Abstract:
A light guide for an automotive tail light may be efficiently made with a plurality of thick planar light guides stacked side by side to have a common input source point at one end, but spread at their respective opposite ends to be arranged to form parallel planes separated sufficiently to project a relatively larger combined image that may suggest in outline a larger object. The relatively thick plates efficiently transmit light. The planar structures direct light efficiently in the horizontal plane. The side by side offset of the output windows creates an image of a larger more readily seen structure.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    Not applicable 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention relates to electric lamps and particularly to automotive electric lamps. More particularly the invention is concerned with automotive taillamps with LED light sources and light guides. 
         [0004]    2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98 
         [0005]    Light production in an LED is concentrated in a tiny volume. Directly viewing a nearly point source of emitted light is uncomfortable. Human response studies have found response times are faster when sensing a change in a large image as opposed to a small image. There is then a general need to both spread the emitted light from LED taillight source in all the required directions, and to do so while forming a conveniently large image, one not so small as to be offensively intense, one sufficiently large to invoke a rapid response and yet one not so large as to be unnecessarily expensive. Reflectors are commonly used to spread light from filament sources, but they are generally deep and wide, requiring large reflective areas. Light guides are commonly used to spread or diffuse light away from LED sources. Typical taillight designs used in automotive lamps have used flexible fiber optics with a lens at the end of each fiber, or solid body light guides with features to direct light perpendicular to the light guide axis. Fiber optics are hard to assembly into practical devices. Fiber units can also be difficult to optically point correctly. On the other hand, solid light guides with features to direct light perpendicular to the light guide axis are generally inefficient and leave gaps between the directing features. Increasing the number of directing features and making them small increases the tooling and manufacturing costs. There is then a need for an automotive LED light distributing method that is accurate, large in area and still inexpensive. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    An automotive taillight light guide for receiving light from a light source with a minimal beam width and a corresponding maximal beam angle. The light guide may be made from a plurality of light transmissive plates. Each plate has a first broad side and a second broad side joined by a narrow circumferential edge. The first broad side and the second broad side are separated by an approximately constant thickness. The broad sides have lengths and widths ten or more times greater than the thickness. An input window formed along the edge receives light from an LED light source. The input window has a central normal that serves to define an input axis. An output window is formed along the edge comprising a plurality of light intercepting faces directing light to a field to be illuminated. The light guide includes at least one plate that extends from the input window toward the output window as a first planar portion extending along a first plane including the input axis, the plate then bends away from such first planar portion and then bends back to extend in a second planar portion along a second plane that is substantially parallel to the input axis but is offset from the input axis. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0007]      FIG. 1  shows a front perspective view of a preferred embodiment of an automotive light guide and LED light source. 
           [0008]      FIG. 2  shows a rear perspective view of two sections of the automotive light guide of  FIG. 1 . 
           [0009]      FIG. 3  shows an end perspective view of one section of the automotive light guide and LED light source of  FIG. 1 . 
           [0010]      FIG. 4  shows a front perspective view of a preferred embodiment of an automotive light guide. 
           [0011]      FIG. 5  shows a front perspective view of the automotive LED light source of  FIGS. 1 and 3 . 
           [0012]      FIG. 6  shows a perspective view of a preferred embodiment of an automotive light guide mounted in an automotive rear light housing. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0013]      FIG. 1  shows a front perspective view of a preferred embodiment of an automotive light guide  10  and LED light source.  FIG. 2  shows a rear perspective view of two plate sections of the automotive light guide of  FIG. 1 . The automotive taillight light guide  10  is formed from a plurality of light transmissive plates  12 . The number of plates  12  preferred by the Applicant varies from two to four, but ten or more plates  12  are expected to still be practical. Each plate  12  has a first broad side  14  and a second broad side  16  that are joined by a narrow circumferential edge  18 . The first broad side  14  and the second broad side  16  are each locally substantially flat and separated by an approximately constant thickness  20  thereby providing a substantially totally internally reflective light guide. The thickness  20  should be at least as large as the least transverse dimension  22  (=W) of the input light beam received from a light source  26 . Preferably, the thickness  20  should be sufficiently greater than the least beam width to allow a typical internal refection angle of the beam that is much less than 45 degrees. The transiting light should preferably be made up of long straight segments with only a few, small (glancing) angle reflections, and few if any, large angle reflections. A thickness  20  that is two more times the minimal beam  22  width is preferred. A planar input window  28  for receiving light is formed along the edge  18 . The central normal to the input window  28  defines an input axis  30 . In particular, the combined input window  28  thicknesses  20  (=T) for receiving light should be equal to or greater than the minimal light source  26  beam width W, and the combined input window should be offset from the light source  26  by less than a spacing S such that the difference between the combined plate thicknesses  20  forming the combined (common) window thickness  24  (=T) and the beam  27  width W divided by two times the spacing S is greater than the sine of one half the light source beam angle A, that is (T−W)/2S&gt;sin(λ/2). 
         [0014]    An output window  32  is formed also along the edge  18 , generally along the opposite end of the light guide from where the input window  28  is positioned. The preferred output window  32  comprises a plurality of light intercepting faces  34  directing light to a field to be illuminated. For example, the output window  32  may have a saw tooth pattern, preferable with one face of each tooth being parallel to the input axis  30  and one face of each tooth being at an angle (not being parallel) to the input axis  30 . The saw tooth pattern may be more specifically a staircase pattern, where the steps are approximately perpendicular to the input axis  30  and the risers are approximately parallel to the input axis  30 . The steps may be formed with pillow optics to evenly spread the exiting light. Other output window  32  formations may be used, such as sandblasting a section of the edge  18  or forming side facing (not staircased) pillow or similar optics on the circumferential edge  18 . It is only necessary that the light supplied through the input window  28  to the light guide be intercepted and refracted along the output window  32  that is along the front edge  18  to be directed toward the field to be illuminated.  FIG. 3  shows an end perspective view of one section of the automotive light guide and LED light source of  FIG. 1 . A back side  38  is also formed along the circumferential edge  18 . The preferred back side  38  extends substantially in a plane parallel to the input axis  30 , and is formed to be internally reflective so as to lose little or none of the light transmitted into the light guide at the input window  28 . 
         [0015]    At least one of the plates  12  extending from the input window  28  toward the output window  32  has a first planar portion  40 . The first planar portion  40  extends along a first plane including the input axis  30 . The plate  12  is then gently curved or bent away from such first plane so as to not lose light and is then gently curved or bent back, again to not lose light, to extend in a second planar portion  42 . The second planar portion  42  is generally along a second plane that parallels the input axis  30  but is offset from the input axis  30 . The plate  12  then forms a gentle S curve bending from the first planar portion  40  to extend in the second planar portion  42 . The plate  12  then gently guides light received into the first planar portion  40  to the second planar portion  42 , where the light is transmitted out, the output window  32 . The planar offset from the first planar portion to the second planar portion may vary from plate to plate but would typically be at least as large as the plate thickness, perhaps as much at ten or more times the plate thickness. The preferred back side  38  extends along the second planar portion  42  as a straight section parallel to the input axis  30 . 
         [0016]    The preferred output window  32  extends along a front side of the second planar portion  42 . The front side with the output window  32  curves around toward the back side  38  or extends substantially as a straight line (may be staircased) at an angle to the input axis  30  aimed to intercept the back side  38 . In either case, the output window  32  extends to across a direction line pointing to the field to be illuminated to intercept the back side  38 . 
         [0017]    In the preferred embodiment, there is a plurality of such plates  12  that are roughly similarly in form. The plates  12  are arrayed in parallel, so the respective broad sides  14 ,  16  of the second planar portions  42  are parallel thereby forming offset slices through a three dimensional space. Preferably these offset slices are spaced apart by three or more times the thickness of the plate  42 . The respectively more exterior plates  12  (those at the top of the stack or those at the bottom of the stack) may have relatively more bend to their respective S curves. The respective plates  12  may having differing widths or lengths to the respective second planar portion  42  to thereby suggest in outline a common intercepted surface (imaginary). The plurality of output windows  32  then appear widely spread but as parallel slices through the defined or suggested commonly intercepted surface (imaginary). Each slice being defined by a respective coplanar second planar portion  42 . In the preferred embodiment, the respective second planar portions  42  are offset one from the other by an equal amount. The offset output windows expand the optical image, and create or simulate a larger illuminated region that is more easily responded to mentally by a viewer. 
         [0018]    In the preferred embodiment, the respective input windows  28  are arranged side by side to form a common input window  28  facing a common light source or sources. The respective input windows  28  may be joined (strapped, glued, clamped, or similarly coupled) as a group, thereby aligning, joining or trapping the respective sides  50  (edge  18  portions) adjacent the respective input windows  28  with or in a socket  52 . The socket  52  may then pin the input ends  50  of the plates  12  as a group. Of course, the plates  12  may otherwise be grouped as a unit along the input window  28  face area. The aligned input window faces  28  then, as a group have or define a common input face that may be optically coupled or pressed to an adjacent a light source  26 ; such as an LED array, or similar light source  26  as an input.  FIG. 4  shows a front perspective view of a preferred embodiment of an automotive light guide.  FIG. 5  shows a front perspective view of the automotive LED light source of  FIGS. 1 and 3 . By aligning each plate  12  with a separated row of LEDs, the stack of differing plates  12  may be illuminated separately or jointly. 
         [0019]      FIG. 6  shows a perspective view of a preferred embodiment of an automotive light guide mounted in an automotive rear light housing. The stack of a relatively few number of light guides having modestly large thicknesses  20  and long output windows  32  efficiently captured the input light and accurately spread it horizontally to the field to be illuminated from a visually large (spread) source  26  that was comfortable to view. The tail light optic was then efficient, and visually effective and not offensive. In one embodiment four transparent plastic plates (sheets) about 5 mm. thick with a narrow light input end were arrayed in a vertical stack. The top and bottom sheets were bent out of plane and then back into parallel planes with maximum angles of up to about 25 degrees. The output ends were generally sculpted as a group to follow (mimic) the exterior curvature of the vehicle. The window output ends had pillow optics to create a horizontally spread beam pattern. The emission pattern from the plates was already collimated with an emission angle of plus or minus 30 degrees from the input axis. No focusing optics were needed. Pillow optics spread the pattern horizontally to create visibility at wider angles. Losses were small as the beam from the LED source was already collimated. The total internal reflection angle of the guide was about 45 degrees, while the source had a spread of plus or minus 30 degrees in air (plus or minus 20 degrees in the optic) which gave the optic about 20 degrees of head room for loss. Even though the planar bends were more than 25 degrees, the losses were less than with a lambertian (hemispherical) emission pattern. 
         [0020]    While there have been shown and described what are at present considered to be the preferred embodiments of the invention, it will be apparent to those skilled in the art that various changes and modifications can be made herein without departing from the scope of the invention defined by the appended claims.