Abstract:
A lighting apparatus ( 10 ) comprises a light engine ( 12 ) producing ultra violet radiation. An enclosure ( 14 ) surrounds a radiation generating area of the light engine ( 12 ) to encompass the radiation. At least one wall ( 28 ) of the enclosure ( 14 ) is substantially reflective of the ultraviolet radiation. The enclosure ( 14 ) includes a replaceable top portion ( 30 ) which includes a phosphor portion ( 32 ). The phosphor portion ( 32 ) is spaced from the radiation generating area of the light engine ( 12 ) by a height of the enclosure ( 14 ).

Description:
BACKGROUND  
       [0001]     The present application relates to the art of the LED lighting systems that produce visible light. It finds application in general purpose lighting and will be described with particular reference thereto. Those skilled in the art will appreciate applicability of the present application to a variety of applications such as ornamental, special effects lighting, and other.  
         [0002]     Typically, the LED lighting systems, which produce white or visible light, incorporate blue LEDs coated with phosphor that converts some of the blue light radiation to a complimentary color, e.g. yellow-green emission. Combined blue, yellow and green emissions produce a white light, which typically has a correlated temperature of about 5000K and a color rendition index (Ra) of about 70-75.  
         [0003]     In recent years, newly developed white LED lighting systems unitize a UV emitting chip coated with phosphors which are designed to convert the UV radiation to visible light. Often, two or more phosphor emission bands are employed to approximate white light.  
         [0004]     There are several problems associated with phosphor coated LEDs. Historically, phosphor coated LEDs have rather low package efficiencies. The package efficiency is defined as the ratio of the actual light output of the LED to the light that would be obtained if all the radiation generated escaped from the package without being absorbed. Because phosphor particles generate light that is radiated equally in all directions, some of the light is directed backwards, e.g. toward the LED chip, substrate, submount, and lead structure which absorb a substantial amount of light. In addition, because the phosphors typically are not perfect absorbers of UV or blue radiation, some of the radiation emitted by the LED chip itself is also reflected back onto the structural elements mentioned above.  
         [0005]     Additionally, in order to avoid the UV bleed through, the phosphor coating typically must be relatively thick, e.g. at least 5-7 particles thick, which increases the coating&#39;s visible reflectance. The light lost due to an absorption of radiation (both initial and converted) by the LED chip, submount, reflector and lead structure limits the package efficiency of phosphor coated LEDs to typically 50-70%.  
         [0006]     Furthermore, certain phosphors, such as some from the manganese family, have excessive decay times. When the phosphors with excessive decay times are exposed to high flux emission, i.e., in the close proximity to the LEDs, the effective efficiency is reduced.  
         [0007]     The present application contemplates a new and improved apparatus that overcomes the above-reverenced problems and others.  
       BRIEF DESCRIPTION  
       [0008]     In accordance with one aspect of the present application, a lighting apparatus is disclosed. The lighting apparatus comprises a light engine for producing an ultra violet radiation and an enclosure which surrounds a radiation generating area of the light engine to at least substantially encompass the radiation. The enclosure includes a first portion which is substantially reflective of the ultra violet radiation, and at least one second portion which includes a phosphor portion. The second portion is spaced from the radiation generating area of the light engine and includes a radiation receiving surface and a light emitting surface to render visible light.  
         [0009]     In accordance with another aspect of the present application, a lighting system is disclosed. The light system includes a light engine having a direction of primary radiation emission. The light engine includes a PC board, a plurality of UV LEDs disposed on the PC board, and a heat sink disposed on a side of the PC board opposed to the LEDs. The lighting system further includes an enclosure surrounding the direction of radiation emission. The enclosure includes at least one portion which substantially reflects UV radiation, and a phosphor containing portion generally opposite and spaced from the light engine. The phosphor containing portion includes a visible light reflecting layer on a first side of the phosphor facing the light engine and a UV light reflecting layer on a second side of the phosphor away from the light engine.  
         [0010]     One advantage of the present application resides in remotely placing the phosphor away from the LED sources.  
         [0011]     Another advantage resides in providing a structure in which phosphor mix and concentration are adjusted remotely.  
         [0012]     Another advantage resides in interchangeability of the phosphor containing panel. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     The application may take form in various components and arrangements of components, and in various steps and arrangements of steps. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the application.  
         [0014]      FIG. 1  is a schematic view of an LED lighting assembly in accordance with the present application;  
         [0015]      FIG. 2  is a cross-sectional view of a phosphor containing element;  
         [0016]      FIG. 3  is a schematic view of the LED lighting assembly with a removable top panel; and  
         [0017]      FIG. 4  is a cross-sectional view of the LED lighting assembly having a bulb shape enclosure. 
     
    
     DETAILED DESCRIPTION  
       [0018]     With reference to  FIGS. 1 and 3 - 4 , an LED panel light assembly  10  generally comprises a light engine  12  and an enclosure  14  which surrounds the radiation emitted by the light engine  12 . The light engine  12  includes an interconnect system  16  for mounting and connecting light emitting devices or LEDs  18  such as chip or packaged UV LEDs. Preferably, the LEDs  18  have wavelengths less than 510 nm. A heatsink  20 , including a plurality of heat dissipating elements such as wings  12 , is disposed in thermal connection with the LEDs  18  and the interconnect system  16  to dissipate heat generated by the LEDs  18 . Preferably, the interconnect system  16  includes a printed circuit board or an interconnect board or interconnect boards  24  which includes circuitry for powering the LEDs  18  and the leads for electrical communication with a power source. The interconnect boards  24  are selected from commercially available circuit boards, such as the circuit boards available from BERGQUIST, to provide suitable means for removing heat generated by the LEDs  18  and dissipating it in the heatsink  20 . Preferably, the interconnect board  24  is a thermally conductive type, an epoxy glass resin board with thermal vias, or the like. A mounting surface  26  of the interconnect system  16  is preferably manufactured from a highly reflective material. In one embodiment, the surface  26  is coated with a reflective material leaving the openings for the emitters. Preferably, the light assembly  10  utilizes internal or external electronics to achieve the desired voltage and current drive levels. In one embodiment, series and/or parallel circuits are created to provide the desired operating voltage and improve reliability of the overall system.  
         [0019]     The LEDs  18  are attached to the interconnect board(s)  24  in arrays or strips depending on the requirements of the lighting system. In one embodiment, in which the packaged LEDs are used, the LEDs  18  are soldered, adhered by a use of a conductive adhesive, or otherwise conductively fastened to the interconnect board  24 . In another embodiment, in which the chip LEDs or LEDs on submounts are used, the LEDs  18  are directly attached to the interconnect board  24  by a use of a thermally conductive adhesive and are electrically wirebonded to the circuitry. Alternatively, chip LEDs are flip mounted and directly attached to the board  24  using conductive adhesive, solder, thermosonic, or thermo-compression methods. An index matching gel is preferably applied over the chip surface of the chip LEDs. The interconnect system  16  is attached to the heatsink  20  using a thermally conductive compound.  
         [0020]     With continuing reference to  FIG. 1 , the enclosure  14  includes four walls or sides  28  and a top panel  30 . At least a portion of the enclosure  14  includes a phosphor layer  32  to convert the UV radiation, emitted by the LEDs  18 , to visible light. In one embodiment, the phosphor layer  32  is a tri-color (red-green-blue) phosphor which is dispersed within or exists in an internal uniform layer of the panel  30 . Preferably, the control optics are integrated into the panel structure. An air gap between the top panel  30  and the LEDs  18  is controlled by a height of the enclosure  14 , e.g. height of the walls  28 . The enclosure height is determined such that the light system  10  provides an uniform emission pattern. Typically, the enclosure height is selected depending on spacing and the angular emission pattern of the LEDs  18 .  
         [0021]     Preferably, at least a portion of the enclosure walls  28  includes a UV reflective coating such that a substantial amount of the UV radiation striking the walls  28  is reflected back into the enclosure  14 . Optionally, the walls  28  are constructed from the UV reflective material. In one embodiment, an interior of the walls  28  is coated with a material that is highly reflective to the wavelengths of light generated by the phosphor that exists within the system.  
         [0022]     Typically, the phosphors for the lighting system  10  are selected for high efficiency and proper color during the light system  10  operation, and to minimize the intensity of saturation effects. Preferably, the phosphors are selected from the phosphors with color temperatures (CCTs) ranging from 2500 to 10000 K and color rendering indicies (CRIs) ranging from 50 to 99. The phosphor blend or concentration are readily changed to create a wide variety of color temperatures, color points or CRIs for an individual user without changes to the light engine  12 . Examples of inorganic phosphors that are used in the present application are given in Table 1. In one embodiment, the organic phosphors or combinations of inorganic and organic phosphors are used. Examples of the organic phosphors for a use with the present application are the BASF Lumogen F dyes such as Lumogen F Yellow 083, Lumogen F Orange 240, Lumogen F Red 300, and Lumogen F Violet 570. Of course, it is also contemplated that other phosphors such as the earth complexes with organic component described in the U.S. Pat. No. 6,366,033; quantum dot phosphors described in the U.S. Pat. No. 6,207,229; nanophosphors described in the U.S. Pat. No. 6,048,616; or other suitable phosphors are used.  
         [0023]     Preferably, the saturation effects are minimized by choosing phosphors with the fast decay times (τ&lt;1 ms). Optionally, the saturation effects are minimized by diffusing the incidental UV flux on phosphors which have slower decay times. In one embodiment, the diffusing the incidental UV flux on phosphors is achieved by moving the phosphor layers further away from the UV emitting LEDs.  
                   TABLE 1                       Phos-           phor       Color   Power Material                   Blue   (Ba,Sr,Ca) 5 (PO 4 ) 3 (Cl,F,Br,OH): Eu 2+ , Mn 2+ , Sb 3+             (Ba,Sr,Ca)MgAl 10 O 17 : Eu 2+ , Mn 2+             (Ba,Sr,Ca)BPO 5 : Eu 2+ , Mn 2+             (Sr,Ca) 10 (PO 4 ) 6 *nB 2 O 3 : Eu 2+             2SrO*0.84P 2 O 5 *0.16B 2 O 3 : Eu 2+             Sr 2 Si 3 O 8*2 SrCl 2 : Eu 2+             Ba 3 MgSi 2 O 8 : Eu 2+             Sr 4 Al 14 O 25 : Eu 2+  (SAE)           BaAl 8 O 13 : Eu 2+         Blue-   Sr 4 Al 14 O 25 : Eu 2+         Green   BaAl 8 O 13 : Eu 2+             2SrO-0.84P 2 O 5-0.16 B 2 0 3 : Eu 2+             (Ba,Sr,Ca)MgAl 10 O 17 : Eu 2+ , Mn 2+             (Ba,Sr,Ca) 5 (PO 4 ) 3 (Cl,F,OH): Eu 2+ , Mn 2+ , Sb 3+         Green   (Ba,Sr,Ca)MgAl 10 O 17 : Eu 2+ , Mn 2+  (BAMn)           (Ba,Sr,Ca)Al 2 O 4 : Eu 2+             (Y,Gd,Lu,Sc,La)BO 3 : Ce 3+ , Tb 3+             Ca 8 Mg(SiO 4 ) 4 Cl 2 : Eu 2+ , Mn 2+             (Ba,Sr,Ca) 2 SiO 4 : Eu 2+             (Ba,Sr,Ca) 2 (Mg,Zn)Si 2 O 7 : Eu 2+             (Sr,Ca,Ba)(Al,Ga,In) 2 S 4 : Eu 2+             (Y,Gd,Tb,La,Sm,Pr,Lu) 3 (Al,Ga) 5 O 12 : Ce 3+             (Ca,Sr) 8 (Mg,Zn)(SiO 4 ) 4 Cl 2 : Eu 2+ , Mn 2+  (CASI)           Na 2 Gd 2 B 2 O 7 : Ce 3+ , Tb 3+             (Ba,Sr) 2 (Ca,Mg,Zn)B 2 O 6 : K, Ce, Tb       Or-   (Sr,Ca,Ba,Mg,Zn) 2 P 2 O 7 : Eu 2+ , Mn 2+  (SPP);       ange-   (Ca,Sr,Ba,Mg) 10 (PO 4 ) 6 (F,Cl,Br,OH): Eu 2+ , Mn 2+  (HALO);       yel-   ((Y,Lu,Gd,Tb) 1-x Sc x Ce y ) 2 (Ca,Mg) 1-r (Mg,Zn) 2+r Si z-q Ge q O 12+□ ,       low       Red   (Gd,Y,Lu,La) 2 O 3 : Eu 3+ , Bi 3+             (Gd,Y,Lu,La) 2 O 2 S: Eu 3+ , Bi 3+             (Gd,Y,Lu,La)VO 4 : Eu 3+ , Bi 3+             (Ca,Sr)S: Eu 2+ , Ce 3+             SrY 2 S 4 : Eu 2+ , Ce 3+             CaLa 2 S 4 : Ce 3+             (Ca,Sr)S: Eu 2+             3.5MgO*0.5MgF 2 *GeO 2 : Mn 4+  (MFG)           (Ba,Sr,Ca)MgP 2 O 7 : Eu 2+ , Mn 2+             (Y,Lu) 2 WO 6 : Eu 3 +, Mo 6+             (Ba,Sr,Ca) x Si y N z : Eu 2+ , Ce 3+                    
 
         [0024]     With reference to  FIG. 2 , a coating  40  is disposed on a radiation receiving or an interior surface  42  of the phosphor layer  32 . The coating  40  is transmissive to the wavelengths of the LEDs  18  yet reflective to the wavelengths produced by the phosphors of the phosphor layer  32 . Optionally, a second coating  44  is disposed on a light emitting or an exterior surface  46  of the phosphor layer  32  to reflect any non-converted LED bleed through back into the phosphor layer  32 .  
         [0025]     With reference again to  FIG. 3 , in one embodiment, the enclosure  14  includes the top panel  30  which is a replaceable or removable panel that fits into an opening  50  in a top part of the enclosure  14 . Such construction of the enclosure  14 , e. g. including the removable phosphorescent top panel, allows for an interchangeability of the panel  30  to meet custom color temperatures and color rendition indexes for an individual user while utilizing the same light engine  12  and enclosure walls  28 .  
         [0026]     With reference again to  FIG. 4 , in one embodiment, the lighting system  10  is constructed to resemble the standard incandescent bulb type. Of course, it is also contemplated that the lighting system  10  may be constructed to resemble other geometric shapes, such as spheres, ellipses, or is custom built to fit the needs of an individual user. The enclosure  14  includes a first portion  52  which is disposed on the interconnect board  16  and extends longitudinally in the direction opposite the heatsink  20 . A second portion  54  of the enclosure  14  fits into the opening  50  (not shown) on the top of the first portion  52  to enclose the radiation emitted by the lighting engine  12 . Preferably, the first portion  52  of the enclosure  14  includes a UV reflective coating of inherent material property while the second portion  54  includes a radiation converting phosphor  32 .  
         [0027]     The application has been described with reference to the preferred embodiments. Modifications and alterations will occur to others upon a reading and understanding of the preceding detailed description. It is intended that the application be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.