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  
       [0001]    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  
         [0002]    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  
         [0003]    A luminaire is provided which includes a light source, a light guide that receives light radiating from the light source, and a plurality of tilted prism arrays for redirecting the light in a first direction. In one embodiment, the plurality of prism arrays, which can include linear prisms, periodically alternate orientation along the light guide. The linear prisms can have included angles of 25, 90, and 65 degrees. The prism arrays can alternate or flip-flop in orientation every few millimeters, for example, one to two millimeters. A tilted prism can have sides on each side of the 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.  
           [0004]    The prism arrays can include peaks and valleys along a first axis. The prism arrays can also include peaks and valleys along a second axis different than the first axis, such as substantially perpendicular or offset about 60 degrees relative to the first axis. The prism arrays can further include peaks and valleys 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 plurality of prism arrays can be disposed on a top surface of the light guide.  
           [0005]    An optical microstructure is also provided which includes a plurality of tilted prism arrays that periodically alternate orientation of the tilted prism arrays along a first axis. The prism arrays can also periodically alternate orientation along a second axis and, in alternative embodiments, along a third axis. The optical microstructure can be disposed on a first surface of a film. A plurality of prism arrays can be disposed on a second surface of the film. The plurality of prism arrays 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.  
           [0006]    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 prisms tips and valleys. These features are used to smooth the resulting light distribution.  
           [0007]    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 plurality of tilted prism arrays that periodically alternate orientation along a first axis. The plurality of tilted prism arrays can periodically alternate orientation along a second axis different than the first axis. The plurality of tilted prism arrays can further periodically alternate orientation along a third axis which is different than the second axis. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    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.  
         [0009]    [0009]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.  
         [0010]    [0010]FIG. 2 is a cross-sectional view of a luminaire employing waveguide of FIG. 1.  
         [0011]    [0011]FIG. 3 is a cross-sectional view of a pair of waveguides which receive and direct light from a light source substantially downward.  
         [0012]    [0012]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°.  
         [0013]    [0013]FIG. 5 are graphs illustrating light output of an exemplary backlit display apparatus at viewing range of about −70° to +70°.  
         [0014]    [0014]FIG. 6 is a cross-sectional view of an alternative embodiment of a luminaire in accordance with the present invention.  
         [0015]    [0015]FIG. 7 illustrates photometric data from the luminaire of FIG. 6.  
         [0016]    [0016]FIG. 8 is a cross-sectional view of another embodiment of a luminaire in accordance with the present invention.  
         [0017]    [0017]FIG. 9 is a cross-sectional view of yet another embodiment of a luminaire in accordance with the present invention.  
         [0018]    [0018]FIG. 10 is a cross-sectional view taken along line  10 - 10  of FIG. 6.  
         [0019]    [0019]FIG. 11 is an enlarged view of the prisms shown in FIG. 6. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0020]    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.  
         [0021]    [0021]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 arrays preferably alternate or flip-flop in orientation, i.e., they are mirror images with respect to line L. In one embodiment, the prism arrays flip-flop every few millimeters, for example, one to two millimeters.  
         [0022]    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, Attorney&#39;s Docket No. 1571.1140-001, filed on even date herewith, the contents of which are incorporated herein by reference.  
         [0023]    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.  
         [0024]    [0024]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.  
         [0025]    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.  
         [0026]    [0026]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.  
         [0027]    [0027]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).  
         [0028]    [0028]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.  
         [0029]    [0029]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.  
         [0030]    [0030]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.  
         [0031]    [0031]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 .  
         [0032]    [0032]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.  
         [0033]    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                  
 
         [0034]    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 running along one  
         [0035]    axis. In alternative embodiments, the prisms  12  can include multiple-dimensional structures, such as two-dimensional structures and three-dimensional structures.  
         [0036]    For example, in the embodiment of FIG. 6, a two-dimensional prism structure can be constructed by forming a second array of linear prisms perpendicular to the linear prisms  12 ′. More particularly, a row of linear prisms having peaks  26  and valleys  28  is formed perpendicular to the longitudinal axis 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 spaced apart, the peaks  26  will 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 arrays. This facilitates controlling of the light rays exiting the waveguide at every angle. In alternative embodiments, the peaks and valleys can be offset at about 60 degree intervals to provide a three-dimensional structure. In further embodiments, the peaks and valleys can be offset at various angles to provide a multiple-dimensional structure.  
         [0037]    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.  
         [0038]    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 prisms tips and valleys. These features can be used to smooth the resulting light distribution.  
         [0039]    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.