Abstract:
An LED signal module includes a casing defining a cavity. Within the cavity is an array of LEDs. Individual reflectors are placed around individual LEDs of the array. The individual reflectors are structured to receive direct light from their associated individual LEDs and substantially to prevent direct light from their associated individual LEDs from impinging upon the individual reflectors of other LEDs of the array of LEDs. Also included, and covering the cavity, is a lens shaped to direct the output luminance of the LEDs below a horizontal axis of the module.

Description:
TECHNICAL FIELD 
     The invention relates to an LED illuminated traffic signal. 
     BACKGROUND 
     Traffic signal lamps or illuminated overhead road signs have conventionally used incandescent lamps for lighting. More recently, efforts have been made to replace the incandescent lamps with light emitting diodes (LEDs). LEDs offer the considerable advantage of consuming significantly less power than incandescent lamps. LEDs also generally require less frequent replacement due to burn out than incandescent lamps. LEDs, in short, offer a desirable reduction in power and maintenance costs as compared to incandescent lamps. 
     There are, however, several issues to consider when using LEDs in lieu of incandescent lamps for traffic signals and other applications. First, the light emitted from a given LED is of low intensity compared to that of a comparably sized incandescent lamp. Second, conventional LEDs emit light in a relatively tight pattern that requires the redistribution of that light in order to attain spatial distributions in compliance with, for example, Institute of Transportation Engineers (ITE) requirements or other regulations. Also, due to their thermal-sensitivity, heat generated during operation of the LEDs and associated components must be low enough (or adequately dissipated) to assure reliable operation over extreme temperature ranges. 
     Known implementations of LED signal modules make use of hundreds of individual LEDs to generate light that is sufficient and of satisfactory spatial distribution. The large number of LEDs leads to a more expensive module and one with greater power consumption. The increased power usage leads to greater thermal output, which, if not adequately addressed at additional expense, impacts device reliability. 
     SUMMARY 
     An overhead signal module may provide improved illumination qualities through use of LEDs with associated individual reflectors. The individual reflectors provide a substantial increase in the useful luminous output of the signal module relative to a signal module without the reflectors. 
     The increased efficiency of LEDs coupled with reflectors allows for the use of fewer LEDs in a signal module. This, in turn, leads to lower component cost and reduced power consumption. The reliability of the signal module is also improved due to a reduced part count and a decrease in self-generated thermal energy, which can reduce component life. 
     A further advantage of this signal module is that it is considerably less prone to the “blink out” effect associated with other LED signals. When viewed from their periphery and off of their optical axis these signals appear to “blink out” due to the tight emission pattern of their LEDs. Multiple individual reflectors increase this signal module&#39;s output of anecdotal light, thereby providing a signal more readily visible from the module&#39;s periphery. 
     In one general aspect, an overhead signal module includes a module casing defining a cavity. Positioned within this cavity is a mounting board which carries an array of LEDs. Each LED is equipped with an individual reflector shaped to capture and direct side lobe light of the LED. Mounted parallel to the LED array and covering the cavity is a lens. The lens is shaped to efficiently focus the luminous output of the LEDs below the horizontal plane and to provide the appearance, when viewed from below the horizontal plane, of full uniform illumination. 
     Embodiments may include one or more of the following features. For example, the reflectors used to gather the side lobe light may be conical. Alternatively, parabolic reflectors may be used. In either case, the reflectors may be formed into an insert assembly which will fit over the LED mounting board and integrate each LED with its corresponding reflector. 
     The signal module lens may be manufactured of clear polycarbonate and may be either flat or domed. When the lens is clear, the color of the output light will be generated by use of appropriate color LEDs. 
     The lens may be compound, and may include fresnel lenses positioned to provide each LED with a fresnel lens aligned with the optical axis of the LED. The outer surface of the lens may be smooth, with all of the optical details of the component fresnel lenses on the inner surface of the lens. An advantage of this configuration is that it helps prevent the accumulation of dirt on the lens. 
     Each fresnel lens may include a two facet upper portion which refracts upward directed light downward below the horizontal axis. The lower portion of the lens may act as a simple window and may be configured to have a neutral effect upon the direction of light propagating through it. 
     Implementations of the signal module may include an eight-inch diameter and a twelve-inch diameter module. In the case of an eight-inch diameter module, illumination may be provided by 72 LEDs and associated reflectors. A twelve-inch module may include 144 LEDs. In either case, the LEDs are symmetrically distributed in a generally uniform manner. 
     An individual overhead signal may include a clear lens designed to efficiently redirect light to conform with ITE specifications or other regulations. This lens may be, in turn, a composite of individual fresnel lenses, including one for each LED. Furthermore, each of the LEDs may be provided with its own individual reflector to redirect the LEDs&#39; side lobe light which would otherwise be lost. 
     Other features and advantages will be apparent from the following description, including the drawings, and from the claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a perspective view of a standard three-light traffic signal. 
     FIG. 2 is a sectional perspective view of an individual signal module of the traffic signal of FIG.  1 . 
     FIGS. 3A and 3B are top and side views of a latching structure of a casing of the module of FIG.  2 . 
     FIGS. 3C and 3D are side and end views of a latching structure of a lens of the module of FIG.  2 . 
     FIG. 4A shows a side view of the lens assembly of the signal module of FIG.  2 . 
     FIG. 4B shows detail B—B of FIG. 4A, illustrating one of the component fresnel lenses. 
     FIG. 5 provides a side view ray diagram showing the redirection of an LED&#39;s light by its individual reflector and its corresponding fresnel lens. 
     FIG. 6 shows the distribution of the 72 reflectors of an eight inch round overhead signal. 
     FIG. 7 shows a front view of the lens for the eight inch signal and the corresponding distribution of the fresnel lenses which compose it. 
     FIG. 8 shows the distribution of the 144 LEDs of a twelve inch round overhead signal. 
     FIG. 9 shows a front view of the lens for the twelve inch signal and the corresponding distribution of the fresnel lenses which compose it. 
     FIG. 10 shows detail  10 — 10  of FIG. 7, illustrating the orientation of a row of fresnel lenses. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIG. 1, a traffic signal  100  includes three separate LED light modules  105 . Each module emits a different color of light, either red, yellow, or green. 
     As illustrated by FIG. 2, an LED light module includes a lens  110  and LEDs  115 . The LEDs are attached to a mounting board  120  and powered and controlled by a circuit board assembly  125 . 
     A reflector assembly  130  provides an individual reflector  135  for each LED  115  to capture and redirect otherwise dissipated side lobe light of the LED  115 . The reflector assembly  130  fits over the LEDs  115 , with each LED  115  protruding into an open bottom end of a corresponding reflector  135 . The reflector assembly  130  includes a circular upper section  140  having a flat upper surface  145 . In general, the surface  145  is black and nonreflective. The reflectors  135  are defined as holes  150  in the surface  145 . The reflectors  135  are generally conical and extend from the bottom of the section  140 . The inside surfaces  155  of the reflectors  135  are silver and reflective. 
     The mounting board  120 , the circuit board assembly  125 , and the reflector assembly  130  are secured in a housing  160  defined by a casing  165  and the lens  110 . Referring also to FIGS. 3A-3D, the lens  110  is secured to the casing  165  by a set of interlocking mechanisms. In particular, casing  165  includes a set of tabs  170 , one of which is shown in FIGS. 3A and 3B, defined in a rim  172  of the casing. The tabs  170  interact with a set of arms  174 , one of which is shown in FIGS. 3C and 3D, that extend from a rim  176  of the lens  110 . 
     A ridge  178  extends from the bottom of the lens  110  along the entire circumference of the lens  110 . The ridge  178  mates with a groove  180  defined in the casing  165  to aid in providing a watertight seal between the lens  110  and the casing  165 . An annular rubber cover  182  is attached over the interface between the lens  110  and the casing  165  to further enhance this watertight seal. 
     Referring to FIGS. 4A and 4B, the lens  110  is a planar compound lens including fresnel lenses  400 . The lens  110  is preferably formed of clear polycarbonate and includes a smooth exterior surface  405  and an interior surface  410  which provides the optical details of the fresnel lenses  400 . 
     The optical details of a fresnel lens  400  are illustrated in the expanded view provided by FIG.  4 B. Each fresnel lens includes an upper region  415  and a lower region  420 . The upper and lower regions each extend a distance  425 . Referring also to FIG. 5, a line  430  separates the upper region  415  and the lower region  420  and lies on the optical axis  435  of an LED  115 . Upper region  415  includes, in turn, two linear planar regions  440 ,  445 . The upper of these regions, region  440 , extends for a distance  450 , while the lower region  445  extends for a distance  455 . Region  440  forms, for example, a 64.75 degree angle  460  with the vertical axis, while region  445  forms, for example, a 78.75 degree angle  465  with the vertical axis. These angles are selected to refract upward headed light downward below the horizontal axis. Additionally, the lower region  420  is at an angle of, for example, 85.75 degrees with the vertical axis in order to provide a slight downward modification to the direction of light propagating through it. 
     Referring now to FIGS. 7,  9 ,  10 , the individual fresnel lenses  400  making up each of lenses  710  and  910  are divided into three roughly vertical bands  720 ,  725 ,  730  or  920 ,  925 ,  930 . These bands are defined by dividing lines  735 ,  740  or  935 ,  940 . Each fresnel lens  400  of each band has an orientation determined by its band membership. The orientation of a fresnel lens  400  can be described by an angle lying in the plane formed by the optical axis  435  of an LED  115  and the horizontal axis of the signal module perpendicular to the LED&#39;s optical axis  435 . The fresnel lenses of the center bands  725 ,  925  are aligned parallel to the x-y plane and are perpendicular to the optical axis of their LEDs. The fresnel lenses of outer left bands  720 ,  920  are at an angle  1010  of, for example, eight degrees so as to be slanted rightward toward the center axis of the signal module. In a like manner, the fresnel lenses of outer right bands  730 ,  930  are at an angle  1010  of, for example, eight degrees and are slanted leftward toward the center axis of the signal module. The angling of the outer band fresnels is designed to concentrate a greater measure of emitted light at the right and left peripheries of the signal. FIG. 10, in particular, is a detail of view  10 — 10  of FIG. 7 illustrating from a top view the orientation of a row of fresnel lenses as determined by their row, and also their effect upon the direction of light propagation. 
     Two implementations of the signal modules are an eight inch diameter implementation and a twelve inch diameter implementation. The reflector assemblies for these implementations are illustrated, respectively, in FIGS. 6 and 8. The eight-inch reflector assembly  630  has an array of 72 reflectors  135  which are distributed in symmetrical and generally uniform fashion, while the twelve-inch reflector assembly  830  has a symmetrical and generally uniform array of 144 reflectors  135 . 
     Referring to FIGS. 7 and 9, the compound lens  710  (FIG. 7) for the eight-inch module and the compound lens  910  (FIG. 9) for the twelve-inch module are constructed to provide each LED  115  with a fresnel lens  400  centered upon its optical axis  435 . Due to the optical characteristics of the fresnel lenses, the module lenses  710 ,  910  have a top and a bottom and must be mounted accordingly for proper operation. In this regard, each of the lenses  710 ,  910  includes a mounting indicia  715 ,  915  identifying the top of the lens and which match similar mounting indicia  640 ,  840  found at the top of reflector assemblies  630 ,  830 . 
     Other embodiments are within the scope of the following claims. For example, the signal light module may be implemented as a pedestrian walk/don&#39;t walk signal, a turn arrow signal, or a railroad crossing signal.