ASYMMETRIC ALTERNATING PRISM ARRAYS

Abstract: A luminaire (8) is provided which includes a light source (14), a light guide (10) that receives light radiating from the light source (14), and a plurality of prisms (12) adjacent the light guide (10) that redirect the light guide (10) substantially perpendicular to a longitudinal axis of the light guide (10). The prism angles, in one embodiment, are 25 DEG -90 DEG -65 DEG . 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: ASYMMETRIC ALTERNATING PRISM ARRAYS 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 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. 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. 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 fonn 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 prisms 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 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. BRTEF 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. Figure 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. Figure 2 is a cross-sectional view of a luminaire employing waveguide of Figure 1. Figure 3 is a cross-sectional view of a pair of waveguides which receive and direct light from a light source substantially downward. Figure 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°. Figure 5 are graphs illustrating light output of an exemplary backlit display apparatus at viewing range of about -70° to +70°. Figure 6 is a cross-sectional view of an alternative embodiment of a luminaire in accordance with the present invention. Figure 7 illustrates photometric data from the luminaire of Figure 6. Figure 8 is a cross-sectional view of another embodiment of a luminaire in accordance with the present invention. Figure 9 is a cross-sectional view of yet another embodiment of a luminaire in accordance with the present invention. Figure 10 is a cross-sectional view taken along line 10-10 of Figure 6. Figure 11 is an enlarged view of the prisms shown in Figure 6. 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. Patent 5,629,784, issued to Abileah et al. on May 13, 1997. Figure 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 anays 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. 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. 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 referced 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. Figure 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 Figure 2 are substantially enlarged for illustrative purposes only. Figure 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. Figure 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). Figure 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 Figure 5. Figure 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 (UN) 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. Patents 6,119,751, and 6,120,636. Figure 7 illustrates photometric data from a light system, such as shown in Figure 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 anow 18 of Figure 6. Figure 8 illustrates another embodiment of a luminaire 19 having minors 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. Figure 9 illustrates a luminaire 22 which is similar to the embodiment of Figure 8 but instead of a minor 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 Figure 8 and theoretical output for a luminaire having a baffle such as the luminaire 22 of Figure 9. In this embodiment, the pitch of the prisms is about 0.254 mm (0.01 inches). The linear prisms 12 as described above can be refened to as a one- dimensional structure. That is, the prism structures 12 have peaks and valleys running along one axis. In alternative embodiments, the prisms 12 can include multiple-dimensional structures, such as two-dimensional structures and three- dimensional structures. For example, in the embodiment of Figure 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 Figure 10. If the prisms are spaced apart, the peaks 26 will have a flat portion as also illustrated in Figure 10. Figure 11 illustrates an enlarged view of the prisms of Figure 6 which illustrates peaks 26 and valleys 28 of the prism anays. 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. 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 anays 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 prisms 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 prefened 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.

Claims: CLAΓMS What is claimed is: 1. A luminaire, comprising: a light source; a light guide that receives light radiating from the light source; and a plurality of tilted prism anays for redirecting the light in a first direction, wherein the plurality of prism arrays periodically alternate orientation along the light guide. 2. The luminaire of Claim 1 wherein the plurality of prism arrays include linear prisms. 3. The luminaire of Claim 2 wherein the linear prisms have included angles of 25, 90, and 65 degrees. 4. The luminaire of Claim 1 wherein the prism anays include peaks and valleys along a first axis. 5. The luminaire of Claim 1 wherein the prism arrays include peaks and valleys along a second axis different than the first axis. 6. The luminaire of Claim 5 wherein the second axis is substantially perpendicular to the first axis. 7. The luminaire of Claim 5 wherein the second axis is offset about 60 degrees relative to the first axis. 8. The luminaire of Claim 5 wherein the prism anays include peaks and valleys along a third axis that is different than the second axis and the first axis. 9. The luminaire of Claim 8 wherein the third axis is offset about 60 degrees relative to the second axis. 10. The luminaire of Claim 1 wherein the light guide is substantially solid. 11. The luminaire of Claim 10 wherein the light guide includes polymethyl methacrylate. 12. The luminaire of Claim 1 wherein the plurality of prism anays are disposed on a top surface of the light guide. 13. The luminaire of Claim 1 further comprising a reflective surface below the light surface for redirecting light into the light guide. 14. The luminaire of Claim 1 further comprising a reflective surface adjacent at least one end of the light guide for redirecting light toward the light guide. 15. The luminaire of Claim 1 further comprising a baffle for scattering light into the light guide. 16. The luminaire of Claim 1 wherein the prism anays include prism facets having more than one plane on at least one facet. 17. The luminaire of Claim 1 wherein the prism anays include curved prism tips. 18. The luminaire of Claim 1 wherein the prism anays include curved valleys. 19. An optical microstructure comprising a plurality of tilted prism anays that periodically alternate orientation of the tilted prism anays along a first axis. 20. The optical microstructure of Claim 19 wherein the prism anays periodically alternate orientation of the tilted prism anays along a second axis. 21. The optical microstructure of Claim 19 wherein the prism anays periodically alternate orientation of the tilted prism arrays along a third axis. 22. The optical microstructure of Claim 19 wherein the optical microstructure is disposed on first surface of a film, further comprising a plurality of prism anays on a second surface of the film. 23. The optical microstructure of Claim 22 wherein the plurality of prism anays on the second surface are tilted and periodically alternate orientation along at least one axis. 24. The luminaire of Claim 19 wherein the prism anays include prism facets having more than one plane on at least one facet. 25. The luminaire of Claim 1 wherein the prism anays include curved prism tips. 26. The luminaire of Claim 1 wherein the prism anays include curved valleys. 27. A luminaire comprising: a light source; a light guide that receives light radiating from the light source; and a plurality of tilted prism anays for redirecting the light exiting the light guide, the prism anays periodically alternating orientation along a first axis. 28. The luminaire of Claim 27 wherein the prism anays periodically alternate orientation along a second axis. 29. The luminaire of Claim 28 wherein the prism anays periodically alternate orientation along a third axis. 30. The luminaire of Claim 27 wherein the plurality of prism anays are disposed on a top surface of the light guide. 31. A method for redirecting light comprising: 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 anays that periodically alternate orientation along a first axis. 32. The method of Claim 31 further comprising the step of periodically alternating the plurality of tilted prism anays along a second axis different than the first axis. 33. The method of Claim 31 further comprising the step of periodically alternating the plurality of tilted prism anays along a third axis different than the second axis and the first axis. 34. The method of Claim 31 further comprising the step of redirecting the light radiating from the light source toward the plurality of tilted prism arrays.

Inventors: FUTHEY JOHN A, MUNRO JAMES F, FUTHEY, JOHN, A., MUNRO, JAMES, F.
Applicants: REFLEXITE CORP, REFLEXITE CORPORATION
Application year: 2000
Main classification: F21V8
IPC codes: F21V8