Abstract:
A back-up lens for a stop, tail and signal lamp comprising a body of clear plastic material having an inner surface with dioptrics and catadioptrics thereon and an outer surface with cylindrical surfaces thereon.

Description:
DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front elevational view of a lens embodying the invention. 
     FIG. 2 is a rear elevational view of the back-up lens. 
     FIG. 3 is a sectional view taken along the line 3--3 in FIG. 2. 
     FIG. 4 is a sectional view taken along the line 4--4 in FIG. 2. 
     FIG. 5 is a view similar to FIG. 4 on an enlarged scale showing typical light rays. 
     FIG. 6 is a sectional view similar to FIG. 3 on an enlarged scale showing typical light rays. 
    
    
     DESCRIPTION 
     Referring to FIG. 1, lamp 20 conventionally comprises a housing on which a lens 21 is provided that is made of plastic and has an insert 22 therein. The lens 21 has a smooth outer surface and an upper portion including retro-reflective prisms 23 and a lower portion having dioptrics and catadioptrics 24 on the inner surface thereof. 
     Referring to FIGS. 2-4, the back-up lens 22 comprises a body of clear plastic material, sometimes referred to as white, and has an inner surface with dioptrics 25 on the opposite sides of the center line and catadioptrics 26 below the dioptrics 25. 
     The body of the back-up lens 22 has an outer surface with a convex centrally located surface 27 and concave cylindrical surfaces 28. 
     As shown in the drawings, the lens including the back-up lens 22 is adapted to be mounted in vertical position with the dioptrics extending generally horizontally. 
     Referring to FIG. 5, the dioptrics 25 comprise four horizontal prisms 1-4 which have concave upper surfaces, dioptrics 5, 6, 7, having concave surfaces, and dioptrics 8, 9, 10, 11, 12, with lower concave surfaces. The dioptrics function to redirect the light from the filament F toward the horizontal. The catadioptrics also extend horizontally and comprise prisms 13, 14, 15, which redirect the light from the filament by refraction and reflection toward the horizontal. 
     The cylindrical surface 16 functions to redirect the light in the horizontal plane toward the axis of the back-up lens 22 while the cylindrical portions 17, 18, 19 tend to direct the light in a horizontal plane to provide lateral dispersion thereof. 
     As shown in FIG. 6, the cylindrical surfaces are indicated as 16, 17, 18 and 19. 
     The manner in which the optics on the inner surface tend to redirect the light is shown by the following Table I: 
     
                       TABLE I______________________________________        Angle of      Angle of        Entering      RedirectedOptic        Ray           Ray______________________________________1            39.5°  6.7°2            34.0°  4.7°3            27.5°  1.5°3-4          23.0°  6.5°4            17.5°  -6.5°5            12.0°  9.5°6            4.5°   4.5°7            -4.5°  -4.5°8            -12.5° 0°9            -20.0° -3.5°10           -27.5° -4.2°11           -34.0° -4.6°12           -39.5° -5.7°13           -43.0° -5.0°14           -46.0° 0°15           -49.0° 5.0°______________________________________ 
    
     The manner in which the optics on the outer surface redirect the light is shown by the following Table II: 
     
                       TABLE II______________________________________        Angle of      Angle of        Entering      RedirectedOptic        Ray           Ray______________________________________16           12°    6.5°17           21°    40.0°18           22°    -26.0°19           40°    48.0°______________________________________ 
    
     The manner in which the back-up lens functions to meet the S.A.E. standards and the Canadian standards for minimum candle power is shown by the following Table III: 
     
                       TABLE III______________________________________Test Points Min. Spec.     MeasuredDegrees     Candle Power   Candle Power______________________________________10L         10             1910U-V       15             4510R         10             1945L         15             1910L         20             545U-V        25             9110R         20             3645R         15             2545L         15             3230L         25             6810L         50             101H-V         80             16610R         50             7430R         25             6545R         15             2945L         15             2530L         25             6110L         50             1045D-V        80             17010R         50             6630R         25             5945R         15             23______________________________________ 
    
     In the above test results shown in Table III, the maximum candle power was 195 at 2.9° L., 3.5° D.