Patent Publication Number: US-2021174676-A1

Title: Led light fixture

Description:
RELATED APPLICATIONS 
     This application clams priority from U.S. Provisional Application Ser. No. 62/943,283, filed Dec. 4, 2019, the entirety of which is incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     The present invention is directed to an LED light fixture that may be exposed to weather, and more specifically, to an LED light fixture having a heater element provided on a visor for helping to improve visibility of the LEDs. 
     BACKGROUND 
     Light Emitting Diodes (LED) are becoming the primary lighting source for traffic signals due to the energy savings, performance, and lifespan. Energy savings alone, which is as high as 90%, would be enough reason to use LED lights. Additionally, traditional incandescent bulbs, that were widely used prior to the introduction of LEDs, are rated for two years of traffic use. Changing the bulbs is challenging and costly. Lastly, LEDs are becoming brighter and more energy efficient every year. 
     LEDs may not generate enough heat to melt snow that accumulates inside the visor of the traffic light and covers the LED lens, not allowing light to penetrate through. It is known to include a heater directly on the surface of the LED lens, which have been ineffective at eliminating the snow buildup inside the visor. Some municipalities have made the decision not to replace the incandescent bulbs with LEDs because of the snow buildup issues. Other municipalities have changed back from LED to incandescent lights. Traffic signals, pedestrian signals, pre-emption receiver sensors, and railroad crossings may also have LEDs and can be impacted by snow and ice buildup. 
     SUMMARY 
     In one example, a light fixture includes a housing and an LED light assembly in the housing. A visor extends from the housing at least partially around the LED light assembly. A heater element is connected to the visor. 
     Other objects and advantages and a fuller understanding of the invention will be had from the following detailed description and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a schematic illustration of a light fixture including an example heater system. 
         FIG. 1B  is a front view of the light fixture of  FIG. 1  with a door opened. 
         FIG. 2  is a top view of a heater element for the light fixture of  FIG. 1 . 
         FIG. 3  is an exploded view of the heater element of  FIG. 2 . 
         FIG. 4  is a schematic illustration of a module for the heater system. 
         FIG. 5  is a wiring schematic for the light fixture. 
         FIG. 6  is a schematic illustration of another example light fixture including solar panels. 
         FIG. 7  is a top view of another example heater element. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention provides a light fixture heating system that is cost effective, easy to integrate, and will provide heat in and around the light fixture visor/LED efficiently while providing significant energy savings over traditional technology. The heating system shown and described herein can be very effective at melting snow that has built up within the visor/light assembly and can help prevent ice and snow from building up in the first place. In one example, the heating system includes a self-regulating heater element provided on the light fixture visor that at least partially surrounds the LED light assembly. A supplemental heater element can optionally be added around the perimeter of the LED light assembly. 
     The heater element can be formed as a fixed wattage heater or a positive temperature coefficient (PTC) heater element. In the latter case, the PTC heater element contains conductor particles, e.g., a conductive carbon black filler material, dispersed in a polymer base or matrix having a crystalline structure. The crystalline structure of the matrix densely packs the conductor particles into its boundary so they are close enough together at room temperature to form chains and allow conductive paths of current to flow through the polymer insulator via these carbon chains. 
     When the resistive layer is at room temperature, there are numerous carbon chains forming conductive paths through the matrix. In some embodiments, there are two conductive buses with each having a corresponding terminal connected to the resistive layer. When a voltage is applied across the resistive layer from the conductive buses, the layer carries a current via the conductor particles. As a result, the temperature of the resistive polymer layer rises until it exceeds the polymer&#39;s transition temperature, causing the polymer to change from its initial crystalline phase to an amorphous phase. In the amorphous phase, the conductor particles are spaced further apart from one another [relative to the crystalline phase] and, thus, the electrical resistance of the resistive polymer layer increases until current is prevented from passing through the resistive layer. This, in turn, prevents current from passing through the conductive buses to prevent further heating thereof. 
     An insulating layer on the heater element can be configured to work in relation to the heat generated by the resistive layer to direct heat in a direction or to block heat flow emanating towards a region. The insulating layer can be positioned as a layer over or under the resistive layer. 
     The present technology provides a low profile, e.g., flat, and highly adaptable/flexible device that can be integrated into LED light fixtures while providing heating at the same or similar level to an incandescent bulb for a similar application. The heater system can be adapted to fit the LED light fixture. This allows end users to conveniently retrofit the heater element to existing light fixtures and eliminate the cost of purchasing and replacing an entirely new light fixture. 
     With this in mind,  FIGS. 1A-1B  illustrate an example light fixture  10  having a series of LED light assemblies  20 . As shown, the light fixture  10  is a traffic light having three round/circular LED light assemblies  20  for helping to control or direct vehicle traffic. To this end, the respective light assemblies  20  can provide red/“stop” indication, yellow/“warning” indication, green/“go” indication or turn indication. Alternatively, the light fixture  10  and light assemblies  20  can be configured as pedestrian/cross-walk lights, pre-emption receiver sensors, railroad crossing lights or other roadway signaling or indicating lights (not shown). Regardless, it will be appreciated that the light fixture of the present invention can use any number of LED light assemblies  20 , including one, in any number of shapes and sizes. 
     The housing  12  shown includes one to five doors  14  (three doors shown) on which the respective light assemblies  20  are mounted. The doors  14  are removably and pivotably connected to the housing  12  and selectively close an interior space  16  thereof. Each light assembly  20  includes an enclosure  22  having a lens  26  connected thereto that faces away from the housing  12 . The enclosure  22  is secured to the door  14  along a sealed interface  23 . In one example, the periphery of the enclosure  22  includes a gasket (not shown) for sealing the interface  23 . 
     The lens  26  can be round, square, etc. An LED circuit board assembly (not shown) is provided within the enclosure  22  behind the lens  26 . A series of LEDs  24  is mounted to the LED board assembly so as to emit light through the lens  26 . 
     A shroud or visor  30  is connected to and extends from each door  14 . The visor  30  can be, for example, ball-cap or visor-shaped. In any case, the visor  30  includes an inner surface  34  and an outer surface  32 . The inner surface  32  defines a passage  36  extending away from the door  14  along a centerline  38 . The visor  30  can partially (as shown) or fully (not shown) encircle/surround the centerline  38 . Consequently, the visor  30  can partially or fully encircle/surround the respective light assembly  20 . As shown, a notch  40  extends radially through the bottom of the visor  30  to the passage  36 . The notch  40  can allow for rain, snow, melted snow, etc. to flow out of the passage  36  and away from the lens  26 . In any case, the visor  30  helps to focus light emitted by the LEDs  24  along the passage  36 , thereby increasing the visibility of the LEDs. 
     A heater system is provided on the visor  30  for helping to prevent/reduce the buildup of snow, ice, etc. on the lens  26 . The heater system includes at least one heater element formed as a composite  50 . One or more of the composites  50  can be secured to the inner surface  34  of each visor  30  (as shown) and/or the outer surface  32  (not shown). Consequently, the composite(s)  50  can cover a portion of the inner surface  34  and/or the outer surface  32  or the entirety of either/both surfaces. In any case, the composite  50  can be flexible or rigid. 
     In one example, the composite  50  is a positive temperature coefficient (PTC) heater element. Alternatively, the heater element can be formed as a fixed wattage heater (not shown). Referring to  FIGS. 2-3  the PTC composite  50  includes a first or carrier layer  51  made of an electrically insulating material, e.g., Mylar®, that can be impervious to water and other debris to extend the service life of the products. The carrier layer  51  includes a tab  49  and can be made the same color as the inner surface  34  of the visor  30 , e.g., painted black, to prevent altering the light output of the LEDs  24 . 
     The composite  50  further includes a polymer base layer  52  formed from a conductive material. The polymer base layer  52  can be, for example, a screen printed, flexible polymeric ink. The polymer base layer  52  includes a first bus  54  and second bus  56  spaced from each other. The first bus  54  includes a base  58  and finger portions  60  extending away from the base. The second bus  56  includes a base  64  and finger portions  66  extending away from the base. The finger portions  60 ,  66  extend towards one another and can be interdigitated. That said, the finger portions  60 ,  66  are spaced from one another. The polymer base layer  52  includes a tab  59  aligned with and overlying the tab  49  on the carrier layer  51 . 
     A resistive layer  70  is connected to, e.g., screen printed on, the polymer base layer  52  and can be modified or formed in desired shapes to electrically connect the first bus  54  to the second bus  56 . The resistive layer  70  can be formed in one or more pieces. The resistive layer  70  includes a tab  71  aligned with and overlying the tabs  49 ,  59  in the carrier and polymer base layers  51 ,  52 . 
     The resistive layer  70  can be positioned between the polymer base layer  52  and the carrier layer  51  (not shown) or on top of the polymer base layer to sandwich the same between the layers  51 ,  70  (as shown). In any case, the resistive layer  70  can have a higher electrical resistance than the polymer base layer  52  and experience a PTC effect when heated by current. 
     That said, the resistive layer  70  will ultimately reach a designed steady-state temperature in which current is restricted/slowed from passing through the resistive layer and, thus, restricted/slowed from passing through the buses  54 ,  56 . The resistive layer  70  will thereafter draw a reduced amperage required to maintain the steady state temperature, thereby self-regulating its temperature and helping to prevent overheating. The resistive layer  70  will stay “warm”—remaining in the high electrical resistance state as long as power is applied. 
     On the other hand, removing power will reverse the phase transformation—causing contraction of the matrix—and allow the carbon chains to re-form as the polymer matrix re-crystallizes. The electrical resistance of the resistive layer  70  (and therefore of the composite  50 ) thereby returns to its original value. In other words, the resistive layer  70  is electrically conductive at room temperature but heating the resistive layer reduces its electrical conductivity until current is restricted/slowed from passing therethrough. 
     An interface layer  80  helps to connect the composite  50  to the inner surface  34  of the visor  30  and completely seals the composite. In one example, the interface layer  80  directly engages the inner surface  34 . The interface layer  80  can be directly connected to at least one of the polymer base layer  52  and the resistive layer  70 . The interface layer  80  can be, for example, a double-sided adhesive, e.g., acrylic adhesive or thermally conductive foam adhesive. 
     The interface layer  80  can include a peelable adhesive liner or backing including, for example, paper, vinyl or mixtures thereof (not shown). Alternatively or additionally, mechanical fasteners (not shown) can connect the composite  50  to the visor  30 . The composite  50  can also be provided in the visor  30  via overmolding, heat staking or by welding the composite between the surfaces  32 ,  34  (not shown). Regardless, when the composite  50  is assembled ( FIG. 2 ), the components  51 ,  52 ,  70 ,  80  are oriented such that the respective tabs  49 ,  59 ,  71 ,  81  are aligned with one another, thereby collectively forming a composite tab or connector tail  90 . 
     The heater system further includes a riveted or crimped first terminal  84  connected to the first bus  54 . A rivet or crimped second terminal  82  is connected to the second bus  56 . In one example, the terminals  82 ,  84  are secured to the connector tail  90  in a manner that electrically connects the terminals to the respective buses  54 ,  56 . The terminals  82 ,  84  can be generally planar (as shown) or angled, e.g., 90° terminals (not shown). 
     Referring to  FIG. 4 , the heater system further includes a control module  98  for connecting each composite  50  to a power source and regulating the power distribution to each composite. To this end, the module  98  includes a printed circuit board (PCB)  100  having a controller and being connected to a power source via a connector  102 . The voltage input to the module  98  can be, for example, 48 VDC or 120 VAC. 
     A series of connectors  104 ,  106 ,  108 ,  110 ,  112  are also provided on the circuit board  100  to enable one or more of the composites  50  to be connected to the module  98  via the terminals  82 ,  84 . One or more sensors  118 , e.g., temperature sensor, humidity sensor, and/or snow sensor, can be connected to a connector  113  on the circuit board. The sensors  118  can be positioned inside or outside the visor  30  and monitor the environmental conditions in/around each lens  26 . The connectors  102 - 113  can be standard wire-to-board connectors, e.g., PID connectors, GEZ connectors, HYV connectors and the like. More or fewer of the connectors  104 - 113  are contemplated. 
     The module  98  can include a thermostat  140  associated with each connector  104 ,  106 ,  108 ,  110 ,  112  to control power flow between the module and the respective connector. Alternatively, a separate thermostat  140  can be associated with each connector  104 ,  106 ,  108 ,  110 ,  112  (not shown). Regardless, the thermostat  140  controls power flow between the module  98  and each composite  50 . In one example, the thermostat  140  enables current flow from the module  98  to the corresponding composite  50  when the temperature around the corresponding LED light assembly  20  falls below a predetermined value, e.g., about 0° C. On the other hand, the thermostat  140  prevents current flow from the module  98  to each composite  50  when the temperature is above the predetermined value. 
     It will be appreciated that the thermostat  140  can be omitted entirely. In this construction, the module  98  can be connected to or provided with a breaker (not shown) that either continuously enables or continuously prevents current flow to the connectors  104 - 112  regardless of environmental conditions. In other words, the composites  50  are either always on or always off depending solely on whether the user has activated the breaker. 
     The module  98  is secured to the traffic light housing  12  within the interior space  16  (see also  FIG. 1B ). To this end, fasteners can extend through mounting openings  114  in the module  98  to secure the module to existing screw holes/standoffs within the housing  12  (not shown). Alternatively, the module  98  can be secured to the housing  12  with mounting tape/foam, Velco®, etc. Regardless, a single module  98  can be used for all the light assemblies  20  in the light fixture  10  or each light assembly can have its own module associated therewith. 
       FIG. 5  illustrates a schematic diagram of a circuit for the traffic light  10  in which two composites  50  are secured to the inner surface  32  of the visor  30  associated with one lens  26 . Wiring  151  connects the LED light assemblies  20  to a common voltage supply device or power supply  196 . The wires  120  electrically connects the terminals  82 ,  84  from each composite  50  to the corresponding connector  104 ,  106  on the module  98 . Wiring  120  also connect any sensor(s)  118  to the module  98 . Wiring  130  connects the power supply  196  to the connector  102  on the module  98  to power the module. 
     When the composites  50  are installed, the tabs  90  extend through the sealed interface  23  between the LED light assembly  20  and the associated door  14  (see  FIG. 1B ). This positions the tabs  90 —and therefore the terminals  82 ,  84  connected thereto—within the interior space  16 . The wires  120  then connect the module  98  to the terminals  82 ,  84 . Once the door  14  is closed, the tabs  90  and terminals  82 ,  84  are sealed within this housing  12  away from wind, rain, snow, dirt, etc. It will be appreciated that the doors  14  of the traffic light  10  can be removable, thereby enabling a maintenance technician to install/inspect the light assemblies  20  and associated composites  50  on the doors at a more desirable location, e.g., on the ground, in a vehicle, at a facility, etc. 
     During operation of the traffic light  10 , the thermostat  140  passively monitors the temperature around each lens  26 . When the temperature falls below the predetermined value on one or more of the lenses  26 , the thermostat  140  automatically closes to initiate/enable current flow to the composites  50  associated with the cold lenses. As the temperature of the composites  50  rise and cause the PTC effect, the heat is transferred to the visors  30 , which thereby helps to prevent, reduce or remove snow and ice accumulation on the lens  26  associated therewith. Heat from the composite  50  can also directly heat the associated lens and snow thereon. In other words, the lenses  26  can be directly and indirectly heated by the composites  50  associated therewith. 
     The thermostat  140  can continue enabling current flow to the composites  50  so long as the air temperature around the visor  30  is below the predetermined value, thereby helping to ensure light from the LEDs  24  is visible through the lens  26  despite inclement weather. Any melted snow can flow along the inner surface  32  and composite  50  and out of the visor  30  through the notch  40 . Once the air temperature around the visor  30  reaches the predetermined value the thermostat  140  automatically opens to cut off power supply to the composites  50 . 
     Alternatively or additionally, the sensor(s)  118  can monitor the temperature, humidity, onset of snow and/or accumulation thereof around the lenses  26  and send signals to the module  98  indicative thereof. The module  98  controller can evaluate the signals and selectively supply current to the composites  50  in response thereto. 
     In one example, the module  98  controller is configured to initiate supplying power to the composites  50  when the air temperature around the visor  30  falls below about 38° F. and subsequently cut power to the composites when the air temperature reaches about 42° F. Alternatively or additionally, the module  98  controller can also take humidity into account, e.g., supply power to the composites  50  when the air temperature around the visor  30  falls below about 38° F. and the relative humidity is above 50%. The module  98  controller can also selectively power the composites  50  when the snow sensor  118  detects an amount of snowfall on/around the lens  26  that exceeds a predetermined amount. Other factors that can be used to determine composite  50  activation, including when and how long, include a timer circuit and/or battery backup sensor. 
     The module  98  can be controlled wirelessly by a web-based application or app that allows a user to directly control individual heating of the composites  50  regardless of the sensed environmental conditions. In other words, the app allows a user to override or ignore any signals received by the module  98  from the sensors  118  or thermostat  140 . 
     In another example shown in  FIG. 6 , solar panels or cells  170  can be secured to the outer surfaces  32  of the visors  30  for powering the heater system, including the module  98  and components  50 ,  118  connected thereto. The solar panels  170  can also power the light assemblies  20 . A rechargeable battery (not shown) can be electrically connected to the solar panels  170  and mounted in the interior space  16  of the housing  12  to protect the battery from the elements. The battery can replace or supplement the power supply  196 . When the composites  50  are in use, heat therefrom radiates outward through the visor  30  and heats the solar panels  170 , thereby helping to keep snow and ice from building thereon. 
     Another example composite  250  is illustrated in  FIG. 7 . Features in the composite  250  that are similar those in  FIGS. 2-3  are given reference numbers  200  higher. The composite  250  includes the carrier layer (not shown) and base layer  252  with corresponding busses  254 ,  256  having interdigitated fingers  260 ,  266 . The resistive layer  270  is provided over, e.g., printed on, the base layer  252  in a manner that resembles a checkboard pattern. More specifically, the resistive layer  270  is formed as a series of conductive portions  272  spaced apart from one another by non-conductive portions, i.e., voids or empty spaces  274 , arranged collectively in a checkboard pattern. In this manner, the resistive layer  270  does not cover every portion of the base layer  252 , i.e., there are discontinuities in the printing pattern. 
     The checkerboard pattern exemplifies how the resistive layer can be provided in the composite in any desirable configuration, e.g., symmetric, asymmetric, random, patterned, variable density, etc. This flexibility allows the resistive layer to have a desired watt density at each and every position on the composite. Consequently, a specific heating profile can be provided depending on the application where the heating system will be used. 
     The heater systems shown and described herein, e.g., heater elements formed as fixed wattage heaters or phase-changing composites, are advantageous in helping to avoid a hazardous condition as a result of snow buildup on LED lights, such as traffic lights, pedestrian crosswalk lights, railroad crossings, and pre-emptive receiver sensors. 
     The PTC heater element may be installed without the need for sensors, thermostats, or other feedback electronics. The PTC heater element is efficient and runs at very low steady state current. Current draw increases as temperatures decrease or snow attempts to stick to the surface, returning to steady state after melting. The PTC heater element is configurable to many different shapes, contours, and sizes of visors. Custom shapes ensure proper assembly and flexibility. 
     What have been described above are examples of the present invention. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing the present invention, but one of ordinary skill in the art will recognize that many further combinations and permutations of the present invention are possible. Accordingly, the present invention is intended to embrace all such alterations, modifications and variations that fall within the spirit and scope of the appended claims.