Abstract:
A light emitting diode signal with reduced susceptibility to the “sun phantom” effect. A single printed circuit board populated with both the power supply circuitry and the light emitting diodes is located at an increased distance from the front cover which is angled to direct extraneous light away from the viewers position. A snap together housing reduces overall cost and assembly time. Light from the light emitting diodes distributed across the single printed circuit board to project an overlapping light pattern is collimated by a multiple collimating zone optical element which creates a uniform display aspect without discernable individual points of light.

Description:
This application is a continuation of U.S. application Ser. No. 09/756,670 filed Jan. 10, 2001, now U.S. Pat. No. 6,509,840. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to signals, in particular, Light Emitting Diode (LED) Signals. More specifically, the present invention relates to an LED traffic signal that is less susceptible to the “sun phantom” effect, having an improved viewing aspect, as well as materials, manufacturing and installation cost advantages. 
     DESCRIPTION OF THE RELATED ART 
     LED traffic signals present numerous advantages over common incandescent lamp traffic signals. Use of LED&#39;s provides a power consumption savings and extremely long life in comparison to common incandescent light sources. The long life span creates improved reliability and sharply lowered maintenance costs. 
     As an individual LED is not bright enough to equal the light output of an incandescent lamp, multiple LED&#39;s are used. Previously, multiple LED&#39;s created a display aspect with multiple individual points of light readily discernible by the viewer. A non-uniform display aspect is commercially undesirable for traffic signals. One method of preventing discernable individual light points has been to use a full array of LED&#39;s. However this is not commercially competitive as each additional LED is a significant percentage of the signals total cost. Each generation of LED&#39;s is becoming brighter and brighter requiring fewer and fewer LEDs to equal the light output of an incandescent lamp but at the same time increasing the likelihood that the individual point sources and/or shadows between each LED are then detectable by the viewer. 
     Due to the large installed base, worldwide, of incandescent traffic signal systems, most LED traffic signals are designed to be retrofitted into existing traffic signal systems originally designed for incandescent lamps. To allow an easy retrofit to an LED light source, without requiring large changes to existing intersection alternating current power distribution and logic circuits, signal assemblies incorporate a power supply to drive LED&#39;s at a lower, controlled, direct current power level. In the past, this has resulted in an LED traffic signal assembly with a separate power supply built on a Printed Circuit Board (PCB) and a separate LED matrix PCB connected via wiring between the two PCB&#39;s as well as spliced into the original incandescent power wiring. Integration of LEDs onto a single PCB including the power supply results in a smaller PCB with corresponding manufacturing and cost of materials benefits. 
     Cost of materials and assembly time contribute to total cost and therefore to commercial success. Previous LED traffic signals used a large number of total components, each individual component adding material cost, assembly cost and introducing a potential quality control, moisture, and/or vibration failure opportunity. 
     Traffic signals are susceptible to “sun phantom” phenomena. When a light source, for example the sun, shines upon the face of a traffic signal, a bright spot, or worse, internal reflection from within the signal, may make it appear to a viewer that the signal is energized when, in fact, it is not, leading to an increased chance for accidents. 
     Previous incandescent signals have attempted to prevent the “sun phantom” phenomena by using a visor, internal or external baffles and/or a flat outer face angled towards the ground. Visor&#39;s and external baffles limit the viewing angle of the signal. Internal baffles add cost to the signal by introducing an element that has no other purpose. Flat outer faces are not allowed, according to some traffic signal specifications which require a spherical front element. 
     Previous LED signal lamps are especially susceptible to “sun phantom” phenomena because the rear surface of each LED is highly reflective. Previous LED signal designs located the LED&#39;s on or close to the outer surface where the rear surface of each LED could easily be reached by stray light, creating an increased opportunity for “sun phantom” reflections. 
     Therefore, the present invention has the following objectives: 
     1. An LED signal which minimizes the problem of “sun phantom” erroneous signal aspects. 
     2. An LED signal which presents a uniform brightness display aspect equal to or better than a common incandescent lamp traffic signal. 
     3. An LED signal that has materials and manufacturing assembly cost advantages. 
     4. An LED signal comprised of a single printed circuit board carrying both the LED&#39;s and the power supply components. 
     5. An LED signal retro-fitable into existing incandescent traffic signals, without requiring removal of the existing reflector assembly. 
     6. An LED signal capable of easy upgrade to higher output LEDs without requiring recalculation of the optical elements. 
     7. An LED signal with a display aspect unaffected by changes in individual LED light output. 
     8. An LED signal usable in multiple configurations, each specific to a given application, with a minimum of unique components being required. 
     Further objects will be realized by one skilled in the art, through review of the following description and appended claims. 
     SUMMARY OF THE INVENTION 
     The above objects and other advantages are achieved with the present invention. Placement of the LEDs, to create an overlapping light emission pattern at an increased distance from a Multiple Collimating Zone Element (MCZE) creates a uniform display aspect for the signal, without individual points of light. The increased distance also allows placement of power supply components and circuitry on a single PCB with the LEDs, spaced so as to prevent interference with the LED light. The “sun phantom” phenomena is prevented by a large radius spherical outer distribution cover, angled to reflect stray light away from the viewer, towards the ground. A complex inner surface on the distribution cover creates a shaped light distribution, focused upon the viewer, while at the same time further directing stray light reflections, again, towards the ground. Materials, assembly and installation cost efficiencies are realized by a novel snap together housing design which adds to an overall reduction in total number of components. The signal fits into existing standard incandescent traffic signals upon removal only of the incandescent bulb and original outer lens. Electrical connection is made by merely screwing a socket mating connector into the existing incandescent socket. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded view showing the major components of the 12″ linear MCZE embodiment of the invention. 
     FIG. 2 is an exploded view showing the major components of the 12″ circular MCZE embodiment of the invention. 
     FIG. 3 is a cross section of a circular embodiment of the MCZE showing LED light ray pattern distribution to the collimating zones. 
     FIG. 4 is a diagram showing light distribution and intensity for circular, horizontal and vertical embodiments of the MCZE. 
     FIG. 5 is a diagram demonstrating the “sun phantom” effect. 
     FIG. 6 is a cut-away side view of the 12″ embodiment of the invention (electrical components omitted for clarity). 
     FIG. 7 is a cut-away side view of the 12″ embodiment of the invention (electrical and interior components omitted for clarity), showing a ray diagram between the LEDs and the distribution cover and an example of the distribution covers optical effect. 
     FIG. 8 shows a cut-away view of an 8″ embodiment of the invention (power supply components omitted for clarity). 
     FIG. 9 is a close-up view of the o-ring sealing means and connection tab into tab socket connection means. 
     FIG. 10 is a three dimensional view of one-half of the back side of the distribution cover, detailing the compound optical correction surfaces. 
     FIG. 11 is a close-up three dimensional view of the optical correction surfaces of FIG.  10 . 
     FIG. 12 is a three dimensional view of another embodiment of the back side of the distribution cover, detailing the optical correction surfaces. 
     FIG. 13 is a view of a typical traffic signal housing, showing retrofitting of the present invention, replacing the original outer lens and incandescent lamp. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIG. 1, the main components of a 12″ traffic signal embodiment of the invention are visible. A housing  10  holds the components of the traffic signal. The housing  10  may be formed from, for example, polycarbonite material. Polycarbonite material having excellent strength and impact resistance characteristics. Formed into the base of the housing  10  are metal power terminals  12 . The metal power terminals  12  have exposed threaded posts on the internal side upon which a power connector spacer may be attached. The PCB  28  is attached to the power connector  14  with screws. The PCB  28  has mounted upon it a pattern of LEDs  26 . The LEDs  26  are arranged in horizontal rows. Between the rows are arranged the power supply components  24 . The power supply components  24  are arranged in a way that minimizes the interference with the light emitted from the LEDs  26 . The PCB  28  fits into the housing  10  via mounting posts  20  and is fixed in place with screws. To allow as large a PCB  28  as possible, thereby allowing a larger distribution of LEDs  26 , the PCB  28  is angled within the housing  10 . The mounting posts  20  orient the PCB  28 , precisely aligning the LEDs  26  of the PCB  28  with respect to the MCZE  30  into parallel planes. The MCZE  30  is oriented with respect to the housing  10  by placement upon the top surface of the housing  10  upon which it is retained by mounting posts on the housing  10  and distribution cover  32 . 
     The MCZE  30  may also be formed in, for example, a circular, or horizontal/vertical linear configuration. An embodiment with a circular MCZE  30  is shown in FIG.  2 . Here, the PCB  28  is powered via a power connector cable  18  which connects to a power connector board  14 , mounted on the metal power terminals  12  using nuts  16 . 
     As shown in FIG. 4, the different MCZE configurations (circular, vertical and horizontal) result in different light distribution patterns with corresponding spatial intensities of the collimated light exiting the MCZE. 
     Depending on the application, a different MCZE configuration and matching PCB layout may be selected. For example, a railroad application may use a vertical linear MCZE as the required horizontal viewing aspect is very narrow (generally the train track width), while the wide vertical aspect allows viewing of the signal from a wide vertical range, corresponding to viewing locations near and far from the signal at either track or train cab level. Similarly, an automobile traffic signal may be designed with a horizontal linear MCZE to have a wide spread horizontally, across many lanes of traffic. Final tuning of the light distribution is made by the distribution cover  32 . Ray tracing computer software allows calculation of very specific optical solutions for both the MCZE  30  and distribution cover  32 . 
     Materials reduction cost savings and increased assembly efficiencies are realized by the snap together housing  10  and distribution cover  32 . 
     As shown in FIG. 6, the distribution cover  32  snap fits into the housing  10 . A detailed, close-up view of the connection and sealing means, discussed below, is shown in FIG.  9 . Connection tabs  34 , arranged around the periphery of distribution cover  32 , fit into tab sockets  36 . Tab socket keys  38  located proximate the tab sockets  36  lock the connection tabs  34  in place upon insertion. The mating point between the tab socket key  38  and a corresponding hole in the connection tab  34  is arranged and configured to retain the distribution cover  32  at the location where the DC foot  42  bottoms against the housing  10 . One connection tab  34  and corresponding tab socket  36  are slightly wider than the others, thereby allowing assembly of the distribution cover  32  and housing  10  in only a single, proper, orientation. 
     A dust and water resistant seal is provided by o-ring  40 . The o-ring  40 , preferably made of EDAM material, is sized to elastically fit upon housing shoulder  44 . Distribution cover  32  has a primary radius  48  which allows the distribution cover  32  and housing  10  to be initially loosely fitted together, aligned by the connection tabs  34  fitting into tab sockets  36 . A final snap fit bottoms DC foot  42  against the housing  10 , engages the tab socket keys  38  to the corresponding holes in connection tabs  34  and seats o-ring  40  between housing shoulder  44  and cover shoulder  46 . In addition to providing the closure seal between the distribution cover  32  and housing  10 , the o-ring  40  provides a shock dissipation function for impacts upon the distribution cover during use. 
     Power may be supplied to the traffic signal via main power wires  49 . The main power wires  49 , having the ends stripped to expose the bare conductor, fit into holes in the outside surface of the power terminals  12 . The fit of the main power wires  49  into the power terminals  12  is loose. Electrical contact between the main power wires  49  and power terminals  12  is insured by the use of main power connector covers  45 . With the main power wires  49  inserted into the power terminals  12  the main power connector covers  45  are friction fit into the holes thereby retaining the main power wires  49  in electrical contact with power terminals  12 . The main power connector covers  45  have a cover extending along the main power wires  49  in the down direction, thereby shedding any moisture which may collect or be moving across the back of the housing  10 . The main power wires, as shown in FIG. 1, may connect to a standard incandescent lamp socket using an incandescent lamp socket plug  50 . 
     As shown by FIG. 3, the calculation of the pattern of the MCZE  30 , preferably made of acrylic material, with respect to the PCB  28  and the location of the LEDs  26  thereon is very precise. Taking into account the constraints of the size of the housing  10 , allowing it to fit within existing signal openings, the distance between the PCB  28  and the MCZE  30  is made as large as possible. Then, taking into account the angle of light emitted from the LEDs  26  a pattern of concentric circles or linear rows is formed on the PCB  28  to cover the surface of the MCZE  30  fully with LED light. The MCZE  30  has multiple circular or linear collimating zones arranged matching the concentric circles or linear rows of LEDs  26  on the PCB  28 . Each circular or linear collimating zone collimates the light emanating from its respective LED  26  ring or linear rows. As shown in FIG. 7, the LED light patterns slightly overlap within and between the rings or rows thus preventing the appearance of shadows, lines, or rings. Due to the overlap, individual LED  26  failure, or variation in LED  26  output between adjacent LEDs  26  will not be discernable by the viewer. At the outer edge of the MCZE  30 , fringe elements collect spurious light from within the housing and collimate it in a forward direction. The end result of the combination of the PCB  28  having LEDs  26  and matching patterned collimating elements of the MCZE  30  is to produce a full pattern of collimated light emitted from the MCZE  30  without gaps discernable to the viewer. The collimated light from the MCZE  30  passes next to the distribution cover  32 . The distribution cover  32  has a further pattern on its inside surface, shown in FIGS. 10,  11  and in a second embodiment, 12, which directs the collimated light into a final distribution pattern optimized for viewing at the normal design distance from the front of the signal. 
     The “sun phantom” effect is minimized in the present invention by the use of a large radius (more than 24″ radius for the 12″ embodiment and more than 18″ radius for the 8″ embodiment) outer surface of the distribution cover  32 . The large radius also simplifies the optical solution for the pattern on the back of the distribution cover. The outer surface of the distribution cover  32  is aligned at an angle inclined towards the ground. As shown by FIG. 5, this has the effect as compared to a conventional forward facing small radius spherical lens traffic signal of reflecting any sun light or other light source towards the ground rather than back towards the viewing position intended for the signal. A problem of LED signals in the past has been that external light sources reflecting into the signal encountering the LEDs which have a highly reflective back surface which could create a noticeable “sun phantom” effect. In the present invention the increased distance between the LEDs  26  and the outer surface of the distribution cover  32  minimizes the chance for internal reflection resulting in a “sun phantom” effect. Further the back face of distribution cover  32  is designed to again direct any external light source to the ground rather than back to the intended viewing position of the traffic signal. 
     As shown in FIG. 13, the present invention may be easily retrofitted into an existing traffic signal having an incandescent lamp, optical elements and an incandescent light source reflector  52 , upon removal of the original outer lens and incandescent lamp. The housing outer rim  47  may be designed to have the same thickness as the lens it replaces. Power connection of the retrofitted light may be performed, without requiring an electrician, by simply screwing the incandescent lamp socket plug  50  into the original incandescent lamp socket  54 . 
     In another embodiment, shown in FIG. 8, the invention is adapted to fit in an existing 8″ incandescent traffic signal upon removal only of the incandescent bulb and outer lenses. As space permits, the PCB  28  is not angled and therefore direct connection to power terminals  12  can be made without use of a separate power connector board  14  and power connector cable  18  or power connector spacer  13 . The MCZE  30  and inner surface of the distribution cover  32  are optimized for the different LED  26  layout and angles of the PCB  28  and MCZE  30  with respect to the distribution cover  32 . 
     The above invention is optimized for presently available cost effective LED&#39;s. As higher output, cost effective LED&#39;s become available, fewer LED&#39;s will be required to obtain the same light output. Due to the overlapping output of the present LEDs, when higher output LEDs become available, modification of only the LED spacing on the PCB is required. 
     If output of the LEDs increases beyond the point where placement of fewer LEDs in the concentric rings or linear rows still results in overlap, then only the MCZE need be recalculated. The distribution cover is independent of the light source as it receives an even distribution of collimated light from the MCZE for final distribution to the viewer. 
     A family of signal devices may be created from the present invention using common components. Different distribution covers, creating different distribution patterns may be snap fitted onto a common housing with standardized PCB and MCZE. Information and/or directional signals may be created by masking portions of the distribution cover into, for example, turn signal arrows. 
     A variation of the housing, using otherwise similar components may be used to create stand alone signals or even general illumination light sources useful, for example, when it is foreseen that the light source will be located where maintenance will be difficult and an extreme service interval is desired. 
     Further, although particular components and materials are specifically identified herein, one skilled in the art may readily substitute components and/or materials of similar function without departing from the invention as defined in the appended claims. 
     The present invention is entitled to a range of equivalents, and is to be limited only by the following claims.