Patent Publication Number: US-2013249375-A1

Title: Anti-icing solid state aircraft lamp assembly with defroster apparatus, system, and method

Description:
BACKGROUND 
     The present disclosure is related generally to an anti-icing solid state aircraft lamp assembly comprising a defroster apparatus, system, and method. A defroster apparatus, system, and method includes any defogger, demister, or deicing apparatus, system, and method to clear or evaporate condensation or fog and thaw or deice rime, frost, snow, or ice that may develop on the clear cover portion of the anti-icing lamp assembly. More particularly, the present disclosure is directed to a light emitting diode (LED) based solid state lamp assembly with defroster elements to defog the clear cover of the lamp assembly. 
     Conventional aircraft landing and taxiing lights on transport and commercial aircraft utilize a filament or gas that emits light when a voltage is applied. In addition, such conventional aircraft landing and taxiing lights produce heat through infrared (IR) wavelength transmission during operation. Such IR radiation generally develops enough heat to prevent the formation of rime or clear ice in adverse weather conditions. Solid state lamps such as LED based aircraft lamps emit light and/or pump phosphor to produce white light. Such solid state lamps, however, do not produce a significant amount of energy in the IR wavelength band and therefore do not radiate enough heat to the cover (e.g., glass enclosure) of the lamp assembly during operation. As a result, condensation, fog, rime, frost, snow, or ice, and the like, can form on the cover of solid state LED lamp assemblies used in external aircraft lighting applications, such as landing and taxiing, to degrade the ability of LED based lamps to properly illuminate runway during landing and taxiing operations. 
     The present disclosure provides a brief review of the current state of LED technology. In addition, the present disclosure considers the fabrication and radiation emitted by white LEDs, their size, as well as their potential for increasing nighttime visual acuity. Further, the compelling reasons for LEDs gaining market share as a light source for both new and retrofit lamps for the large commercial aircraft is examined. State-of-the-art LED metrics such as chip size, lumens per watt, thermal resistance, and heat transfer properties are also examined. Finally, the present disclosure describes the importance of non-imaging optics for both optically efficient and extremely compact LED lighting systems as direct drop-in replacements for conventional and ubiquitous incandescent aircraft lamps, such as incandescent aircraft lamps available from General Electric known as GE 4553 aircraft landing lights. Additionally, the present disclosure describes how LED based lamps consume much less power than the conventional incandescent and halogen lamps and have lifetimes on the order of 500-1000 times those of existing lamps. 
     Prior to describing the various embodiments of defroster elements, this disclosure will turn briefly to a discussion of the historical context of the LED as a light source generally. It is generally accepted that there have been two major revolutions in lighting technology during the 19th and 20th centuries. The first revolution would consist of the development of the incandescent light bulb from the early 1800s, through Thomas Edison&#39;s commercialization of the technology in 1880. Actually the incandescent bulb, as we know it, was not in its final form until approximately 1910 when the tungsten filament was invented and the cost of incandescent lamps came down to level that most people could afford. The second revolution in lighting occurred in 1938 when researchers at General Electric Corp. (GE) invented the fluorescent lamp. This new fluorescent lamp had twice the energy efficiency of the incandescent lamp and twice its lifetime. Continued refinements of the fluorescent lamp over the past 73 years have resulted in its efficacy growing to seven times that of the incandescent lamp (100 lumens per watt [lm/W]) and its lifetime growing to 10 times that of incandescent lamp (20,000 hours). Because of these characteristics, the fluorescent lamp has become the lamp of choice for most commercial, government, and institutional facilities. Further, the incandescent lamp (and its offshoot the halogen lamp) continues to be the lamp of choice for most residential and high-power parabolic reflector (PAR) lamp applications. An example would be landing lights on large commercial aircraft because of the incandescent bulbs relatively small filament and high luminance when compared to fluorescent lamps. 
     The third revolution in lighting got started quietly in 1962 with the first practical demonstration of the LED by Nick Holonyak (N. Holonyak Jr., S. F. Bevaqua, Appl. Phys. Lett. 1, 82 (1962), the disclosure of which is herein incorporated by reference) working at General Electric Laboratories. The first LEDs had luminous efficacies of only about 0.1 lm/W (i.e. about 1/20 the efficacy of Edison&#39;s first electric light bulb), and came only in red and yellow colors. During the ensuing 30 years, LEDs&#39; efficiencies gradually increased, with their chief applications being as idiot lights, to alert you as to when your stereo or radio was on or off. In 1992, however, there was a dramatic increase in the efficacy of the red and amber LEDs, which previously had been made from GaAsP or GaP material, were now made from a new quatenary solid state material, AlInGaP, and their efficiency jumped from 1 to 2 lm/W into the range of 10 to 20 lm/W. At this point LEDs exceeded the efficiency of red color filtered incandescent lamps and the consumer began seeing applications of red LEDs into automobile taillight assemblies and red traffic signals. 
     Even with all progress made in development of LEDs over this 30 year period, there was still a key missing link, bright blue and green LEDs. This problem was soon-to-be remedied, however, by Shuji Nakamura (S. Nakamura, M. Senoh, N. Iwasa, S. Nagahama, T. Yamada, T. Mukai, Jpn. J. Appl. Phys. 34, L1332 (1995), the disclosure of which is herein incorporated by reference) working at Nichia Corporation in late 1993 with his new method of producing very bright blue and green LEDs from GaN material. These new Nichia blue and green LEDs had approximately 100 times the flux output of the previous best blue and green LEDs, and opened up a whole range of new applications for LEDs in the general lighting marketplace. In addition, Nichia introduced a “white LED” by taking a blue LED and covering it with a YAG (yttrium aluminum garnet) yellow phosphor. During the past twenty years there have continued to be dramatic increases in the efficiency of all these LEDs, and there are now compelling reasons to believe that these solid state lighting (SSL) devices will indeed usher in a third revolution in lighting. The compelling reasons for LEDs being hailed as the 3rd revolution in lighting will now be examined in some detail. 
     An LED in its simplest form is a semiconductor p-n junction device that, when forward biased with a direct current (dc) flowing through its p-n junction emits photons as a result of the electrons and holes recombining near the junction. The energy of the photons is primarily determined by the energy band gap of the semiconductor where the recombination occurs. Compound semiconductor materials composed of column III and V elements (from the Periodic Chart) are the materials of choice for LEDs because they have direct band gap properties and band gap energies necessary for efficiently producing visible photons. The best AlInGaP LEDS (red and amber) convert about 50% of the electrons sent into their p-n junctions directly into useful light output. The best InGaN LEDs (UV, blue, green and white) convert 40% of electrons traveling through their p-n junctions into useful light output. 
     The drive voltages for AlInGaP LEDs are typically from 1.8V-3.0V dc, while drive voltages for InGaN are in the range of from 3.0V-3.6V dc. In general, LED manufacturers recommended that the junction temperature of all LEDs be kept at less than 150° C. Most LEDs are encapsulated by an epoxy which undergoes thermal degradation (epoxy yellowing) at temperatures in excess of 125° C. This yellowing greatly reduces light output and lifetime, particularly for the blue and green LEDs, if this metric is not adhered to. The size of LED die for the ordinary LED packages range from 0.25 mm-0.35 mm on a side while those for the so called power (high flux) LED packages range from 1.0 mm to 2.0 mm on a side. 
     LEDs are provided in three fundamental packages: (1) 5 mm so called “bullet” lens, with typical drive currents of 20-40 mA and with thermal resistances of 200-300° C./W (this is the thermal resistance between the LED die to ambient); (2) surface mount (SMT)LEDs (high speed pick and place), with typical drive currents of 10-100 ma and with thermal resistance of 150-300° C./W; and (3) Power (high flux) LEDs, with typical drive currents from 350-3000 ma with thermal resistances of 3-10° C./W. 
     One misconception regarding LEDs is that they are a cool light source. This probably stems from the fact that most people have experience with 5 mm bullet lens packages which typically run at 30 mA and 3.3 V for the white LEDs, for power consumption of approximately 0.1 watts. Recall that about 40% of this power goes into creating light, while 60% is emitted as heat from the LED. Thus, when dealing with power consumption as low as 0.06 watts, one can easily come away with the false impression that LEDs are indeed a cool light source. 
     Taking into consideration the case of using white high-power LEDs to replace a 250 watt GE model 4553 incandescent aircraft landing lamp, which when new is rated at approximately 4500 lumens, and see if we still believe that LEDs are a cool light source. At today&#39;s efficacy figures of 100 lm/W for the white high-power LEDs, for example the Cree XM-L LED run at 3,000 mA at 3.35 Vdc (a 10 watt source) produces about 680 lumens, we would require about 7 of these 10 watt LEDs to produce the 4500 lumens. Assuming that 40% of the power goes into creating light and that 60% goes into creating heat, we would need to dissipate 42 watts of heat, far from a cool light source. While this is not a tough task if one can radiate this power away as the temperature to the fourth power (T 4 ) as an incandescent lamp does via radiative heat transfer, it is a much more difficult task for an LED lamp composed of this array of 7 LEDs which can basically only use conduction in order to remove the 42 watts of heat through the base of the LED array. Indeed, when one takes into account that LED light output degrades with rising junction temperature, it becomes almost inescapable that one requires a lot of intelligent design for the heat transfer to be used in conjunction with his LED array. Even if one projects forward one year and assuming that white LEDs have achieved an efficacy of 150 lm/W, one would still require three of the these 10 W white LEDs to create the 4500 lumens and that still implies the need to dissipate approximately 18 watts of power. 
     The conclusion one is left with is that LEDs are not a cool light source even though today they have approximately seven times the efficacy of an incandescent bulb, and in the near future probably 10× the efficacy of an incandescent bulb. The ability of incandescent lamps to get rid of excess heat via radiation transfer is their fundamental advantage over LEDs. Since LEDs must have their junction temperature maintained at no more than 150° C., they are constrained to basically use only conduction to rid themselves of excess heat. 
     The luminous efficacy (ηL) of incandescent lamps, halogen lamps, fluorescent lamps, sodium-vapour lamps and commercial white LEDs is discussed in a historical context in Urataki E. and Suzuki Y. 2001 J. Illum. Eng. Inst. Japan 85 4, the disclosure of which is incorporated herein by reference. The incandescent lamp was developed in 1879, and in the 150 years that followed, the ηL of incandescent lamps was enhanced from 1.5 to 16 lmW −1 . The fluorescent lamp was developed in 1938, and their luminous efficacy was enhanced from 50 to 100 lmW −1  over the following 60 years. The sodium-vapour lamp was developed in 1965, and its ηL was enhanced from 106 to 146 lmW −1  over the next 40 years. Thus, the typical improvement rate in traditional lamps was only 1.1-1.2 times per decade. Within the past 30 years, the ηL of these lamps has remained nearly constant. On the other hand, the white LED was first commercialized in 1996. The ηL of white LEDs in 1996 was only 5 lmW −1 , much lower than that of an incandescent lamp (13 lmW −1  However, the ηL of white LEDs was very rapidly enhanced due to improvements in the external quantum efficacy (ηex) of blue LEDs. The highest ηL of current commercial white LED has reached 150 lmW −1 , the highest value of all white light sources. The white LEDs was drastically improved, compared with that of traditional lamps, by about 30 times per decade, and has not yet saturated. The possibility of further enhancement of the ηL of white LEDs remains. 
     SUMMARY 
     In one embodiment, an anti-icing solid state aircraft lamp comprises at least one solid state light source, a substantially optically transparent cover optically coupled to the at least one solid state light source, and at least one defroster element coupled to the optically transparent cover. 
    
    
     
       DESCRIPTION OF THE FIGURES 
         FIGS. 1A ,  1 B and  1 C are perspective views of a front, back and side, respectively, of an anti-icing lamp assembly according to one embodiment. 
         FIG. 2  is a perspective cross-sectional view of the anti-icing lamp assembly of  FIGS. 1A-1C . 
         FIG. 3  is an exploded view of the anti-icing lamp assembly of  FIGS. 1A-1C . 
         FIG. 4A  illustrates a physical layout of the LED arrays and controller circuit of  FIG. 3 . 
         FIG. 4B  illustrates a configuration of the PCB substrate of  FIG. 4A  according to one embodiment 
         FIGS. 5A and 5B  illustrate configurations of an LED array of  FIG. 3  according to various embodiments. 
         FIG. 6  is a cross-sectional view of the structure of a phosphor-conversion white LED lamp shown in  FIG. 6  using a blue LED die and a yellow phosphor material. 
         FIG. 7  is a schematic diagram of the white LED lamp shown in  FIG. 6  producing white light. 
         FIG. 8  is a graphical depiction of a typical emission spectrum of a white LED using a Yttrium-Aluminum-Garnet (YAG) phosphor at a forward-bias current of about 20 mA. 
         FIG. 9  shows the spectrum of an ultra-high Ra white LED (UHR-white), with a T cp , of 5000 K. 
         FIG. 10  is a block diagram of the LED arrays and controller circuit of  FIG. 3  according to one embodiment. 
         FIGS. 11A ,  11 B,  11 C are front, back and perspective side views, respectively, of the base of  FIG. 3  according to one embodiment. 
         FIGS. 12A and 12B  are perspective views of one set of electrical connectors of  FIG. 3  according to one embodiment. 
         FIGS. 13A ,  13 B, and  13 C are front, back and perspective side views, respectively, of the cover of  FIG. 3  according to one embodiment. 
         FIGS. 14A and 14B  illustrate diffuser optics according to various embodiments. 
         FIG. 15  is a cross-sectional view of a non-imaging lens called a total internal reflection (TIR) lens according to one embodiment. 
         FIG. 16  shows an incandescent landing light comprising a parabolic reflector. 
         FIG. 17  shows one embodiment of an m-TIR lens comprising a mushroom-shaped deviator lens and a TIR lens according to one embodiment. 
         FIG. 18  shows one embodiment of the mushroom-shaped deviator lens shown in  FIG. 17  in combination with the TIR lens denoted as m-TIR lens with computer generated ray tracing according to one embodiment. 
         FIG. 19  is a computer modeled performance of an m-TIR lens assembly where the solid line is the relative intensity for degrees off-axis and the dotted line is cumulative according to one embodiment. 
         FIG. 20  illustrates a lamp assembly comprising a plurality of m-TIR lenses according to one embodiment. 
         FIGS. 21 ,  22 ,  23  illustrate an anti-icing lamp assembly comprising a transparent electrically conductive coating according to one embodiment, where  FIG. 21  is perspective cross-sectional view,  FIG. 22  is a detail view of a cross-section of a cover of the anti-icing lamp assembly, and  FIG. 23  is an exploded view. 
         FIG. 24  illustrates an anti-icing lamp assembly comprising an electrically resistive conductor according to one embodiment. 
         FIG. 25  illustrates an anti-icing lamp assembly comprising an electrically resistive conductor according to one embodiment. 
         FIG. 26  illustrates an anti-icing lamp assembly comprising an electrical resistance conductive grid element according to one embodiment. 
         FIG. 27  illustrates an anti-icing lamp assembly comprising an exothermic deicing system according to one embodiment. 
         FIG. 28  illustrates an anti-icing lamp assembly comprising an infrared thermal energy sources according to one embodiment. 
         FIGS. 29 and 30  illustrate an anti-icing lamp assembly comprising a heat sink thermal energy transfer system according to one embodiment. 
         FIGS. 31A ,  31 B and  31 C are perspective views of a front, back and side, respectively, of an anti-icing lamp assembly according to one embodiment. 
         FIGS. 32 and 33  are exploded views of the anti-icing lamp assembly of  FIGS. 31A-31C  according to one embodiment. 
         FIG. 34  is a perspective cross-sectional view of one embodiment of an anti-icing lamp assembly according to one embodiment. 
         FIG. 35  is a detail view of a cross-section of the lens cover of the anti-icing lamp assembly of  FIG. 34  according to one embodiment. 
         FIG. 36  illustrates an exploded view the anti-icing lamp assembly with the retainer ring removed to more clearly show the outer surface  602  of the cover according to one embodiment. 
         FIG. 37  illustrates an anti-icing lamp assembly comprising electrically resistive heater conductors according to one embodiment. 
         FIG. 38  illustrates an anti-icing lamp assembly comprising electrically resistive heater conductors according to one embodiment. 
         FIG. 39  illustrates an anti-icing lamp assembly comprising electrically resistive heater conductors according to one embodiment. 
         FIG. 40  illustrates an anti-icing lamp assembly comprising an exothermic deicing thermal energy system according to one embodiment. 
         FIG. 41  illustrates one embodiment of an anti-icing lamp assembly comprising an infrared (IR) thermal energy source according to one embodiment. 
         FIG. 42  illustrates one embodiment of an anti-icing lamp assembly comprising a heat sink thermal energy transfer system according to one embodiment. 
         FIG. 43  illustrates one embodiment of a controller circuit for controlling the operation of the anti-icing lamp assembly according to one embodiment. 
         FIG. 44  illustrates one embodiment of a control circuit suitable for use with a thermistor type feedback element. 
         FIG. 45  illustrates an installed configuration of an anti-icing lamp assembly according to one embodiment. 
     
    
    
     DESCRIPTION 
     Before explaining the present disclosure in detail, it should be noted that the disclosed embodiments are not limited in application or use to the details of construction and arrangement of parts illustrated in the accompanying drawings and description. The disclosed embodiments may be implemented or incorporated in other embodiments, variations and modifications, and may be practiced or carried out in various techniques. Further, unless otherwise indicated, the terms and expressions employed herein have been chosen for the purpose of describing the illustrative embodiments for the convenience of the reader and are not for the purpose of limitation thereof. Additionally, it should be understood that any one or more of the disclose embodiments, expressions of embodiments, and examples, can be combined with any one or more of the other disclosed embodiments, expressions of embodiments, and examples in whole or in part without limitation. 
     The present disclosure is directed generally to an anti-icing solid state aircraft lamp assembly comprising a defroster apparatus, system, and method. A defroster apparatus, system, and method includes any defogger, demister, or deicing apparatus, system, and method to clear or evaporate condensation or fog and thaw or deice rime, frost, snow, or ice that may develop on the clear cover portion of the anti-icing lamp assembly. More particularly, the present disclosure is directed to an LED based solid state lamp assembly with defroster elements to defog the clear cover of the lamp assembly. The embodiments of the anti-icing solid state aircraft lamp assemblies disclosed herein are configured with defroster elements to defog, demist, deice, prevent icing, clear or evaporate condensation or fog and thaw rime, frost, snow, or ice that may develop on the clear cover portion of the lamp assembly or prevent the buildup of any of these conditions on the clear cover portion of the lamp assembly. In one embodiment, the clear cover portion of the lamp assembly comprises a feedback element, which provides a feedback signal indicative of a condition of the clear cover, such as, for example, fog, mist, ice, rime, frost, snow, ice or temperature to the controller circuit. In response to the feedback signal, the controller circuit activates the defroster element to defog, demist, deice, prevent icing, clear or evaporate condensation or fog and thaw rime, frost, snow, or ice that forms on the clear cover. 
     It will be appreciated that the controller circuit may be activated in response to monitored environmental conditions external to the lamp assembly, such as temperature, for example, to prevent or arrest the development of fog, mist, ice, rime, frost, or snow. For conciseness and clarity of disclosure, for example, these functions are referred to herein simply as “deicing” the clear cover portion of the lamp assembly, without limitation. For example, in the context of the present disclosure, the term “deicing” may be used to describe the function of: removing or getting rid of fog, mist, ice, rime, frost, snow, or ice that had already developed on the cover; or preventing the development of fog, mist, ice, rime, frost, snow, or ice before it forms on the cover. 
     The defroster elements as described hereinbelow will enable the use of a solid state lamp, such as an LED based lamp, to perform without degradation during adverse weather conditions as described hereinbelow. As previously discussed, conventional aircraft landing and taxiing lamps utilize a filament or gas that emits heat in the IR spectrum when a voltage is applied to the lamp. In order to compensate for the lack of IR radiation in a solid state lamp suitable for defrosting the cover of a lamp assembly, for example, the present disclosure provides various embodiments of solid state LED based aircraft lamps comprising defroster elements formed integrally with, formed in, formed on, or coupled to an optically transparent cover of the solid state LED lamp for deicing the clear cover of an aircraft lamp assembly, for example. 
     One consideration that LED based aircraft lamp assemblies must overcome is one of deicing of landing lights in an aircraft. For incandescent lamps about 90% of their light is emitted as IR radiation that is heat, and therefore no ice can form on these incandescent landing lamps. LEDs, however, emit virtually no IR radiation and therefore augmentation must be added for the deicing function for LED landing lights. This can be accomplished via a transparent conductive surface coating that supplies heat, or by allowing for a conductive path from the base of the LED array to a conductive glass cover, or finally by either adding IR emitting LEDs into the array or tailoring the phosphor coating to emit some of its radiation in the IR portion of the spectrum. Various embodiments of these techniques are described hereinbelow in connection with various embodiments of aircraft lamp assemblies. 
     Prior to describing various embodiments of defroster elements for use in an anti-icing lamp assembly, the disclosure turns to  FIGS. 1-30 , which provides an overview of the optical, mechanical, and electronic components of one embodiment of an anti-icing lamp assembly, which may employ the various embodiments of defroster elements described herein.  FIGS. 1A ,  1 B and  1 C are perspective views of a front, back and side, respectively, of an anti-icing lamp assembly  5  according to one embodiment.  FIG. 2  is a perspective cross-sectional view of the anti-icing lamp assembly  5 , and  FIG. 3  is an exploded view of the anti-icing lamp assembly  5  illustrating components thereof. As discussed in further detail below, embodiments of the anti-icing lamp assembly  5  utilize LED technology to generate a light output. Light emitting diodes do not exhibit the large inrush current characteristics of incandescent filaments and are generally impervious to vibration. The anti-icing lamp assembly  5  thus provides significantly greater operating lifetimes in harsh mechanical environments, such as, for example, aircraft, motorcycle and off-road vehicle (e.g., Baja 500) environments or the like than may be realized using incandescent filament technology. Advantages of the anti-icing lamp assembly  5  are not limited to increased durability and longevity in harsh operating environments, and it will be appreciated that the anti-icing lamp assembly  5  may be used in other operating environments, such as, for example, automobile forward lighting environments, marine (e.g., underwater) environments and stage lighting operating environments, and not just for aircraft applications. Because embodiments of the anti-icing lamp assembly  5  may utilize an array of total internal reflection (TIR) lenses to extract light from LEDs, the light may be collected and redirected more efficiently and compactly compared to non-TIR light processing elements used for external aircraft lighting and other applications. Moreover, because embodiments of the anti-icing lamp assembly  5  may conform to certain mechanical, electrical and/or light output specifications of any of a number of existing incandescent filament lamps, aircraft, motorcycles, off-road vehicles and other equipment (vehicular or non-vehicular) may be retrofitted with the anti-icing lamp assembly  5  without the need for substantial modification, if any, of the associated equipment. 
     With reference to  FIG. 3 , the anti-icing lamp assembly  5  may comprise at least one solid state light source, for example. In one embodiment, the solid state light source comprises at least one LED. In some embodiments, the solid state light source comprises at least one LED array  10 , a controller circuit  15  electrically coupled to the LED arrays  10 , a lens array  20 , a base  25 , and a cover  30 . The cover  30  may be configured and adapted to accommodate various embodiments of the defroster elements described hereinbelow. The cover  30  may be formed of any suitable glass or plastic substrate. A glass substrate may be formed of borosilicate, whereas a plastic substrate may be formed of polycarbonate resin, acrylic resin, polyarylate resin, polyester resin, polysulfone resin, polyvinyl butyral resin (PVB), and copolymers and mixtures thereof. 
     The anti-icing lamp assembly  5  comprises a cover  30  that is substantially optically transparent. The cover  30  may comprise one or more defroster elements in accordance with the present disclosure to deice the cover  30 , for example. As previously discussed, the term “deice” is used for conciseness and clarity and is intended to mean defog, demist, deice, prevent icing, clear or evaporate condensation or fog and thaw rime, frost, snow, or ice that may develop on the clear cover  30  of the anti-icing lamp assembly  5 . The defroster elements may be configured to passively or directly provide thermal energy to an exterior surface  102  of the cover  30 . In one embodiment, the defroster elements may be configured to generate thermal energy by conducting electrical current, alternating or direct current (AC or DC), pulsed, or modulated, through a resistive layer, coating, sheet, grid, or wire, or any combination thereof, formed integrally with or on an optically transparent substrate, e.g., the cover  30 . In other embodiments, the defroster elements may be configured to generate thermal energy by exothermic chemical reactions that release energy in the form of heat. In other embodiments, the defroster elements may be configured to generate IR radiation energy. In other embodiments, the defroster elements may be configured as heat sinks to recover or recycle wasted heat from other sources in the lamp assembly or other aircraft systems. In other embodiments, heat sink elements embedded in the optically transparent substrate may be thermally coupled to other heat sink elements of the anti-icing lamp assembly  5  system. Before describing the various embodiments of defroster elements, the present disclosure continues with a description of one embodiment of the anti-icing lamp assembly  5 . 
     In the assembled state of the anti-icing lamp assembly  5 , as shown in  FIG. 2 , the LED arrays  10 , the controller circuit  15  and the lens array  20  may be received onto a front surface  195  of the base  25 , with the cover  30  being disposed over the front surface  195  and attached to the base  25 . The LED arrays  10 , the controller circuit  15  and the lens array  20  may thus be protectably enclosed between the cover  30  and the base  25 . The anti-icing lamp assembly  5  may additionally comprise a set of electrical connectors  36  disposed through the base  25  between the front surface  195  of the base  25  and a back surface  200  of the base  25 . As discussed in further detail below, the electrical connectors  36  enable an electrical power system external to the anti-icing lamp assembly  5  (e.g., an aircraft electrical power system) to electrically connect to the LED arrays  10  and controller circuit  15  and supply electrical power thereto. 
       FIG. 4A  illustrates a physical layout of the LED arrays  10  and controller circuit  15  of  FIG. 3 . As shown, the LED arrays  10  and controller circuit  15  may be mounted on a front surface of a printed circuit board (PCB) substrate  40 , with the LED arrays  10  symmetrically spaced on an outer periphery of the substrate  40 , and with the controller circuit  15  contained on a portion of the substrate  40  generally centered between the LED arrays  10 . In certain embodiments and as shown in  FIG. 4A , the anti-icing lamp assembly  5  may comprise four LED arrays  10 , although it will be appreciated that any number of LED arrays  10 , additional or fewer, may generally be used depending upon, for example, light output requirements of the particular lighting application and flux characteristics of the LED arrays  10 . In certain embodiments and with reference to  FIG. 4B , the substrate  40  may be in the form of a metal core PCB (MCPCB) comprising a metal base  41  (e.g., copper or aluminum), which may act as a heat sink, a dielectric layer  42  and a circuit layer  43  (e.g., copper) that are laminated together. At each location on the front surface of the substrate  40  at which an LED array  10  is mounted, a cutout  44  may be defined through the dielectric and circuit layers  42 ,  43  such at least a portion of each LED array  10  (e.g., an electrically insulated metal heat sink  46  of the LED array  10 ) is in direct thermal contact with the metal base  41 . In one embodiment, for example, the heat sink  46  may be soldered to the metal base  41  via the cutout  44 . In this way, a direct thermal path may be established between the LED arrays  10  and the base  25  through the metal base  41 . In certain embodiments and as shown, the metal base  41  may be punched or slightly indented such that the portion of the metal base  41  exposed through each cutout is substantially flush with the front surface of the substrate  40 . The LED arrays  10  and controller circuit  15  may be electrically connected by electrical conductors (not shown), such as, for example, electrical conductors formed in the circuit layer  43  using known circuit-forming technologies (e.g., photoengraving). 
     The front surface of the substrate  40  may comprise an alignment post  45  centered on the front surface and extending normally therefrom. When received into a corresponding alignment opening (not shown) of the lens array  20 , the alignment post  45  ensures proper alignment of the lens array  20  with the LED arrays  10 . The substrate  40  may define a number of suitably positioned openings  50  for enabling attachment of the substrate  40  and the lens array  20  to the base  25 , using for example, fasteners (e.g., screws) introduced through the openings  50  that are retained in openings  205 ,  215  defined by the base  25  ( FIGS. 11A-11C ). The substrate  40  may additionally comprise a set of electrical input connection points in the form of openings  55  defined by the substrate  40 , with each opening  55  having a conductive periphery electrically coupled to a corresponding input of the controller circuit  15 . In the assembled state of the anti-icing lamp assembly  5  and with reference to  FIG. 2 , a fastener (e.g., a screw) received through each opening  55  may be retained by an end of a corresponding electrical connector  36 , thereby mechanically anchoring the electrical connectors  36  to the substrate  40  and electrically connecting the electrical connectors  36  to the LED arrays  10  and controller circuit  15  via the conductive peripheries of the openings  55 . 
       FIGS. 5A and 5B  illustrate configurations of an LED array  10  of  FIG. 3  according to various embodiments. In certain embodiments and with reference to  FIG. 5A , the LED array  10  may comprise four LED die, or “LEDs,”  60  (D 1 -D 4 ), with the LEDs  60  mounted onto a substrate  65  (which may or may not be the same as substrate  40 ) in the general form of a square when viewed from their light-emitting surfaces. In one embodiment, all LEDs  60  of the LED array  10  may be configured to radiate electromagnetic energy at substantially the same wavelength, or at a number of wavelengths that are substantially the same. In another embodiment, at least one of the LEDs  60  may be configured to radiate electromagnetic energy at one or more wavelengths that are not emitted by at least one other of the LEDs  60  of the LED array  10 . The specific spectral output of the LED array  10  may be suitable for use in existing incandescent filament lamp applications, such as, for example, aircraft, motorcycle and off-road vehicle (e.g., Baja 500) applications, among others. Electrical connections to the LEDs  60  may be made through conventional electrical contacts. 
     Although the LED array  10  of  FIG. 5A  comprises four LEDs  60  arranged in a square-like configuration, it will be appreciated that that the LED array  10  may generally comprise one or more LEDs  60 , and that the one or more LEDs  60  may be mounted onto the substrate  65  to form any of a number of geometrical shapes (e.g., circle, line, rectangle, triangle, rhombus, or any suitable polygonal shape) depending on, for example, the number of LEDs  60  and a desired light distribution. It will further be appreciated that the number of LEDs  60  in each LED array  10  of the anti-icing lamp assembly  5  may or may not be the same. For example, in one embodiment all of the LED arrays  10  may comprise four LEDs  60 , while in another embodiment a first LED array  10  may comprise four LEDs  60  and a second LED array  10  may comprise a number of LEDs  60  that is more or less than four. Similarly, it will be appreciated that the collective spectral output of each LED array  10  may or may not be the same as the spectral output of other LED arrays  10  of the anti-icing lamp assembly  5 . In other embodiments, the LED array  10  also may include one or more IR LED heat sources for the purpose of generating heat to defrost the cover  30 . Such IR heat sources can be controlled by the electronic circuit  15  separately from the lighting control only when defrosting is necessary to avoid wasting power. At least one additional embodiment of an IR LED heat source is described hereinbelow in connection with  FIG. 41 . 
     In certain embodiments and with reference now to  FIG. 5B , the LED array  10  may be implemented using a commercially available LED package  70 . The LED package  70  may be in the form of a surface-mount technology (SMT) component, for example, and comprise a number of LEDs  60  mounted onto a substrate  65 , a lens  75  disposed over the LEDs  60 , a heat sink (not shown) in thermal communication with the LEDs  60 , and a set of pins or leads  80  electrically connected to each LED  60 . In one such embodiment, for example, the LED package  70  may be implemented using an LED package known under the trade name of XLamp MC-E LED package available from Cree, Durham, N.C. 
     The LED array  10  may define a spatial radiation pattern having a central axis  85  about which light emitted by the LED array  60  is distributed in a generally symmetrical manner. With reference to  FIG. 5B , for example, the central axis  85  may be centrally located between the LEDs  60  and extend normally from the substrate  65 . In certain embodiments, the central axis  85  may coincide with a viewing angle of the LED array  10  (e.g., 0 degrees) at which the relative luminous intensity of the LED array  10  is at a maximum. 
       FIG. 6  is a cross-sectional view of the structure of a phosphor-conversion white LED lamp  11  that may be used in the LED array  10  of the anti-icing lamp assembly  5  discussed above with reference to  FIGS. 5A ,  5 B and the anti-icing lamp assembly  600  discussed below. The LED lamp  11  comprises a blue LED die  12  and a yellow phosphor material  14 . The LED die  12  is mounted in a cup  20  on a lead frame  18   b  and coated by the yellow phosphor material  14 . Gold wires  16   a ,  16   b  are bonded to the corresponding lead frames  18   a ,  18   b  to provide the electrical contact. The LED die  12  and the phosphor material  14  are packaged by a resin formed into the shape of an optical lens  23 .  FIG. 7  is a schematic diagram of the white LED lamp  11  shown in  FIG. 6  producing white light  24 . The white LED lamp  11  produces white light  24  by mixing the blue emission from the LED die  12  with the yellow fluorescence from the phosphor material  14 , which is excited by the blue emission of the LED die  12 , as shown in  FIG. 7 . A commonly used yellow phosphor material  14  is YAG phosphor, which has very high wavelength conversion efficiency, high thermal stability, high material toughness, and a low production cost. Recently, several other yellow phosphors have been developed. However, there is not yet a yellow phosphor better than YAG phosphor overall, in terms of cost, optical properties and stability. 
       FIG. 8  is a graphical depiction of a typical emission spectrum of a white LED using a YAG phosphor, such as the phosphor-conversion white LED lamp  11  shown in  FIGS. 6-7 , at a forward-bias current of about 20 mA. The EI Intensity in arbitrary units is shown along the vertical axis and Wavelength (nm) is shown along the horizontal axis. The correlated color temperature T cp  is 6500 K. The spectrum consists of two peaks  26 ,  28 , which correspond to the blue emission of the LED die at 460 nm and the yellow emission of the YAG phosphor at 555 nm, respectively. The full width at half maximum (FWHM) of the yellow emission is about 150 nm. Therefore, the spectrum of the white LEDs includes all visible wavelengths from blue to red. As a result, white LEDs have a high general color rendering index (Ra) of 85, which is equal to that of a tri-phosphor fluorescent lamp (Ra=85). This enables the use of white LEDs for general illumination. Unfortunately, the amount of luminescence in the red region of white LEDs is low. In order to enhance this red light, a red phosphor SrCaSiN: Eu can be added to a YAG white LED (Yamada M, Naitou T, Izuno K, Tamaki H, Murazaki Y, Kameshima M, and Mukai T, 2003 Japan J. App. Phys. 42L20 and Narukawa Y 2004 Opt. Photon News 15 24, the disclosures of each is herein incorporated by reference). As a result, CRI-No. 9, which shows color reproduction in the red region, was significantly enhanced from −2.5 to 62.6. Moreover, by using three phosphors (bluish-green, yellow and red), it is possible to obtain an Ra above 93, for all T cp  (Narukawa Y., Narita J., Sakamoto T., Yamada T., Narimatsu H., Sano M., and Mukai T., 2007 Phys. Status Solid at 204 2087, the disclosure of which is herein incorporated by reference). 
       FIG. 9  shows the spectrum of an ultra-high Ra white LED (UHR-white), with a T cp  of 5000 K. Intensity in arbitrary units is shown along the vertical axis and Wavelength (nm) is shown along the horizontal axis. The spectra of a CIE Standard Illuminates (D50) and a conventional white LED (T cp =5000 K), fabricated using only YAG phosphor, are also shown in  FIG. 9 . In UHR-white, the amount of luminescence in the blue-green and red regions was significantly enhanced compared with a conventional white LED. As a result, spectra of the high-Ra white LED were very similar to that of D50. Ra and CRI-No. 9 of the UHR-white were 97 and 96, respectively. Thus the color reproduction of this white LED was the highest of all white light sources. 
       FIG. 10  is a block diagram of the LED arrays  10  and controller circuit  15  of  FIG. 3  according to one embodiment. In various embodiments, the LED array  10  may comprise an LED  60  described in connection with  FIGS. 5A-5B  and  10  or the LED lamp  11  described in connection with  FIGS. 7-8 , without limitation. During operation of the anti-icing lamp assembly  5 , the controller circuit  15  functions as a current source to supply operating power to the LED arrays  10  in the form of an output voltage V OUT1  and an output current I LED . In certain embodiments and as discussed above, the lamp assembly  5  may comprise four LED arrays  10 , with each LED array  10  comprising four LEDs  60 . In the embodiment of  FIG. 10 , the LED arrays  10  and the LEDs  60  in each LED array  10  are connected in a series configuration to define a 16-LED string. Because the LED arrays  10  require constant current to produce a light output having a constant brightness, the controller circuit  15  may comprise a DC-DC controller  90 , such as a DC-DC switching controller, operating as a constant current source. In certain embodiments, the DC-DC controller  90  may be implemented using a commercially available DC-DC switching controller package, such as the LT3755 DC-DC switching controller available from Linear Technology, Milpitas, Calif. 
     In certain embodiments, the controller circuit  15  may be configured for bipolar operation to ensure that an operating voltage of proper polarity is applied to inputs of the DC-DC controller  90  irrespective of the polarity of the input voltage V IN  applied to inputs of the controller circuit  15 . In one embodiment, for example, the controller circuit  15  may comprise a bridge rectification circuit  95  for receiving an input voltage V IN  at either polarity and outputting a voltage of constant polarity to serve as the operating voltage of the DC-DC controller  90  (V′ IN ). The bridge rectification circuit  95  may comprise, for example, four diodes connected in a bridge rectifier configuration. In certain embodiments, the diodes of the bridge rectification circuit  95  may comprise relatively low voltage drops (i.e., Schottky diodes) such that power consumption of the circuit  95  is reduced, although it will be appreciated that other types of diodes may be used instead. The bridge rectification circuit  95  thus ensures that an operating voltage V′ IN  of proper polarity is applied to the DC-DC controller  90  regardless of the polarity of the input voltage V IN  applied to the controller circuit  15 , thereby simplifying installation of the anti-icing lamp assembly  5  and protecting against component damage that might otherwise result from a reversed polarity of the input voltage V IN . 
     In certain cases, and especially those in which the LED arrays  10  and LEDs  60  are connected in a series configuration, the forward voltage required to drive the LEDs  60  may exceed an available input voltage V IN . For example, the forward voltage required to drive the 16-LED chain of  FIG. 6  may range from about 45 to 70 VDC, while the nominal value of the input voltage V IN  may be approximately 14 or 28 VDC (e.g., in the case of aircraft lighting applications). Accordingly, in certain embodiments, the DC-DC controller  90  may be configured to operate in a boost mode whereby the output voltage V OUT1  of the controller circuit  15  is suitably increased above the operating voltage V′ IN  supplied to inputs of the DC-DC controller  90  via the bridge rectification circuit  95  (e.g., approximately 14 or 28 VDC) such that the output voltage V OUT  satisfies the forward voltage requirements of the LEDs  60  (e.g., 45 to 70 VDC). In order to accommodate unexpected fluctuations of V IN  from its nominal value, the controller circuit  15  may be configured to maintain a suitable output voltage V OUT1  over a range of input voltage V IN  values. In one embodiment, for example, the controller Circuit  15  may be designed to generate a suitable output voltage V OUT1  based on nominal input voltages of 14 or 28 VDC, but may nonetheless maintain a suitable output voltage V OUT1  for input voltages V IN  within a range of approximately 4.5 to 40 VDC. It will be appreciated that the values of V IN  and V OUT1  described above are provided by way of example only, and that embodiments of the controller circuit  15  may generally be configured to operate using different values of V IN  and V OUT  based on, among other things, available input voltages V IN , the number of LED arrays  10 , the number of LEDs  60  in each array, and the manner in which the LED arrays  10 /LEDs  60  are connected (e.g., series configuration, parallel configuration, or a combination thereof). According to various embodiments, for example, the DC-DC controller  90  may be configured to operate in a buck mode (e.g., in cases in which the forward voltage required to drive the LED arrays  10  is less than V IN ) or in a buck-boost mode (e.g., in cases in which V IN  may initially be larger than the forward voltage required to drive the LED arrays  10  but subsequently decreases below the required forward voltage, such as may occur in battery-powered LED applications). 
     According to various embodiments, the controller circuit  15  may comprise at least one control input for receiving a signal to selectively control the amount of current I LED  in the LEDs  60 , thus enabling dimmability of the LEDs  60 . In certain embodiments, such as those in which the DC-DC controller  90  is implemented using the LT3755 DC-DC switching controller, for example, the DC-DC controller  90  may comprise a first control input  100  to receive a pulse-width modulated (PWM) waveform (e.g., V PWM  in  FIG. 10 ) to control a switch duty cycle of the DC-DC controller  90  such that the output current I LED  may be modulated substantially between zero and full current based on a PWM dimming ratio of the PWM waveform. The PWM dimming ratio may be calculated as the ratio of the maximum PWM period to the minimum PWM pulse width and may have a maximum value of 1500:1, for example. In certain embodiments and as shown in  FIG. 6 , the controller circuit  15  may comprise a PWM controller  105  for outputting a user-controllable (e.g., using a potentiometer or jumpers coupled to the PWM controller  105 ) PWM waveform to the first control input  100  of the DC-DC controller  90 . In other embodiments, the PWM waveform may be supplied from a user-controllable PWM waveform source external to the anti-icing lamp assembly  5 . 
     In addition or as an alternative to the use of a PWM waveform to control output current I LED  via a first control input  100 , certain embodiments of the controller circuit  15 , such as those in which the DC-DC controller  90  is implemented using the LT3755 DC-DC switching controller, for example, may comprise a second control input  110  to control the amount of current I LED  in the LEDs  60  based on DC voltage signal V CTRL  applied to the second control input  110 . For example, when V CTRL  is maintained above a threshold value (e.g., 1.1 VDC), the current I LED  may be dictated by the combined resistances R LED  of the LEDs  60 , e.g., I LED  is about 100 mV/R LED . When V CTRL  is reduced below the threshold value, the current I LED  may be dictated by the values of both R LED  and V CTRL , e.g., I LED  is about (V CTRL −100 mV)/R LED . In accordance with this example, for a threshold value of 1.1 VDC, the current I LED  may be varied substantially between zero and full current by suitably varying V CTRL  between about 100 mVDC and about 1.1 VDC, respectively. In certain embodiments, the controller circuit  15  may comprise a voltage controller  115  for deriving a value of V CTRL  from another voltage present within the controller circuit  15  (e.g., V IN ). In one embodiment, for example, the voltage controller  115  may be implemented using a potentiometer to enable manual adjustment of V CTRL , and thus I LED , by a user. In another embodiment, voltage controller  115  may be implemented using a thermistor to automatically adjust V CTRL  based on a temperature sensed within the lamp assembly  5  ( FIG. 7B ). For example, an NTC (negative temperature coefficient) thermistor may be coupled to the second control input  110  such that decreasing thermistor resistance (indicative of increasing temperature) causes V CTRL  to decrease, thus decreasing I LED . Conversely, increasing thermistor resistance (indicative of decreasing temperature) may cause V CTRL , to increase, thus increasing I LED . In this way, if a temperature within the anti-icing lamp assembly  5  becomes excessive due to, for example, environmental conditions, the controller circuit  15  may compensate by reducing the output current L ED  to reduce the amount of heat dissipated by the LED arrays  10  and controller circuit  15 , thus maintaining the reliability and operating lifetime of the anti-icing lamp assembly  5 . 
     In embodiments in which the LED arrays  10  and LEDs  60  are connected in a series configuration, such as that of  FIG. 10 , it will be appreciated that failure of a single LED  60  may cause the failure of the entire LED chain if, for example, the LED fails in an open circuit mode. Accordingly, a failure of the LED chain due to an open LED mimics the failure of an incandescent filament. In order to provide a positive confirmation that a lack of output light is due to an open LED, the controller circuit  15  may comprise a fault indicator  120  to indicate the existence of this condition. In certain embodiments of the controller circuit  15 , such as those in which the DC-DC controller  90  is implemented using the LT3755 DC-DC controller, for example, the DC-DC controller  90  may comprise an open LED output  125  (e.g., an open-drain status output) that electrically transitions (e.g., pulls low) when an open LED fault is detected by the DC-DC controller  90 . The transition of the open LED output  125  may be used to control operation of the fault indicator  120 . In one embodiment, for example, the transition of the open LED output  125  may cause a driver circuit (not shown) of the controller circuit  15  to energize a low-power LED of the fault indicator  120  that is visible through the lens array  20  and cover  30  to provide a visual indication of the open LED fault. In another embodiment, the fault indicator  120  may not be a component of the anti-icing lamp assembly  5  and instead may be located remotely therefrom, such as on a dashboard or display that is visible to an operator. 
     According to various embodiments, the DC-DC controller  90  may be configured to turn off when the input voltage V IN  of the controller circuit  15  (or the input voltage V′ IN  of the DC-DC controller  90 ) falls below a pre-determined turn-off threshold and to subsequently resume operation when the input voltage V IN  rises above a pre-determined turn-on threshold. In one embodiment, for example, although it may be feasible to operate the controller circuit  15  using input voltage V IN  in a range of approximately 4.5 to 40 VDC, the controller circuit  15  may nonetheless be configured to turn off when the input voltage V IN  falls below 10 VDC (turn-off threshold), for example, and to subsequently resume operation when the input voltage V IN  rises to a pre-determined value above the turn-off threshold, such as 10.5 VDC (turn-on threshold), for example. In certain embodiments of the controller circuit  15 , such as those in which the DC-DC controller  90  is implemented using the LT3755 DC-DC switching controller, for example, the turn-off and turn-on thresholds may be programmed using an external resistor divider connected to a shutdown/undervoltage control input of the DC-DC controller  90 . In this way, when the voltage of the electrical power system falls below a pre-determined value (due to an electrical malfunction or low battery charge, for example), the electrical load represented by the DC-DC controller  90  and the LEDs  60  may be removed from the electrical power system. 
     Additional details of one embodiment of the controller circuit  15  for driving the LED array  10  is described in commonly assigned U.S. Patent Application Publication No. 2011/0043120 to Panagotacos et al and entitled “Lamp Assembly,” the disclosure of which is incorporated herein by reference. It will be appreciated that, in one embodiment, the controller circuit  15  may be used and/or configured to drive the phosphor-conversion white LED lamp  11  shown in  FIGS. 6-7 . 
     In one embodiment, the controller circuit  15  may comprise a control circuit  52  for controlling the defroster elements  51  of the lamp assembly  5 . Embodiments of defroster elements  51  include, without limitation, transparent electrically conductive coatings for glass substrates, resistive conductive elements for transparent substrates, exothermic deicing thermal energy systems, infrared thermal energy sources, heat sink thermal energy transfer systems, among others. In one embodiment, the control circuit  52  is configured to operate a switch  54  at an output portion of the DC-DC controller  90  in order to apply a voltage V OUT2  to the defroster element. Based on the type of defroster element  51  employed, the voltage V OUT2  may be employed directly to heat the cover  30  of the lamp assembly  5  or may used as a control signal to operate other devices, such as a pump, for example. In one embodiment, a feedback element  53  may be provided on the cover  30  to provide a feedback signal  57  to the control circuit  52 . In various embodiments, the feedback element  53  may be any type of sensor capable of detecting condensation, fog, ice, rime, frost, and/or snow that may develop on the clear cover  30  and/or temperature of the clear cover  30 . In operation, the control circuit  52  activates the output switch  54  to couple V OUT2  to the defroster element  53  in response to the feedback signal  57 . Examples of defroster elements  51  and feedback elements  53  are described hereinbelow. It will be appreciated that the controlling the defroster elements  51  and feedback elements  53  using conventional circuits is within the knowledge of one skilled in the art. 
       FIGS. 11A ,  11 B, and  11 C are front, back and perspective side views, respectively, of the base  25  of  FIG. 3 . The base  25  may be generally circular in shape when viewed from the front and back and comprise a front surface  195  to receive the LED arrays  10  and controller circuit  15  (e.g., via the substrate  40 ) and the lens array  20 . The base  25  may also comprise a back surface  200  opposite the front surface  195  that is structured to be removably received by a lamp holder, such as, for example, an incandescent lamp holder. To maintain a suitable temperature of the anti-icing lamp assembly  5  during its operation, the base  25  may be configured to receive and dissipate heat generated by the LED arrays  10  and controller circuit  15 . The base  25  may therefore comprise a material having a suitably high thermal conductively, such as, for example, aluminum or copper. It will be appreciated, however, that the base  25  may additionally or alternatively comprise other materials, such as thermoplastic, for example. In certain embodiments, the base  25  may be formed as a single element using, for example, a die casting or injection molding process. The front surface  195  may be generally planar and define a number of openings  205  to retain fasteners (e.g., screws) for attaching the LED arrays  10 , the controller circuit  15  and the lens array  20  to the front surface  195 . The base  25  may additionally comprise a lip  210  disposed about a periphery of the front surface  195  to receive the cover  30 . The lip  210  may define a number of openings  215  to retain fasteners (e.g., screws) for attaching the cover  30  to the lip  210 . The lip  210  may additionally define a groove  220  to receive a gasket  225  ( FIG. 3 ), such as, for example, an elastomeric O-ring gasket. In the assembled state of the anti-icing lamp assembly  5 , the gasket  225  be disposed between and compressed by the cover  30  and the base  25  to form a weather-tight barrier between the cover  30  and the base  25 . 
     With reference to  FIG. 11C , the back surface  200  of the base  25  may comprise a generally outward-curving geometry, such as, for example, a circular paraboloid geometry, that is suitably dimensioned for removable receipt by a lamp holder designed to accommodate a lamp having a standard shape and size. In certain embodiments, for example, the back surface  200  may be dimensioned for removable receipt by a conventional incandescent lamp holder designed to accommodate a parabolic aluminum reflector (PAR) lamp, such as, for example, a PAR-36 lamp, a PAR-56 lamp or a PAR-64 lamp. The back surface  200  may also define a collar  230  disposed about a periphery of the back surface  200  adjacent the lip  210 , at least a portion of which is configured for removable engagement by a corresponding portion of the lamp holder when the anti-icing lamp assembly  5  is received therein. In certain embodiments, the engaged portion of the collar  230  may be suitably smooth to provide a weather-tight seal between the collar  230  and an opposing gasket of the lamp holder. The back surface  200  may additionally define a key  235  adjacent the collar  230  to be removably received into a corresponding slot of the lamp holder, thereby ensuring proper rotational alignment of the anti-icing lamp assembly  5  with the lamp holder. 
     In certain embodiments and as shown in  FIGS. 11B and 11C , the front and back surfaces  195 ,  200  may define a plurality of close-ended openings  240  that substantially increase the surface area of the surfaces  195 ,  200 . The collective surfaces of the openings  240  thus provide a cooling structure to increase the heat-dissipative properties of the base  25 . 
     As shown in  FIGS. 11A and 11B , the base  25  may define a set of apertures  245  extending between and connecting the front and back surfaces  195 ,  200  of the base  25  in order to accommodate the set of electrical connectors  36  of the anti-icing lamp assembly  5  ( FIG. 3 ). The apertures  245  may be located such that, in the assembled state of the anti-icing lamp assembly  5 , openings of the apertures  245  on the front surface  195  are respectively aligned with electrical input connection points (e.g., openings  55 ) of the substrate  40 . Additionally, openings of the apertures  245  may define a non-circular shape (e.g., a hexagon) to prevent rotation of similarly-shaped electrical connectors  36  within the apertures  245 . 
       FIGS. 12A and 12B  are perspective views of one of the set of electrical connectors  36  of the anti-icing lamp assembly  5  according to one embodiment. Each connector  36  may comprise a conductor  255  in the form of metal rod defining an opening  260  at each end configured to retain a fastening member (e.g., a screw). The connector  36  may further comprise an electrical insulator  265  (e.g., a nylon resin) formed on an exterior surface of the conductor  255  such that each end of the conductor  255  and its respective opening  260  are the only exposed portions of the conductor  255 . The electrical insulator  265  may define a shape that conforms to the shape of the apertures  245  defined by the base  25 . For example, as shown in  FIGS. 8A and 8B , the electrical insulator  265  may define a hexagonal shape that conforms to the hexagonal shape of the apertures  245  of  FIGS. 7A and 7B . 
     In the assembled state of the anti-icing lamp assembly  5  and with reference to  FIG. 2 , the electrical connectors  36  may respectively extend through the apertures  245  of the base  25 , with a first end of each connector  36  being electrically coupled to the controller circuit  15  by, for example, a fastener (e.g., screw, bolt, rivet, snap) that extends through a corresponding opening  55  of the substrate  40  to be retained in an opening  260  of the electrical connector  36 . In this manner, the first end of each electrical connector  36  may be electrically coupled to the controller circuit  15  via the conductive periphery of the openings  55 . A second end of each electrical connector  36  may be accessible from the back surface  200  of the base  25  and be electrically connected to an electrical power system external to the anti-icing lamp assembly  5  using, for example, a fastener (e.g., a screw, bolt, rivet, snap) retained in an opening  260  of the electrical connector  36 . As will be appreciated from  FIG. 2 , the conductor  255  of each electrical connector  36  is electrically insulated from the base  25  by virtue of the electrical insulator  265  formed on the exterior surface of the conductor  255 . In certain embodiments, a sealant and/or adhesive material may be disposed between each electrical insulator  265  and the inner surface of its corresponding aperture  245  to provide a weather-tight barrier between the electrical connectors  36  and the base  25  and/or to ensure a suitably strong mechanical bond therebetween. 
       FIGS. 13A ,  13 B, and  13 C are front, back and perspective side views, respectively, of the cover  30  of  FIG. 3 . As shown, the cover  30  may be in the general shape of a disc and comprise a convex front surface  270  and a concave back surface  275 . It will be appreciated that one or more of the surfaces  270 ,  275  may alternatively comprise another suitable surface profile, such as a flat profile, for example. The cover  30  may be integrally formed from a suitably light-transmissive material, such as a clear polycarbonate material, for example. A diameter of the cover  30  may be such that, in the assembled state of the anti-icing lamp assembly  5 , a peripheral portion of the back surface  275  opposes the lip  210  of the base  25 . As discussed above, the gasket  225  may be disposed between and compressed by the cover  30  and the base  25 , thereby forming a weather-tight barrier therebetween. With reference to  FIG. 12C , the cover  30  may comprise standoffs  280  formed on a periphery of the back surface  275  that correspond in number to the openings  215  of the lip  210 . Each standoff  280  may define an opening  285  therethrough that, in the assembled state of the anti-icing lamp assembly  5 , aligns with a corresponding opening  215  of the lip  210 . The cover  30  may thus be attached to the base  25  using, for example, a faster (e.g., a screw, bolt, rivet, snap) that extends through each opening  285  from the front surface  270  to be retained in the corresponding opening  215  of the lip  210 . 
     According to various embodiments, the lamp assembly  130  may comprise one or more diffuser optics for modifying a distribution of light emitted by the TIR lens  130 . In certain embodiments, a diffuser optic may be formed on the surface of the exit face (not shown) of each TIR lens  130 , as shown in  FIG. 14A , or on a surface of the cover  30 . In other embodiments, diffuser optics may be formed as separate elements. As shown in  FIG. 14B , for example, diffuser optic  290  may be formed as an element that is separate from the TIR lenses  130 . The diffuser optic(s)  290  may be configured to shape light emitted from the TIR lens  130  to conform to a particular shape or a predetermined field-of-view. As shown in  FIGS. 14A and 14B , for example, diffuser optics  290  operate to spread the light distributed from the exit face  180  of the TIR lens  130 , thus increasing the angular spectrum of illumination. In certain embodiments, the diffuser optic(s)  290  may be implemented using a diffuse glass or plastic. In other embodiments, the diffuser optics(s)  290  may be implemented using a holographic diffuser, otherwise known as a kinoform diffuser. Examples of holographic diffusers are described in “An Overview of LED Applications for General Illumination” (Conference Proceedings Paper), David G. Pelka, Kavita Patel, SPIE Vol. 5186, November 2003; and “Keen Forms of Kinoforms—Kinoform-based Diffusers Help Lighting Designers Leverage Unique LED Advantages,” David G. Pelka, OE Magazine, Vol. 3 No. 10, p. 19, October 2003, both of which are incorporated herein by reference. In other embodiments, the diffuser optic(s)  290  may be formed using microlens arrays comprising multiple lenses formed in a two-dimensional array on a supporting substrate, such as those manufactured by Rochester Photonics Corp., Rochester, N.Y. 
     LEDs by their very nature are extremely small, an almost perfect thermodynamic light source, and are easily integrated with optical systems. The ability of any optical system to gather up the light from any source is directly proportional to the size of the optical system relative to the size of light source. Consequently LEDs enjoy a fundamental advantage over incandescent lamps, fluorescent lamps, and high-intensity discharge sources because of LEDs&#39; intrinsically small size and the fact that they do not require a large glass envelope as many of their competitive light sources do. 
     Optics can broadly be broken down into the two fields of imaging and non-imaging optics. Imaging optics has been around for well over 300 years and is the optics of parabolas, ellipses, thick lenses, thin lenses and Fresnel lenses. The one characteristic that all of these optical technologies have in common is that they form images of objects (see  FIG. 3 ) and are frequently used in such things as cameras, movie and 35 mm slide projectors, automobile headlights, flashlights, eyeglasses, etc. As the lighting industry developed over the past 200 years it was natural to incorporate this already existing imaging optical technology into new lighting systems. However, a little thought experiment will show that imaging optics is far from optimum. Consider for the moment the simple example of a parabola used in a flashlight to project a beam. Depending upon the depth of the parabola, only about 40% of the light leaving the light bulb will reflect off the parabolic mirror be collimated and projected into the beam. The other 60% of the light leaves the flashlight in an unguided way and is typically not useful and in many applications considered a negative attribute known as glare. This is particularly true for automobile headlights. It is obvious that the optimum optical system should completely surround the source, gathering up every photon leaving the source and delivering those photons into a prescribed field of view or flux pattern, regardless of whether an image is formed or not. This is exactly what the field of non-imaging optics seeks to do as shown in  FIG. 8 . 
     The field of non-imaging optics relaxes the constraint that an image be formed and in so doing allows the resulting optical system to be both much more efficient and compact than imaging optical systems. The field of non-imaging optics first got its start in the United States in the 1930s and &#39;40s at lighting companies such as General Electric. However, it was not until the 1970s when Roland Winston (W. T. Welford, R. Winston, The Optics of Nonimaging Concentrators, Academic Press, New York, 1978 and W. T. Welford, R. Winston, High Collection Nonimaging Optics, Academic Press, New York, 1989, the disclosure of each is herein incorporated by reference) of the Physics Department of the University of Chicago and W. T. Welford of the Physics Department of University of London, began formulating the principles, theory and mathematics of non-imaging optics that the field began to gain recognition. One of its first applications was to the field of solar energy concentration for both photovoltaic and solar thermal systems. Subsequently, applications such as fiber-optic couplers, backlights for liquid crystal displays, and sensors for high-energy particle physics all came to benefit from the increased optical efficiency and compactness that non-imaging optics could supply. In fact, it is not unusual for non imaging optics to have increased efficiencies from 50%-150% over corresponding imaging optical systems and at the same time to be a much more compact, typically 4 to 12 times more compact, than the corresponding imaging optical system it replaces. 
       FIG. 15  is a cross-sectional view of a non-imaging lens called a total internal reflection (TIR) lens  300 , according to one embodiment. A radiant energy redirecting system may comprise a radiant energy transmitting body structure, where the structure comprises multiple elements, each of which acts as a radiant energy redirecting module, having on its cross-sectional perimeter an entry face to receive incidence of the energy into the interior of the perimeter, an exit face to pass the energy to the exterior of the perimeter in a direction towards the reverse side of the body from the side of the incidence. A TIR face angled relative to the entry and exit faces to redirect towards the exit face the radiant energy incident from the entry face. The body structure generally redirecting incident radiant energy towards a predetermined target zone situated apart from and on the reverse side of the body relative to the side of the incidence. The lens structure associated with at least one of the faces for redirecting radiant energy passing between the entry and exit faces via a TIR face. 
     As shown in  FIG. 15 , the axis of the annular, radiant energy transmitting body  340  appears at  351 . The body has multiple annular facets  342  to  346  which are generally concentrically arranged, but having tips  342   d  to  346   d  progressively closer to plane  350  normal to axis  351 . The face  342   a  of the facet  342  is convex toward face  342   b ; and the face  342   b  is concave toward the face  342   a  in the section shown. This relationship obtains for other facets, as shown. An LED  358  is located at the intersection of plane  350  with axis  351  and emits light rays toward the body  340 . A ray  353  passes through the face  342   a , is refracted toward the TIR face  342   b  and is reflected toward and passes through the upper flat face  348 . See also the ray  352  passing through the face  343   a , reflecting at the TIR face  343   b , and passing through the upper face  348   a , angled as shown. All rays passing upwardly beyond the faces  348  and  348   a  are collimated. The transverse width of the body  340  may be from about 0.12 to about one inch, for example, and the transparent body  340  may consist of molded plastic material. A refractive section without facets appears at  319 . Smaller ratios of lens diameter to LED size may have outermost facets large, and successively inward facets smaller, in order to have a higher lens profile and better collimation curved facets are necessary for. 
     The TIR lens  300  captures almost 100% of the light leaving the LED light source and yet has an f #&lt;0.25. Recall that the definition of the f # of a lens is the ratio of its focal length divided by the aperture (diameter) of the lens. Imaging lenses typically have f #s in the range of 1 to 5, which implies that they are of 4 times to 20 times less compact than the TIR lens. The LED source located at the point  358  and emits in a hemispherical pattern and there is refraction at the entry face of the TIR facet as with the ray  345  and total internal reflection at the back of the facet, followed by refraction as the ray exits the top of the lens in a collimated series of rays. The TIR lens  300  is a combination of both an imaging and non-imaging lens. It is imaging in the most central part of the lens as the ray  319  illustrates, but all of the facets to the right and left of the central part of the TIR lens  300  are non-imaging in so far as the TIR face is a mirror which reverses left for right and thus eliminates the ability to form an image. Many times a TIR lens is confused with a Fresnel lens, which also has facets, but is an imaging lens and which only uses refraction on the entry and exit facets to form a beam and image of the source. 
     To understand the importance of completely surrounding the light source and the improved candlepower of the resulting lamp, we must undertake a direct comparison of the TIR lens  300  with the most common technology previously used for incandescent landing lights, that of the parabolic reflector.  FIG. 16  shows an incandescent landing light  400  comprising a parabolic reflector  410 . As shown in  FIG. 16 , of the approximate 3800 lumens emitted by the GE 4553 landing light lamp  402  that only 2200 lumens or about 42% of the emitted flux  406  (shown in solid line) actually strikes the reflector  404  and thus results in the directed beam  406 . About 58% of the emitted flux  408  (shown in broken line) goes out and never strikes the reflector and for the most part results in unwanted glare. Similarly if one tries to use a lens or its thin lens equivalent, a Fresnel lens, only captures 20% (for an f#1 lens) of the light leaving a hemispherical source such as an LED, this stems from the solid angle that the lens subtends at the source. With reference now to both  FIGS. 15 and 16 , the TIR lens  300 , on the other hand, gathers up all the light from the hemi-spherically emitting LED  358  source and puts that light into the beam. Now the optical efficiency of the parabolic reflector  410  and the TIR lens  300  are similar at about 80% each. For the parabolic reflector  410  this stems from the reflectance of the reflector being about 90% as well as a 90% transmission through the front glass window  412  is about 90% (Fresnel reflection losses of about 10% from the two glass interfaces), whereas the TIR lens  300  has scattering from the facet tips  342   d - 346   d  as well as Fresnel losses from the entrance and exit facet surfaces. Accordingly, the TIR lens  300  can create the same candlepower into the outgoing beam with about 50% of the input flux that the parabolic reflector requires. The TIR lens  300  has quite a significant advantage when using LEDs as the light source compared to parabolic reflectors or Fresnel lenses. 
     One of the issues frequently overlooked in beam forming is the uniformity in the beam cross section. By examining  FIGS. 15 and 16 , it can be seen that the intensity of the light striking the parabolic reflector  410  or the TIR lens  300  falls off as 1/R 2  as one moves away from the source lamp  402   0   r  LED  358  in accordance with the conservation of energy theory. If one imagines spheres surrounding the source of increasing radii R, then the intensity of the radiation must fall off as 1/R 2  as the area of the sphere is increasing as R 2 . This results in non-uniformity of the beam of ratios of 4:1, in other words, the central region of the beam will be 4 times as intense as the outer region of the beam. 
     To overcome this defect, the TIR lens  300  uses a lens to purposely distort the intensity of the light leaving the LED  358  source, affectionately called a deviator (mushroom) lens  502  as shown in  FIGS. 17 and 18 , because of its mushroom like shape. The mushroom deviator lens  502  purposely sends more light to the far-reaches of the lens facets, thus homogenizing the overall beam pattern. 
     Light sources without envelopes, such as light emitting diodes (LEDs), can benefit from a mushroom-shaped light-deviating (deviator) lens  502  as shown in  FIGS. 17 and 18 .  FIG. 17  shows one embodiment of an m-TIR lens  500  comprising a mushroom-shaped deviator lens  502  and a TIR lens  504 . As shown in  FIG. 17 , an LED  506  light source, with typical power-delivery wire  508  and planar reflector  510 , is embedded in the mushroom-shaped deviator lens  502 . The mushroom-shaped deviator lens  502  is shaped to cause the TIR lens  504  to have uniform output at a light exit face  512 . For the sake of accommodating differential thermal expansion from heat generated by the operation of the LED, the mushroom-shaped deviator lens  502  may be made of an elastomeric material such as optical-grade silicone. Since the LED  506  typically has the shape of a cube, their output is greater in the direction of the cube diagonal than in the direction perpendicular to the cube face. To compensate, the mushroom-shaped deviator lens  502  may have somewhat different cross sections in these two directions. 
     In summary, the mushroom-shaped deviator lens  502  is a powerful way to control the output of a TIR lens  504 . Improved collimation is provided because the entire beam will have the same angular spread, resulting in improved beam propagation over conventional parabolic reflectors, which have very non-uniform output. This allows the use of holographic diffusers and lenticular lenslet arrays to produce tailored output intensity, because the uniform output  514  ( FIG. 18 ) of the TIR lens  504  is useful to the use of these devices, which can be made integral with the output face  512  of the TIR lens  504 . This enables compact LED  506  light sources with specifically tailored output to be available for a variety of applications, including the anti-icing lamp assembly  5  described herein. 
       FIG. 18  shows one embodiment of the mushroom-shaped deviator lens  502  shown in  FIG. 17  in combination with the TIR lens  504  denoted as m-TIR lens  500  with computer generated ray tracing  516 . As shown, by examining the computer generated ray tracing  516 , it can be seen that almost perfect uniformity in the beam cross section as a result of the mushroom-shaped deviator lens  502  pre-distortion of the light leaving the LED light source  506 . 
     A modeled performance of an m-TIR LED based lamp (e.g., a lamp employing the m-TIR lens  500  shown in  FIGS. 17 and 18 ) versus a GE Par 46 model 4553 parabolic reflector lamp. To put many of these above noted features of the m-TIR lens  500  assembly into a practical setting, let us consider how we would expect the m-TIR LED lamp to compare to a typical taxi light used in large commercial aircraft, for example, the GE PAR 46 model 4553 parabolic reflector lamp. The LED-chosen for the source is a Cree XM-L LED powered at 3,000 mA and 3.6 Vdc (10.8 watts) which produces a total of 698 lumens out of the LED source as measured in the integrating sphere in Teledyne&#39;s Micro-Electronics Photonic Laboratory. Recall that the TIR lens  504  will allow about 82% of this light into the beam, thus 572 lumens into the total beam. Now the computer modeled performance of the m-TIR lens  500  combination as shown in  FIG. 18  is given by the computer modeled curves  520  in  FIG. 19 .  FIG. 19  is a computer modeled performance of an m-TIR lens assembly where the solid line  522  is the relative intensity for degrees off-axis and the dotted line  524  is cumulative. Percentage is shown along the vertical axis and angular half width in degrees is shown along the horizontal axis. From  FIG. 19  the maximum beam candlepower defined as the lumens per steradian at the 90% point of the intensity curve  528  can be calculated. The 90% curve shows that the angular half width is 2.42° while the cumulative flux  528  associated with that angular width is 38%. So our computer modeled candlepower is: 
         I= 0.38×572 lumens/Ω, where Ω the solid angle subtended=2π(1−cos 2.42°=0.0056 str.
 
         I= 38,814 cd (candel power). 
       FIG. 20  illustrates a lamp assembly comprising a plurality of m-TIR lenses  500  according to one embodiment. As shown in  FIG. 20 , seven m-TIR lens  500  assemblies can fit in a GE Par 46 model 4553 parabolic reflector lamp assembly  530 . Accordingly, a total candle power of approximately I total =7×38,814=271,700 candle power can be expected. 
     From GE&#39;s specification sheet, the model 4553 PAR 46 lamp assembly with a conventional lamp (e.g., lamp  402   FIG. 16 ) should produce 300,000 maximum beam candlepower at 28V while consuming 250 watts. 
     The Cree XM-L LED is currently rated at 100 lumens/watt when powered at 1500 mA and 3.0 Vdc, with 150 lumen/watt expected to be available in the market over the next 12-18 months. Even with today&#39;s LED rating, however, Teledyne Micro-Electronics modeled m-TIR LED lamp comes within 10% of the performance of the GE PAR lamps for large aircraft. If one considers that the Teledyne LED lamp consumes approximately 175 watts less power (75.6 watts vs. 250 watts), while the GE lamp is rated at a nominal 25 hr lifetime while the LED lamp should have a rated lifetime of a minimum of 10,000 his and perhaps as much as 30,000 hrs. This implies drastically less maintenance for the airline companies and corresponding dramatic cost savings. In addition, pilot&#39;s visual acuity is expected to be enhanced as a result of their night time scotopic vision being better aligned with the bluer light emitted by LED light sources as compared to the incandescent or halogen based lamps. Thus, LED lamps with sophisticated optics like Teledyne Micro-Electronics has proposed make a compelling story, indeed, and should come to replace all the incandescent and halogen based lamps used in the aircraft industry over the near future. 
     Having described one embodiment of an anti-icing lamp assembly  5  generally, the description now turns to various embodiments of defroster elements that can be adapted and configured to operate with various embodiments of the anti-icing lamp assembly  5 . The defroster elements embodiments include, among others, transparent electrically conductive coatings for glass substrates, resistive conductive elements for transparent substrates, exothermic deicing thermal energy systems, infrared thermal energy sources, heat sink thermal energy transfer systems. The operation of each of the defroster elements described hereinbelow may be controlled by various embodiments of a defroster controller circuit. In one embodiment, the defroster controller circuit may be incorporated into the controller circuit  15 , whereas in other embodiments the defroster controller circuit may be separately implemented from the controller circuit  15 . In various embodiments, the defroster controller circuit may be configured to receive an activation input or may receive a feedback control signal to automatically activate the defroster elements when temperatures fall below a predetermined temperature (e.g., 32° F.) or when sensed environmental conditions are conducive to condensation, fog, rime, frost, snow, or ice forming on the exterior surface of the cover. Examples of environmental conditions that may be monitored by the aircraft control system include outside temperature, wind speed, humidity, barometric pressure, aircraft speed, and the like. The scope of the present disclosure, however, is not limited in this context. 
       FIGS. 21 ,  22 , and  23  illustrate an anti-icing lamp assembly  5 A comprising a transparent electrically conductive coating according to one embodiment. In one embodiment, the anti-icing lamp assembly  5 A comprises an optically transparent cover  30  comprising a substantially transparent electrically conductive coating  101  formed on the optically transparent cover  30 . One type of electrically conductive coating  101  that may be applied to the glass cover  30  is known under the trade name “TEC Glass” available from Pilkington Specialty Glass Products of Toledo, Ohio. The transparent electrically conductive coating  101  formed on the glass cover  30  substrate is a thin pyrolytic film that can be directly electrically heated to clear or evaporate condensation or fog and thaw or deice rime, frost, snow, or ice that may develop on the clear cover  30  portion of the anti-icing lamp assembly  5 A, for example. Those skilled in the art will appreciate that a pyrolytic coating is a thin film coating that can be applied at high temperatures and deposited onto a glass surface during a process known in the art as a float glass process, where a sheet of glass is made by floating molten glass on a bed of molten metal, typically Tin (Sn), although lead and various low melting point alloys have been used in practice. This method provides a uniform sheet thickness and very flat surfaces. The float glass process is also known as the Pilkington process, named after the British glass manufacturer Pilkington, which pioneered the technique. As shown more clearly in  FIG. 22 , the microscopically thin, durable pyrolytic film coating  101  can be applied to an exterior surface  102  of the glass cover  30  using chemical vapor deposition (CVD) processes, among other processes. 
     In one embodiment, the pyrolytic coating  101  is a tin oxide (SnO) coating applied to the exterior surface  102  of the glass cover  30  using a CVD process. In one embodiment, Indium-Tin-Oxide (InSnO) or Tin-doped Indium-Oxide can be used as the pyrolitic coating  101 . Indium Tin Oxide (ITO, or Tin-doped Indium Oxide) may be formed of a solid solution of Indium(III) Oxide (In2O3) and Tin(IV) Oxide (SnO2), typically 90% In2O3, 10% SnO2 by weight. It is transparent and colorless in thin layers while in bulk form it is yellowish to grey. In the infrared region of the spectrum it acts as a metal-like mirror. Indium-Tin-Oxide is one of the most widely used transparent conducting oxides because of its two chief properties, its electrical conductivity and optical transparency, as well as the ease with which it can be deposited as a thin film. As with all transparent conducting films, a compromise must be made between conductivity and transparency, since increasing the thickness and increasing the concentration of charge carriers will increase the material&#39;s conductivity, but decrease its transparency. Thin films of Indium-Tin-Oxide are most commonly deposited on surfaces by electron beam evaporation, physical vapor deposition, or a range of sputter deposition techniques. 
     The Tin-Oxide (SnO) coating or Indium-Tin-Oxide coating may be applied in desired thicknesses to produce a visible transmission of light from about 80% to greater than about 90% and an electrical sheet resistance of about 6.0 to 8.0 Ohms/sq. (Ohms-per-square) to about greater than 250 Ohms/sq. Accordingly, an electrical current may be applied to the pyrolytic coating to generate heat and prevent ice from forming on the exterior surface  100  of the cover  30 . Sheet resistance is a measure of resistance of thin films that are namely uniform in thickness. It is commonly used to characterize materials made by semiconductor doping, metal deposition, resistive paste printing, and glass coating. Examples of these processes include, without limitation, doped semiconductor regions (e.g., silicon or polysilicon), resistors screen printed onto the substrates of thick-film hybrid microcircuits, and the float glass process, among others. 
     In one embodiment, a first pair of electrically conductive electrode pads  104 ,  106  may be formed on opposite sides of the exterior surface  102  of the cover  30 . The controller circuit  15  is electrically coupled to the electrode pads  104 ,  016  through electrically conductive wires  108 ,  110  coupled to the substrate  40 , or pogo pins as shown in connection with  FIGS. 32-36 , for example. The controller circuit  15  can apply a suitable electrical voltage and/or current can be applied to the electrode pads  104 ,  106  via the electrically conductive wires  108 ,  110 . When a voltage is applied to the electrode pads  104 ,  106 , an electrical current is generated through the resistive pyrolytic coating  101 , which heats the cover  30  to evaporate condensation or fog and thaw frost, snow, or ice on the cover  30  of the lamp assembly  5 A, for example. In the embodiment illustrated in  FIGS. 21 ,  22 , and  23 , the electrical current conducted across the sheet resistance of the coating  101  heats the exterior surface  102  of the cover  30 , thus minimizing the amount of energy required to heat the cover  30 . In other embodiments, for completeness of disclosure, the coating  101  may be applied to an interior portion  111  of the cover  30 . In such embodiment, the heat would be transferred through the glass substrate of the cover  30 , which has poor thermal conduction properties. 
     In one embodiment, the electrode pads  104 ,  106  may be formed as electrically conductive bus bars. The bus bars may be screen printed onto opposing sides of an exterior or interior surface  102 ,  111  of the cover  30  prior to the application of the coating  101 . The bus bars may be screen printed using electrically conductive inks or pastes, such as, for example, Palladium Silver, among other electrically conductive inks or pastes. In other embodiments, the bus bars may be formed of electrically conductive adhesive decals applied to the coating  101  and electrically coupled to the energy source via to the electrode pads  104 ,  106  and corresponding conductors  108 ,  110 . In various embodiments, the electrically conductive adhesive decals may include conductive adhesives, inks, foil, tape, transfer tape, among others. The electrode pads  104 ,  106  are configured to receive an electrical voltage and/or current, which is converted to an electrical current through the sheet resistance of the coating  101 . If the bus bars are formed on the interior surface  111  of the cover  30  an electrical connection may be provided to the coating  101  though the cover  30 . 
     The electrically conductive wires  108 ,  110  are connected on one end thereof to the respective electrode pads  104 ,  106  and on another end are coupled to the energy source of the anti-icing lamp assembly  5 A, which, in one embodiment, is the controller circuit  15  located on the substrate  40 . In one embodiment, the electrically conductive wires  108 ,  110  may be connected to the electrode pads  104 ,  106  and/or the substrate using any suitable electrical connection such as, for example, solder, weld, crimp, clamp-type pressure connector, blade connectors, ring and spade connectors, slotted connectors, plug and socket connectors, terminal blocks, wire nuts, and the like. In one embodiment, the electrically conductive wires  108 ,  110  may be fed through an aperture  103  formed on the lens array  20  substrate, for example. In one embodiment, the output of the controller circuit  15 , which is used to supply power to the LED array  10 , can be adapted to also apply a voltage to the electrode pads  104 ,  106  via the electrically conductive wires  108 ,  110 , respectively. In other embodiments, a separate defroster controller circuit may be employed to apply the voltage to the electrode pads  104 ,  106 . 
     In one embodiment, the controller circuit  15  applies a voltage and/or current to the electrode pads  104 ,  106  in an open loop manner without any feedback. In various other embodiments, the controller circuit  15  applies a voltage and/or current to the electrode pads  104 ,  106  in response to a signal from a feedback element  153 . The feedback element  153  is electrically coupled to electrically conductive electrode pads  113 ,  117 , which are electrically coupled to the controller circuit  15  through the electrically conductive wires  107 ,  109 . In various embodiments, the feedback element  153  may be any type of sensor capable of detecting condensation, fog, ice, rime, frost, and/or snow that may develop on the clear cover  30  and/or temperature of the clear cover  30 . 
     In one embodiment, the feedback element  153  may comprise a solid state optical transducer probe available for aviation purposes. It has no moving parts, is completely solid and its principle of operation is entirely optical. The solid state optical sensor may be located on the interior portion  111  of the cover  30  and uses un-collimated light to monitor the opacity and optical refractive index of the substance on the probe. It may be de-sensitized to ignore a film of water. The device works as a combined optical spectrometer and optical switch. A change in opacity registers as rime ice. A change in refractive index registers as clear ice. Optical components are made of acrylic glass, which is the material used for aircraft covers  30 . The wavelength of the optical transducer&#39;s excitation light is not visible to the human eye so as not to be mistaken for any kind of navigational running light. 
     In another embodiment, the feedback element  153  may be a solid state temperature sensor, including, for example, thermocouples, resistance temperature detectors (RTDs), thermistors. In one embodiment, the temperature sensors may be fabricated using state-of-the art thin film processing techniques. Those skilled in the art will appreciate that a thermocouple is a device consisting of two different conductors (usually metal alloys) that produce a voltage, proportional to a temperature difference, between either end of the two conductors. An RTD is a sensor used to measure temperature by correlating the resistance of the RTD element with temperature. Most RTD elements comprise a length of fine coiled wire wrapped around a ceramic or glass core. The element is usually quite fragile, so it is often placed inside a sheathed probe to protect it. Accordingly, it can be embedded in the cover  30  at the time of fabrication. The RTD element is made from a pure material whose resistance at various temperatures has been documented. The material has a predictable change in resistance as the temperature changes; it is this predictable change that is used to determine temperature. As they are almost invariably made of platinum, they are often called platinum resistance thermometers (PRTs). A thermistor is a type of resistor whose resistance varies significantly with temperature, more so than in standard resistors. The word is a portmanteau of thermal and resistor. Thermistors are widely used as inrush current limiters, temperature sensors, self-resetting overcurrent protectors, and self-regulating heating elements. Thermistors differ from resistance temperature detectors (RTD) in that the material used in a thermistor is generally a ceramic or polymer, while RTDs use pure metals. It will be appreciated, the in one embodiment, the feedback element  153  may comprise a combination of the solid state ice sensor and the temperature sensor operating simultaneously or intermittently, without limitation. 
     In one embodiment, the controller circuit  15  is electrically coupled to the feedback element  153  through the electrically conductive wires  107 ,  109 , which may be fed through the aperture  103  formed on the lens array  20  substrate, for example. Depending on the type of feedback element  153 , additional electrically conductive wires may be provided to couple the feedback element  153  to the controller circuit  15 . Accordingly, in operation, the controller circuit  15  monitors the feedback element  153  and when it detects a signal indicative of condensation, fog, ice, rime, frost, snow, ice, and/or ice on the clear cover  30  and/or the temperature at the clear cover  30 , the controller circuit  15  applies a voltage and/or current to the electrode pads  104 ,  106 . 
     In one embodiment, heat may be conducted to the cover  30  from the lens array  20 . This may be accomplished by physically contacting the surface of the lens array  20  to the bottom of the cover  30  such that heat generated by the LEDs from the LED array  10 . This implementation requires a suitable thermal conductivity of the cover  30 . 
     In various embodiments, a film suitable for use as the coating  101  on the glass cover  30  substrate may be formed of various compositions and thicknesses applied onto a glass substrate to produce a glass having a suitable sheet resistance in Ohms-per-square to generate enough thermal energy when an electrical current is conducted through the film to heat the glass and prevent the development of ice on the glass substrate without substantially affecting the light transmittance properties of the glass. The film composition may comprise tin-oxide or niobium doped tin oxide. 
     Such coatings  101  may be produced on glass substrates through a sputter coating (soft coat) or preferably, through a pyrolytic process, for example chemical vapor deposition. Typically, glass produced through a pyrolytic process yields a coating  101  which is less easily damaged and less likely to deteriorate under exposure to air. 
     Coatings  101  with sheet resistance value less than about 500 Ohms-per-square are generally considered to be electrically conductive coatings. The emissivity of a coated glass article is directly related to its sheet resistance. By lowering the sheet resistance, or increasing the conductivity, of a glass sheet, the emissivity is reduced. Total power to cover  30  suitable to evaporate condensation or fog and thaw frost, snow, or ice on the cover  30  of the lamp assembly  5 A, for example, is about 1 Watt (W) to about 40 W, for a six-inch diameter aperture (e.g., the diameter of the cover  30 ), and more preferably a power density of about 1.5 W/in 2  to about 2.5 W/in 2 . 
     A coating  101  of pure Tin-Oxide (SnO) formed on a glass substrate would have an extremely high sheet resistance. In practice, however, Tin-Oxide coatings typically have a sheet resistance of about 350-400 Ohms-per-square. This is due, at least in part, to an oxygen deficiency in the tin oxide, rendering it at least slightly electrically conductive. Fluorine may be used as a tin oxide dopant in order to increase the electrical conductivity. A fluorine doped tin oxide coating (SnO 2 :F) can produce sheet resistances as low as about 16 Ω/cm 2 . When tin oxide is doped with fluorine, the fluorine will substitute for oxygen in the compound. This substitution of fluorine for oxygen is a factor in the lowered sheet resistance, due to their differing electron configurations. Other materials have been also used as dopants in various glass coating applications. 
     Additional material may be used as dopants, alone or in combination with fluorine or other dopants, which results in a coating having a comparable or lowered emissivity for a given thickness, while maintaining or improving the ease and cost of manufacture of the coated glass products, and without impairing the optical qualities of the glass. 
     For example, in one embodiment, a niobium doped tin oxide is suitable for use with conventional tin oxide deposition precursors. The pyrolytic deposition enables the application of the film onto a float glass ribbon directly in the glass production process, preferably by CVD. 
     Glass substrates suitable for use in preparing the coated glass article may include any of the conventional clear glass compositions known in the art. The preferred substrate is a clear float glass ribbon wherein the coating  101 , possibly with other optional coatings, is applied in the heated zone of the float glass process. Other conventional processes for applying the coating  101  on the glass substrate of the cover  30  are suitable for use in the embodiments according to the present disclosure. 
     For a pyrolytic deposition, the doped tin oxide alloy is deposited onto the glass substrate by incorporating a niobium source with conventional tin oxide precursors. An example would include the use of niobium pentachloride (NbCl 5 ) in an inert gas, such as helium. The NbCl 5  is a solid at normal atmospheric temperatures and pressures. Thus, for use as a dopant in the CVD process, the niobium pentachloride is vaporized and injected into a gas stream. A bubbler could be used, but in production conditions it would be preferable to use equipment such as a thin film evaporator to get the niobium pentachloride into the gas stream. Other possible niobium containing compounds are possible within the scope of the present invention. A significant factor in the selection of the niobium containing material is its volatility. Typically, the Nb containing material should be volatile at temperatures between 0 and 500° F., and in one embodiment, the Nb containing material should be volatile within the temperature range of 300-500° F. Niobium pentachloride is recommended both for its low melting point and because it is readily commercially available, however the present invention is intended to incorporate any known niobium compound suitable for doping tin oxide. 
     If the Tin-Oxide were to be doped with, for example, fluorine and niobium, a fluorine source would also then be used with the conventional tin oxide precursors. One fluorine source would be either HF or trifluoroacetic acid (TFA), but other conventional fluorine sources could be incorporated. 
     Tin precursors for glass coating processes are conventional and well known in the art. An especially suitable Tin containing compound is dimethyltin dichloride (DMT). This substance is well known and readily available, and is commonly used as a tin precursor material in known float glass coating applications. Other known tin precursors are also usable within the scope of the present disclosure. 
     In at least one possible process, NbCl 5  and DMT are run through thin film evaporators and are then mixed with oxygen and water in a helium carrier gas. The oxygen can be provided in the form of elemental oxygen or in the form of air, depending on the process employed. Other oxygen containing materials are certainly usable within the scope of the process, but it is generally most economical to use either air or elemental oxygen. The optional fluorine containing material (preferably HF) would also be added if fluorine doping was desired. The precursor materials can then be introduced into a coater, which directs the materials to the surface of a float glass ribbon. Care must be taken in the introduction of the materials however, as premature reaction of the NbCl 5  and water are possible. A niobium doped tin oxide film is then deposited on a float glass ribbon by conventional chemical vapor deposition techniques. 
     In the event that fluorine and niobium are being added in a dual doping system, the fluorine precursor and the H 2 O can be run through the same thin film evaporator, although this is not necessary. 
     As opposed to conventional fluorine doping of tin oxide, wherein the fluorine atoms replace oxygen, the niobium atoms replace tin atoms in the tin oxide layer. Niobium is especially suited to this as it has a similar outer shell electron configuration to tin (5 electrons in the outer shell), and has an atomic number comparable to that of tin. Therefore, it is theorized that the niobium easily takes the place of the tin atoms in the tin oxide. 
     It has been found that doping with niobium alone can yield similar sheet resistance properties to doping with fluorine. It has also been found, however, that doping with both fluorine and niobium can yield sheet resistances superior to doping with either niobium or fluorine alone. 
     These and other processes for forming tin oxide coatings on glass and coated glass are described in U.S. Pat. No. 6,524,647 to Varanasi et al, entitled “Method of Forming Niobium Doped Tin Oxide Coatings on Glass and Coated Glass Formed Thereby,” and assigned to Pilkington plc., the disclosure of which is incorporated herein by reference. 
       FIGS. 24 and 25  illustrate embodiments of the anti-icing lamp assembly  5 . As shown in  FIGS. 25 and 25  anti-icing lamp assemblies  5 B,  5 C, respectively, comprise electrically resistive heater conductors  112  according to various embodiments.  FIG. 24  illustrates on embodiment of an anti-icing lamp assembly  5 B comprising an electrically resistive heater conductor  112  for a transparent cover  30  according to one embodiment. The electrically resistive heater conductor  112  can have any form provided that it does not substantially affect the light transmittance properties of the cover  30 . In one embodiment, the electrical resistive heater conductor  112  may be formed in a serpentine pattern  114 , although other patterns may be suitable, as shown in accordance with one embodiment with respect to the anti-icing lamp assembly  5 C shown in  FIG. 25 . The electrically resistive heater conductor  112  comprises terminals  116 ,  118 , which are coupled to an energy source (e.g., voltage or current source) via electrically conductive wires in a similar manner to that disclosed in respect to  FIGS. 24 ,  25 , and  26 . In one embodiment, the electrically resistive heater conductor  112  comprises a series of parallel linear resistive conductors in or on the glass. 
       FIG. 26  illustrates one embodiment of the anti-icing lamp assembly  5 . As shown in  FIG. 26  anti-icing lamp assembly  5 D comprises electrically resistive heater conductors  120  according to various embodiments.  FIG. 26  illustrates an anti-icing lamp assembly  5 D comprising an electrically resistive heater grid  122  according to one embodiment. In one embodiment, the electrically resistive heater grid  122  comprises a plurality of electrically resistive heater conductors each having first and second ends  124 ,  126 , where the first and second ends  124 ,  126  are connected to respective first and second bus bars  128 ,  130 . In another embodiment, the electrically resistive heater grid  122  may comprise a first group of resistive grid lines and a second group of resistive grid lines, with opposing ends of each group being connected to the first and second bus bars  128 ,  130 . The resistive grid lines of the second group may be spaced between adjacent resistive grid lines of the first group, and the width of the resistive grid lines in the second group may be equal or less than the width of the grid lines in the first group. The bus bars  128 ,  130  are coupled to terminals  132 ,  134 , which are coupled to a voltage source via electrically conductive wires in a similar manner to those disclosed in respect to  FIGS. 24 ,  25 , and  26 . 
     Referring now to  FIGS. 24-26 , in one embodiment, the electrically resistive heater conductors  112 ,  120  are very fine wires embedded within or on the cover  30  or may be printed on the interior or exterior surface of cover  30  using electrically conductive inks. The electrically resistive heater conductors  112 ,  120  can have a variety of forms provided that they do not substantially affect the light transmittance properties of the cover  30 . In various embodiments the electrically resistive heater conductors  112 ,  120  may be formed of any suitable materials such as Iron-Chrome Aluminum, Nickel-Chrome, Nickel-Iron, Nickel, Stainless Steel, Copper, Molybdenum, Tungsten, Molybdenum Disilicide MoSi2/MOSI, Silver-Ceramic, Silver ink or paste, for example. The electrically resistive conductor  112  in the form of fine wire may be embedded in the substrate using any suitable technique. Otherwise, the electrically resistive heater conductors  112 ,  120  may be deposited, screen printed, baked, or applied as a decal on the substrate. These conductors may be composed of a silver-ceramic material printed and baked onto the interior surface of the glass, or may be a series of very fine wires embedded within the glass. Although the surface-printed variety may be prone to damage by abrasion, it can be repaired easily with a conductive paint material. 
     When electrical power is applied to the terminals  116 ,  118  and  132 ,  134 , the respective heater conductors  112 ,  120  heat up to substantially eliminate condensation, fog, frost, snow, or ice on the cover  30  of the anti-icing lamp assemblies  5 B,  5 C,  5 D. The anti-icing lamp assemblies  5 B,  5 C,  5 D described in  FIGS. 24-26  should achieve a power density suitable to evaporate condensation or fog and thaw frost, rime, snow, or ice that forms on the cover  30  of the anti-icing lamp assemblies  5 B,  5 C,  5 D, for example. A suitable power density is about 1 Watt (W) to about 2 W, and more preferably about 1.5 W/in 2  to about 1.8 W/in 2 . In one embodiment, the energy source may be coupled to and controlled by the controller circuit  15 , which may receive an activation input or a feedback signal to activate the energy source in order to conduct current through the heater conductors  112 ,  120 . 
     Still referencing  FIG. 26 , in one example, the electrically resistive conductive heater grid  122  formed of electrical conductors, such as conductors  112 ,  120 , may comprise multiple parallel gridlines. All spaced grid lines start and end at either a first or second bus bar  128 ,  130 . These grids may be employed in glass panel substrates or polycarbonate panel substrates used to form the cover  30 . Silver paste printed onto a glass panel substrate can be a conventional silver frit material used in the automotive industry. This conductive material can be screen printed onto the glass panel substrate and subsequently sintered at 1100° C. for 3.5 minutes, thereby leaving a silver frit material on the surface of the glass. A silver ink containing an organic binder (#11809 2k Silver, Creative Materials, Tyngsboro Mass.) can be screen printed onto a polycarbonate panel (polycarbonate, known under the trade name Makrolon Al2647, Bayer AG, Leverkusen, Germany) and subsequently cured at 100° C. for 30 minutes. The thickness of the resulting grid lines and bus bars  128 ,  130  on each of the defrosters can be found through the use of profilometry and may be on the order of 10-14 micrometers. The electrically resistive conductive heater grid  122  on the polycarbonate panel was finally subjected to the application of a silicone hard-coat system (SHP401/AS4000, GE Silicones, Waterford, N.Y.) to provide protection against weathering and abrasion. The application of 6.24 volts and 14.45 volts can establish a thermal equilibrium that is slightly less than the maximum limit of 70° C. in electrically resistive conductive heater grids  122  deposited on glass and on polycarbonate, respectively, under ambient (23° C.) air temperature. The electrically resistive conductive heater grid  122  on glass may defrost 75%-95% of the viewing area in a matter of minutes, for example. A further description of such electrically resistive conductive heater grids, including various test results, can be found in U.S. Pat. No. 7,297,902 to Weiss and entitled “High Performance Defrosters for Transparent Panels,” the disclosure of which is incorporated herein by reference. 
       FIG. 27  illustrates one embodiment of the anti-icing lamp assembly  5 . As shown in  FIG. 27 , an anti-icing lamp assembly  5 E comprises an exothermic deicing thermal energy system  136  according to one embodiment. In this embodiment, the anti-icing lamp assembly  5 E comprises a fluid connector  138  to fluidically couple to a reservoir filled with deicing fluid such as, for example, F-1 glycol or alcohol. The fluid connector  138  is fluidically coupled to a pump  140  located within an aperture  148  formed in the anti-icing lamp assembly  5 E. The pump  140  is fluidically coupled to one or more fluid lines  142 , which is fluidically coupled to a spray nozzle  144  located on an exterior surface of the anti-icing lamp assembly  5 E. The spray nozzle  144  sprays the deicing fluid on an exterior surface  146  of the cover  30 . In one embodiment, the pump  140  is electrically coupled to the controller circuit  15 , which may receive an activation input or a feedback signal to activate the pump  140 . 
     Any suitable deicing fluid used in commercial and general aviation may be employed in the exothermic deicing thermal energy system  136 . In various embodiments, the deicing fluids come in a variety of types, and are typically composed of ethylene glycol (EG) or propylene glycol (PG), and may include other ingredients such as thickening agents, surfactants (wetting agents), corrosion inhibitors, and colored, UV-sensitive dye. Propylene glycol-based fluid is more common due to the fact that it is less toxic than ethylene glycol. The main component of deicing fluid is usually propylene glycol or ethylene glycol. Other ingredients vary depending on the manufacturer, but the exact composition of a particular brand of fluid is generally held as confidential proprietary information. Based on chemical analysis, the U.S. Environmental Protection Agency has identified five main classes of additives widely used among manufacturers: 
     Benzotriazole and methyl-substituted benzotriazole, used as corrosion inhibitor/flame retardants to reduce flammability resulting from the corrosion of metal components carrying a direct current. 
     Alkylphenol and alkylphenol ethoxylates, nonionic surfactants used to reduce surface tension. 
     Triethanolamine, used as a pH buffer. 
     High molecular weight, nonlinear polymers, used to increase viscoelasticity. 
     Colored dyes, such as azo, xanthene, triphenyl methane, and anthroquinone, used to aid in identification. 
     The use of 1,3-propanediol (a fermentation product of corn) as a base for deicing fluid is described in U.S. Patent Application Publication No. 2009/0283713 to Sapienza et al and entitled “Environmentally Benign Anti-Icing Or Deicing Fluids Employing Industrial Streams Comprising Hydroxycarboxylic Acid Salts And/Or Other Effective Deicing/Anti-Icing Agents,” which is incorporated herein by reference. Deicing fluids, including 1,3-propanediol, are available from Kilfrost, Inc. of Coral Springs, Fla. in the USA. 
       FIG. 28  illustrates one embodiment of the anti-icing lamp assembly  5 . As shown in  FIG. 28 , an anti-icing lamp assembly  5 F comprising an infrared (IR) thermal energy source  149  according to one embodiment. The anti-icing lamp assembly  5 E comprises at least one infrared LED  150  located on a printed circuit board substrate  151 . In one embodiment, a plurality of infrared LEDs  150  may be arranged in a circular array that produces heat when energized. In one embodiment, the infrared thermal energy source  149  is coupled to the controller circuit  15  by electrically conductive wires  145 ,  147 . The controller circuit  15  is configured to receive an activation input or a feedback signal to activate the infrared thermal energy source  149 . 
       FIGS. 29 and 30  illustrate one embodiment of an anti-icing lamp assembly  5 . As shown in  FIGS. 29 and 30 , an anti-icing lamp assembly  5 G comprises a heat sink thermal energy transfer system  152  according to one embodiment. In one embodiment, a metallic wire mesh  154  having a higher thermal conductivity than the glass substrate of the cover  30  may be embedded or impregnated into the glass substrate to form a heat sink. The metallic wire mesh  154  is thermally coupled to the LED array  10  by thermal conductor  156  through a terminal  158 , in place of the heat sink  46 , to transfer heat from the LED array  10  or any other heat source of the electronic circuits of the anti-icing lamp assembly  5 G. In one embodiment, the mesh  154  may be formed of grid of rectangles or squares, for example, where the individual wires are laid out at a predetermined pitch so as not to substantially affect the light transmittance properties of the glass, for example, such that the transmission of light is from about 80% to greater than about 90%. Accordingly, heat generated by the LED array  10  is transferred to the heat sink formed by the metallic wire mesh  154  to heat the cover  30  through thermal conduction. In this embodiment, no additional circuits are required and the glass of the cover  30  is kept warm by the heat generated by the LED array  10 . In an alternative embodiment, the metallic wire mesh  154  may be thermally coupled to the existing heat sink  46  through the terminal  158  and thermal conductor  156  to transfer thermal energy from the heat sink  46  to the wire mesh  154  and heat the cover  30 . 
     The wire mesh  154  and the thermal conductor  156  can be formed of any material having a thermal conductivity k greater than about 100 Watts per meter-Kelvin (W/m·K). Materials having a relatively high thermal conductivity include, without limitation, aluminum, gold, copper, and silver, among others. For example aluminum alloys have a thermal conductivity of about 120-180 W/m·K; pure aluminum have a thermal conductivity of about 237 W/m·K; gold has a thermal conductivity of about 518 W/m·K; copper has a thermal conductivity of about 401 W/m·K; silver has a thermal conductivity of about 429 W/m·K. In one embodiment, the wire mesh  154  and thermal conductor  156  may be formed of aluminum or any suitable thermal conductor such as, without limitation, gold, copper, or silver, among others. 
     It will be appreciated, that each of the embodiments  5 B,  5 C,  5 D,  5 E,  5 F, and  5 G may comprise the feedback element  153  previously described in connection with  FIG. 23 . As previously discussed, the feedback element  153  provides a feedback signal to the controller circuit  15  that is indicative of condensation, fog, ice, rime, frost, snow, ice, and/or ice detected on the cover  30  and/or the temperature of the cover  30 . 
     Another embodiment of an anti-icing lamp assembly  600  is shown in  FIGS. 31A-31C  are perspective views of a front, back and side, respectively, of an anti-icing lamp assembly  5  according to one embodiment.  FIGS. 32 and 33  are exploded views of the anti-icing lamp assembly  600  illustrating components thereof. As discussed in further detail below, embodiments of the anti-icing lamp assembly  600  utilize LED technology to generate a light output. Light emitting diodes do not exhibit the large inrush current characteristics of incandescent filaments and are generally impervious to vibration. The anti-icing lamp assembly  600  thus provides significantly greater operating lifetimes in harsh mechanical environments, such as, for example, aircraft, motorcycle and off-road vehicle (e.g., Baja 500) environments or the like than may be realized using incandescent filament technology. Advantages of the anti-icing lamp assembly  600  are not limited to increased durability and longevity in harsh operating environments, and it will be appreciated that the anti-icing lamp assembly  600  may be used in other operating environments, such as, for example, automobile forward lighting environments, marine (e.g., underwater) environments and stage lighting operating environments, and not just for aircraft applications. Because embodiments of the anti-icing lamp assembly  600  may utilize an array of total internal reflection (TIR) lenses to extract light from LEDs, the light may be collected and redirected more efficiently compared to non-TIR light processing elements used for external aircraft lighting and other applications. Moreover, because embodiments of the anti-icing lamp assembly  600  may conform to certain mechanical, electrical and/or light output specifications of any of a number of existing incandescent filament lamps, aircraft, motorcycles, off-road vehicles and other equipment (vehicular or non-vehicular) may be retrofitted with the anti-icing lamp assembly  600  without the need for substantial modification, if any, of the associated equipment. 
     Still with reference to  FIGS. 31-33 , in one embodiment, an anti-icing lamp assembly  600  may comprise at least one solid state light source, for example. In one embodiment, the solid state light source comprises at least one LED. In some embodiments, the solid state light source comprises at least one LED array  610 , a controller circuit  615  electrically coupled to the LED arrays  610 , a lens array  620 , a base  625 , and a cover  630 . The cover  630  may be configured and adapted to accommodate various embodiments of the defroster elements described hereinbelow. The cover  630  may be formed of any suitable glass or plastic substrate. A glass substrate may be formed of borosilicate, whereas a plastic substrate may be formed of polycarbonate resin, acrylic resin, polyarylate resin, polyester resin, polysulfone resin, polyvinyl butyral resin (PVB), and copolymers and mixtures thereof. 
     In one embodiment, the anti-icing lamp assembly  600  comprises a cover  630  that is substantially optically transparent. The cover  630  may comprise one or more defroster elements in accordance with the present disclosure to deice the cover  630 , for example. As previously discussed, the term “deice” is used for conciseness and clarity and is intended to mean defog, demist, deice, prevent icing, clear or evaporate condensation or fog and thaw rime, frost, snow, or ice that may develop on the clear cover  630  of the anti-icing lamp assembly  600 . The defroster elements may be configured to passively or directly provide thermal energy to an exterior surface  602  of the cover  630 . In one embodiment, the defroster elements may be configured to generate thermal energy by conducting electrical current, alternating or direct current (AC or DC), pulsed, or modulated, through a resistive layer, coating, sheet, grid, or wire, or any combination thereof, formed integrally with or on an optically transparent substrate, e.g., the cover  630 . In other embodiments, the defroster elements may be configured to generate thermal energy by exothermic chemical reactions that release energy in the form of heat. In other embodiments, the defroster elements may be configured to generate IR radiation energy. In other embodiments, the defroster elements may be configured as heat sinks to recover or recycle wasted heat from other sources in the lamp assembly or other aircraft systems. In other embodiments, heat sink elements embedded in the optically transparent substrate may be thermally coupled to other heat sink elements of the anti-icing lamp assembly  600  system. Before describing the various embodiments of defroster elements, the present disclosure continues with a description of one embodiment of the anti-icing lamp assembly  600 . In one embodiment, the controller circuit  615  is the same or substantially similar to the controller circuit  15  previously discussed in connection with  FIG. 10 , for example. 
     In the assembled state of the anti-icing lamp assembly  600 , as shown in  FIGS. 31-33 , the LED arrays  610 , the controller circuit  615  and the lens array  620  may be received onto a front surface  695  of the base  625 , with the cover  630  being disposed over the front surface  695  and attached to the base  625 . The LED arrays  610 , the controller circuit  615  and the lens array  620  may thus be protectably enclosed between the cover  630  and the base  625 . The anti-icing lamp assembly  600  may additionally comprise a set of electrical connectors  636  disposed through the base  625  between the front surface  695  of the base  625  and a back surface  620  of the base  625 . As discussed in further detail below, the electrical connectors  636  enable an electrical power system external to the anti-icing lamp assembly  600  (e.g., an aircraft electrical power system) to electrically connect to the LED arrays  610  and the controller circuit  615  and supply electrical power thereto. In one embodiment, the electrical connectors  636  are the same or substantially similar to the electrical connectors  36  described in connection with  FIGS. 1-3  and  12 . 
     Still with reference to  FIGS. 31-33 , in one embodiment, the base  625  portion of the anti-icing lamp assembly  600  comprises a housing portion  652  for receiving the controller circuit  615  therein. The base  625  also acts as a heat sink. A substrate  640  mounts to the base  625  via fasteners  648  (e.g., screw, bolt, rivet, snap). The fasteners  648  are received in corresponding threaded apertures  664  in the base  625 . The LED arrays  610  comprising a mushroom-shaped deviator lens  642  are disposed to the substrate  640 . As previously discussed, the mushroom-shaped deviator lens  642  is shaped to cause the TIR lens array  620  to provide uniform light output at an exit face  654  of the TIR lens frame  634 . As shown, the substrate  640  comprises seven LED arrays  610  covered by seven corresponding mushroom-shaped deviator lenses  642 . Each of the mushroom-shaped deviator lenses  642  transmits lights to seven corresponding TIR lenses  658  of the lens array  620 . In various embodiments, the mushroom-shaped deviator lenses  642  and the TIR lens array  620  are the same or substantially similar to those described herein in connection with  FIGS. 14-15  and  17 - 18 . It will be appreciated that additional or fewer LED arrays  610 , mushroom-shaped deviator lenses  642 , and TIR lenses  658  may be provided on the substrate  640 , without limitation. As shown, the LED arrays  610 , the mushroom-shaped deviator lenses  642 , and the corresponding TIR lenses  658  are arranged with six elements around the perimeter of the substrate (outside lenses) and one in the center (central lens). It will be appreciated that other configurations are contemplated and the embodiments should not be limited as such. Pogo pins  651   a ,  651   b ,  651   c ,  651   d  comprising corresponding pogo pin holders  650   a ,  650   b ,  650   c ,  650   d  are provided on the substrate  640 . The pogo pins  651   a - d  may be used to provide electrical contact to corresponding electrode pads  665   a ,  665   b ,  665   c ,  665   d  of the cover  630  through corresponding apertures  663   a ,  663   b ,  663   c ,  663   d  in the TIR lens frame  634 . Accordingly, the electrode pads  665   a - d  are electrically coupled to various circuit elements of the controller circuit  615 . In one embodiment, the cover  630  may comprise a feedback element  667 , which is similar to the feedback element  153  as previously described in connection with  FIG. 23 . As previously discussed, the feedback element  667  provides a signal to the controller circuit  615  that is indicative of condensation, fog, ice, rime, frost, snow, ice, and/or ice detected on the cover  630  and/or the temperature of the cover  630 . The feedback element  667  is electrically coupled between electrode pads  665   c ,  665   d . The pogo pins  651   c ,  661   d  electrically provide the feedback signal generated by the feedback element  667  to the controller circuit  615 . In response the feedback signal, the controller circuit  615  applies a voltage and/or current to the electrode pads  665   a ,  665   b . Either electrode pad  665   a ,  665   b  may act as the positive (+) electrode, provided that the other pad acts as the negative (−) terminal. 
     Electrical connectors  660  provide electrical contact from the controller circuit  615  to the substrate  640  to power LED arrays  610 . A plurality of TIR lens frame fasteners  646  (e.g., screws, bolts, rivets, snaps) connect the TIR lens frame  634  to the base  625 . In the illustrated embodiment, the fasteners  646  couple to standoffs  662  in the base  625 . A retainer ring  632  couples the cover  630  to the base  625 . 
       FIG. 34  is a perspective cross-sectional view of one embodiment of an anti-icing lamp assembly  600 A and  FIG. 35  is a detail view of a cross-section of the lens cover  630  of the anti-icing lamp assembly  600 A.  FIGS. 34-35  illustrate that in one embodiment the anti-icing lamp assembly  600 A comprises an electrically conductive coating  601  according to one embodiment. In one embodiment, the electrically conductive coating  601  is substantially optically transparent and is formed on the exterior surface  602  of the optically transparent cover  630 . One type of electrically conductive coating  601  that may be applied to the glass cover  630  is known under the trade name “TEC Glass” available from Pilkington Specialty Glass Products of Toledo, Ohio. The transparent electrically conductive coating  601  formed on the glass cover  630  substrate is a thin pyrolytic film that can be directly electrically heated to clear or evaporate condensation or fog and thaw or deice rime, frost, snow, or ice that may develop on the clear cover  630  portion of the anti-icing lamp assembly  600 A, for example. In one embodiment, the transparent electrically conductive coating  601  is the same or substantially similar to the electrically conductive coating  101  described in connection with  FIGS. 21 and 22 . Details of the electrically conductive coatings  101 ,  601  have been previously described in connection with  FIGS. 21 and 22  and for conciseness and clarity of disclosure will not be repeated here. In one embodiment, the electrically conductive coating  601  may be electrically driven by the controller circuit  615  by way of the pogo pins  651 , for example, which electrically couple the controller circuit  615  to the coating  601 . 
       FIG. 36  illustrates an exploded view of one embodiment of the anti-icing lamp assembly  600 A with the retainer ring  632  removed to more clearly show the outer surface  602  of the cover  630 . As shown in  FIG. 36 , in one embodiment, the cover  630  may comprise a first pair of electrically conductive electrode pads  655   a ,  655   b , which may be formed on opposite sides of the exterior surface  602  of the cover  630 . A suitable electrical voltage and/or current can be applied to the electrode pads  655   a ,  655   b  via corresponding pogo pins  651   a ,  651   b  through apertures  663   a ,  663   b  formed in the TIR lens frame  634 , for example, or suitable electrically conductive wires, such as electrically conductive wires  108 ,  110  shown in  FIG. 23 . When a voltage is applied to the terminals  604 ,  606 , an electrical current is generated through the resistive pyrolytic coating  601 , which heats the cover  630  to evaporate condensation or fog and thaw frost, snow, or ice on the cover  630  of the lamp assembly  600 A, for example. In the embodiment illustrated in  FIG. 36 , the electrical current conducted across the sheet resistance of the coating  601  heats the exterior surface  602  of the cover  630 , thus minimizing the amount of energy required to heat the cover  630 . In other embodiments, for completeness of disclosure, the coating  601  may be applied to an interior portion  611  of the cover  630 . In such embodiment, the heat would be transferred through the glass substrate of the cover  630 , which has poor thermal conduction properties. 
     As also shown in  FIG. 36 , in one embodiment, the electrically conductive electrode pads  665   a - d  (e.g., or bus bars), which are the same or substantially similar to the electrode pads  104 ,  106  shown in  FIG. 23 . The electrode pads  665   a - d  may be screen printed onto opposing sides of an exterior or interior surface  602 ,  611  of the cover  630  prior to the application of the coating  601 . The electrode pads  665   a - d  may be screen printed using electrically conductive inks or pastes, such as, for example, Palladium Silver, among other electrically conductive inks or pastes. In other embodiments, the electrode pads  665   a - d  may be formed of electrically conductive adhesive decals applied to the coating  601  and electrically coupled to the energy source via terminals provided on the cover  630  and corresponding conductors to couple to the controller circuit  615 , for example. In various embodiments, electrically conductive adhesive decals may include conductive adhesives, inks, foil, tape, transfer tape, among others. The electrode pads  665   a ,  665   b  may be configured to receive an electrical voltage, which is converted to an electrical current through the sheet resistance of the coating  601 . The electrodes  665   a ,  65   b  are electrically coupled to the controller circuit  615  via the pogo pins  651   a ,  651   b . In one embodiment, a constant current may be supplied to the electrode pads  665   a ,  665   b  by a suitable electrical circuit. In one embodiment, the electrode pads  665   c ,  665   d  electrically couple to the feedback element  667  and to the controller circuit  615  via the pogo pins  651   c ,  651   d . If the electrode pads  665   a - d  are formed on the interior surface  611  of the cover  630  an electrical connection may be provided to the coating  601  though the cover  630 . 
       FIGS. 37 and 38  illustrate embodiments of the anti-icing lamp assembly  600 . As shown in  FIGS. 37 and 38  anti-icing lamp assemblies  600 B,  600 C, respectively, comprise electrically resistive heater conductors  612  according to various embodiments.  FIG. 37  illustrates on embodiment of an anti-icing lamp assembly  600 B comprising an electrically resistive heater conductor  612  for a transparent cover  630  according to one embodiment. The electrically resistive heater conductor  612  can have any form provided that it does not substantially affect the light transmittance properties of the cover  630 . In one embodiment, the electrical resistive heater conductor  612  may be formed in a serpentine pattern  614 , although other patterns may be suitable, as shown in accordance with one embodiment with respect to the anti-icing lamp assembly  600 C shown in  FIG. 38 . The electrically resistive heater conductor  612  comprises terminals  616 ,  618 , which are coupled to an energy source (e.g., voltage or current source) via electrically conductive wires in a similar manner previously disclosed herein. In one embodiment, the electrically resistive heater conductor  612  comprises a series of parallel linear resistive conductors in or on the glass. In one embodiment, the electrically resistive heater conductor  612  is the same or substantially similar to the electrically resistive heater conductor  112  described in connection with  FIGS. 24 and 25 . 
       FIG. 39  illustrates one embodiment of the anti-icing lamp assembly  600 . As shown in  FIG. 39  anti-icing lamp assembly  600 D comprises electrically resistive heater conductors  621  according to various embodiments.  FIG. 39  illustrates an anti-icing lamp assembly  600 D comprising an electrically resistive heater grid  622  according to one embodiment. In one embodiment, the electrically resistive heater grid  622  comprises a plurality of electrically resistive heater conductors each having first and second ends  624 ,  626 , where the first and second ends  624 ,  626  are connected to respective first and second bus bars  628 ,  630  (e.g., electrode pads). In another embodiment, the electrically resistive heater grid  622  may comprise a first group of resistive grid lines and a second group of resistive grid lines, with opposing ends of each group being connected to the first and second bus bars  628 ,  630 . The resistive grid lines of the second group may be spaced between adjacent resistive grid lines of the first group, and the width of the resistive grid lines in the second group may be equal or less than the width of the grid lines in the first group. The bus bars  628 ,  630  are coupled to terminals  632 ,  634 , which are coupled to a voltage source via electrically conductive wires in a similar manner to that previously disclosed herein. 
     Referring now to  FIGS. 37-39 , in one embodiment, the electrically resistive heater conductors  612 ,  621  are very fine wires embedded within or on the cover  630  or may be printed on the interior or exterior surface of cover  630  using electrically conductive inks. The electrically resistive heater conductors  612 ,  621  can have a variety of forms provided that they do not substantially affect the light transmittance properties of the cover  630 . In one embodiment, the electrically resistive heater conductors  612 ,  621  are the same or substantially similar to the electrically conductive heaters  612 ,  621  discussed in connection with  FIGS. 24-26 . Accordingly, when electrical power is applied to the terminals  616 ,  618  and  632 ,  634 , the respective heater conductors  612 ,  621  heat up to substantially clear or evaporate condensation or fog and thaw or deice rime, frost, snow, or ice that may develop on the clear cover portion  630  of the anti-icing lamp assemblies  600 B,  600 C,  600 D. The anti-icing lamp assemblies  600 B,  600 C,  600 D described in  FIGS. 37-39  should achieve a power density suitable to substantially clear or evaporate condensation or fog and thaw or deice rime, frost, snow, or ice that may develop on the clear cover portion  630  of the anti-icing lamp assemblies  600 B,  600 C,  600 D, for example. A suitable power density is about 1 W/in 2  to about 2.5 W/in 2 , and more preferably about 1.5 W/in 2  to about 1.8 W/in 2 . In one embodiment, the energy source may be coupled to and controlled by the controller circuit  15 , which may receive an activation input or a feedback signal to activate the energy source in order to conduct current through the heater conductors  612 ,  621 . 
       FIG. 40  illustrates one embodiment of the anti-icing lamp assembly  600 . As shown in  FIG. 40 , an anti-icing lamp assembly  600 E comprises an exothermic deicing thermal energy system  637  according to one embodiment. In this embodiment, the anti-icing lamp assembly  600 E comprises a fluid connector  638  to fluidically couple to a reservoir filled with deicing fluid such as, for example, F-1 glycol or alcohol. The fluid connector  638  is fluidically coupled to a pump  640  located within an aperture  648  formed in the anti-icing lamp assembly  600 E. The pump  640  is fluidically coupled to one or more fluid lines  642 , which are fluidically coupled to one or more spray nozzles  644  located on an exterior surface of the anti-icing lamp assembly  600 E. The spray nozzles  644  spray the deicing fluid on an exterior surface  646  of the cover  630 . In one embodiment, the pump  640  is electrically coupled to the controller circuit  615 , which may receive an activation input or a feedback signal to activate the pump  640 . Any suitable deicing fluid used in commercial and general aviation may be employed in the exothermic deicing thermal energy system  637 , for example, the deicing fluid previously discussed in connection with  FIG. 27 , without limitation. 
       FIG. 41  illustrates one embodiment of the anti-icing lamp assembly  600 . As shown in  FIG. 41 , illustrates an anti-icing lamp assembly  600 F comprises an infrared (IR) thermal energy source  649  according to one embodiment. The anti-icing lamp assembly  600 F comprises at least one infrared LED  653  located on a printed circuit board substrate  655 . In one embodiment, a plurality of infrared LEDs  653  may be arranged in a circular array that produces heat when energized. In one embodiment, the infrared thermal energy  649  is coupled to the controller circuit  615  by electrically conductive wires  645 ,  647 . The controller circuit  615  is configured to receive an activation input or a feedback signal to activate the infrared thermal energy source  649 . 
       FIG. 42  illustrates one embodiment of the anti-icing lamp assembly  600 . As shown in  FIG. 42 , an anti-icing lamp assembly  600 G comprises a heat sink thermal energy transfer system  657  according to one embodiment. In one embodiment, a metallic wire mesh  659  having a higher thermal conductivity than the glass substrate of the cover  630  may be embedded or impregnated into the glass substrate to form a heat sink. The metallic wire mesh  659  is thermally coupled to the heat sink base  625  by a thermal conductor through a terminal  661  to transfer heat generated by the LED array  610 , or any other heat source of the electronic circuits, of the anti-icing lamp assembly  600 G. In one embodiment, the mesh  659  may be formed of grid of rectangles or squares, for example, where the individual wires are laid out at a predetermined pitch so as not to substantially affect the light transmittance properties of the glass, for example, such that the transmission of light is from about 80% to greater than about 90%. Accordingly, heat generated by the LED array  610  is transferred to the heat sink formed by the metallic wire mesh  659  to heat the cover  630  through thermal conduction. In this embodiment, no additional circuits are required and the glass of the cover  630  is kept warm by the heat generated by the LED array  610 . In an alternative embodiment, the metallic wire mesh  659  may be thermally coupled to the existing heat sink  625  through the terminal  661  and thermal conductors to transfer thermal energy from the heat sink  625  to the wire mesh  659  and heat the cover  630 . 
     The wire mesh  659  and the thermal conductor can be formed of any material having a thermal conductivity k greater than about 100 Watts per meter-Kelvin (W/m·K). Materials having a relatively high thermal conductivity include, without limitation, aluminum, gold, copper, and silver, among others. For example aluminum alloys have a thermal conductivity of about 120-180 W/m·K; pure aluminum have a thermal conductivity of about 237 W/m·K; gold has a thermal conductivity of about 318 W/m·K; copper has a thermal conductivity of about 401 W/m·K; silver has a thermal conductivity of about 429 W/m·K. In one embodiment, the wire mesh  659  and thermal conductor may be formed of aluminum or any suitable thermal conductor such as, without limitation, gold, copper, or silver, among others. 
     It will be appreciated, that each of the embodiments  600 B,  600 C,  600 D,  600 E,  600 F, and  600 G may comprise the feedback element  667  previously described in connection with  FIGS. 32-36 . As previously discussed, the feedback element  667  provides a feedback signal to the controller circuit  615  that is indicative of condensation, fog, ice, rime, frost, snow, ice, and/or ice detected on the cover  630  and/or the temperature of the cover  630 . 
     Having described various embodiments of defroster elements that can be employed in various embodiments of anti-icing lamp assemblies  5 ,  5 A-G,  600 ,  600 A- 600 G, the description now turns to a brief discussion of the power dissipated by conventional aircraft lamp assembly as compared with the total power dissipated by an anti-icing solid state aircraft lamp assembly according to the disclosed embodiments. Conventional aircraft lamp assemblies comprising incandescent lamps dissipate anywhere from 250 W to 450 W and up to 600 W for the big landing lights on a Boeing aircraft, for example. A typical solid-state LED aircraft lamp assembly as dissipates a maximum of about 70 W, which is a significant power savings for the airlines even for the 250 W to 450 W aircraft lamp assemblies. In addition, because incandescent lamps burn out and they are relatively inexpensive, for example, an aircraft landing light for a Boeing 747 costs about $130. However, to change an incandescent lamp requires a mechanic to open up the wing of the aircraft and change the lamp. Accordingly, the cost for changing two lamps on a Boeing 747 aircraft may be on the order of $2500 including the labor. So you&#39;re talking about an additional 40 watts. An anti-icing solid state LED lamp assembly comprising heater elements as discussed herein will typically require an additional 30 W to 40 W (for a total of about 100 W to 110 W versus a corresponding 250 W to 450 W) that needs to be expended on the glass surface of the cover  30 ,  630  in order to generate a suitable amount of heat through the resistive or infra-red elements as discussed with reference to the anti-icing lamp assemblies  5 ,  5 A- 5 G,  600 ;  600 A- 600 G. For the larger aircraft lamp assemblies in the 600 W, a corresponding anti-icing solid state aircraft lamp assembly consumes about 200 W. Embodiments of the anti-icing lamp assemblies  5 ,  5 A- 5 G,  600 ,  600 A- 600 G, discussed above, each comprise a controller circuit  15  that may be configured with logic (e.g., software, firmware, hardware, or combination thereof) to monitor for temperatures above a predetermined threshold (e.g., 40° F.) when the defroster elements are turned off to conserve energy. I believe, umm, for the larger, the 600 watt lamp, we were umm, let&#39;s see, we were around 200 watts. 
       FIG. 43  illustrates a block diagram of one embodiment of a controller circuit  170  for controlling the operation of the anti-icing lamp assemblies discussed herein according to various embodiments. In one embodiment, the controller circuit  170  comprises a logic circuit  176  coupled to an energy source  182 . In one embodiment, the energy circuit  182  may be the DC-DC controller  90  described in connection with  FIG. 10 , for example. In one embodiment, the logic circuit  176  may be a programmable device such as a state machine or a processor. One embodiment of a programmable logic circuit  176  includes a processor coupled to a memory  178 . Another embodiment of a programmable logic circuit  176  includes a Programmable Logic Device (PLD) or a Field Programmable Gate Array (FPGA). The logic circuit  176  may receive inputs from multiple sources. In one embodiment, the logic circuit  176  may receive an activation input signal  172 , which may be generated by aircraft personnel such as the pilot or other members of the crew, aircraft mechanics, and the like. In one aspect, the activation input signal  172  may be a simple virtual, mechanical, or electromechanical switch, that the aircraft personnel actuates when the aircraft is landing or taxing under conditions conducive to condensation, fog, frost, snow, or ice forming on the exterior surface of the cover  30 . When the logic circuit  176  receives the activation input signal  172 , the logic circuit  176  activates the energy source  182  to drive the defrosting element  51  of the anti-icing aircraft lamp  5 ,  5 A- 5 G,  600 ,  600 A- 600 G such as, for example, the electrically conductive coating  101 ,  601  the electrically resistive heater conductors  112 ,  120 ,  612 ,  621  the pump  140 ,  640  to activate the exothermic defrosting system  136 ,  637  and/or the IR energy source  149 ,  649  to generate IR heat, among other defrosting elements. 
     In one embodiment, a control circuit  52  is configured to receive a feedback signal  57  from a feedback element  53 , which includes any suitable electronic sensors or electronic components such as the feedback element  153 ,  667  described in connection with FIGS.  23  and  32 - 36 , or other feedback sensors associated with the aircraft. For example, the feedback signal  57  also may be received from temperature sensors configured to measure outdoor ambient temperature, wind speed, humidity, barometric pressure, aircraft speed, and the like. The logic circuit  176  is configured to activate the energy source  182  based on the activation input signal  172  or the output signal  174  of the control circuit  52 , or both the activation input signal  172  and the output signal  174 . When activated, the energy source  182  drives the defroster element  51 . In embodiments where the logic circuit  276  is a processor, logical instructions may be stored in the memory  178  that when executed, cause the processor to determine whether to activate the energy source  182  based on the activation input signal  172  or the output signal  174  of the control circuit  52 , or both the activation input signal  172  and the output signal  174  drive the defroster element  51  in response thereto. Accordingly, the logic circuit  176  may be programmed to automatically activate the energy source  182 . In one embodiment, the control circuit  52  may be integrated with the controller circuit  15 ,  615 . In various embodiments, the energy source  182  may be configured to supply voltage or current, either AC or DC, or may supply voltage or current pulses to an output terminal  184  coupled to the defroster element  51  discussed herein. In various embodiments, an analog-to-digital converter (ADC) may be employed to provide digital inputs to the logic circuit  176 . 
       FIG. 44  illustrates one embodiment of a control circuit  52  suitable for use with a thermistor type feedback element. The control circuit  52  uses the thermistor R 4  as the feedback element  53  to sense low temperatures, such as 32° F. (or 0° C.). Basically, the control circuit  52  uses a thermistor R 4  to sense the temperature of the cover  30 . The control circuit  52  produces an output signal  174  when the temperature falls below zero degrees, for example. An operational amplifier  179  (e.g., Opamp LM7215) is used to compare a reference voltage V REF  at the non inverting input (+) of the amplifier  179  with the voltage V T  from the thermistor R 4  at the inverting input (−) of the amplifier  179 . When temperature of the cover  30  become less than zero degrees, for example, the non inverting input (+) voltage V REF  exceeds the voltage V T  at the inverting input (−), and the amplifier  179  output become high. This makes transistor Q 1  ON and drives a current I L  from the output of the transistor Q 1  when resistor R 7  is connected to a supply voltage. In one embodiment, the thermistor R 4  may be a glass bead type thermistor No: Keystone RL0503-5536-122-MS (361K @ 0 degree Celsius and 100K @ 25 degree Celsius, without limitation. Any other suitable temperature sensor and corresponding circuit may be employed, without limitation. 
       FIG. 45  illustrates an installed configuration of the anti-icing lamp assembly  5  ( 5 A- 5 G,  600 ,  600 A- 600 G), according to one embodiment. As shown, the anti-icing lamp assembly  5  ( 5 A- 5 G,  600 ,  600 A- 600 G) is retrofitted into a cowl-mounted PAR-36 incandescent lamp holder  295  of an aircraft  700  to operate as an aircraft landing light. It will be appreciated that the anti-icing lamp assembly  5  ( 5 A- 5 G,  600 ,  600 A- 600 G) may also be used in other harsh operating environments such as, for example, motorcycle and off-road vehicle (e.g., Baja 500) environments. Notwithstanding the advantages of increased durability and longevity afforded by the anti-icing lamp assembly  5  ( 5 A- 5 G,  600 ,  600 A- 600 G) in such environments, it will be appreciated that the anti-icing lamp assembly  5  ( 5 A- 5 G,  600 ,  600 A- 600 G) may be used in a number of other operating environments, such as, for example, automobile forward lighting environments, marine (e.g., underwater) environments and stage lighting operating environments. 
     While various details have been set forth in the foregoing description, it will be appreciated that the various aspects of the anti-icing solid state aircraft lamp assembly may be practiced without these specific details. 
     It is worthy to note that any reference to “one aspect,” “an aspect,” “one embodiment,” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the aspect is included in at least one aspect. Thus, appearances of the phrases “in one aspect,” “in an aspect,” “in one embodiment,” or “in an embodiment” in various places throughout the specification are not necessarily all referring to the same aspect. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner in one or more aspects. 
     Some aspects may be described using the expression “coupled” and “connected” along with their derivatives. It should be understood that these terms are not intended as synonyms for each other. For example, some aspects may be described using the term “connected” to indicate that two or more elements are in direct physical or electrical contact with each other. In another example, some aspects may be described using the term “coupled” to indicate that two or more elements are in direct physical or electrical contact. The term “coupled,” however, also may mean that two or more elements are not in direct contact with each other, but yet still co-operate or interact with each other. 
     While certain features of the aspects have been illustrated as described herein, many modifications, substitutions, changes and equivalents will now occur to those skilled in the art. It is therefore to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true scope of the disclosed embodiments.