Abstract:
A compact optical assembly includes a linear array of LEDs, a plurality of reflectors, a plurality of lenses, and a cover. The reflectors include two reflecting surfaces that surround the LED light sources. One of the reflecting surfaces is defined by an arc of an ellipse that narrows into a throat in the axial direction away from the LED light source and cooperates with the other reflecting surface and the lens to create a collimated beam of light.

Description:
BACKGROUND 
       [0001]    This disclosure relates generally to LED light sources, and more particularly, to an optical assembly for use with an LED lamp. 
         [0002]    It is traditional to arrange lights on a vehicle to perform a variety of functions, including fog lighting, warning lighting, spot lighting, takedown lighting, scene lighting, ground lighting, and alley lighting. Emergency vehicles such as police, fire, rescue and ambulance vehicles typically include lights intended to serve several of these functions. Generally speaking, larger lights are less useful than smaller lights because of limited mounting space on the vehicles, as well as aerodynamic and aesthetic considerations. The trend is toward very bright, compact lights which use LEDs for a light source. 
         [0003]    Prior art optical configurations may not provide acceptable performance when the size of the light is reduced. These smaller configurations make it particularly difficult to provide focused beams of light of a desired intensity. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]      FIG. 1  is a top plan view of an embodiment of an optical assembly according to aspects of the disclosure; 
           [0005]      FIG. 2  is a partial diagrammatic sectional view of the reflector of  FIG. 1  taken along line A-A thereof; 
           [0006]      FIG. 3  is a diagrammatic sectional view of the reflector of  FIG. 1  taken along line A-A thereof; 
           [0007]      FIG. 4  is a diagrammatic sectional view of the embodiment of the optical assembly of  FIG. 1  taken along line A-A thereof, depicting light ray tracing; 
           [0008]      FIG. 5  is a diagrammatic sectional view of the lens of  FIG. 1  taken along A-A thereof. 
       
    
    
     DETAILED DESCRIPTION 
       [0009]    Referring to  FIG. 1 , an embodiment of the disclosed optical assembly  2  comprises a plurality of reflectors  4  arranged along line M-M. LED light sources  6  are generally disposed in the center of the reflectors  4 . The optical assembly  2  is covered by a light transmissive cover  8  incorporating a plurality of lenses  9 . Each reflector  4  comprises two surfaces of rotation that cooperate to reflect part of the light emitted from LED light source  6 . 
         [0010]    Referring to  FIG. 2 , each LED light source  6  of the depicted embodiment emits light in a hemispherical emission pattern to one side of first plane P 1 , surrounding optical axis A o . Optical axis A o  extends from the area of light emission perpendicular to the first plane P 1 . The reflector  4  comprises two reflecting surfaces  10 ,  20  that are surfaces of rotation about the optical axis A o . The reflecting surfaces are configured to cooperate to redirect light rays divergent from optical axis A o  and incident upon first reflecting surface  10  into a direction substantially parallel with optical axis A o . The first reflecting surface  10  extends from a first terminus  12  to a second terminus  14 . The second reflecting surface  20  extends from a third terminus  22  to a fourth terminus  24 . The first reflecting surface  10  has a larger diameter at the first terminus  12  than at the second terminus  14 , creating a narrow throat. A distance R 1  between the optical axis A o  and the first reflecting surface  10  at the first terminus  12  is larger than a distance R 2  at the second terminus  14 . 
         [0011]    Referring to  FIG. 3 , the first reflecting surface  10  is defined by rotating an arc  17  of an ellipse  11  from the first terminus  12  to the second terminus  14  about optical axis A o . The ellipse  11  has major axis  13  between first and second foci F 1 , F 2  which is canted at an angle θ relative to optical axis A o . In the depicted embodiment θ is approximately 30 degrees and the first focal point F 1  is coincident with the LED light source  6 . Angle θ may range between 10 degrees and 50 degrees. 
         [0012]    The second reflecting surface  20  is defined by rotating an arc  21  of a parabola  23  between the third terminus  22  and the fourth terminus  24  about optical axis A o . In the depicted embodiment, the parabola  23  has a focus offset from the optical axis A o  and coincident with the second focus F 2  of the ellipse  11 . The third terminus  22  is defined axially by the reflection of a light ray  26  that intersects the first reflecting surface  10  at the second terminus  14 . The fourth terminus  24  is defined axially by the reflection of a light ray  28  that intersects the first reflecting surface  10  at the first terminus  12 , which passes the second terminus  14 . 
         [0013]    Referring to  FIG. 4 , in the depicted embodiment light rays emitted from the LED light source  6  may be characterized as either “wide angle” light rays  30  or “narrow angle” light rays  32 . “Wide angle” light rays  30  are defined as light rays that are reflected by the first reflecting surface  10 . In the depicted embodiment, “wide angle” light rays  30  have a trajectory greater than approximately 30 degrees from optical axis A o . “Narrow angle” light rays  32  are defined as light rays that are not reflected by the first reflecting surface  10 . In the depicted embodiment, “narrow angle” light rays  32  have a trajectory less than approximately 30 degrees from optical axis A o . 
         [0014]      FIG. 5  illustrates one embodiment of a cover  8  incorporating the lens  9  compatible with the disclosed reflector  4 . The cover  8  includes a cavity  34  for receiving the reflector  4  and LED light source  6 . The lens  9  includes light entry surface  36  and the cover  8  includes light emission surface  38 . Referring to  FIG. 4 , “narrow angle” light rays  32  are refracted into light entry surface  36  and are emitted by the light emission surface  38  substantially parallel to optical axis A o . In the depicted embodiment, the light entry surface  36  is hyperbolic with a focus on the optical axis A o . The diameter of the light entry surface  36  is defined by the “narrow angle” light rays  32  of the LED light source  6  within the optical assembly  2 . 
         [0015]      FIG. 4  depicts representative light collimation by reflection on the reflecting surfaces  10 ,  20  and by refraction through the lens  9 . Light originates from LED light source  6  as “wide angle” light rays  30  and “narrow angle” light rays  32 . “Wide angle” light rays  30  are reflected by first reflecting surface  10  and second reflecting surface  20 , resulting in a collimated light beam  40  that is substantially parallel to optical axis A o . “Narrow angle” light rays  32  are refracted upon entering lens  9  through light entry surface  36 , also resulting in a collimated light beam  40  that is substantially parallel to optical axis A o . In some embodiments, the collimated beam  40  may spread significantly from the optical axis A o  depending on the application without departing from the spirit of the disclosure and the scope of the claimed coverage. 
         [0016]    In one embodiment, there is a transition surface  15  located between the first  10  and second  20  reflecting surfaces. As depicted in  FIG. 2 , the transition surface  15  extends from the first reflecting surface  10  to the second reflecting surface  20 . The transition surface  15  is defined by a substantially conical surface rotated about the optical axis A o . In one embodiment, the transition surface  15  is reflective to redirect light out of the optical assembly  2 . 
         [0017]    In one embodiment, the optical assembly  2  is divided into upper optical assembly  3  and lower optical assembly  5  along line M-M as depicted in  FIG. 1 . In the depicted embodiment, the upper and lower optical assemblies  3 ,  5  are substantially mirror images of one another. Dividing the optical assembly  2  provides easier manufacturability of the optical assembly. Due to the narrow throat of first reflecting surface  10 , as depicted in detail in  FIGS. 2 and 3 , injection molding or other similar manufacturing methods would be difficult without dividing the optical assembly  2  into multiple portions. 
         [0018]    In one embodiment, the series of lenses  9  are manufactured integral with the cover  8  and are arranged along the line M-M as depicted in  FIG. 1 . The cover  8  provides support and locates the lenses  9  coaxial with the reflectors  4  and LED light sources  6 . Alternate embodiments provide for manufacturing the lenses  9  separate from the cover  8  and using other mounting means.