Patent Publication Number: US-2012032194-A1

Title: Lighting module with high color rending property

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is related to a lighting module, and more particular to a lighting module which used light emitting diodes as a light source having a feature of high color rending index. 
     2. Description of Prior Art 
     Light emitting diode (LED) is kind of semiconductor device, which exploits the property of direct-bandgap semiconductor material to convert electric energy into light energy efficiently and has advantages of long lifetime, high stability and low power consumption. LED is primarily used for the applications of indication lamp, traffic sign and sign broad in its early history, and extend to lighting field when white light LED is successfully developed. 
     The traditional white LED is composed of blue LED chip and yellow phosphor, blue light component occupies major portion of the white light spectrum. The color temperature is high (around 6000K). The red light component in this white light is not sufficient and the color rending property of the white LED is poor. Moreover, in the process of dispensing epoxy, the epoxy tends to overflow to the sidewall of the substrate to influence the uniform of the mixed light. 
     To solve the problem of poor color rending property of the white LED, red phosphor or green phosphor are added in the packaging process of the white LED, thus reducing color temperature and enhancing color rending property. However, the uniformity of the phosphor is difficult to control and the property of thus-formed white LED is not ideal yet. 
     Moreover, a red LED is deposed inside a secondary lens with the white LED, thus achieving a white light lighting module through secondary optics. In the actual application, the white light lighting module emits not only warm light but also red light which human eye can easily observe. 
     Furthermore, the secondary lens will fall off due to an external force; hence, the secondary lens can not protect the LED chip. When the white light lighting module is used for a long time, the heat produced by the LED brings about thermal expansion, this will bring the secondary lens fall off to reduce the luminance intensity of the lighting module. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is direct to a lighting module with high color rendering property and the lighting module can emit warm white light. 
     Therefore, the present invention provides a light module with high color rending property. The lighting module comprises a substrate, a plurality of first light emitting diode chips, a plurality of second light emitting diode chips and a wavelength conversion layer. The first light emitting diode chips are deposed on the substrate and electrically connected to the substrate. The second light emitting diode chips are deposed on the substrate and electrically connected to the substrate and the first light emitting diode chips. The wavelength conversion layer seals the first light emitting diode chips and the second light emitting diode chips. 
     In more particularly, the first light emitting diode chips and the second light emitting diode chips are arranged in number ratio of 2:1, the light emitted from the first light emitting diode chips and the second light emitting diode chips are mixed with light emitted from the wavelength conversion layer after the wavelength conversion layer is excited by the light emitting diode chips to form warm white light with high color rending property. 
     The lighting module with high color rending property according to the present invention mixes the light from the light emitting diode chips of different color and the wavelength conversion layer to provide a light source with low color temperature and high color rending property. The lighting module according the present invention has simply manufacture process and lower cost in comparison with conventional light module. 
    
    
     
       BRIEF DESCRIPTION OF DRAWING 
       The features of the invention believed to be novel are set forth with particularity in the appended claims. The invention itself, however, may be best understood by reference to the following detailed description of the invention, which describes an exemplary embodiment of the invention, taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a top view of the lighting module with high color rending property according to the present invention; 
         FIG. 2  is a sectional view of the lighting module with high color rending property according to the present invention; 
         FIG. 3  is a partially enlarged view for the trench structure shown in  FIG. 2 ; and 
         FIG. 4  shows another top view of the lighting module with high color rending property according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is described below in detail with reference to accompanying drawings. It should be noted that like elements are denoted by the same reference numerals throughout the disclosure. 
       FIG. 1  and  FIG. 2  show the top view and sectional view of the lighting module with high color rending property according to the present invention, respectively. The lighting module comprises a substrate  10 , a plurality of first light emitting diode chips  20 , a plurality of second light emitting diode chips  30 , and a wavelength conversion layer  40 . 
     The substrate  10  further comprises a trench structure  12 . The trench structure  12  is deposed to enclose an island  14 . In this embodiment, the trench structure  12  is circularly deposed on the substrate  10 . The trench structure  12  is provided by etching, plating or machining process. The thickness of the substrate  10  is between 0.1 millimeter and 0.5 millimeter, and the depth of the trench structure  12  is between 0.03 millimeter and 0.1 millimeter. 
       FIG. 3  is a partially enlarged view for the trench structure shown in  FIG. 2 . An interior sidewall  122  of the trench structure  12  and the top surface  102  of the substrate  10  has a lead angle θ, and the lead angle θ is approximately 90 degree. 
     Referring to  FIG. 1  and  FIG. 2 , an electrical connector  16  is through the substrate  10  and deposed on the island  14 . The electrical connector  16  is package by an isolated layer  18  such that the electrical connector  16  is electrically isolated with the substrate  10 . 
     The first light emitting diode chips  20  are deposed on the island  14 , and electrically connected to the substrate  10  (not shown). More particularly, the spectral emission of each first light emitting diode chip  20  lies in the wavelength range from 455 nm to 465 nm, which is corresponding to the wavelength of blue light. 
     The second light emitting diode chips  30  are deposed on the island  14 . The second light emitting diode chips  20  are electrically connected to the substrate  10  and the first light emitting diode  20  (not shown). The spectral emission of each second light emitted chip  30  lies in the wavelength range from 620 nm to 625 nm, which is corresponding to the wavelength of red light. 
     The number ratio of the first light emitting diode chips  20  with respect to the second light emitting diode chips  30  is 2:1. Hence, the lighting module can provide a better color rending property, where the color rendering index is at least 90. 
     Moreover, the first light emitting diode chips  20  and the second light emitting diode chips  30  are axial-symmetrically deposed on the substrate  10 . The second light emitting diode chips  30  are centralized on the center of the island  14 . The first light emitting diode chips  20  surround the second light emitting diode chips  30 . More particularly, the arrangement between each second light emitting diode chips  30  is more concentrative than the arrangement between each first light emitting diode chips  20 . The arrangement capable of well mixing the light emits by the first light emitting chips  20  and the second light emitting diode chips  30 , and enhancing the uniformity of light the lighting module emits. 
     The wavelength conversion layer  40  comprises photoluminescence phosphor, which converts blue light emitted from the first light emitting diode chips  20  into light having a longer wavelength. The wavelength conversion layer  40  is dotted on the substrate  10  such that the wavelength conversion layer  40  covers the first light emitting diode chips  20  and the second light emitting diode chips  30 . The wavelength conversion layer  40  forms a spherical convex emitting surface. The range covered by the wavelength conversion layer  40  is smaller than that of the trench structure  12 . Moreover, the wavelength conversion layer  40  covers the island  14 . A surface tension force of the wavelength conversion layer  40  can prevent the wavelength conversion layer  40  from flowing out of the island  14  and from flowing to the trench structure  12 . Therefore, the wavelength conversion layer  40  can be retained on the surface of the island  14  and cover the light emitting diode chips  20  and  30 . The problem of non-uniform light caused by incomplete covering the light emitting diode chips  20  and  30  can be prevented for the wavelength conversion layer  40 . The wavelength conversion layer  40  can be transparent surface or translucent surface. 
     Moreover, since the limitation of the wavelength conversion layer  40  by the island  14 , the wavelength conversion layer  40  can completely cover the first light emitting diode  20  and the second light emitting diode  30 . The light emits by the light emitting diode chips  20 ,  30  all go through the wavelength conversion layer  40 , whereby the problem of non-uniformity in light emitted from the light emitting diode emits. The diffusion angle of the spherical convex emitting surface which the light goes through are 160 to 170 degrees, thus greatly enhancing light extraction efficiency. 
     In the actual lighting, a white light is generated by mixed the blue light and the light which the wavelength conversion layer  40  emits as being excited by the first light emitting diode chips  20 . The second light emitting diode chips  30  can not excites the wavelength conversion layer  40 , but the red light emitted by the second light emitting diode chips  30  mixing the white light to generate a white light with lower color temperature. 
     The surface of the island  14  can be treated by sand-blasting process to form an uneven surface to increase the adhesive force of the wavelength conversion layer  40 . Moreover the island  14  further comprises characters or a symbol produced by etching, plating or machining process. 
     Moreover, reference is made to  FIG. 4 , which is a top view of the lighting module with high color rending property according to the present invention. The trench structure  12  is of elliptic or double-ring shaped by erosion, etching or machining to prevent the wavelength conversion layer  40  overflow therein in package process. 
     To sum up, the lighting module with high color rending property according to the present invention mixes the light from the light emitting diode chips of different color and the wavelength conversion layer to provide a light source with low color temperature and high color rending property. The lighting device with high color rending property according to the present invention has simple manufacture process and lower cost in comparison with lighting module with phosphor of different colors or the lighting module modifying light with second optical lens. The trench structure deposed on the substrate can effectively solve the problem the overflow of the wavelength conversion layer. 
     Although the present invention has been described with reference to the foregoing preferred embodiments, it will be understood that the invention is not limited to the detail thereof. Various equivalent variations and modifications can still occur to those skilled in this art in view of the teachings of the present inventions. Thus, all such variations and equivalent modifications are also embraced within the scope of the invention as define in the appended claims.