Abstract:
A display device includes: a display panel unit that includes a display screen for displaying information and a light emitting section having a light source for emitting light to illuminate the display screen from back, and that linearly generates heat during light emission; and a radiator that receives the heat generated by the light emitting section and dissipates the received heat. The display device further includes a heat transmission section that transmits the heat generated by the light emitting section to the radiator such that heat generated in the middle of a linear heat generation part of the light emitting section is transmitted faster than heat generated at the end of the linear heat generation part.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a display device which displays information, a display panel unit, and an information processing apparatus which processes information and displays the processed information. 
         [0003]    2. Description of the Related Art 
         [0004]    In the fields of device such as personal computer, there have hitherto been widely used liquid crystal panels being a slim display screen which displays information. Particularly, in laptop personal computers, mobile telephones and the like for which device thickness reduction is especially required, backlight-type display devices in which light is irradiated from the rear face side to the liquid crystal panel have been widely used. 
         [0005]    In the backlight-type display device, a light source extending in a linear shape is arranged at the side of a liquid crystal panel, and a light guide plate is attached to the rear face of the liquid crystal panel. Light emitted by the light source is guided to the liquid crystal panel by the light guide plate and further diffused by the light guide plate, so that the light is irradiated from the back of the liquid crystal panel. In such a backlight-type display device, the light source and the drive board which drives the light source are disposed at a flank of the liquid crystal panel which has a relatively large spatial margin, so that the thickness of the display device can be reduced. 
         [0006]    Conventionally, in the backlight-type display device, CFL tube (cold cathode fluorescent tube) has been used as the light source. However, the CFL tube uses mercury to emit light. Thus, from a viewpoint of environmental protection, LED (light emitting diode) light source which does not use mercury has been increasingly used instead of the CFL tube. The LED light source has the advantages that it is more desirable in terms of environmental protection and less expensive than the CFL tube. However, the LED light source has problems that heat generation is large with respect to the amount of luminescence, and its life and luminance efficiency are significantly reduced by heat. 
         [0007]    In this regard, in the backlight-type display device, the following measures have been taken: a radiator fin which dissipates the heat generated by the LED light source is provided (for example, refer to Japanese Patent Laid-Open No. 2006-267936); a radiator plate for dissipating heat is attached to the LED light source (for example, refer to Japanese Patent Laid-Open Nos. 2006-268066 and 2005-135862); a heat transmission plate which receives the heat generated by the LED light source and transmits the heat to the housing and radiator plate is provided (for example, Japanese Patent Laid-Open No. 2006-293182). When these techniques are applied, the temperature rise within the display device caused by the heat generated by the LED light source can be suppressed to reduce the degradation of LED light source. 
         [0008]    In the backlight-type display device using an LED light source, typically, plural LEDs are arranged linearly along the side surface of the liquid crystal panel. However, heat flows in a different manner in each LED depending on the location of placement, thereby making ambient temperatures of the plural LEDs non-uniform. Accordingly, even when the techniques of the above described patent documents are applied to dissipate the heat generated by the plural LEDs, the degree of degradation is not uniform in the plural LEDs and thus the luminosity of display screen in the liquid crystal panel is very unlikely to be uniform. 
         [0009]    This problem occurs not only in the display device using a liquid crystal panel but also in the backlight-type display device in general. 
       SUMMARY OF THE INVENTION 
       [0010]    The present invention has been made in view of the above circumstances and provides a display device, display panel unit and information processing apparatus which can suppress non-uniformity of light source temperature and thus maintain uniform displaying over a long period of time. 
         [0011]    A display device according to the present invention includes: 
         [0012]    a display panel unit that includes a display screen for displaying information and a light emitting section having a light source for emitting light to illuminate the display screen from back, and that linearly generates heat during light emission; 
         [0013]    a radiator that receives the heat generated by the light emitting section and dissipates the received heat; and 
         [0014]    a heat transmission section that transmits the heat generated by the light emitting section to the radiator such that heat generated in the middle of a linear heat generation part of the light emitting section is transmitted faster than heat generated at the end of the linear heat generation part. 
         [0015]    In a backlight-type display device in which the display screen on which information is displayed is illuminated from the back, light is typically emitted linearly from the side of the display screen; and in the middle of the heat generation part which linearly generates heat during light emission, heat tends to accumulate and thus the temperature tends to rise higher. According to the display device of the present invention, since heat generated in the middle of the linear heat generation part of the light emitting section is transmitted in a more excellent manner than that heat generated the end of the linear heat generation part is transmitted, the heat in the middle of the linear heat generation part where heat tends to accumulate is dissipated more efficiently. Consequently, the non-uniformity of temperature in the linear heat generation part of the light emitting section can be suppressed, so that uniform displaying can be maintained over a long period of time. 
         [0016]    Also, in the display device according to the present invention, it is preferable that the radiator is a housing of the display device. 
         [0017]    Since the radiator is a housing of the display device, a radiator sheet or the like for dissipating the heat generated by the light emitting section does not need to be additionally provided, so size growth and cost increase of the display device can be suppressed. 
         [0018]    Also, in the display device according to the present invention, it is preferable that the light source is a light-emitting diode. 
         [0019]    Light-emitting diodes (LED) generate a large amount of heat with respect to the amount of luminescence and tend to be degraded by heat. Thus, when LEDs are used in the display device of the present invention, a large effect can be achieved. 
         [0020]    Also, in the display device according to the present invention, it is preferable that the radiator has a first area made of a first material, and a second area made of a second material that transmits heat faster than the first material, and a borderline between the first and second areas forms a protrusion in the first area side, and 
         [0021]    the heat transmission section is a member which extends along the linear heat generation part of the light emitting section while contacting the light emitting section, the member has a part corresponding to the protrusion of the radiator, the part includes a central portion and an end portion, and the central portion has a larger contact area contacting the second area of the radiator than the end portion. 
         [0022]    According to the preferred display device of the present invention, a simple configuration is employed in which the radiator is formed by using the first material and the second material being different from each other in thermal conductivity, and the heat transmission section is made to contact the radiator. Consequently, heat generated in the middle of the linear heat generation part of the light emitting section can be dissipated in a more excellent manner, allowing prevention of an increase in device complexity and the number of components, and thus allowing improvement of device life. 
         [0023]    Also, in the display device according to the present invention, it is preferable that the heat transmission section becomes gradually narrower as the heat transmission section extends along the linear heat generation part of the light emitting section toward the end of the heat transmission section while contacting both the light emitting section and the radiator plate. 
         [0024]    When the width of the heat transmission section which transmits heat from the light emitting section to the radiator is made wider in the middle of the linear heat generation part of the light emitting section than in the end thereof, the variation in temperature of the heat generation part can be also suppressed. 
         [0025]    A display panel unit according to the present invention includes: 
         [0026]    a panel body that includes a display screen for displaying information and a light emitting section having a light source for emitting light to illuminate the display screen from back, and that linearly generates heat during light emission; and 
         [0027]    a radiator plate which receives the heat generated by the light emitting section and dissipates the received heat, and extends along a linear heat generation part of the light emitting section, in which the middle of the radiator plate has a wider heat dissipation area than the end of the radiator plate. 
         [0028]    According to the display panel unit of the present invention, in the radiator plate which extends along the linear heat generation part of the light emitting section, the middle of the heat generation part where heat tends to accumulate is formed wider in heat dissipation area than the end thereof. Accordingly, non-uniformity of temperature in the heat generation part can be suppressed and thus uniform displaying can be maintained over a long period of time. 
         [0029]    Also, in the display panel unit according to the present invention, it is preferable that the radiator plate becomes gradually narrower from the middle to the end thereof. 
         [0030]    According to the preferred display panel unit of the present invention, in the linear heat generation part of the light emitting section, heat dissipation is larger in the middle thereof where heat tends to accumulate than in the end thereof, so that the temperature of the heat generation part can be accurately made uniform. 
         [0031]    Also, in the display panel unit according to the present invention, it is preferable that the light source is a light-emitting diode. 
         [0032]    Light-emitting diodes are easily degraded by heat. Thus, when light-emitting diodes are used in the display panel unit of the present invention, a large effect can be achieved. 
         [0033]    A first information processing apparatus according to the present invention includes: 
         [0034]    a display section having: 
         [0035]    a display panel unit that includes a display screen for displaying information and a light emitting section having a light source for emitting light to illuminate the display screen from back, and that linearly generates heat during light emission, 
         [0036]    a radiator that receives the heat generated by the light emitting section and dissipates the received heat, and 
         [0037]    a heat transmission section that transmits the heat generated by the light emitting section to the radiator such that heat generated in the middle of the linear heat generation part of the light emitting section is transmitted faster than heat generated at the end of the linear heat generation part; and 
         [0038]    a processing section that processes information and causes the display section to display the processed information on the display section of the display panel unit included in the display section. 
         [0039]    A second information processing apparatus according to the present invention includes: 
         [0040]    a display section having a display panel unit including: 
         [0041]    a panel body that includes a display screen for displaying information and a light emitting section having a light source for emitting light to illuminate the display screen from back, and that linearly generates heat during light emission, and
       a radiator plate which receives the heat generated by the light emitting section and dissipates the received heat, and which extends along a linear heat generation part of the light emitting section, in which the middle of the radiator plate has a wider heat dissipation area than the end of the radiator plate; and   a processing section that processes information and causes the display section to display the processed information on the display section of the display panel unit included in the display section.       
 
         [0044]    According to the first information processing apparatus or the second information processing apparatus of the present invention, non-uniformity of temperature in the linear heat generation part of the light emitting section can be suppressed, so light can be uniformly irradiated on the display screen over a long period of time. 
         [0045]    According to the present invention, partial non-uniformity of temperature in the light source can be suppressed and thus light can be uniformly irradiated on the backlight-type display screen over a long period of time. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0046]      FIG. 1  is an external perspective view of a personal computer to which an embodiment of the present invention is applied; 
           [0047]      FIG. 2  is a hardware configuration diagram of the personal computer; 
           [0048]      FIG. 3A  is a view illustrating a front cover as viewed from the front; 
           [0049]      FIG. 3B  is a view illustrating a display panel unit as viewed from the front; 
           [0050]      FIG. 3C  is a view illustrating a rear cover as viewed from the front; 
           [0051]      FIG. 4A  is a view illustrating the front cover as viewed from the back; 
           [0052]      FIG. 4B  is a view illustrating the display panel unit as viewed from the back; 
           [0053]      FIG. 4C  is a view illustrating the rear cover as viewed from the back; 
           [0054]      FIG. 5  is a view illustrating the internal configuration of the front cover in which the display panel unit and an antenna are arranged; 
           [0055]      FIG. 6  is a view illustrating the display panel unit from which a control board has been removed; 
           [0056]      FIG. 7  is a cross-sectional view of a display device taken along a direction in which a radiator plate extends; 
           [0057]      FIG. 8  is a cross-sectional view of a conventional display device taken along a direction in which a radiator plate extends; 
           [0058]      FIG. 9  is a view illustrating a display panel unit as viewed from the front according to a second embodiment of the present invention; 
           [0059]      FIG. 10  is a view illustrating the display panel unit as viewed from the back according to the second embodiment of the present invention; 
           [0060]      FIG. 11  is a view illustrating a rear cover which covers the rear face of the display panel unit; 
           [0061]      FIG. 12  is a view illustrating the positional relationship between the display panel unit and rear cover when the display panel unit is received in the rear cover; and 
           [0062]      FIG. 13  is a view illustrating the rear face of a display panel unit according to a third embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0063]    Embodiments of the present invention will be described with reference to the drawings. 
         [0064]      FIG. 1  is an external perspective view of a personal computer  10  to which an embodiment of the present invention is applied. 
         [0065]    Referring to  FIG. 1 , the personal computer  10  includes a main device  11 , a display device  12  which displays various types of information on a display screen  12 A according to a command from the main device  11 , a keyboard  13  for inputting various types of information dependent on a key operation into the main device  11 , and a mouse  14  by which a position on the display screen is specified, so that a command dependent on an icon or the like displayed on that position is inputted. Further, though not illustrated in  FIG. 1 , the personal computer  10  includes an FD mounting opening for mounting a flexible disk (hereinafter referred to as an FD) and a CD-ROM mounting opening for mounting a CD-ROM. The display screen  12 A corresponds to an example of the display screen according to the present invention. 
         [0066]    In the personal computer  10 , the display device  12  is joined to the main device  11  via a hinge  10 A. In the display device  12 , the width W of a housing  12 B at a margin beside the display screen  12 A is small, thus achieving device downsizing. The display device  12  corresponds to an example of the display section according to the present invention, and also corresponds to one embodiment of the display device according to the present invention; and the main device  11  corresponds to an example of the processing section according to the present invention. 
         [0067]    The configuration in the inside of the housing  12 B of the display device  12  will be described in detail later. 
         [0068]      FIG. 2  is a hardware configuration diagram of the personal computer  10 . 
         [0069]    As illustrated in  FIG. 2 , incorporated in the inside of the main device  11  are: a CPU  21  which controls the whole personal computer  10 ; a main memory  22  into which a program stored in a hard disk device  23  is read to be executed by the CPU  21 ; the hard disk device  23  in which various types of programs, data and the like are stored; an FD drive  24  which an FD  30  mounted therein; a CD-ROM drive  25  which accesses a CD-ROM  40 ; an input interface  26  which is connected to various devices and receives various data; and an output interface  27  which is connected to a printer or the like and sends various data. These components, the display device  12 , the keyboard  13  and the mouse  14  illustrated as well in  FIG. 1  are connected to each other via a bus  15 . 
         [0070]    The personal computer  10  basically has the above-described configuration. 
         [0071]    The internal configuration of the display device  12  will now be described in detail. In the following description, the “front” means the front side of the display device  12  illustrated in  FIG. 1  where the display screen  12 A for displaying information is disposed, and the “rear” means the rear side of the display device  12  (the other side with respect to the front side where the display screen  12 A is disposed). 
         [0072]      FIGS. 3A ,  3 B,  3 C,  4 A,  4 B and  4 C are views illustrating major components of the display device  12 ;  FIGS. 3A and 4A  illustrate a front cover  100 ;  FIGS. 3B and 4B  illustrate a display panel unit  200 ;  FIGS. 3C and 4C  illustrate a rear cover  300 .  FIGS. 3A ,  3 B and  3 C illustrate each component as viewed from the “front”;  FIGS. 4A ,  4 B and  4 C illustrate each component as viewed from the “rear”. Descriptions will be given below with reference to these component diagrams and  FIG. 1 . 
         [0073]    In the display device  12 , the display panel unit  200  is received in the housing  12 B composed of two covers. The housing  12 B includes: the front cover  100  covering the edge of the display screen  12 A of the display panel unit  200 ; and the rear cover  300  covering the back of the display panel unit  200 . The front cover  100  and the rear cover  300  are fit into each other at both sides of the display panel unit  200 . The display panel unit  200  corresponds to an example of the display panel unit according to the present invention. 
         [0074]      FIG. 3A  illustrates the “front” side of the front cover  100 . 
         [0075]    The front cover  100  includes: an edge cover section  110  covering the edge of the display panel unit  200 , a hinge joint section  130  to which the hinge  10 A illustrated in  FIG. 1  is attached, and a wiring cover section  140  which covers various connection lines and the like for connecting the main device  11  and the display device  12 . An opening  120  is formed in that part of the edge cover section  110  which faces the display screen  12 A of the display panel unit  200 . 
         [0076]      FIG. 3B  illustrates the “front” side of the display panel unit  200 . 
         [0077]    The display panel unit  200  includes a panel body  210  that includes stacked components such as a liquid crystal layer having liquid crystal encapsulated between two plates, a light guide plate which guides light to the liquid crystal layer, and a reflection prevention sheet which suppresses light reflection, and also includes plural LED light sources  201  linearly arranged and fitted into the lower edge of the panel body  210 . The display panel unit  200  also includes a control board  220  (refer to  FIG. 4B ) that controls the whole display panel unit  200 . Light emitted by the LED light sources  201  is guided to the liquid crystal layer by the light guide plate provided on the panel body  210 , and irradiated on the display screen  12 A from the rear side. The LED light sources  201  tend to generate heat and further tend to be degraded by the heat. According to the present embodiment, the plural LED light sources  201  are linearly arranged; thus a linear area P into which the LED light sources  201  are fitted tends to have a high temperature and particularly in the central part P′ of the area P, heat tends to accumulate. 
         [0078]      FIG. 3C  illustrates the “front” side of the rear cover  300 . 
         [0079]    The rear cover  300  includes a rear cover section  300 A that covers the rear face of the display panel unit  200 , and a hinge joint section  310  to which the hinge  10 A is attached. And plural through holes  301  are formed in that part of the rear cover section  300 A which covers the side of the display panel unit  200 . 
         [0080]      FIG. 4A  illustrates the “rear” side of the front cover  100 . 
         [0081]    Plural protrusions  101  are provided in that part of the edge cover section  110  of the front cover  100  which covers the side of the display panel unit  200 ; when these protrusions  101  are fitted into the plural through holes  301  arranged in the rear cover section  300 A, the rear cover  300  and the front cover  100  are joined in a separable manner. 
         [0082]      FIG. 4B  illustrates the “rear” side of the display panel unit  200 . 
         [0083]    In the rear face of the panel body  210 , a radiator plate  230  for dissipating heat is attached onto area P which is heated by the LED light sources  201 , and further the control board  220  which controls the whole display panel unit  200  is placed on the radiator plate  230 . According to the present embodiment, the width W 1  of the control board  220  is smaller than the width W 2  of the panel body  210 , and thus steps are formed at both sides of the control board  220 . 
         [0084]      FIG. 4C  illustrates the “rear” side of the rear cover  300 . 
         [0085]    The rear cover  300  is also provided with a wiring cover section  320  which fits in the wiring cover section  140  of the front cover  100  and covers various connection lines from the back of the display panel unit  200 . 
         [0086]    In assembling the display device  12 , firstly the display panel unit  200  is received in the front cover  100  so that the display screen  12 A of the display panel unit  200  fits into the opening  120  of the front cover  100 . 
         [0087]    Subsequently, an antenna  400  (refer to  FIG. 5 ) is arranged in an open space between the front cover  100  and the display panel unit  200 , the open space being formed in the upper part of the front cover  100 . 
         [0088]      FIG. 5  is a view illustrating the internal configuration of the front cover  100  in which the display panel unit  200  and the antenna  400  are arranged. 
         [0089]    As illustrated in  FIG. 5 , the display panel unit  200  is received in the front cover  100  while the front cover  100  has a remaining space in the upper part thereof; the antenna  400  is arranged in the space. According to the present embodiment, the width W 1  of the control board  220  is smaller than the width W 2  of the panel body  210 , and thus steps are formed at both sides of the control board  220 ; a signal line  410  extending from the antenna  400  runs through the steps to the wiring cover section  140 . 
         [0090]    As illustrated in  FIG. 3B , of the linear area P having fitted therein the LED light sources  201  of the panel body  210 , particularly the central part P′ tends to have a high temperature. 
         [0091]      FIG. 6  is a view illustrating the display panel unit  200  from which the control board  220  has been removed. 
         [0092]    As illustrated in  FIG. 6 , the radiator plate  230  extends along the linear area P; the width of the linear area P becomes smaller from the central part P′ to the end of the linear area P. Accordingly, heat is dissipated relatively efficiently in the central part P′, suppressing non-uniformity of temperature in the linear area P and thus allowing improvement of life of all the plural LED light sources  201 . 
         [0093]    As described above, after the display panel unit  200  and antenna  400  are received in the front cover  100 , the protrusions  101  of the front cover  100  are fitted into the through holes  301  of the rear cover  300 , whereby the housing  12 B is assembled. 
         [0094]      FIG. 7  is a cross-sectional view of the display device  12  taken along a direction in which the radiator plate  230  extends;  FIG. 8  is a cross-sectional view of a conventional display device taken along a direction in which the radiator plate extends. 
         [0095]    In the display device  12  according to the present embodiment, as illustrated in  FIG. 7 , the rear cover  300  is formed so that the wall thickness d 1  in the face side thereof is thinner than the wall thickness d 2  in the rear side; the change in thickness of the rear cover  300  takes place across the through holes  301 . Further, the front cover  100  is formed so that the wall thickness d 3  in the face side thereof is approximately equal to a wall width difference (d 2 −d 1 ) of the rear cover  300 ; the change in thickness of the front cover  100  takes place across the protrusions  101 . Accordingly, when the front cover  100  and the rear cover  300  are joined, the external surface of the housing  12 B becomes smooth. Also, the protrusions  101  of the front cover  100  are fitted into the through holes  301  of the rear cover  300  while pressed to the side surfaces of the rear cover  300  and bent toward the outside of the housing  12 B; further, assist protrusions  302  are fitted into the rear cover  300 . As a result, the front cover  100  and rear cover  300  are secured to each other. 
         [0096]    In the conventional display device  12 ′, as illustrated in  FIG. 8 , because clicks  101 ′ and  301 ′ provided in a front cover  100 ′ and a rear cover  300 ′, respectively engage with each other in the inside of the housing  12 B′, there must be a sufficient space between the housing  12 B′ and display panel unit  200 ′ so that these clicks  101 ′ and  301 ′ can bend. In the display device  12  according to the present embodiment illustrated in  FIG. 7 , the protrusions  101  bend toward the outside, so that the space between the housing  12 B and display panel unit  200  can be reduced, allowing downsizing of the display device  12 . 
         [0097]    Further, in the conventional display device  12 ′, as illustrated in  FIG. 8 , the width of the control board  220 ′ is appropriately identical to that of the panel body  210 ′ and thus a space for receiving signal lines  410 ′ extending from the antenna  400  (refer to  FIG. 5 ) must be prepared between the display panel unit  200 ′ and housing  12 B′. In the display device  12  illustrated in  FIG. 7 , the signal lines  410  are laid through the space beside the control board  220 , allowing reduction of the width of display device. 
         [0098]    As described above, according to the display device  12  of the present embodiment, the space between the housing and display panel unit  200  can be reduced, so that the display device  12  can be downsized without reducing the size of the display screen  12 A. 
         [0099]    Further, non-uniformity of temperature in the area around the heat-vulnerable LED light sources can be suppressed to efficiently dissipate heat, allowing improvement in life of the display device  12 . 
         [0100]    Now, the description of the first embodiment of the present invention is finished, and a second embodiment of the present invention will be described. The difference between the first embodiment and second embodiment lies in the structure of display panel unit and rear cover; apart from this difference, the second embodiment has substantially the same structure as the first embodiment. Accordingly, the same reference alphanumeric characters are applied to parts corresponding to the first embodiment, and hence an explanation thereof is omitted; only the points different from the first embodiment will be described. 
         [0101]      FIG. 9  is a view illustrating the front of a display panel unit  500  of the present embodiment. 
         [0102]    The display panel unit  500  of the present embodiment illustrated in  FIG. 9  includes, similarly to the display panel unit  200  of the first embodiment illustrated in  FIG. 3B , a panel body  210  and control board  220 ; plural LED light sources  201  are fitted in the panel body  210 . In the display panel unit  500 , however, the control board  220  is not laid on the panel body  210 , but disposed inside the housing while extending from the panel body  210 . 
         [0103]      FIG. 10  is a view illustrating the back of the display panel unit  500  according to the present embodiment. 
         [0104]    In the display panel unit  500  of the present embodiment, a heat transmission plate  510  of rubber for transmitting heat to a rear cover  600  (refer to  FIG. 11 ) is attached to the linear area P in which heat generated by the LED light sources  201  is accumulated. 
         [0105]      FIG. 11  is a view illustrating the rear cover  600  that covers the back of the display panel unit  500 . 
         [0106]    The rear cover  600  of the present embodiment has the same shape as the rear cover  300  of the first embodiment illustrated in  FIG. 3C , but is composed of two kinds of materials having thermal conductivity different from each other. According to the present embodiment, a metal area  610  of a metal having a high thermal conductivity and a plastic area  620  of a plastic having a relatively low thermal conductivity are formed in a hybrid manner, and the borderline between them protrudes downward in the rear cover  600 . 
         [0107]      FIG. 12  is a view illustrating the positional relationship between the display panel unit  500  and rear cover  600  when the display panel unit  500  is received in the rear cover  600 . 
         [0108]    As illustrated in  FIG. 12 , the heat transmission plate  510  arranged in the linear area P heated by the LED light sources  201  contacts the boundary and its vicinities between the metal area  610  and plastic area  620  of the rear cover  600 ; the central part P′ of the linear area P (see  FIG. 10 ) has a large contact area with the metal area  610 , and the both ends of the linear area P have a large contact area with the plastic area  620 . The heat generated by the linear area P is transmitted via the heat transmission plate  510  to the rear cover  600  and dissipated through the rear cover  600 . In this case, since the central part P′ in which heat tends to accumulate contacts the metal area  610 , the heat is efficiently transmitted and dissipated; since the ends of the linear area P in which heat hardly accumulates contact the plastic area  620  having a low thermal conductivity, the heat is transmitted and dissipated with a low efficiency. Consequently, non-uniformity of temperature in the linear area P is reduced, allowing improvement of device life. 
         [0109]    Now, the description of the second embodiment of the present invention is finished, and a third embodiment of the present invention will be described. The difference between the second embodiment and third embodiment lies in the configuration of the heat transmission plate mounted in the display panel unit and the structure of the rear cover; apart from this difference, the third embodiment has substantially the same structure as the second embodiment. Accordingly, the same reference alphanumeric characters are applied to parts corresponding to the second embodiment, and hence an explanation thereof is omitted; only the points different from the second embodiment will be described. 
         [0110]    In the display device according to the present embodiment, there is used a rear cover which has the same configuration as the rear cover  600  of the second embodiment illustrated in  FIG. 12  but has its whole surface composed of metal except for its part which covers the edge of the display panel unit. 
         [0111]      FIG. 13  is a view illustrating the back of a display panel unit  700  of the present embodiment. 
         [0112]    The display panel unit  700  of the present embodiment includes, similarly to the display panel unit  500  of the second embodiment illustrated in  FIG. 10 , a panel body  210 , a control board  220  and a heat transmission plate  510 ′. However, the configuration of the heat transmission plate  510 ′ is different from that of the heat transmission plate  510  of the second embodiment. In the heat transmission plate  510 ′ of the present embodiment, the width of the linear area P heated by the LED light sources becomes smaller from the central part P′ to the ends of the linear area P; and the whole heat transmission plate  510 ′ contacts the metal surface of the rear cover  600 . 
         [0113]    In the central part P′, a larger amount of heat generated in the linear area P is transmitted through the heat transmission plate  510  to the rear cover  600  and dissipated through the rear cover  600 . In this way, when the central part of the linear area P in which heat tends to accumulate has a larger width, also, non-uniformity of temperature in the linear area P can be suppressed. 
         [0114]    The above description is of an example in which the present invention is applied to a personal computer. However, the present invention may be applied to, for example, a liquid crystal television set or a mobile telephone terminal. 
         [0115]    Also, the above description is of an example in which non-uniformity of temperature in the linear area is suppressed by forming the heat transmission plate so that the central part of the linear area has a larger width. However, non-uniformity of temperature in the linear area may also be suppressed by using a heat transmission plate having a uniform width over the entire linear area, the both ends of the heat transmission plate being coated with resin which prevents heat transmission.