Patent Publication Number: US-2019187356-A1

Title: Display device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2017-243983, filed Dec. 20, 2017, the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to a display device. 
     BACKGROUND 
     Liquid crystal displays are widely used as display devices used for smart phones, tablet computers, car-navigation systems, etc. Generally, liquid crystal displays comprise a liquid crystal panel and an illumination device (a backlight or front-light) disposed to be overlaid on a rear surface or a front surface of the liquid crystal panel. The illumination device includes comprises has a light guide, a light source emitting light to enter the light guide, and the like. As the light source, for example, a white light emitting diode (LED) is employed in many cases. The light emitted from white LEDs contains the so-called “blue light”, which is light having a wavelength of 380 to 495 nm. The blue light has properties most close to those of ultraviolet rays, and has such a property that it reaches the retina without being absorbed by the cornea and crystalline lens of eyeballs. Therefore, when the operator sees the blue light for a long time, he or she easily feel eyestrain, which is problematic. Under these circumstances, such a display device has been proposed that a resin layer (blue-light cut layer) to attenuate the blue light is overlaid on a display surface or a rear surface of the liquid crystal panel. 
     With the above-described display device, it is possible to attenuate the blue light; however, at the same time, the color tone of the display image changes to easily become, for example, yellowish or orange-emphasized, thus, deteriorating the display quality. 
     SUMMARY 
     The present application relates generally to a display device. 
     According to one embodiment, a display device includes a display panel including a display surface, and an illumination device including a light guide having an emission surface opposing the display surface of the display panel and an incidence surface intersecting the emission surface, a light source configured to emit light entering the incidence surface, and a light cut layer provided between the light source and the incidence surface, to suppress transmission of light having a predetermined wavelength range. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded perspective view of a liquid crystal display according to a first embodiment. 
         FIG. 2A  is a cross section of a light-source side portion of the liquid crystal display. 
         FIG. 2B  is a cross section a portion of the liquid crystal display, which is on an opposite side to the light source. 
         FIG. 3  is a plan view schematically showing a light-source side end portion of a light guide and a light source unit. 
         FIG. 4  is a diagram showing a wavelength distribution of illumination light entering the light guide. 
         FIG. 5  is a block diagram schematically showing the liquid crystal display. 
         FIG. 6  is a cross section schematically showing arrangement of the light source and light guide with relative to each other in a liquid crystal display according to a second embodiment. 
         FIG. 7  is a plan view schematically showing a light source-side end portion of the light guide and a light source portion in a liquid crystal display according to the second embodiment. 
         FIG. 8A  is a plan view schematically showing a light-source side end portion of a light guide and a light source portion in a liquid crystal display according to a modified example. 
         FIG. 8B  is a plan view schematically showing a light-source side end portion of a light guide and a light source portion in a liquid crystal display according to another modified example. 
         FIG. 8C  is a plan view schematically showing a light-source side end portion of a light guide and a light source portion in a liquid crystal display according to another modified example. 
         FIG. 9  is a perspective view showing a light source-side portion of a front-light device in a liquid crystal display according to a third embodiment. 
         FIG. 10  is a cross section of the light source-side portion of the liquid crystal display according to the third embodiment. 
         FIG. 11  is a cross section of a light source-side portion of a display device according to the fourth embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments will be described hereinafter with reference to the accompanying drawings. In general, according to one embodiment, a display device comprises a display panel comprising a display surface and an illumination device comprising a light guide comprising an emission surface opposing the display surface of the display panel, and an incidence surface intersecting the emission surface, a light source emitting light entering the incidence surface, and a light cut layer provided between the light source and the incidence surface, to suppress transmission of light having a predetermined wavelength range. 
     The disclosure is merely an example, and proper changes in keeping with the spirit of the invention, which are easily conceivable by a person with ordinary skill in the art, come within the scope of the invention as a matter of course. In addition, in some cases, in order to make the description clearer, the widths, thicknesses, shapes, etc., of the respective parts are illustrated schematically in the drawings, rather than as an accurate representation of what is implemented. However, such schematic illustration is merely exemplary, and in no way restricts the interpretation of the invention. In addition, in the specification and drawings, the same elements as those described in connection with preceding drawings are denoted by like reference numbers, and detailed description thereof is omitted unless necessary. 
     First Embodiment 
       FIG. 1  is an exploded perspective view of a liquid crystal display according to the first embodiment.  FIG. 2A  is a cross section of a light-source side portion of the liquid crystal display device.  FIG. 2B  is a cross section a portion of the liquid crystal display device, which is on an opposite side to the light source. 
     A liquid crystal display device  10  can be built in, for example, various kinds of electronic devices such as smart phones, tablet devices, notebook personal computers, a handheld game machine, electronic dictionaries, television devices, and car-navigation systems. 
     As shown in  FIG. 1 , the liquid crystal display device (display device)  10  comprises an active-matrix liquid crystal display panel (to be referred to as “liquid crystal panel” hereinafter)  12 , a front-light device  30  disposed as an illumination device to oppose one of flat surfaces of the liquid crystal panel  12 , that is, a display surface  12 , and a cover panel  14  disposed to be overlaid on the front light device  30  to cover the display surface  12   a  and the front-light device  30 . 
     As shown in  FIGS. 1 and 2A , the liquid crystal panel  12  comprises a rectangular first substrate SUB 1 , a rectangular second substrate SUB 2  opposed to the first substrate SUB 1 , and a liquid crystal layer LQ held between the first substrate SUB 1  and the second substrate SUB 2 . The second substrate SUB 2  is attached by its peripheral portion onto the first substrate SUB 1  with a sealing material SE. A polarizer PL 2  is attached on a surface of the second substrate SUB 2  so as to form the display surface  12   a  of the liquid crystal panel  12 . A polarizer PL 1  is attached on a surface of the first substrate SUB 1  (a rear surface of the liquid crystal panel  12 ). 
     In the liquid crystal panel  12 , a rectangular display area (active area) DA is provided in a region located an inner side surrounded by the sealing material SE as viewing the liquid crystal panel  12  in plan view(, which is, here and hereinafter, a state where the liquid crystal panel is viewed from the normal direction of the display surface  12   a ), and images are displayed on the display area DA. A rectangular frame area ED is provided to surround the display area DA. The liquid crystal panel  12  is a reflective liquid crystal panel which displays images by reflecting external light and the light from the front-light device  30 . The liquid crystal panel  12  may be of a structure provided for either one the lateral electric field mode mainly using a lateral electric field along the surface of the substrate, or the vertical electric field mode mainly using a vertical electric field which intersects the surface of the substrate. 
     The liquid crystal panel  12  comprises a plurality of pixels PX arranged in a matrix in the display area DA. As schematically shown in  FIG. 1 , the first substrate SUB 1  comprises, in the display area DA, gate lines G extending in a first direction X, source lines S extending in a second direction Y which intersects the first direction X, switching elements SW each electrically connected to the respective gate line G and the respective source line S in each respective pixel PX, pixel electrodes PE each connected to the respective switching element SW, and the like. A common electrode CE of common potential is provided on the first substrate SUB 1  or the second substrate SUB 2  so as to oppose a plurality of pixel electrodes PE. 
     As shown in  FIG. 2A , according to this embodiment, a pixel circuit PC containing a source line S, a gate line G and a switching element SW, a pixel electrode PE formed of a reflecting electrode, and an alignment film (not shown) are formed on an inner surface of the first substrate SUB 1 . The pixel electrode PE constitutes a reflective film or a reflective layer, which reflects external light and the light from the front-light device  30 . On an inner surface of the second substrate SUB 2 , a color filter CF and a common electrode CE formed of a transparent conducting film such as indium-tin-oxide (ITO), and an alignment film (not shown) are provided. The liquid crystal layer LQ is enclosed between these alignment films. 
     Thus, the liquid crystal panel  12  of this embodiment is a reflective type which displays images by reflecting external light and the light from the front-light device  30  by the pixel electrodes PE. The reflective film does not limited to the pixel electrode, and another reflective film may be provided on the first substrate SUB 1 . In a reflective type liquid crystal panel, the polarizer PL 1  on the rear surface of the liquid crystal display panel may be omitted. 
     In the example illustrated, a flexible printed circuit (main FPC)  23  is joined to a short-side end portion of the first substrate SUB 1  to extend outward from the liquid crystal panel  12 . The main FPC  23  contains semiconductor devices of a driver IC  24 , an IC chip  25  which constitutes a controller, mounted therein as signal supply sources which supplies signals required to drive the liquid crystal panel  12 . 
     The front-light device  30  is an auxiliary light source which supplies reflection light to the pixel electrode PE when there is no sufficient external light used as a light source, or no external light. As shown in  FIGS. 1 and 2A , the front-light device  30  includes a rectangular light guide LG, a light source unit  34  emit illumination light to enter the light guide LG, a blue-light cut layer (light cut layer) BC provided between an incidence surface of the light guide LG and a light-emitting surface of the light source, a resin frame  40 , and a pair of optical sensors. The light guide LG comprises a first main surface S 1  as an emission surface, a second main surface S 2  opposing the first main surface S 1 , a pair of long-side side surfaces, and a pair of short-side side surfaces. In this embodiment, one of the short-side side surface of the light guide LG is the incidence surface EF. The light guide LG is formed from, for example, polycarbonate or an acrylic or silicon transparent resin. 
     The light guide LG is disposed on the liquid crystal panel  12  while the first main surface (emission surface) S 1  opposing the display surface  12   a  of the liquid crystal panel  12 . The first main surface S 1  is attached onto the polarizer PL 2  by, for example, a light-transmissive adhesives or an adhesive AD 1 . The incidence surface EF is located substantially perpendicular to the liquid crystal panel  12 , and extends substantially parallel to the short sides of the second substrate SUB 2 . As will be described later, in this embodiment, a thin film of the blue-light cut layer BC is formed on the incidence surface EF. 
     The light source unit  34  comprises, for example, a belt-like wiring substrate  36  and a plurality of light sources mounted and arranged on the wiring substrate  36 . As the light sources, light emitting devices, for example, light emitting diodes (LED)  38  are used. As the LED, white LEDs or pseudo-white LED (LED in which a phosphor which glows yellow is disposed on a light-emitting surface of a blue LED) can be used. The wiring substrate  36  is formed from a flexible printed circuit (FPC). A plurality of LEDs  38  are mounted on the FPC  36  and arranged along the short sides of the first substrate SUB 1 . Each LED  38  comprises a mounting surface  38   b  to be mounted on the FPC  36  and a light-emitting surface  38   a  located substantially perpendicular to the FPC  36 . 
     The FPC  36  extends along the incidence surface EF. One side edge portion of the FPC  36  is adhered on a light source-side end portion of the second main surface S 2  of the light guide LG by, for example, a double-sided tape TP 1 . Another side edge portion of the FPC  36  is attached on the resin frame  40  by a double-sided tape TP 2 . Thus, the FPC  36  is disposed on substantially the same plane as that of the second main surface S 2  of the light guide LG 
       FIG. 3  is a plan view schematically showing the light source-side end portion of the light guide LG and the light source unit  34 . As shown in  FIGS. 2A and 3 , a plurality of LEDs  38  are arranged all along the incidence surface EF at a predetermined gap. The LEDs  38  are arranged in such a state that the light-emitting surfaces  38   a  adjacently oppose the incidence surface EF of the light guide LG. In this embodiment, the light-emitting surfaces  38   a  adjacently oppose or are brought into contact in parallel to the blue-light cut layer BC. 
     As shown in  FIGS. 1, 2A and 2B , the cover panel  14  is formed into a rectangular plate from, for example, a glass plate or an acrylic transparent resin. A lower surface (rear surface, a surface on the side of the liquid crystal panel) of the cover panel  14  is attached on the second main surface S 2  of the light guide LG by an adhesive layer AD 2  made from, for example, a transparent adhesive or tacky agent. In this manner, the cover panel  14  covers the entire surfaces of the front-light device  30  and the display surface  12   a  of the liquid crystal panel  12 . 
     A frame-like light-shielding layer RS is formed on the lower surface of the cover panel  14 . In the cover panel  14 , the region of the liquid crystal panel  12 , other than the regions opposing the display area DA is shielded by a light-shielding layer RS. The light-shielding layer RS may be formed on the upper surface (outer surface) of the cover panel  14 . Note that the cover panel  14  may be omitted in accordance with the condition where how the liquid crystal display  10  is used. 
     The resin frame  40  of the front-light device  30  is attached on the light-shielding area of the cover panel  14  by, for example, a double-sided tape TP 3 . Further, in the light-source side end portion, the FPC  36  of the light source unit  34  is brought into contact with the light-shielding layer RS while interposing a spacer SP therebetween. 
     Next, the blue-light cut layer (light cut layer) BC will be described in detail. The blue-light cut layer BC is formed from a photo-curing resin which is cured by ultraviolet rays or visible light, or a transparent material obtained by mixing a predetermined amount of a coloring material to a base resin of a transparent epoxy resin or the like. 
     For the base resin, it is preferable to select a type which as an optical transmissivity (to a wavelength of 400 nm or more) after being cured, which is 90% or higher, in order not to lower the optical transmissivity of the light guide LG. Examples of the base resin are a monomer, a polymerization initiator, photo-curing resin, a transparent epoxy resin or the like. 
     Examples of the coloring material are a perylene-based pigment and an azo-based pigment. These coloring materials dissolve in ethyl alcohol at a predetermined concentration, to be mixed with the base resin. For example, when a photo-curing resin is used as the base resin and a perylene-based pigment is used as the coloring material, the coloring material is dissolved in ethyl alcohol at a ratio of 0.1% by weight, and further mixed into a coloring material solution at 0.1% by weight with respect to the base resin. Thus, the resin material is prepared to contain 0.01% by weight of the coloring material with respect to the base resin. 
     The resin material is applied on the entire incidence surface EF of the light guide LG, to form the blue-light cut layer BC. Examples of the application method are dispenser application, slot die-coating, slit coater application, screen printing, and spin coating. 
     The thickness of the coating of the resin material needs to be set according to the concentration of the coloring material mixed to the base resin. For example, when using a photo-curing resin as the base resin and a perylene-based pigment as the coloring material, the thickness of the coating of the resin material should preferably be about 150 to 250 μm, and more preferably 200 μm. In order to cure the resin material applied, for example, the resin material is irradiated with ultraviolet rays in nitrogen atmosphere. In this manner, the resin layer is cured up to its surface, and thus the blue-light cut layer BC can be obtained. 
     The illumination light emitted from the light-emitting surface  38   a  of the LED  38  enters the incidence surface EF of the light guide LG, after passing through the blue-light cut layer BC.  FIG. 4  shows spectral characteristics of the illumination light. In  FIG. 4 , a solid line indicates the spectral characteristic of the light emitted from the LED  38  and a dashed line indicates the spectral characteristic of the illumination light after passing through the blue-light cut layer BC. As shown in the figure, by passing through the blue light cut layer BC, a peak value of a light intensity of a wavelength of 380 to 495 nm, which is that of blue light, can be reduced by about 25 to 40% as compared to the case where the blue-light cut layer BC is not provided. Therefore, the blue light cut layer BC has a transmissivity to light of a wavelength of 380 to 495 nm of 60 to 75%, and thus a function of suppressing the transmission of blue light, that is, cutting the blue light by 25 to 40%. 
     Note that the materials of the blue-light cut layer BC are not limited to the base resin and the coloring material described above, but may be selected from other various materials. Moreover, the transmissivity of the blue-light cut layer BC, i.e., the blue-light cut rate, is not limited to the value mentioned above, but can be adjusted to arbitrary cut rates by adjusting the concentration of the coloring material. 
     The blue-light cut layer BC is formed to have a uniform thickness over the entire incidence surface EF, but the structure thereof is not limited to this. The blue-light cut layer BC may change its thickness from one place to another, or may be provided in a plurality of locations on the incidence surface EF instead of being formed on the entire surface. Generally, the spectral characteristics of LEDs are uniform, but they may vary from one LED to another (dispersion). Therefore, the thickness of the blue-light cut layer BC or the locations thereof may be changed according to the spectral characteristics of each LED. For example, in the blue-light cut layer BC, the region opposing LEDs with high blue light intensity may be formed thicker than the other regions. Or, the region opposing LEDs with low blue light intensity may be formed thicker than the other regions. Moreover, in the region opposing LEDs with low blue light intensity, the blue-light cut layer BC may be formed thinner than the other regions, or the blue-light cut layer may be even omitted. 
     As shown in  FIGS. 1 and 2B , a light source-side optical sensor  54   a  and an external light sensor  54   b  make a pair of optical sensors, and both are formed near a side surface SF which is opposite to the incidence surface EF of the light guide LG. The light source-side optical sensor  54   a  is disposed in the state the light-receiving surface thereof faces the side surface SF. That is, the light source-side optical sensor  54   a  is provided at a position which opposes the light source (LED  38 ) via the light guide LG. Thus, the light source-side optical sensor  54   a  receives light from the LED light source, having passed through the blue-light cut layer BC and the light guide LG, and detects the wavelength and intensity of the light. 
     Moreover, the external light sensor  54   b  is disposed in the state the light receiving surface faces the rear surface of the cover panel  14 . The light-shielding layer RS comprises an opening  55  at a position opposing the light-receiving surface of the external light sensor  54   b . The external light sensor  54   b  receives external light having passed through the cover panel  14  and detects the wavelength and intensity of the light. The light source-side optical sensor  54   a  and the external light sensor  54   b  are both connected to a controller  56 , which will be described later. The optical sensors  54   a  and  54   b  may be configured to detect the wavelength and intensity, or to convert the received light into signal data (RAW data) and then output it to the controller  56 . In the latter case, the wavelength and intensity of each of light rays are calculated by the controller  56  based on the signals. 
     The liquid crystal display  10  configured as described above, when used in a bright room or outdoor, reflects external light entering the liquid crystal panel  12  via the cover panel  14  and the light guide LG, by the pixel electrode PE of the liquid crystal panel  12 , and displays display images of the liquid crystal panel  12  on the display surface  12   a  using the reflection light. When used in a dark place, the LEDs  38  of the light source unit  34  are turned on and display images of the liquid crystal panel  12  are displayed on the display surface  12   a  using the emitted light from the LEDs  38 . That is, the light emitted from the light-emitting surface  38   a  of the LED  38  passes through the blue-light cut layer BC, and enters the light guide LG from the incidence surface EF. During this period, the blue light component of the incidence light is cut by 25 to 40% with the blue-light cut layer BC. The incidence light propagates inside the light guide LG and is reflected by the first main surface S 2 . Then, it is irradiated from the first main surface S 1  towards the liquid crystal panel  12 . The irradiated light is reflected by the pixel electrode PE of the liquid crystal panel  12 , and the reflection light is used to display the display images of the liquid crystal panel  12  on the display surface  12   a.    
     As described above, the blue-light cut layer BC is provided between the incidence surface of the light guide LG and the light source, and thus the blue light component of the illumination light entering the light guide LG from the LEDs  38  is reduced, thereby making it possible to realize image display easy on eyes. Moreover, when displaying images by reflection of external light, the external light does not pass through the blue-light cut layer BC. Therefore, the image display is not affected by the blue-light cut layer BC, or variation in the color tone thereof can be suppressed, thereby maintaining high quality in display. Thus, according to this embodiment, a liquid crystal display which can display images of high display quality while reducing the blue light can be obtained. 
     On the other hand, the liquid crystal display  10  according to this embodiment is configured to adjust display images optimally according to the intensity of external light at each wavelength and according to the intensity of the light of the front-light device at each wavelength.  FIG. 5  schematically shows an entire configuration of the liquid crystal display. As shown in the figure, the liquid crystal display  10  includes the display drive circuit  50  which drives pixels of the liquid crystal panel  12 , the light source drive circuit  52  which drives the LEDs  38  of the light source unit  34 , the light source-side optical sensor  54   a  which detects the intensity (brightness) of the light of the light source unit  34  at each wavelength, the external light sensor  54   b  which detects the intensity (brightness) of the external light at each wavelength, and the controller (controller)  56  which controls the display drive circuit  50  and the light source drive circuit  52 . 
     The display drive circuit  50  includes the driver IC  24 , and a gate drive circuit and a signal line drive circuit (not shown), formed on the first substrate SUB 1 . The controller  56  and the light source drive circuit  52  are incorporated in the IC chip  25  on the FPC  23  and are provided next to the driver IC  24 . Note that such a structure is adoptable as well that either or both of the controller  56  and the light source drive circuit  52  are built in the driver IC. 
     The controller  56  turns on or off the LEDs  38  by the light source drive circuit  52  according to the light intensity (brightness) at each wavelength, detected by the external light sensor  54   b . For example, when a predetermined brightness or higher is detected by the external light sensor  54   b , the liquid crystal panel  12  is driven by the display drive circuit  50  to display images without turning on the LEDs  38 . In this operation, the controller  56  controls the liquid crystal panel  12  to drive at the optimal display state according to the brightness of the external light. When the intensity of the blue light is high, that is, for example, light from fluorescent lights occupies the majority portion of the external light, is high, the voltage applied to blue pixels is reduced to lower the optical transmissivity of the blue pixels, and thus the color tone of the entire display image is adjusted. 
     When a predetermined brightness or higher is not detected by the external light sensor  54   b , that is, when dark, the controller  56  drives the LEDs  38  to be on by the light source drive circuit  52 , and drives the liquid crystal panel  12  by the display drive circuit  50 . Thus, the images on the liquid crystal panel  12  are displayed by the illumination light from the LEDs  38  and the external light. Moreover, the illumination light from the LEDs  38  is detected by the light source-side optical sensor  54   a  via the blue-light cut layer BC and the light guide LG. At this time, the controller  56  adjusts the RGB display of the liquid crystal panel  12  according to the brightness (intensity at each wavelength) of each type of light, detected by the external light sensor  54   b  and the light source-side optical sensor  54   a , thus setting display images of the optimal color tone. 
     As described above, according to the liquid crystal display of this embodiment, it is possible to perform the optimal image display according to the external light and the illumination light of the front-light device while reducing the blue light. 
     Next, liquid crystal displays according to other embodiments will be described. In the other embodiment described below, structural parts identical to those of the first embodiment described above will be designated by the same reference numbers, and detailed descriptions therefor may be omitted or simplified. Only the different portions from those of the first embodiment will be mainly described in detail. 
     Second Embodiment 
       FIG. 6  is a cross section showing a light source-side portion of a front-light device in a liquid crystal display according to the second embodiment, and  FIG. 7  is a plan view schematically showing the light source-side portion. 
     As shown in  FIGS. 6 and 7 , according to this embodiment, a blue-light cut layer is provided on a light-emitting surface  38   a  of each of LEDs  38 . A blue-light cut layer BC is formed by thin film formation on the light-emitting surface  38   a  of each of the LEDs  38 , so as to adjacently oppose the incidence surface EF of the light guide LG. In this embodiment, the blue-light cut layers BC are formed to have a fixed thickness on the light-emitting surfaces  38   a  of all the LEDs  38 , with a common transmissivity. 
     In the second embodiment, the other structure of the liquid crystal display is the same as that of the liquid crystal display according to the first embodiment described above. With the second embodiment as well, a liquid crystal display of high display quality can be obtained while reducing the blue light. 
     In the second embodiment, the thickness of the blue-light cut layers BC and the locations where they are formed can be changed arbitrarily. As described above, the spectral characteristics of the LEDs  38  may vary from one LED to another. Therefore, the thickness of the blue light cut layers BC and the locations where they should be formed can be selected according to the spectral characteristics of each LED. 
       FIGS. 8A, 8B and 8C  are plan views schematically showing light source-side portions of the front-light device according to various modified examples, respectively. 
     As shown in  FIG. 8A , according to the first modified example, the blue-light cut layer BC is not formed for LEDs  38 A, which have comparatively low wavelength intensity of the blue light, of the plurality of LEDs  38 . 
     As shown in  FIG. 8B , according to the second modified example, of the plurality of LEDs  38 , LEDs  38 A, which have comparatively low wavelength intensity of the blue light, are provided with blue-light cut layer BC thinner than those of the other blue-light cut layers BC. 
     As shown in  FIG. 8C , according to the second modified example, of the plurality of LEDs  38 , LEDs  38 A, which have comparatively low wavelength intensity of the blue light, are provided with the blue-light cut layer BC not entirely on their light-emitting surfaces  38   a , but on, for example, only a half area of each. 
     Third Embodiment 
       FIG. 9  is a perspective view showing a light source-side portion of a front-light device in a liquid crystal display according to the third embodiment, and  FIG. 10  is a cross section schematically showing the light source-side portion. 
     As shown in  FIGS. 9 and 10 , according to this embodiment, the front-light device  30  employs a sheet-or film-like blue-light cut layer BC. For example, the blue-light cut sheet BCF is formed by applying a blue light cut layer BC described above on a transparent film. The blue-light cut sheet BCF is disposed between a light-emitting surface  38   a  of each LED  38  and incidence surface EF of a light guide LG 
     For example, a blue-light cut sheet BCF is formed into, for example, a belt-like shape and fixed to an incidence-side end portion of the light guide LG. A central portion of the blue light cut sheet BCF along its width direction is tightly attached onto the incidence surface EF, to cover the incidence surface EF. Both edge portions of the blue light cut sheet BCF are bent towards a light guide LG side and are adhered onto end portions of the first main surface S 1  and the second main surface S 2  by double-sided tapes TP 4  and TP 5 , respectively. On a second main surface S 2 , an FPC  36  of the light source unit  34  is attached to partially overlap a respective side edge portion of the blue light cut sheet BCF. Note that the blue-light cut sheet BCF may be brought into contact with the light guide LG by its film side or blue-light cut layer BC. 
     In the third embodiment, the other structure of the liquid crystal display is the same as that of the liquid crystal display according to the first embodiment described above. Even when a sheet-like blue-light cut layer is employed as in the third embodiment, a liquid crystal display of high display quality can be obtained while reducing the blue light. 
     Note that in the third embodiment described above, the blue-light cut sheet BCF is not limited to the size which covers the entire incidence surface EF, but may be of a size which partially covers arbitrary regions of the incidence surface. 
     Fourth Embodiment 
       FIG. 11  is a cross section of a light source-side end portion of a display device according to the fourth embodiment. As shown, according to the fourth embodiment, a display panel  12  which employs an electrophoretic element is used as a display panel of the display device  10 . 
     The display panel  12  comprises a rectangular plate-shaped first substrate SUB 1 , a rectangular plate-shaped second substrate SUB 2  disposed to oppose the first substrate SUB 1 , and an electrophoretic element  70  held between the first substrate SUB 1  and the second substrate SUB 2 . The second substrate SUB 2  is attached by its peripheral portion onto the first substrate SUB 1  by a sealing material SE. A barrier layer BA 2  is attached on a surface of the second substrate SUB 2 , to form a display surface  12   a . A barrier layer BA 1  is attached on a surface (rear surface of the display panel  12 ) of the first substrate SUB 1 . 
     On an inner surface of the first substrate SUB 1 , pixel circuits PC including source lines, gate lines, switching elements, and pixel electrodes PE formed of reflecting electrodes are provided. The pixel electrodes PE constitute reflective films or reflective layers provided on the first substrate SUB 1 . On an inner surface of the second substrate SUB 2 , a common electrode CE formed of a transparent conducting film such as of ITO, is provided. The electrophoretic element  70  comprises a number of microcapsules  60  dispersedly arranged on substantially an entire area between the first substrate SUB 1  and the second substrate SUB 2 . The electrophoretic element  70  can as well adopt, for example, a sheet type comprising a pair of films formed from a transparent resin and disposed to oppose each other, and microcapsules dispersedly arranged between these films. 
     The microcapsules  60  have a particle diameter of, for example, about 50 to 100 μm. The microcapsules  60  each comprise a spherical outer shell  62 , a plurality of white particles (electrophoretic particles)  60   a , a plurality of black particles (electrophoretic particles)  60   b  and a dispersion medium  64 , contained in the outer shell  62 . In the example illustrated, only a less number of capsules are schematically shown, one or more microcapsules  60  are formed in a region opposing one pixel electrode PE. The microcapsules  60  are dispersed arranged over the entire display area DA. 
     In place of the white particles  60   a  and the black particles  60   b , for example, pigments of red, green, blue, yellow, cyan, magenta or the like, may be used. With such structure, red, green, blue, yellow, cyan, magenta and the like can be displayed on the display surface  12   a . Or such structure as well is adoptable that particles of one of the above-listed colors are provided in microcapsules in addition to the white particles and black particles. 
     The display panel  12  is attached onto the first main surface S 1  of the light guide LG with, for example, a light-transmissive adhesive or adhesive AD 1 . In the fourth embodiment, the other structure of the display device which includes, for example, a front-light device  30  and a cover panel  14 , is the same as that of the liquid crystal display according to the first embodiment described above. With the fourth embodiment as well, a liquid crystal display of high display quality can be obtained while reducing the blue light. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions. 
     All structures which can be implemented by a person of ordinary skill in the art through arbitrary design changes based on the structures described above as the embodiment of the present invention come within the scope of the present invention as long as they encompass the spirit of the present invention. Regarding advantages other than those described in the embodiment, advantages obvious from the description and advantages appropriately conceivable by a person of ordinary skill in the art are regarded as advantages achievable from the present invention as a matter of course. 
     For example, the LEDs are not limited to a side view type, but top-view LEDs may as well be used. The LEDs are not limited to white light LEDs, but those emitting colors of RGB may as well be used. In this case, the light emission of the front-light device is controlled according to the intensity of external light at each respective wavelength, thereby making it possible to adjust the color tone of display images.