Abstract:
A light fixture is provided with a heating element. The heating element can be a resistive heating element, such as a Nichrome wire, and resides in grooves of a cover (e.g., a glass globe) of the light fixture. Thus, the heating element acts to directly heat the cover of the light fixture to prevent, decrease, or otherwise correct frosting, freezing, and other elemental effects on the cover when it is exposed to the environment. The heating element is capable of raising the temperature of the cover at least 15° C. from an initial temperature of −20° C. in 30 minutes. A heat sensing element may provide feedback regarding the temperature of the cover for controlling power supplied to the heating element.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The application described herein is directed to a light fixture and, more particularly, to a runway/taxiway light fixture in which the globe or glass lens of the light fixture is heated. 
         [0002]    Light fixtures located in harsh environments, for example, those located outdoors on runways/taxiways are subject to conditions that can diminish or prevent the proper operation of the light fixture. For example, in cold climates, the globe or glass lens of the light fixture may frost or otherwise have ice formed thereon. As a result, emitted light from the light fixture cannot sufficiently penetrate the globe or glass lens or, in doing so, is altered, thereby impairing the function of the light fixture. When interior temperatures are cold enough, the light fixture may suffer from similar problems even when it is located inside a closed structure. 
       BRIEF SUMMARY OF THE INVENTION 
       [0003]    Accordingly, the application herein describes a more efficiently heated fixture. 
         [0004]    According to one example, a light fixture comprises a first power element and a second power element; a lighting element powered by the first power element; a cover; and a heating element powered by the second power element, wherein the heating element is provided in grooves along a bottom surface of the cover for heating the cover, and an electrically insulating material is provided between the cover and the heating element. 
         [0005]    In various embodiments of the above example, the light fixture further comprises a heat sensing element, wherein a feedback signal from the heat sensing element is used to control the heating element via the second power element; the heat sensing element is a thermistor or thermocouple interior to the cover; the light fixture is an elevated runway or taxiway light fixture; the cover is a glass globe; the heating element is a Nichrome wire; and/or the heating element is capable of raising the temperature of the cover at least 15° C. from an initial temperature of −20° C. in 30 minutes. 
         [0006]    According to another example, a runway and/or taxiway light fixture comprises a base; a lighting element secured to the base; a cover having a resistive heating element; and a heat sensing element; wherein the cover is secured to the base, the cover and base encapsulate the lighting element, the resistive heating element generates heat via power from a power element and is provided in grooves of a surface of the cover with an electrically insulating material provided between the surface of the cover and the heating element, and the heat sensing element is provided on the interior of the fixture. 
         [0007]    In various embodiments of the above example, a feedback signal from the heat sensing element is used to control the heating element via control of the power element; the heat sensing element is a thermistor or thermocouple; the cover is glass globe; the resistive heating element is a Nichrome wire; the heating element is capable of raising the temperature of the cover at least 15° C. from an initial temperature of −20° C. in 30 minutes; the lighting element is a light emitting diode; and/or the surface of the cover is a bottom surface and the cover is securely engaged to the base along the bottom surface of the cover, such that the heating element is secured in the grooves at least in part by the base. 
     
    
     
       BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWING 
         [0008]      FIG. 1  is a perspective view of an elevated runway/taxiway fixture; 
           [0009]      FIG. 2  is a bottom view of an elevated runway/taxiway fixture according to an embodiment; 
           [0010]      FIG. 3  is a bottom view of an elevated runway/taxiway fixture according to an embodiment; and 
           [0011]      FIG. 4  is a cross-section view of an elevated runway/taxiway fixture. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0012]    Light fixtures useful for runway/taxiway illumination are described herein, however the description of them relative to runways and taxiways merely represents an exemplary embodiment and is not intended to be limiting. That is, the various aspects described herein are applicable to other objects providing other functions in which it is desired to heat a part of a surrounding encasement. For example, the light fixture may be elevated or in-ground. In other examples, the various aspects described herein may be applicable to any form of electromagnetic-wave-transmitting-devices used for other functions, such as roadway lighting or the lamps/lenses of lighthouses. 
         [0013]    It is further noted that the various aspects described herein are sufficient to satisfy the requirements of optional arctic kits as set forth in Federal Aviation Administration (FAA) Engineering Brief EB67D. Specifically, sections 2.13 and 2.13.1 of EB67D are directed to optional arctic kits, and provide that any fixture may have arctic kits for addressing potential icing conditions and that the arctic kits must be self-activating. Brief EB67D further requires the main beam light emitting surface (e.g. a fixture cover) temperature must rise a minimum of 15° C. from −20° C. after 30 minutes operation in still air with the light source activated at the highest intensity setting. 
         [0014]    Current arctic kits utilize heating elements that heat the air located inside the fixture. However, the subsequent heat transfer between the heating element, air, and fixture cover can be inefficient with respect to required power and time. In contrast, the fixture described herein heats the fixture cover directly by providing the heating element inside grooves on a surface the cover. 
         [0015]    Turning now to a description of the figures,  FIG. 1  illustrates a perspective view of an elevated runway/taxiway fixture. The fixture can include at least one power element  102 ,  104 , a lighting element  106  (not explicitly shown in  FIG. 1 ), a cover  108 , a heating element  110  (not shown in  FIG. 1 ), a heat sensing element (not shown), and a base  114 . The power element(s)  102 ,  104  may be, for example, a battery included in the fixture, other direct current power source (such as a generator), alternating current power source (such as a line voltage), and the like. The lighting element  106  may be, for example, a light emitting diode (LED), incandescent light bulb, florescent light bulb, and the like for emitting a light from the fixture. The lighting element  106  may be mounted on the base  114  and powered by the power element  102 . Some embodiments may also include a drive element  116  that supplies a proper voltage and current to the lighting element  106  based on the voltage and current from the power element  102 . In embodiments where the power element  102  is externally located, power may be supplied to the drive element  116  or lighting element  106  via power cables. 
         [0016]    The cover  108  protects and encapsulates the lighting element  106  and may be mounted to the base  114 . As illustrated in  FIGS. 1 and 4 , the cover  108  may resemble a globular like shape, however, any shape may be suitable. The cover  108  may be made of any number of materials, for example, glass or polymers, that allow light emitted from the lighting element  106  to be transmitted from the fixture  100 . In some embodiments, the cover  108  may have light transmitting properties, for example, diffracting and/or reflecting properties. 
         [0017]    The heating element  110  (e.g., Nichrome wire) resides in a groove  118  (e.g., round, square, rectangular, triangular) or multiple electrically isolated grooves  118  in the cover  108 . There may also be a non-conductive or electrically insulating material  120  between the groove(s)  118  and any electrically conductive material of the heating element  110 . The ends of the heating element can be attached to flexible insulated leads  122 , which connect to the power element  104 . The power element  104  may be the same power element that powers the lighting element  106 , or a different power element separate from the existing power element  104 . 
         [0018]    The heating element  110  is, for example, a resistive heating element that generates and dissipates heat based on a supplied electrical voltage and current. In one embodiment, Nichrome wire may be used as the heating element  110 . The heating element  110  is used to heat the cover  108  of the fixture  100 . For example, rather than heating an interior air volume inside the fixture  100  (e.g., encapsulated by the cover  108  and base  114 ), which is then transferred to the cover  108  itself, the heating element  110  substantially directly heats the cover  108 . 
         [0019]    The amount of required heat can be controlled by varying length (e.g., continuously, forming a spiral, and double backed), finished shape (round, square, rectangular), and/or diameter or area of the heating element  110 . 
         [0020]    The heat sensing element  112  may be, for example, a thermistor or thermocouple as part of a feedback control system for the heating element  110 . As illustrated in  FIG. 4 , the heating sensing element  112  is interior to the cover  108 , to take into account interior heat generating sources. In various other embodiments, the heat sensing element  112  may be attached to inner and outer surfaces of the cover  108  to provide temperature information relating to the part of the fixture  100  exposed to environmental elements. While  FIG. 4  only illustrates the heat sensing element  112  interior to the cover  108 , it is to be noted that the heat sensing element  112  may be at any one, or a combination, of locations. 
         [0021]    The heat sensing element  112  may be electrically connected to a processor  124  for measuring and providing a temperature of the fixture interior to the processor  124 . The processor  124  may then be used to control the output of the power element  102 ,  104  and/or the drive element  116 , thereby controlling the heating element  110 . For example, if the heat sensing element  112  indicates that a pre-determined temperature of the fixture interior is so low as to allow freezing, frosting, and the like to the cover  108 , a user may be alerted to the issue by a display or sound generated by the processor  124 . The user may then cause the processor  124  to control and increase the voltage and/or current of the power element  102 ,  104  and/or driver  114  to a level sufficient to cause the heating element  110  to increase the temperature of the cover  108  to an acceptable level in a desired time period. As discussed above, these temperatures and time periods may be defined by FAA EB67D. Similarly, the processor  124  may be used to control on/off and other lighting functions of the lighting element  106 . 
         [0022]    The function of the processor  124  may also perform in accordance with FAA EB67D, which requires that light fixtures be self-activating. For example, the heat sensing element  112  may provide feedback to the processor  124 , where the processor  124  automatically controls the power element(s)  102 ,  104  for the lighting element  106  and the heating element  110 . In this way, when the heat sensing element  112  senses that a temperature on a surface of the cover  108  is below a predetermined threshold, the heating element  110  may be automatically powered to prevent the cover  108  from frosting or icing, or to defrost/deice the cover. 
         [0023]      FIGS. 2 and 3  illustrate bottom views of the fixture  100  and the application of the heating element  110  in grooves  118  of the cover  108 . That is,  FIGS. 2 and 3  illustrate the heating element  110  as a Nichrome wire fitted into etchings  118  (or similarly formed grooves) on the bottom of the cover  108 . In  FIG. 2 , the heating element  110  is formed in a continuous spiral-shaped groove  118  in the bottom of the cover  108 . In  FIG. 3 , the heating element  110  is formed in a double-backed manner. While  FIGS. 2 and 3  illustrate the heating element  110  in grooves  118  along the bottom of the cover  108 , it is to be understood that the grooves  118  may be located anywhere on the cover  108 . 
         [0024]      FIG. 4  illustrates a cross-section of the fixture  100 . The lighting element  106  is located near the center of the base  114 . Grooves  118  are shown along the bottom of the cover  108 . The heating element  110  (illustrated as a wire) is located in the grooves  118  and is encased by an electrically non-conductive material. The heating element  110  may be secured in the grooves  118 , for example, with an adhesive. Alternatively, the heating element  110  may be secured in the grooves  118  by attachment of the cover  108  to the base  114 . As noted above, heat sensing elements  112  are illustrated attached to an inner surface of the cover  108  and interior to the cover  108 . 
         [0025]    As discussed above, the cover  108  in  FIGS. 1-4  is formed as a globe like shape, with an outwardly protruding rim  126 . The grooves  118  are provided along a bottom surface of the rim  126 . The bottom surface of the rim  126  is also where the cover  108  may be secured to the base  114 , as discussed above. While a partial-globular shape of the cover has been described herein, it is to be understood that the cover  108  may take any shape that is conducive to perform as described. Furthermore, the grooves  118  provided in the cover (and the heating element  110  provided therein) may be applied at any location on the cover  108 . 
         [0026]    Certain terminology is used herein for convenience only and is not to be taken as a limitation on the present invention. Relative language used herein is best understood with reference to the drawings, in which like numerals are used to identify like or similar items. Further, in the drawings, certain features may be shown in somewhat schematic form.