Abstract:
A luminaire is provided which includes a light source, a light guide that receives light radiating from the light source, and a plurality of prisms adjacent the light guide that redirect the light from the light guide substantially perpendicular to a longitudinal axis of the light guide. The prism angles, in one embodiment, are 25°-90°-65°. The fine pitch prism arrays preferably alternate or flip-flop every few millimeters, for example, one to two millimeters to create the visual appearance of bright and dark bands which cause the structure to appear like macro prisms.

Description:
RELATED APPLICATIONS 
     This application is a divisional of U.S. application Ser. No. 09/726,239, filed on Nov. 29, 2000, which claims the benefit of U.S. application Ser. No. 60/208,339, filed May 31, 2000, and U.S. application Ser. No. 60/168,586, filed on Dec. 2, 1999, the entire teachings of the above applications are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     Luminaires typically include a lighting source, a waveguide, and microprisms used to redirect the light in a desired direction. These luminaires are used to provide a more uniform light distribution than conventional light systems and alleviate glare in applications such as office space, boardrooms, and customer service centers. 
     SUMMARY OF THE INVENTION 
     A luminaire is provided which includes a light source, a light guide that receives light radiating from the light source, and a tilted prism array for redirecting the light in a first direction. In one embodiment, the prism array, which can include linear prisms, includes a cross-sectional profile that periodically alternates orientation along the light guide. The linear prisms can have included angles of 25, 90, and 65 degrees. The prism array can alternate or flip-flop in orientation every few millimeters, for example, one to two millimeters. A tilted prism can have two sides which meet at a peak with a first length from the valley to the peak on one side and a second length from the valley to the peak on a second side of the prism, where the first length is different in length from the second length, thereby tilting or canting the prisms. The tilting angle of the prisms is between the optical axis and a line perpendicular to the window side. The tilting angle can be in the range between about 20 and 70 degrees. 
     The prism array can include peaks and valleys that form the cross-sectional profile that alternates along a first axis. The prism array can also include a second cross-sectional profile that alternates orientation along a second axis that is different than the first axis, such as substantially perpendicular or offset about 60 degrees relative to the first axis. The prism array can further include a third cross-sectional profile that alternates orientation along a third axis that is different than the second axis and the first axis. In one embodiment, the third axis is offset about 60 degrees relative to the second axis. The prism array can be disposed on a top surface of the light guide. 
     An optical microstructure is also provided which includes a tilted prism array that periodically alternates orientation of the tilted prism array along a first axis. The prism array can also include a cross-sectional profile that includes peaks and valleys that periodically alternate orientation along a second axis. In alternative embodiments, the prism array includes another cross-sectional profile that periodically alternates along a third axis. The optical microstructure can be disposed on a first surface of a film. A prism array can be disposed on a second surface of the film. The prism array on the second surface can be tilted and periodically alternate orientation along at least one axis. The purpose of the periodic alternate orientation of the prism angles is to create alternating bands of bright and dark lines which can be seen viewing the surface of the luminaire. Very small or fine pitch prisms that are not visible to the human eye beyond 0.5 meters can be made to look like macro prisms because of the visibility of the bright and dark bands. Low cost manufacturing concepts, such as continuous casting, can be used to form the precision fine pitch alternating prism groups and achieve the appearance of a precision macro prism, for example, 0.508 to 2.54 mm (0.02 to 0.1 inch) pitch, which would normally be made with a more expensive manufacturing concept, such as compression molding. 
     Multi-faceted prisms can be used, for example, prisms that have more than one slope on a facet. Further, prisms can be used which have curved facets or curved prism tips and valleys. These features are used to smooth the resulting light distribution. 
     A method for redirecting light is also provided which includes providing a light source, receiving light radiating from the light source in a light guide, and redirecting the light in a first direction with a tilted prism array that includes a cross-sectional view that periodically alternates orientation along a first axis. The tilted prism array can include a second cross-sectional profile that periodically alternates orientation along a second axis that is different than the first axis. The tilted prism array can further include a third cross-sectional profile that includes peaks and valleys that periodically alternate orientation along a third axis which that is different than the second axis. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. 
         FIG. 1  is a partial cross-sectional view of a waveguide for use in a display apparatus particularly illustrating linear prisms arranged in accordance with the present invention. 
         FIG. 2  is a cross-sectional view of a luminaire employing waveguide of FIG.  1 . 
         FIG. 3  is a cross-sectional view of a pair of waveguides which receive and direct light from a light source substantially downward. 
         FIG. 4  is a graph illustrating light output of an exemplary backlit display apparatus at an observation or viewing angle range of about −90° to +90°. 
         FIG. 5  are graphs illustrating light output of an exemplary backlit display apparatus at viewing range of about −70° to +70°. 
         FIG. 6  is a cross-sectional view of an alternative embodiment of a luminaire in accordance with the present invention. 
         FIG. 7  illustrates photometric data from the luminaire of FIG.  6 . 
         FIG. 8  is a cross-sectional view of another embodiment of a luminaire in accordance with the present invention. 
         FIG. 9  is a cross-sectional view of yet another embodiment of a luminaire in accordance with the present invention. 
         FIG. 10  is a cross-sectional view taken along line  10 — 10  of FIG.  6 . 
         FIG. 11  is an enlarged view of the prisms shown in FIG.  6 . 
         FIG. 12A  is a top view of a luminaire having two cross-sectional profiles formed at 60 degrees relative to one another. 
         FIG. 12B  is a cross-sectional view of the luminaire of  FIG. 12A  taken along line  12 B— 12 B. 
         FIG. 12C  is a cross-sectional view of the luminaire of  FIG. 12A  taken along line  12 C— 12 C. 
         FIG. 13A  is a top view of a luminaire having three cross-sectional profiles formed at 60 degree intervals. 
         FIG. 13B  is a cross-sectional view of the luminaire of  FIG. 13A  taken along line  13 B— 13 B. 
         FIG. 13C  is a cross-sectional view of the luminaire of  FIG. 13A  taken along line  13 C— 13 C. 
         FIG. 13D  is a cross-sectional view of the luminaire of  FIG. 13A  taken along line  13 D— 13 D. 
         FIG. 14  is a cross-sectional view of a luminaire having multi-planar facets. 
         FIG. 15  is a cross-sectional view of a luminaire having curved prism tips and valleys. 
         FIG. 16  is a cross-sectional view of a luminaire having linear prisms on a first surface and a second surface. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A description of preferred embodiments of the invention follows. Generally, the invention is directed to a backlit display apparatus (“BLDA”) having a coarse appearance. An example of a BLDA is disclosed in U.S. Pat. No. 5,629,784, issued to Abileah et al. on May 13, 1997, the teachings of which are incorporated herein in its entirety by reference. 
       FIG. 1  is a partial cross-sectional view of a waveguide or light guide  10  for use in a BLDA particularly illustrating the linear prisms  12 . The prism angles, in one embodiment, are 25°-90°-65° (90° is the peak angle with a first side of the prism is 25° from the horizontal to peak and a second side of the prism is 65° from the horizontal to the peak). The pitch, or tip to tip spacing, in one embodiment, is in the range from about 0.0508 to 0.254 mm (0.002 to 0.01 inches). The tilting angle, as measured from the peak angle, can be in the range between about 20 and 70 degrees. The prism array preferably alternates or flip-flops in orientation, i.e., the array includes mirror images with respect to line L. In one embodiment, the prism array flip-flops every few millimeters, for example, one to two millimeters. The waveguide  10  can be solid being formed from a material such as polymethyl methacrylate (PMMA) or other suitable materials. In alternative embodiments, any of the prisms disclosed herein can be used with hollow waveguides in any of the embodiments as disclosed in U.S. application Ser. No. 09/725,338, filed on even date herewith, now U.S. Pat. No. 6.612.723, the contents of which are incorporated herein by reference. 
     When viewed from below, one set of fine pitch prisms  12  is generally oriented to reflect light towards the viewer, and the neighboring pair away from the viewer. Thus, the viewer sees a set of alternating bright and dark lines, which can be referred to as a coarse appearance. It is understood that the number of prisms  12  within a prism grouping is variable, which means that the width of a group and its coarseness can be easily controlled. 
       FIG. 2  illustrates a luminaire  8  having an exemplary waveguide  10  coupled to a light source  14 , such as a fluorescent cylindrical bulb. A viewer at point X sees the center group of prisms  12  as brighter because they direct light from the source  14  to point X. Since the light from adjacent prism groups is directed elsewhere, these groups appear dark. At point Y, the center group can appear dark, and the adjacent groups are brighter. At some point between X and Y, the groups appear to be equal in brightness. 
     Further, the output light distribution is such that the image of the light source  14 , such as a cylindrical bulb, is masked. It is noted that the prisms  12  of  FIG. 2  are substantially enlarged for illustrative purposes only. 
       FIG. 3  illustrates a luminaire  9  having a pair of waveguides  10  which receive and direct light from source  14  substantially downward. A reflective coating  16 , such as vacuum metalized aluminum or metalized polyester (PET) or polished aluminum, is provided on the top and end surfaces of the waveguide  10  to allow the light rays to be directed substantially downward. 
       FIG. 4  is a graph illustrating light output (luminance: y axis) of an exemplary BLDA at an observation or viewing angle range of about −90° to +90° (x axis). The coarseness or banding appears in this embodiment from approximately −45° to +45°. In this embodiment, the pitch, or tip to tip spacing, is in the range from about 0.0508 to 0.254 mm (0.002 to 0.01 inches). 
       FIG. 5  are graphs illustrating light output (lux: y axis) of an exemplary BLDA at viewing angle range of about −70° to +70° from normal (x axis). One graph illustrates the light output across the light source or bulb while the second graph illustrates the light output with the bulb. The data for the graphs are shown in FIG.  5 . 
       FIG. 6  illustrates an alternative embodiment of a luminaire  11  having an exemplary waveguide  10 ′ and prisms  12 ′ wherein the waveguide and prisms are formed separately and laminated together, for example, with a pressure sensitive adhesive (PSA). The waveguide  10 ′ and prisms  12 ′ can be formed from different materials. In one embodiment, the prisms  12 ′ can be formed from an ultraviolet (UV) curable acrylate thermoset or other suitable materials. Either the waveguide  10 ′ or the prisms  12 ′ (or both) can be colored and/or have printed patterns formed thereon (e.g., logos) to customize the appearance of the luminaire as disclosed in U.S. application Ser. Nos. 09/013,696, now U.S. Pat. No. 6,119,751, and 09/170,014, now U.S. Pat. No. 6,120,636, filed Jan. 26, 1998 and Oct. 13, 1998, respectively, the teachings of each being incorporated herein in their entirety by reference. 
       FIG. 7  illustrates photometric data from a light system, such as shown in FIG.  6 . The photodetector was placed about 1.0 meter from the light source. The data represents theoretical and actual measurements taken across the bulb direction, i.e., in the direction of the two-headed arrow  18  of FIG.  6 . 
       FIG. 8  illustrates another embodiment of a luminaire  19  having mirrors  20  positioned on the ends of the waveguide  10  and above and below the light source  14 . The prisms  12 ′ can be integral to the waveguide  10 , or alternatively, be laminated to the waveguide  10 . 
       FIG. 9  illustrates a luminaire  22  which is similar to the embodiment of  FIG. 8  but instead of a mirror above the light source  14 , a baffle  24  is provided there instead. The baffle  24  can include a white surface which absorbs, diffracts, and scatters light from the light source  14 . It is believed that this baffle  24  more uniformly directs the light rays into the waveguide  10  for achieving a more uniform distribution of the light rays in the waveguide. 
     The table below compares the viewing angle, the measured luminance for the luminaire  19  of FIG.  8  and theoretical output for a luminaire having a baffle such as the luminaire  22  of FIG.  9 . In this embodiment, the pitch of the prisms is about 0.254 mm (0.01 inches). 
     
       
         
               
               
               
             
               
               
               
             
           
               
                   
               
               
                   
                 Measured Luminance 
                   
               
               
                 Angle 
                 (cd/lux/m 2 ) 
                 Theoretical with Baffle 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 180 
                 5.7 
                 16.8458 
               
               
                 185 
                 5.1 
                 18.9760 
               
               
                 190 
                 5.1 
                 15.2260 
               
               
                 195 
                 5.3 
                 8.9539 
               
               
                 200 
                 7.6 
                 15.5152 
               
               
                 205 
                 13.8 
                 27.0215 
               
               
                 210 
                 19.9 
                 37.7291 
               
               
                 215 
                 28.2 
                 33.6113 
               
               
                 220 
                 37.0 
                 37.6789 
               
               
                 225 
                 44.7 
                 44.4249 
               
               
                 230 
                 48.9 
                 40.6028 
               
               
                 235 
                 47.4 
                 41.2673 
               
               
                 240 
                 39.3 
                 35.1872 
               
               
                 245 
                 26.1 
                 24.0277 
               
               
                 250 
                 10.9 
                 10.6000 
               
               
                 255 
                 4.9 
                 4.7000 
               
               
                 260 
                 4.6 
                 4.5000 
               
               
                 265 
                 4.3 
                 4.2000 
               
               
                 270 
                 1.7 
                 1.6000 
               
               
                 275 
                 2.8 
                 2.7000 
               
               
                 280 
                 5.5 
                 5.4000 
               
               
                 285 
                 9.5 
                 8.8104 
               
               
                 290 
                 13.0 
                 10.9029 
               
               
                 295 
                 15.5 
                 5.3704 
               
               
                 300 
                 17.0 
                 8.9190 
               
               
                 305 
                 18.7 
                 5.3252 
               
               
                 310 
                 21.7 
                 13.4086 
               
               
                 315 
                 26.2 
                 18.7654 
               
               
                 320 
                 31.8 
                 22.4112 
               
               
                 355 
                 38.3 
                 32.3889 
               
               
                 330 
                 45.6 
                 43.3254 
               
               
                 335 
                 54.5 
                 45.7689 
               
               
                 340 
                 53.0 
                 56.6042 
               
               
                 345 
                 45.1 
                 49.3210 
               
               
                 350 
                 33.0 
                 45.7512 
               
               
                 355 
                 21.8 
                 47.1792 
               
               
                 0 
                 17.4 
                 41.8723 
               
               
                 5 
                 20.2 
                 54.5000 
               
               
                 10 
                 30.4 
                 48.0831 
               
               
                 15 
                 41.6 
                 46.7072 
               
               
                 20 
                 49.6 
                 45.5090 
               
               
                 25 
                 5136 
                 47.0374 
               
               
                 30 
                 44.0 
                 38.3052 
               
               
                 35 
                 36.0 
                 32.6696 
               
               
                 40 
                 29.2 
                 21.6011 
               
               
                 45 
                 23.8 
                 19.2380 
               
               
                 50 
                 19.2 
                 11.7001 
               
               
                 55 
                 15.7 
                 6.5985 
               
               
                 60 
                 13.4 
                 4.6328 
               
               
                 65 
                 12.0 
                 7.7141 
               
               
                 70 
                 10.0 
                 9.9115 
               
               
                 75 
                 7.5 
                 7.4000 
               
               
                 80 
                 7.4 
                 7.3000 
               
               
                 85 
                 3.1 
                 3.0000 
               
               
                 90 
                 1.9 
                 1.8000 
               
               
                 95 
                 3.4 
                 3.3000 
               
               
                 100 
                 3.7 
                 3.6000 
               
               
                 105 
                 4.0 
                 3.9000 
               
               
                 110 
                 7.2 
                 7.1000 
               
               
                 115 
                 21.5 
                 21.4000 
               
               
                 120 
                 37.2 
                 35.3846 
               
               
                 125 
                 46.5 
                 42.8789 
               
               
                 130 
                 49.7 
                 45.9643 
               
               
                 135 
                 46.7 
                 45.6916 
               
               
                 140 
                 38.6 
                 38.2638 
               
               
                 145 
                 29.6 
                 36.6630 
               
               
                 150 
                 21.1 
                 33.6147 
               
               
                 155 
                 14.3 
                 32.8648 
               
               
                 160 
                 8.2 
                 13.3652 
               
               
                 165 
                 5.5 
                 10.2196 
               
               
                 170 
                 5.1 
                 15.5559 
               
               
                 175 
                 5.3 
                 18.9760 
               
               
                   
               
             
          
         
       
     
     The linear prisms  12  as described above can be referred to as a one-dimensional structure. That is, the prism structures  12  have peaks and valleys that form a cross-sectional view running along one axis. In alternative embodiments, the prisms  12  can include multiple-dimensional structures, such as two-dimensional structures and three-dimensional structures that form cross-sectional profiles along second and third axes, respectively. 
     For example, in the embodiment of  FIG. 6 , a two-dimensional prism structure can be constructed by forming peaks  26  and valleys  28 , i.e., a second cross-sectional profile, perpendicular to the longitudinal axes of the existing linear prisms  12  ′, i.e., into the paper. Thus, a cross-sectional view taken along line  10 — 10  is seen in FIG.  10 . If the prisms are spared apart, the peaks  26  have a flat portion as also illustrated in FIG.  10 .  FIG. 11  illustrates an enlarged view of the prisms of  FIG. 6  which illustrates peaks  26  and valleys  28  of the prism array. This facilitates controlling of the light rays exiting the waveguide at every angle. In alternative embodiments, the prism array can include cross-sectional profiles that can be offset at about 60 degree intervals to provide a three-dimensional structure. In further embodiments, the cross-sectional profiles can be offset at various angles to provide a multiple-dimensional structure. 
     A luminaire having cross-sectional profiles formed at 60 degrees relative to one another is shown in  FIGS. 12A-12C . A luminaire having cross-sectional profiles formed at 60 degree intervals is shown in  FIGS. 13A-13D . A perspective view of a luminaire having multi-planar facets is shown in  FIG. 14. A  perspective view of a luminaire having curved prism tips and valleys is shown in FIG.  15 .  FIG. 16  is a cross-sectional view of a luminaire  8  having linear prisms  12  on a first surface and a second surface. 
     In alternative embodiments, optical microstructures can be formed on, laminated to, or otherwise provided on sheets, panels, or films for use in luminaires in which control of light distribution is desired. Furthermore, each side of the sheet, panel, or film can have an optical microstructure thereon. These optical microstructures can have tilted prism arrays which alternate orientation along one or more axes. 
     In any of the disclosed embodiments, multi-faceted prisms can be used, for example, prisms that have more than one slope on a facet. Further, prisms can be used which have curved facets or curved prism tips and valleys. These features can be used to smooth the resulting light distribution. 
     While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.