Patent Publication Number: US-2015085473-A1

Title: LED Backlight Display Device and LED Backlight Arrangement Method

Description:
TECHNICAL FIELD 
     The present invention relates to an LED backlight display device and an LED backlight arrangement method, which are applied to a light source such as a liquid crystal panel, and pertains to a technique which makes it possible to measure luminance and chromaticity utilizing a front sensor that is not affected by temporal change of LEDs. 
     BACKGROUND ART 
     Most conventional liquid crystal monitors or the like employ a backlight utilizing a CCFL (Cold Cathode Fluorescent Lamp). Therefore, even though a front sensor is arranged in the vicinity of the CCFL in an edge-type backlight, a phenomenon in which the luminance and chromaticity varies in only part of the CCFL does not occur, and thus the display condition of the entire display screen does not change. 
     However, in recent years, an LED backlight is watched with interest as a backlight (light emitting device) which irradiates a light modulating element (e.g., a liquid crystal panel) from the back of the element. 
     For example, Patent Document 1 discloses LED backlights which emit irradiation light of white light by arranging white LEDs or emit white light by arranging LEDs of three colors that are R (red), G (green), and B (blue) mixed together. 
     The LED backlight is arranged on the longer sides (lengths) of the body of a liquid crystal panel and controls the luminance and chromaticity of the screen based on a measurement signal sent from a front sensor. 
     More specifically, in an ordinary display device  1  shown in  FIGS. 4 and 5 , an LED backlight  3  is arranged on each longer side  2 A of an liquid crystal panel body  2  which generally has a rectangular shape that includes the longer sides  2 A and shorter sides  2 B (widths). 
     The LED backlight  3  has a plurality of light emitting elements  3 A aligned vertically along the longer sides  2 A of the liquid crystal panel body  2  and a front sensor S 1  is provided at the LED light emitting elements  3 A. 
     Similar to the LED backlight  3 , the front sensor S 1  is arranged on the longer sides  2 A of the liquid crystal panel body  2 . The front sensor S 1  measures the luminance and chromaticity of the LED light emitting elements  12 A so as to control the luminance and chromaticity of the relevant screen. 
     Generally, at the time of shipping the products, the luminance and chromaticity measured utilizing the front sensor S 1  do not always coincide with the luminance and chromaticity shown at a central part A of the screen, due to a variation in the screen or the like. Therefore, a factory worker or the like calibrates the screen in advance so that the measured values of the front sensor S 1  coincide with the luminance and chromaticity at the central part A of the screen. 
     Additionally, in most ordinary edge-type backlights utilizing a CCFL (Cold Cathode Fluorescent Lamp), a front sensor S 1  is also arranged on the longer sides of the body, as shown in  FIG. 5 , so as to attach the front sensor S 1  at a relatively inconspicuous position. 
     PRIOR ART DOCUMENT 
     Patent Document 
     Patent Document 1: Japanese Unexamined Patent Application, First Publication No. 2010-91816. 
     DISCLOSURE OF INVENTION 
     Problem to be Solved by the Invention 
     As described above, the LED backlight  3  is arranged on the longer sides of the liquid crystal panel body  2 . When the front sensor S 1  is also arranged at the longer sides, the front sensor S 1  strongly correlates with the LED light emitting elements  3 A (specifically, LED light emitting elements  3 A indicated by “LED_R 1 ” to “LED_R 3 ” in  FIG. 5 ) in the vicinity of the front sensor S 1 . 
     More specifically, in a light source such as the LED backlight  3  formed by a plurality of small light sources, the LED light emitting elements  3 A in the vicinity of the front sensor S 1  (i.e., those indicated by LED_R 1  to LED_R 3  in  FIG. 5 ) considerably affects the measurement of the luminance and chromaticity utilizing the front sensor S 1 . Therefore, if performing the screen control based on the measured values of the front sensor S 1  in an abnormal state of the LED light emitting elements  3 A in the vicinity of the front sensor S 1 , the screen may not be accurately controlled. 
     That is, when a dispersion due to a temporal change occurs between the individual LED light emitting elements  3 A, even though controlling the screen based on the measured values of the front sensor S 1 , a variation occurs, in particular, in the luminance and chromaticity of the central part A of the screen due to the LED light emitting elements  3 A having such a dispersion. 
     In light of the above circumstances, an object of the present invention is to provide an LED backlight display device and an LED backlight arrangement method, which remove an effect such as a dispersion due to a temporal change that occurs at the individual LED light emitting elements so as to reduce the relevant influence on the measurement of the luminance and chromaticity utilizing a front sensor to a minimum degree. 
     Means for Solving the Problem 
     In order to achieve the above object, the present invention provides an LED backlight display device comprising: 
     a display panel body having a substantially rectangular shape which includes longer sides and shorter sides as edge portions; and 
     a backlight arranged in a manner such that LED light emitting elements are aligned along the edge portions of the display panel body, 
     wherein the backlight is arranged at any one of the longer sides and the shorter sides of the display panel body; and 
     a front sensor that measures luminance and chromaticity of the backlight is arranged at one side among the longer sides and the shorter sides of the display panel body where the backlight is not arranged at said one side. 
     The present invention also provides an LED backlight arrangement method comprising: 
     providing a display panel body having a substantially rectangular shape which includes longer sides and shorter sides as edge portions, and a backlight arranged in a manner such that LED light emitting elements are aligned along the edge portions of the display panel body; 
     arranging the backlight at any one of the longer sides and the shorter sides of the display panel body; and 
     arranging a front sensor that measures luminance and chromaticity of the backlight at one side among the longer sides and the shorter sides of the display panel body where the backlight is not arranged at said one side. 
     Effect of the Invention 
     In accordance with the present invention, the backlight is arranged at any one of the longer sides and the shorter sides of the display panel body, and a front sensor that measures luminance and chromaticity of the backlight is arranged at one side among the longer sides and the shorter sides where the backlight is not arranged at said one side. Therefore, the front sensor is positioned away from the LED light emitting elements which form the LED backlight by a specific distance or greater. 
     Accordingly, there is no considerable difference between the quantities of light received from the individual LED light emitting elements to the front sensor. Even if one of the LED light emitting elements has a variation in the light emission efficiency due to temporal and temperature changes thereof and the luminance and chromaticity of this LED light emitting elements varies, no considerable variation occurs in the measured values of the front sensor. As a result, regarding the light measurement utilizing the front sensor, it is possible to remove the influence for a dispersion due to a temporal change or the like between the individual LED light emitting elements, and thereby the luminance and chromaticity measurement utilizing the front sensor can be stably performed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front view that shows an appearance of an LED backlight display device  10  according to an embodiment of the present invention. 
         FIG. 2  is a front view that shows an arrangement of LED light emitting elements  12 A, which form in a backlight  12 , and a front sensor S 2  in the LED backlight display device  10  of  FIG. 1 . 
         FIG. 3  is a front view that shows a state in which light emitted from the LED light emitting elements  12 A is received by the front sensor S 2  in the LED backlight display device  10  of  FIG. 2 . 
         FIG. 4  is a front view that shows an appearance of a conventional LED backlight display device  1 . 
         FIG. 5  is a front view that shows an arrangement of LED light emitting elements  3 A, which form a backlight  3 , and a front sensor S 1  in the LED backlight display device  1  of  FIG. 5 . 
     
    
    
     MODE FOR CARRYING OUT THE INVENTION 
     Below, an embodiment of the present invention will be explained with reference to  FIGS. 1 to 3 . The embodiment explained below is an example of embodiments of the present invention and the present invention is not limited to the present embodiment. 
       FIGS. 1 and 2  show an LED backlight display device  10  according to the present invention, in which an LED backlight  12  is arranged on each longer side  11 A of an liquid crystal panel body  11  that generally has a rectangular shape and has a frame consisting of the longer sides  11 A (lengths) and shorter sides  11 B (widths). The LED backlight  12  has a plurality of LED light emitting elements  12 A aligned along the longer sides  11 A of the liquid crystal panel body  11 . 
     In addition, a front sensor S 2  is provided at a shorter side  11 B. Specifically, the front sensor S 2  is arranged at the center of the shorter side  11 B of the liquid crystal panel body  11 . Based on measurement signals output from the front sensor S 2 , the luminance and chromaticity of the entire LED backlight  12  are controlled. 
     Generally, at the time of shipping the products, the luminance and chromaticity measured utilizing the front sensor S 2  do not always coincide with the luminance and chromaticity shown at a central part A of the screen, due to a variation in the screen or the like. Therefore, a factory worker or the like performs a calibration in advance so that the measured values of the front sensor S 2  indicate the luminance and chromaticity at the central part A of the screen. 
     In a display device having a structure in which a plurality of edge-type and LED backlight type light sources are discretely arranged, as shown in  FIGS. 4 and 5 , LED light emitting elements  3 A that functions as a light source are generally arranged at longer sides of the relevant body. In such a case, the front sensor S 1  is most strongly affected by the luminance and chromaticity of the nearest one or two LED light emitting elements  3 A (specifically, see the LED light emitting elements  3 A indicated by “LED_R 1 ” to “LED_R 3 ” in  FIG. 5 ), and influence by the distant LED light emitting elements  3 A is extremely weak. When only the light emission efficiency of the strongly affecting LED light emitting elements  3 A varies due to a dispersion in the light emission efficiency typically caused by a temporal change and a temperature change, the luminance and chromaticity of the central part A of the screen, which were calibrated utilizing the values of the front sensor, may be deviated from accurate values. 
     Therefore, in the present embodiment, as shown in  FIG. 2 , the front sensor S 2  is arranged at a shorter side  11 B (of the liquid crystal panel body  11 ) along which no light emitting elements  12 A are arranged. 
     That is, the front sensor S 2  is arranged at the center of the shorter side  11 B of the liquid crystal panel body  11 , such position being distant from the longer sides  11 A (of the liquid crystal panel body  11 ) where the LED light emitting elements  12 A are arranged. Therefore, the front sensor S 2  is distant from the individual light emitting elements  12 A by a specific distance or greater, by which influence for a dispersion in the light emission efficiency due to temporal and temperature changes of the LED light emitting elements  12 A is disregarded or averaged. 
     Accordingly, values measured by the front sensor S 2  make it possible to disregard the influence for a dispersion in the light emission efficiency due to the temporal and temperature changes of the individual LED light emitting elements  12 A. Therefore, it is possible to prevent bad influence by the control of the backlight  12  based on the measurement values of the front sensor S 2 , on the luminance and chromaticity of the central part A of the screen. 
     The above function will be specifically explained with reference to  FIGS. 2 and 3 . First, as shown in  FIG. 2  pertaining to the present invention, regarding the quantity of light received by the central part A of the screen, the quantity of light from the LED light emitting elements  12 A arranged at a central portion of each longer side  11 A of the liquid crystal panel body  11  is greatest while the quantity of light from the LED light emitting elements  12 A arranged at both end portions of each longer side  11 A of the liquid crystal panel body  11  is smallest. 
     However, the individual LED light emitting elements  12 A are distant from the central part A of the screen. Therefore, even if one LED light emitting element  12 A has varied in a manner different from those of the other LED light emitting elements  12 A, typically due to a dispersion in the light emission efficiency caused by a temporal change and a temperature change, the influence on the luminance and chromaticity of the central part A of the screen is very small and thus can be disregarded. 
       FIG. 5  shows the position of the front sensor S 1  pertaining to the conventional technique. The luminance and chromaticity measured by the front sensor S 1  does not always coincide with the luminance and chromaticity represented at the central part A of the screen, due to a variation in the screen or the like. Therefore, it is necessary to perform a calibration in advance so that the measured values of the front sensor S 1  indicate the luminance and chromaticity at the central part A of the screen. The quantity of light received by the front sensor S 1  in  FIG. 5  is greatly affected by LED light emitting elements  3 A in the vicinity of the sensor (specifically, the LED light emitting element  3 A indicated by “LED_R 1 ” in  FIG. 5 ), and thus it can be said that the luminance and chromaticity of the central part A of the screen is determined almost by the LED light emitting element  3 A indicated by LED_R 1 . Therefore, if only the LED light emitting element  3 A indicated by LED_R 1  has a failure in the measurement due to a dispersion in the light emission efficiency typically caused by a temporal change and a temperature change, the luminance and chromaticity of the central part A of the screen cannot be accurately controlled. 
     In contrast, in the display device  10  according to the embodiment of the present invention, as shown in  FIG. 3 , the front sensor S 2  is arranged at the center of the shorter side  11 B of the liquid crystal panel body  11 , and thus the longer the distance between the front sensor S 2  and each LED light emitting element  12 A, the smaller the quantity of light received by the front sensor S 2  from the element (see the LED light emitting elements  12 A indicated by Rn, Rn- 1 , Rn- 2 , . . . or Ln, Ln- 1 , Ln- 2 , . . . ). Additionally, the front sensor S 2  is distant from the plurality of the LED light emitting elements  12 A by a specific distance or greater. Therefore, even if only one of the LED light emitting elements  12 A has a failure in the measurement due to a dispersion in the light emission efficiency typically caused by a temporal change and a temperature change, the relevant influence on the front sensor S 2  is remarkably small in comparison with the case shown in  FIG. 5 . Accordingly, it is possible to reduce the influence on the luminance and chromaticity of the central part A of the screen, which are controlled based on the measured values of the front sensor S 2 , to a minimum degree. 
     As described above in detail, in accordance with the LED backlight display device  10  and the LED backlight arrangement method of the present embodiment, the LED backlight  12  is arranged at the pair of the longer sides  11 A of the liquid crystal panel body  11  while the front sensor S 2  utilized to measure the luminance and chromaticity of the LED backlight  12  is arranged at the center of a shorter side  11 B of the liquid crystal panel body  11 , at which no LED backlight  12  is arranged. Therefore, the front sensor S 2  is positioned away from the LED light emitting elements  12 A which form the LED backlight  12  by a specific distance or greater. 
     Therefore, there is no considerable difference between the quantities of light received from the individual LED light emitting elements  12 A to the front sensor S 2 . Even if one of the LED light emitting elements  12 A has a variation in the light emission efficiency due to temporal and temperature changes thereof and the luminance and chromaticity of this LED light emitting elements  12 A varies, no considerable variation occurs in the measured values of the front sensor S 2 . As a result, regarding the light measurement utilizing the front sensor S 2 , it is possible to remove the influence for a dispersion due to a temporal change or the like between the individual LED light emitting elements  12 A, and thereby the luminance and chromaticity measurement utilizing the front sensor S 2  can be stably performed. 
     Therefore, in accordance with the LED backlight display device  10  and the LED backlight arrangement method of the present embodiment, even if a dispersion in the light emission efficiency typically caused by a temporal change or a temperature change in the individual LED light emitting elements  12 A occurs, the relevant influence on the front sensor S 2  can be reduced to a minimum degree. Therefore, it is possible to perform stable luminance and chromaticity control of the screen based on the measured values of the front sensor S 2 . 
     In the above embodiment, the LED backlight  12  is arranged at the pair of the longer sides  11 A of the liquid crystal panel body  11  while the front sensor S 2  utilized to measure the luminance and chromaticity of the LED backlight  12  is arranged at the center of a shorter side  11 B of the liquid crystal panel body  11 , at which no LED backlight  12  is arranged. However, the positional relationship between the LED backlight  12  and the front sensor S 2  may be reversed. That is, the LED backlight  12  may be arranged at the shorter sides  11 B of the liquid crystal panel body  11  while the front sensor S 2  may be arranged at the longer sides  11 A of the liquid crystal panel body  11 . Also in this case, similar to the above embodiment, influence of a dispersion in the light emission efficiency between the individual LED light emitting elements  12 A on the front sensor S 2  can be reduced to a minimum degree. 
     That is, since the present invention is not limited to the above embodiment, the LED light emitting elements  12 A of the LED backlight  12  may be arranged at the shorter sides  11 B of the liquid crystal panel body  11  while the front sensor S 2  may be arranged at the center of one of the longer sides  11 A of the liquid crystal panel body  11 . 
     In another example, the LED light emitting elements  12 A of the LED backlight  12  are arranged at only one of the longer sides  11 A or the shorter sides  11 B (i.e., only one of the four sides) while the front sensor S 2  is arranged at any one of the three sides other than the side along which the LED light emitting elements  12 A are arranged. 
     That is, the LED backlight  12  may be arranged at one of the longer sides  11 A or the shorter sides  11 B while the front sensor S 2  utilized to measure the luminance and chromaticity of the LED backlight  12  may be arranged at a longer side  11 A or a shorter side  11 B at which no LED backlight  12  is arranged. 
     In addition, the position at which the front sensor S 2  of the above embodiment is attached is not limited to that corresponding to the central part A of the screen and thus may be shifted from the central position toward either side thereof if the front sensor S 2  is sufficiently distant from the LED light emitting elements  12 A of the LED backlight  12 . That is, the arrangement position can be appropriately modified according to existing circumstances. 
     The whole or part of the above-described embodiment can be described as, but not limited to, the following supplementary notes. 
     Supplementary Note 1 
     An LED backlight display device comprising: 
     a display panel body having a substantially rectangular shape which includes longer sides and shorter sides as edge portions; and 
     a backlight arranged in a manner such that LED light emitting elements are aligned along the edge portions of the display panel body, 
     wherein the backlight is arranged at any one of the longer sides and the shorter sides of the display panel body; and 
     a front sensor that measures luminance and chromaticity of the backlight is arranged at one side among the longer sides and the shorter sides where the backlight is not arranged at said one side. 
     Supplementary Note 2 
     The LED backlight display device in accordance with Supplementary note 1, wherein: 
     the backlight is arranged at both the longer sides of the display panel body; and 
     the front sensor is arranged at any shorter side of the display panel body. 
     Supplementary Note 3 
     The LED backlight display device in accordance with Supplementary note 1, wherein: 
     the backlight is arranged at both the shorter sides of the display panel body; and 
     the front sensor is arranged at any longer side of the display panel body. 
     Supplementary Note 4 
     The LED backlight display device in accordance with any one of Supplementary notes 1 to 3, wherein: 
     the backlight is arranged at a central part of any longer side or shorter side of the display panel body. 
     Supplementary Note 5 
     An LED backlight arrangement method comprising: 
     providing a display panel body having a substantially rectangular shape which includes longer sides and shorter sides as edge portions, and a backlight arranged in a manner such that LED light emitting elements are aligned along the edge portions of the display panel body; 
     arranging the backlight at any one of the longer sides and the shorter sides of the display panel body; and 
     arranging a front sensor that measures luminance and chromaticity of the backlight at one side among the longer sides and the shorter sides where the backlight is not arranged at said one side. 
     While embodiments of the present invention have been explained in detail referring to the drawings, specific structures are not limited to the embodiments. Design modification or the like can be made without departing from the scope of the present invention. 
     REFERENCE SYMBOLS 
     
         
           10  LED backlight display device 
           11  liquid crystal panel body (display panel body) 
           11 A longer side 
           11 B shorter side 
           12  backlight 
           12 A LED light emitting element 
         S 2  front sensor