JP5779930B2 - Optical sheet, backlight unit using the same, and image display device - Google Patents

Description

  The present invention relates to an optical sheet, a light source unit, and an image display device used for illumination optical path control. In particular, the present invention relates to an optical sheet, a backlight unit, and an image display device used for illumination light path control in an image display device typified by a flat panel display.

  In recent years, liquid crystal display devices using TFT (Thin Film Transistor) type liquid crystal panels and STN (Super Twisted Nematic) type liquid crystal panels are mainly commercialized mainly for color notebook PCs (personal computers) in the OA field. Such a liquid crystal display device employs a so-called backlight method in which a light source is arranged on the back side of the liquid crystal panel (the side opposite to the observer) and the liquid crystal panel is illuminated with light from the light source. Yes. The backlight unit employed in this type of backlight system is roughly divided into a light source lamp such as a cold cathode fluorescent tube (CCFT) and a flat plate made of acrylic resin having excellent light transmittance. “Light guide plate light guide method” (so-called edge light method) that makes multiple reflections in the light plate, and “direct type method” that directly illuminates with light from a light source lamp such as a cold cathode tube (CCFT) without using a light guide plate There are two types of methods.

  As a liquid crystal display device on which a light guide plate light guide type backlight unit is mounted, for example, the one shown in FIG. 16 is generally known. In this type of liquid crystal display device, a liquid crystal panel 172 having both front and back surfaces sandwiched between polarizing plates 171 and 173 is disposed at an upper portion, and a PMMA (substantially rectangular plate shape) is formed on the lower surface side of the liquid crystal panel 172. A light guide plate 179 made of a transparent base material such as polymethyl methacrylate or acrylic is disposed, and a diffusion film (diffusion layer) 178 is provided on the upper surface (light emission side) of the light guide plate 179. Further, a scattering reflection pattern portion (not shown) for scattering and reflecting the light introduced into the light guide plate 179 toward the liquid crystal panel 172 efficiently and uniformly is printed on the lower surface of the light guide plate 179. And a reflection film (reflection layer) 177 is provided below the scattering reflection pattern portion.

Further, the light guide plate 179 is provided with a light source lamp 176 at the side end thereof, and further covers the back side of the light source lamp 176 so that the light of the light source lamp 176 is efficiently incident on the light guide plate 179. Thus, the lamp reflector 181 having a high reflectance is provided. The scattering reflection pattern portion is formed by printing, drying, and forming a mixture of white titanium dioxide (TiO ₂ ) powder in a solution such as a transparent adhesive in a predetermined pattern, for example, a dot pattern. A directivity is imparted to the light incident on the light plate 179, and the light is guided to the light exit surface side. This is a device for increasing the luminance.

  However, in these liquid crystal display devices, there is a problem that control of the viewing angle is entrusted only to the diffusion characteristics of the diffusion films 178 and 182 and the control is difficult. For example, when viewed from the front, the display screen of the liquid crystal display is bright, but when viewed from the lateral, the display screen may be dark. There is also a problem that the center of the liquid crystal display is bright and the periphery is dark. Thus, there was a problem that the light utilization efficiency was poor.

The direct type backlight is used in an image display device such as a large liquid crystal TV in which it is difficult to use a light guide plate. A liquid crystal display device shown in FIG. 17 is generally known as a direct backlight type image display device. In this liquid crystal display device, a liquid crystal panel 172 having both front and back surfaces sandwiched between polarizing plates 171 and 173 is disposed at an upper portion, and a light source 151 composed of a fluorescent tube or the like is disposed on the lower surface side of the liquid crystal panel 172. Further, an optical sheet such as a diffusion film 182 is provided on the upper surface side of the light source 151. In addition, on the back surface of the light source 151, a reflector 152 that reflects light traveling from the light source 151 in a direction opposite to the liquid crystal panel 172 to the liquid crystal panel 172 side is disposed. Therefore, the light emitted from the light source 151 is diffused by the diffusion film 182, and the diffused light is condensed on the effective display area of the liquid crystal panel 172 with high efficiency.

  However, the liquid crystal display device shown in FIG. 17 has a problem in that it is difficult to control the viewing angle because only the diffusibility of the diffusion films 173 and 182 is controlled. For example, when the liquid crystal display screen is viewed from the front direction, the display screen is bright, but when the liquid crystal display screen is viewed from the horizontal direction, the display screen may be dark. There is also a problem that the center of the liquid crystal display screen is bright and the periphery is dark. Thus, there was a problem that the light utilization efficiency was poor.

  Therefore, as one method for solving the above-described problem, as shown in FIG. 18, a brightness enhancement film (BEF) 185, which is a registered trademark of 3M USA, is positioned above the illumination light source 190 for the backlight. Further, a method of arranging a light diffusion film (not shown) on the light emitting surface side above the BEF 185 is employed. As shown in FIGS. 18 and 19, the BEF 185 is a film in which unit prisms 187 having a triangular cross section are arranged at a constant pitch in one direction on the light emitting surface which is the upper surface of the transparent substrate 186. The unit prism 187 has a size (pitch) larger than the wavelength of light. BEF collects light from “off-axis” and directs this light “on-axis” to the viewer, either “redirect” or “recycle”. To do.

  The brightness enhancement film 185 increases the on-axis brightness by reducing the off-axis brightness when using the image display apparatus (when observing), and improves the display quality of the image display apparatus. Here, “on-axis” is a direction that coincides with the visual direction of the viewer, and is generally a normal direction to the display screen. In addition, the brightness enhancement film 185 normally has a repetitive array structure of unit prisms arranged in only one direction, and can only change direction or be recycled in the arrangement direction. Therefore, in order to control the luminance of the display light in both the horizontal direction and the vertical direction, it is necessary to use two BEF sheets in combination so that the arrangement directions of the unit prism groups are substantially orthogonal to each other. .

  Therefore, recently, in order to increase the light utilization efficiency and increase the brightness, as shown in FIG. 20, a prism film (prism) having a light condensing function between the diffusion film 178 and the liquid crystal panel 172 is used. Layer) 174, 175 has been proposed. The prism films 174 and 175 are emitted from the light exit surface of the light guide plate 179 and concentrate the light diffused by the diffusion film 178 on the effective display area of the liquid crystal panel 172 with high efficiency. By adopting such BEF, the display designer can achieve a desired on-axis brightness while reducing power consumption. A technique in which a luminance control member having a repetitive array structure of prisms represented by BEF is adopted in a display device has been conventionally known in Patent Documents 1 to 3 and the like.

Japanese Patent Publication No. 1-378001 JP-A-6-102506 Japanese National Patent Publication No. 10-506500

  In recent years, it is advantageous in terms of miniaturization, weight reduction, and power saving design, it does not contain mercury, and no high voltage circuit is required, so the safety design load and harmonic current / high frequency noise generation have been reduced. In order to have various merits such as excellent resistance to vibration and shock, low temperature startability and wide dimming range, a backlight unit using LED as a light source is used. Liquid crystal displays that have been used are becoming mainstream.

  With this trend, liquid crystal displays have become thinner and lighter. Realization of light weight enables installation at a high place, and through an image display device such as a digital signage or the like in a transportation system such as a train car as shown in FIG. At the same time, people are looking up at images and information from various positions and angles.

  However, when the image display device 4 that is installed so as to view an image with a normal eye level as shown in FIG. 14 is installed at a high place, the vertical cross-sectional shape of the optical sheet that determines the viewing angle is Since it is almost vertically symmetrical, the vertical field of view is uniform. Therefore, the image light L1 to the observer side visual field and the image light L2 to the non-observer side visual field necessary for the observer spread. However, since the image light L2 for the non-observer is not necessary, there is a problem that the amount of light is lost.

  Accordingly, since the viewing angle on the viewer side is insufficient, it is necessary to search for a position where the viewer himself can easily see. In addition, when considering the observer, it is necessary to install the image display device by tilting the front of the image display device toward the observer, and thus there is a problem that the degree of freedom in selection is low in terms of installation space and design.

  In addition, there is a similar problem when an image display device is installed in a low place so that an image from a high place can be viewed.

  Furthermore, in the liquid crystal display, the VA (Virtual Alignment) method has become mainstream because the front contrast ratio is higher than that of the IPS (In-Plane-Switching) method, but the viewing angle is wide, so the height is high and low. When an image display device is installed, the loss of image light has further increased.

  An object of the present invention is an optical sheet used for illumination light path control of an image display device in which an image display device is installed at a high or low position with respect to the line of sight of an observer, When the front of the optical sheet is used as a reference, the image light emitted to the unnecessary observer's non-observer side is limited, and the limited amount of light is distributed to the observer's side, thereby observing the viewer's field of view. An optical sheet capable of improving corners, a backlight unit including the optical sheet, and a display device are provided.

The present invention solves the above-mentioned problems, and the invention according to claim 1 of the present invention is installed above the height of the eyes of the observer in the transportation system, and the light beam on the ground direction side with respect to the ceiling direction side. An optical sheet used for illumination light path control of an image display device that emits a large amount of light , having a cross-sectional asymmetric lens composed of a large number of asymmetric unit lenses on one surface of a substrate, and the ceiling direction side of the asymmetric unit lens Of the asymmetric unit lens in contact with the substrate, the angle a of the asymmetric unit lens at the end on the ground direction side is 90 degrees with respect to the light exit surface. And the inclination angle b of the curved tangent at the end on the ceiling direction side is not less than 35 degrees and not more than 50 degrees with respect to the light exit surface, and is asymmetric from the end on the ceiling direction side. To the top of the unit lens Te is an optical sheet continuously in the range of 10 degrees or more the inclination angle b tangent slope angle b'of the face song shape characterized in that decreasing.

According to a second aspect of the present invention, there is provided a backlight unit for an image display device comprising the optical sheet according to the first aspect .

According to a third aspect of the present invention, there is provided an image display element that defines a display image in accordance with transmission / shielding in pixel units, and an image display device according to claim 2 on the back surface of the image display element. An image display device comprising a backlight unit for use .

  According to the present invention, in a display device installed so that the display device is different from the height of the line of sight, an optical sheet capable of suppressing a loss of light amount to an unnecessary viewing angle and improving a visual field, the optical sheet A backlight unit and a display device can be provided.

It is sectional drawing which shows Embodiment 1 of the optical sheet concerning this invention. It is sectional drawing of the unit lens of the optical sheet concerning this invention. It is sectional drawing which shows Embodiment 2 of the optical sheet concerning this invention. It is sectional drawing of the unit lens which shows Embodiment 2 of the optical sheet concerning this invention. It is sectional drawing which shows the direction of the light in the vertical visual field of the optical sheet concerning this invention. It is a schematic sectional drawing which shows Embodiment 1 of the optical sheet concerning this invention, and Embodiment of an image display apparatus which comprises a backlight unit using the same. It is a schematic sectional drawing which shows Embodiment 2 of the optical sheet concerning this invention, and Embodiment of an image display apparatus which comprises a backlight unit using the same. It is a figure which shows the simulation result in embodiment of this invention. It is a figure which shows the simulation result in embodiment of this invention. It is a figure which shows the simulation result in embodiment of this invention. It is a figure which shows the simulation result in another embodiment of this invention. It is a figure which shows the cross-sectional shape of the aspherical lens of this invention. It is a figure which shows the simulation result in another embodiment of this invention. It is a schematic sectional drawing which shows an example of the image display apparatus installation in the conventional high place. It is a schematic sectional drawing which shows an example of image display apparatus installation in the high place in this invention. It is a schematic sectional drawing which shows an example of the conventional image display apparatus. It is a schematic sectional drawing which shows the other example of the conventional image display apparatus. It is a schematic sectional drawing which shows an example of the conventional backlight unit. It is a perspective view which shows an example of the conventional BEF. It is a schematic sectional drawing which shows the other example of the conventional image display apparatus.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of an optical sheet according to the present invention, a backlight unit using the optical sheet, and a liquid crystal image display device including the backlight unit will be described in detail with reference to the drawings. In addition, the scale or ratio of each part shown to a figure does not correspond with actual. Moreover, it is not limited to this.

(Embodiment 1 of optical sheet)
FIG. 1 is a cross-sectional view of an optical sheet A1 according to Embodiment 1 of the present invention.

  It is preferable that the optical sheet A1 has a structure in which a plurality of unit lenses 41 are arranged on a plane that forms a light emission surface, and extends in the horizontal visual field direction of the observer. Further, the cross-sectional shape of the unit lens 41 is preferably an asymmetric prism shape. By making the shape asymmetrical, the amount of light emitted in an unnecessary direction can be suppressed and the amount of light emitted in a more necessary direction can be increased. it can.

  As a manufacturing method of the unit lens 41, an extrusion method, a UV exposure forming method, and an injection molding method can be used. In terms of cost, the extrusion method is preferable. The main material is not particularly limited as long as the light transmittance is 88% or more. For example, polyethylene terephthalate (PET), polycarbonate, acrylic, acrylic-styrene copolymer, polystyrene, styrene / butadiene / Acrylonitrile copolymer, amorphous polyarylate, polyethersulfone, bulky cyclic olefin polymer and the like can be used.

  FIG. 2 is an enlarged view of a cross section of the unit lens 41 of the first embodiment. The cross-sectional shape of the unit lens 41 is preferably a right-angled triangular asymmetric prism shape in which the angle “a” at the end on the viewer side is 90 ° with respect to the light exit surface.

  The image display device 1 shown in FIG. 6 has a configuration in which the optical sheet A1 and the illumination unit 2 of the first embodiment and the liquid crystal display panel 3 are disposed. The liquid crystal display panel 3 is a typical element that transmits and blocks light in pixel units and displays an image, and can improve image quality as compared with other display elements.

  The illumination unit 2 is an edge light type illumination device, and is disposed facing the light incident side of the liquid crystal display panel 3. A light source 176, a light guide plate 179, a concealing lens sheet 10, and a light collecting function are arranged along the light optical path. It is comprised including the said optical sheet A1 which has. Examples of the light source 176 include a linear light source and a point light source. Examples of the linear light source include fluorescent tubes such as CCFL, HCFL, and EEFL. Moreover, as point light source, LED, such as white LED and RGB-LED, is mentioned. The light source 176 is not limited to being disposed on one end surface of the light guide plate 179, but may be employed when disposed on two opposing end surfaces or when disposed on four end surfaces. At this time, the light guide plate 179 may have a flat plate shape as shown in FIG. 6 or a wedge shape.

FIG. 5 shows the direction of light in the vertical visual field of the optical sheet A1 of the first embodiment. Therefore, in the image display device 1 shown in FIG. 6, when the observer's line of sight is at a low position with respect to the image display device 1, the light amount loss to an unnecessary viewing angle on the non-observer side is suppressed, In order to improve the visual field on the observer side, the light quantity L1 in the vertical visual field direction on the observer side and the light quantity L2 in the vertical visual field direction on the non-observer side when the horizontal axis is used as a reference, It is preferable to satisfy.
L1 / L2> 1.0 (1)

  FIG. 8 is a graph showing the result of simulating the viewing angle characteristics of the image display device 1 according to Embodiment 1 of the present invention shown in FIG. Here, when the angle a of the end portion on the observer side of the unit lens of the optical sheet is set to the angle b of the end portion on the non-observer side, the horizontal axis represents the angle b of the end portion on the non-observer side, and the vertical axis. The axis indicates L1 / L2. It can be seen from FIG. 8 that the amount of light toward the viewer can be more effectively increased by setting the angle a at the end on the viewer side to 90 °.

  FIG. 9 is a result of simulating the observer's vertical viewing angle characteristics of the image display apparatus 1 when the angle a at the end on the viewer side is 90 ° according to the first embodiment of the present invention shown in FIG. It is a graph which shows. The vertical axis of the graph represents the luminance ratio when the luminance of the front is 0 °, and the horizontal axis represents the vertical viewing angle (°). Further, the minus notation of the vertical viewing angle (°) indicates the field of view to the observer side. Furthermore, the most commonly used end angle a = b = 45 ° was added to the simulation as a comparison. The light source used for the simulation is uniform diffused light (Lambert light).

  FIG. 10 is a diagram showing luminance-viewing angle distribution. In FIG. 10, (I) is a = 90 °, b = 6 °, (II) is a = 90 °, b = 19 °, (III) is a = 90 °, b = 35 °, (IV) is a = 45 °, b = 45 °, the darker the color in the figure, the more light is emitted.

  The optical sheet A1 composed of unit lenses of a = b = 45 ° emits the same amount of light to the non-observer side from the observer side as shown in FIGS. 9 and 10 (IV), and the vertical viewing angle ± It can be seen that there is a light amount loss because leakage light called sidelobe light is generated in the vicinity of 70 °. Further, when b <15 °, the effect of suppressing the emitted light toward the non-observer is weak, and when b> 30 °, L1 / L2 toward the non-observer is large as can be seen from the graph of FIG. Nevertheless, the light cannot be effectively controlled due to the large amount of leakage light. However, in the case of 15 ° ≦ b ≦ 30 ° of the solid line of the graph, the amount of light emitted to the viewer can be increased while suppressing sidelobe light, and the light is effectively controlled. Further, it can be seen that the viewing angle in the horizontal direction is also enlarged. Therefore, it is preferable that the angle b of the end portion on the non-observer side of the optical sheet A1 according to the present invention has a prism shape satisfying 15 ° ≦ b ≦ 30 °.

(Embodiment 2 of optical sheet)
FIG. 3 is a cross-sectional view of the optical sheet A2 according to Embodiment 2 of the present invention.

  FIG. 4 is a cross-sectional view of the unit lens 42 of the optical sheet A2 according to the second embodiment. The cross-sectional shape of the unit lens 42 is such that the angle “a” at the end on the viewer side is 90 ° with respect to the light exit surface, and the non-viewer side has a curved surface shape. The inclination angle is 35 ° to 50 °, and the inclination angle of the tangent line continuously decreases from the end toward the observer side up to 10 °. FIG. 12 shows the cross-sectional shape of the aspherical lens, and the slope df (x) / x when the hypotenuse curve at the end on the non-observer side is f (x).

  FIG. 7 is a schematic cross-sectional view showing an embodiment of an image display apparatus including an optical sheet A2 according to Embodiment 2 of the present invention and a backlight unit using the same.

  FIG. 11 is a graph showing the result of simulating the viewing angle characteristics of the image display device shown in FIG. The light source used for the simulation is uniform diffused light (Lambert light). From the result of the solid line in the graph, the inclination angle b of the tangent to the end portion of the surface curved shape on the non-observer side is in the range of 35 ° to 50 °, up to 10 ° from the end portion toward the viewer side. If the shape is such that the tangential inclination angle continuously decreases, an optical sheet that satisfies the formula (1) and controls the emitted light to the viewer side while suppressing light leakage to the non-viewer side is realized. can do.

  FIG. 15 is a diagram when the optical sheet according to the present invention and an image display device using the same are used in a transportation system such as a train car. As a result, the loss due to the light amount L2 to the non-observer side is suppressed, and not only the image can be observed from various angles even when looking up from below, but also the degree of freedom of the installation location of the image display device is increased. Can do.

  The image display device 1 and the illumination unit 2 according to the embodiment of the present invention have been described above. However, the illumination unit 2 according to the present embodiment is not applied only to a display device such as the image display device 1. For example, it goes without saying that the illumination unit 2 having a function of efficiently condensing light emitted from the light source 176 can be used for, for example, an illumination device. Next, examples based on the present embodiment will be described in detail, but the present invention is not limited to the following examples.

  Hereinafter, the present invention will be described specifically by way of examples.

Example 1
An optical sheet A1 having an asymmetric prism shape in the following cross section was produced by an extrusion method using a polycarbonate resin (trade name “Panlite L-1225ZL” manufactured by Teijin Chemicals Ltd.).
Angle a = 90 ° at the end on the viewer side
Non-observer side angle b = 15 °

(Example 2)
An optical sheet A1 was obtained in the same manner as in Example 1 except that the angle b = 30 ° at the end on the non-observer side.

(Example 3)
An optical sheet A2 having the following asymmetric aspherical lens shape was produced by extrusion using a polycarbonate resin (trade name “Panlite L-1225ZL” manufactured by Teijin Chemicals Ltd.).
Angle a = 90 ° at the end on the viewer side
Inclination angle b = 35 ° of the tangent to the end of the curved surface on the non-observer side
A shape in which the continuous inclination angle of the tangent of the curved surface is reduced to a maximum of 10 °

Example 4
An optical sheet A2 was produced in the same manner as in Example 3 except that the inclination angle b = 50 ° of the tangent at the end of the curved surface on the non-observer side.

(Comparative Example 1)
An optical sheet A1 was produced in the same manner as in Example 1 except for the following conditions.
Angle a = 55 ° at the end on the viewer side
Non-observer side angle b = 25 °

(Comparative Example 2)
An optical sheet A1 was produced in the same manner as in Example 1 except for the following conditions.
Angle a = 75 ° at the end on the viewer side
Non-observer side angle b = 20 °

(Comparative Example 3)
An optical sheet A1 was produced in the same manner as in Example 1 except that the angle b = 10 ° at the end on the non-observer side.

(Comparative Example 4)
An optical sheet A1 was produced in the same manner as in Example 1 except that the angle b = 35 ° at the end on the non-observer side.

(Comparative Example 5)
An optical sheet A2 was produced in the same manner as in Example 3 except for a shape in which the continuous inclination angle of the tangent to the curved surface decreased to a maximum of 20 °.

(Comparative Example 6)
An optical sheet A2 was produced in the same manner as in Example 3 except for the following conditions.
Inclination angle b = 50 ° of the tangent to the end of the curved surface on the non-observer side
A shape in which the continuous inclination angle of the tangent of the curved surface decreases to a maximum of 20 °

<Evaluation items and evaluation methods>
The following items were evaluated using the optical sheets prepared in Examples 1 to 4 and Comparative Examples 1 to 6.

  As shown in FIGS. 6 and 7, the light guide plate 179 has a white LED as the light source 176 on the end side, and the concealing lens sheet 10, the optical sheet A1 or A2, the diffusion sheet (see FIG. Using the image display device 1 composed of the light unit 2 and the liquid crystal panel 3 that are sequentially arranged, the vertical viewing direction was visually observed with reference to the front of the display device to evaluate the viewing angle. At this time, the lower side of the screen was set as the observer side. Further, using an EZContrast viewing angle characteristic measurement and evaluation device manufactured by ELDIM, a viewing angle-luminance was measured using a white display on the screen. In addition, the character display was used for the image for evaluation.

  Regarding the viewing angle characteristics, a case where leakage light (side lobe light) to the non-observer side was visually observed was evaluated as “◯”, and a case where it was viewed was evaluated as “X”. In addition, when the front of the screen is set to 0 °, when viewing from a viewer's vertical viewing angle of 0 ° to 70 °, the image is easy to see when the characters are not visible. The thing which may become impossible was set as x evaluation. The evaluation results are shown in Table 1.

<Comparison result>
In the products of the present invention obtained in Examples 1 to 4, leakage is a viewing angle characteristic regardless of whether the unit lens shape of the optical sheet is an asymmetric prism shape (shape type A1) or an asymmetric aspheric lens shape (shape type A2). Both the light (side lobe) and the visibility of the image on the viewer's side were good. On the other hand, the comparative example products obtained from Comparative Examples 1 to 6 did not have the effect of satisfying both the leakage light (side lobe) that is the viewing angle characteristic and the visibility of the image on the viewer side.

DESCRIPTION OF SYMBOLS 1, 4, ... Image display apparatus, 2 ... Illumination unit, 3 ... Liquid crystal panel, 176 ... Light source, 179 ... Light guide plate, 180 ... Dot, 10 ... Concealment lens sheet, 13 ... Output surface, A1, A2 ... Optical sheet, 41, 42 ... Unit lens, 60 ... Transparent substrate

Claims (3)

An optical sheet that is installed above the eye level of an observer in a transportation facility and is used for illumination light path control of an image display device that emits a large amount of light on the ground direction side with respect to the ceiling direction side ,
Having a cross-sectional asymmetric lens consisting of multiple arrays of asymmetric unit lenses on one surface of the substrate;
The cross-sectional shape of the asymmetric unit lens on the ceiling direction side is a curved surface,
Of the end portions of the asymmetric unit lens in contact with the base material, the angle a of the asymmetric unit lens at the end portion on the ground direction side is 90 degrees with respect to the light exit surface, and the end on the ceiling direction side An inclination angle b of the tangent of the surface curved shape in the part is 35 degrees or more and 50 degrees or less with respect to the light exit surface,
The inclination angle b ′ of the tangent of the curved surface decreases continuously in the range of 10 degrees or more and the inclination angle b or less from the end on the ceiling direction side toward the top of the asymmetric unit lens. A featured optical sheet.   A backlight unit for an image display device, comprising the optical sheet according to claim 1.   An image display element that defines a display image in accordance with transmission / shading in pixel units, and a backlight unit for an image display device according to claim 2 provided on the back surface of the image display element. An image display device.