Patent Publication Number: US-2019196270-A1

Title: Display device

Description:
TECHNICAL FIELD 
     The present invention relates to a display apparatus in which a display panel is illuminated with light of a light source unit through a fluorescent film. 
     BACKGROUND ART 
     Liquid crystal displays (LCDs), which are the mainstream of flat panel displays, have in recent years been widely used in the field of large-size panels for televisions, etc., as well as the field of middle- or small-size panels. In such a liquid crystal display, an optical member is disposed behind a display panel, and the display panel is illuminated with light of a light source unit through the optical member to display an image. 
     In the display panel, for example, a liquid crystal layer is sandwiched by two glass substrates. A color filter is formed on the inner surface of the front glass substrate, and thin film transistors (TFTs) are formed on the inner surface of the rear glass substrate. Each picture element (pixel) includes three sub-pixels having R, G, and B color filters. 
     A display apparatus in which a quantum dot (QD) film is employed as an example of the optical member has been disclosed (see Patent Document No. 1). The QD film is a fluorescent film containing light-emitting fine metal particles, and having the function (color conversion function) of converting excited light having a single wavelength into light having a plurality of wavelengths (blue, green, red, etc.). 
     CITATION LIST 
     Patent Literature 
     Patent Document No. 1: Japanese National Phase PCT Laid-Open Patent Publication No. 2013-544018 
     SUMMARY OF INVENTION 
     Technical Problem 
     However, in the conventional display apparatus disclosed in Patent Document No. 1, light rays from the light source unit strike the incident surface of the QD film at various angles. The light rays entering the QD film from the incident surface have different lengths of optical paths (optical path lengths) in the QD film that depend on the angle of incidence. A light ray having a greater optical path length has more chances to excite fine metal particles, resulting in a greater amount of emission of red and/or green light. Thus, light rays emitted from the light-emitting surface of the QD film have different colors due to their different optical path lengths, resulting in color nonuniformity on the light-emitting surface of the QD film. 
     With the above in mind, the present invention has been made. It is an object of the present invention to provide a display apparatus in which the occurrence of color nonuniformity can be prevented or reduced. 
     Solution to Problem 
     A display apparatus according to an embodiment of the present invention in which light from a light source unit is transmitted through a fluorescent film before reaching a display panel, the display apparatus including an optical path changing member provided between the light source unit and the fluorescent film and for changing optical path lengths within the fluorescent film of light rays entering the fluorescent film from an incident surface of the fluorescent film. 
     Advantageous Effects of Invention 
     According to the present invention, the occurrence of color nonuniformity can be prevented or reduced. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is an exploded perspective view showing an example of main parts of a configuration of a display apparatus according to an embodiment of the present invention. 
         FIG. 2  is a schematic diagram showing a first example of a configuration of an optical member in an embodiment of the present invention. 
         FIG. 3  is a schematic diagram showing an example of changing of an optical path by a prism film in an embodiment of the present invention. 
         FIG. 4  is a schematic diagram showing as example of a configuration of a conventional optical member. 
         FIG. 5  is a schematic diagram showing an example of a display surface of a conventional liquid crystal display apparatus. 
         FIG. 6  is a schematic diagram showing an example of a display surface of a display apparatus according to an embodiment of the present invention. 
         FIG. 7  is a schematic diagram showing a second example of a configuration of an optical member in an embodiment of the present invention. 
         FIG. 8  is a schematic diagram showing a third example of a configuration of an optical path changing member in an embodiment of the present invention. 
         FIG. 9  is a schematic diagram showing a fourth example of a configuration of an optical path changing member in an embodiment of the present invention. 
         FIG. 10  is a schematic diagram showing a fifth example of a configuration of an optical path changing member in an embodiment of the present invention. 
         FIG. 11  is a schematic diagram showing a sixth example of a configuration of an optical path changing member in an embodiment of the present invention. 
         FIG. 12  is an explanatory diagram showing an example of evaluation data of color nonuniformity in the case of an optical path changing member in an embodiment of the present invention. 
         FIG. 13  is an explanatory diagram showing evaluation data of luminance in the case of an optical path changing member in an embodiment of the present invention. 
         FIG. 14  is an explanatory diagram showing an example of evaluation data of chromaticity (y-coordinate) in the case of an optical path changing member in an embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The present invention will now be described with reference to the accompanying drawings showing embodiments thereof.  FIG. 1  is an exploded perspective view showing an example of main parts of a configuration of a apparatus  100  according to an embodiment of the present invention. As shown in  FIG. 1 , the display apparatus  100  includes a liquid crystal panel  10  as a panel for displaying an image (including a video), a backlight unit  30  that is provided behind the liquid crystal panel  10  and illuminates the liquid crystal panel  10  with light required to display an image, etc. Note that, in  FIG. 1 , members of the display apparatus  100 , such as an outer frame for covering the liquid crystal panel  10 , are not shown for the same of convenience. Regarding terminology concerning directions as used herein, “front” refers to the direction in which the display apparatus  100  displays an image; the opposite direction of thereof is referred to as “rear”. 
     The liquid crystal panel  10  includes a liquid crystal layer (not shown), a light-transmissive front substrate  12  and rear substrate  13  that sandwich the liquid crystal layer, a pair of polarizing plates  11  and  14  that are provided on outer surfaces of the front substrate  12  and the rear substrate  13 , respectively, etc. A color filter is formed on an inner surface of the front substrate  12 , and each picture element (pixel) includes three sub-pixels having R, G, and B color filters. Data lines and scan lines are arranged in a matrix, extending in vertical and horizontal directions, on an inner surface of the rear substrate  13 . A thin film transistor (TFT) is provided at each of intersections between the data lines and the scan lines. A drive circuit that drives the data lines and the scan lines is formed in a peripheral region of the rear substrate  13 . The amount of light transmitted through the pair of polarizing plates  11  and  14  is controlled on a pixel-by-pixel basis by illuminating the liquid crystal panel  10  with light from LEDs  33  (described below) provided in the backlight unit  30 , and modulating the polarized state of the illumination light using the liquid crystal layer, whereby a predetermined image can be displayed. The two substrates included in the liquid crystal panel  10  that are located on the front side and the rear side are herein referred to as a “front substrate” and a “rear substrate,” respectively. 
     The backlight unit  30  (light source unit) includes a box-shaped chassis  31  having an opening on the front side thereof, a substrate  32  fixed to a bottom plate of the chassis  31 , a plurality of LEDs (light source units)  33  mounted on the substrate  32  and arranged in a grid pattern with a predetermined space between each LED, etc. The arrangement of the plurality of LEDs  33  is not particularly limited if it is a grid pattern. The plurality of LEDs  33  may be arranged not only in the so-called matrix (i.e., in vertical and horizontal directions), but also in the so-called staggered arrangement. In addition, the arrangement (the direction and pitch of aligned LEDs  33 ) of LEDs  33  provided in a peripheral region of the substrate  32  may be slightly different from the arrangement of LEDs  33  in a central region of the substrate  32 . 
     The optical member  20  is disposed at the opening of the chassis  31 , facing the substrate  32 . The optical member  20 , which is, for example, formed of a plurality of optical films stacked together, homogenizes light from the plurality of LEDs  33 . The optical member  20  is described in detail below. 
     The LED  33  includes a blue LED and a secondary lens provided to cover the blue LED. Light emitted from the blue LED is diffused by the secondary lens. 
       FIG. 2  is a schematic diagram showing a first example of a configuration of the optical member  20  in an embodiment of the present invention. As shown in  FIG. 2 , the optical member  20  and the substrate  32  on which the plurality of LEDs  33  are mounted are spaced a predetermined distance apart. The optical member  20  includes a light condensing member  21  whose surface closer to the liquid crystal panel  10  has an uneven curved shape, a fluorescent film  22 , a prism film  23  as a first example of the optical path changing member, and a diffusion plate  24  having a surface on which minute recesses and protrusions are provided, which are successively stacked in that order with the light condensing member  21  closest to the liquid crystal panel  10 . The prism film  23  has, on a front surface thereof, a plurality of grooves that are formed so as to form a plurality of ridges extending in the same direction. A cross-section of the plurality of ridges that is perpendicular to that direction (also referred to as a “groove direction”) has a shape that a plurality of isosceles triangles are linked together with their bases aligned. In an embodiment of the present invention, the prism film  23  is disposed such that the ridges are located close to the fluorescent film  22 . 
     Thus, the prism film  23  is disposed between the fluorescent film  22  and the LEDs  33 . The fluorescent film  22  has an incident surface  221  and a light-emitting surface  222 . Although  FIG. 2  illustrates that the members (the light condensing member  21 , the fluorescent film  22 , the prism film  23 , and the diffusion plate  24 ) constituting the optical member  20  are tightly attached together, a feature of the present embodiment is achieved by the presence of an air layer having such a thickness that the layer cannot be depicted, between each member. 
     The fluorescent film  22  contains light-emitting fine metal particles that are excited to generate red and/or green light when blue light from the LEDs  33  travels within the fluorescent film  22 . Thus, in the objective perspective, the fluorescent film  22  is considered to have the function of converting a portion of blue light entering thereinto into red and/or green light, and emitting out the red and/or green light (color conversion function). Blue light having a greater optical path length (also referred to as the “length of an optical path”) within the fluorescent film  22  has more chances to excite light-emitting fine metal particles, so that fine metal particles convert the blue light into a greater amount of red and/or green light. A combination of the fluorescent film  22  with a color filter can generate color components (red, green, and blue) for providing white. 
       FIG. 3  is a schematic diagram showing an example of changing of an optical path by the prism film  23  in the present embodiment. Although light emitted from the LED  33  is diffused,  FIG. 3  shows light P 1  that is emitted in a direction perpendicular to the incident surface  221  of the fluorescent film  22 , and light P 2  that is emitted in a direction oblique to the incident surface  221  of the fluorescent film  22 , for the sake of convenience and for ease of understanding of changing of an optical path. 
     As shown in  FIG. 3 , the blue light P 1  from the LED  33  perpendicularly strikes the incident surface  221  of the fluorescent film  22 . The light P 1 , which is blue light, enters the fluorescent film  22  from the incident surface  221 , and in the objective perspective, when traveling within the fluorescent film  22 , is partially converted into red light and/or green light by light-emitting fine metal particles in the fluorescent film  22 . In this case, the optical path length of the light P 1  within the fluorescent film  22  is equal to the thickness of the fluorescent film  22  (the distance between the incident surface  221  and the light-emitting surface  222 : reference sign d 1  in  FIG. 3 ). The light P 1  is emitted, as white light that is a suitable combination of red (R), green (G), and blue (B) spectra, from the light condensing member  21  toward the liquid crystal panel  10 . 
     Meanwhile, the optical path of the blue light P 2  from the LED  33  is changed by the prism film  23  before arriving at the incident surface  221  of the fluorescent film  22 . Specifically, the prism film  23  changes the optical path of the light P 2  that would otherwise obliquely strike the incident surface  221  such that the light P 2  perpendicularly strikes the incident surface  221  of the fluorescent film  22 . After the optical path is changed, the blue light P 2  enters the fluorescent film  22 , and in the objective perspective, when traveling within the fluorescent film  22 , is partially converted into red light and/or green light by light-emitting fine metal particles in the fluorescent film  22 . In this case, the optical path length of the light P 2  within the fluorescent film  22  is equal to the thickness (reference sign d 1  in  FIG. 3 ) of the fluorescent film  22 . As with the light P 1 , the light P 2  is emitted, as white light that is a suitable combination of red (R), green (G), and blue (B) spectra, from the light condensing member  21  toward the liquid crystal panel  10 . Note that light outgoing from the light condensing member  21  toward the liquid crystal panel  10  diffuses or spreads over a certain wide area, which is however indicated by arrows R, G, and B in  FIG. 3  for the sake of convenience. 
     In the case where the prism film  23  is not provided, the light P 2  enters the fluorescent film  22  from the incident surface  221  of the fluorescent film  22  without changing the optical path along a direction oblique to the incident surface  221  as indicated by a dashed line in  FIG. 3 , and therefore, the optical path length (length indicated by reference sign d 2  in  FIG. 3 ) of the light P 2  within the fluorescent film  22  is greater than d 1  (d 1 &lt;d 2 ). 
     As described above, the prism film  23  changes the optical path lengths within the fluorescent film  22  of light rays that enter the fluorescent film  22  from the incident surface  221 . Specifically, the prism film  23  changes the optical paths of light rays from the LED  33  and thereby changes the angles of incidence of the light rays to the incident surface  221  of the fluorescent film  22  before the light rays arrive at the incident surface  221  of the fluorescent film  22 , so as to change the optical path lengths within the fluorescent film  22  of light rays (e.g., the light P 2  in  FIG. 3 ) entering the fluorescent film  22  from the incident surface  221 . 
     The prism film  23  can change the optical path lengths within the fluorescent film  22 , and therefore, can change the conversion amount of light, so that color nonuniformity on the light-emitting surface  222  of the fluorescent film  22  can be prevented or reduced. Note that the conversion amount of light refers to the amount of light whose wavelength is converted by the color conversion function of the fluorescent film  22  (e.g., the amount of a portion of blue light emitted from the LED  33  that is converted into red light and/or green light). 
     The prism film  23  also changes the optical paths of light rays (e.g., the light P 1  and P 2  in  FIG. 3 ) traveling toward the incident surface  221  of the fluorescent film  22  at different angles with respect to the incident surface  221  before the light rays arrive at the incident surface  221  so as to reduce the differences in optical path lengths within the fluorescent film  22  among the light rays traveling after entering the fluorescent film  22 . Specifically, the prism film  23  changes the optical paths of light rays from the LED  33  and thereby changes the angles of incidence of the light rays to the incident surface  221  of the fluorescent film  22  before the light rays arrive at the incident surface  221  of the fluorescent film  22  so as to reduce the differences in optical path lengths within the fluorescent film  22  among the light rays traveling within the fluorescent film  22 . 
     The prism film  23  can reduce the differences in optical path lengths within the fluorescent film  22  among light rays traveling within the fluorescent film  22 , and therefore, can reduce the differences in conversion amounts among the light rays within the fluorescent film  22 , so that color nonuniformity on the light-emitting surface  222  of the fluorescent film  22  can be prevented or reduced. 
     The prism film  23  also changes the optical paths of light rays before the light rays arrive at the incident surface  221  so as to reduce the differences in optical path lengths within the fluorescent film  22  between the light rays emitted from the LED  33  in a direction oblique to the incident surface  221  of the fluorescent film  22  and a light ray emitted from the LED  33  in a direction perpendicular to the incident surface  221  of the fluorescent film  22 . As a result, the differences in optical path lengths within the fluorescent film  22  among light rays are reduced, so that the differences in conversion amounts in the fluorescent film  22  among the light rays can be reduced, and therefore, color nonuniformity on the light-emitting surface  222  of the fluorescent film  22  can be prevented or reduced. Although  FIGS. 2 and 3  show the optical member  20  including the four members, i.e., the light condensing member  21 , the fluorescent film  22 , the prism film  23 , and the diffusion plate  24 , an additional sheet may be provided on top of the light condensing member  21  in order to prevent or reduce luminance nonuniformity on the front surface of the optical member  20 . Specifically, a diffusion sheet for reducing the degree of light condensation by the light condensing member  21 , a light condensing sheet for further enhancing the degree of light condensation by the light condensing member  21 , a reflection sheet, a polarization sheet, etc., may be provided on top of the light condensing member  21 . 
       FIG. 4  is a schematic diagram showing an example of a configuration of a conventional optical member. As shown in  FIG. 4 , the conventional optical member includes a prism film having ridges formed on a surface thereof closer to a liquid crystal panel, a fluorescent film, and a diffusion plate having minute recesses and protrusions on a surface thereof, with the prism film closest to the liquid crystal panel. 
     As shown in  FIG. 4 , the blue light P 1  from LEDs perpendicularly strikes the incident surface of the fluorescent film. The light P 1 , which is blue light, enters the fluorescent film from the incident surface, and in the objective perspective, when traveling within the fluorescent film, is partially converted into red light and/or green light by light-emitting fine metal particles in the fluorescent film. In this case, the optical path length of the light P 1  within the fluorescent film is equal to the thickness of the fluorescent film  22  (reference sign d 1  in  FIG. 4 ). The light P 1  is emitted, as white light that is a suitable combination of red (R), green (G), and blue (B) spectra, from the prism film toward the liquid crystal panel. 
     Meanwhile, blue light P 2  from LEDs enters the fluorescent film from the incident surface of the fluorescent film without changing the optical path along a direction oblique to the incident surface. Therefore, the optical path length of the light P 2  within the fluorescent film (length indicated by reference sign d 2  in  FIG. 4 ) is greater than the optical path length d 1  of the light P 1 . As described above, as the optical path lengths within the fluorescent film increase, the conversion amount of light that is converted into red light and/or green light by light-emitting fine metal particles increases, so that more red (R) and green (G) light components are emitted from the light-emitting surface of the fluorescent film, leading to an imbalance between red (R), green (G), and blue (B) spectra, which is unsuitable for generation of white light. 
       FIG. 5  is a schematic diagram showing an example of a display surface  1  of a conventional liquid crystal display apparatus.  FIG. 5  shows an enlarged view of a small region A of the display surface  1 . The small region A is, for example, a square with a side of several pitches of LEDs of the backlight device. As shown in  FIG. 5 , color nonuniformity occurs due to the appearance of regions  2  and regions  3 . The region  2  is located directly in front of the LED, and has a relatively low chromaticity in the CIE chromaticity diagram, i.e., exhibits the so-called “blue.” The region  3  surrounds the region located directly in front of the LED, and has a relatively high chromaticity, i.e., exhibits the so-called “yellow.” Such a region  2  and region  3  appear at the pitch of LEDs, and therefore, the conventional liquid crystal display apparatus as shown in  FIG. 5  does not have good display quality. Although, in  FIG. 5 , two different regions indicate two different chromaticities for the sake of convenience, the actual chromaticity continuously changes over the regions. 
     In contrast, in an embodiment of the present invention, the prism film  23  changes the optical paths of light rays that will enter the fluorescent film  22  from the incident surface  221  so as to reduce the optical path lengths of the light rays within the fluorescent film  22 . Specifically, in the present embodiment, the optical path lengths within the fluorescent film  22  of light rays emitted from the LED  33  in a direction oblique to the incident surface  221  of the fluorescent film  22  can be made closer the optical path lengths within the fluorescent film  22  of light rays emitted from the LED  33  in a direction perpendicular to the incident surface  221 . 
       FIG. 6  is a schematic diagram showing an example of the display surface  1  of the display apparatus  100  of the present embodiment.  FIG. 6  shows an enlarged view of a small region A of the display surface  1 . The small region A is, for example, a square with a side of several pitches of LEDs of the backlight device  30 . As described above, in the present embodiment, the conversion amount in the fluorescent film  22  of light emitted from the LED  33  in a direction oblique to the incident surface  221  of the fluorescent film  22  can be reduced, and therefore, the amount of red and/or green components of light emitted from a region of the light-emitting surface  222  of the fluorescent film  22  that surrounds the region located directly in front of the LED  33  reduced, so that the degree of balance between the components of the light can be made closer the degree of balance between the components of light emitted from the region located directly in front of the LED  33 . As a result, variations in chromaticity in the small region A can be reduced, resulting in a region  4  having substantially uniform chromaticity. Thus, the occurrence of color nonuniformity can be prevented or reduced. 
       FIG. 7  is a schematic diagram showing a second example of a configuration of the optical member  20  in the present embodiment. The configuration of  FIG. 7  is different from that of  FIG. 2  in that the prism film  23  is disposed such that the ridges are located closer to the diffusion plate  24 . In other words, compared to the case shown in  FIG. 2 , the prism film  23  is turned upside down, i.e., with the front surface at the bottom, and the rear surface at the top. The prism film  23  as the second example of the optical path changing member in which the ridges are located closer to the diffusion plate  24  as shown in  FIG. 7  is referred to as an “inverted prism.” 
       FIG. 7  also schematically shows an example of changing of an optical path by the prism film  23  in the present embodiment. Although light emitted from the LED  33  is diffused,  FIG. 7  illustrates light P 3  emitted from the LED  33  in a direction perpendicular to the incident surface  221  of the fluorescent film  22 , and light P 4  emitted from the LED  33  in a direction oblique to the incident surface  221  of the fluorescent film  22 , for the sake of convenience and for ease of understanding of a change in optical path. 
     As shown in  FIG. 7 , the blue light P 4  from the LED  33  obliquely strikes the incident surface  221  of the fluorescent film  22 . The optical path length within the fluorescent film  22  of the light P 4  entering the fluorescent film  22  from the incident surface  221  is represented by d 4 . 
     In contrast, the optical path of the blue light P 3  from the LED  33  is changed by the prism film  23  before the light P 3  arrives at the incident surface  221  of the fluorescent film  22 , and then obliquely strikes the incident surface  221  of the fluorescent film  22 . The optical path length within the fluorescent film  22  of the blue light P 3  from the LED  33  that would otherwise perpendicularly strike the incident surface  221  of the fluorescent film  22  without changing the optical path is represented by d 3 . The optical path length d 3  is equal to the thickness of the fluorescent film  22 . When the light P 3  enters the fluorescent film  22  from the incident surface  221  of the fluorescent film  22  after the optical path thereof is changed by the prism film  23 , the optical path length within the fluorescent film  22  is greater than d 3  and is closer to the optical path length of the blue light P 4  (in  FIG. 7 , the optical path length of the light P 3  is represented by reference sign d 4 ). 
     As described above, the prism film  23  changes the optical paths of light rays emitted from the LED  33  in a direction perpendicular to the incident surface  221  of the fluorescent film  22  so as to increase the optical path lengths of the light rays within the fluorescent film  22 . Specifically, the prism film  23  changes the optical paths of light rays traveling from the LED  33  in a direction perpendicular to the incident surface  221  of the fluorescent film  22  (the light P 3  of  FIG. 7 ) before the light rays enter the fluorescent film  22 , so as to increase the optical path lengths within the fluorescent film  22  of the light rays entering the incident surface  221  of the fluorescent film  22 . Thus, the optical path lengths within the fluorescent film  22  of light rays traveling in a direction perpendicular to the incident surface  221  can be changed to be closer to the optical path lengths within the fluorescent film  22  of light rays emitted from the LED  33  in a direction oblique to the incident surface  221  (the light P 4  of  FIG. 7 ). 
     As a result, the amount of light rays perpendicularly entering the incident surface  221  and then traveling within the fluorescent film  22  is reduced, and therefore, the amount of a blue component of light emitted from a region of the light-emitting surface  222  of the fluorescent film  22  located directly in front of the LED  33  can be reduced. 
     In addition, the optical paths of light rays traveling in a direction perpendicular to the incident surface  221  are changed so as to increase the optical path lengths within the fluorescent film  22  of the light rays entering from the incident surface  221 , and therefore, the conversion amount of the light within the fluorescent film  22  is increased. As a result, the amounts of a red component and/or a green component of light emitted from a region of the light-emitting surface  222  of the fluorescent film  22  surrounding the region located directly in front of the LED  33  can be increased, and therefore, color nonuniformity can be prevented or reduced on the light-emitting surface of the fluorescent film  22 . 
     In the above embodiment, the prism film as a first example of the optical path changing member, and the prism film (inverted prism) that is turned upside down, i.e., with the front surface at the bottom, and the rear surface at the top, as a second example of the optical path changing member, have been described. The optical path changing member is not limited to these examples. Other examples of the optical path changing member will now be described. 
       FIG. 8  is a schematic diagram showing a third example of a configuration of the optical path changing member in the present embodiment. In the example of  FIG. 8 , an optical path changing member includes two prism films  23  and  25 . Specifically, as shown in  FIG. 8 , the prism film  23  and the prism film  25  are disposed so that the ridges of the prism film  23  and the ridges of the prism film  25  intersect at right angles. The two prism films  23  and  25  exhibit the desired effect due to the presence of an air layer therebetween. Specifically, as shown in  FIG. 8 , a distance a between the apex of the ridge of the prism film  23  and the rear surface of the prism film  25  is not zero. The two prism films  23  and  25  are also referred to a “double prism film.” 
       FIG. 9  is a schematic diagram showing a fourth example of a configuration of the optical path changing member in the present embodiment. In the example of  FIG. 9 , two prism films  23  and  25  are integrally formed. Specifically, as shown in  FIG. 9 , the ridges of the rear prism film  23  are continuous to the front prism film  25  with the apexes of ridges crushed. The two prism films integrally formed are also referred to as a “composite film 1 (prism-on-prism)”. Only one of the prism film  23  and the prism film  25  is referred to as a “prism film.” 
       FIG. 10  is a schematic diagram showing a fifth example of a configuration of the optical path changing member in the present embodiment. A microlens film  26  shown in  FIG. 10  includes microlenses  261  arranged in a grid pattern on a surface of a substrate. 
       FIG. 11  is a schematic diagram showing a sixth example of a configuration of the optical path changing member in the present embodiment. The optical path changing member of  FIG. 11  is referred to as a “composite film 2 (microlens-on-prism)”. As with the above composite film 1 (prism-on-prism), the composite film 2 (microlens-on-prism) includes a prism film  23  and a microlens film  26  that are integrally formed without an interstice therebetween. In the composite film 2, the ridges of the rear prism film  23  are continuous to the front microlens prism film  25  with the apexes of ridges crushed. 
       FIG. 12  is an explanatory diagram showing an example of evaluation data of color nonuniformity in the case of the optical path changing member in the present embodiment.  FIG. 12  shows color nonuniformity that occurred when the two prism films, the composite film 1 (prism-on-prism), the composite film 2 (microlens-on-prism), the inverted prism, the prism film, and the microlens film were used as the optical path changing member, and the two prism films, the composite film 1 (prism-on-prism), the composite film 2 (microlens-on-prism), the prism film, and the microlens film were used as the light condensing member (a member provided on a surface closer of the fluorescent film  22  to the liquid crystal panel  10 , using a scale of one to eight. A smaller numerical value of the rating indicates a greater amelioration of color nonuniformity. Note that  FIG. 12  also shows ratings of conventional configurations including a diffusion sheet. Note that color nonuniformity can be evaluated by detecting light emitted out from the light condensing member. 
     As shown in  FIG. 12 , for example, in the case where the two prism films were used as the optical path changing member, the rating was one irrespective of the type of the light condensing member. In the case where the prism film was used as the optical path changing member, the ratings were 5 and 6. Note that in the case where no optical path changing member was used as a conventional example, the rating was eight irrespective of the type of the light condensing member. As can be seen from  FIG. 12 , color nonuniformity is ameliorated in the case where the two prism films, the composite film 1 (prism-on-prism), the composite film 2 (microlens-on-prism), the inverted prism, the prism film, the microlens film, and the diffusion sheet were used as the optical path changing member, compared to the conventional cases. Note that it may be determined, as appropriate, which of the prism films, the composite film 1 (prism-on-prism), the composite film 2 (microlens-on-prism), the inverted prism, the prism film, the microlens film, and the diffusion sheet should be used as the optical path changing member, depending on the size or type of the liquid crystal panel  10 , the pitch of the LEDs  33  of the backlight unit  30 , the distance between the LEDs  33  and the optical member  20 , the desired display quality level, etc. Note, that, as shown in  FIG. 12 , color nonuniformity can be further ameliorated using the inverted prism instead of the prism film. It is not easily foreseeable that a more excellent effect can be obtained on the basis of such a difference in configuration. 
       FIG. 13  is an explanatory diagram showing evaluation data of luminance in the case of the optical path changing member in the present embodiment. The same optical path changing members and light condensing members as those of  FIG. 12  were used. The levels of the luminance were evaluated using a scale of one to four. A greater numerical value of the rating indicates a higher luminance. 
     As shown in  FIG. 13 , for example, in the case where the two prism films were used as the light condensing member, and the composite film 2 (microlens-on-prism), the inverted prism, the prism film, the microlens film, and the diffusion sheet were used as the optical path changing member, the ratings were four, which indicates the highest luminance. In the case where the composite film 1 (prism-on-prism) was used as the light condensing member, and the microlens film was used as the optical path changing member, the rating was also four, which indicates the highest luminance. As can be seen from  FIG. 13 , the luminance tends to increase in the case where the two prism films are selected as the light condensing member, compared to the microlens film, or in the case where the two prism films are selected as the optical path changing member, compared to the microlens film. In other words, the luminance tends to increase as one proceeds leftward in the diagram, and as one proceeds downward in the diagram. It may be determined, as appropriate, which of the members should be used as the light condensing member or the optical path changing member, depending on the predetermined luminance. 
       FIG. 14  is an explanatory diagram showing an example of evaluation data of chromaticity (y-coordinate) in the case of the optical path changing member in the present embodiment. The same optical path changing members and light condensing members as those of  FIGS. 12 and 13  were used. The level of the chromaticity y is evaluated using a scale of one to five. A greater numerical value of the rating indicates a greater chromaticity y. Specifically, the chromaticity y becomes closer to yellow as the numerical value of the rating increases, and closer to blue as the numerical value of the rating decreases. As shown in  FIG. 14 , the chromaticity y tends to be substantially independent of the type of the optical path changing member. The chromaticity y also tends to increase and be closer to yellow in the case where the two prism films are used as the light condensing member (i.e., a light condensing member closer to the left end in  FIG. 14 ), compared to the microlens film. It may be determined, as appropriate, which of the members should be used as the light condensing member, depending on the predetermined chromaticity y. The rating of the chromaticity y tends to be independent of which of the members is used as the optical path changing member. 
     In the present embodiment, the case where the so-called direct-lit backlight is used has been described. Alternatively, in the present embodiment, an edge-lit backlight can be used. 
     In the display apparatus of the present embodiment, light from the light source unit is transmitted through the fluorescent film before reaching the display panel, and an optical path changing member that changes the optical path length within the fluorescent film of light entering the fluorescent film from the incident surface is provided between the light source unit and the fluorescent film. 
     The optical paths of light rays from the light source unit are changed by the optical path changing member before the light rays arrives at the incident surface of the fluorescent film. As a result, the angles of incidence to the incident surface of the fluorescent film are changed, so that the optical path lengths within the fluorescent film of the light rays entering from the incident surface are changed. 
     By providing the optical path changing member, the optical path lengths within the fluorescent film can be changed. For example, the optical paths of light rays entering the fluorescent film from the incident surface can be changed, so that the optical path lengths within the fluorescent film can be changed, and therefore, the conversion amount of light (e.g., the amount of a portion of blue light emitted from the light source unit that is converted into red and/or green light) can be changed. As a result, color nonuniformity on the light-emitting surface of the fluorescent film can be prevented or reduced. 
     In the display apparatus of the present embodiment, the optical path changing member changes the optical paths of light rays traveling toward the incident surface at different angles with respect to the incident surface such that the differences in optical path lengths within the fluorescent film among the light rays traveling after entering the fluorescent film are reduced. 
     The optical path changing member changes the optical paths of light rays from the light source unit that travels toward the incident surface of the fluorescent film at different angles with respect to the incident surface, before the light rays enter the fluorescent film, and thereby changes the angles of incidence of the light rays to the incident surface of the fluorescent film, such that the differences in optical path lengths within the fluorescent film among the light rays entering the fluorescent film are reduced. 
     The optical path changing member can reduce the differences in optical path lengths within the fluorescent film among light rays traveling toward the incident surface of the fluorescent film at different angles with respect to the incident surface, and thereby reduce the differences in conversion amounts within the fluorescent film among the light rays. As a result, color nonuniformity on the light-emitting surface of the fluorescent film can be prevented or reduced. 
     In the display apparatus of the present embodiment, the light source unit includes a substrate disposed to face the fluorescent film, and a plurality of LEDs (light sources) disposed on the substrate. A diffusion member that diffuses light rays from the light source unit is provided between the substrate and the fluorescent film. The optical path changing member is disposed between the fluorescent film and the diffusion member. 
     Light rays from the LEDs disposed on the substrate is transmitted through the diffusion member, and thereafter, the optical paths of light rays are changed by the optical path changing member. The changes in optical paths by the optical path changing member results in changes in the angles of incidence to the incident surface of the fluorescent film, so that the optical path lengths within the fluorescent film of the light rays entering the fluorescent film can be changed. 
     In the display apparatus of the present embodiment, the optical path changing member changes the optical paths so as to reduce the differences in optical path lengths within the fluorescent film among light rays emitted from the LED in a direction oblique to the incident surface and light rays emitted from the LED in a direction perpendicular to the incident surface. 
     For example, the optical path changing member changes the optical paths of light rays from the light source unit before the light rays arrive at the incident surface of the fluorescent film, so as to reduce the differences in angles of incidence to the incident surface of the fluorescent film among the light rays from the LEDs on the substrate. As a result, the differences in optical path lengths within the fluorescent film among light rays entering the fluorescent film can be reduced, resulting in a reduction in the differences in conversion amounts of light. Therefore, color nonuniformity on the light-emitting surface of the fluorescent film can be prevented or reduced. 
     In the display apparatus of the present embodiment, the optical path changing member changes the optical paths of light rays emitted from the LED in a direction oblique to the incident surface so as to reduce the optical path lengths of the light rays within the fluorescent film. 
     The optical path changing member changes the optical paths of light rays emitted from the LED in a direction oblique to the incident surface of the fluorescent film before the light ray enter the fluorescent film, so as to reduce the optical path lengths of the light rays within the fluorescent film. Specifically, the optical path lengths within the fluorescent film of light rays emitted from the LED in a direction oblique to the incident surface are changed to be closer to the optical path lengths within the fluorescent film of light rays emitted from the LED in a direction perpendicular to the incident surface. As a result, the conversion amounts within the fluorescent film of light rays emitted from the LED in a direction oblique to the incident surface can be reduced. As a result, the amounts of a red component and/or a green component of light rays emitted from a region surrounding a region of the light-emitting surface of the fluorescent film located directly in front of the LED can be reduced, and therefore, the components of light rays emitted from the surrounding region can be changed to be closer to the components of light rays emitted from the region located directly in front of the LED. Therefore, color nonuniformity can be prevented or reduced on the light-emitting surface of the fluorescent film. 
     In the display apparatus of the present embodiment, the optical path changing member changes the optical paths of light rays emitted from the LED in a direction perpendicular to the incident surface so as to increase the optical path lengths of the light rays within the fluorescent film. 
     The optical path changing member changes the optical paths of light rays emitted from the LED in a direction perpendicular to the incident surface of the fluorescent film before the light rays enter the fluorescent film so as to increase the optical path lengths of the light within the fluorescent film. Specifically, the optical path lengths within the fluorescent film of light rays emitted from the LED in a direction perpendicular to the incident surface are changed to be closer to the optical path lengths within the fluorescent film of light rays emitted from the LED in a direction oblique to the incident surface. As a result, the amount of light rays that perpendicularly strikes the incident surface and then travels within the fluorescent film is reduced, and therefore, the amount of a blue component of light emitted from a region of the light-emitting surface of the fluorescent film located directly in front of the LED can be reduced. 
     In addition, the optical paths of light rays traveling in a direction perpendicular to the incident surface are changed so as to increase the optical path lengths within the fluorescent film of the light rays entering from the incident surface, and therefore, the conversion amount of the light within the fluorescent film is increased. As a result, the amounts of a red component and/or a green component of light emitted from a region surrounding a region of the light-emitting surface of the fluorescent film located directly in front of the LED can be increased. Therefore, color nonuniformity can be prevented or reduced on the light-emitting surface of the fluorescent film. 
     REFERENCE SIGNS LIST 
       10  liquid crystal panel (display panel)
 
 11 ,  14  polarizing plate
 
 12  front substrate
 
 13  rear substrate
 
 20  optical member
 
 30  backlight unit (light source unit)
 
 31  chassis
 
 32  substrate
 
       33  LED 
       21  light condensing member
 
 22  fluorescent film
 
 23 ,  25  prism film (optical path changing member)
 
 24  diffusion plate
 
 26  microlens film (optical path changing member)
 
 100  display apparatus