Abstract:
A light emitting device includes at least three light emitting source and a phosphor, with the three light sources consisted of following light emitting diodes (LED) emitting lights having different wavelengths. Wherein, two light sources are used to excite the phosphor to produce a distinct wavelength different from those of the two light sources. The distinct wavelength is blended with portions of the two light sources and a light source from another independent light source, and a blended light is released to obtain a white light having an excellent color rendering index.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     (a) Field of the Invention  
         [0002]     The invention relates to a light emitting device, and more particularly, to a light emitting device comprising three light emitting diodes (LED) and a phosphor. The phosphor is excited by absorbing lights from first and second light sources to emit a distinct light. The distinct light is blended with a red light from the third light source and unexcited blue lights from the first and second light sources, and a blended light is released to obtain a white light having an excellent color rendering index.  
         [0003]     (b) Description of the Prior Art  
         [0004]     With reference to  FIG. 8  showing a curve diagram of natural sunlight (natural white light), a light wavelength of the light therein ranges between 360 and 750 nm.  
         [0005]     To manufacture a white light emitting device having a wavelength approaching that of natural sunlight (white light), the Taiwan Patent Publication No. 383508 discloses a light emitting device and a display device, in that a blue light emitting diode serves as a blue light source for exciting a phosphor, such that the excited phosphor emits a light having a wavelength different from that of the blue light. A white light is obtained when the different light is blended with the unexcited blue light emitted by the light source. Referring to  FIG. 9 , a curve S 2  showing a spectrum of the white light obtained is compared with a curve of the natural white light (sunlight) in  FIG. 8 , and it is observed that a rather large deviation exists between the two curves. A reason behind is that, the “white light” defined by blending the light having a larger wavelength emitted by the phosphor excited by the blue light with the unexcited blue light, when compared with natural sunlight, has unsatisfactory color rendering effects.  
         [0006]     Therefore, it is a vital task of the invention as how to provide a white light approaching natural sunlight.  
       SUMMARY OF THE INVENTION  
       [0007]     The object of the invention is to provide a light emitting device that utilizes two light sources for exciting a phosphor to produce light wavelengths different from those emitted by the two light sources. The two different light wavelengths are blended with portions of the two light sources and a light from another independent light source, and a blended light is released to obtain a white light having an excellent color rendering index.  
         [0008]     Referring to  FIGS. 1 and 5 , a light emitting device  10  according to the invention comprises: 
        at least three light emitting sources and a phosphor  50 , with the three light sources being consisted by following light emitting diodes (LED) having different wavelengths; wherein:     a first light source A is formed by at least one first LED  20  capable of emitting a blue light having a wavelength ranging between 360 nm and 480 nm;     a second light source B is formed by at least one second LED  30  capable of emitted a blue to green light having a wavelength ranging between 480 nm and 570 nm;     a third light source R formed is by at least one third LED  40  capable of emitting a red light having a wavelength ranging between 585 nm and 780 nm;     and a phosphor  50  is for absorbing lights having different wavelengths and emitted by the first and second light sources A and B, and is excited to emit a light  60  having a wavelength distinct from those of the first and second light sources A and b; wherein, the distinct light  60  is blended with the red light emitted from the third light source R and the lights emitted from the first and second light sources A and B, and a blended light is released to obtain a white light W having an excellent color rendering index.        
 
         [0014]     According to the aforesaid primary characteristics, wherein the phosphor receives lights having different wavelengths and emitted from the first and second light sources A and B, so as to be excited to emit a distinct light  60 . The distinct light  60  has a wavelength different from those of the first and second light sources A and B, and ranging between 500 nm and 585 nm.  
         [0015]     According to the aforesaid primary characteristics, wherein the phosphor  50  is selected from at least of the following materials: 
        (a) yttium alumimium garnet (YAG);     (b) S im  O 4−   n ; and     (c) BxOy 3− .        
 
         [0019]     According to the aforesaid primary characteristics, wherein an activator of the phosphor  50  selected from one or several of the following compounds: 
        (a) YAG: Ce 3+  having Ce as an activator for activating the phosphor;     (b) YAG: Eu 2+/3+  having Eu as an activator for activating the phosphor; and     (c) YAG: Tb 3+  having Tb as an activator for activating the phosphor.        
 
         [0023]     According to the aforesaid primary characteristics, wherein the device  10  is a printed circuit board (PCB)  80 , to which conducting pins of the first, second and third light sources A, B and R are soldered to form an electric loop. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]      FIG. 1  shows a schematic view of a device consisted of three light emitting diodes (LED) and a phosphor according to the invention.  
         [0025]      FIG. 2  shows a schematic view of a device consisted of three LEDs and two phosphors according to the invention.  
         [0026]      FIG. 3  shows a schematic view of a device consisted of three LEDs encapsulated a phosphor according to the invention.  
         [0027]      FIG. 4  shows a schematic view of a device consisted of three LEDs and two phosphors according to the invention.  
         [0028]      FIG. 5  shows a block diagram illustrating formation of a white light according to the invention.  
         [0029]      FIG. 6  shows a planar schematic view illustrating a device installed at a PCB according to the invention.  
         [0030]      FIG. 7  shows a curve diagram illustrating a spectrum of a white light according to the invention.  
         [0031]      FIG. 8  shows a curve diagram illustrating a spectrum of natural sunlight of a prior invention.  
         [0032]      FIG. 9  shows a curve diagram illustrating a spectrum obtained from a phosphor layer excited by a blue light source of a prior invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0033]     Referring to  FIGS. 1 and 6 , a device may include a PCB or other modularized base. Conducting pins  22 ,  32  and  42  of the first LED  20 , the second LED  30  and the third LED  40  are soldered to the device  10  to form an electric loop. The third LED  40  is located between the first and second LEDs  20  and  30 . The phosphor  50  is formed by mixing transparent resin and phosphor powder, and is encapsulated around the first LED  20 . When being triggered by an electrode, the first LED  20  emits a blue light having a wavelength ranging between 360 nm and 480 nm for serving as a first light source A. When being triggered by an electrode, the second LED  30  emits a blue to green light defined by naked eye and having a wavelength ranging between 480 nm and 570 nm for serving as a second light source B. When being triggered by an electrode, the third LED  40  emits a red light having a wavelength ranging between 585 nm and 780 nm for serving as a third light source R. Referring to  FIG. 5 , the phosphor  50  is for accepting the blue light serving as the first light source A, which is emitted from an interior to an exterior of the phosphor  50  and absorbed by the phosphor  50 . The second light source B emits a blue to green light, and a portion thereof is penetrated into the phosphor  50  from an exterior. Hence, the first and second light sources A and B are simultaneously acted upon the phosphor  50 , such that the phosphor  50  absorbs wavelengths of the first and second light sources A and B at the same time, thereby becoming excited to emit a distinct light  60  having a wavelength ranging between 500 nm and 585 nm. The distinct light  60  is blended with lights from the first light source A, the second light source B and the third light source R, with a blended light released to obtain a white light having an excellent color rendering index.  
         [0034]     Referring to  FIG. 2  showing another embodiment according to the invention, the first LED  20  and the third LED  40  located at two sides are both encapsulated by the phosphors  50 . Thus, the device  10  has each of left and right sides thereof provided with a phosphor  50  ( 50 ), and a second LED  30  disposed at a center section thereof. For that the third light source R emits a red light having a wavelength ranging between 585 nm and 780 nm that is not absorbed by the phosphor  50 , the red light, theoretically, is incapable of exciting the phosphor  50 . Blue lights having a wavelength ranging between 360 nm and 480 nm from the two first LEDs  20  ( 20 ) at the left and right sides are emitted from an interior to an exterior of the phosphors  50  to excite a distinct light  60  having a different wavelength. Meanwhile, the red light from the third light source R is emitted from an interior to an exterior of the phosphors  50 , and a wavelength emitted from the second LED  30  ranges between 480 nm and 570 nm (with a color appearing as blue to green). Therefore, the lights from the first, second and third light source A, B and R, and the distinct light  60  are blended above the device  10  to output a light defined as a white by naked eye. For that the white light obtained from the three independent lights from the first, second and third light sources A, B and R, and the distinct light  60  all have different wavelengths, the white light W has an excellent color rendering index.  
         [0035]     Referring to  FIG. 7  showing a curve diagram illustrating experimental white light according to the invention, a curve S obtained is compared with a curve S 1  of sunlight shown in  FIG. 8 , and it is observed that the two curves S and S 1  appear rather alike. Therefore, the experimental white light has a color rendering index (CRI) as high as over 90%.  
         [0036]     Referring to  FIG. 3  showing yet another embodiment according to the invention, the first, second and third LEDs  20 ,  30  and  40  are all encapsulated by the phosphors  50 . Using the first and second light sources A and B, the phosphors  50  are excited to emit a distinct light  60 . The distinct light  60  is blended with portions of wavelengths of the first and second light sources A and B, and the wavelength of the third light source R, with a white light W displayed above the device  10 .  
         [0037]     Referring to  FIG. 3  showing still another embodiment according to the invention, the device  10  is soldered with first and second LEDs  20  and  30  at left and right sides thereof, and the third LED  40  joined at a center section thereof. Two phosphors  50  ( 50 ) are respectively encapsulated around the first and second LEDs  20  and  30 . Similarly, when the first, second and third LEDs  20 ,  30  and  40  emit the first, second and third light sources A, B and R, the two phosphors  50  ( 50 ) are excited to emit a distinct light  60 . The distinct light  60  are blended with wavelengths of the first, second and third light sources A, B and R, with a light defined as a white light by naked eye and having an excellent color rendering index obtained.  
         [0038]     The phosphor  50  may be made of yttium alumimium garnet (YAG), S im  O 4−   n , or BxOy 3 .  
         [0039]     When the phosphor  50  is selected from YAG, the phosphor may be YAG:Ce 3+  having Y and Al, with Ce as an activator thereof. When the phosphor  50  is selected from YAG, the phosphor  50  may be YAG:Eu 2+/3+ , with Eu as an activator thereof. The phosphor  50  may also be YAG:Tb 3+ , with Tb as an activator thereof.  
         [0040]     It is of course to be understood that the embodiment described herein is merely illustrative of the principles of the invention and that a wide variety of modifications thereto may be effected by persons skilled in the art without departing from the spirit and scope of the invention as set forth in the following claims.