Abstract:
An traffic light capable of utilizing both natural sunlight and artificial light for illuminating selective traffic signals. Natural light is directed to a natural light router or switch and to a color switch for providing a red, amber or yellow, and a green light for each bank of traffic light signals. A controller is coupled to the natural light router and light emitting diodes for controlling the mode of operation for operating the traffic light with either electrically powered light emitting diodes or with natural light collected by the natural light collector. A sensor detects the adequacy of the natural light, and when insufficient, causes the controller to power an LED signal light. The natural light may either be amplitude modulated or time modulated so as to provide a desired high illumination output to the desired signal light. The power consumption is greatly reduced, as well as providing a more reliable traffic light substantially independent of power line interruptions or fluctuations. Any information, not only traffic signals, may be displayed.

Description:
RELATED APPLICATION 
     This application claims priority on U.S. Provisional Patent Application No. 60/531,773, filed Dec. 22, 2003, which is herein incorporated by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates in general to a self contained traffic signal or light, and more particularly to a traffic light using natural light in combination with light emitting diodes to illuminate the signal lights. 
     BACKGROUND OF THE INVENTION 
     Traffic lights are routinely used to control traffic along roadways and intersections. These traffic lights are often required to be powered by line voltage supplied by overhead wires. These traffic lights, while individually not requiring substantial amounts of power to illuminate the individual traffic signals, in total relatively large amounts of electrical power is used in the illumination of the traffic lights. Recently, there has been much development in traffic lights utilizing light emitting diodes rather than other forms of incandescent illumination. While the light emitting diodes are relatively efficient and have a relatively long life, during daylight hours it is often difficult for a light emitting diode to generate sufficient illumination to be clearly visible. There have been many efforts to aid in making more visible the illumination from a traffic signal utilizing light emitting diodes. 
     One such light emitting diode signal light is disclosed in U.S. Pat. No. 6,599,002 issuing to Hsieh et al on Jul. 29, 2003 and entitled “LED Signal Light”. Therein disclosed is a light emitting diode signal light using a plurality of lens cells. The plurality of lens cells is used to redistribute the light in vertical and horizontal directions and adjust orientation of light to the specified illumination areas. 
     Another effort to enhance light emitting diode illumination, which may be used in a traffic light, is disclosed in U.S. Pat. No. 5,174,649 issuing to Alston on Dec. 29, 1992 and entitled “LED Lamp Including Refractive Lens Element”. Therein disclosed are a plurality of facets that allow a large area on the lamp to appear to viewers to be uniformly illuminated. 
     In addition to the problems associated with the use of LED lights, there is also a problem of power interruptions or reduced line voltage which reduces the light emitting diode output. One solution to reduced light emitting diode illumination caused by interruptions in line voltage is disclosed in U.S. Pat. No. 5,457,450 issuing to Deese et al on Oct. 10, 1995 and entitled “LED Traffic Signal Light With Automatic Low-Line Voltage Compensating Circuit”. Therein disclosed is a traffic light or signal using LED lights with a voltage compensating circuit that disables or re-engages a first and then a second set of LEDs in a traffic light as the input power voltage drops below a first and then a second threshold voltage. This results in the remaining LEDs being driven by an increased current, resulting in a greater light intensity. 
     While these prior patents disclose enhancements to LED traffic lights, there is a continuing need to improve LED traffic lights so as to be more visible and to conserve power. Additionally, there is a strong safety concern to develop a signal light that can function even during interruptions in line voltage or power. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a traffic light that is self contained and utilizes both natural light and artificial light for efficiently illuminating traffic signals that have the capability of operating with little electrical power and independently during blackouts or when external power is not available. Collected natural light is time modulated and routed to a plurality of color separator switches, one color separator switch is used for each bank of signal lights on each side of the traffic light. The color separator switch divides the time modulated natural light into time modulated separate colors of red, amber or yellow, and green, which are directed to the respective signal lights with fiber optics. A sensor detects when sufficient natural light is not available and causes independent light emitting diode lights to be used in lighting the traffic signals. Photovoltaic cells are used to charge a re-chargeable battery. The battery is used to provide power to the electronic systems for controlling the natural lighting portion of the traffic light and for providing power to the light emitting diodes when natural light is not available. 
     It is an object of the present invention to provide a traffic light that is efficient and requires substantially less power than prior traffic lights. 
     It is another object of the present invention to provide a traffic light that can operate during power interruptions or outages. 
     It is an advantage of the present invention that it is substantially self-contained. 
     It is another advantage of the present invention that it requires less maintenance. 
     It is a feature of the present invention that the natural light is time modulated so that substantially all of the illumination intensity of the natural light is utilized by each traffic signal light at a different time providing the brightest possible perceived illumination. 
     It is another feature of the present invention that light emitting diodes or LEDs are used. 
     These and other objects, advantages, and features will become more readily apparent in view of the following more detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  schematically illustrates a traffic light according to the present invention. 
         FIG. 2A  schematically illustrates the optical path of the collected natural light of an embodiment of the present invention. 
         FIG. 2B  graphically illustrates the amplitude of the colored light as a function of time. 
         FIG. 2C  schematically illustrates the optical path of the collected natural light of another embodiment of the present invention. 
         FIG. 3  schematically illustrates an electronic controller used for controlling the electronic components of the traffic signal of the present invention. 
         FIG. 4  is a side elevational view schematically illustrating a hybrid illuminating unit comprising a light emitting diode and fiber optic light bundle used in the present invention. 
         FIG. 5  is a front elevational view schematically illustrating the hybrid illuminating unit illustrated in  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  schematically illustrates a traffic light  10  according to an embodiment of the present invention. The traffic light  10  comprises a natural light collector  12  for collecting natural light. The natural light collector  12  may be any type of lens for collecting, concentrating, and directing natural light. For example, the natural light collector may be a Fresnel lens dome having a diameter of approximately nine inches or 23 cm. The natural light collector may be sized to acquire sufficient light on an overcast day to provide sufficient energy to illuminate at least four traffic signals. The collected light is directed to any light conductor, such as a fiber optic, to a natural light router and switch  14 . The natural light router and switch  14  redirects or routes the natural light to different banks of signal lights for directing traffic. Each bank of signal lights typically would have red, amber or yellow, and green signal lights for directing traffic. The wavelength of the red light is approximately 624 nm, the wavelength of the amber or yellow light is approximately 588 nm, and the wavelength of the green light is approximately 505 nm. The natural light router or switch  14  time modulates the natural light such that the full intensity of the collected natural light is directed for short periods of time to each of the different banks of signal lights. The natural light or white light is directed through fiber optics from the natural light router and switch  14  to a plurality of color separator switches  16 A and  16 B, each associated with a bank of signal lights. The color separator switch  16 A separates and further time modulates the three different colors, red, amber or yellow, and green, used to provide illumination for the traffic signal. The different colors for each of the traffic light signals are modulated so that the collected natural light is not split, preventing the amplitude or intensity from being reducing. The full intensity of the natural light that is collected is utilized to provide a bright traffic signal light, but for a relatively short duration. However, when the time modulation is such that the duration of the relatively bright intensity light traffic signal occurs sufficiently rapidly, an observer viewing the traffic signal cannot detect the flicker or modulation due to the natural retinal retention of the light receptors in the human eye. 
     The color separator switches  16 A and  16 B provide a different color to each of the different signal lights, such as the red lights  18 A and  18 B and the amber or yellow lights  20 A and  20 B and the green lights  22 A and  22 B. The color separator switches  16 A and  16 B may be any conventional color separator, such as an LCD color switch, prism, or dichroic mirror. The color separator switches  16 A and  16 B are coupled to a controller  24 . The controller  24  is also coupled to the natural light router and switch  14  which therethrough is coupled to a light sensor  30 . The controller  24  is used to properly sequence the time modulation of the natural or white light from the natural light router and switch  14  and for controlling the operation of the color separator switches  16 A and  16 B so that the natural or white light entering from the natural light router and switch  14  can be separated into the different colors red, amber or yellow, and green, as well as time modulating for directing the different colors to their respective signal lights for sequencing the required color signal. The rechargeable battery  26  provides power to the controller  24 . The controller  24  is also coupled directly to the different colored signal lights  18 A through  22 B for controlling light emitting diodes that provide the illumination for the signal lights  18 A– 22 B when natural light is not available or sufficient to provide the required intensity illumination to the signal lights  18 A,  20 A,  22 A, and  18 B,  20 B, and  22 B. The light sensor or detector  30  is used to determine when the natural light is insufficient, requiring the light emitting diodes or LEDs to be used. The controller  24  may also be connected through the battery  26  to an external power and traffic control  31 . The external power and traffic control  31  provides external power when required during extended overcast days or when there is insufficient natural light for long periods of time, in addition to providing any traffic control signals that may be used to coordinate different traffic lights from a central location. The battery  26  may be charged by photovoltaic cells  28 . 
       FIG. 2A  schematically illustrates in more detail the operation of an embodiment of the natural light collection and traffic signal illumination system. The natural light is collected by natural light collector  112 , which directs the natural light through fiber optics  113  to a natural light valve, switch, or router  114 . The different channels of the output of the natural light valve, switch, or router  114  are directed to color switches  116 A,  116 B,  116 C, and  116 D through fiber optics  131 A,  131 B,  131 C, and  131 D. Partially reflective mirrors  115 A,  115 B,  1115 C, and  115 D may be used to redirect the natural light. Prism beamsplitters may also be used, or any other known optical device. While only four color switches  116 A,  116 B,  116 C, and  116 D are illustrated, it should be readily apparent that additional color switches may be used, depending on the number of sets of traffic light signals used for a particular application. Typically, in a four-way intersection there are four sets or banks of traffic signal lights, one for each side of the traffic signal or for each road, as illustrated in  FIG. 2A . 
     The color switches  116 A,  116 B,  116 C, and  116 D divide the natural white light into three different colors, red, amber or yellow, and green. The color switches  116 A,  116 B,  116 C, and  116 D may be liquid crystal display or LCD color switches. The three different colors are separated or modulated in time so as to provide the different colors red, amber or yellow, and green at full intensity for only a relatively short time or duration. The time separated or modulated distinct colors are split or separated for each channel or bank by a dichroic beamsplitter  117 A,  117 B,  117 C, and  117 D and directed through fiber optics to each of the respective traffic signal lights. For example, the red light signals  118 A,  118 B,  118 C, and  118 D; the amber or yellow light signals  120 A,  120 B,  120 C, and  120 D; and the green light signals  122 A,  122 B,  122 C, and  122 D. A liquid crystal display or LCD switch  119 A R ,  119 A Y ,  119 A G ,  119 B R ,  119 B Y ,  119 B G ,  119 C R ,  119 C Y ,  119 C G ,  119 D R ,  119 D Y ,  119 D G  may also be utilized to control the on and off of the different red, amber or yellow, and green colored illumination for each bank of signal lights, respectively. 
       FIG. 2B  graphically illustrates the intensity or amplitude A of the three different colors, red, amber or yellow, and green as a function of time t. Each of the three different colors used for the signal light are modulated in time by each of the color switches  116 A,  116 B,  116 C, and  116 D for each respective channel. The graph in  FIG. 2B  represents the light after emerging from each of the respective color switches  116 A,  116 B,  116 C, and  116 D. 
     The embodiment illustrated in  FIGS. 2A and 2B  has the advantage of providing the red, amber or yellow, and green colored light to the respective light signal in each bank of signals. However the natural light received by the natural light collector  113  is divided in amplitude or intensity by the natural light router or switch  114  effectively reducing the available intensity of illumination for each bank of light signals. This may result in the illuminated signal in each bank to appear dimmer than desired. 
       FIG. 2C  schematically illustrates another embodiment of a natural light router or switch  214 . In this embodiment, the natural light router or switch  214  modulates the natural light in time rather than intensity or amplitude. The fiber optic  213  directs natural light from a collector to the natural light router or switch  214 . By way of example, the natural light router or switch  214  may be comprised of a plurality of movable mirrors  215 A,  215 B,  215 C, and  215 D. Mirrors  215 A,  215 B and  215 C are positioned initially so as to permit light to pass and strike angled mirror  215 D. Mirror  215 D directs substantially all of the natural light to a fiber optic  231 D. The directed natural light is represented by a light packet  238 D having a predetermined duration. The mirrors  215 A,  215 B,  215 C and  215 D selectively and sequentially at predetermined times redirect the natural illumination received by the fiber optic  213  through the fiber optics  231 A,  231 B,  231 C and  231 D. Accordingly, sequential light packets  238 A,  238 B,  238 C, and  238 D are formed with a combined period P. The light packet sequence and period P are repeated. While a plurality of movable mirrors have been illustrated for redirecting the natural light into a plurality of channels, any other known optical means for redirecting light may be used. 
     In this embodiment, the light amplitude or intensity is not split and the entire light amplitude or intensity is used for each light packet  238 A–D. However, each light packet  238 A–D has a duration of only one-quarter of the period P. The duration of each light packet may be selected so as to take advantage of a characteristic of the human eye. Generally, the human eye cannot detect flashing above about twenty Hertz. The human eye generally perceives any flashing above about twenty Hertz as a continuous illumination. Accordingly, the incoming light in this embodiment is sequentially and equally split or divided into four channels. Each of the four channels has a light packet that carries one hundred percent of the light intensity. In this way, all four channels have one hundred percent of the light intensity available, but for only one-quarter of the time. By properly selecting the duration of the light packet or its frequency, the human eye will detect a continuous illumination. If a frequency of forty Hertz is selected, each channel or light packet will result in fifty milliseconds of light, which is repeated at forty Hertz. The one hundred percent intensity at a duration of fifty milliseconds at a frequency of forty Hertz should present itself as a continuous light intensity to the human eye. Therefore, the light signal perceived by the human viewer should appear relatively bright and be steady or continuous. It is possible to optimize this frequency to establish the highest light retention to be produced. 
       FIG. 3  schematically illustrates a control circuit used with the signal light that may be utilized to switch between or select operation in a light emitting diode mode or a natural light mode. The control selection circuitry  324  may consist of a light sensor  330  coupled to a mode control circuit  324 A. The mode control circuit  324 A will pass control to an LED control  324 B or a natural light control  324 C, depending upon the output of the light sensor  330 . When there is insufficient natural light or illumination, the light sensor  330  provides a signal to the mode control circuit  324 A. The mode control circuit  324 A then directs the LED controller  324 B to use the LEDs to illuminate the light signals in the traffic light. However, when the light sensor  330  detects sufficient natural light to illuminate the light signals in the traffic light, the light sensor  330  provides a signal to the mode control circuit  324 A wherein the mode control circuit  324 A directs the LED control  324 B not to provide signal illumination to the traffic signal LEDs and directs the natural light control  324 C to provide the natural light illumination to the light signals of the traffic light. The natural light control  324 C controls the color switches  316 A,  316 B,  316 C, and  316 D on each of the four sides or banks of light signals of the traffic light. The natural light control  324 C also controls the LCD switches  319 A R ,  319 A Y ,  319 A G ,  319 B R ,  319 B Y ,  319 B G ,  319 C R ,  319 C Y , and  319 C G ,  319 D R ,  319 D Y ,  319 D G . The natural light control therefore controls the release of natural light to illuminate selectively each of the three different colors on the four different sides of a traffic light. The control selection circuit  324  may be utilized with the amplitude controlled natural light router or switch  114  illustrated in  FIG. 2A  or the time controlled or modulated natural light router or switch  214  illustrated in  FIG. 2C . 
     The control selection circuit  324  may be used to selectively control the use of natural light when it is sufficient or when it is insufficient, the light emitting diodes may be used to illuminate the traffic signals in the traffic light. The control selection circuit  324  may easily be made form conventional circuits, for example field programmable gate arrays, FPGA, or application specific integrated circuits, ASIC. The software to operate the traffic light may be application specific and interface with conventional traffic light control software. 
       FIGS. 4 and 5  illustrate a single hybrid light emitting diode and natural light illumination cell or unit  118 A. It will be appreciated that a plurality or an array of these hybrid illumination units  118 A may be utilized for any light signal and for each color signal. The hybrid illumination unit or cell  118 A comprises a fiber optic bundle  132  that carries natural light illumination received by collector  112 , illustrated in  FIG. 2A . A light emitting diode  134  is coupled to a light emitting diode control, such as that illustrated in  FIG. 3  as LED control  324 B, so as to be selectively illuminated when needed. The light emitting diode  134  has a hole or opening therein that permits the fiber optic bundle  132  to pass therethrough. At the end of the fiber optic bundle  132 , adjacent the emitting surface of a light emitting diode  134 , is placed a lenticular lens  140 . Adjacent the lenticular lens  140  and the light emitting diode  134  is a lens  136 . The lenticular lens  140  spreads the light from the fiber optic bundle  132  to fill the lens  136 . An array of the hybrid illumination units  118 A are utilized for each of the light signals of the traffic light. Therefore, each of the hybrid illumination units  118 A may be selectively illuminated by either the natural light within the fiber optic bundle  132  or by selectively energizing the LED  134  in order to illuminate the desired traffic signal of the traffic light. 
     While the preferred embodiment of the present invention is related to a traffic light having three colored lights, the term traffic light or signal may include other informational displays to control vehicles, pedestrians, or other things. For example, a traffic light may be defined as any informational display to control traffic, including pedestrian traffic such as a walk, don&#39;t walk display at a cross walk, train signals, traffic information displays, and any other illuminated display. 
     Additionally, while the preferred embodiment of the present invention has been described with respect to a traffic light, the present invention may by embodied in any informational display having a plurality of illuminated information signals forming words or symbols to convey any desired information. For example, rather than information related to traffic signals, the present invention may be used to display any information such as news, warnings, weather, advertising, or any other information wishing to be conveyed to an individual through an illuminated display. 
     While several different embodiments of the present invention have been illustrated and described, it will be obvious to those skilled in the art that various modifications may be made without departing from the spirit and scope of this invention.