Patent Publication Number: US-2009231847-A1

Title: Led illuminating device

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to an illuminating device, and more particularly to a LED illuminating device. 
     2. Description of the Related Art 
     Light emitting diodes (LED), with advantages of lower power consumption and higher illumination efficiency, are more and more popular to be used as a light source. The conventional LED includes a chip, which is the light emitting unit, and an enclosure encapsulating the chip therein. In conventional semiconductor process, the chips of LED are cut from a wafer, and the chips on the same wafer have different properties, such as the driving voltage, the peak wavelength, the brightness, and so on that make individual chips have different optical and electrical properties, so that the chips will be classified into different classes, a class is known as a bin. When someone would accept the less numbers of bins, the cost gets higher. 
     More and more liquid crystal displays (LCDs) use white-light LEDs to be the light sources of the backlight modules (BLMs). The conventional backlight modules using white-light LEDs have following drawbacks. LED is a kind of the point light sources. When the backlight module has white-light LEDs as the light source, LEDs are mounted on a substrate by surface mount technology (SMT) to form a substantial line or surface light source for backlight modules. Due to the limitation of manufacture, the white-light LEDs would suffer the position errors, the angle deviations of its optical axis and the gaps between neighboring ones, those cause the curtain mura and the non-uniform brightness distribution. Furthermore, in traditional packaging design of the white-light LEDs, the chip emitting blue rays is changed to white light first, then performs mixing and collimation, divergence, or convergence. Due to white light contains many different wavelength rays, and the optical properties of material depend on the wavelengths, the dispersion phenomenon raises, and causes a non-uniform hue distribution. When the white light LEDs are adopted as the light sources of the backlight modules, the non-uniform brightness distribution and hue distribution will make users have unpleasure viewing experience. 
     SUMMARY OF THE INVENTION 
     The primary objective of the present invention is to provide a LED illuminating device and a backlight module incorporated with the LED illuminating device, which the LEDs may have various optical properties. 
     The secondary objective of the present invention is to provide a LED illuminating device and a backlight module incorporated with the LED illuminating device, which has less non-uniform brightness distribution and non-uniform hue distribution. 
     According to the objective of the present invention, a LED illuminating device includes a substrate having a circuit, a plurality of blue LEDs mounted on the substrate and electrically connected to the circuit, and an optical layer, which is kept a predetermined distance from the blue LEDs, for diffusing rays of the blue LEDs and for converting the rays of the blue LEDs to white light. 
     The LED illuminating device of the present invention may be incorporated in a direct-light backlight module, which includes a frame including a bottom plate and an annular wall, a substrate, which has a circuit, mounted on the bottom plate of the frame, a plurality of blue LEDs mounted on the substrate and electrically connected to the circuit, and an optical layer, which is mounted on the frame and is kept a predetermined distance from the blue LEDs, for diffusing rays of the blue LEDs and for converting the rays of the blue LEDs to white light LEDs. 
     The LED illuminating device of the present invention also may be incorporated in an edge-light backlight module, which includes a light guide plate and a light source mounted in front of an entry side of the light guide plate, wherein the light source includes a substrate having a circuit, a plurality of blue LEDs mounted on the substrate and electrically connected to the circuit, and an optical layer, which is kept a predetermined distance from the blue LEDs, for diffusing light of the blue LEDs and for converting the rays of the blue LEDs to white light LEDs. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded view of a first preferred embodiment of the present invention; 
         FIG. 2  is a sectional view of the first preferred embodiment of the present invention; 
         FIG. 3  is a sectional view of a second preferred embodiment of the present invention; 
         FIG. 4  is a sectional view of a third preferred embodiment of the present invention; 
         FIG. 5  is a sectional view of a fourth preferred embodiment of the present invention; 
         FIG. 6  is a perspective view of a fifth preferred embodiment of the present invention; and 
         FIG. 7  is a sectional view of the fifth preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As shown in  FIG. 1  and  FIG. 2 , a light emitting diode (LED) illuminating device of the preferred embodiment of the present invention is incorporated in a direct-light backlight module  10 , which includes: 
     A frame  12  includes a bottom plate  14  and an annular wall  16 . 
     A substrate  18 , which has a circuit (not shown) thereon, is mounted on the bottom plate  14  of the frame  12 . 
     A plurality of blue light emitting diodes (blue LED)  20  are mounted on the substrate  18  in a matrix layout and are electrically connected to the circuit. The blue LEDs here are packed LEDs. 
     A diffusing plate  22  is mounted on a top of the annular wall  16  of the frame  12 . The diffusing plate  22  is kept a predetermined distance (H) from the blue LEDs  20 . The diffusing plate  22  has an optical layer  24  and a filter layer  30  at opposite sides. The optical layer  24  has a converting layer  26  and a diffusing layer  28 . The diffusing layer  28  is closer to the blue LEDs  20  than the converting layer  26 . The diffusing layer  28  has diffusing particles therein to diffuse light traveling therethrough, and the converting layer has phosphor powder to convert blue light to whit light. The filter layer  30  may reflect the rays with wavelengths greater than 530 nm. The blue LEDs  20  emit blue light traveling through the filter layer  30 , the diffusing layer  28  and the converting layer  26  in sequence. 
     The present invention provides the blue LEDs  20  in matrix layout that the blue LEDs  20  may have brightness in a wider range. In practice, the tolerance of brightness of the blue LEDs  20  is about ±10%. Even more when a few of blue LEDs  20  damage, the present invention still can provide a uniform light source. It can reduce the cost of LEDs due to the more brightness tolerance. 
     In general, the blue LEDs  20  of the present invention are the LED emitting rays with narrow spectrum or the single color rays. In the present invention, the blue LEDs  20  emit blue rays with the peak wavelength between 400 nm and 480 nm. The circuit on the substrate  18  provides the blue LEDs  20  power to emit blue rays. The blue rays travel through the filter layer  30  first, which could reflect the rays with wavelength greater than 530 nm, and transmit the other rays (wavelength under 530 nm), and arrive at the optical layer  24 . The diffusing layer  28  of the optical layer  24  will diffuse the rays through the filter layer  30  first, and the diffused rays will be converted to white light in the converting layer  26 . As a result, the direct-light backlight module  10  of the present invention will provide a uniform surface white light. 
     Because the rays traveling through the diffusing layer  28  are the blue rays with very narrow spectrum, which means the refractive indices of the material for the entire blue rays are almost the same, therefore there is less dispersion in the diffusing layer  28 . After that, the blue rays are converted to white light in the converting layer  26  to provide a uniform line or surface white light. 
     In fact, the phosphor powder in the converting layer, except for converting blue light to white light, is high reflective particles, which means the phosphor powder may diffuse light also. Therefore, as shown in  FIG. 3 , a direct-light backlight module  32  of the second embodiment of the present invention has an optical layer  34  having only phosphor powder, it serves the same functions as the diffusing layer  28  and the converting layer  26 , diffusing and converting light in the same time. 
     Wavelength of the phosphor powder in the optical layer is chosen according to the emission peak wavelength of the blue LEDs. In our test, the relationship of the wavelength of the phosphor powder and the wavelength of light of the blue LEDs is shown in the following table: 
     
       
         
           
               
               
             
               
                   
               
               
                   
                 Emission wavelength 
               
               
                 Emission wavelength of phosphor powder 
                 of the light of blue LED 
               
               
                   
               
             
            
               
                 525~535 nm 
                 452.5~457.5 nm 
               
               
                 535~545 nm 
                 457.5~462.5 nm 
               
               
                 545~555 nm 
                 462.5~467.5 nm 
               
               
                 550~560 nm 
                 467.5~472.5 nm 
               
               
                   
               
            
           
         
       
     
     It has to be mentioned here that the optical layer (or the phosphor powder layer) has to keep a predetermined distance from the blue LEDs. In optical theory, the distance between the optical layer and the blue LEDs is positive relative to a uniform distributed light source. But in a limited size of backlight module, a distance (H) between the optical layer and the blue LEDs is relative to a distance (P) between the neighboring blue LEDs, referring to  FIG. 2 . According to our experience, the distance (H) between the optical layer and the blue LEDs is 1.5 times greater than the distance (P) between the neighboring blue LEDs, or greater. 
       FIG. 4  shows a direct-light backlight module  36 , which is similar to the backlight module  32  of  FIG. 3 . The differences are: unpacked LED chips  38  are mounted on a substrate  40 , and a protective layer  42  is coated on the substrate  40  to cover the LED chips  38 . The protective layer  42  may be epoxy, silicon, or other relative materials. A diffusing plate  44  is doped with phosphor powder  44 . Another direct-light backlight module, as shown in  FIG. 5 , is provided with cup-like walls  52  on a substrate  50  and LED chips are mounted in the walls  52  respectively, and then epoxy is filled in the walls  52  to form protective layers  56 . 
     The LED illuminating device of the present invention may be incorporated in an edge-light backlight module. As shown in  FIG. 6  and  FIG. 7 , an edge-light backlight module  58  includes a light guide plate  60  and a light source  62  incorporated with the LED illuminating device of the present invention. The light source  62  includes a substrate  64  having a circuit (not shown), a plurality of blue LEDs  66  mounted on the substrate  64 , an separating layer  68  with a predetermined width provided on the substrate  64  and covering the blue LEDs  66 , a filter layer  70  provided on the separating layer  68  and an optical layer  72  provided on the filter layer  70 . The separating layer  68  may be epoxy, silicon, or other relative materials. The filter layer  70  is closer to the blue LEDs  66  than the optical layer  72 . The optical layer  72  is a phosphor powder layer. The edge-light backlight module  58  further has a lens layer on the optical layer  72  facing an enter side  78  of the light guide plate  60 . The light  62 , except the lens layer  74 , is coated with a reflective layer  76 . The light  68  provides white light entering the light guide plate  60  via the enter side  78  and traveling out via an exit side  80  at a top of the light guide plate  80 . 
     The light  62  serve the same function as described above. The lens layer  74  is a convex lens in the present embodiment to change paths of the white light to a parallel direction. 
     In conclusion, the main character of the present invention is that the blue LEDs provide rays with narrow spectrum. The rays are diffused, and then are converted to white light, or the rays are diffused and converted in a single optical layer. It may provide a uniform light source with higher brightness and more uniform hue.