Not applicable
1. Field of the Invention
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.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
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.
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.
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.
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.
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.
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.
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.
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.