Patent Publication Number: US-8982348-B2

Title: Light source classification system and method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to Korean Patent Application No. 10-2011-0129674 filed on Dec. 6, 2011, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND 
     1. Field of the Disclosure 
     The present disclosure relates to a classification system and method for light sources, and more particularly, to a classification system and method for light sources such as light emitting diodes (LEDs) and the like based on color differences. 
     2. Background 
     Various light sources, such as illuminating light sources and the like, may be classified as desired into categories according to characteristics of light emitted therefrom. For example, light sources for illumination may be classified into light sources having different color regions according to color characteristics of light emitted therefrom. 
     In particular, even in a case in which white light emitting devices are manufactured to produce monochromatic white light, they may emit light of different colors, depending on differences in color temperature or the like due to inevitable errors occurring during the manufacturing process. Such color differences may be used to classify light sources as being within corresponding color regions, according to color differences of light emitted from individual light sources, based on classification regions of the CIE chromaticity diagram. 
     However, even in the case that light sources are classified based on classification regions of the chromaticity diagram by measuring the characteristics of light emitted therefrom, light sources belonging to the same classification region may exhibit substantially different color properties. 
     SUMMARY OF THE DISCLOSURE 
     An aspect of the present disclosure provides a light source classification method capable of effectively reducing color differences. 
     An aspect of the present disclosure provides a system and method of light source classification including: determining a plurality of color regions in a CIE 1976 chromaticity diagram according to desired classification criteria; determining a plurality of color classification regions corresponding to the plurality of color regions through coordinate conversion, thereby allowing the plurality of color regions of a CIE 1976 chromaticity diagram to be converted into the plurality of color classification regions defined by color coordinates of the CIE 1931 chromaticity diagram; measuring CIE 1931 color coordinates of light emitted from a light source to be classified; and classifying the light source based on one of the plurality of color classification regions, in which the measured CIE 1931 color coordinates are located. 
     The determining of the plurality of color classification regions may include converting coordinates (u′, v′) defining each of the color regions of the CIE 1976 chromaticity diagram into coordinates (x, y) of the CIE 1931 chromaticity diagram based on equations (1) and (2): 
                     u   ′     =         4   ⁢   X       X   +     15   ⁢   Y     +     3   ⁢   Z         =       4   ⁢   x           -   2     ⁢   x     +     12   ⁢   y     +   3                 Equation   ⁢           ⁢     (   1   )                   v   ′     =         9   ⁢   Y       X   +     15   ⁢   Y     +     3   ⁢   Z         =       9   ⁢   y           -   2     ⁢   x     +     12   ⁢   y     +   3                 Equation   ⁢           ⁢     (   2   )                 
wherein X, Y, and Z are coordinates of the color of the CIE 1931 chromaticity diagram.
 
     The determining of the plurality of color regions in the CIE 1976 chromaticity diagram may include setting variations (Δu′, Δv′) in coordinates to range from 0.001 to 0.05 in the same color region. 
     Each of the plurality of color regions may be subdivided into a plurality of sub-color regions, and each of the plurality of color classification regions may be subdivided into a plurality of sub-color classification regions corresponding to the plurality of sub-color regions. 
     The light source may be a white LED device. The white LED device may include at least one LED chip emitting light having a first wavelength, and a wavelength conversion material converting the light having the first wavelength into light having a second wavelength. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features and other advantages of the present disclosure will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a flowchart illustrating a classification method for light emitting diode (LED) devices according to an example of the present disclosure; 
         FIGS. 2 and 3  depict the CIE 1976 chromaticity diagram and the CIE 1931 chromaticity diagram for illustrating color coordinate conversion; 
         FIGS. 4 and 5  illustrate examples of white LED devices adopting a light source classification method according to an example of the present disclosure; 
         FIGS. 6 and 7  depict the CIE 1931 chromaticity diagram according to the standard of the United States Department of Energy (DOE) and the CIE 1931 chromaticity diagram according to an example of the present disclosure, respectively; and 
         FIG. 8  depicts sub-regions of the CIE 1931 chromaticity diagram according to an example of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Various examples of the present disclosure will now be described in detail with reference to the accompanying drawings. 
       FIG. 1  is a flowchart illustrating a classification method for light emitting diode (LED) devices according to an example of the present disclosure. 
     In a light source classification method according to an example of the present disclosure, a plurality of color regions may be determined based on desired criteria for classification of light sources in the CIE 1976 chromaticity diagram in operation S 12 . 
     While the CIE 1931 chromaticity diagram, commonly used as the standard for the classification of light sources, is based on the brightness of light, the CIE 1976 chromaticity diagram adopted in operation S 12  is based on luminosity levels able to be sensed by humans, that is, actual visible light colors. 
     In the case of the CIE 1931 chromaticity diagram, a green region having the greatest influence on the brightness of light is set to have the largest area and a blue region having the least influence on the brightness of light is set to have the smallest area. However, in the case of the CIE 1976 chromaticity diagram, the green region is relatively reduced and the blue region is increased so that classification criteria close to an actual luminosity level may be provided. 
     In operation S 12 , the plurality of color regions may be determined according to desired criteria for classification of light sources close to actual luminosity levels provided in the CIE 1976 chromaticity diagram. When the plurality of color regions are determined in the CIE 1976 chromaticity diagram, variations (Δu′, Δv′) in coordinates within the same region may be set to be 0.05 or less in order to minimize color differences within the same region. 
     However, in a case in which the variations are excessively low, precise classification may be difficult due to measurement errors. Therefore, the variations (Δu′, Δv′) in coordinates within the same region may be set to be 0.001 or greater. As such, in an example of the present disclosure, variations in coordinates may be set in a range of 0.001 to 0.05 in the same color region. 
     Then, the plurality of color regions of the CIE 1976 chromaticity diagram may be correspondingly converted into a plurality of color classification regions of the CIE 1931 chromaticity diagram through coordinate conversion in operation S 14 . 
     That is, the plurality of color regions determined in the CIE 1976 chromaticity diagram according to the classification criteria are reflected in the CIE 1931 chromaticity diagram using a coordinate conversion equation. Coordinates actually obtained by a measurement device are based on the CIE 1931 chromaticity diagram. Therefore, the CIE 1931 chromaticity diagram may be adopted in order to use actually measured coordinates of light emitted from a light source. 
     Coordinates (u′, v′) defining color regions of the CIE 1976 chromaticity diagram may be converted into coordinates (x, y) defining color regions of the CIE 1931 chromaticity diagram using the following equations (1) and (2), such that a plurality of color classification regions may be definitely determined. Here, X, Y and Z denote the coordinates of the color of the CIE 1931 chromaticity diagram. 
     
       
         
           
             
               
                 
                   
                     u 
                     ′ 
                   
                   = 
                   
                     
                       
                         4 
                         ⁢ 
                         X 
                       
                       
                         X 
                         + 
                         
                           15 
                           ⁢ 
                           Y 
                         
                         + 
                         
                           3 
                           ⁢ 
                           Z 
                         
                       
                     
                     = 
                     
                       
                         4 
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                         x 
                       
                       
                         
                           
                             - 
                             2 
                           
                           ⁢ 
                           x 
                         
                         + 
                         
                           12 
                           ⁢ 
                           y 
                         
                         + 
                         3 
                       
                     
                   
                 
               
               
                 
                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     ( 
                     1 
                     ) 
                   
                 
               
             
             
               
                 
                   
                     v 
                     ′ 
                   
                   = 
                   
                     
                       
                         9 
                         ⁢ 
                         Y 
                       
                       
                         X 
                         + 
                         
                           15 
                           ⁢ 
                           Y 
                         
                         + 
                         
                           3 
                           ⁢ 
                           Z 
                         
                       
                     
                     = 
                     
                       
                         9 
                         ⁢ 
                         y 
                       
                       
                         
                           
                             - 
                             2 
                           
                           ⁢ 
                           x 
                         
                         + 
                         
                           12 
                           ⁢ 
                           y 
                         
                         + 
                         3 
                       
                     
                   
                 
               
               
                 
                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     ( 
                     2 
                     ) 
                   
                 
               
             
           
         
       
     
     These coordinate conversions will be described with reference to  FIGS. 2 and 3 . 
     With reference to  FIG. 2 , as described in operation S 12 , three color regions are determined according to desired classification criteria. Here, each color region may be defined by two iso-u′ lines and two iso-v′ lines. 
     Coordinates (a1-a4, b1-b4) of respective corners of color regions expressed in the CIE 1976 chromaticity diagram of  FIG. 2  may be converted into coordinates (a1′-a4′, b1′-b4′) of the CIE 1931 chromaticity diagram based on equations (1) and (2), such that color classification regions may be determined as shown in  FIG. 3 . 
     The color classification regions defined in the chromaticity diagram of  FIG. 3  are expressed based on the CIE 1931 chromaticity diagram; however, those are to be construed as being based on the CIE 1976 chromaticity diagram in consideration of luminosity levels. 
     Then, coordinates of light emitted from a light source to be classified may be measured using the CIE 1931 chromaticity diagram in operation S 16 , and the light source may be classified based on a color classification region in which the measured color coordinates are located in operation S 18 . 
     The measurement device is substantially based on the CIE 1931 chromaticity diagram measured in consideration of the brightness of light. Therefore, the classification criteria are converted into the coordinates of the CIE 1931 chromaticity diagram in the preceding operation S 16 , such that the light source may be directly classified based on the color coordinates thereof obtained by the measurement device. 
     Types of light sources to which the classification method according to the example of the present disclosure is applicable are not particularly limited. However, this classification method may be useful and important for white light emitting devices in terms of determination of color differences. In particular, the classification method may provide criteria for precise classification based on color differences which may be variable according to a distribution of wavelength conversion materials such as phosphors and/or quantum dots or wavelength characteristics of a LED chip in a white LED device. 
     In general, a measurement device for classifying color coordinate characteristics measures light sources using the CIE 1931 chromaticity diagram in such a manner that it determines classification regions in the CIE 1931 chromaticity diagram according to desired classification criteria such as color temperature and a black body locus, and classifies measured light sources based on the classification regions. In this case, coordinates obtained by the measurement device correspond to coordinates of the CIE 1931 chromaticity diagram, so that classification may be facilitated. However, since the CIE 1931 chromaticity diagram is based on the brightness of light, a green region having the greatest influence on the brightness of light is set to have the largest area, while a blue region having the least influence on the brightness of light is set to have the smallest area, as illustrated in  FIG. 7 . 
     Accordingly, the light sources may be classified while being less sensitive to the influence of the blue region. Even in the case that the light sources are located within the same color classification region, they may exhibit large color differences in consideration of luminosity levels able to be sensed by humans. Therefore, appropriate classification may not be implemented. 
     In order to alleviate such a problem, color regions are set in the CIE 1976 chromaticity diagram in consideration of luminosity levels able to be sensed by humans, and are then converted into color coordinates of the CIE 1931 chromaticity diagram according to measurement criteria to thereby determine classification regions. Therefore, this classification method may allow for precise classification based on actual color differences, while providing light sources having color uniformity in the same classification region. 
     The light sources may be white LED devices, especially white LED devices including at least one LED chip emitting light having a first wavelength and a wavelength conversion material converting the light having the first wavelength into light having a second wavelength. 
       FIGS. 4 and 5  illustrate examples of white LED devices advantageously adopting a light source classification method according to an example of the present disclosure. 
     A white LED device  20  in  FIG. 4  includes lead frames  22   a  and  22   b , a package body  21  combined with the lead frames  22   a  and  22   b , and an LED chip  25  electrically connected to the lead frames  22   a  and  22   b.    
     In the white LED device  20 , the package body  21  may be formed of resin manufactured by injection molding so as to fix the lead frames  22   a  and  22   b . Here, the lead frames  22   a  and  22   b  may be exposed through a lower surface of the package body  21  to facilitate thermal emission. The LED chip  25  may be electrically connected to the lead frame  22   a  using a wire, and may be enclosed by a resin encapsulating part  28 . 
     As shown in  FIG. 4 , a wavelength conversion layer  27  is formed on an upper surface of the LED chip  25 . The wavelength conversion layer  27  may include at least one wavelength conversion material such as phosphors or quantum dots so as to convert at least a portion of light emitted from the LED chip  25  into light having a different wavelength therefrom. This wavelength conversion may allow the white LED device  20  to produce white light. 
     A white LED device  30  in  FIG. 5  includes lead frames  32   a  and  32   b , a package body  31  combined with the lead frames  32   a  and  32   b , and an LED chip  35  electrically connected to the lead frames  32   a  and  32   b.    
     Unlike the structure of the package body shown in  FIG. 4 , the package body  31  may be formed to fix the lead frames  32   a  and  32   b , while allowing the lead frames  32   a  and  32   b  to remain unexposed through a lower portion thereof. The LED chip  35  may be electrically connected to the lead frame  32   a  using a wire. 
     In the present example shown in  FIG. 5 , a resin encapsulating part  38  including a wavelength conversion material may enclose the LED chip  35 . 
     In the white LED devices as shown in  FIGS. 4 and 5 , color distribution of white light may be generated due to variations in each product such as variations in manufacturing a wavelength conversion material such as contents or distribution of the wavelength conversion material or location of the wavelength conversion material and differences in peak wavelengths of the LED chips  25  and  35 , and thus, it is necessary to classify the devices according to appropriate criteria for color classification. In this case, the classification method according to the example of the present disclosure may be useful so as to appropriately classify light sources in consideration of actual light colors. 
       FIGS. 6 and 7  illustrate the CIE 1931 chromaticity diagram according to the standard of the United States Department of Energy (DOE) and the CIE 1931 chromaticity diagram according to an example of the present disclosure, respectively. 
       FIG. 6  shows the CIE 1931 chromaticity diagram for illuminating light sources according to the DOE standard. This chromaticity diagram includes eight color classification regions F 27  to F 65 . Here, F 27  refers to a color classification region corresponding to a color temperature of 2700K. The existing color classification regions may be represented as shown in Table 1 below. 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 CCT 
                 CIE x 
                 CIE y 
               
               
                   
               
             
            
               
                 6500K 
                 0.3093 
                 0.2993 
               
               
                   
                 0.3231 
                 0.3120 
               
               
                   
                 0.3196 
                 0.3602 
               
               
                   
                 0.3005 
                 0.3415 
               
               
                 5700K 
                 0.3231 
                 0.3120 
               
               
                   
                 0.3361 
                 0.3245 
               
               
                   
                 0.3381 
                 0.3762 
               
               
                   
                 0.3196 
                 0.3602 
               
               
                 5000K 
                 0.3361 
                 0.3245 
               
               
                   
                 0.3495 
                 0.3339 
               
               
                   
                 0.3571 
                 0.3907 
               
               
                   
                 0.3381 
                 0.3762 
               
               
                 4500K 
                 0.3495 
                 0.3339 
               
               
                   
                 0.3640 
                 0.3440 
               
               
                   
                 0.3771 
                 0.4034 
               
               
                   
                 0.3571 
                 0.3907 
               
               
                 4000K 
                 0.3670 
                 0.3578 
               
               
                   
                 0.3898 
                 0.3716 
               
               
                   
                 0.4006 
                 0.4044 
               
               
                   
                 0.3736 
                 0.3874 
               
               
                 3500K 
                 0.3889 
                 0.3690 
               
               
                   
                 0.4147 
                 0.3814 
               
               
                   
                 0.4299 
                 0.4165 
               
               
                   
                 0.3996 
                 0.4015 
               
               
                 3000K 
                 0.4147 
                 0.3814 
               
               
                   
                 0.4373 
                 0.3893 
               
               
                   
                 0.4562 
                 0.4260 
               
               
                   
                 0.4299 
                 0.4165 
               
               
                 2700K 
                 0.4373 
                 0.3893 
               
               
                   
                 0.4593 
                 0.3944 
               
               
                   
                 0.4813 
                 0.4319 
               
               
                   
                 0.4562 
                 0.4260 
               
               
                   
               
            
           
         
       
     
     With reference to  FIG. 6 , boundaries among the color classification regions may coincide with or be parallel to color temperature lines and may be divided based on a black body locus. Since the chromaticity diagram of  FIG. 6  is based on the brightness of light, actual light colors may be different even in the same color classification region. 
     In particular, since the blue region is very narrow in the CIE 1931 chromaticity diagram, actual light colors may be different even in the same color classification region close to the blue region. 
     On the other hand, the CIE 1931 chromaticity diagram of  FIG. 7  includes color classification regions in consideration of color differences. That is, color regions are set in the CIE 1976 chromaticity diagram in consideration of luminosity levels according to color differences, and then coordinate conversion thereof is performed to thereby determine classification regions of the CIE 1931 chromaticity diagram. Table 2 shows color coordinates of the converted classification regions of the CIE 1931 chromaticity diagram. 
     
       
         
           
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                 RANK 
                 CIE x 
                 CIE y 
               
               
                   
               
             
            
               
                 6500K 
                 0.2992 
                 0.3139 
               
               
                   
                 0.3090 
                 0.3114 
               
               
                   
                 0.3277 
                 0.3453 
               
               
                   
                 0.3175 
                 0.3484 
               
               
                 5700K 
                 0.3169 
                 0.3279 
               
               
                   
                 0.3268 
                 0.3253 
               
               
                   
                 0.3446 
                 0.3577 
               
               
                   
                 0.3343 
                 0.3607 
               
               
                 5000K 
                 0.3305 
                 0.3395 
               
               
                   
                 0.3405 
                 0.3366 
               
               
                   
                 0.3610 
                 0.3721 
               
               
                   
                 0.3507 
                 0.3755 
               
               
                 4500K 
                 0.3452 
                 0.3502 
               
               
                   
                 0.3563 
                 0.3468 
               
               
                   
                 0.3791 
                 0.3851 
               
               
                   
                 0.3675 
                 0.3891 
               
               
                 4000K 
                 0.3650 
                 0.3618 
               
               
                   
                 0.3764 
                 0.3582 
               
               
                   
                 0.4027 
                 0.4008 
               
               
                   
                 0.3908 
                 0.4051 
               
               
                 3500K 
                 0.3882 
                 0.3724 
               
               
                   
                 0.4004 
                 0.3683 
               
               
                   
                 0.4296 
                 0.4134 
               
               
                   
                 0.4168 
                 0.4183 
               
               
                 3000K 
                 0.4116 
                 0.3831 
               
               
                   
                 0.4261 
                 0.3780 
               
               
                   
                 0.4575 
                 0.4243 
               
               
                   
                 0.4423 
                 0.4305 
               
               
                 2700K 
                 0.4364 
                 0.3921 
               
               
                   
                 0.4508 
                 0.3868 
               
               
                   
                 0.4810 
                 0.4296 
               
               
                   
                 0.4661 
                 0.4358 
               
               
                   
               
            
           
         
       
     
     The color classification regions of  FIGS. 6 and 7  are slightly different in terms of widths and shapes of the regions.  FIG. 6  may fail to reflect color differences even in the case that the measured color coordinates are present in the same color classification region of the CIE 1931 chromaticity diagram. On the other hand, the color classification regions of  FIG. 7  may be determined as regions close to actual light colors by overcoming the above-mentioned problem. 
     As shown in  FIG. 7 , boundaries among the color classification regions of the CIE 1931 chromaticity diagram do not coincide with or are not parallel to color temperature lines or a black body locus, unlike the existing color classification regions of  FIG. 6 . 
     The plurality of color regions may be subdivided into a plurality of sub-color regions and the plurality of color classification regions may be subdivided into a plurality of sub-color classification regions corresponding to the plurality of sub-color regions. As an example of sub-color classification, sub-color classification regions of  FIG. 8  may be obtained by subdividing F 57  of  FIG. 7 , i.e., a color classification region corresponding to a color temperature of 5700K. Table 3 shows color coordinates with respect to the sub-color classification regions of F 57 . 
     
       
         
           
               
               
               
             
               
                 TABLE 3 
               
               
                   
               
               
                 Sub-Rank 
                 CIE x 
                 CIE y 
               
               
                   
               
             
            
               
                 a 
                 0.3346 
                 0.3607 
               
               
                   
                 0.3398 
                 0.3591 
               
               
                   
                 0.3334 
                 0.3477 
               
               
                   
                 0.3346 
                 0.3492 
               
               
                 b 
                 0.3398 
                 0.3591 
               
               
                   
                 0.3449 
                 0.3575 
               
               
                   
                 0.3384 
                 0.3462 
               
               
                   
                 0.3334 
                 0.3477 
               
               
                 c 
                 0.3283 
                 0.3492 
               
               
                   
                 0.3334 
                 0.3477 
               
               
                   
                 0.3272 
                 0.3366 
               
               
                   
                 0.3222 
                 0.3381 
               
               
                 d 
                 0.3334 
                 0.3477 
               
               
                   
                 0.3384 
                 0.3462 
               
               
                   
                 0.3322 
                 0.3352 
               
               
                   
                 0.3272 
                 0.3366 
               
               
                 e 
                 0.3222 
                 0.3381 
               
               
                   
                 0.3272 
                 0.3366 
               
               
                   
                 0.3213 
                 0.3260 
               
               
                   
                 0.3164 
                 0.3274 
               
               
                 f 
                 0.3272 
                 0.3366 
               
               
                   
                 0.3322 
                 0.3352 
               
               
                   
                 0.3262 
                 0.3247 
               
               
                   
                 0.3213 
                 0.3260 
               
               
                   
               
            
           
         
       
     
     As set forth above, according to examples of the disclosure, color regions are set in the CIE 1976 chromaticity diagram in consideration of luminosity levels able to be sensed by humans, and are then converted into color coordinates of the CIE 1931 chromaticity diagram according to measurement criteria to thereby determine classification regions. Therefore, this classification method may allow for precise classification based on actual color differences, while providing light sources having color uniformity in the same classification region. 
     While the present disclosure has been shown and described in connection with the examples, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the spirit and scope of the disclosure as defined by the appended claims.