Abstract:
Assemblies compliant with night vision imaging system (NVIS) standards are described. Versions of the assemblies incorporate filtering material into an encapsulant for a light-emitting diode (LED) die, avoiding any necessity of using external filtering agents. Alternatively or additionally, filtering material may be incorporated into a housing of an encapsulated LED.

Description:
REFERENCE TO PROVISIONAL APPLICATION 
     This application is based on, claims priority to, and hereby refers to U.S. Provisional Patent Application Ser. No. 61/112,228, filed Nov. 7, 2008, entitled “Night Vision LEDs,” the entire contents of which are incorporated herein by this reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to lighting systems and more particularly, although not necessarily exclusively, to lighting systems compliant with requirements for night vision imaging systems (NVISs) or compatible with NVIS equipment. 
     BACKGROUND OF THE INVENTION 
     Cockpit lighting demands for military or other professional aircraft may be impacted by nighttime, or other low light, operations. In particular, at times during operation of the aircraft, flight crews may have donned night vision goggles or similar equipment to enhance visibility of terrain and other features outside the aircraft. Because these goggles are sensitive to infrared and near-infrared radiation, cockpit illumination often must be designed to minimize output in these regions of the lighting spectrum. Illumination of this type that meets military or other recognized standards in this area is frequently referred to as “NVIS compliant.” 
     U.S. Pat. No. 6,786,617 to Lemay, et al., whose contents are incorporated herein in their entirety by this reference, discusses use of light-emitting diodes (LEDs) for these purposes. Although LEDs are advantageous over incandescent lighting in many ways, visible-wavelength LEDs can also emit energy in the infrared and near-infrared portions of the spectrum and thus must have their light filtered for use with NVIS equipment. Accordingly, the Lemay patent describes an assembly of green and blue LEDs whose light is filtered to be NVIS compliant. See Lemay, col. 2, 11. 47-58. As detailed in the Lemay patent:
         It is another object of this invention to provide an electronic component for use in a night vision imaging system environment comprising a printed circuit board assembly comprising a light source having an emission non-compliant to the night vision imaging system standard, a conformal coating covering the printed circuit board assembly, including an absorbing agent, for filtering quantities of energy of the emission, such that the infrared emission of the printed circuit board assembly is filtered by the absorbing agent.
 
Id., col. 3, ll. 1-9.
       

     Illustrated in  FIG. 2  of the Lemay patent is “a typical assembly of light emitting diodes producing light compliant with a night vision imaging system standard.” Id., ll. 28-30. Shown in the figure are two LEDs (green and blue) assembled on a printed circuit board and coated externally with a conformal coating to which absorbing dye has been added. An optical filter and diffusing film may also be positioned atop the LEDs, with the conformal coating instead applied to the diffusing film in an alternative version of the assembly. See id., col. 5, ll. 7-48. Absent inclusion of (at least) the external conformal coating with its absorbing dye, the assembly would not be NVIS compliant. 
       FIG. 1  of this application depicts a conventional system similar to that of the Lemay patent. As shown in  FIG. 1 , a standard surface-mount LED package  10  includes an encapsulated LED die  14  positioned within a housing  18 , with the encapsulant  22  typically comprising phosphor  26 . An external filtering dye or pigment  30  (which may be in the form of a doped glass or polymeric film) is then coated onto or bonded to the exterior of the housing  18 . In yet other existing systems, the filtering material is separated from—but still external to—the housing of the LED. 
     Unaddressed by these or any other existing NVIS-compliant systems known to applicant is the concept of providing filtering material internal to an LED package. Such concept avoids any necessity of coating or bonding external filters to the package, reducing manufacturing time and expense. It also reduces the possibility of the external filtering material abrading or otherwise wearing in use. 
     SUMMARY OF THE INVENTION 
     The present invention provides systems with internal filtering that are NVIS-compliant or, at least, compatible with NVIS equipment. Certain presently-preferred versions of the systems incorporate filtering material into the encapsulant for an LED. Additionally or alternatively incorporated into the encapsulant may be phosphor or quantum dots. Although not presently preferred, systems of the present invention alternatively or additionally could incorporate filtering material into the housing of the encapsulated LED. In any circumstance, common to all of these systems is that need for an external filtering agent is eliminated. 
     In at least one presently-preferred version of the invention, both phosphor and an absorber of infrared and near-infrared energy, in the form of a dye or pigment, are incorporated into the encapsulant of a blue (or other wavelength) LED die. The encapsulated die is then positioned within a housing (typically, but not necessarily, made of polymeric material or ceramic). Alternatively, component assembly may occur in any other appropriate order. The preferred result, in any event, is an NVIS-compliant LED ready for installation and use. 
     It thus is an optional, non-exclusive object of the present invention to provide lighting systems that are NVIS compliant or, at least, compatible with NVIS equipment. 
     It is another optional, non-exclusive object of the present invention to provide NVIS-compliant lighting systems utilizing one or more LEDs. 
     It is an additional optional, non-exclusive object of the present invention to provide NVIS-compliant lighting systems in which only a single LED die need be included in an LED package. 
     It is a further optional, non-exclusive object of the present invention to provide lighting systems in which filtering material external to an LED package is not required to achieve NVIS compliance. 
     It is also an optional, non-exclusive object of the present invention to provide lighting systems in which filtering material is incorporated into either or both of an encapsulant of an LED die or a housing of the encapsulated die. 
     It is, moreover, an optional, non-exclusive object of the present invention to provide lighting systems in which energy-absorbing filtering material is incorporated into an encapsulant together with phosphor or quantum dots (or both). 
     Other objects, features, and advantages will be apparent to those skilled in appropriate fields with reference to the remaining text and the drawings of this application. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematicized view of an existing LED package with external filtering material. 
         FIG. 2  is a schematicized view of an exemplary LED package of the present invention omitting external filtering material. 
     
    
    
     DETAILED DESCRIPTION 
     Unlike the assembly of  FIG. 1  discussed above, exemplary assembly  50  of  FIG. 2  preferably omits external filtering dye or pigment  30 . This omission simplifies creation of NVIS-compliant or compatible lighting systems, as assembly  50  need not be coated with (or otherwise processed to include) an external filtering agent to ensure NVIS compliance. Avoiding any need for use of an external filtering agent also reduces time and expense associated with processing assembly  50 , as the assembly  50  effectively may be supplied usage-ready without modification. 
     Assembly  50  may comprise LED die  54 , encapsulant  58 , and housing  62 . For most cockpit illumination systems, die  54  preferably—although not necessarily—will be blue, green, or red. Encapsulant  58  may encapsulate die  54 , with both encapsulant  58  and die  54  being housed in housing  62 . 
     Like the assembly of  FIG. 1 , assembly  50  too preferably contains filtering material. Such filtering material  66  is illustrated in  FIG. 2  as dye or pigment configured to absorb at least some energy in either or both of the infrared and near-infrared portions of the light spectrum. It may absorb some energy in the visible portion of the light spectrum as well. Material  66  need not necessarily be dye or pigment or in the form of a doped film, however; instead, it may comprise any agent and structure satisfactory for reducing emissions of die  54  in one or more regions of the spectrum. 
     Filtering material  66  is, however, incorporated into encapsulant  58 . It thus is internal to housing  62 , rather than external to housing  18  as shown in  FIG. 1  or to the LED packages of the Lemay patent. Also shown as incorporated into encapsulant  58  is phosphor  26 , although inclusion of phosphor  26  is optional in some embodiments of assembly  50 . Alternatively or additionally, quantum dots may be incorporated into encapsulant  58 . In any event, preferred versions of assembly  50  are NVIS compliant. 
     Certain alternate versions of assembly  50  incorporate filtering material  66  into housing  62 . This filtering material  66  may be in lieu of or in addition to that discussed in the preceding paragraph. It nevertheless continues to be internal to assembly  50  as opposed to the external coatings of existing systems. Other alternate versions of assembly  50  may involve coating die  54  directly with phosphor  26  while continuing to incorporate filtering material  66  into encapsulant  58 . Yet other versions of assembly  50  contemplate injecting a mixture of phosphor  26  and filtering material into encapsulant  58  in a manner permitting the (higher) specific gravity of phosphor  26  to cause it to settle onto die  54 . 
     Assembly  50  may, if desired, be attached to a printed circuit board similar to the system of the Lemay patent. However, because assembly  50  typically is already NVIS compliant, at least the conformal coating of the Lemay patent is unnecessary. (Although unnecessary, such conformal coating may, however, be added to assembly  50  if desired.) Likewise, if desired, the diffusing film and optical filter of the Lemay patent may also be used with assembly  50 . 
     Any number of LED packages of the present invention, on or off any number of integrated circuits or printed circuit boards, may be included in lighting systems of the present invention. Notably, however, an assembly  50  of the present invention may include as few as one LED die  54 , whereas assemblies of the Lemay patent require a minimum of two LED dies (one blue, one green). Assembly  50  nevertheless may include both blue and green (or other color) LED dies if desired, as the concept of incorporating filtering material  66  into encapsulant  58  (or into housing  62 ) is independent of the type of die  54  included. 
     The foregoing is provided for purposes of illustrating, explaining, and describing embodiments of the present invention. Modifications and adaptations to these embodiments will be apparent to those skilled in the art and may be made without departing from the scope or spirit of the invention.