Abstract:
Shielding radio frequency interference (RFI) using reflector optics is disclosed. A simplified non-sealed reflector is used in conjunction with a mounting system, resulting in desired amounts of visible and non-visible light using radio frequency driven luminaries and emitters without sacrificing output or coverage area. Configurations are disclosed such that achieved RF grounding is compliant with FCC regulations. Accordingly, the disclosed RFI shielding improves optical design options, increased output, and decreased manufacturing costs over traditional sealed enclosures.

Description:
CROSS REFERENCE TO RELATED PATENT APPLICATION 
       [0001]    This patent application claims priority from U.S. Provisional Application No. 62/026,239, filed Jul. 18, 2014, which application is hereby incorporated in its entirety by reference. 
     
    
     BACKGROUND 
       [0002]    Electronic systems produce and are susceptible to electromagnetic interference (EMI), created through either electromagnetic induction or electromagnetic radiation from an external source. In the context of radio waves, radio frequency interference (RFI), is produced. The interference created has the potential to interrupt, deteriorate, or cause other unwanted performance in many common devices ranging from radios to cellular phones to televisions. Federal Communications Commission (FCC) requirements for the mitigation RFI are extremely strict, down to microvolts, thus it is important RFI be mitigated using appropriate radio frequency (RF) grounding. 
         [0003]    To suppress RFI radiation, many enclosures are designed to form a sealed container for whatever may be producing the RFI. For example, an integrated circuit (IC) chip generating radio frequencies for a plasma lighting system may be contained within a housing that is sealed using the correct RFI gaskets. What is more difficult is the containment of RFI that escapes through the bulb of a lighting system that uses radio waves, i.e. plasma lighting. To contain the RFI produced from the light source, complicated housings, referred to from here on as “RFI Boxes”, must be employed to contain the escaping radiation. Conventional hardware required to successfully contain RFI from a light source as described above includes a sealable cavity to which the light source is attached, a gasket, and a piece of glass which is sealed against the gasket using a fastened flange. 
         [0004]    However, these additional materials add cost to the production process as well as time to assembly. Moreover, present RFI boxes cause a loss of total electromagnetic output per area of coverage i.e. watts per square meter, also known as irradiance. Irradiance comprises not only the visible spectrum, but UVB and infrared wavelengths as well. Additionally, glass reduces output by an additional eight percent, and blocks the beneficial UV wavelengths UVA and UVB. Some plasma technologies produce UVC, which demands the use of glass to filter this wavelength out which can cause damage on the cellular level. 
         [0005]    Aside from these concerns, the geometry of conventional RFI boxes for lamps causes coverage area to be diminished considerably, requiring increased distance from a desired coverage plane to reach a desired coverage area. For example in terms of horticulture, coverage of a 4 foot by 4 foot area should be achievable at 12 to 18 inches from the desired plane, i.e. the canopy, to produce adequate intensity for growth. When using a conventional RFI box, this distance must be increased dramatically, causing output at the desired plane to be less than optimal. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    The Detailed Description is set forth with reference to the accompanying figures. 
           [0007]      FIG. 1  is a luminaire for horticulture utilizing reflection optics to shield lamp RFI. 
           [0008]      FIG. 2  is a side view of a lamp assembly mounted to a frame with a bracket. 
           [0009]      FIG. 3  is a section view of an exemplary RF shielding contact between a reflector and a lamp. 
           [0010]      FIG. 4  is a luminaire for horticulture utilizing reflection optics and a whisker assembly. 
           [0011]      FIG. 5  is an exploded view of an exemplary luminaire for horticulture utilizing reflection optics, a whisker assembly, and a wire mesh screen to shield lamp RFI. 
           [0012]      FIG. 6  is a section view of an exemplary wire mesh shield assembly mounted to a fixture housing. 
           [0013]      FIG. 7  is flow diagram of an exemplary method of RFI shielding for a horticultural lighting system. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    This disclosure describes, in part, a luminaire which utilizes an optical reflector in conjunction with a mounting system capable of shielding RFI produced by a lamp. 
         [0015]    In various embodiments, the optical reflector may be any device, used to guide or manipulate in any way, electromagnetic output of a luminaire. Each luminaire may contain one or more light sources used in tandem, depending on the design. 
         [0016]    In various embodiments, the lamp may be any lamp capable of generating EMI or RFI when operating. EMI would be generated by light sources such as high intensity discharge (HID), LED, incandescent, etc. whereas RFI would be generated by light sources driven by RE such as a plasma. light source. 
         [0017]    In some embodiments, a mounting system may be any method of ensuring physical contact between conductive components in order to shield radiated electromagnetic waves from leaving the luminaire. 
         [0018]    The luminaire of this disclosure may allow energy from radiated RF electromagnetic waves to be conducted to ground as an electrical current, thus minimizing radiated electromagnetic waves that leave the fixture after being emitted from the lighting apparatus. In various embodiments, the luminaire may be controlled by a network controller. The network controller operable to connect to a master control software program, via a communications network. The master control software program may be configured to control the horticultural light&#39;s output spectrum. 
         [0019]      FIG. 1  is a luminaire  100 . The luminaire  100  may be a horticultural lighting fixture. The lighting fixture  100  may include a housing  102 , an optical reflector  104 , a lamp  106 , and a conductive fastener  108 . The fastener may fasten at least a one surface of the lamp  106  to be in physical contact with at least one surface the reflector  104 . 
         [0020]    The housing  102  may be constructed of electrically conductive material, such as a metal or an engineered polymer. The housing  102  may include a housing opening, through which light may be emitted by a lamp  106  and directed by an optical reflector  104 . In some embodiments, the housing may be constructed at least partially of an engineered polymer that may contain metal fibers that make the engineered polymer conductive. 
         [0021]    In various embodiments, the housing  102  may enclose internal components of the luminaire  100 . The housing  102  may be constructed of housing components fastened together. In alternative embodiments, the housing  102  may be constructed as one solid component. 
         [0022]    As illustrated, a luminaire  100  may include optical reflector  104 . The optical reflector  104  may provide adequate RFT shielding by being secured to the lamp  106  using a conductive fastener  108 . 
         [0023]    In various embodiments, the luminaire  100  may be any sort of device capable of producing visible and non-visible light, such as a light-emitting plasma luminaire. Alternatively, the luminaire  100  may produce another type of light that may use radio frequencies to produce electromagnetic energy. The optical reflector  104  may be any sort of device capable of reflecting light output produced by the lamp  106 . The optical reflector  104  may possess varying geometry. In various embodiments, the optical reflector  104  may a horizontal surface through which at least one bulb may protrude. Additionally, the horizontal surface may have holes through which prongs of a whisker assembly may protrude around the bulb in order for the prongs of the whisker assembly to serve as an added faraday cage. The whisker assembly is described in detail in  FIG. 4 . 
         [0024]    The optical reflector may additionally have a plurality of surfaces for reflecting light set at an angle of 135 degrees with respect to the horizontal surface, or set at an angle of 45 degrees with respect to the horizontal plane of the housing opening. 
         [0025]    The lamp  106  in various embodiments may be any device capable of producing electromagnetic energy within the visible spectrum as well as beyond the visible spectrum, such as UV wavelength below 400 nm, or infrared wavelengths above 700 nm. The lamp  106  may utilize lighting technologies such as plasma, LED, HID, or any other form of lighting technology. 
         [0026]    The lamp  106  may comprise a resonator and a bulb. The resonator may receive a radio frequency (RF) output signal from a driver and may emit a concentrated RF field based on the RE output signal. The RE field may drive a bulb to emit light through the housing opening. 
         [0027]    The lamp  106  may be a source of stray radio waves which require shielding through the methods described herein. By conductively coupling the optical reflector  104  to the lamp  106 , the optical reflector  104  may be an RF shielding component. 
         [0028]    In some embodiments, the optical reflector  104  is conductively coupled to a chassis, to which the lamp  106  is in turn conductively fastened to the chassis. A chassis may be constructed of electrically conductive material, such as a metal or a metal polymer. The chassis is described in further detail in the detailed description of  FIG. 2 . 
         [0029]    A conductive fastener  108  may be any fastener capable of maintaining physical contact between the optic reflector  104  and the lamp  106  to produce adequate RF grounding between the lamp and the rest of the fixture, including the housing  102 . 
         [0030]    By ensuring contact, all components may be interconnected, allowing stray radio waves from the lamp to be captured and grounded to prevent interference with the light output and other sensitive components. The conductive fastener  108  may be a machine screw, bolt, or any other fastener capable of providing contact between the optical reflector  104  and the lamp  106 . 
         [0031]      FIG. 2  is a side view  200  of a lamp module  202  as it is shown underneath the housing  102 . The lamp module  202  may be coupled to the lamp  106 . The lamp module  202  may be fastened to a mounting bracket  204 , which may be fastened to a chassis  206 . The chassis  206  may be in turn mounted to the housing. The chassis may include at least one electrically conductive surface. 
         [0032]    The mounting bracket  204  may provide adequate grounding in conjunction with the optical reflector  104  by being secured to a chassis  206  using an adequate fastener  208  to ensure proper contact between metallic surfaces. The fastener  208  may be a conductive fastener, and may be machine screw, bolt, or any other fastener capable of providing contact between the optical reflector  104  and the lamp module  202 . 
         [0033]    The lamp module  202  may be any device requiring RF grounding to function as desired, such as plasma, lighting. 
         [0034]    In some embodiments, the mounting bracket  204  may be any device capable of securing the lamp module  202  to a chassis  206 . The bracket  204  ensures the optical reflector  104  is in continuous contact with the chassis  206  through contact with the lamp module  202 . The continuity of contact between all components may ensure that stray RF signals are grounded and that unwanted effects may be mitigated. 
         [0035]    In some embodiments, the chassis  206  may be any device capable of supporting components as well as providing a common point for radio grounding to occur. The chassis  206  in many instances may be a metallic material or other material capable of grounding stray RF signals through contact with an EMI shield such as an optical reflector  104 . 
         [0036]    In various embodiments, the fastener  208  may be any device capable of providing firm contact between the lamp module  202 , the bracket  204 , and the chassis  206 , or any combination of these devices. The efficacy of the optical reflector  104  as an EMI shield may be reliant on the physical contact established through all previously mentioned devices. The fastener  208  may include the combination of a nut and bolt, a threaded insert and bolt, or any other fastening method capable of providing firm contact. 
         [0037]      FIG. 3  is a section view  300  of  FIG. 2  that may provide clarity on the physical interaction between previously described components. The optical reflector  104  and the lamp  106  are described above in detail with regard to  FIG. 1 . The lamp module  202 , the mounting bracket  204 , the chassis  206 , and the fastening method  208  are described in detail above with regard to  FIG. 2 . As previously described, the physical contact made between the optical reflector  104  and the lamp module  202  is made possible by the conductive fastener  108 . 
         [0038]    The Whisker assembly  302  may be coupled to the chassis  206  by a conductive fastener  108 . The whisker assembly  302  may have a metallic base and an array of metallic prongs perpendicularly extending from the metallic base. Each metallic prong may be a steel wire at least one inch long and may be between 0.04″ and 0.06′ in diameter. The whisker assembly  302  may act as a faraday cage and may shield or absorb a portion of RFI. 
         [0039]      FIG. 4  is an exemplary horticultural luminaire  400  utilizing an optical reflector  104 , a whisker assembly  302 , and a wire mesh frame  402 . The optical reflector  104  is described in detail above with regard to  FIG. 1 . The whisker assembly  302  is described in detail above with regard to  FIG. 3 . The wire mesh frame  402  may be used to allow wire mesh screen to extend across the housing opening, thus increase performance of RFI shielding while allowing greater than 80% light transmission. 
         [0040]    In some embodiments, the metallic base may be coupled between the optical reflector  104  and the lamp module  202 . The array of metallic prongs may positioned so that the bulb is positioned within the array. The array of metallic prongs may protruding through a corresponding set of holes in the optical reflector  104 . 
         [0041]    Alternatively, the metallic base may be clipped onto an exposed surface of optical reflector  104  surrounding the bulb, and the array of metallic prongs positioned so that the bulb is positioned within the array. In some embodiments, the array of metallic prongs may comprise at least three metallic prongs equally spaced. 
         [0042]    In some embodiments, the whisker assembly may be at least partially constructed of aluminum. 
         [0043]      FIG. 5  is an exploded view  500  of an exemplary luminaire for horticulture utilizing an optical reflector  104 , a whisker assembly  302 , a bracket  406 , and a wire mesh screen  508  to shield lamp RFI. 
         [0044]    The wire mesh screen  508  may be coupled to the housing  102 . The wire mesh screen may be fastened to a wire mesh frame  502 . The wire mesh screen may extend across the housing opening and may be configured to absorb at least a portion of the RF field emitted by the resonator. 
         [0045]    The wire mesh screen may be configured to have a transparency of 88% ( 50  openings per inch [OPI]). In some embodiments, the wire mesh screen may have a transparency as low as 100 OPI, which may more effectively shield RFI and EMI. 
         [0046]    In some embodiments, the wire mesh screen may be at least partially constructed from a ferrous material or a nickel alloy. 
         [0047]      FIG. 6  is a section view  600  of an exemplary wire mesh shield assembly mounted to a fixture housing. 
         [0048]    The wire mesh screen  508  may be coupled to a conductive gasket  602 . The conductive gasket  602  may be configured to hold a portion of the wire mesh screen  508  into a corresponding gasket groove in the bracket  406 . A wire mesh frame  402  may mount to at least one bracket  406  in a plurality of locations. In several embodiments, the number of mounting locations may be more than seven. A conductive adhesive may bond the perimeter of the wire mesh screen  508  to the wire mesh frame  402  utilizing the corresponding gasket groove. 
         [0049]      FIG. 7  is flow diagram of an exemplary method  700  of RFI shielding for a horticultural lighting system. 
         [0050]    At  702 , the chassis  206  may be coupled to the housing  102 . 
         [0051]    At  704 , the lamp module  202  may be coupled to the chassis  206  with a conductive fastener. 
         [0052]    At  706 , the optical reflector  104  may be coupled to chassis  206  with a conductive fastener  108 . 
         [0053]    At  708 , whisker assembly  302  may be coupled to chassis  206  with conductive fastener  108 , positioned between the lamp module  202  and the optical reflector  104 . 
         [0054]    At  710 , the whisker assembly  302  may be positioned so that the array of metallic prong protrudes through a corresponding set of holes in the optical reflector. 
         [0055]    At  712 , mounting bracket  204  may be coupled to the housing  102  along at least one side of the housing opening. 
         [0056]    At  714 , a wire mesh screen  508  may be coupled to the mounting bracket by an additional conductive fastener. The wire mesh screen may be formed of woven conductive strands extending across the housing opening. 
         [0057]    Accordingly, an RF grounding path may be provided from each shielding component to the housing. 
       CONCLUSION 
       [0058]    Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.