Abstract:
A lens for preventing the build-up of snow and ice on LED traffic lights. The lens is hollow and fits over the LED signal beacon of the traffic light. The lens has a sidewall defined by a right circular conical frustum between a circular base and a plane spaced apart from the base and oriented at an oblique angle to the base. A convex face portion of the lens extends from the sidewall and closes the hollow space within the lens.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to lenses for traffic lighting. In particular, the invention relates to lenses for traffic lights using an LED light source as compared to the traditional prior art incandescent bulbs. 
       BACKGROUND 
       [0002]    A benefit of LED (light emitting diode) lighting is a significant reduction in power use for an equivalent light output, compared to incandescent lighting. The use of LED lighting in traffic lights, however, has led to the problem of unacceptable snow and ice build-up on the lens and consequently raised potential safety concerns. The reason for the snow build up is that there may not be sufficient heat generated by the LED lighting to melt any snow and ice that may have accumulated on the lens surface. In turn, this results in a visual impairment of the traffic light signal indication. 
         [0003]    The comparative absence of the snow build-up problem with incandescent lighting has apparently depended on the fact that incandescent lighting generates thermal energy in the form of heat which is useful in melting snow and ice from the face of the lens. Since the advent of LED lighting, there has arisen an increased number of reported incidents of obstructed signal beacons due to the accumulation of snow and ice thereon. It has been particularly observed that the build-up of snow and/or ice on prior art LED traffic lights starts at the bottom of the LED signal beacon and progressively moves upward to obstruct the traffic light. 
       SUMMARY OF THE INVENTION 
       [0004]    A lens, according to the present invention, has a sidewall defined by a hollow right circular conical frustum between a circular base and a plane spaced apart from the base and oriented at an oblique angle to the base. A convex face portion extends from the sidewall at the plane. 
         [0005]    According to another embodiment, the sidewalls taper outwardly from the face portion to the circular base. 
         [0006]    According to another embodiment, the length of the sidewall at the top is less than the adjacent lateral dimension of the cowl visor and the length of the sidewall at the bottom is greater than the adjacent lateral dimension of the cowl visor. 
         [0007]    According to another embodiment, the lens has a flange extending radially outwardly from the circular base. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS, 
         [0008]    In order that the invention may be more clearly understood, a preferred embodiment thereof will now be described in detail by way of example, with reference to the accompanying drawings, in which: 
           [0009]      FIG. 1A  is a perspective view of the lens, according to the present invention. 
           [0010]      FIG. 1B  is a top plan view of the lens of  FIG. 1A . 
           [0011]      FIG. 1C  is a front elevation view of the lens of  FIG. 1A . 
           [0012]      FIG. 1D  is a left side elevation view of the lens of  FIG. 1A . 
           [0013]      FIG. 1E  is a rear elevation view of the lens of  FIG. 1A . 
           [0014]      FIG. 1F  is a right side elevation view of the lens of  FIG. 1A . 
           [0015]      FIG. 1G  is a bottom plan view of the lens of  FIG. 1A . 
           [0016]      FIG. 2  is a schematic side profile view of the lens. 
           [0017]      FIG. 3  is a side view of the lens installed on a traffic light. 
           [0018]      FIG. 4  is an exploded view of a traffic light assembly, wherein the lens is installed on a traffic light by way of retrofit, as described herein. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0019]    According to the present invention, a specialized lens is disclosed which is retrofitted or installed on an LED traffic light having an LED signal beacon  10  and a cowl visor  11 . The lens is placed over the LED signal beacon  10  and, together with the cowl visor  11 , assists in wholly or partially preventing snow build up thereon. In the case of partial obstruction, the traffic light nonetheless remains visible to the driver and therefore operational. 
         [0020]    A preferred embodiment of the lens  12  according to the present invention is shown in the Figures. The shape of the lens  12  is defined by a right circular cone intersected along plane AA at an oblique angle by a convex shaped face portion  14  to form a non-parallel conical frustum, as shown in  FIG. 2 . At the opposing end of the lens  12  from the face portion  14  is a circular base, with a diameter D and a flange  13  extending radially outwardly from the lens  12 . The lens  12  has a continuous side wall  15 , between the flange  13  and the face portion  14 , which is defined by the hollow frustum of the cone between the circular base and the plane AA. 
         [0021]    Referring to  FIGS. 2 and 3 , the length L 1  of the sidewall  15  of the lens  12  at the top is dimensioned to be less than the adjacent lateral dimension Dt of the cowl visor  11  to ensure that there is no protrusion of the lens  12  beyond the leading edge of the cowl visor  11 . The length L 2  of the sidewall  15  of the lens  12  at the bottom exceeds the adjacent lateral dimension Db of the cowl visor  11  at the bottom so that the bottom portion of the lens  12  protrudes a distance d outwardly beyond the cowl visor  11  at the bottom. The lateral distance L 1  is greater than the lateral distance L 2 , thereby orienting the face portion of the lens  12  at an oblique angle to the flange  13  at the base of the lens  12 . 
         [0022]    Referring to  FIG. 3 , it can be seen that the face portion  14  of the lens  12  protrudes beyond the cowl visor  11  over approximately one half its bottom width. 
         [0023]    Referring to  FIG. 2 , the lens  12  is tapered outwardly from the face portion  14  to the flange  13 , at an angle a, which is preferably between 3° and 4° to ensure no physical interference between the lens  12  and the cowl visor  11 . 
         [0024]    The lens  12  forms an air cavity over the LED signal beacon  10  into which dissipates any heat generated by the LED lighting with the result that the surface temperature of the lens  12  is substantially identical to the temperature of the external environment. This assists in preventing snow and ice from adhering to the lens  12 , thereby helping maintain visibility of the traffic light signal. 
         [0025]    The convex face portion  14  of the lens  12  and its orientation at an oblique angle to the flange  13  at the base of the lens  12  offers streamlining against the elements borne by the wind and assists in redirecting the snow and ice approaching from all directions, or angles of contact, away from the face portion  14  of the lens  12 . The downward re-direction of the elements is assisted by the angle θ of the plane AA, on which the face portion  14  is oriented. This orientation also maximizes the effect of the force of gravity to counteract any build-up of snow and ice on the face portion  14 . Obstruction of the traffic signal by the accumulation of snow and ice on the inside bottom of the cowl visor  11  in prior art traffic signal installations is thus prevented or minimized. 
         [0026]    The lens  12  is made translucent so as not to cause any optical distortion of the signal beacon and the convex surface additionally assists in reducing the amount of light that may be reflected directly by a vertical lens. 
         [0027]    The dimensions of a preferred embodiment of a lens  12 , according to the present invention, offered by way of example only, are as follows. They are with reference to a standard 12″ diameter lens  12  and may be adjusted proportionately for other standard sizes, such as an 8″ diameter lens  12 .
       D=11″   L1=5½″   L2=2″   θ=26°       
 
         [0032]    The lens  12  may be retrofitted on existing traffic light installations by installing the lens  12  over the pre-existing LED signal beacon  10 , as shown in  FIG. 4 . An environmental gasket (not shown) should be provided between the adjacent surfaces of the traffic light and the flange  13  of the lens  12 . Special fasteners may be required on the frame of the traffic light in order to secure the retrofitted assembly at the rear of the traffic light. The retrofit will result in raising the rear of the traffic light a distance equal to the thickness of the flange  13  of the lens  12  and any gaskets placed between the flange  13  and the traffic light. Accordingly, the fastener must be crimped to accommodate the resulting raise with reference to the frame. 
         [0033]    Other advantages which are inherent to the invention are obvious to one skilled in the art. The embodiments are described herein illustratively and are not meant to limit the scope of the invention as claimed. Variations of the foregoing embodiments will be evident to a person of ordinary skill and are intended by the inventor to be encompassed by the following claims.