Abstract:
Methods and apparatus are provided for projecting light carrying a data image. The apparatus comprises a first layer having regions of electrically alterable variable light transmittance adapted to form the data image, and a hollow cavity backlight having a light exiting surface coupled to the first layer and adapted to provide light to the first layer through the light exiting surface from one or more light emitters some of which point in a principal direction other than at right angles to the light exiting surface. In a preferred embodiment, LEDs are used as the light emitters and are preferably mounted on one or more printed circuit boards or other support tilted at non-zero angles with respect to the light exiting surface.

Description:
TECHNICAL FIELD 
   The present invention generally relates to electronic displays, and more particularly to flat panel transmissive displays employing backlights and backlights therefore. 
   BACKGROUND 
   Modern display applications often use a backlight in combination with, for example, a transmissive liquid crystal display (LCD) layer to provide a variety of alphanumeric and/or graphical information to a viewer. For convenience of explanation such alphanumeric and/or graphical information is hereafter collectively referred to as “data” and the word “data” is intended to include all types of visually perceivable information. The most common types of backlights are fluorescent lamp backlights. While they are effective they suffer from a number of disadvantages, among which are the need for comparatively high driving voltage and the complexity or difficulty of providing dimming (variable luminescence) and user alterable color (variable chrominance). Also, in applications such as avionics systems where mechanical ruggedness is desired, the comparative fragility of fluorescent backlights can be a drawback. 
   It is known to use light emitting diodes (LEDs) in backlights.  FIG. 1A  shows a plan view and  FIG. 1B  shows partially cut-away side view of LED backlight  10  according to the prior art. Backlight  10  has multiple LEDs  12  mounted on printed circuit board (PCB)  14  or equivalent, with the PCB generally oriented perpendicular to backlight propagation direction  13 . LEDs  12  are oriented so that principal light rays  19  emitted therefrom are coincident with, or parallel to, light  13  emitted from open surface  17  of backlight  10 . Light  13  is the sum of light rays  19  emitted by individual LEDs  12 . Heat sink  16  is generally provided behind PCB  14  to aid in extraction of heat generated by LEDs  12 . LEDs  12  and PCB  14  are generally enclosed in box or frame  18  whose interior surfaces  11 ,  15  are desirably reflective and with surface  17  open. Additional optical elements such as diffusers are often placed adjacent open surface  17 . 
   While prior art backlights such as are shown in  FIGS. 1A-B  are useful they often do not provide as much brightness (luminance) as is desired. This is especially troublesome in connection with head-up displays (HUDs) where the highest possible luminance is often needed. In a HUD, the data generated by the display is projected onto an angled transparent screen through which the background scene is being simultaneously viewed. The data is reflected from the angled screen toward the viewer while the background scene is transmitted through the same screen to the viewer. When the background scene is bright, the data may not be visible unless the data display is also very bright. For transmissive displays such as LCDs, the display luminance depends on the backlight luminance. Hence, there is an ongoing need for high luminance displays with high luminance backlights. 
   Accordingly, it is desirable to provide an improved backlight, backlit display and method, especially apparatus and methods with high luminance. In addition, it is desirable that the backlight and backlit display be simple, rugged and reliable. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background. 
   BRIEF SUMMARY 
   An apparatus is provided for projecting light carrying a data image. The apparatus comprises a first layer having regions of electrically alterable variable light transmittance adapted to form the data image, and a backlight having a light exiting surface coupled to the first layer and adapted to provide light to the first layer through the light exiting surface from one or more light emitters some of which point in a principal direction other than at right angles to the light exiting surface. In a preferred embodiment, LEDs are used as the light emitters and are mounted on one or more printed circuit boards (PCBs) or other support tilted at various non-zero angles with respect to the light exiting surface and the first layer. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and 
       FIG. 1A  is a plan view and  FIG. 1B  is a partially cut-away side view of an LED backlight according to the prior art; 
       FIG. 2  is a simplified exploded view of a typical backlit display according to the present invention; 
       FIG. 3A  is a plan view and  FIG. 3B  is a partially cut-away side view of an LED backlight according to a first embodiment of the present invention; 
       FIG. 4A  is a plan view and  FIG. 4B  is a partial cross-sectional side view of an LED backlight according to another embodiment of the present invention; 
       FIG. 5A  is a plan view and  FIG. 5B  is a partial cross-sectional side view of an LED backlight according to a still further embodiment of the present invention; 
       FIG. 6A  is a plan view and  FIG. 6B  is a partial cross-sectional side view of an LED backlight according to a yet further embodiment of the present invention; 
       FIG. 7A  is a plan view and  FIG. 7B  is a partial cross-sectional side view of an LED backlight according to yet another embodiment of the present invention; 
       FIG. 8A  is a plan view and  FIG. 8B  is a partial cross-sectional side view of an LED backlight according to a yet further embodiment of the present invention. 
       FIG. 9A  is a plan view and  FIG. 9B  is a partial cross-sectional side view of an LED backlight according to an additional embodiment of the present invention. 
       FIG. 10  is a perspective view of an LED backlight according to a further additional embodiment of the present invention; and 
       FIG. 11  is a simplified schematic side view of a directional backlight according to another additional embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
   The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description. For convenience of explanation, the LEDs used in the present invention are described as being mounted on a printed circuit board but this is not intended to be limiting and any convenient substrate may be used. Accordingly, the term “printed circuit board” and the abbreviation “PCB” are intended to include such alternative support means. 
     FIG. 2  is a simplified exploded view of backlit display  20 , according to an exemplary embodiment of the present invention. Display  20  comprises backlight  22  fed by electrical leads  21 , and optional diffuser  24  that assists in homogenizing light  23  emitted from backlight  22 . Light  25  exiting diffuser  24  enters LCD layer or other electrically alterable transmission layer  26  where it is patterned according to the electrical signals provided to layer  26  via leads  27 . Thin film transistors (TFTs) are conventionally incorporated in layer  26  where layer  26  employs active liquid crystal switching. For the purposes of the present invention, layer  26  may be any type of layer having optical transmission characteristics that may be electrically altered in different regions of the layer so as to create an optical image of the desired data. Where optical signal  29  (e.g., data) emitted by display  20  is to have color variation, then optional color filter layer  28  is preferably provided to receive output  29 ′ from image forming layer  26 . Display  20  can be monochromatic or colored according to the needs of the particular application. 
   In the preferred embodiment, light  23  emitted from backlight  22  is directed approximately normal to the surface of alterable transmission layer  26 , and includes light output distributed about the normal direction. Various arrangements  22 A,  22 B,  22 C,  22 D,  22 E,  22 F,  22 G,  22 H,  22 J for implementing backlight  22  are shown in  FIGS. 3A-B ,  4 A-B,  5 A-B,  6 A-B,  7 A-B,  8 A-B,  9 A-B,  10 ,  11  respectively and will now be discused. In  FIGS. 1A-B ,  3 A-B,  4 A-B,  5 A-B,  6 A-B,  7 A-B,  8 A-B,  9 A-B the numbers of LEDs shown in each figure are merely for purposes of illustration and not intended to provide a quantitative comparison of the LED packing density that may be achieved with the different geometrical arrangements shown in these figures. 
     FIGS. 3A  is a plan view and  FIG. 3B  is a partially cut-away side view of LED backlight  22 A according to a first exemplary embodiment of the present invention. Backlight  22 A is a hollow cavity backlight defined by a number of surfaces. As a hollow cavity backlight, the enclosed volume is filled with a medium having a refractive index of approximately 1.0, such as air. Backlight  22 A comprises LEDs  32  mounted on sloped surfaces  33 A,  33 B of PCBs  34 A,  34 B (or equivalent), respectively. PCB surfaces  33 A,  33 B on which LEDs  32  are mounted are considered as light emitting surfaces and face opening  37 , making an oblique (neither parallel nor perpendicular) angle α(A) with respect to the plane of opening  37  (the light exiting surface) of backlight  22 A. PCB surfaces  33 A,  33 B likewise make angle β(A)=(90−α(A)) degrees with respect to backlight propagation direction  23 A. PCB surfaces  33 A,  33 B are inclined with respect to each other, meaning that they are not parallel. In general, principal light emission direction  39  from LEDs  32  is parallel to normal  33 N to PCB surfaces  33 A,  33 B on which LEDs  32  are mounted. Normal  33 N to either PCB surfaces  33 A,  33 B defines the direction each respective surface is facing, and makes an angle of magnitude α(A) with respect to backlight propagation direction  23 A. Stated alternatively, principal light ray  39  of LEDs  32 , which is approximately normal to PCB surfaces  33 A,  33 B, makes an angle α(A) with respect to backlight propagation direction  23 A. Angle α(A) is usefully in the range 15 to 65 degrees, conveniently in the range of about 25 to 50 degrees, more conveniently in the range of about 35 to 45 degrees, and preferably about 40 degrees. Accordingly, β(A) is usefully in the range 25 to 75 degrees, conveniently in the range of about 40 to 65 degrees, more conveniently in the range of about 45 to 55 degrees, and preferably about 50 degrees. While α(A)˜40 degrees is preferred, this is not critical. 
   The hollow cavity containing LEDs  32  is preferably fully enclosed with the exception of opening  37 . Interior surfaces  33 A,  33 B and  35  of case or frame  38  are desirably reflective so as to redirect light impinging thereon from LEDs  32  generally in direction  23 A toward opening  37  of backlight  30 . Surfaces  33 A,  33 B and  35  may be specularly reflective, diffusely reflective or have surface variations so as to scatter as well as reflect the impinging light. What is preferable is that such interior surfaces have low optical absorption since a portion of light  23 A emitted through opening or surface  37  will undergo at least one reflection. Efficiency is further enhanced in this embodiment by having each emitting surface, in this case PCB surface  33 A or  33 B on which LEDs  32  are mounted, face the light exiting surface or opening  37 , meaning that the surface normal to the nominal center of the emitting surface generally points in the direction of the light exiting surface without predominant intervening light blocking structure. This enhances the coupling of the emitting surface to light exiting surface  37 . 
   In general, the number of LEDs that can be incorporated in a backlight is limited by the available PCB area and dissipation capabilities of associated heat sink  36 . Other things being equal, providing a larger available PCB area allows the light generation to be spread out and thereby allows for improved thermal management. This is beneficial in multiple ways. The increased area gives better access for cooling heat sinks, for example on the rear side of the emitting area. In addition, many light sources including LEDs exhibit an efficiency that is temperature dependent. With LEDs, for example, the efficiency can degrade as the semiconductor junction temperature goes up. The larger the available PCB area, the more LEDs that can be accommodated, allowing the necessary power to be distributed over more devices. While the larger surface area and increased number of LEDs can slightly reduce the optical efficiency of the cavity, this is offset by the improved thermal environment of the LED junctions when using the configuration of  FIGS. 3A-B , resulting in greater luminance capability from the backlight. It will be noted that, for the same backlight footprint (W×L), the backlight structures of the present invention provides greater PCB area and, therefore, can accommodate a larger number of LEDs. For example, where α(A)=45 degrees and for the same overall footprint (W×L), backlight structure  22 A of  FIGS. 3A-3B  provides a PCB area that is approximately (2) 1/2  times the PCB area of prior art unit  10  of  FIGS. 1A-1B . This increase in available PCB area for mounting LEDs without an increase in the overall backlight footprint is a particular feature of the present invention. This preferred embodiment thereby allows the use of emitting surface  33 A,  33 B larger than the light exiting surface  37 , and with each emitting surface  33 A,  33 B facing the light exiting surface without intervening structures. 
     FIG. 4A  is a plan view and  FIG. 4B  is a partial cross-sectional side view of LED backlight  22 B according to another embodiment of the present invention. Backlight  22 B includes LEDs  42  and heat sink  46  analogous to LEDs  32  and heat sink  36  of  FIGS. 3A-B . Backlight  22 B of  FIGS. 4A-B  differs from backlight  22 A of  FIGS. 3A-B  in the number of sloped surfaces. Backlight  22 A of  FIGS. 3A-B  has two sloped surfaces  33 A,  33 B forming a V-shaped structure with the open portion of the “V” oriented toward opening  37  and backlight propagation direction  23 A. Backlight  22 B of  FIGS. 4A-4B  has four sloped surfaces  43 A,  43 B,  43 C,  43 D forming a pyramidal structure whose open base is aimed toward opening or surface  47  and backlight propagation direction  23 B, analogous to direction  23 A. LEDs  42  are mounted on surfaces  43 A-D. Surfaces  43 A-D of backlight  22 B conveniently make angles α(B), β(B) with respect to opening  47  and principal light rays  49 , analogous to angles α(A), β(A) with respect to opening  47  and principal light rays  49  of backlight  22 B. For the same overall backlight footprint (W×L) and light exiting surface area, the pyramidal structure of backlight  22 B provides larger PCB area as compared to the arrangement of  FIGS. 1A-B , and other things being equal, can accommodate more LEDs and provide correspondingly greater luminance in the same overall footprint. As before, this is in large part due to the relaxation of thermal constraints on the LED junctions, as described above, allowing either higher efficiency at an equivalent power level or higher total power at an equivalent LED efficiency level. (The numbers of LEDs shown in  FIGS. 1-9  are merely for convenience of explanation and not intended to provide a quantitative comparison of the achievable LED packing density for the various backlight structures.) Angle α(B) is usefully in the range 15 to 65 degrees, more conveniently in the range of about 25 to 50 degrees and preferable about 40 degrees. Accordingly, β(B) is usefully in the range 25 to 75 degrees, more conveniently in the range of about 40 to 65 degrees and preferably about 50 degrees. While α(B)˜40 degrees is preferred, this is not critical. As with  FIGS. 4A-B , light emitting surfaces  43 A,  43 B,  43 C,  43 D are inclined with respect to each other and with respect to light exiting surface  47 , and each of the emitting surfaces faces light exiting surface  47  enhancing the coupling efficiency to the output. If instead, for example, each emitting surface directly faced another emitting surface, it would take the light emitted along principal direction  49  (or surface normal  43 N) additional bounces back and forth to eventually reach the light exiting surface, thereby reducing the coupling efficiency. 
     FIG. 5A  is a plan view and  FIG. 5B  is a partial cross-sectional side view of LED backlight  22 C according to a still further embodiment of the present invention. Heat sink  56  analogous to heat sinks  36 ,  46  is desirably provided. Backlight  22 C comprises LEDs  52  mounted on sloped surfaces  53 A,  53 B of PCBs  54 A,  54 B (or equivalent). Surfaces  53 A,  53 B of PCBs  54 A,  54 B make angle α(C) with respect to the plane of opening  57  of backlight  22 C or angle β(C)=(90−α(C)) degrees with respect to backlight propagation direction  23 (C). Assuming that surfaces  53 A,  53 B have equal inclination, normal  53 N to either PCB surfaces  53 A,  53 B makes angle α(C) with respect to backlight propagation direction  23 (C). Stated alternatively, principal light direction  59  of LEDs  52  makes angle α(C) with respect to backlight propagation direction  23 C. Angle α(C) is usefully in the range 25 to 65 degrees, more conveniently in the range of about 35 to 55 degrees and preferable about 45 degrees. Accordingly, β(C) is usefully in the range 25 to 65 degrees, more conveniently in the range of about 35 to 55 degrees and preferably about 45 degrees. While α(C)=45 degrees is preferred, this is not critical. The arrangement of  FIGS. 5A-B  can provide up to (2) 1/2  times the PCB area as the arrangement of  FIGS. 1A-B  and correspondingly greater luminescence for the same footprint. The emitting surfaces defined by surfaces  53 A,  53 B and LEDs  52  in this case face rear surface  55 , which is preferably a highly efficient diffusely scattering surface, and which in turn faces light exiting surface opening  57 . The efficiency of this backlight configuration may be further enhanced by reducing or eliminating any subsequent diffuser (e.g.,  24  in  FIG. 2 ) that would otherwise be placed over opening  57 , provided the angles required are within the range −β(C) to +β(C). It is evident from  FIGS. 5A-B  that this embodiment is particularly beneficial in the case that the area of light exiting surface  57  is smaller than the backlight footprint (W×L). In this case the emitting surface area exceeds both the area of light exiting surface  57  and the backlight footprint (W×L), while maintaining excellent coupling to the light exiting surface. Other surfaces  55 ′ of backlight case  58  are also desirably highly reflective. 
     FIG. 6A  is a plan view and  FIG. 6B  is a partial cross-sectional side view of LED backlight  22 D according to a yet further embodiment of the present invention. Backlight  22 D includes LEDs  62 , heat sink  66  and case  68  analogous to LEDs  52 , heat sink  56  and case  58  of  FIGS. 5A-B . Whereas backlight  22 C of  FIGS. 5A-B  has two sloped surfaces  53 A,  53 B forming a truncated V-shaped structure with the open truncated portion of the “V” oriented toward opening  57  and backlight propagation direction  23 C, backlight  22 D of  FIGS. 6A-6B  has four sloped surfaces  63 A,  63 B,  63 C,  63 D forming a truncated pyramid structure whose open truncated portion  67  is oriented toward backlight propagation direction  23 D, analogous to direction  23 C. LEDs  62  are mounted on surfaces  63 A-D. Surfaces  63 A-D of backlight  22 D conveniently make angles α(D), β(D) with respect to the plane of opening  67  and principal light rays  69  (and surface normal  63 N), analogous to angles α(C), β(C) with respect to the plane of opening  57  and principal light rays  59  (and surface normal  53 N) of backlight  22 C. For the same overall backlight footprint (W×L), the pyramidal structure of backlight  22 D can provide up to twice the PCB area as the arrangement of  FIGS. 1A-B , and other things being equal, can accommodate up to twice as many LEDs and provide correspondingly greater luminance in the same overall footprint. Angle α(D) is usefully in the range 25 to 65 degrees, more conveniently in the range of about 35 to 55 degrees and preferable about 45 degrees. Accordingly, β(D) is usefully in the range 25 to 65 degrees, more conveniently in the range of about 35 to 55 degrees and preferably about 45 degrees. While α(D)˜45 degrees is preferred, this is not critical. This embodiment also provides increased emitting surface area, and each of the emitting surfaces faces highly reflective rear surface  65 , which in turn faces the light exiting surface, opening  67 . 
     FIG. 7A  is a plan view and  FIG. 7B  is a partial cross-sectional side view of LED backlight  22 E according to yet another embodiment of the present invention. Backlight  22 E of  FIGS. 7A-B  is similar to backlight  22 D of  FIGS. 5A-B  except for the additional of further LEDs on backplane  75 . Elements  72 ,  73 ,  74 ,  75 ,  76 ,  77 ,  79  of backlight  22 E are analogous to corresponding elements  62 ,  63 ,  64 ,  65 ,  66 ,  67 ,  69  of backlight  22 D. In backlight  22 E, further LEDs  72 ′ are mounted on backplane PCB  75 , and heat sink  76 ′ is provided behind backplane PCB  75  to aid in removal of heat from LEDs  72 ′ mounted on PCB backplane  75 . It is will be appreciated that significantly more LEDs can be accommodated in the same overall footprint (W×L) of backlight  22 E of  FIGS. 7A-B  than prior art backlight  10  of  FIGS. 1A-B , allowing for increased efficiency at a given power level, or increased power capability at a given efficiency due to the improved thermal configuration. This relationship is particularly beneficial at very high luminance levels and elevated ambient temperatures, due to the inherent temperature sensitivity and temperature tolerance of typical light sources such as LEDs. In this configuration, effective coupling is maintained by having the emitting surfaces corresponding to  73 A,  73 B (along with their respective LEDs  72 ) facing backplane  75 , and backplane  75  (along with its respective LEDs  72 ′) facing light exiting surface  77 . 
   Each of the backlight structures illustrated in  FIGS. 3-7  provide a relatively direct path to the light exiting surface, either by having the emitting surface facing the exit or facing a surface which directly faces the exit. Nevertheless, these structures also provide for additional scattering reflections of a portion of the light before it exits backlight  22 . This increases the uniformity of illumination, which is a desirable feature. The degree of uniformity mixing of this type is conveniently configurable by the selection of the slant angles of the various surfaces, as well as by light source output profiles and diffuser scattering properties. 
     FIGS. 8A-B  show a yet further embodiment of the present invention. The backlight  22 F of  FIGS. 8A-B  is similar in many respects to the backlight  22 A of  FIGS. 3A-B , and hence some of the analogous details are not repeated. In  FIGS. 8A-B , reflector  180  has been added to the middle of otherwise hollow cavity  183 . Reflector  180  is preferably a specular mirror, although some degree of scatter is acceptable, and reflector  180  is oriented perpendicular to opening  87 , the light exiting surface in this embodiment. In the presence of reflector  180 , backlight  22 F appears to have a symmetric second half, virtual backlight  22 FV, where the term virtual in this case refers to an element which is present only in the virtual reflection but is not physically present. It is referenced only to simplify the description in the context of prior embodiments, especially the embodiment of  FIGS. 3A-B . Backlight  22 F includes surface  83  and associated LEDs  82 , which together form an emitting surface for the purpose of this invention. Surface  181  has also been added relative to  FIGS. 3A-B  to close the hollow cavity with the exception of open light exiting surface  87 . Surface  181  and any other surfaces (e.g., surfaces  185 ) which are required to close the hollow cavity are preferably highly reflective and may be either specular or scattering. In  FIG. 8B  virtual backlight half  22 FV appears to be above mirror  180 , along with various virtual backlight components which are reflections of the components of backlight  22 F. Virtual surface  83 V, along with virtual LEDs  82 V, is a virtual emitting surface and is inclined (non-parallel) with respect to surface  83 . Virtual opening  87 V is a virtual light exiting surface for the virtual backlight half  22 FV, and virtual surface  181 V is a reflection of surface  181 . Backlight  22 F has all of the symmetry and advantages of the configuration of  FIGS. 3A-B , with the exception that with the addition of reflector  180 , the section above centerline  33 C in  FIGS. 3A-B  has been removed and become virtual. This offers significant additional benefits in terms of geometric flexibility and placement, as well as thermal management opportunities as will be described further below. It will be noted that even though only surface  83  has LEDs mounted thereon, the use of mirror  180  creates second light emitting surface  83 V. Thus, the arrangement of  FIGS. 8A-B  (and also  FIGS. 9A-B ) behaves as if there are at least two light emitting surfaces. 
     FIGS. 9A  is a plan view and  FIG. 9B  is a partial cross-sectional side view of an LED backlight according to additional embodiment  22 G of the present invention. The embodiment of  FIGS. 9A-B  is similar to  FIGS. 8A-B , with the distinction that reflector  190  in back-light  22 G is now tilted with respect to surface normal of opening  97 , the light exiting surface. Reflector  190  forms angle  191  with respect to the plane of opening  97 , and while shown as an acute angle less than ninety degrees, angle  191  can also be greater than 90 degrees. As can be seen by comparison with  FIGS. 8A-B  and  FIGS. 3A-B , backlight  22 G together with its virtual backlight half  22 GV again form an effective cavity, but in this case the combined opening of opening  97  and virtual opening  97 V do not form a single flat surface. The advantages and description given in connection with  FIGS. 8A-B  still hold, however, as long as each emitting surface  93  (with LEDs  92 ), and  93 V (with LEDs  92 V) face the combined light exiting surface ( 97  and  97 V) in the virtual backlight configuration. As with the previous embodiments, this slanted configuration supports an emitting surface that is larger than light exiting surface  97 , which is also the footprint in this case. 
     FIG. 10  is a view of LED backlight  22 H according to a further additional embodiment of the present invention. Backlight assembly  22 H comprises backlight  22 G according to  FIGS. 9A-B , heat sink  106  and mounting means (not shown) to align emitting surface  103  and heat sink  106  with vertical axis  102  to maximize convective cooling effectiveness. As was described previously, the system can be conveniently designed to effectively support any of a range of values for angle  104  between light exiting surface  107  and emitting surface  103 . 
     FIG. 11  is a view of directional backlight  22 J according to another additional embodiment of the present invention. The arrangement of backlight  22 J combines any of backlights  22 A-H with prismatic directionality elements  111 . An example of directionality element  111  is Brightness Enhancement Film (BEF) available in several forms from 3M Corporation of St. Paul, Minn. When placed subsequent to the backlight  22 A-H, directionality element  111  narrows the range of propagation angles from diffuse (e.g., angular range  112 ) to narrow (e.g., angular range  113 ). In practice, however, the majority of the light rays  114  in angular range  113  are incident upon element  111  in angular ranges  115  and  116 . As can be seen from observation of each of the foregoing embodiments, ranges  115  and  116  correspond generally to the surface normals of the surfaces facing the light exiting port or surface in several of the described embodiments. Having the surfaces face toward the input angles, ranges  115  and  116 , of the directionality element  111  further enhances the efficient coupling aspects of the present invention. Optional diffuser  117 , if used, is conveniently placed between directionality element  111  and backlight cavity  22 A-H and is preferably a high gain diffuser, for example a textured surface diffuser, although other diffusers can also be used. Any of the previously described backlight embodiments of the present invention may be used for backlight  22 A-H. 
   While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. For example, while particular shapes have been illustrated for heat-sinks  36 ,  46 ,  56 ,  66 ,  76 ,  76 ′,  106  these are not intended to be limiting and any shape heat-sink may be used that can dissipate the heat generated by the LEDs installed in the corresponding backlight. Just as the sloped PCB arrangement of the present invention can increase the available PCB area for mounting LEDs, so the sloped arrangement also permits greater heat dissipation area. Thus, more LEDs be accommodated and the heat generated per unit PCB area is the same or less. Further, while the present invention has been described with light emitting diodes (LEDs) as the light sources, persons of skill in the art will understand that any directional or quasi-directional light source can also be used and that the present invention is not limited merely to structures and methods employing LEDs. In addition, while layer  26  has been illustrated as being an LCD layer, any layer or region exhibiting electrically alterable transmission properties can also be used and that the present invention is not limited merely to structures and methods employing LCD layers or regions. 
   It will also be appreciated that while the backlight and backlight incorporating display of the present invention has been illustrated as using a small number of sloping and preferably but not essentially planar PCB mounting surfaces for the LEDs, that many other configurations are also possible and intended to be included within the scope of the present invention. Non-limiting examples of other useful LED mounting arrangements are: (i) replacing the V-shaped PCB arrangement of  FIGS. 3A-B ,  5 A-B, etc., with a half-cylinder or half-parabola or segmented half-shape with the LEDs mounted on the interior surface thereof and the open plane or surface or truncated portion thereof corresponding to light exit plane or surface  37 ,  57 ; (ii) replacing the pyramidal PCB arrangement of  FIGS. 4A-B ,  6 A-B, etc., with a hemisphere or hemi-ellipsoid or other 3-D curved or segmented shape with an open plane or truncated portion, and with the LEDs mounted on the interior surface thereof and the open plane or truncated portion corresponding to light exit plane or surface  47 ,  67 ; and (iii) employing analogous curved or segmented surfaces such as discussed in (i) and (ii) above combined with and/or replacing some or all of the PCB surfaces in backlight  22 E of  FIGS. 7A-B ,  8 A-B,  9 A-B. Persons of skill in the art will understand based on the description herein that many other variations and combinations are possible. 
   It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing the exemplary embodiment or exemplary embodiments. It should be understood that various changes can be made in the function and arrangement of elements without departing from the scope of the invention as set forth in the appended claims and the legal equivalents thereof.