS. 23A and 23B . 
         [0123]    The diagonal stripes  2202  can be made of a resin, such as a UV curable fluid, as well as paint or resin having fillers that is optimized to form a spacer  1601  between the assembled optical elements  110  shown in  FIGS. 23A and 23B . Each spacer  1601  then also contributes to the spread of light from each slat  600  over the specular TIR reflection that occurs on the intervening portion  1302  of surface  110   a ′. Hence, the process described with respect to the embodiment of  FIGS. 14A-C  and  15 A-B can be deployed to form a patterned region of stripes  2202  having the desired waviness in either 2 or 3 dimensions. Alternatively, the paint or curable fluid used to form stripes  2202  can be a commercial transparent non-gloss or semi gloss finish that scatters incident light. In this case, when the resulting optical elements  110  are stacked and attached to a common substrate such as  120 ′ (optionally with adhesive layer  130 ′) to form a slat  600  in  FIG. 23B , TIR would still occur on the non-contacting portion  1302  between regions  1601 . TIR would also occur on some portion of the striped regions  2022  that do not contact the adjacent optical element  110 . 
         [0124]    Alternatively, substrate  1400  is coated in the stripped portion  2202  with a paint, resin or curable fluid  1501  having dispersed filler particles  1502  (as previously described with respect to  FIG. 15B ) that are comparable in size to the thickness of the fluid to form a wavy surface pattern. However, the pattern will not need to be periodic as long as the mean repeat distance is much smaller than the width of the TIR surface  110   a ′ and the surface slope is between about 1-4° as the anticipated benefit of spreading light from each slat  600  should be achieved. When the objective of the filler particles  1502  are simply to form the wavy surface pattern it may be preferable that they are transparent and non-scattering internally, as well as at the interface with the cured coating, by having the same index of refraction. However, it is also possible to use the filler  1502  to create a diffusing portion, in which case the filler should be one of internally scattering and having a different refractive index than the resin  1501 . It is also possible to provide the desired spreading of the redirected light by any combination of the wavy surface with diffusion from the particles  1502 . The portions  2202  can be applied in other patterns than stripes, such as irregular or regular patterns, including continuous and discontinuous lines, dots, rectangle and polygons by screen printing as well as other methods of depositing paints, resins and curable fluids. It should be appreciated that the wavy surface pattern also serves to separate optical elements  110  when stacked to provide spaces apart TIR surface. 
         [0125]      FIG. 23A  is intended to illustrate a close spacing of stripes  2202  that form  2  spacers  1601  in each cross-section of the optical elements  110 ′ and  110 . In contrast,  FIG. 23B  is intended to illustrate the opposite principles in which the spacers  1601  are more widely separated so each cross-section has only one spacer  1601 , but the spacer is optionally more highly diffusing of incident ray  10  either from a greater variation in surface curvature on the wavy portion where TIR occurs, or from scatter within the spacer  1601  before and after TIR on the wavy portion. Highly scattering finishes can be applied as relatively narrow stripes with respect to the width of surfaces  110   a  and  110   a ′ to provide sufficient spreading of the otherwise collimated specular reflection off portions  1302 . 
         [0126]    The higher the diffusing power of these spacers  1601  formed by stripes  2202 , the lower total proportion of surface region  110   a ′ they need to occupy. In either case, as the spacer  1601  is a small percentage of the total thickness of surface  110   b , the diffusion therein and the angular spread of the TIR beam at surface  110   a ′ will not affect see through visibility. 
         [0127]    The bias angle, width and spacing of the stripes  2202  can provide at least 2 such spacers per optical surface  110   a ′ to provide sufficient spreading of the otherwise highly collimated reflection from the TIR surface  110   a ′. However, this will depend on the level of light spreading or diffusion provided by the spaced regions  1601 . The bias of the stripes with respect to the placement of the cuts  2201  for forming the elongated optical elements  110  is also selected to provide sufficient spacers  1601  per optical element  110  so that the faces  110   a ′ are generally parallel and the louvers or slats  600  are generally rectangular with orthogonal adjacent sides when the optical elements  110  are stacked for assembly to faces  120  and  120 ′. 
         [0128]      FIG. 24  illustrates rays tracing in a plan view in slats  600  of  FIGS. 23A and 23B  at a high azimuthal angle (ψ) of incidence of ray  10  on glazing surface  15  the optical element  110 , when the sun elevation is decreased. The optical element  110  has a specular reflective portion  1302  of the lower surface  110   a ′ and the more diffusing spacers  1601 , shown in elevation in  FIGS. 23A and 23B . The rays  10  that are incident on portions  1302  are reflected and exit the element  110  as parallels rays  12 . In contrast, rays  10  that enter spacer  1601  have a main reflected beam  12 ′ shown as a broken line, but also a wider beam that results from scattering and/or TIR off slightly tilted surface, shown as the narrower broken lines on both sides of the ray  12 ′.  FIGS. 23A and 23B  show how the beam  12 ′ has spread in the upward and downward direction, whereas  FIG. 24  shows beam  12 ′ also spreading in the lateral direction along the length of the optical element  110 . Hence, either a wavy surface pattern or diffusion by light scattering in the spacers  1601  can also spread the light laterally along the slat  600  so that any recurring or periodic placement of the stripes  2202  within each optical element  110  of slat  600  does not form a discrete sub-patterns as the light is reflected toward the ceiling or a distant wall. 
         [0129]    While the invention has been described in connection with a preferred embodiment, it is not intended to limit the scope of the invention to the particular form set forth, but on the contrary, it is intended to cover such alternatives, modifications, and equivalents as may be within the spirit and scope of the invention as defined by the appended claims.