Abstract:
An LED device includes a substrate, a plurality of LEDs, a first light pervious layer, a reflective plate, and a plurality of phosphor particles contained in the first light pervious layer. The LEDs are electrically mounted on the substrate and configured for emitting light of a first wavelength. The reflective plate is mounted on the substrate for directing the light of the first wavelength to transmit through the first light pervious layer. The phosphor particles are configured for converting the light of the first wavelength into light of a second wavelength. A distribution of the phosphor particles in the first light pervious layer gradually decreases from a center to a periphery thereof.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application is related to commonly-assigned copending applications Ser. No. 12/192,382, entitled “LIGHT SOURCE MODULE OF LIGHT EMITTING DIODE” (attorney docket number US 18594). Disclosures of the above-identified application are incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    The present invention relates to illuminating devices, and particularly to a full color light emitting diode (LED) illuminating device. 
         [0004]    2. Description of related art 
         [0005]    Generally, LEDs include a substrate, an LED chip disposed on the substrate, and a light pervious encapsulation covering the LED chip. Usually, a bowl or cup shaped space is defined in the substrate for receiving the LED chip, and for receiving silicon or epoxy resin. One or more visible light-emitting phosphors are integrated in the silicon or epoxy resin. Light emitted from the LED chip excites the phosphors to emit a desired color of light. Light in proper combination can produce a net emission of white light. 
         [0006]    However, the phosphors are integrated into the LED package, which makes the manufacturing process of the LED more complex. In addition, because the silicon or epoxy resin is directly contacted to the LED chip, the luminous efficiency of the phosphor is easily influenced by the heat dissipated from the LED chip. Furthermore, each LED has a particular light intensity distribution, therefore when a number of LEDs are arranged in an array, the mix of colors is difficult to control. 
         [0007]    Therefore, what is needed, is an LED device to overcome the above-described deficiencies. 
       SUMMARY 
       [0008]    One present embodiment provides an LED device. The LED device includes a substrate, a plurality of LEDs, a first light pervious layer, a reflective plate, and a plurality of phosphor particles contained in the first light pervious layer. The LEDs are electrically mounted on the substrate and configured for emitting light of a first wavelength. The reflective plate is mounted on the substrate for directing the light of the first wavelength to transmit through the first light pervious layer. The phosphor particles are configured for converting the light of the first wavelength into light of a second wavelength. A distribution of the phosphor particles in the first light pervious layer gradually decreases from a center to a periphery thereof. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    Many aspects of the present embodiments can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present embodiments. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
           [0010]      FIG. 1  is a schematic, cross-sectional view of an LED device according to a first embodiment. 
           [0011]      FIG. 2  is a schematic, cross-sectional view of an LED device according to a second embodiment. 
           [0012]      FIG. 3  is a schematic, cross-sectional view of an LED device according to a third embodiment. 
           [0013]      FIG. 4  is a schematic, cross-sectional view of an LED device according to a fourth embodiment. 
           [0014]      FIG. 5  is a schematic, cross-sectional view of an LED device according to a fifth embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0015]    Embodiments will now be described in detail below and with reference to the drawings. 
         [0016]    Referring to  FIG. 1 , an exemplary full color LED device  10  according to a first embodiment is shown. The LED device  10  includes a printed circuit board  11 , a light converting layer  12  and a plurality of LEDs  13 . 
         [0017]    The LEDs  13  can produce light from a particular part of the light spectrum. In the present embodiment, the LEDs  13  produce blue light (in wavelengths from 430 to 470 nanometers in the light spectrum). The LEDs  13  are electrically connected to the printed circuit board  11  and an outside power source(not shown). 
         [0018]    The printed circuit board  11  can be an FR4 printed circuit board (PCB), a metal core printed circuit board (MCPCB), a silicon substrate having a circuit printed thereon, or a ceramic substrate having a circuit printed thereon. FR4 is a known type of epoxy resin substrate, so named by the National Electrical Manufacturers Association (NEMA). FR denotes that a material of the substrate is a flame retardant and flame resistant material. 
         [0019]    The LED device  10  further includes an annular reflective plate  14 . The annular reflective  14  has a first end (not labeled) and a second end (not labeled) opposite to the first end. The first end of the annular reflective plate  14  is mounted on the bottom surface  14   b  of the printed circuit board  11 . The inner surface  141  of the annular reflective plate  14  and the bottom surface  14   b  of the printed circuit board  11  cooperatively define an accommodating room  14   a.  The LEDs  13  are received in the accommodating room  14   a  and mounted on the bottom surface  14   b  of the printed circuit board  11 . In the present embodiment, the plurality of LEDs is arranged in an array. 
         [0020]    The annular reflective plate  14  can be made of a reflective material. The reflective material can be a metal such as silver, aluminum, copper and so on. The reflective material also can be ceramic or silicon. 
         [0021]    The inner surface  141  of the annular reflective plate  14  is inclined relative to the bottom surface  14   b  of the printed circuit board  11 . Light emitted from the LEDs is reflected by the inner surface  141  of the annular reflective plate  14 , and then transmitted out from the opening of the annular reflective plate  14 . 
         [0022]    The light converting layer  12  is mounted on the second end of the annular reflective plate  14  and covers the LEDs  13 . The light converting layer  12  contains a number of phosphor particles  124 . Because the light converting layer  12  and the LEDs  13  are partitioned by the annular reflective plate  14 , the luminous efficiency of the phosphor particle  124  is not likely to be influenced by the heat dissipated from the LEDs. Thus the luminous efficiency of the LED device  10  is increased. 
         [0023]    The light converting layer  12  includes a light pervious layer  126 . The phosphor particles  124  is doped in the light pervious layer  126 . The light pervious layer  126  can be made of silicon or epoxy resin. The phosphor particle  124  can be a yellow phosphor, such as a cerium-doped yttrium-aluminum garnet phase (YAG: Ce) phosphor, a yellow nitride phosphor, a yellow silicate phosphor and so on. The phosphor particle  124  also can be a green phosphor, such as green nitride phosphor, a green silicate phosphor and so on. In operation, a part of the blue light emitted from the blue LEDs  13  strike the yellow phosphors or green phosphors doped in the light pervious layer  126 , and the phosphors correspondingly fluoresce yellow or green light. The combination of the blue light that passes through the light pervious layer  126  without striking the phosphors and the light emitted by the phosphors produce a net emission of white light. 
         [0024]    In the first embodiment, the light pervious layer  126  includes a first surface  121  on one side facing the LEDs  13  and a second surface  122  on the opposite side. The first surface  121  is a planar surface. The second surface  122  is a convex surface. A thickness D 1  of the central portion of the light pervious layer  126  is larger than a peripheral thickness D 2  thereof. 
         [0025]    The light pervious layer  126  can be further doped with diffusing particles  128 . The diffusing particles  128  can be made of a light-permeable material including but not limited to polymethylmethacrolate (PMMA), fused silica, fused quartz, aluminum oxide (Al 2 O 3 ), magnesium oxide (MgO), or titanium dioxide (TiO 2 ). The diffusing particles  128  can also be calcium fluoride (CaF 2 ) particles, silicon dioxide (SiO 2 ) particles, calcium carbonate (CaCO 3 ) particles, or barium sulfate (BaSO 4 ) particles. 
         [0026]    Referring to  FIG. 2 , an exemplary LED device  20  according to a second embodiment is shown. The LED device  20  is similar to the LED device  10  in the first embodiment. However, the LED device  20  further includes an auxiliary light converting layer  24 . The auxiliary light converting layer  24  includes a second light pervious layer  241 . The second light pervious layer  241  is doped with red phosphors  242 . In operation, a part of light emitted from LEDs  23  strikes red phosphors  242 , causing the red phosphors  242  to fluoresce red light. 
         [0027]    The auxiliary light converting layer  24  is sandwiched between the light converting layer  22  and the LEDs  23 , thereby preventing the red phosphors  242  absorbing the light converted by the light converting layer  22 . Because the auxiliary light converting layer  24  is applied in the LED device  20 , the color rendering index (CRI) thereof can exceed  90 , and the color saturation can exceed 85%. 
         [0028]    Referring to the  FIG. 3 , an exemplary LED device  30  according to a third embodiment is shown. The LED device  30  is similar to the LED device  10  in the first embodiment. However, the LEDs  33  in the third embodiment are unpackaged LED chips electrically mounted on a printer circuit board  31  via gold wires  332 . The LED device  30  further includes a light pervious encapsulation  35 . The light pervious encapsulation  35  is received in an accommodating room (not shown) defined cooperatively by the printed circuit board  31 , an annular reflective plate  34  and a light converting layer  32 . The light pervious encapsulation  35  can be made of silicon or epoxy resin. In this embodiment, the refractive index of the light pervious encapsulation  35  is larger than that of the light converting layer  32 . 
         [0029]    The light pervious encapsulation  35  can be further doped with diffusing particles  351 . The diffusing particles  351  can be made of a light-permeable material including but not limited to PMMA, fused silica, fused quartz, Al 2 O 3 , MgO, or titanium dioxide TiO 2 . The diffusing particles  351  can also be CaF 2  particles, SiO 2  particles, CaCO 3  particles, or BaSO 4  particles. 
         [0030]    Referring to the  FIG. 4 , an exemplary LED device  40  according to a fourth embodiment is shown. The LED device  40  is similar to the LED device  10  in the first embodiment. However, a first surface  421  and a second surface  422  of a light converting layer  42  in the fourth embodiment are convex surfaces. The thickness of the light converting layer  42  is gradually decreased from a central portion to a peripheral portion thereof. 
         [0031]    Referring to the  FIG. 5 , an exemplary LED device  50  according to a fifth embodiment is shown. The LED device  50  is similar to the LED device  10  in the first embodiment. However, a light converting layer  52  includes a first surface  521  on one side facing the LEDs  53  and a second surface  522  on the opposite side. The first surface  521  is a convex surface. The second surface  522  is a planar surface. The first surface  521  curves or bulges towards the LEDs  53 . 
         [0032]    While certain embodiment has been described and exemplified above, various other embodiments will be apparent to those skilled in the art from the foregoing disclosure. The present invention is not limited to the particular embodiments described and exemplified but is capable of considerable variation and modification without departure from the scope of the appended claims.