Patent Publication Number: US-2015062873-A1

Title: Lighting fixture

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to the lighting industry and more particularly to high-power, exterior lighting fixtures. 
     BACKGROUND OF THE INVENTION 
     A lighting fixture, also commonly referred to simply as a light fixture or a light, is an electrical device that is commonly utilized to create artificial illumination. As can be appreciated, lighting fixtures are constructed in a wide array of different designs, with certain designs particularly well suited for use in specific environments. 
     A high power, exterior, lighting fixture is one type of lighting fixture that is well known in the art. A high power, exterior, light fixture typically includes, among other things, an enclosed outer housing, a light source (e.g., at least one light-emitting diode (LED)) disposed within the enclosed outer housing, wiring for electrically connecting the light source to a power source, and a switch for regulating the flow of current from the power source to the light source. In use, illumination from the light source is directed through a transparent window in the outer housing, often with the aid of one or more optical components, to create externally visible light. 
     Due to its relatively enclosed construction, exterior (i.e., outdoor) lighting fixtures of the type as described above can be utilized in environments that are subject to potentially hazardous conditions, such as extreme temperature variations, humidity fluctuations, exposure to precipitation, such as rain and snow, and even direct immersion in water. As such, high power, exterior light fixtures are commonly used in outdoor architectural, landscape and fountain lighting applications that require high light output (e.g., to illuminate building exteriors, gardens, walkways, pools and the like). 
     Although well known in the art, high power exterior light fixtures of the type as described above have been found to suffer from a notable drawback. Specifically, the light source in the fixture typically generates heat when activated. Accordingly, the act of switching the fixture on and off during routine use causes rapid cycles of heating and cooling within the housing which, in turn, causes the air sealed within the housing to expand and contract, respectively, in response thereto. If the expansion and contraction of the sealed air exceeds a particular threshold, the light fixture can potentially explode or implode, which not only results in the permanent inoperability of the fixture but also a potentially destructive condition. 
     Additionally, it has been found that the change in pressure within the housing can cause external air to be drawn into the interior of the housing through any wiring that is connected to an externally located power source (i.e., in a similar fashion to the application of suction force through a straw, with the wiring functioning as the straw). Even lighting fixtures with adequately sealed outer housings have been found to draw external air into its interior cavity. Moisture present in the external air (e.g., on a particularly humid day) that is drawn into the interior of the outer housing condenses as the air cools (e.g., from changes in the ambient temperature or through deactivation of the light source). As a result, a considerable amount of water often collects within the interior of the fixture. 
     Approximately half of all outdoor light fixtures currently in use accumulate moisture within its housing. This collection of water within the interior of the lighting fixture can ultimately result in permanent inoperability of the fixture, either through power supply failure, shorting of the electrical circuitry or, in certain circumstances, catastrophic explosion. 
     To remedy the aforementioned effects, outdoor light features are often provided with protective means to treat routine variances in the interior air pressure. 
     As an example, outdoor light fixtures are often provided with check valves to equalize pressure within the housing. However, although effective in minimizing the risk of fixture implosion and explosion, check valves have been found to be inadequate in preventing the condensation of moisture within the fixture housing. 
     As another example, outdoor light fixtures are often provided with vapor passing breathers, which allow for vapor to be repeatedly drawn into and expelled out from the housing. Through repetition of this cyclical process, the light fixture ultimately breathes the interior of the housing dry. However, although useful in certain circumstances, vapor passing breathers have been found to be ineffective in selected environments, such as in underwater lighting applications. In fact, there is currently no adequate protective measure for minimizing the accumulation of moisture in underwater light fixtures, other than the utilization of water tight seals and routine maintenance. 
     Lastly, it should be noted that although the aforementioned means for regulating interior air pressure within a light fixture can be somewhat effective, it has been found that the constant stress applied to any fixture seals as a result of the fluctuations in air pressure between the interior and exterior of the housing can cause the seals to dry out and shrink. This decrease in the volume of the seals, in turn, can result in the leakage of air therethrough. In hazardous locations where high concentrations of flammable gasses (e.g., hydrocarbons), vapors, or dusts occur (e.g., a Zone 0 area where flammable gasses or vapors are continuously present), any leakage of air through a seal in the fixture housing can result in a potentially catastrophic reaction. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a new and improved lighting fixture. 
     It is another object of the present invention to provide a new and improved lighting fixture that generates high-power light and that is particularly well suited for use in a wide range of outdoor environments including submersion in water. 
     It is yet another object of the present invention to provide a lighting fixture as described above that is less susceptible to variances in pressure within its housing. 
     It is still another object of the present invention to provide a lighting fixture as described above that is less susceptible to the collection of water content within its housing. 
     It is yet still another object of the present invention to provide a lighting fixture as described above that has a limited number of parts, is inexpensive to manufacture and is simple to use. 
     Accordingly, as a feature of the present invention, there is provided a lighting fixture comprising (a) a housing shaped to define an interior cavity, the interior cavity having a volume, (b) a light source for producing light, the light source being disposed within the interior cavity, and (c) an electrically insulating, thermally conductive, and transparent liquid that substantially fills the interior cavity. 
     Various other features and advantages will appear from the description to follow. In the description, reference is made to the accompanying drawings which form a part thereof, and in which is shown by way of illustration, an embodiment for practicing the invention. The embodiment will be described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that structural changes may be made without departing from the scope of the invention. The following detailed description is therefore, not to be taken in a limiting sense, and the scope of the present invention is best defined by the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings wherein like reference numerals represent like parts: 
         FIG. 1  is a top perspective view of a light fixture constructed according to the teachings of the present invention; 
         FIG. 2  is a simplified section view of the light fixture shown in  FIG. 1  taken along lines  2 - 2 , the fixture being shown producing light; and 
         FIG. 3  is a top perspective view, broken away in part, of a modification to the outer housing shown in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Construction of Light Fixture  11   
     Referring now to  FIGS. 1 and 2 , there are shown top perspective and section views, respectively, of a lighting fixture constructed according to the teachings of the present invention, the lighting fixture being identified generally by reference numeral  11 . As will be described in detail below, lighting fixture  11  is specifically designed, inter alia, to minimize (i) fluctuations in interior pressure, and (ii) the accumulation of water content therein. As such, lighting fixture  11  is particularly well suited for outdoor use in a wide range of environmental conditions, including submersion in water, which is a principal object of the present invention. 
     Lighting fixture, or fixture,  11  comprises an outer housing  13  shaped to define an interior cavity  15 , a light source  17  disposed within interior cavity  15 , an optical component  19  disposed within interior cavity  15  for treating light produced by light source  17 , a power source  21  disposed within interior cavity  15  for supplying current to light source  17 , and an electrically insulating, thermally conductive, and transparent liquid  23  that substantially fills interior cavity  15  and submerges light source  17 , optical component  19  and power source  21 . 
     Outer housing, or casing,  13  is constructed as a block-like enclosure that protects the various components retained therein. Outer housing  13  is represented herein as comprising an open box-shaped base  25  and a removable, generally planar cover  27  that together define enlarged, enclosed, interior cavity  15 . 
     Base  25  is preferably constructed out of any suitable rigid, durable and thermally conductive material, such as metal or a thermally conductive plastic, and includes a generally rectangular, planar bottom wall  29  and four upstanding sidewalls  31 - 1  thru  31 - 4  which extend orthogonally up from the outer periphery of bottom wall  29  (i.e., along its free edges) so as to define interior cavity  15 . As will be explained further in detail below, the thermally conductive construction of base  25  serves to draw heat retained by liquid  23  in cavity  15 , primarily from light source  17 , to its exposed external surfaces for cooling (e.g., by ambient air). 
     Cover  27  is a generally planar member that is preferably constructed out of any suitable rigid, durable and transparent material, such as a clear plastic. Cover  27  is dimensioned to overlie the open top wall of base  25  and includes a downwardly projecting, block-like portion  27 - 1  that fittingly projects between the distal ends of sidewalls  31 - 1  thru  31 - 4  so as to enclose interior cavity  15 . 
     A plurality of fastening elements  33 , represented herein as screw fasteners, is driven vertically downward through cover  27 , at various locations along its periphery, and into sidewalls  31  to permanently secure cover  27  onto base  25 . In addition, one or more compression gaskets  35  are disposed between cover  27  and sidewalls  31  to create a watertight seal therebetween. Furthermore, although not shown herein, at least a portion of the exterior of housing  13  is preferably applied with an optically transmissible, static dissipative coating. In this capacity, housing  13  can be assembled into a unitary, watertight, and static dissipative enclosure. 
     Housing  13  is additionally preferably provided with a fluid inlet port  39  and an air pressure port  41 , the function of each port to become apparent in detail below. Inlet port  39  is in the form of a small one-way valve that extends transversely through sidewall  31 - 1  in close proximity to bottom wall  29 . Air pressure port  41  is in the form of a small one-way valve that extends transversely through sidewall  31 - 3  in close proximity to cover  27  (i.e., at the highest location within interior cavity  15 ). 
     It should be noted that the construction of housing  13  could be modified to more adequately suit the needs of the intended application. For instance, it is to be understood that the particular size, shape and/or number of separable pieces for housing  13  could be modified without departing from the spirit of the present invention. As another example, it is to be understood that the transparent region in housing  13  could be relocated, increased (e.g., to include additional walls) or decreased (e.g., limited to a small window formed in cover  27 ) without departing from the spirit of the present invention. 
     As referenced briefly above, a light source  17  is disposed within interior cavity  15  and serves to produce artificial illumination. In the present embodiment, light source  17  is represented as first and second light emitting diodes (LEDs)  43 - 1  and  43 - 2 . However, it is to be understood that the number and particular type of lights utilized to form light source  17  could be modified without departing from the spirit of the present invention. 
     LEDs  43 - 1  and  43 - 2  are fixedly mounted on support blocks  45 - 1  and  45 - 2 , respectively, which are located within interior cavity  15  in close proximity to opposing sidewalls  31 - 1  and  31 - 3 , respectively, of housing  13 . Each support block  45 , which is preferably constructed of an electrically insulated and minimally thermally conductive material, is coupled to housing  13  via optical component  19 . Accordingly, each support block  45  serves to securely retain and orientate its associated light-emitting diode  43  such that light generated therefrom projects downward and inward towards optical component  19  at an angle of approximately  45  degrees. 
     Heat sinks  47 - 1  and  47 - 2  are mounted directly on LEDs  43 - 1  and  43 - 2 , respectively. Each heat sink  47  is preferably constructed as a unitary block of thermally conductive material, such as metal, that includes a plurality of parallel fins to assist in heat dissipation, as will be explained further below. 
     Optical component  19  is preferably constructed as a unitary member that is fixedly disposed within interior cavity  15 . Optical component  19  includes a pair of bulk optical elements  49 - 1  and  49 - 2  that are fixedly spaced way from bottom wall  29  of base  25  by corresponding vertical mounting blocks  51 - 1  and  51 - 2 , respectively. As can be seen in  FIG. 2 , optical elements  49 - 1  and  49 - 2  are arranged as mirror images of one another. 
     The underside of each optical element  49  includes a parabolic reflective surface  53 . As will be explained further in detail below, reflective surface  53  directs light produced by LEDs  43  out though transparent cover  27 . 
     As referenced briefly above, power source  21  is responsible for supplying current to light source  17 . In the present embodiment, power source  21  is disposed within interior cavity  15  and is permanently affixed to the inner surface of bottom wall  29 . However, it is to be understood that power source  21  could be disposed at an alternative location within housing  13  without departing from the spirit of the present invention. For example, power source  21  could be alternatively affixed to the interior of one or more of sidewalls  31  and cover  27 . In fact, it is envisioned that power source  21  could be mounted onto the exterior of housing  13  or even located remotely from fixture  11  without departing from the spirit of the invention. 
     Power source  21  represents any suitable device for storing energy, such as a battery, and includes a positive terminal  55  and a negative terminal  57 . A first conductive element, such as a wire,  59  electrically connects positive terminal  55  to first LED  43 - 1 . A second conductive element, such as a wire,  61  electrically connects LED  43 - 1  to LED  43 - 2 . Lastly, a third conductive element, such as a wire,  63  electrically connects LED  43 - 2  to negative terminal  57 . As such, LEDs  43 - 1  and  43 - 2  are connected in series and together form a daisy chain connection scheme with power source  21 . In this manner, current can be delivered from power source  21  to LEDs  43 - 1  and  43 - 2  in an energy-efficient manner. 
     To control the operation and recharging of power source  21 , bottom wall  29  is provided with a charging port  65  and a control port  67  in close proximity to power source  21 . In the present embodiment, each of charging port  65  and control port  67  is represented as an externally accessible opening that is enclosed at its interior end so as to prevent the passage of liquid  23  therethrough. However, the thickness of the enclosed end of each of port  65  and  67  is limited to enable the control and the transfer of energy into power source  21  to be achieved in a wireless fashion. In other words, external control and energy transfer with power source  21  can be achieved without direct penetration through housing  13  with an external wire. As a result, fixture  11  is a modular unit that remains completely sealed. 
     For instance, energy may be inductively applied to power source  21  by disposing a conductive coil (not shown) inside charging port  65 . The generation of an alternating field by the conductive coil would excite a corresponding resonant circuit in power source  21 , thereby resulting in an efficient, wireless delivery of energy to power source  21 . In a similar fashion, a control signal may be applied to power source  21  through inductive coupling (or even through the delivery of an optical signal through a transparent window formed in bottom wall  29  of housing  13 ). 
     As referenced briefly above, liquid  23  is an electrically insulating, thermally conductive, and transparent liquid that fills the entirety of interior cavity  15  and envelops light source  17 , optical component  19  and power source  21 . Accordingly, filling the entirety of cavity  15  with liquid  23  eliminates the presence of air within fixture  11  and some of the shortcomings associated therewith, such as internal pressure fluctuations, condensation and flammability. 
     It is to be understood that liquid  23  represents any electrically insulating, thermally conductive and transparent liquid. For example, liquid  23  may be in the form of mineral oil, a clear heat stable Phenylmethyl Siloxane (e.g., of the type sold by Dow Corning Corporation of Midland, Mich. as Dow Corning® 550 fluid), or a mixture thereof. However, it should be noted that alternative types of electrically insulating, thermally conductive and transparent liquids could be used for liquid  23  without departing from the spirit of the present invention. 
     It is also to be understood that the particular type of liquid  23  utilized in the construction of light fixture  11  could be selected based upon certain optical characteristics. As an example, a liquid with particular optical properties could be utilized in order to filter out light that falls outside of a desired wavelength spectrum. As another example, a liquid with particular optical properties (e.g., with an index of refraction in the range between  1 . 3  and  1 . 8 ) could be utilized to direct light emitted by LEDs  43  along a desired path. 
     As part of the assembly process, cover  27  is fixedly secured to base  25  using fastening elements  33 , the presence of compression gaskets  35  creating a watertight seal therebetween. Liquid  23  is then filled into cavity  15  through inlet port  39 , with any air present in cavity  15  exiting housing  13  through port  41 . Subsequently thereafter, inlet port  39  is preferably sealed closed by any suitable means, such as through the fitted insertion of a screw with external sealant, a gasket, a pipe thread or any combination thereof. As such, it is to be understood that liquid  23  fills the entirety of the empty space within cavity  15  and envelopes all components located therein. 
     Operation of Light Fixture  11   
     Light fixture  11  is designed to operate in the following manner. Specifically, upon completion of its assembly, light fixture  11  is disposed in any environment that requires high power illumination. Activation (i.e., switching) of light fixture  11  is achieved through control port  67 , which in turn results in the supply of current to LEDs  43 . Upon receiving the necessary current from power source  21 , each LED  43  illuminates. 
     Light emitted from LEDs  43 - 1  and  43 - 2  is directed downward and inward towards reflective surface  53  of optical component  19 , as represented by arrows A and A′, respectively. The light then reflects off surface  53  and penetrates through light intensifying optical elements  49 - 1  and  49 - 2 , as represented by arrows B and B′, respectively. As can be seen, the treated light, as represented by arrows B and B′, continues by passing through both transparent liquid  23  and transparent cover  27 . In this manner, high power light exits fixture  11  (e.g., as a collimated beam). 
     It should be noted that any heat generated by LEDs  43 - 1  and  43 - 2  is extracted by heat sinks  47 - 1  and  47 - 2 , respectively, and transferred to thermally conductive liquid  23  that envelopes the exposed parallel fins on each heat sink  47 . Due to its thermally conductive nature, liquid  23  effectively transfers heat away from heat sinks  47 , or any other heat producing component in cavity  15 . In turn, heat is transferred from liquid  23  to at least one of thermally conductive bottom wall  29  and sidewalls  31  (i.e., without the use of an electrically conductive physical path). Any heat retained by base  25  can then be efficiently cooled due to its relatively large, flat, and exposed, exterior surface (i.e., through heat transfer to the surrounding environment, such as ambient air or water). In fact, although not shown herein, base  25  could even be provided with a plurality of flat, parallel fins, or other similar structures, to assist in heat dissipation. 
     Features and Advantages of Light Fixture  11   
     As set forth in detail below, light fixture  11  is constructed with a number of notable design features that enables fixture  11  to produce high power, high quality light in an intrinsically safe and reliable fashion. 
     As a first feature, light fixture  11  utilizes optical liquid  23 , rather than air, to fill the entirety of interior cavity  15 . Using a liquid, instead of a gas, to fill enclosed housing  13  eliminates significant fluctuations in internal pressure, since the liquid, by its nature, is non-compressible. By minimizing pressure changes within interior cavity  15 , fixture  11  is rendered less susceptible to (i) explosion, (ii) implosion, (iii) internal condensation (e.g., from the drawing of humid external air through its wiring), or (iv) sealant stress and resultant shrinkage. Accordingly, it is to be understood that light fixture  11  could be safely used in a wide range of potential applications, including in high pressure environments (e.g., at significant ocean depths) as well as in hazardous locations with high concentrations of flammable gasses. 
     As a second feature, light fixture  11  is designed to safely dissipate heat produced therefrom. Specifically, the use of a thermally conductive liquid  23 , which envelops all heat producing components, as well as a thermally conductive housing  13  enables heat produced by any component within interior cavity  15 , such as light source  17 , power source  21  and/or any connective wiring, to be efficiently transferred to thermally conductive base  25 . In turn, heat retained by base  25  can be readily cooled by the surrounding environment. Because liquid  23  fills the entirety of interior cavity  15  and is in thermal contact with bottom wall  29  and sidewalls  31 , liquid  23  effectively provides three dimensional paths for thermal conduction and thereby efficiently eliminates any hot spots within fixture  11 . Consequently, it is to be understood that light fixture  11  could be safely utilized in hazardous locations where high concentrations of flammable gas, vapor or dust are present (e.g., a Zone 0 area), which is an object of the present invention. 
     As a third feature, light fixture  11  is designed to minimize the risk of short circuits. Specifically, enveloping the various electrical components in light fixture  11  with electrically insulating liquid  23  limits the risk of a shorting condition. As a result, enlarged metal heat sinks  47  can be utilized to dissipate heat without risk of a short circuit or arcing condition with another electrically conductive member (e.g., a wire) in close proximity thereto. Additionally, the minimized risk of shorting enables LEDs  43  to be connected in series, rather than in parallel, which thereby reduces the current requirement for power source  21 . For instance, a high power fixture with ten LEDs connected in parallel might require a 150 ampere, 3.5 volt power supply and a high number of corresponding conductive wires, with each LED drawing up to 15 amperes of current. By comparison, connecting the same ten LEDs in series would only require a 15 ampere, 35 volt power supply, which is more a manageable power requirement. 
     As a fourth advantage, optical liquid  23  provides light fixture  11  with additional means to optimize the quality of light output therefrom. For instance, as noted above, a liquid with particular optical properties could be selected in order to, among other things, (i) filter out light that falls outside of a desired wavelength spectrum, and/or (ii) direct light along a desired path. 
     Additional Embodiments and Design Modifications 
     It is to be understood that the embodiment described in detail above is intended to be merely exemplary and those skilled in the art shall be able to make numerous variations and modifications without departing from the spirit of the present invention. All such variations and modifications are intended to be within the scope of the present invention as defined in the appended claims. 
     For instance, although light fixture  11  is rendered less susceptible to significant fluctuations in internal pressure than traditional air-filled light fixtures, it is to be understood that light fixture  11  may still experience an implosion or explosion condition when exposed to an extreme variance in temperature. Either of the aforementioned conditions is possible because housing  13 , which is preferably constructed of a rigid material, would typically be constructed out of a material with a lower coefficient of thermal expansion than liquid  23 , as well as optical component  19 . 
     Specifically, if constructed out of aluminum, housing  13  would experience a 0.59% change in volume over 150 degrees. By comparison, mineral oil and one well known type of Phenylmethyl Siloxane, both of which were suggested above as possible materials for liquid  23 , would experience 5.25% and 10.50% changes in volume over 150 degrees, respectively. Furthermore, the use of acrylic for optical component  19  would result in a 1.80% volume change over 150 degrees. As can be appreciated, if housing  13  has a relatively low coefficient of thermal expansion, the volume of interior cavity  15  would not increase to the extent necessary to support the corresponding volumetric expansion of the relatively high coefficient of thermal expansion for liquid  23 , as well as any other components disposed in cavity  15 . 
     It is to be understood that the aforementioned problem associated with the mismatch in the coefficient of thermal expansion for the various components of light fixture  11  could be resolved in a couple different ways. 
     As a first solution, a volumetric compensation element with a lower coefficient of thermal expansion than the coefficient of thermal expansion for housing  13  could be deposited into interior cavity  15  to offset the higher coefficient of thermal expansion of liquid  23 . In particular, it is envisioned that silicon sand, glass and quartz, all of which have considerably low coefficients of thermal expansion, could be disposed into interior cavity  15 , either as a solid nonfunctional object (e.g., as a block or plate), as a functional component (e.g., as a portion of optical component  19 ) or in direct communication within liquid  23  (i.e., to form a mixture with liquid  23 ). 
     For example, if housing  13  is constructed out of aluminum and defines an interior cavity  15  that is 100 cubic inches in size, a temperature change of 150 degrees would result in a volumetric increase of 0.59 cubic inches. By filing interior cavity  15  with a mixture that consists of  11  cubic inches of mineral oil and  89  cubic inches of quartz, the mineral oil would experience a 0.572 cubic inch increase in volume, whereas the quartz would experience a 0.018 cubic inch increase in volume (based on the coefficient of thermal expansion for each item). Combining the increase in volume of the mineral oil (i.e., 0.572 cubic inches) with the increase in volume of the quartz (i.e., 0.018 cubic inches) would thus equal the 0.572 cubic inch increase in interior cavity  15  due to the expansion of housing  13 , thereby minimizing the risk of implosion or explosion of lighting fixture  11 . 
     As a second solution, housing  13  could be provided with means to vary the volume of interior cavity  15  to accommodate volumetric changes in the components disposed therein, such as liquid  23 . Specifically, referring now to  FIG. 3 , there is shown a modification to outer housing  13  for light fixture  11 , the modified outer housing being identified generally by reference numeral  113 . 
     As can be seen, housing  113  is similar to housing  13  in that outer housing, or casing,  113  includes an open box-shaped base  125  and a removable, generally planar cover  127 . Together, base  125  and cover  127  define an enlarged, enclosed, interior cavity  115 . 
     Housing  113  differs primarily from housing  13  in that housing  113  is provided with a deflectable component  129  for selectively adjusting the volume of interior cavity  115  to accommodate for substantial variations in temperature. Specifically, in the present example, deflectable component  129  is represented as a flexible diaphragm, or panel, that is integrated into base  125 . Preferably, deflectable component  129  is constructed to be more flexible than the remainder of base  125 . The increased flexibility of component  129  can be achieved, for example, by (i) constructing component  129  out of a different material than the remainder of base  125  (e.g., of a resilient, elastic material, such as rubber) or (ii) constructing component  129  with a reduced thickness relative to the remainder of base  125 . 
     In use, component  129  can deflect outward, or expand, to the extent necessary so that the volume of interior cavity  115  increases by the same amount that liquid  23  (and any other components retained within cavity  115 ) expands in volume due to a change in temperature. Similarly, component  129  can deflect inward, or collapse, to the extent necessary so that the volume of interior cavity  115  decreases by the same amount that liquid  23  (and any other components retained within cavity  115 ) contracts in volume due to a change in temperature. 
     It should be noted that deflectable component  129  is not limited to a flexible diaphragm. Rather, it is to be understood that deflectable component  129  represents any structure that can be incorporated into outer housing  113  for selectively modifying the volume of interior cavity  115 . For example, although not shown herein, deflectable component  129  could be in the form of a piston, or chamber, that is adapted to either (i) selectively expand or collapse, or (ii) selectively displace, or slide, relative to the remainder of housing  113  (e.g., in the form of a piston that telescopingly displaces in relation to the remainder of housing  113 ) in response to variations in temperature.