Patent Document

CROSS-REFERENCE TO RELATED PATENTS AND APPLICATIONS 
   This application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/592,992 filed on Jul. 30, 2004 and entitled “LED Traffic Signal” and U.S. Provisional Patent Application Ser. No. 60/642,170 filed on Jan. 7, 2005 now abandoned and entitled “LED Traffic Signal,” the entireties of which are incorporated herein by reference. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to signals, in particular, Light Emitting Diode (LED) traffic signals. More specifically, the present invention relates to a LED traffic signal having a protective cover that protects collimating and diffusing optical elements from environmental conditions. 
   2. Description of Related Art 
   LED signals such as LED traffic signals, present numerous advantages over incandescent lamp traffic signals. Use of LEDs provides a power consumption savings and extremely long life compared to incandescent light sources. The long life span of the LED signals leads to improved reliability and lower maintenance costs. Typical LED signals use multiple LEDs in an array to replicate the light output of the incandescent lamp. Multiple LEDs can create a display aspect within which the individual points of light from each LED are discernable. Thus, the lit appearance of the signal is visually displeasing. If one or more LED burns out, a void is left in the lit appearance of the lens. Further, if the LEDs are not closely matched in intensity and color the resultant lit appearance is non-homogenous. Each generation of LEDs is brighter, requiring fewer LEDs to meet the intensity specification. While using fewer LEDs reduces the cost of the signal, it also increases the potential for viewing the LEDs as individual point sources and for having undesirable shadows. 
   There is an unmet need for an improved LED signal that overcomes the aforementioned, as well as other, deficiencies with conventional LED signals. 
   SUMMARY OF THE INVENTION 
   In one aspect of the invention, a LED signal having a protective cover is provided. The LED signal includes at least one LED arranged on a PCB. An optical element that collimates light energy emitted from the at least one LED is positioned adjacent to the at least one LED. A diffusing element is positioned adjacent to the optical element and spreads collimated light transmitted through the optical element. The PCB, the optical element, and the diffusing element are disposed between the cover and a housing of the LED signal, and the cover provides a protective barrier between environmental conditions and the optical and diffusing elements. 

   
     BRIEF DESCRIPTION OF THE FIGURES 
     The drawings are only for purposes of illustrating embodiments and are not to be construed as limiting the claims. 
       FIG. 1  illustrates an exploded view of a Light Emitting Diode (LED) signal. 
       FIG. 2  illustrates an exemplary collimating optical element of a LED signal. 
       FIG. 3  illustrates a cross sectional view showing both dioptic rings and catadioptric rings of a collimating optical element. 
       FIG. 4  illustrates exemplary light collection angles of dioptric and catadioptric rings of a collimating optical element. 
       FIG. 5  illustrates various characteristics associated with dioptic rings of a collimating optical element. 
       FIG. 6  illustrates an exemplary spreading or diffusing optical element. 
       FIG. 7  illustrates exemplary light output patterns through horizontal and vertical axes associated with a spreading or diffusing optical element. 
       FIG. 8  graphically depicts horizontal and vertical axes of a spreading or diffusing optical element. 
       FIG. 9  illustrates an exemplary pillow optic of a spreading or diffusing optical element. 
       FIG. 10  illustrates an exploded view of a LED signal with a single collimating/diffusing element. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  illustrates an exploded view of Light Emitting Diode (LED) signal  2 . The LED signal  2  includes a housing  4  having an inner volume  6  and at least one surface  8  facing an opening  10  of the housing  4 . A circuit board (“PCB”)  12  is attached to the at least one surface  8 . The circuit board  12  can be a metal core PCB or other type of PCB. Various techniques can be used to attach the circuit board  12  to the at least one surface  8 . For example, the circuit board  12  can be attached through one or more rivets, screws, adhesives, snaps, tape, wires, other circuit boards, etc. Alternatively, the circuit board  12  can be integrated within the surface  8  of the housing  4 . In another alternative, the circuit board  12  sits in a predefined position on the surface  8  and is held in place through various other components within the housing  4 . For instance, the circuit board  12  can be held in place by one or more mounting brackets, heat sinks, a control module, a power supply, etc. A suitable heat sink includes a heat sink with fins. 
   The circuit board  12  includes one or more LEDs  14 , which are coupled to the circuit board  12  via through-hole (e.g., soldered and wire wrapped) and/or surface mount (e.g., short pins, flat contacts, matrix of balls (BGAs), etc.) technology. 
   The circuit board  12  is positioned on the surface  8  such that the LEDs  14  emit light energy through the opening  10 . Essentially any number of LEDs  14  can be coupled to the circuit board  12 . In addition, one or more of the LEDs  14  can be a similar and/or different color. Different LED manufacturers provide LEDs  14  with distinctive light patterns. 
   An optional lens  15  can be placed over each LED  14  to change the light pattern so that different LEDs can be used without adversely affecting efficiency and/or the uniformity of the signal and/or light patterns can be changed based on the application. To facilitate controlling the light from the LEDs, an injection molded optical element typically is used. 
   A first optical element  16  is positioned adjacent to the opening  10  of the housing  4 . The optical element  16  includes a collecting and/or collimating surface that collects and/or collimates light energy emitted by the LEDs  14 . A second optical element  18  is positioned adjacent to the first optical element  16 , on a side of the first optical element  16  opposite the LEDs  14 . The second element  18  includes a spreading or diffusing surface, which suitably spreads light energy transmitted through the first optical element  16 . A third optical element  20  is positioned adjacent to the second optical element  18 , on a side of the second optical element  18  opposite the first optical element  16 . It connects to the housing  4  and secures the first and second optical elements  16  and  18  in place. A sealing technique such as an O-ring can be used to facilitate attaching the third optical element  20  to the housing  4  and sealing the attachment region. Typically, the third optical element  20  includes a clear, neutral outer cover. 
   However, it can additionally or alternatively include at lease one of a tinted or colored surface, a textured surface, and/or optics such as a filter. 
   It is to be appreciated that one or more of the first, second, and third optical elements can have substantially planar surfaces. 
   The third optical element  20  also shields the first and second optical elements  16  and  18 , the LEDs  14 , the circuit board  12  or other components residing between the third optical element  20  and the surface  8  of the housing  4  from the environment. Thus, when an object (e.g., a stone, a tree branch, a bird, etc.) contacts the optical portion of the signal  2 , the object is shielded from the first and second optical elements  16  and  18  by the third optical element  20 . If the object damages the third optical element  20 , it can be replaced at a cost relatively lower than replacing the first and/or second optical elements  16  and  18 , for example. In addition, in many instances a damaged third optical element still provides adequate protection from the environment, does not substantially degrade light output from the signal  2 , and does not have to be replaced. 
   The third optical element  20  can also protect the first and second optical elements  16  and  18 , the LEDs  14 , the circuit board  12  or other components from any of rain, snow, the wind, or the sun. 
   Conventional traffic signals typically do not employ an outer neutral cover. Instead, the diffusing and/or collimating optical element is exposed to the environment and susceptible to damage from the environment. As noted above, replacing diffusing and/or collimating optical elements is relatively more costly than replacing a neutral cover protecting such optical elements. In addition, damaging the diffusing and/or collimating optical elements may render the light output inadequate for its application. For instance, the light output may no longer be visible to the intended viewer. Thus, the novel invention described herein provides advantages over and/or overcomes deficiencies with conventional traffic signals. 
   It is to be appreciated the signal  2  can be adapted to retrofit into an existing traffic light and/or incorporated into a new traffic light. To allow an easy retrofit without requiring significant changes to the preexisting AC power distribution and logic circuits, the LED signal assemblies can incorporate a power supply (not shown) to drive the LEDs at a lower, controlled, direct current power level. 
     FIG. 2  illustrates a non-limiting example of a suitable first optical element  16 . As depicted, a surface of the first optical element  16  can include one or more Fresnel rings  22 . The light energy from the LEDs  14  is collimated by the one or more Fresnel rings  22 . 
   In one instance, the one or more Fresnel rings  22  include one or more dioptric rings  24  and/or one or more catadioptric rings  26  that collimate the light. 
     FIG. 3  illustrates a cross section view of the first optical element  16 , showing both dioptric rings  24  and catadioptric rings  26 . Returning to  FIG. 2 , the dioptric rings  24  generally refract light, and catadioptric rings  26  generally refract and substantially internally reflect the rays of light. 
   Typically, the dioptric rings  24  are employed relatively nearer to the center of the first optical element  16 , as depicted in  FIG. 2 , and the catadioptric rings  26  are employed farther from the center of the first optical element  16 , as depicted in  FIG. 2 . After the light passes through the first optical element  16 , the light is substantially collimated. 
   An optical element characteristic that can affect the efficiency of the first optical element  16  includes, but is not limited to, light collection angles of the optical faces of each of the dioptric rings  24  and catadioptric rings  26 .  FIG. 4  illustrates the light collection angle “α” of the optical face  28  of a catadioptric ring and the light collection angle “β” of the optical face  30  of a dioptric ring. As depicted, the angle of the catadioptric rings  26  typically is more acute than the angle of the dioptric rings  24 . In addition, with the dioptric rings  24 , the radii represent a much larger percentage of the collection angle than on the catadioptric rings  26 . Typically, the dioptric rings  24  and the catadioptric rings  26  do not have a constant height. In addition, the catadioptric rings  26  typically are taller than the dioptric rings  24 , and the rings  24  and  26  typically are as tall as practically possible to minimize the number of fillet radii. A typical height ratio of the dioptric rings height to catadioptric ring height is about 1.5:1 to about 2:1. 
   Another optical element characteristic that affects the efficiency of the first optical element  16  is a transition region between the dioptric rings  24  and the catadioptric rings  26 . For a given focal length, lens diameter, inner and/or outer fillet radii, and optic height, this transition region typically is determined based on one or more assumptions, including that the light source is a point source. However, the LEDs  14  are not a point source, but approximate a point source and, thus, the transition region typically is additionally tuned. The light energy that falls within the prescribed optical pattern is measured and compared against optical designs that have slightly larger and slightly smaller transition regions to tune the transition region. 
   Typical transition regions reside in a range from about F=0.5 to about F=1.5 (e.g., typically about 0.84), where F is a ratio of focal length to a diameter of the dioptric rings  24 . 
     FIG. 5  illustrates suitable locations for obtaining a focal length  32  and a diameter  34  for computing F. 
     FIG. 6  illustrates a non-limiting example of a suitable second optical element  18 . The second optical element  18  includes spreading optics  38  that generate a light output pattern that is generally Gaussian shaped through a horizontal axis and relatively non-symmetrical through a vertical axis with a predominance of light below the horizontal axis.  FIG. 7  illustrates exemplary light output patterns through the horizontal axis and the vertical axis, and  FIG. 8  graphically depicts typical views of horizontal axis at  40  and vertical axis  42  of second optical element  18 . 
   Returning to  FIG. 6 , suitable spreading optics  38  of the second optical element  18  include, but is not limited to, pillow optics, prism optics, cylindrical optics, etc. Pillow optics are based on a spheroid or a toroid, wherein a square or rectangular portion of the spheroid or toroid is utilized as the optic.  FIG. 9  illustrates an exemplary pillow optic  44 . Each optic  44  is variously shaped on the horizontal and vertical axes to control the light. The shape of each optic  44  is determined based at least in part on an optical intensity at various positions along the vertical and horizontal axes. One or more, including all of the optics  44  can be similarly and/or differently shaped. Alternatively, a cluster approach can be used. With the cluster approach, smaller optics are positioned between each of the optics  44 . Typically, all of the clusters are the same in order to provide a uniform lit appearance regardless of viewing angle. 
   If one or more LEDs  14  in a cluster becomes non-functional (e.g., Produces less than adequate light), the light output remains substantially lit, provided there is still at least one functioning LED. The cluster also provides a more aesthetically pleasing appearance than a signal with a patterned array of LEDs spread behind the entire face of the lens. 
   Returning to  FIG. 1 , typically it is desirable to illuminate substantially The entire optical areas of the first and second optical elements  16  and  18 . In order to facilitate such coverage, the first and second optical elements  16  and  18  are suitably positioned at a distance from the LEDs  14  that allows maximum illumination of the cover with a minimum, or preferably no, light lost by illuminating areas other than the optical elements  16  ands  18 . In order to mitigate spreading the light beyond the optical areas of the first and second optical elements  16  and  18 , an optional lens can be positioned over the LEDs  14  to adjust the light pattern accordingly. 
     FIG. 10  illustrates an embodiment in which the first and second optical elements  16  and  18  are incorporated into a single optical element  46 , which is positioned between the cover  20  and the opening  10 . As described above, the one or more LEDs  14  are grouped about a common focal point or central axis perpendicular to the optical element. Both collimation and distribution element are achieved through the single optical element  46 . 
   The invention has been described with reference to the various embodiments. Modifications and alterations may occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be constructed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.

Technology Category: f