Patent Publication Number: US-8982039-B2

Title: Display device having luminance detecting optical sensor

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims the benefit of priority under 35 U.S.C. 119 to Korean Patent Application No. 10-2010-0114290 filed on Nov. 17, 2010 which is hereby incorporated by reference in its entirety. 
     BACKGROUND 
     Embodiments relate to a display device, and more particularly, to a display device, which more precisely detects luminance of a lighting source. 
     Liquid crystal displays (LCDs) display images using electrical and optical properties of liquid crystal. The LCDs have lots of advantageous merits such as thinness, lightness, low power consumption, and low operational voltage so that the LCDs are widely used for a variety of industrial fields. 
     Such an LCD includes a liquid crystal display panel in which liquid crystal is injected and encapsulated between two sheets of transparent substrates and a voltage is applied to change the orientation of liquid crystal molecules and vary optical transmittance, thereby optically displaying images and a backlight assembly for providing light to the liquid crystal display panel. 
     A cold cathode fluorescent lamp (CCFL), an external electrode fluorescent lamp (EEFL), a flat fluorescent lamp (FFL), and the like are used as light sources of the backlight assembly. 
     However, since the CCGL has disadvantages in that it is difficult to realize high-fidelity devices and light, thin, and small devices, light emitting diodes (LEDs) having improved performance such as high luminance, long lifetime, and high color purity are being widely used as lighting sources. Furthermore, since the regulation of a toxic environmental substance such as mercury has been greatly reinforced, the use of the CCFL is being gradually decreased. Thus, the changeover to the LEDs that are the environment-friendly products is a trend. 
     An LCD using the backlight assembly as a lighting source should have uniform illumination and intensity of the lighting source. However, the lighting source has a significant influence on its surroundings and operation time. 
       FIG. 1  is a graph of an illumination variation according to an operation time of a general lighting source. 
     Referring to  FIG. 1 , the lighting source is changed in illumination in proportion to an operation time. 
     That is, the lighting source has a limitation that the illumination and intensity thereof are non-uniformly changed by its surroundings and operation time. 
     Here, when the illumination and intensity of the lighting source are non-uniform, an image displayed on a display device is deteriorated in the image quality. Specifically, when illumination and intensity of a lighting source used for a medical display device are deteriorated, there is a limitation that it is difficult to check precise conditions of patients. 
     Thus, it is necessary to seek for acceptable solution to uniformly maintain the illumination and intensity of the lighting source in the display device using the backlight assembly as the lighting source. 
     SUMMARY 
     Embodiments provide a display device in which a backlight assembly is used as a lighting source and non-uniformity of luminance and intensity of the lighting source is accurately grasped to compensate the luminance and intensity of the lighting source. 
     The object of the present disclosure is not limited to the aforesaid, but other objects not described herein will be clearly understood by those skilled in the art from descriptions below. 
     In one embodiment, a display device includes: a display module on which a lighting source for supplying light is disposed on a back surface thereof; an optical sensor detecting luminance of the light supplied from the lighting source; and a light transmission member disposed between the lighting source and the optical sensor, the light transmission member providing a transmission path of the light generated in the lighting source to transmit the light into the optical sensor. 
     In another embodiment, a display device includes: a display module outputting an image using light supplied through a lighting source disposed on a back surface; a light transmission member in which a through hole for providing a transmission path of the light is defined, the light transmission member being coupled to the back surface of the display module; and an optical sensor disposed on an outlet of the through hole, the optical sensor detecting luminance of light supplied through the through hole. 
     The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims. 
     According to the embodiments, the display device which can precisely detect the luminance and intensity of the lighting source to previously prevent limitations occurring due to non-uniformity of the luminance and intensity of the lighting source, thereby displaying an image with precise luminance. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  is a graph of an illumination variation according to an operation time of a general lighting source. 
         FIG. 2  is an exploded perspective view of a display device according to an embodiment. 
         FIG. 3  is a perspective view of a display module according to an embodiment. 
         FIG. 4  is a view of a sensing unit according to a first embodiment. 
         FIG. 5  is a view of a sensing unit according to a second embodiment. 
         FIG. 6  is a view of a sensing unit according to a third embodiment. 
         FIG. 7  is a view of a sensing unit according to a fourth embodiment. 
         FIG. 8  is a view of a sensing unit according to a fifth embodiment. 
         FIG. 9  is a view illustrating a luminance value detected according to an embodiment. 
         FIG. 10  is a view for explaining a PWM frequency according to an embodiment. 
         FIG. 11  is a view illustrating a configuration of a display device according to an embodiment. 
         FIG. 12  is a flowchart illustrating a method of controlling a display device according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Exemplary embodiments will be described below. Reference will now be made in detail to the embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings. The spirit and scope of the present disclosure, however, shall not be construed as being limited to embodiments provided herein. Rather, it will be apparent that other embodiments that fall within the spirit and scope of the present disclosure may easily be derived through adding, modifying, and deleting elements herein. 
     Meanwhile, for the terms used in the present disclosure, general terms widely currently used have been selected as possible as they can. In a specific case, terms arbitrarily selected by an applicant may be used. In this case, since the meaning thereof is described in detail in the detailed description of the specification, the present disclosure should be understood in an aspect of meaning of such terms, not the simple names of such terms. 
     That is, in following descriptions, the meaning of ‘includes’, ‘comprise’, ‘including’, or ‘comprising specifies components or processes but does not exclude other components or processes. 
       FIG. 2  is an exploded perspective view of a display device according to an embodiment. 
     Referring to  FIG. 2 , a display device  1  according to an embodiment includes a display module  13  for outputting an image, a front panel  11  for protecting a front surface of the display module  13 , a panel fixing unit  12  having a front surface fixed to the front panel  11  and a rear surface fixed to the display module  13 , a bracket (not shown) connecting the panel fixing unit  12  to the display module  13 , a rear cabinet coupled to a rear side of the front panel  11  to surroundedly protect the display module  13 , an adhesion member  20  fixing the panel fixing unit  12  to the front panel  11 , and a sensing unit coupled between the rear cabinet  15  and the display module  13  to detect luminance of a backlight assembly  134  included in the display module  13 . 
     In detail, the display module  13  is a device for displaying an image according to a signal inputted into the display device  1 . For example, the display module may be a liquid crystal display module (hereinafter, referred to as an LCD module). 
     The front panel  11  defines a front appearance of the display device  1 . For example, an opening (not shown) for viewing the image provided through the display module  13  may be defined in the front panel  11 . Alternatively, when the opening is not provided, the front panel  11  may include a plate formed of a transparent material. When the front panel  11  includes the plate formed of the transparent material, the front panel  11  may be formed of any transparent material having a strength above a predetermined level, for example, a tempered glass or a resin member. Also, in a state where the front panel  11  is disposed in the display device  1 , a portion of a circumference or the entire circumference of the front panel  11  may be exposed to the outside of the display device  1 . 
     An inner surface  111  of the front panel  11  faces a rear side of the display device  1 , and the panel fixing unit is fixed to a panel-side adhesion surface  112  by the adhesion member  20 . Also, an opaque film layer (not shown) for preventing the panel fixing unit  12  from being viewed to the front side of the display module  12  and a grounding unit (not shown) for preventing electromagnetic waves generated in the display module  13  from being radiated to the outside of the display device  1  may be further disposed on the inner surface  111 . 
     For example, the panel fixing unit  12  may have a square frame shape with an opened inside space. In a state where the panel fixing part  12  is disposed in the display device  1 , the panel fixing part  12  fixes a position of the front panel  11  with respect to the display module  12  and the rear cabinet  15  and defines a lateral appearance of the display device  1 . Although the rear cabinet  15  and the front panel  11  do not directly contact each other in the current embodiment, the present disclosure is not limited thereto. For example, when the rear cabinet  15  and the front panel  11  directly contact each other to define the lateral appearance of the display device  1  by the rear cabinet  15 , the panel fixing part  12  may not be exposed to the outside and fix only the position of the front panel  11 . 
     A fixing part for fixing the display module  13  or the rear cabinet  15  is disposed on one surface of the panel fixing unit  12  facing a rear side of the display device  1 . A fixing part-side adhesion surface  122  is disposed on the other surface of the panel fixing unit  12 . 
     The fixing part-side adhesion surface  122  has a shape corresponding to that of the panel-side adhesion surface  112  of the front panel  11 . The adhesion member  20  is disposed on the fixing part-side adhesion surface  122  to provide an adhesion force for fixing the front panel  11  to the panel fixing unit  12 . 
     The adhesion member  20  has a shape corresponding to those of the fixing part-side adhesion surface  122  and the panel-side adhesion surface  112 . The adhesion member  20  has one surface adhering to the fixing part-side adhesion surface  122  and the other surface adhering to the panel-side adhesion surface  112  of the front panel  11 . 
     The sensing unit  14  for providing a path of light provided from the backlight assembly  134  disposed on the display module  13  and measuring luminance of the light is disposed between the display module  13  and the rear cabinet  15 . 
     The sensing unit  14  detects the luminance of the light provided through the backlight assembly  134  to transmit data depending on the detected luminance to a control unit  322  that will be described later. 
       FIG. 3  is a perspective view of a display module according to an embodiment. 
     Referring to  FIG. 3 , the display module according to an embodiment includes a liquid crystal panel  131  disposed on a front surface of the display module to display an image, a panel guide  132  on which the liquid crystal panel  131  is seated, the backlight assembly  134  provided at a rear side of the liquid crystal panel  131  to provide light, an optical sheet part  133  for processing the light generated in the backlight assembly  134  to provide the processed light to the liquid crystal panel  131 , and a bottom cover  135  disposed on a back surface of the display module  130 . 
     For example, the panel guide  132  may have a square frame shape with an opened inside space. Also, the panel guide  132  may be formed of a mold material using a metal or a resin material. The panel guide  132  has one side on which the liquid crystal panel  131  is seated and the other side contacting the bottom cover  135 . The optical sheet part  133  and the backlight assembly  134  may be received into an inner space defined by the bottom cover  135  and the panel guide  132 . 
     Also, a separate connection member (not shown) for fixing positions of the optical sheet part  133  and the backlight assembly  134  or connecting the panel guide  132  to the bottom cover  135  may be disposed on the panel guide  132 . 
     An opening  136  having a through-hole shape may be defined in an approximately central portion of the bottom cover  135 . The sensing unit  14  is disposed in the opening  136 . 
     The backlight assembly  134  may include a lighting source (not shown) for providing light, a driver (not shown) for driving the lighting source, a reflector (not shown) for reflecting the light generated in the lighting source forward, and a light guide plate for converting the light to planar light. For example, the lighting source may include a lamp or a light emitting diode (hereinafter, referred to as an LED). 
     The optical sheet part  133  may include a plurality of optical sheets to enhance efficiency of the light generated from the backlight assembly  134 . For example, the optical sheets may be a plurality of sheets such as a diffusion sheet, a prism sheet, and a protection sheet. 
       FIG. 4  is a view of a sensing unit according to a first embodiment. 
     Referring to  FIG. 4 , a sensing unit  14  includes a light transmission member  141  coupled to a back surface of a display module  13 , a through hole  142  that is a light transmission path defined in the light transmission member  141 , an optical sensor  143  coupled at a position corresponding to that of the through hole  142  that is the light transmission path, and a printed circuit board (PCB)  144  coupled to the optical sensor  143 . 
     The light transmission member  141  may be a kind of bracket coupled to a back surface of a bottom cover  135  of the display module  13 . The light transmission member  141  may be formed of a material such as a metal member, a plastic synthetic resin material, or a sponge. Here, a material blocking ambient light incident from the periphery may be used as the material of the light transmission member  141 . 
     The light transmission member  141  may have the same area as the display module  13 . Alternatively, the light transmission member  141  may have an area less than that of the display module  13 . 
     That is, the light transmission member  141  may have an area equal to a light luminance detection area with respect to a backlight assembly  134  in the entire area of the display module  13 . 
     Here, the light transmission member  141  may be coupled at a position corresponding to that of an opening  136  of the bottom cover  135  coupled to a back surface of the display module  13  by a separate auxiliary adhesion member  30 . 
     Here, the auxiliary adhesion member  30  may serve as an attaching member for closely attaching the light transmission member  141  to the display module  13 . For example, a tape or sponge may be used as the auxiliary adhesion member  30 . 
     Alternatively, the light transmission member  141  may be fixed using a screw member passing through a PCB  144  (that will be described later) and fixed to the bottom cover  135 . When the light transmission member  141  is fixed using a screw, the screw may be used at two positions different from each other. Also, a support member (not shown) for maintaining a distance with the bottom cover  135  may be used at the two positions. 
     The through hole  142  that is the light transmission path is defined in the light transmission member. 
     The through hole  142  has an inlet and an outlet. The through hole  142  passes through one surface of the light transmission member  141  and the other surface disposed on a side opposite to that of the one surface. 
     A reflective member (not shown) for reflecting light may be disposed on an inner surface of the through hole  142 . 
     The backlight assembly  134  of the display module  13  is disposed on the inlet of the through hole  142 , and the optical sensor  143  is disposed on the outlet of the through hole  142 . 
     The through hole  142  provides a path of light generated from the light transmission member  141 . That is, the through hole  142  provides a light transmission path for transmitting light generated from the backlight assembly  134  disposed on the inlet to the optical sensor  143  disposed on the outlet. 
     That is, as shown by an arrow illustrated in  FIG. 4 , the through hole  142  transmits light leaking from the backlight assembly  134  to the optical sensor  143 . 
     Here, when the through hole  142  has the same area as the entire area of the backlight assembly  134 , it is difficult to detect more precise luminance value of the light. That is, when the through hole  142  has a relatively large area or the light transmission member  141  itself has a through hole shape, a light detection area of the optical sensor  143  becomes wide. Thus, an error range of the detected luminance value may be relatively large due to the interference by ambient light. 
     That is, when the through hole  142  has a very large area, since the light generated from the backlight assembly  134  is sporadically detected by the optical sensor  143 , it is difficult to more precisely measure the light luminance value. 
     Thus, the through hole  142  may have an area corresponding to that of a portion of the light detection area set to detect the light luminance value in the entire region of the backlight assembly  134 . 
     That is to say, the light transmission member  141  removes ambient light generated by its surroundings to prevent the ambient light from being transmitted to the optical sensor  143 . 
     Also, the through hole  142  defined in the light transmission member  141  transmits only light provided from the backlight assembly  134  to the optical sensor  143  except for the ambient light. 
     Here, the through hole  142  defined in the light transmission member  141  may have one of a circular shape, an oval shape, a triangular shape, and a polygonal shape. 
     The optical sensor  143  is connected to the PCB  144 . Also, the optical sensor  143  is disposed at an outlet of the through hole  142  defined in the light transmission member  141  to detect luminance of the light provided through the through hole  142 . 
     As described above, according to the first embodiment, since the light transmission path for transmitting the light generated through the backlight assembly  134  to the optical sensor  143  is provided, the luminance of the backlight assembly may be more precisely detected by the optical sensor  143 . 
       FIG. 5  is a view of a sensing unit according to a second embodiment. 
     In  FIG. 5 , the substantially same component as that shown in  FIG. 4  will be denoted by the same reference numerals. 
     Referring to  FIG. 5 , the sensing unit  14  includes a light transmission member  141  coupled to a back surface of a display module  13 , a through hole  142  defined in the light transmission member  141 , an optical sensor  143  disposed at a position corresponding to that of the through hole  142 , and a PCB coupled to the optical sensor  143 . 
     The light transmission member  141  may be a kind of bracket coupled to the back surface of the display module  13 . The light transmission member  141  may be formed of a material such as a metal material, a plastic synthetic resin material, or a sponge. Here, a material blocking ambient light incident from the periphery may be used as the material of the light transmission member  141 . 
     The through hole  142  that is a light transmission path is defined in the light transmission member  141 . 
     The through hole  142  has an inlet and an outlet. The through hole  142  passes through one surface of the light transmission member  141  and the other surface disposed on a side opposite to that of the one surface. 
     The display module  13  is disposed on the inlet of the through hole  142 , and the optical sensor  143  is disposed on the outlet of the through hole  142 . 
     The through hole  142  provides a path of light generated from the light transmission member  141 . That is, the through hole  142  provides a light transmission path for transmitting light generated from a backlight assembly  134  disposed on the inlet to the optical sensor  143  disposed on the outlet. 
     That is, as shown by an arrow illustrated in  FIG. 4 , the through hole  142  transmits light generated through the backlight assembly  134  to the optical sensor  143 . 
     Here, the inlet of the through hole  142  has an inclined angle (a) having a predetermined angle. 
     That is, the inclined angle defined on the inlet of the through hole  142  reflects the light generated through the backlight assembly  134  to transmit a more amount of light to the optical sensor  143 , thereby more precisely detecting a light luminance value. 
     That is to say, the inlet of the through hole  142  may have an area greater than that of the outlet to more precisely detect the light luminance value. 
     As described above, according to the second embodiment, the through hole  142  may be changed in shape to more precisely detect the light luminance value. 
       FIG. 6  is a view of a sensing unit according to a third embodiment. 
     In  FIG. 6 , the substantially same component as that shown in  FIG. 4  will be denoted by the same reference numerals and their descriptions will be omitted. 
     Referring to  FIG. 6 , the sensing unit  14  includes a light transmission member  141  coupled to a back surface of a display module  13 , a through hole  142  defined in the light transmission member  141 , an optical sensor  143  disposed at a position corresponding to that of the through hole  142 , and a PCB coupled to the optical sensor  143 . 
     The through hole  142  that is a light transmission path is defined in the light transmission member  141 . 
     Furthermore, the through hole  142  defined in the light transmission member  141  may have a circular or polygonal shape in which an inlet (a) and an outlet (b) of the through hole  141  have areas different from each other. Here, the inlet (a) has an area greater than that of the outlet (b). Thus, light generated from a backlight assembly  134  may be more easily transmitted through the through hole  142 . 
     The optical sensor  143  is connected to the PCB  144 . Also, the optical sensor  143  is disposed on the outlet (b) of the through hole  142  defined in the light transmission member  141  to detect luminance of light. 
     As described above, according to the third embodiment, the through hole  142  may have a circular or polygonal shape in which the inlet (a) has an area greater than that of the outlet (b) to collect the light into the optical sensor  143 . 
       FIG. 7  is a view of a sensing unit according to a fourth embodiment. 
     Referring to  FIG. 7 , the sensing unit  14  includes a light transmission member  141  coupled to a back surface of a display module  13 , a through hole  142  defined in the light transmission member  141 , an optical sensor disposed at a position corresponding to that of the through hole  142 , a PCB  144  coupled to the optical sensor  143 , and a light transmission auxiliary member  145  inserted into the through hole  142 . 
     The through hole  142  that is a light transmission path is defined in the light transmission member  141 . 
     The light transmission auxiliary member  145  is inserted into the through hole  142 . 
     The light transmission auxiliary member  145  is inserted into the through hole  142  to minimize light losses occurring in the through hole  142  and provide a light transmission path. 
     Here, the light transmission auxiliary member  145  may be formed of an optical fiber or optical fiber bundle or a transparent plastic such as polycarbonate. Also, the light transmission auxiliary member  144  may have a circular or polygonal shape equal to that of the through hole  142 . 
     As described above, according to the fourth embodiment, the light transmission auxiliary member  145  may be inserted into the through hole  142  to minimize light losses occurring during the transmission of the light, thereby precisely detecting a light luminance value. 
       FIG. 8  is a view of a sensing unit according to a fifth embodiment. 
     Referring to  FIG. 8 , the sensing unit  14  includes a light transmission member  141  coupled to a back surface of a bottom cover  135  of a display module  13 , a through hole  142  that is a light transmission path defined in the light transmission member  141 , an optical sensor  143  disposed at a position corresponding to that of the through hole  142 , and a PCB  144  coupled to the optical sensor  143 . 
     The through hole  142  that is the light transmission path is defined in the light transmission member  141 . 
     Here, the through hole  142  has a reflective surface  146  therein and a bent shape. 
     That is, the through hole  142  has a first hole defined in a back surface side of a backlight assembly  134  and a second hole defined in a side surface of the display module  13  with respect to the reflective surface. 
     That is, when the through hole  142  is defined in only the back surface side of the display module  13 , components of the optical sensor  143  should be disposed on the back surface side of the display module  13 . Thus, the display device may be increased in thickness. 
     Thus, in the current embodiment, the through hole  142  may have a shape bent at about 90 degrees with respect to the reflective surface  146  to realize the slim display device. 
     The reflective surface  146  totally reflects light to provide the reflected light to the optical sensor  143 . 
     Also, due to the above-described structure, the optical sensor  143  is disposed on a side surface of the display module  13 . 
     Here, the through hole  142  may be changed in shape to dispose the optical sensor  143  on a top surface and a bottom surface of the display module  13 . 
     As described above, according to the fifth embodiment, the through hole  142  may be changed in shape to realize the slim display device. 
       FIG. 9  is a view illustrating a luminance value detected according to an embodiment. 
     Referring to  FIG. 9 , in a luminance value (a) detected according to a related art, it is seen that a luminance value detected by interference of ambient light and light losses is non-uniform. That is, error probability may be increased according to the detected luminance value. 
     However, in a luminance value (b) detected according to the embodiments, since the light losses may be minimized by the sensing unit  14  and the interference of the ambient light may be restricted, the uniform and precise luminance value may be detected. 
       FIG. 10  is a view for explaining a PWM frequency according to an embodiment. 
     Referring to  FIG. 10 , a pulse width modulation (PWM) frequency for operating the backlight assembly  134  is set to a reference symbol ‘a’. Here, the reference symbol ‘a’ has 256 levels for 8 bits. 
     However, since 10 bits are used in the embodiments to expand the PWM frequency, the more expanded luminance of the back light unit  134  may be adjusted. When the PWM frequency is expanded, the luminance value of light generated in the back light unit  134  may be further precisely controlled. As a result, brightness may be more precisely controlled. 
       FIG. 11  is a view illustrating a configuration of a display device according to an embodiment. 
     Referring to  FIG. 11 , a display device  300  includes a data receiving unit  302 , a video/audio decoder  304 , a voice processing unit  306 , a speaker  308 , an image processing unit  310 , a display module  312 , a backlight assembly  314 , a backlight assembly driving unit  316 , a storage unit  318 , an optical sensor  320 , and a control unit  333 . 
     The data receiving unit  302  receives data inputted from the outside. 
     Here, the data receiving unit  302  may be a digital recorder such as a digital tuner for receiving a digital broadcasting signal, an analog tuner for receiving an analog broadcasting signal, digital and analog external signal input terminals connected to an external device, a personal video recorder (PVR), and a digital video recorder (DVR). 
     Here, the digital external signal input terminal may be an input terminal for a digital cable broadcasting signal or a terminal connected to a digital external recorder such as a DVD. The analog external signal input terminal may be a VCR signal input terminal or an input terminal for an analog cable broadcasting signal. 
     Also, the digital tuner may tune a transport stream (ST) of a desired channel by a user&#39;s selection in transport streams that are digital broadcasting transport signals inputted through a digital broadcasting antenna. The analog tuner may tune an image program of a desired channel by a user&#39;s selection in image programs that are analog broadcasting signals inputted through an analog broadcasting antenna. 
     Thus, the data received through the data receiving unit  302  may include analog and digital television broadcasting programs which run in real time, a replaying program inputted from an external player, a recording program, and a cable broadcasting program. Here, in case of the digital signal, the data includes an image signal, a voice signal, and a data signal. Also, in case of the analog signal, the data includes an image signal and a voice signal. 
     The video/audio decoder  304  decodes image data and voice data of the data received through the data receiving unit  302 . Then, the video/audio decoder  304  transmits the decoded data into the voice processing unit  306  and the image processing unit  310 . 
     The voice processing unit  306  performs a signal processing such as digitalization and filtering of the voice data transmitted from the video/audio decoder  304 . The voice data in which the signal processing is performed is outputted through the speaker  308 . 
     The image processing unit  310  performs a signal processing such as digitalization and filtering from the image data transmitted from the video/audio decoder  304  into RGB signals. The image data in which the signal processing is performed is displayed through the display module  312 . 
     Although not shown, the display module  312  includes a liquid crystal panel including a plurality of gate lines and an LCD transistor, a data driver for operating the plurality of data lines according to the image data of the image processing unit  110 , and a gate driver for receiving a driving signal from a timing control unit (not shown) to operate the plurality of gate lines. 
     The backlight assembly  314  is a lighting source for supplying light onto a front surface of the display module  312 . The backlight assembly  314  includes a plurality of backlight units overlapping the display module  312 . 
     Here, according to the embodiments, the backlight assembly  314  includes a light emitting diode (LED). 
     The LED may significantly reduce power consumption when compared to the existing cold cathode fluorescent lamp (CCFL), external electrode fluorescent lamp (EEFL), and flat fluorescent lamp (FFL) which are used as lighting sources. 
     The backlight assembly driving unit  316  supplies a driving current according to a level of luminance transmitted through the control unit  322  to the backlight assembly  314 . Thus, the display module may have high luminance and a wide light emitting surface. 
     Here, when the backlight assembly  314  is not operated in a state an image signal is displayed through the display module  312 , a user does not view the image displayed through the display module  312 . 
     That is, when the driving current is applied to the backlight assembly  314  through the backlight assembly driving unit  316  to emit light from the backlight assembly  314 , the user may view the image displayed through the display module  312 . 
     Also, brightness of a displayed screen of the display module  312  may be adjusted by changing a driving current value supplied into the backlight assembly  314  through the control unit  322 . The brightness of the displayed screen may be changed according to an increase/decrease of the driving current value supplied into the backlight assembly  314 . 
     The storage unit  318  stores programs related to the operation of the display device  300  and various data generated during the operation of the display device  300 . 
     Also, a preset reference luminance value of the backlight assembly  314  is stored in the storage unit  318 . 
     The optical sensor  320  detects a luminance value of light generated through the backlight unit  314  and transmits the detected luminance value to the control unit  322 . 
     The control unit  322  controls an overall operation of the display device  300 . 
     Specifically, the control unit  322  compensates the luminance of the backlight assembly  314  in a case where a variation in the luminance of the backlight assembly  314  occurs. 
     That is, the control unit  322  compares the luminance value detected through the optical sensor  320  to the reference luminance value stored in the storage unit  318 . Accordingly, when the two values do not accord with each other, driving conditions of the backlight assembly  314  are changed to allow the two values to accord with each other. 
     That is, when the luminance value is less or greater than the reference luminance value, the control unit  322  controls a PWM frequency supplied into the backlight assembly  314  to allow the luminance value to accord with the reference luminance value. 
     Specifically, the control unit  322  integrates a plurality of luminance values provided through the optical sensor  320  to calculate a mean value corresponding to the plurality of luminance values. Accordingly, the driving conditions of the backlight assembly are changed to allow the calculated mean value and the reference luminance value to accord with each other. 
       FIG. 12  is a flowchart illustrating a method of controlling a display device according to an embodiment. 
     Referring to  FIG. 12 , in operation S 102 , a transmission path of light generated through a backlight assembly is formed in a light transmission member  141  in which a through hole  142  is defined. 
     Here, a light transmission auxiliary member  144  may be inserted into the through hole  142 . 
     In operation S 104 , an optical sensor detects a luminance value of light provided through the through hole  142  to transmit the detected luminance value to a control unit. 
     In operation S 106 , a storage unit stores the luminance value transmitted through the optical sensor, and then the control unit integrates the plurality of luminance values detected in one period to calculate a mean value thereof. 
     In operation S 108 , the control unit compares the calculated mean value to a reference value stored in a storage unit to determine whether the two values accord with each other. 
     In the determination result in operation S 108 , when the two values accord with each other, the control unit maintains driving conditions of the backlight assembly in operation S 110 . On the other hand, when the two values do not accord with each other, the driving conditions of the backlight assembly are changed to allow the two value to accord with each other in operation S 112 . 
     Although embodiments have been described with reference to a number of illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this disclosure. More particularly, various variations and modifications are possible in the component parts and/or arrangements of the subject combination arrangement within the scope of the disclosure, the drawings and the appended claims. In addition to variations and modifications in the component parts and/or arrangements, alternative uses will also be apparent to those skilled in the art.