Abstract:
A solid state light apparatus with a solar shielded heatsink ideally suited for traffic controls. The current state of the art solid state traffic signals utilize LED arrays encased in the existing plastic or metal traffic signal cases which were originally design for incandescent bulbs. Unlike LED&#39;s, incandescent bulbs are insensitive to high temperatures. As a result heat will build up on the LED die because of the limitations of the existing incandescent case design. The apparatus mounts the LED array directly to a louvered external heatsink in contact with the air outside of the traffic signal case facilitating the dissipation of heat generated from the LED die and from the sunlight shining on the case. For 25% of all signals (those facing west), during the late afternoon sunset the lensing system will focused the sunlight directly on the LED die raising the die temperature an additional 20 C. The louvered external heatsink dissipates this form of heat as well allowing the LED die to remain much cooler.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     Cross reference is made to commonly assigned co-pending patent application entitled “Solid State Light Apparatus” filed herewith, the teachings of which are incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention is generally related to light sources, and more particularly to traffic signal lights including those incorporating both incandescent and solid state light sources. 
     BACKGROUND OF THE INVENTION 
     Traffic signal lights have been around for years and are used to efficiently control traffic through intersections. While traffic signals have been around for years, improvements continue to be made in the areas of traffic signal light control algorithms, traffic volume detection, and emergency vehicle detection. 
     There continues to be a need to be able to predict when a traffic signal light source will fail. The safety issues of an unreliable traffic signal are obvious. The primary failure mechanism of an incandescent light source is an abrupt termination of the light output caused by filament breakage. The primary failure mechanism of a solid state light source is gradual decreasing of light output over time, and then ultimately, no light output. 
     The current state of the art for solid state light sources is as direct replacements for incandescent light sources. The life time of traditional solid state light sources is far longer than incandescent light sources, currently having a useful operational life of 10-100 times that of traditional incandescent light sources. This additional life time helps compensate for the additional cost associated with solid state light sources. 
     However, solid state light sources are still traditionally used in the same way as incandescent light sources, that is, continuing to operate the solid state light source until the light output is insufficient or non existent, and then replacing the light source. The light output is traditionally measured by a person with a light meter, measuring the light output from the solid state light source from a Department of Transportation (DOT) “bucket”. 
     Other problems with traditional traffic signal light sources is the intense heat generated by the light source. In particular, temperature greatly affects the life time of solid state light sources. If the temperature can be reduced, the operational life of the solid state light source may increase between 3 fold and 10 fold. Traditionally, solid state light sources today are designed as individual light emitting diodes (LEDs) individually mounted to a printed circuit board (PCB), and placed in a protective enclosure. This protective enclosure produces a large amount of heat and has severe heat dissipation problems, thereby reducing the life of the solid state light source dramatically. 
     In addition to temperature, oxidation also greatly effects the lifetime of solid state light sources. For instance, when oxygen is allowed to combine with aluminum on an aluminum gallium arsenide phosphorus (AlInGaP) LED, oxidation will occur and the light output is significantly reduced. 
     With specific regards to solid state light sources, typical solid state light sources comprised of LEDs are traditionally too bright early in their life, and yet not bright enough in their later stages of life. Traditional solid state light sources used in traffic control signals are traditionally over driven initially so that when the light reduces later, the light output is still at a proper level meeting DOT requirements. However, this overdrive significantly reduces the life of the LED device due to the increased, and unnecessary, drive power and associated heat of the device during the early term of use. Thus, not only is the cost for operating the signal increased, but more importantly, the overall life of the device is significantly reduced by overdriving the solid state light source during the initial term of operation. 
     Still another problem with traditional light sources for traffic signals is detection of the light output using the traditional hand held meter. Ambient light greatly affects the accurate detection of light output from the light source. Therefore, it has been difficult in the past to precisely set the light output to a level that meets DOT standards, but which light source is not over driven to the point of providing more light than necessary, which as previously mentioned, increases temperature and degrades the useful life of the solid state device. 
     Still another problem in prior art traffic signals is that signal visibility needs to be controlled so only specific lanes of traffic are able to see the traffic light. An example is when a left turn lane has a green light, and an adjacent lane is designated as a straight lane. It is necessary for traffic in the left turn lane to see the green light. The current visibility control mechanism is mechanical, typically implementing a set of baffles inserted into the light system to carefully point the light in the left lane in the correct direction. The mechanical direction system is not very controllable because it is controlled in only one dimension, typically either up or down, or, either right or left, but not both. Consequently, the light is undesirable often seen in the adjacent lane. There is arisen a need for a better method to control the visibility range of a traffic signal. 
     Traditionally, old technology is typically replaced with new technology by simply disposing of the old technology traffic devices. Since most cities don&#39;t have the budget to replace all traffic control devices when new ones come to market, they have traditionally taken the position of replacing only a portion of the cities devices at any given time, thereby increasing the inventory needed for the city. Larger cities end up inventorying between four and five different manufacture&#39;s traffic signals, some of which are not in production any longer. The added cost is not only for storage of inventoried items, but also the overhead of taking all different types of equipment to a repair site, or cataloging the different inventoried items at different locations. 
     With respect to alignment systems for traffic lights, traditionally alignment traffic control devices provide that one person points the generated light beam in the desired direction from a bucket while above the intersection, while another person stands in the traffic lanes to determine if the light is aligned properly. The person on the ground has to move over the entire field of view to check the light alignment. If the light is masked off (such as a turn arrow), there are more alignment iterations. There is desired a faster and more reliable method of aligning traffic signals. 
     Traffic lights also have a problem during darker conditions, i.e. at night or at dusk when the light is not well defined. This causes a problem if the light has to be masked off for any reason, whereby light may overlap to areas that should be off. This imprecise on/off boundary is called “ghosting”. There is a need to find an improved way to define the light/dark boundary of the traffic light to reduce ghosting. The ghosting is primarily caused by the angle the light hits on the “risers” on a Fresnel lens. A traffic light with a longer focal length reduces the angle, therefore decreasing the amount of ghosting. Therefore, devices with shorter focal lengths have increased ghosting. Another cause of ghosting is stray light from arrays of LED lights. Typical LED designs have a rather large intensity peek, that is, a less uniform beam of light being generated from the array. 
     SUMMARY OF THE INVENTION 
     The present invention achieves many technical advantages including an extended operating lifetime as an improved traffic control signal having a solar shielded external heatsink allowing ambient airflow to cool the heatsink and LEDs mounted thereto. The solar shielded external heatsink significantly reduces the LED die temperatures, especially when the signal faces west into a setting sun late in the afternoon. 
     The solid state light source has many other advantageous features including the ability to predict failure of the light source, hermetically sealing the array of LEDs, and controlling the light output over time to prevent overdrive of the LED array. Other features of the present invention include providing a constant output of light from a solid state light source by providing optical feedback of light and electronic filtering to accurately detect and discern generated light from ambient light. 
     Other advantages of the solid state light source include an electronically steerable light beam having the ability to steer light into two dimensions, insuring only the intended lane of traffic is able to visually perceive the beam of light. In addition, the solid state light source is modularly upgradeable to allow upgrades of existing components, and the adaption of new components to keep the traffic signal state of the art. An optical sight alignment mechanism is also provided with the light source allowing a technician at the light source to determine where a beam of light generated from the light array is directed, without requiring the assistance of an on ground technician. Yet another feature of the present invention is an opto-electronic ghosting control for a light source reducing ghosting of a generated beam of light. 
     The solid state light of the present invention includes several new features, and several improved features, providing a state of the art solid state light source that overcomes the limitations of prior art traffic sources, including those with conventional solid state light sources. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG.  1 A and FIG. 1B is a front perspective view and rear perspective view, respectively, of a solid state light apparatus according to a first preferred embodiment of the present invention including an optical alignment eye piece; 
     FIG.  2 A and FIG. 2B is a front perspective view and a rear perspective view, respectively, of a second preferred embodiment having a solar louvered external air cooled heatsink; 
     FIG. 3 is a side sectional view of the apparatus shown in FIG. 1 illustrating the electronic and optical assembly and lens system comprising an array of LEDs directly mounted to a heatsink, directing light through a diffuser and through a Fresnel lens; 
     FIG. 4 is a perspective view of the electronic and optical assembly comprising the LED array, lense holder, light diffuser, power supply, main motherboard and daughterboard; 
     FIG. 5 is a side view of the assembly of FIG. 4 illustrating the array of LEDs being directly mounted to the heatsink, below respective lenses and disposed beneath a light diffuser, the heatsink for terminally dissipating generated heat; 
     FIG. 6 is a top view of the electronics assembly of FIG. 4; 
     FIG. 7 is a side view of the electronics assembly of FIG. 4; 
     FIG. 8 is a top view of the lens holder adapted to hold lenses for the array of LEDs; 
     FIG. 9 is a sectional view taken alone lines  9 — 9  in FIG. 8 illustrating a shoulder and side wall adapted to securely receive a respective lens for a LED mounted thereunder; 
     FIG. 10 is a top view of the heatsink comprised of a thermally conductive material and adapted to securingly receive each LED, the LED holder of FIG. 8, as well as the other componentry; 
     FIG. 11 is a side view of the light diffuser depicting its radius of curvature; 
     FIG. 12 is a top view of the light diffuser of FIG. 11 illustrating the mounting flanges thereof; 
     FIG. 13 is a top view of a Fresnel lens as shown in FIG. 3; 
     FIG. 14 is a perspective view of the lid of the apparatus shown in FIG. 1; 
     FIG. 15 is a perspective view of the optical alignment system eye piece adapted to connect to the rear of the light unit shown in FIG. 1; 
     FIG. 16 is a schematic diagram of the control circuitry disposed on the daughterboard and incorporating various features of the invention including control logic, as well as light detectors for sensing ambient light and reflected generated light from the light diffuser used to determine and control the light output from the solid state light; 
     FIG. 17 is an algorithm depicting the sensing of ambient light and backscattered light to selectably provide a constant output of light; 
     FIG.  18 A and FIG. 18B are side sectional views of an alternative preferred embodiment including a heatsink with recesses, with the LED&#39;s wired in parallel and series, respectively; 
     FIG. 19 is an algorithm depicting generating information indicative of the light operation, function and prediction of when the said state apparatus will fail or provide output below acceptable light output; 
     FIGS. 20 and 21 illustrate operating characteristics of the LEDs as a function of PWM duty cycles and temperature as a function of generated output light; 
     FIG. 22 is a block diagram of a modular light apparatus having selectively interchangeable devices that are field replaceable; 
     FIG. 23 is a perspective view of a light guide having a light channel for each LED to direct the respective LED light to the diffuser; 
     FIG. 24 shows a top view of FIG. 23 of the light guide for use with the diffuser; and 
     FIG. 25 shows a side sectional view taken along line  24 — 24  in FIG. 3 illustrating a separate light guide cavity for each LED extending to the light diffuser. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring now to FIG. 1A, there is illustrated generally at  10  a front perspective view of a solid state lamp apparatus according to a first preferred embodiment of the present invention. Light apparatus  10  is seen to comprise a trapezoidal shaped housing  12 , preferably comprised of plastic formed by a plastic molding injection techniques, and having adapted to the front thereof a pivoting lid  14 . Lid  14  is seen to have a window  16 , as will be discussed shortly, permitting light generated from within housing  12  to be emitted as a light beam therethrough. Lid  14  is selectively and securable attached to housing  12  via a hinge assemble  17  and secured via latch  18  which is juxtaposed with respect to a housing latch  19 , as shown. 
     Referring now to FIG.  1 B and FIG. 2B, there is illustrated a second preferred embodiment of the present invention at  32  similar to apparatus  10 , whereby a housing  33  includes a solar louver  34  as shown in FIG.  2 B. The solar louver  34  is secured to housing  33  and disposed over a external heatsink  20  which shields the external heatsink  20  from solar radiation while permitting outside airflow across the heatsink  20  and under the shield  34 , thereby significantly improving cooling efficiency as will be discussed more shortly. 
     Referring to FIG. 2A, there is shown light apparatus  10  of FIG. 1A having a rear removable back member  20  comprised of thermally conductive material and forming a heatsink for radiating heat generated by the internal solid state light source, to be discussed shortly. Heatsink  20  is seen to have secured thereto a pair hinges  22  which are rotatably coupled to respective hinge members  23  which are securely attached and integral to the bottom of the housing  12 , as shown. Heatsink  20  is further seen to include a pair of opposing upper latches  24  selectively securable to respective opposing latches  25  forming an integral portion of and secured to housing  12 . By selectively disconnecting latches  24  from respective latches  25 , the entire rear heatsink  20  may be pivoted about members  23  to access the internal portion of housing  12 , as well as the light assembly secured to the front surface of heatsink  20 , as will be discussed shortly in regards to FIG.  3 . 
     Still referring to FIG. 2A, light apparatus  10  is further seen to include a rear eye piece  26  including a U-shaped bracket extending about heatsink  20  and secured to housing  12  by slidably locking into a pair of respective locking members  29  securely affixed to respective sidewalls of housing  12 . Eye piece  26  is also seen to have a cylindrical optical sight member  28  formed at a central portion of, and extending rearward from, housing  12  to permit a user to optically view through apparatus  10  via optically aligned window  16  to determine the direction a light beam, and each LED, is directed, as will be described in more detail with reference to FIG.  14  and FIG.  15 . Also shown is housing  12  having an upper opening  30  with a serrated collar centrally located within the top portion of housing  12 , and opposing opening  30  at the lower end thereof, as shown in FIG.  3 . Openings  30  facilitate securing apparatus  10  to a pair of vertical posts allowing rotation laterally thereabout. 
     Referring now to FIG. 3, there is shown a detailed cross sectional view taken along line  3 — 3  in FIG. 1, illustrating a solid state light assembly  40  secured to rear heatsink  20  in such an arrangement as to facilitate the transfer of heat generated by light assembly  40  to heatsink  20  for the dissipation of heat to the ambient via heatsink  20 . 
     Solid state light assembly  40  is seen to comprise an array of light emitting diodes (LEDs)  42  aligned in a matrix, preferably comprising an 8×8 array of LEDs each capable of generating a light output of 1-3 lumens. However, limitation to the number of LEDs or the light output of each is not to be inferred. Each LED  42  is directly bonded to heatsink  20  within a respective light reflector comprising a recess defined therein. Each LED  42  is hermetically sealed by a glass material sealingly diffused at a low temperature over the LED die  42  and the wire bond thereto, such as 8000 Angstroms of, SiO 2  or Si 3 N 4  material diffused using a semiconductor process. The technical advantages of this glass to metal hermetic seal over plastic/epoxy seals is significantly a longer LED life due to protecting the LED die from oxygen, humidity and other contaminants. If desired, for more light output, multiple LED dies  42  can be disposed in one reflector recess. Each LED  42  is directly secured to, and in thermal contact arrangement with, heatsink  20 , whereby each LED is able to thermally dissipate heat via the bottom surface of the LED. Interfaced between the planar rear surface of each LED  42  is a thin layer of heat conductive material  46 , such as a thin layer of epoxy or other suitable heat conductive material insuring that the entire rear surface of each LED  42  is in good thermal contact with rear heatsink  20  to efficiently thermally dissipate the heat generated by the LEDs. Each LED connected electrically in parallel has its cathode electrically coupled to the heatsink  20 , and its Anode coupled to drive circuitry disposed on daughterboard  60 . Alternatively, if each LED is electrically connected in series, the heatsink  20  preferably is comprised of an electrically non-conductive material such as ceramic. 
     Further shown in FIG. 3 is a main circuit board  48  secured to the front surface of heatsink  20 , and having a central opening for allowing LED to pass generated light therethrough. LED holder  44  mates to the main circuit board  48  above and around the LED&#39;s  42 , and supports a lens  86  above each LED. Also shown is a light diffuser  50  secured above the LEDs  42  by a plurality of standoffs  52 , and having a rear curved surface  54  spaced from and disposed above the LED solid state light source  40 , as shown. Each lens  86  (FIG. 9) is adapted to ensure each LED  42  generates light which impinges the rear surface  54  having the same surface area. Specifically, the lenses  86  at the center of the LED array have smaller radius of curvature than the lenses  86  covering the peripheral LEDs  42 . The diffusing lenses  46  ensure each LED illuminates the same surface area of light diffuser  50 , thereby providing a homogeneous (uniform) light beam of constant intensity. 
     A daughter circuit board  60  is secured to one end of heatsink  20  and main circuit board  48  by a plurality of standoffs  62 , as shown. At the other end thereof is a power supply  70  secured to the main circuit board  48  and adapted to provide the required drive current and drive voltage to the LEDs  42  comprising solid state light source  40 , as well as electronic circuitry disposed on daughterboard  60 , as will be discussed shortly in regards to the schematic diagram shown in FIG.  16 . Light diffuser  50  uniformly diffuses light generated from LEDs  42  of solid state light source  40  to produce a homogeneous light beam directed toward window  16 . 
     Window  16  is seen to comprise a lens  70 , and a Fresnel lens  72  in direct contact with lens  70  and interposed between lens  70  and the interior of housing  12  and facing light diffuser  50  and solid state light source  40 . Lid  14  is seen to have a collar defining a shoulder  76  securely engaging and holding both of the round lens  70  and  72 , as shown, and transparent sheet  73  having defined thereon grid  74  as will be discussed further shortly. One of the lenses  70  or  72  are colored to produce a desired color used to control traffic including green, yellow, red, white and orange. 
     It has been found that with the external heatsink being exposed to the outside air the outside heatsink  20  cools the LED die temperature up to 50° C. over a device not having a external heatsink. This is especially advantageous when the sun setting to the west late in the afternoon such as at an elevation of 10° or less, when the solar radiation directed in to the lenses and LEDs significantly increasing the operating temperature of the LED die for westerly facing signals. The external heatsink  20  prevents extreme internal operating air and die temperatures and prevents thermal runaway of the electronics therein. 
     Referring now to FIG. 4, there is shown the electronic and optic assembly comprising of solid state light source  40 , light diffuser  50 , main circuit board  48 , daughter board  60 , and power supply  70 . As illustrated, the electronic circuitry on daughter board  60  is elevated above the main board  48 , whereby standoffs  62  are comprised of thermally nonconductive material. 
     Referring to FIG. 5, there is shown a side view of the assembly of FIG. 4 illustrating the light diffuser  50  being axially centered and disposed above the solid state LED array  40 . Diffuser  50 , in combination with the varying diameter lenses  86 , facilitates light generated from the LEDs  42  to be uniformly disbursed and have uniform intensity and directed upwardly as a light beam toward the lens  70  and  72 , as shown in FIG.  3 . 
     Referring now to FIG. 6, there is shown a top view of the assembly shown in FIG. 4, whereby FIG. 7 illustrates a side view of the same. 
     Referring now to FIG. 8, there is shown a top view of the lens holder  44  comprising a plurality of openings  80  each adapted to receive one of the LED lenses  86  hermetically sealed to and bonded thereover. Advantageously, the glass to metal hermetic seal has been found in this solid state light application to provide excellent thermal conductivity and hermetic sealing characteristics. Each opening  80  is shown to be defined in a tight pack arrangement about the plurality of LEDs  42 . As previously mentioned, the lenses  86  at the center of the array, shown at  81 , have a smaller curvature diameter than the lenses  86  over the perimeter LEDs  42  to increase light dispersion and ensure uniform light intensity impinging diffuser  50 . 
     Referring to FIG. 9, there is shown a cross section taken alone line  9 — 9  in FIG. 8 illustrating each opening  80  having an annular shoulder  82  and a lateral sidewall  84  defined so that each cylindrical lens  86  is securely disposed within opening  80  above a respective LED  42 . Each LED  42  is preferably mounted to heatsink  20  using a thermally conductive adhesive material such as epoxy to ensure there is no air gaps between the LED  42  and the heatsink  20 . The present invention derives technical advantages by facilitating the efficient transfer of heat from LED  42  to the heatsink  20 . 
     Referring now to FIG. 10, there is shown a top view of the main circuit board  48  having a plurality of openings  90  facilitating the attachment of standoffs  62  securing the daughter board above an end region  92 . The power supply  48  is adapted to be secured above region  94  and secured via fasteners disposed through respective openings  96  at each corner thereof. Center region  98  is adapted to receive and have secured thereagainst in a thermal conductive relationship the LED holder  42  with the thermally conductive material  46  being disposed thereupon. The thermally conductive material preferably comprises of epoxy, having dimensions of, for instance, 0.05 inches. A large opening  99  facilitates the attachment of LED&#39;s  42  to the heatsink  20 , and such that light from the LEDs  42  is directed to the light diffuser  50 . 
     Referring now to FIG. 11, there is shown a side elevational view of diffuser  50  having a lower concave surface  54 , preferably having a radius A of about 2.4 inches, with the overall diameter B of the diffuser including a flange  56  being about 6 inches. The depth of the rear surface  52  is about 1.85 inches as shown as dimension C. 
     Referring to FIG. 12, there is shown a top view of the diffuser  50  including the flange  56  and a plurality of openings  58  in the flange  56  for facilitating the attachment of standoffs  52  to and between diffuser  50  and the heatsink  20 , shown in FIG.  4 . 
     Referring now to FIG. 13 there is shown the Fresnel lens  72 , preferably having a diameter D of about 12.2 inches. However, limitation to this dimension is not to be inferred, but rather, is shown for purposes of the preferred embodiment of the present invention. The Fresnel lens  72  has a predetermined thickness, preferably in the range of about {fraction (1/16)} inches. This lens is typically fabricated by being cut from a commercially available Fresnel lens. 
     Referring now to FIG. 14, there is illustrated the lid  14 , the hinge members  17 , and the respective latches  18 . Holder  14  is seen to further have an annular flange member  70  defining a side wall about window  16 , as shown. Further shown is transparent sheet  73  and grid  74  comprises of thin line markings defined over openings  16  defining windows  78 . The sheet can be selectively placed over window  16  for alignment, and which is removable therefrom after alignment. Each window  78  is precisionally aligned with and corresponds to one sixty four (64) LEDs  42 . Indicia  79  is provided to label the windows  78 , with the column markings preferably being alphanumeric, and the columns being numeric. The windows  78  are viable through optical sight member  28 , via an opening in heatsink  20 . The objects viewed in each window  78  are illuminated substantially by the respective LED  42 , allowing a technician to precisionally orient the apparatus  10  so that the desired LEDs  42  are oriented to direct light along a desired path and be viewed in a desired traffic lane. The sight member  28  may be provided with cross hairs to provide increased resolution in combination with the grid  74  for alignment. 
     Moreover, electronic circuitry  100  on daughterboard  60  can drive only selected LEDs  42  or selected 4×4 portions of array  40 , such as a total of 16 LED&#39;s  42  being driven at any one time. Since different LED&#39;s have lenses  86  with different radius of curvature different thicknesses, or even comprised of different materials, the overall light beam can be electronically steered relative to a central axis defined by window  16 . 
     For instance, driving the lower left 4×4 array of LEDs  42 , with the other LEDs off, in combination with the diffuser  50  and lens  70  and  72 , creates a light beam 10 degrees off a horizontal axis normal to the center of the 8×8 array of LEDs  42 , and −8 degrees off a vertical axis. Likewise, driving the upper right 4×4 array of LEDs  42  would create a light beam +10 degrees off the horizontal axis and +8 degrees to the right of a normalized vertical axis. The radius of curvature of the center lenses  86  may be, for instance, half that of the peripheral lenses  86 . A beam steerable +1−14 degrees in 2 degree increments is selectable. This feature is particularly useful when masking the opening  16 , such as to create a turn arrow. This further reduces ghosting or roll-off, which is stray light being directed in an unintended direction and viewable from an unintended traffic lane. 
     Referring now to FIG. 15, there is shown a perspective view of the eye piece  26  as well as the optical sight member  28 , as shown in FIG.  1 . the center axis of optical sight member  28  is oriented along the center of the 8×8 LED array. 
     Referring now to FIG. 16, there is shown at  100  a schematic diagram of the circuitry controlling light apparatus  10 . Circuit  10  is formed on the daughter board  60 , and is electrically connected to the LED solid state light source  40 , and selectively drives each of the individual LEDs  42  comprising the array. Depicted in FIG. 16 is a complex programmable logic device (CPLD) shown as U 1 . CPLD U 1  is preferably an off-the-shelf component such as provided by Maxim Corporation, however, limitation to this specific part is not to be inferred. For instance, discrete logic could be provided in place of CPLD U 1  to provide the functions as is described here, with it being understood that a CPLD is the preferred embodiment is of the present invention. CPLD U 1  has a plurality of interface pins, and this embodiment, shown to have a total of 144 connection pins. Each of these pin are numbered and shown to be connected to the respective circuitry as will now be described. 
     Shown generally at  102  is a clock circuit providing a clock signal on line  104  to pin  125  of the CPLD U 1 . Preferably, this clock signal is a square wave provided at a frequency of 32.768 KHz. Clock circuit  102  is seen to include a crystal oscillator  106  coupled to an operational amplifier U 5  and includes associated trim components including capacitors and resistors, and is seen to be connected to a first power supply having a voltage of about 3.3 volts. 
     Still referring to FIG. 16, there is shown at  110  a power up clear circuit comprised of an operational amplifier shown at U 6  preferably having the non-inverting output coupled to pin  127  of CPLD U 1 . The inverting input is seen to be coupled between a pair of resistors providing a voltage divide circuit, providing approximately a 2.425 volt reference signal based on a power supply of 4.85 volts being provided to the positive rail of the voltage divide network. The inverting input is preferably coupled to the 4.85 voltage reference via a current limiting resistor, as shown. 
     As shown at  112 , an operational amplifier U 9  is shown to have its non-inverting output connected to pin  109  of CPLD U 1 . Operational amplifier U 9  provides a power down function. 
     Referring now to circuit  120 , there is shown a light intensity detection circuit detecting ambient light intensity and comprising of a photodiode identified as PD 1 . An operational amplifier depicted as U 7  is seen to have its non-inverting input coupled to input pin  99  of CPLD U 1 . The non-inverting input of amplifier U 7  is connected to the anode of photodiode PD 1 , which photodiode has its cathode connected via a capacitor to the second power supply having a voltage of about 4.85 volts. The non-inverting input of amplifier U 7  is also connected via a diode Q 1 , depicted as a transistor with its emitter tied to its base and provided with a current limiting resistor. The inverting input of amplifier U 7  is connected via a resistor to input  108  of CPLD U 1 . 
     Shown at  122  is a similar light detection circuit detecting the intensity of backscattered light from Fresnel lens  72  as shown at  124  in FIG. 3, and based around a second photodiode PD 2 , including an amplifier U 10  and a diode Q 2 . The non-inverting output of amplifier U 10 , forming a buffer, is connected to pin  82  of CPLD U 1 . 
     An LED drive connector is shown at  130  serially interfaces LED drive signal data to drive circuitry of the LEDs  42 . (Inventors please describe the additional drive circuit schematic). 
     Shown at  140  is another connector adapted to interface control signals from CPLD U 1  to an initiation control circuit for the LED&#39;s. 
     Each of the LEDs  42  is individually controlled by CPLD U 1  whereby the intensity of each LED  42  is controlled by the CPLD U 1  selectively controlling a drive current thereto, a drive voltage, or adjusting a duty cycle of a pulse width modulation (PWM) drive signal, and as a function of sensed optical feedback signals derived from the photodiodes as will be described shortly here, in reference to FIG.  17 . 
     Referring to FIG. 17 in view of FIG. 3, there is illustrated how light generated by solid state LED array  40  is diffused by diffuser  50 , and a small portion  124  of which is back-scattered by the inner surface of Fresnel lens  72  back toward the surface of daughter board  60 . The back-scattered diffused light  124  is sensed by photodiodes PD 2 , shown in FIG.  16 . The intensity of this back-scattered light  124  is measured by circuit  122  and provided to CPLD U 1 . CPLD U 1  measures the intensity of the ambient light via circuit  120  using photodiode PD 1 . The light generated by LED&#39;s  42  is preferably distinguished by CPLD U 1  by strobing the LEDs  42  using pulse width modulation (PWM) to discern ambient light (not pulsed) from the light generated by LEDs  42 . 
     CPLD U 1  individually controls the drive current, drive voltage, or PWM duty cycle to each of the respective LEDs  42  as a function of the light detected by circuits  120  and  122 . For instance, it is expected that between 3 and 4% of the light generated by LED array  40  will back-scatter back from the fresnel lens  72  toward to the circuitry  100  disposed on daughter board  60  for detection. By normalizing the expected reflected light to be detected by photodiodes PD 2  in circuit  122 , for a given intensity of light to be emitted by LED array  40  through window  16  of lid  14 , optical feedback is used to ensure an appropriate light output, and a constant light output from apparatus  10 . 
     For instance, if the sensed back-scattered light, depicted as rays  124  in FIG. 3, is detected by photodiodes PD 2  to fall about 2.5% from the normalized expected light to be sensed by photodiodes PD 2 , such as due to age of the LEDs  42 , CPLD U 1  responsively increases the drive current to the LEDs a predicted percentage, until the back-scattered light as detected by photodiodes PD 2  is detected to be the normalized sensed light intensity. Thus, as the light output of LEDs  42  degrade over time, which is typical with LEDs, circuit  100  compensates for such degradation of light output, as well as for the failure of any individual LED to ensure that light generated by array  40  and transmitted through window  16  meets Department of Transportation (DOT) standards, such as a 44 point test. This optical feedback compensation technique is also advantageous to compensate for the temporary light output reduction when LEDs become heated, such as during day operation, known as the recoverable light, which recoverable light alos varies over temperatures as well. Permanent light loss is over time of operation due to degradation of the chemical composition of the LED semiconductor material. 
     Preferably, each of the LEDs is driven by a pulse width modulated (PWM) drive signal, providing current during a predetermined portion of the duty cycle, such as for instance, 50%. As the LEDs age and decrease in light output intensity, and also during a day due to daily temperature variations, the duty cycle may be responsively, slowly and continuously increased or adjusted such that the duty cycle is appropriate until the intensity of detected light by photodiodes PD 2  is detected to be the normalized detected light. When the light sensed by photodides PD 2  are determined by controller  60  to fall below a predetermined threshold indicative of the overall light output being below DOT standards, a notification signal is generated by the CPLD U 1  which may be electronically generated and transmitted by an RF modem, for instance, to a remote operator allowing the dispatch of service personnel to service the light. Alternatively, the apparatus  10  can responsively be shut down entirely. 
     Referring now to FIG.  18 A and FIG. 18B, there is shown an alternative preferred embodiment of the present invention including a heatsink  200  machined or stamped to have an array of reflectors  202 . Each recess  202  is defined by outwardly tapered sidewalls  204  and a base surface  208 , each recess  202  having mounted thereon a respective LED  42 . A lens array having a separate lens  210  for each LED  42  is secured to the heatsink  200  over each recess  202 , eliminating the need for a lens holder. The tapered sidewalls  206  serve as light reflectors to direct generated light through the respective lens  210  at an appropriate angle to direct the associated light to the diffuser  50  having the same surface area of illumination for each LED  42 . In one embodiment, as shown in FIG. 18A, LEDs  42  are electrically connected in parallel. The cathode of each LED  42  is electrically coupled to the electrically conductive heatsink  200 , with a respective lead  212  from the anode being coupled to drive circuitry  216  disposed as a thin film PCB  45  adhered to the surface of the heatsink  200 , or defined on the daughterboard  60  as desired. Alternatively, as shown in FIG. 18B, each of the LED&#39;s may be electrically connected in series, such as in groups of three, and disposed on an electrically non-conductive thermally conductive material  43  such as ceramic, diamond, SiN or other suitable materials. In a further embodiment, the electrically non-conductive thermally conductive material may be formed in a single process by using a semiconductor process, such as diffusing a thin layer of material in a vacuum chamber, such as 8000 Angstroms of SiN, which a further step of defining electrically conductive circuit traces  45  on this thin layer. 
     FIG. 19 shows an algorithm controller  60  applies for predicting when the solid state light apparatus will fail, and when the solid state light apparatus will produce a beam of light having an intensity below a predetermined minimum intensity such as that established by the DOT. Referring to the graphs in FIGS. 20 and 21, the known operating characteristics of the particular LEDs produced by the LED manufacture are illustrated and stored in memory, allowing the controller  60  to predict when the LED is about the fail. Knowing the LED drive current operating temperature, and total time the LED as been on, the controller  60  determines which operating curve in FIG.  20  and FIG. 21 applies to the current operating conditions, and determines the time until the LED will degrade to a performance level below spec, i.e. below DOT mininum intensity requirements. 
     FIG. 22 depicts a block diagram of the modular solid state traffic light device. The modular field-replaceable devices are each adapted to selectively interface with the control logic daughterboard  60  via a suitable mating connector set. Each of these modular field replacable devices  216  are preferably embodied as a separate card, with possibly one or more feature on a single field replacable card, adapted to attach to daughterboard  60  by sliding into or bolting to the daughterboard  60 . The devices can be selected from, alone or in combination with, a pre-emption device, a chemical sniffer, a video loop detector, an adaptive control device, a red light running (RLR) device, and an in-car telematic device, infrared sensors to sense people and vehicles under fog, rain, smode and other adverse visual conditions, automobile emission monitoring, various communication links, electronically steerable beam, exhaust emission violations detection, power supply predictive failure analysis, or other suitable traffic devices. 
     The solid state light apparatus  10  of the present invention has numerous technical advantages, including the ability to sink heat generated from the LED array to thereby reduce the operating temperature of the LEDs and increase the useful life thereof. Moreover, the control circuitry driving the LEDs includes optical feedback for detecting a portion of the back-scattered light from the LED array, as well as the intensity of the ambient light, facilitating controlling the individual drive currents, drive voltages, or increasing the duty cycles of the drive voltage, such that the overall light intensity emitted by the LED array  40  is constant, and meets DOT requirements. The apparatus is modular in that individual sections can be replaced at a modular level as upgrades become available, and to facilitate easy repair. With regards to circuitry  100 , CPLD U 1  is securable within a respective socket, and can be replaced or reprogrammed as improvements to the logic become available. Other advantages include programming CPLD U 1  such that each of the LEDs  42  comprising array  40  can have different drive currents or drive voltages to provide an overall beam of light having beam characteristics with predetermined and preferably parameters. For instance, the beam can be selectively directed into two directions by driving only portions of the LED array in combination with lens  70  and  72 . One portion of the beam may be selected to be more intense than other portions of the beam, and selectively directed off axis from a central axis of the LED array  40  using the optics and the electronic beam steering driving arrangement. 
     Referring now to FIG. 23, there is shown at  220  a light guide device having a concave upper surface and a plurality of vertical light guides shown at  222 . One light guide  222  is provided for and positioned over each LED  42 , which light guide  222  upwardly directs the light generated by the respective LED  42  to impinge the outer surface of the diffuser  54 . The guides  222  taper outwardly at a top end thereof, as shown in FIG.  24  and FIG. 25, such that the area at the top of each light guide  222  is identical. Thus each LED  42  illuminates an equal surface area of the light diffuser  54 , thereby providing a uniform intensity light beam from light diffuser  54 . A thin membrane  224  defines the light guide, like a honeycomb, and tapers outwardly to a point edge at the top of the device  220 . These point edges are separated by a small vertical distance D shown in FIG. 25, such as 1 mm, from the above diffuser  54  to ensure uniform lighting at the transistion edges of the light guides  222  while preventing bleeding of light laterally between guides, and to prevent light roll-off by generating a homogeneous beam of light. Vertical recesses  226  permit standoffs  52  extending along the sides of device  220  (see FIG. 3) to support the peripheral edge of the diffuser  54 . 
     While the invention has been described in conjunction with preferred embodiments, it should be understood that modifications will become apparent to those of ordinary skill in the art and that such modifications are therein to be included within the scope of the invention and the following claims.