Patent Application
20140085570
The present invention relates to a backlight used in liquid crystal display devices and a liquid crystal display device equipped with the backlight.
In general, a liquid crystal display device of transmissive type or semi-transmissive type is equipped with a liquid crystal display panel having a liquid crystal layer and a backlight for projecting beams toward a rear surface of the liquid crystal display panel. Previously, a liquid crystal display device of narrow viewing angle type has been proposed, in which an emission beam distribution is narrowed by providing a prism sheet at the beam emission surface side of a light guide plate of the backlight for the purpose of reducing power consumption, increasing brightness, protecting privacy, and the like (for example, see Patent Document 1).
In the above-described liquid crystal display device of narrow viewing angle type, the emission beams projected from a display surface of the liquid crystal display panel have high directivity all over the display surface in the normal direction of the display surface. Therefore, when viewed at close range, there has been a problem that brightness at a peripheral portion of the liquid crystal display panel is greatly reduced compared to that at a central portion, depending on the difference of angles into which the liquid crystal display panel is looked. This tendency becomes prominent as the viewing distance decreases and as the size of the liquid crystal display panel increases, and, in an extreme case, the brightness of the peripheral portion becomes too low to be able to visually recognize.
In order to solve this problem, a configuration is proposed in which a sheet is provided at the beam emission surface side of a light guide plate of a backlight. Here, the sheet has a prism whose cross section is a triangular shape and that has ridgelines arranged so as to make a principal ray of beams, which are emitted from an arbitrary position of a beam emission surface of the backlight, to be oriented to the direction of a predetermined viewing point (for example, see Patent Document 2).
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2001-143515
Patent Document 2: Japanese Unexamined Patent Application Publication No. H07-318729
In the above-described backlight, because a principal ray of beams projected from a beam emission surface is oriented toward a predetermined viewing point, while uniform brightness is observed when viewed from the predetermined viewing point, uniform brightness is not observed when viewed from a position deviated from the predetermined viewing position. Thus, there has been a problem that brightness at a peripheral portion is reduced as a viewing distance changes.
The present invention has been made in order to solve the above-described problem, and an objective thereof is to obtain a backlight and a liquid crystal display device in which a decrease in brightness at a peripheral portion associated with the change of viewing distance is reduced.
A backlight according to the present invention is comprised with a light source; an optical member for transforming beams projected from the light source into beams having a narrow-angle light distribution in which rays having intensity of no less than a predetermined value are localized within a predetermined angle range centered in the normal direction of a display surface of a liquid crystal display panel, and for projecting the transformed beams in the direction of the liquid crystal display panel; and a light distribution control member for receiving the beams that are projected from the optical member and that have the narrow-angle light distribution, and for projecting the received beams in the direction of the liquid crystal display panel, wherein a plurality of curved surfaces are provided at the light distribution control member for each transforming a beam, from among the beams having the narrow-angle light distribution, that enters a peripheral portion of the liquid crystal display panel so that the narrow-angle light distribution of the entered beam is broadened compared to that of a beam that enters a central portion of the liquid crystal display panel; and curvature radiuses of the plurality of curved surfaces are formed so that a curvature radius of a curved surface located at a peripheral portion of the light distribution control member is smaller than a curvature radius of a curved surface located at a central portion of the light distribution control member.
In a backlight according to the present invention, a decrease in brightness at a peripheral portion associated with the change of viewing distance can be reduced.
As shown in
The liquid crystal display panel 106 has the rear surface 106a and a display surface 106b, and the display surface 106b is provided to be parallel to the X-Y plane that includes the X-axis and Y-axis which are orthogonal to the Z-axis. The normal direction of the display surface 106b is parallel to the Z-axis, and the X-axis and Y-axis are mutually orthogonal.
The backlight 108 includes a light distribution control member 83, an optical member 107 comprised with a downward prism sheet 82 (optical sheet) and a light guide plate 81, a light reflection sheet 80, and light sources 117A and 117B.
The light sources 117A and 117B are provided face to face with both end surfaces (incident edge surfaces) of the light guide plate 81 in its Y-axis direction, respectively, and are configured with, for example, plural laser-emitting devices or light-emitting diodes arranged in the X-axis direction. Beams projected from the light sources 117A and 117B enter the light guide plate 81 from the end surfaces thereof; are projected from the light guide plate 81 after transmitting therethrough; pass through a downward prism sheet 82 and the light distribution control member 83 in this order; and enter the liquid crystal display panel 106. Image light is generated by the liquid crystal display panel 106 spatially modulating the beams that enter from the rear surface 106a, and is projected from the display surface 106b. The projected light is recognized as an image.
The light guide plate 81 is a plate-like member made of a transparent optical material such as an acrylic resin (PMMA), and its rear surface (surface opposite to liquid crystal display panel 106 side) has a configuration in which microscopic optical elements 81a, which protrude to the opposite direction of the liquid crystal display panel 106 side, are regularly-arranged along a surface parallel to the display surface 106b. The shape of microscopic optical element 81a forms a part of a spherical shape, and the surface thereof has a constant curvature. The microscopic elements 81a having the spherical shape are provided in a two-dimensional manner along the X-Y plane.
As a working example of the microscopic optical element 81a, a microscopic optical element may be employed having, for example, a surface curvature of about 0.15 mm, a maximum height of about 0.005 mm, and a refractive index of about 1.49. The distance between the centers of microscopic optical elements may be 0.077 mm. Note that, while the acrylic resin can be employed as a material for the light guide plate 81, the material is not limited thereto. Another resin material such as a polycarbonate resin or a glass material may be used in place of the acrylic resin, as long as the material has high light transmittance and high molding processability.
As described above, the beams projected from the light sources 117A and 117B enter the light guide plate 81 from the lateral end surfaces thereof. While transmitting through the light guide plate 81, the incident beams are reflected totally, due to the refractive index difference between the microscopic optical element 81a of the light guide plate 81 and the airspace, and are projected from a front surface of the light guide plate 81 in the direction of the liquid crystal display panel 106. In order to equalize a planar brightness distribution of the emission beams projected from the front surface of the light guide plate 81, the microscopic optical elements 81a are more densely provided as getting away from the lateral end surface, while more sparsely provided as coming close to the lateral end surface. Note that, not limited to this, the microscopic optical elements 81a may be provided more uniformly on the surface so that a desired planar brightness distribution will be obtained.
The light reflection sheet 80 is provided so that beams projected from the rear surface of the light guide plate 81 will be reflected and reutilized as illumination beams to be emitted onto the rear surface 106a of the liquid crystal display panel 106, and, for example, a light reflection sheet whose base material is a resin such as polyethylene terephthalate or a light reflection sheet in which a metal is vapor-deposited onto a substrate surface may be used.
The downward prism sheet 82 is a transparent optical sheet, and its rear surface has a configuration in which microscopic optical elements 82a, which protrude to the opposite direction of the liquid crystal display panel 106 side, are regularly-arranged along a plane parallel to the display surface 106b. The shape of microscopic optical element 82a forms a triangular prism that has a constant vertex angle. As shown in
As a working example of the microscopic optical element 82a, a microscopic optical element may be employed, for example, having a vertex angle, formed by two slanted planes, of 68 degrees, a height of 0.022 mm, and a refractive index of 1.49. The microscopic optical elements 82a may be arranged to have a pitch of 0.03 mm in the Y-axis direction. Note that, while PMMA can be employed as a material for the downward prism sheet 82, the material is not limited thereto. Another resin material such as a polycarbonate resin or a glass material may be used, as long as the material has high light transmittance and high molding processability.
The light distribution control member 83 is a transparent and plate-like or sheet-like member, and includes an incident surface 83a in which beams projected from the optical member 107 enter and an emission surface 83b from which the beams that enter from the incident surface 83a are emitted. Plural concaves 109 are provided, each extending in the X-axis direction, on the emission surface 83b of the light distribution control member 83. The concaves 109 are regularly-arranged in the Y-axis direction along the plane parallel to the display surface 106b. The respective concaves 109 are formed so that their curvature radiuses decrease in the order of a central portion 110A, an intermediate portion 110B, and a peripheral portion 110C. It is desirable that the width of the concave 109 in the Y-direction is almost equal to or less than the width of a pixel (not shown here) of the liquid crystal display panel 106, and, further, it is desirable to be no more than the width of a picture element that will be described later.
The beams projected from the light sources 117A and 117B enter the light guide plate 81 from the incident end surfaces thereof and transmit through the light guide plate 81 while being reflected totally. During the transmission, a part of the transmitted beams are reflected by the microscopic optical element 81a located at the rear surface of the light guide plate 81, and are projected from the front surface (emission surface) of the light guide plate 81 as the illumination beams. The beams transmitting through the light guide plate 81 are transformed by the microscopic optical element 81a into beams that have a light distribution centered in the direction slanted by a predetermined angle from the Z-axis direction, and the transformed beams are projected from the front surface. The beams projected from the light guide plate 81 with the predetermined angle enter the microscopic optical element 82a of the downward prism sheet 82, are totally reflected internally by the slanted plane of the microscopic optical element 82a, and then are projected from the front surface (emission surface) with high directivity in the normal direction of the emission surface. That is, owing to a function of the optical member 107 configured with the light guide plate 81 and the downward prism sheet 82, the beams projected from the light sources 117A and 117 are transformed into beams having a narrow-angle light distribution and the transformed beams are projected from the optical member 107 in the direction of the liquid crystal display panel 106.
The beam having the narrow-angle light distribution is a beam with high directivity in which rays having intensity of no less than a predetermined value are localized within a predetermined angle range centered in the Z-axis direction which is the normal direction of the display surface 106b of the liquid crystal display panel 106.
The beams projected from the downward prism sheet 82 enter the incident surface 83a of the light distribution control member 83, and then are projected, with their light distribution being controlled as will be described later, by the plural concaves 109 provided on the emission surface 83b. The beams projected from the light distribution control member 83 are utilized as illumination beams to be emitted onto the rear surface 106a of the liquid crystal display panel 106.
Before explaining a function of the light distribution control member 83 in the liquid crystal display device in Embodiment 1, a relationship will be described between a viewing distance and a planar brightness distribution in a conventional liquid crystal display device which serves as a comparative example.
Meanwhile, when viewed from the viewpoint “Q”, while brightness at the central portion is similar to that when viewed from the viewpoint “P”, brightness of the beam projected from the peripheral portion is observed to be decreasing as coming close to the peripheral portion. Furthermore, when viewed from the viewpoint “R”, while brightness at the central portion is not different from that when viewed from “P” and “Q”, brightness of the beam projected from the peripheral portion is observed to be decreasing as coming close to the peripheral portion. When viewed from “R”, brightness at the peripheral portion greatly decreases compared to that when viewed from “Q”. That is, in the liquid crystal display device in Comparative Example 1, a decrease in brightness at the peripheral portion becomes prominent as the viewing distance decreases.
In this configuration, brightness is observed to be uniform at the central portion and the peripheral portion when viewed from the viewpoint “Q”. However, brightness at the peripheral portion decreases when viewed from both viewpoints “P” and “R”. Thus, in the method using the Fresnel lens sheet 102, a viewpoint in which planar brightness is observed to be uniform is merely changed from the conventional infinite point to a point having a finite distance. Therefore, since the method does not fundamentally fix the problem of decreasing the planar brightness, the decrease in peripheral brightness similar to the conventional case arises when getting away from the finite distance viewpoint.
The light distribution control member 83 in the liquid crystal display device in Embodiment 1 is a member for alleviating the decrease in peripheral brightness associated with the change of viewing distance described above.
Since the emission surface 83b of the light distribution control member 83 has the planar shape at the central portion 110A, the beam that is projected from the downward prism sheet 82 and that has the narrow-angle light distribution is projected from the light distribution control member 83 without changing its light distribution. At the intermediate portion 110B, since the concave 109 having a certain curvature radius is provided on the emission surface 83b, the beam that is projected from the downward prism sheet 82 and that has the narrow-angle light distribution is projected from the light distribution control member 83 with its light distribution broadened. At the peripheral portion 110C, since the concave 109 having a smaller curvature radius is provided, the beam that is projected from the downward prism sheet 82 and that has the narrow-angle light distribution is projected from the light distribution control member 83 with its light distribution more broadened.
As a result, as for the beams projected from the light distribution control member 83 shown in
In the liquid crystal display device in Embodiment 1, the light distribution control member 83 is provided, for receiving the beams that are projected from the optical member 107 and that have the narrow-angle light distribution and for projecting the beams in the direction of the liquid crystal display panel 106; the plural concaves 109 are provided on the light distribution control member 83; and the curvature radiuses of the plural concaves 109 are formed to be decreasing as coming close to the peripheral portion 110C of the light distribution control member 83. Therefore, since the beams that have the narrow-angle light distribution are transformed into beams whose light distributions are gradually broadened as moving on from the central portion toward the peripheral portion of the liquid crystal display panel 106, the decrease in brightness at the peripheral portion can be alleviated when observed from any viewpoint located between the infinite distance and the short distance.
As will be described later, plural convexes in place of the plural concaves 109 may be provided on the emission surface 83b of the light distribution control member 83. In that case, however, since the beams projected from the optical member 107 are necessary to be once condensed and then again diverged, a convex having power of large absolute value compared to that of the concave 109 is needed in order to broaden the beams having the narrow-angle light distribution. Therefore, when there is an error in a curved surface shape of the convex, the error in the shape greatly affects the light distribution of the beams projected from the emission surface 83b of the light distribution control member 83. On the other hand, in Embodiment 1, since the plural concaves 109 are provided on the emission surface 83b of the light distribution control member 83, the beams having the narrow-angle light distribution can be broadened with comparatively low power. Therefore, even if there is an error in the spherical shape of the concave 109, the error in the shape less affects the light distribution of the beams projected from the emission surface 83b of the light distribution control member 83. That is, sensitivity against the error in shape can be reduced when fabricating the concave 109.
The optical member 107 is configured with the light guide plate 81 for internally reflecting the beams projected from the light sources 117A and 117B at the rear surface located at the opposite direction of the liquid crystal display panel 106 side and for projecting the reflected beams in the direction of the liquid crystal display panel 106, and with the downward prism sheet 82 for transforming the beams projected from the light guide plate 81 in the direction of the liquid crystal display panel 106 into the beams having the narrow-angle light distribution. Therefore, a backlight with less decrease in brightness at the peripheral portion can be fabricated easily by only providing the light distribution control member 83, which is designed to be applicable to various purposes, over the downward prism sheet 82 that has been widely used conventionally.
Note that, while a configuration is shown in Embodiment 1 in which the plural concaves 109 are provided on the emission surface 83b of the light distribution control member 83, the position for providing the concaves 109 is not limited thereto.
In addition, plural concaves 109 may be provided on both surfaces of the light distribution control member 83.
Note that, while the incident surface 83a of the light distribution control member 83 has the planar shape in the backlight in Embodiment 1, an arbitrary curved surface may be employed so that a desired light distribution will be obtained.
In a light guide plate of a conventional backlight, it is common that the microscopic optical elements provided at the rear surface of the light guide plate are more sparsely provided as coming close to the light source, while more densely provided as coming close to the central portion so that the planar brightness of the backlight will be equalized. The reason is that, if the microscopic optical elements are densely provided at the portion close to the light source, the amount of beams projected from the light guide plate increases at the peripheral portion and decreases at the central portion, thereby reducing brightness at the central portion.
Meanwhile, in the backlight in Embodiment 2, the microscopic optical elements 81a are more densely provided at the portion close to the light sources 117A and 117B compared to the above-described arrangement in which the planar brightness distribution is equalized. As a result, as shown in
In this case, at the viewpoint “P”, a beam 87a projected from the central portion 110A, a beam 88c projected from the intermediate portion 110B, and a beam 89c projected from the peripheral portion 110C are observed. At the viewpoint “Q”, the beam 87a projected from the central portion 110A, a beam 88a projected from the intermediate portion 110B, and a beam 89a projected from the peripheral portion 110C are observed. At the viewpoint “R”, the beam 87a projected from the central portion 110A, a beam 88b projected from the intermediate portion 110B, and a beam 89b projected from the peripheral portion 110C are observed. Here, the intensity of the beam 89b, to be observed at “R”, projected from the peripheral portion 110C is larger than that of the corresponding beam 86b projected from the peripheral portion 110C in Embodiment 1.
In the backlight in Embodiment 2, since the microscopic optical elements 81a at the light guide plate 81 are provided so as to be more densely provided at the peripheral portion than the configuration in Embodiment 1 when the number of elements per unit area is compared, the intensity of the beam at the peripheral portion in the direction having a large angle against the normal direction of the liquid crystal display panel 106 can be increased. Therefore, the decrease in brightness at the peripheral portion can be more alleviated in addition to the effect in Embodiment 1.
As shown in
While the emission surface 83b of the central portion 110A in (a) in
Since the emission surface 83b of the light distribution control member 83 is a planar shape at the central portion 110A, a beam that is projected from the downward prism sheet 82 and that has a narrow-angle light distribution is projected from the light distribution control member 83 without changing its light distribution. Because the concave 109 having the curvature radius of r1 is provided on the emission surface 83b at the intermediate portion 110B and the concave 109 is slanted by ω1 against the Z-axis in the direction of the peripheral portion of the light distribution control member 83, a distribution of a beam that is projected from the downward prism sheet 82 and that has the narrow-angle light distribution is broadened in the Y-axis direction and the direction of the peak component of the beam is slanted to be directed to the normal line passing through the central portion of the display surface 106b of the liquid crystal display panel 106, thereby being slanted as a whole in the direction of the central portion.
Since the concave 109 having the curvature radius of r2, which is smaller than the above-described curvature radius of r1, is provided at the peripheral portion 110C and the concave 109 is slanted by ω2, which is larger than ω1, against the Z-axis in the direction of the peripheral portion of the light distribution control member 83, a distribution of a beam that is projected from the downward prism sheet 82 and that has the narrow-angle light distribution is more broadened in the Y-axis direction compared to the above-described case in the intermediate portion 110B, and also the direction of the peak component of the beam is more slanted to be directed to the normal line passing through the central portion of the display surface 106b of the liquid crystal display panel 106 compared to the above-described case in the intermediate portion 110B.
As a result, as shown in
In this case, at the viewpoint “P”, a beam 90a projected from the central portion 110A, a beam 91c projected from the intermediate portion 110B, and a beam 92c projected from the peripheral portion 110C are observed. At the viewpoint “Q”, the beam 90a projected from the central portion 110A, a beam 91a projected from the intermediate portion 110B, and a beam 92a projected from the peripheral portion 110C are observed. At the viewpoint “R”, the beam 90a projected from the central portion 110A, a beam 91b projected from the intermediate portion 110B, and a beam 92b projected from the peripheral portion 110C are observed. Now, the beams 90a, 91a, and 92a are peak components projected from the light distribution control member 83. Here, the intensity of the beam 92b, which is observed at “R”, projected from the peripheral portion 110C is larger than that of the corresponding beam 86b projected from the peripheral portion 110C in Embodiment 1. Therefore, since the beams that are projected from the optical member 107 and that have the narrow-angle light distribution are transformed so as to have the broadened light distribution using the light distribution control member 83, and the beams are also transformed so that the direction of the peak component thereof is slanted to be directed to the normal line passing through the central portion of the display surface 106b of the liquid crystal display panel 106, the decrease in brightness at the peripheral portion can be alleviated when observed from any viewpoint located between the infinite distance and the short distance.
In the backlight in Embodiment 3, since the concave 109 is slanted against the normal direction of the display surface 106b so that the direction of the peak component of the beams projected from the light distribution control member 83 will be slanted to be directed to the normal line passing through the central portion of the display surface 106b of the liquid crystal display panel 106, the decrease in brightness at the peripheral portion can be more alleviated in addition to the effect in Embodiment 1.
In addition, because the slant angle of the concave 109 increases as coming close to the peripheral portion 110C of the light distribution control member 83, uniformity of the planar brightness distribution of the backlight can be improved.
Note that, while the concaves 109 are provided on the emission surface 83b of the light distribution control member 83 in Embodiment 3, the concaves 109 may be provided on the incident surface 83a and the concaves 109 may be slanted so that the direction of the peak component of the beams projected from the light distribution control member 83 will be directed to the normal line passing through the central portion of the display surface 106b of the liquid crystal display panel 106. In addition, the concaves 109 may be provided on both the incident surface 83a and the emission surface 83b and the concaves 109 may be slanted so that the direction of the peak component of the beams projected from the light distribution control member 83 will be directed to the normal line passing through the central portion of the display surface 106b of the liquid crystal display panel 106. The effect similar to the above-described one can be obtained in these configurations.
While the incident surface 83a and emission surface 83b of the central portion 110A in (a) in
The concave 109 having a curvature radius of r2 is formed on the emission surface 83b at the peripheral portion 110C, and a straight line connecting the center point of the concave 109 and the curvature center O4 thereof is parallel to the Z-axis. The slanted plane 116 opposite to the concave 109 is formed on the incident surface 83a, and the slanted plane 116 is slanted by ω4 against the X-axis and Y-axis, which are in parallel direction to the liquid crystal display panel 106, in the direction of the peripheral portion of the light distribution control member 83. The curvature radius r2 is smaller than r1, and the slant angle ω4 is larger than ω3. While configurations are shown here only at three areas, i.e. central, intermediate, and peripheral portions 110A, 110B, and 110C, the curvature radius of the concave 109 is formed to be decreasing as coming close to the peripheral portion 110C, and the slant angle of the slanted plane 116 is formed to be increasing as coming close to the peripheral portion 110C, including the other areas.
Since the incident surface 83a and emission surface 83b of the light distribution control member 83 are planar shapes at the central portion 110A, a beam that is projected from the downward prism sheet 82 and that has a narrow-angle light distribution is projected from the light distribution control member 83 without changing its light distribution. Because the concave 109 having the curvature radius of r1 is provided on the emission surface 83b and the slanted plane 116 slanted by ω3 against the X-axis and Y-axis is formed on the incident surface 83a at the intermediate portion 110B, the direction of the peak component of a beam that is projected from the downward prism sheet 82 and that has the narrow-angle light distribution is directed to the normal line passing through the central portion of the display surface 106b of the liquid crystal display panel 106 by the slanted plane 116 of the incident surface 83a, and a distribution of the beam is broadened in the Y-axis direction by the concave 109 of the emission surface 83b.
Since the concave 109 having the curvature radius of r2, which is smaller than the above-described curvature radius of r1, is provided on the emission surface 83b and the slanted plane 116 slanted by ω4, which is larger than the above-described slant angle ω3, against the X-axis and Y-axis is formed on the incident surface 83a at the peripheral portion 110C, a beam that is projected from the downward prism sheet 82 and that has the narrow-angle light distribution is more slanted compared to the above-described case in the intermediate portion 110B by the slanted plane 116 on the incident surface 83a, and a distribution of the beam is more broadened in the Y-axis direction compared to the above-described case in the intermediate portion 110B by the concave 109 of the emission surface 83b. As a result, the beams that are projected from the optical member 107 and that have the narrow-angle light distribution are transformed so that the light distributions thereof are gradually broadened as moving on from the central portion toward the peripheral portion of the liquid crystal display panel 106 and that the direction of the peak component thereof is directed to the normal line passing through the central portion of the display surface 106b of the liquid crystal display panel 106, and the transformed beams are projected from the light distribution control member 83. Therefore, the decrease in brightness at the peripheral portion can be alleviated when observed from any viewpoint located between the infinite distance and the short distance.
In the backlight in Embodiment 4, since the plural concaves 109 are provided on the emission surface 83b and, at the same time, the plural slanted planes 116 opposite to the plural concaves 109 are provided on the incident surface 83a of the light distribution control member 83, and the slanted planes 116 are formed so that the direction of the peak component of the beams projected from the light distribution control member 83 will be directed to the normal line passing through the central portion of the display surface 116b of the liquid crystal display panel 116, the effect similar to that in Embodiment 3 can be obtained.
Note that, while a configuration is shown here in which the plural slanted planes 116 are provided on the incident surface 83a and the plural concaves 109 are provided on the emission surface 83b, the similar effect can be obtained when the plural concaves 109 are provided on the incident surface 83a and the plural slanted planes 116 are provided on the emission surface 83b.
As shown in
As shown in (a) and (b) in
As shown in (a) in
As for a beam that has been projected from the downward prism sheet 82 and is projected from the light distribution control member 83 via the third surface 103c, the directions of beams 94c and 95c, which are the peak components of the beam having a narrow-angle light distribution, coincide with the direction of the viewpoint “P.”
Meanwhile, as for a beam projected from the light distribution control member 103 via the second surface 103b, the directions of beams 94a and 95a, which are the peak components of the beam having the narrow-angle light distribution, are changed corresponding to the slants of the second surface 103b, i.e. ω5 and ω7, respectively, and coincide with the direction of the viewpoint “Q”. Also, as for a beam projected from the light distribution control member 103 via the first surface 103a, the directions of beams 94b and 95b, which are the peak components of the beam having the narrow-angle light distribution, are changed corresponding to the slants of the first surface 103a, i.e. ω6 and ω8, respectively, and coincide with the direction of the viewpoint “R”.
As a result, as shown in
Note that, while explanations on the central, intermediate, and peripheral portions 110A, 110B, and 110C are made in the above, optical surfaces provided at areas other than the three portions are formed so that the peak components of the beams projected from the third, second, and first surfaces 103c, 103b, and 103a will be observed at the viewpoints “P”, “Q”, and “R”, respectively.
Next, how to calculate the angle ω formed between each surface of the optical surface 1000 and the X-Y plane will be described. Note that, while a case of the first surface 103a will be exemplified here, ω for another surface can be determined in a similar way. In
tan(π/2+ω−ω′)=d/l (1)
n·sin ω=sin ω′ (2)
Where, n: refractive index of light distribution control member 83; and refractive index of air: 1.
In Formulas (1) and (2), if “d”, “n”, and “l” are determined, ω at an arbitrary position can be calculated. That is, a slant of each surface in an optical surface at an arbitrary position of the light distribution control member 83 at an arbitrary viewpoint can be calculated.
In the backlight in Embodiment 5, since the plural optical surfaces 1000, which have the first, second, and third surfaces 103a, 103b, and 103c and which transforms the direction of the peak component of the beams that are projected from the optical member 107 and that have the narrow-angle light distribution to be directed to each of the directions of the viewpoints “P”, “Q”, and “R”, are provided on the light distribution control member 83, certain brightness at the peripheral portion can be ensured at “P”, “Q”, and “R”.
Because the slant angles of the first and second surfaces 103a and 103b increase as coming close to the peripheral portion of the light distribution control member 83, uniformity of the planar brightness distribution of the backlight can be improved.
In the liquid crystal display device in Embodiment 5, since the above-described backlight is provided, certain brightness at the peripheral portion can be ensured at the viewpoints “P”, “Q”, and “R”.
When the width or arrangement interval (pitch) in the Y-axis direction of the adjacent optical surfaces 1000 on the light distribution control member 83 increases, since the emission direction of beams differ depending on the positions of the display surface 106b of the liquid crystal display panel 106, non-uniformity of the planar brightness in the X-axis direction is observed on the display surface 106b. On the other hand, when the width or pitch is too small, its fabrication becomes difficult and, at the same time, efficiency for light utilization of the light distribution control member 83 decreases.
In general, an image displayed on a liquid crystal display panel is configured with pixels which are basic display units. A pixel is further configured with picture elements of RGB. Intensity of a beam from each of the picture elements is adjusted at the liquid crystal display panel, and a color of a pixel is determined by synthesizing each of the beams with human eyes. When the width and pitch in the Y-axis direction of the optical surfaces 1000 are larger than each RGB picture element size, chromaticity or brightness of a pixel at a viewpoint is sometimes differently observed from chromaticity or brightness to be displayed originally. Thus, it is desirable that the width and pitch of the optical surfaces 1000 are configured to be smaller than the picture element size in its Y-axis direction. It is also desirable that the numbers of optical surfaces 1000 included within the respective RGB picture element widths in their Y-axis direction are each configured to be in a comparable level.
Note that, while the first, second, and third surfaces 103a, 103b, and 103c are described to be planar surfaces in Embodiment 5, this is not a limitation and curved surfaces, etc. may be employed. For example, when concave surfaces are employed, since a light distribution of a beam projected from each of the surfaces can be broadened as described in Embodiments 1 and 2, the decrease in peripheral brightness can be alleviated at a broader range of the viewing distance.
Also, while a case in which the viewpoint “P” is located at the infinite and the third surface 103c is parallel to the X-Y plane is shown in the above, the viewpoint, except for the central portion 110A, may be set at a position other than the infinite, and the third surface 103c may be slanted against the X-Y plane.
In addition, while the optical surface 1000 is shown in Embodiment 5 in which the third, second, and first surfaces 103c, 103b, and 103a are provided from the central portion toward the peripheral portion in this order, the order can be reshuffled.
Furthermore, while a configuration is shown in which the optical surfaces 1000 are provided at the emission surface 83b side of the light distribution control member 83, optical surfaces 1000 may be provided at the incident surface 83a side.
Still further, while the light distribution control member 83 is shown in Embodiment 5 in which the beams that are projected from the optical member 107 and that have the narrow-angle light distribution are transformed to be directed to three viewpoints, i.e. the viewpoint “P” serving as the infinite viewpoint, viewpoint “Q” the middle-distance viewpoint, and viewpoint “R” the short-distance viewpoint, this is not a limitation. The number of viewpoints can be two or more, and the viewing distance can be selected from arbitrary values.
The liquid crystal display device 100 further includes a panel driving unit 102 for driving the liquid crystal display panel 10, a light source driving unit 103A for driving light sources 3A and 3B included in the first backlight unit 1, and a light source driving unit 103B for driving light sources 6A and 6B included in the second backlight unit 2. Operations of the panel driving unit 102 and the light source driving units 103A and 103B are controlled by a control unit 101.
Control signals are generated by performing image processing on an image signal supplied by a signal source (not shown) and the control signals are supplied to the panel driving unit 102 and the light source driving units 103A and 103B, by the control unit 101. The light sources 3A/3B and 6A/6B are driven by the light source driving units 103A and 103B in response to the control signal from the control unit 101, and beams are projected from the light sources 3A/3B and 6A/6B, respectively.
In the first backlight unit 1, emission beams from the light sources 3A and 3B are transformed into illumination beams 11 having a narrow-angle light distribution (a distribution in which rays having intensity of no less than a predetermined value are localized within a comparatively narrow angle range centered in the Z-axis direction which is the normal direction of the display surface 10a of the liquid crystal display panel 10), and the beams are projected toward a rear surface 10b of the liquid crystal display panel 10. The illumination beams 11 are projected onto the rear surface 10b of the liquid crystal display panel 10 via the optical sheet 9. The optical sheet 9 is a member for suppressing optical effects of minute non-uniformity of illumination, etc. Meanwhile, in the second backlight unit 2, emission beams from the light sources 6A and 6B are transformed into illumination beams 12 having a wide-angle light distribution (a distribution in which rays having intensity of no less than a predetermined value are localized within a comparatively wide angle range centered in the Z-axis direction), and the beams are projected toward the rear surface 10b of the liquid crystal display panel 10. After transmitting the first backlight unit 1 and optical sheet 9, the illumination beams 12 are projected onto the rear surface 10b of the liquid crystal display panel 10.
The light reflection sheet 8 is provided immediately below the second backlight unit 2. Beams which transmit the second backlight unit 2 from among beams projected from the first backlight unit 1 to its rear surface side, and beams projected from the second backlight unit 2 to its rear surface side, are reflected by the light reflection sheet 8 and utilized as illumination beams for illuminating the rear surface 10b of the liquid crystal display panel 10. As the light reflection sheet 8, a light reflection sheet may be used whose base material is a resin such as polyethylene terephthalate or a light reflection sheet in which a metal is vapor-deposited onto a substrate.
The liquid crystal display panel 10 includes a liquid crystal layer 10c extendedly-provided along the X-Y plane which is orthogonal to the Z-axis. The display surface 10a of the liquid crystal display panel 10 has a rectangular shape, and the X-axis and Y-axis directions shown in
As shown in
The upward prism sheet 5V includes an optical configuration for transmitting the illumination beams 12 that are projected from the second backlight unit 2 and that have the wide-angle light distribution, and further includes an optical configuration for reflecting the beams projected from the rear surface 4a of the light guide plate 4 to return the beams to the direction of the light guide plate 4. The beams projected from the rear surface 4a of the light guide plate 4 are reflected by the upward prism sheet 5V so that their traveling direction will be changed into the direction of the liquid crystal display panel 10, and transmit the light guide plate 4 and the downward prism sheet 5D, thereby being utilized as the illumination beams having the narrow-angle light distribution.
The light sources 3A and 3B are provided face to face with both end surfaces (incident edge surfaces) 4c and 4d of the light guide plate 4 in the Y-axis direction, respectively, and are configured with, for example, plural laser-emitting devices arranged in the X-axis direction. The beams projected from the light sources 3A and 3B enter the light guide plate 4 from the incident end surfaces 4c and 4d thereof, respectively, and transmit through the light guide plate 4 while being reflected totally. During the transmission, a part of the transmitted beams are reflected by the microscopic optical element 40 located at the rear surface 4a of the light guide plate 4, and are projected from the front surface (emission surface) of the light guide plate 4 as illumination beams 11a. The beams transmitting through the light guide plate 4 are transformed by the microscopic optical element 40 into beams that have a light distribution centered in the direction slanted by a predetermined angle from the Z-axis direction, and the transformed beams are projected from the front surface 4b. The beams 11a projected from the light guide plate 4 enter a microscopic optical element 50 of the downward prism sheet 5D, are totally reflected internally by the slanted plane of the microscopic optical element 50, and then are projected from the front surface (emission surface) 5b as the illumination beams 11.
As a working example of the microscopic optical element 40, a microscopic optical element may be employed having, for example, a surface curvature of about 0.15 mm, a maximum height Hmax of about 0.005 mm, and a refractive index of about 1.49. The distance Lp between the centers of microscopic optical elements 40 may be 0.077 mm. Note that, while the acrylic resin can be employed as a material for the light guide plate 4, the material is not limited thereto. Another resin material such as a polycarbonate resin or a glass material may be used in place of the acrylic resin, as long as the material has high light transmittance and high molding processability.
As described above, the beams projected from the light sources 3A and 3B enter the light guide plate 4 from the lateral end surfaces 4c and 4d thereof, respectively. While transmitting through the light guide plate 4, the incident beams are reflected totally, due to the refractive index difference between the microscopic optical element 40 of the light guide plate 4 and the airspace, and are projected from the front surface 4b of the light guide plate 4 toward the liquid crystal display panel 10. Although the microscopic optical elements 40 shown in (a) and (b) in
As will be described later, by generating the emission beams 11a localized in these two angle ranges, the emission beams 11a entered the microscopic optical element 50 of the downward prism sheet 5D can be totally reflected by the inner surface of the microscopic optical element 50. The beams totally reflected by the inner surface of the microscopic optical element 50 are localized within a relatively narrow angle range centered in the Z-axis direction, thereby forming the illumination beams 11 having the narrow-angle light distribution.
Next, an optical configuration of the downward prism sheet 5D will be described.
The emission beams 11a projected from the front surface 4b of the light guide plate 4 enter the rear surface 5a of the downward prism sheet 5D, i.e. the microscopic optical element 50. Because the incident beams are totally reflected internally by either of the slanted planes 50a and 50b which configure the triangular prism of the microscopic optical element 50 and then are bent so as to come close to the normal direction of the liquid crystal display panel 10 (Z-axis direction), the incident beams turn into the illumination beams 11 that have high brightness at their center and a light distribution of a narrow distribution width.
As a working example of the microscopic optical element 50, a microscopic optical element may be employed having, for example, a vertex angle, formed by the slanted planes 50a and 50b (vertex angle of isosceles triangle shape at the cross section in (b) in
The narrow-angle light distribution shown in
Next, an optical configuration of the upward prism sheet 5V will be described.
As a working example of the microscopic optical element 50 of the upward prism sheet 5V, a microscopic optical element may be employed having, for example, a vertex angle, formed by the slanted planes 51a and 51b (vertex angle of isosceles triangle shape at cross section in (b) in
In the upward prism sheet 5V, by totally reflecting internally the beams (return beams), entering the microscopic optical element 51 from the light guide plate 4, by a rear surface 5e, the traveling direction of the return beams can be changed into the direction of the liquid crystal display panel 10. Examples of the return beams from the light guide plate 4 are beams projected in the opposite direction of the liquid crystal display panel 10 side because the beams do not satisfy the total reflection condition at the rear surface 4a of the light guide plate 4, and beams projected from the downward prism sheet 5D in the opposite direction of the liquid crystal display panel 10 side. Since these return beams can be used again as the illumination beams for the first backlight unit 1 by the upward prism sheet 5V, efficiency for light utilization can be improved.
Next, an optical function of the microscopic optical element 51 will be described.
As shown in (a) in
As shown in (a) in
In this way, by transmitting through the light guide plate 4 and entering the downward prism sheet 5D, the beams projected from the upward prism sheet 5V in the direction of the liquid crystal display panel 10 are transformed into the illumination beams 11 having high brightness at their center and a light distribution of narrow distribution width, and illuminate the rear surface 10b of the liquid crystal display panel 10. Thus, increased can be the ratio of light quantity of the illumination beams 11 that are projected from the first backlight unit 1 and that have the narrow-angle light distribution to light quantity projected from the light sources 3A and 3B configuring the first backlight unit 1 (the ratio is defined as efficiency for light utilization of the first backlight unit 1). Therefore, since the light quantity of the light source necessary for ensuring predetermined brightness at the display surface 10a can be decreased compared to that of a conventional device, power consumption of the liquid crystal display device 100 can be reduced.
As shown in (a) in
The liquid crystal display device 100 in Embodiment 6 has a configuration in which the first backlight unit 1 and the second backlight unit 2 are stacked, and the first backlight unit 1 is provided between the second backlight unit 2 and the liquid crystal display panel 10. Because the illumination 12 that is projected from the second backlight unit 2 and that has the wide-angle light distribution is necessary to be transmitted through the first backlight unit 1, it is not preferable in the first backlight unit 1 that a light reflection sheet, like the light reflection sheet 8, having low light transmittance and high reflectivity is used as a means for reflecting the return beams RL in the direction of the liquid crystal display panel 10. Since the first backlight unit 1 does not use such kind of light reflection sheet and has the upward prism sheet 5V having very high light transmittance, the increase of power consumption can be reduced without decreasing the ratio of light quantity of the beams that are projected from the display surface 10a of the liquid crystal display device 100 and that have the wide-angle light distribution to light quantity projected from the light sources 6A and 6B configuring the second backlight unit 2 (the ratio is defined as efficiency for light utilization of the second backlight unit 2).
The light reflection sheet 8 is provided so that the return beams transmitted from the first backlight unit 1 and the second backlight unit 2 will be reflected in the direction of the liquid crystal display panel 10 and reutilized as the illumination beams. Here, the beams entering the surface of the light reflection sheet 8 are beams that are diffused by a diffusion reflection structure 70 of the second backlight unit 2 and that have the wide-angle light distribution, and the beams reflected by the surface of the light reflection sheet 8 in the direction of the liquid crystal display panel 10 are diffused when reflected by the surface of the light reflection sheet 8 or when transmitting through the diffusion reflection structure 70. Therefore, in the beams that enter the first backlight unit 1 from the rear surface side thereof, the percentage of beams is decreased that have the angle necessary for being transformed into the illumination beams 11 having the narrow-angle light distribution. Meanwhile, as described above, the beams can be projected from the upward prism sheet 5V, which have the light distribution necessary for the incident beams that enter the downward prism sheet 5D to be totally reflected internally by the microscopic optical element 50 and to be transformed into the illumination beams 11 having the narrow-angle light distribution. Thus, since the return beams RL that enter from the light guide plate 4 are efficiently transformed into the beams having the narrow-angle light distribution centered in the normal direction of the display surface 10a of the liquid crystal display panel 10, efficiency for light utilization in the first backlight unit 1 can be improved.
Since it is obvious from
Next, a configuration of the second backlight unit 2 will be described. As shown in
In the liquid crystal display device 100 having the above described configuration, the light distribution of illumination beams for the rear surface 10b of the liquid crystal display panel 10 can be made not only to be the narrow-angle light distribution or the wide-angle light distribution, but also to be an intermediate light distribution between the narrow-angle light distribution and the wide-angle light distribution.
Meanwhile, when the light sources 6A and 6B of the second backlight unit 2 are turned on and the light sources 3A and 3B of the first backlight unit 1 are turned off, the rear surface of the liquid crystal display panel 10 is illuminated by the illumination beams having the wide-angle light distribution of D4 shown in (b) in
In the liquid crystal display device 100 in Embodiment 6, the luminescence amount of the light sources 3A and 3B of the first backlight unit 1 and the luminescence amount of the light sources 6A and 6B of the second backlight unit 2 are controlled by the control unit 101 according to the observing direction. For example, as shown in (c) in
Because the observer feels the glare when the display surface 10a of the liquid crystal display device 100 is too bright, excessive brightness is not necessary. Therefore, as shown in
In the first backlight unit 1 and the second backlight unit 2, it is desirable that the light sources 3A, 3B, 6A, and 6B have the same luminescence system. The reason is that, when the viewing angle is modified by changing the percentage of the luminescence amount of the first backlight unit 1 and the luminescence amount of the second backlight unit 2, possibility can be avoided in which luminescence color change etc. is generated, caused by the difference of luminescence characteristics (emission spectrum, etc.) between the light sources 3A, 3B, 6A, and 6B. By using the same luminescence system in the first backlight unit 1 and the second backlight unit 2, this possibility can be avoided and good image quality can be maintained when the viewing angle is changed. Examples of the light sources having the same luminescence system are illuminants having the same structure, illuminants having the same luminescence characteristics such as luminescence wavelength band, illuminant modules including the same combination of plural illuminants having different luminescence characteristics, or illuminants driven by the same driving method.
In a liquid crystal display device having the above-described variable viewing angle function, the decrease in peripheral brightness also happens as the viewpoint changes, as described above. Therefore, in the liquid crystal display device 100, the light distribution control member 83 in Embodiment 1 is provided between the backlight unit 1 and the liquid crystal display panel 10. Thus, in the liquid crystal display device having the variable viewing angle function, the decrease in peripheral brightness due to the change in the viewing distance can be reduced even if the viewing angle is narrowed.
Note that, while the microscopic optical element 40 has the convex spherical shape as shown in
As described above, in the liquid crystal display device 100 in Embodiment 6, the viewing angle can be controlled by adjusting the percentage of the luminescence amount of the first backlight unit 1 and the luminescence amount of the second backlight unit 2, without using complicated and expensive active optical devices. Therefore, since the beams projected from the display surface 10a in the unnecessary direction are minimized in the liquid crystal display device 100, the viewing angle control function effective for reducing the power consumption can be obtained. The liquid crystal display device 100 in Embodiment 6 has a configuration that is simple and low-cost, and that is effective without depending on the screen size, i.e. from small through large size. Because the luminescence amount and the luminescence direction of the first backlight unit 1 and the second backlight unit 2 can be controlled accurately and easily in the liquid crystal display device 100, the viewing angle can be changed in a finely-tuned and optimum manner without generating the color change, etc. of the display image.
The illumination beams 11 having the narrow-angle light distribution can be generated, without using active optical devices, using the light guide plate 4 of the first backlight unit 1 and the downward prism sheet 5D. As described above, by totally reflecting internally the illumination beams 11a, which enter from the front surface 4b of the light guide plate 4, by the slanted planes 50a and 50b, the illumination beams 11 having the narrow-angle light distribution can be generated by the microscopic optical element 50 formed on the rear surface 5a of the downward prism sheet 5D.
Since the first backlight unit 1 has the upward prism sheet 5V, also in the liquid crystal display device 100 of a backlight laminating type in Embodiment 6, the efficiency for light utilization of the first backlight unit 1 can be improved without the loss of the emission beams from the second backlight unit 2. As described above, because the return beams RL projected from the light guide plate 4 of the first backlight unit 1 in the rear surface direction thereof are refracted by the microscopic optical element 51 of the upward prism sheet 5V and then are totally reflected by the rear surface 5e in the direction of the liquid crystal display panel 10, the beams can become the illumination beams 11.
The illumination beams 12 projected from the second backlight unit 2 can illuminate the rear surface of the liquid crystal display panel 10 without narrowing the width of their light distribution by the slanted planes 50a and 50b of the microscopic optical element 50 protruded in the rear surface side. As a configuration for achieving the narrow viewing angle, employed may be a combination of a sheet-like light source emitting illumination beams having the wide-angle light distribution and an optical structure for condensing the illumination beams and transforming the beams into illumination beams having the narrow-angle light distribution (for example, an optical structure whose surface not facing the sheet-like light source is an emission surface). However, in this configuration, since the emission beams from the sheet-like light source are transformed into beams having the narrow-angle light distribution, even the illumination beams that are projected from the second backlight unit 2 and that have the wide-angle light distribution are also made narrow-angled. Thus, it is impossible to obtain the desired light distribution shown in
As shown in
In Embodiment 6, since the luminescence amounts of the first backlight unit 1 and the second backlight unit 2 are independently controlled by the control unit 101 while keeping the brightness directly in front of the display surface 10a at the predetermined commanded value “L”, excessive brightness is not supplied and the most suitable light distribution according to the observing direction can be obtained. In addition, because the beams projected in the unnecessary direction are minimized, the power consumption can be greatly reduced.
In order to control the light distribution of the illumination beams for the rear surface of the liquid crystal display panel 10, it is desirable that the luminescence amount of the light sources 3A, 3B, 6A, and 6B can be controlled freely. From such a standpoint, it is desirable to use a solid-state light source, such as a laser light source or a light-emitting diode, whose luminescence amount can be easily controlled. In this way, more optimal viewing angle control can be made.
In order that the illumination beams 11 projected from the first backlight unit 1 have the narrow-angle light distribution, as described above, the illumination beams 11a projected from the light guide plate 4 are necessary to have the light distribution localized in the angle range which is greatly slanted from the normal direction of the surface (Z-axis direction). It is desirable that the directivity of the beams transmitting through the light guide plate 4 is high, because, if so, the emission angle of the beams projected from the light guide plate 4 can be easily controlled and the narrowing of the width of the light distribution (rays having intensity of no less than a predetermined value are localized within a specific angle range) is possible. Therefore, it is desirable to use a laser light source having high directivity as the light sources 3A and 3B. Thus, the viewing angle can be controlled in a finely-tuned and optimum manner and, at the same time, a strong effect for reducing power consumption can be obtained.
In Embodiment 6, while both end surfaces of the light guide plate 4 in its Y-axis direction work as light incident surfaces and the light sources 3a and 3b which are located face to face with these end surfaces are provided in the first backlight unit 1, the configuration is not limited to this. The first backlight unit 1 may be configured such that only one end surface of both end surfaces of the light guide plate 4 works as a light incident surface and a light source which is located face to face with this end surface is provided. In this case, it is desirable that the planar brightness distribution of the beams projected from the light guide plate 4 is equalized by appropriately changing the arrangement interval and the specifications of the microscopic optical elements 40 provided on the rear surface 4a of the light guide plate 4. Similarly, the second backlight unit 2 may be configured such that only one end surface of both end surfaces of the light guide plate 7 works as a light incident surface and a light source which is located face to face with this end surface is provided.
While the light distribution control member in Embodiment 1 is used as the light distribution control member 83 in Embodiment 6, the configuration is not limited to this. Any one of the light distribution control members in Embodiments 2 through 5, or a variant thereof can be employed.
As shown in
A control signal is generated by performing image processing on an image signal (not shown) supplied by a signal source (not shown), and the control signal is supplied to the panel driving unit 202 and the light source driving units 203A and 203B by the control unit 201. The light sources 3C and 19 are driven by the light source driving units 203A and 203B according to the control signal from the control unit 201, and beams are projected from the light sources 3C and 19, respectively.
In the first backlight unit 16, emission beams from the light sources 3C are transformed into illumination beams 13 having a narrow-angle light distribution (a distribution in which rays having intensity of no less than a predetermined value are localized within a comparatively narrow angle range centered in the Z-axis direction which is the normal direction of the display surface 10a of the liquid crystal display panel 10), and the beams 13 are projected toward a rear surface of the liquid crystal display panel 10. The illumination beams 13 are projected onto the rear surface of the liquid crystal display panel 10 via the optical sheet 9. Meanwhile, in the second backlight unit 17, emission beams from the light sources 19 are transformed into illumination beams 14 having a wide-angle light distribution (a distribution in which rays having intensity of no less than a predetermined value are localized within a comparatively wide angle range centered in the Z-axis direction), and the beams 14 are projected toward the first backlight unit 16. After transmitting the first backlight unit 16, the illumination beams 14 are projected onto the rear surface of the liquid crystal display panel 10 via optical sheet 9.
As shown in
The light source 3C is provided face to face with an end surface 4g (incident edge surface) of the light guide plate 4R in the Y-axis direction, and is configured with arranging, for example, plural light-emitting diodes in the X-axis direction. The beams projected from the light source 3C enter the light guide plate 4R from the incident end surface 4g of the light guide plate 4R and transmit through the light guide plate 4R while being reflected totally. During the transmission, a part of the transmitted beams are reflected by the microscopic optical element 40R located at the rear surface 4e of the light guide plate 4R, and are projected from a front surface 4f of the light guide plate 4R as illumination beams 13a. The beams transmitting through the light guide plate 4R are transformed by the microscopic optical element 40R into beams that have a light distribution centered in the direction slanted by a predetermined angle from the Z-axis direction, and the transformed beams are projected from the front surface 4f. After entering the downward prism sheet 5D, the beams 13a projected from the light guide plate 4R are totally reflected internally by the microscopic optical element 50 in
The microscopic optical element 40R can be the same shape as the microscopic optical element 40 in Embodiment 6. The material for the light guide plate 4R having the microscopic optical elements 40R can be the same material as the light guide plate 4 in Embodiment 6. Thus, as a working example of the microscopic optical element 40R, a microscopic optical element may be employed having, for example, a surface curvature of about 0.15 mm, a maximum height of about 0.005 mm, and a refractive index of about 1.49.
The pitch of centers of the microscopic optical elements 40R are set to be smaller as the distance from the incident edge surface 4g, in which the incident beams from the light source 3C enter, becomes larger, and to be larger as the distance from the incident edge surface 4g becomes smaller. As described above, the incident beams from the light source 3C enter the light guide plate 4R through the incident edge surface 4g located at the lateral side of the light guide plate 4R. While transmitting through the light guide plate 4R, the incident beams are reflected totally, due to the refractive index difference between the microscopic optical element 40R of the light guide plate 4R and the airspace, and is projected from the front surface 4f of the light guide plate 4R in the direction of the liquid crystal display panel 10. Here, the microscopic optical elements 40R are more sparsely formed as coming close to the incident edge surface 4g located near the light source 3C (i.e. the number of the microscopic optical elements 40R per unit area (density) decreases as coming close to the incident edge surface 4g), while more densely formed as getting away from the light source 3C (i.e. the density of the microscopic optical elements 40R increases as getting away from the incident edge surface 4g). The reason is to equalize a planar brightness distribution of the emission beams 13a. Since the beam intensity becomes high as coming close to the incident edge surface 4g, the density of the microscopic optical element 40R is lowered so that percentage of the transmitted beams totally reflected internally by the microscopic optical element 40R will be decreased. Meanwhile, because the beam intensity becomes low as getting away from the incident edge surface 4g, the density of the microscopic optical element 40R is raised so that percentage of the transmitted beams totally reflected internally by the microscopic optical element 40R can be increased. Thus, it is possible to equalize the planar brightness distribution of the emission beams 13a.
Similar to the case in Embodiment 6, the beams enter the front surface 5c of the upward prism sheet 5V include beams projected from the rear surface 4e of the light guide plate 4R because the beams do not satisfy the total reflection condition at the surface, and beams projected from the downward prism sheet 5D in the opposite direction of the liquid crystal display panel 10 side. In the upward prism sheet 5V, by totally reflecting internally the beams (return beams), which enter the microscopic optical element 51 from the light guide plate 4R, by the rear surface 5e, the traveling direction of the return beams can be changed into the direction of the liquid crystal display panel 10. In this way, the beams totally reflected internally by the rear surface 5e are projected in the direction of the liquid crystal display panel 10 and transmit through the light guide plate 4R, and then are transformed into beams having a light distribution necessary for being transformed into the illumination beams 13 having the narrow-angle light distribution by totally reflected internally by the microscopic optical element 50 of the downward prism sheet 5D. Thus, increased can be the ratio of light quantity of the illumination beams 13 that are projected from the first backlight unit 16 and that have the narrow-angle light distribution to light quantity projected from the light source 3C configuring the first backlight unit 16 (the ratio is defined as efficiency for light utilization of the first backlight unit 16). Therefore, since the light quantity of the light source necessary for ensuring predetermined brightness at the display surface 10a can be decreased compared to that of a conventional device, power consumption of the liquid crystal display device 200 can be reduced.
Next, a configuration of the second backlight unit 17 will be described. As shown in
This second backlight unit 17 is effective as a backlight unit that emits the illumination beams 14 having the wide-angle light distribution and that are also required a large luminescence amount. For example, even if the screen size of the liquid crystal display device 200 is enlarged, sufficient brightness can be ensured using the second backlight unit 17 having light sources at its bottom.
When using the second backlight unit 17 having light sources at its bottom, a complicated structure is necessary for equalizing the light distribution of the illumination beams 14 if a laser light source whose luminescence area is small and that has high directivity is used as the light sources 19. Therefore, in Embodiment 7, it is desirable that a light-emitting diode is used as the light source of the second backlight unit 17, whose luminescence is easily controllable similar to the laser light source and in which the light distribution of the illumination beams 14 is easily equalized thanks to its planar emission characteristics. Thus, because the second backlight unit 17 can be configured simply, further cost reduction can be achieved.
As the light source 3C in the first backlight unit 16 and the light sources 19 in the second backlight unit 17, it is desirable to employ a light source having the same luminescence system. The reason is that, when the viewing angle is modified by changing the percentage of the luminescence amount of the first backlight unit 16 and the luminescence amount of the second backlight unit 17, possibility can be avoided in which luminescence color change etc. is generated, caused by the difference of luminescence characteristics (emission spectrum, etc.) between the light sources 3C and 19.
In a liquid crystal display device having the above-described variable viewing angle function, the decrease in peripheral brightness also happens as the viewpoint changes, as described above. Therefore, in the liquid crystal display device 100, the light distribution control member 83 in Embodiment 1 is provided between the backlight unit 1 and the liquid crystal display panel 10. Thus, in the liquid crystal display device having the variable viewing angle function, the decrease in peripheral brightness due to the change in the viewing distance can be reduced even if the viewing angle is narrowed.
As described above, in the liquid crystal display device 200 in Embodiment 7, similar to the liquid crystal display device 100 in Embodiment 6, the viewing angle can be controlled by adjusting the percentage of the luminescence amount of the first backlight unit 16 and the luminescence amount of the second backlight unit 17, without using complicated and expensive active optical devices. In the liquid crystal display device 200, since the beams projected from the display surface 10a in the unnecessary direction can be minimized, the viewing angle control function effective for reducing the power consumption can be obtained. Also, the liquid crystal display device 200 has a configuration that is simple and low-cost, and that is effective without depending on the screen size, i.e. from small through large size.
In addition, similar to the liquid crystal display device 100 in Embodiment 6, since the first backlight unit 16 has the upward prism sheet 5V, the return beams projected from the light guide plate 4R in the rear surface direction thereof in the first backlight unit 16 are totally reflected internally by the rear surface 5e due to the microscopic optical element 51 of the upward prism sheet 5V, thereby becoming the illumination beams 13 having the narrow-angle light distribution. Thus, the return beams can be utilized as the emission beams of the first backlight unit 16. Therefore, in the liquid crystal display device of backlight laminating type in Embodiment 7, the efficiency for light utilization of the first backlight unit 16 can be also improved without the loss of the emission beams 14 from the second backlight unit 17.
Furthermore, in the liquid crystal display device 200, since the second backlight unit 17 for emitting the illumination beams 14 having the wide-angle light distribution is configured as a backlight having light sources at its bottom, enlarging the screen size and reducing the power consumption of the liquid crystal display device 200 having the viewing angle control function can be achieved with low cost.
Note that, while the light distribution control member in Embodiment 1 is used as the light distribution control member 83 in Embodiment 7, the configuration is not limited to this. Any one of the light distribution control members in Embodiments 2 through 5, or a variant thereof can be employed.
In the above, while different embodiments according to the present invention have been described with reference to the drawings, these are exemplifications of the present invention and various configurations other than the above can be employed. For example, while the shape of the microscopic optical element 50 is the triangular prism as shown in
In addition, while the upward prism sheet 5V, for example, has the microscopic optical element 51 having a convex triangular prism shape as shown in
Furthermore, while the liquid crystal display devices 100 and 200 in Embodiments 6 and 7 has the upward prism sheet 5V, an embodiment that does not have the upward prism sheet 5V may be feasible. In addition, in the first backlight units 1 and 16 in Embodiments 6 and 7, while a preferable configuration is employed in which the arranging direction of the microscopic optical elements 51 of the upward prism sheet 5V is almost orthogonal to the arranging direction of the microscopic optical elements 50 of the downward prism sheet 5D as described above, the configuration in the present invention is not limited thereto. Even in a case when an angle formed between the arranging direction of the microscopic optical elements 51 and the arranging direction of the microscopic optical elements 50 is shifted from 90 degrees by a certain amount, efficiency for light utilization of the first backlight units 1 and 16 can be improved compared to the embodiment in which the upward prism sheet 5V is not provided.
As described above, in the liquid crystal display devices 100 and 200 in Embodiments 6 and 7, a finely-tuned viewing angle control can be made regardless of the size. Thus, since an optimum viewing angle can be selected in accordance with the number and positions of observers, the effect for reducing power consumption can be obtained by employing lean illumination. Also, while this function is utilized in improving visibility from the observers and their surroundings with a wide viewing angle display in a normal mode, the function can be also employed as an application for creating a private mode in which the display portion cannot be observed from the surroundings by changing to a narrow viewing angle display.
While the emission surface 83b of the central portion 110A in (a) in
Since the emission surface 83b of the light distribution control member 83 has the planar shape at the central portion 110A, the beam that is projected from the downward prism sheet 82 and that has the narrow-angle light distribution is projected from the light distribution control member 83 without changing its light distribution. At the intermediate portion 110B, since the convex 209 having a certain curvature radius is provided on the emission surface 83b, the beam that is projected from the downward prism sheet 82 and that has the narrow-angle light distribution is once condensed by the convex 209 and then again diffused, thereby being projected from the light distribution control member 83 with its light distribution broadened. At the peripheral portion 110C, since the convex 209 having a smaller curvature radius is provided, the beam that is projected from the downward prism sheet 82 and that has the narrow-angle light distribution is projected from the light distribution control member 83 with its light distribution more broadened.
As a result, the beams that are projected from the optical member 107 and that have the narrow-angle light distribution are transformed into beams whose light distributions are gradually broadened as moving on from the central portion toward the peripheral portion of the liquid crystal display panel 106, and the transformed beams are projected from the light distribution control member 83. That is, the percentage of an emission component having a slant angle from the Z-axis gradually increases as moving on from the central portion toward the peripheral portion of the liquid crystal display panel 106. As a result, similar to the case in Embodiment 1, the decrease in brightness at the peripheral portion can be alleviated when observed from any viewpoint located between the infinite distance and the short distance.
In the liquid crystal display device in Embodiment 8, the light distribution control member 83 is provided, for receiving the beams that are projected from the optical member 107 and that have the narrow-angle light distribution and for projecting the beams in the direction of the liquid crystal display panel 106; the plural convexes 209 are provide on the light distribution control member 83; and the curvature radiuses of the plural convexes 209 are formed to be decreasing as coming close to the peripheral portion 110C of the light distribution control member 83. Therefore, since the beams that have the narrow-angle light distribution are transformed into beams whose light distributions are gradually broadened as moving on from the central portion toward the peripheral portion of the liquid crystal display panel 106, the decrease in brightness at the peripheral portion can be alleviated when observed from any viewpoint located between the infinite distance and the short distance.
When providing a concave on the light distribution control member 83, it is necessary to fabricate a convex metal mold for manufacturing the concave using the molding, and when providing a convex on the light distribution control member 83, it is necessary to fabricate a concave metal mold for manufacturing the convex using the molding. In Embodiment 8, since fabricating a convex metal mold is more difficult than fabricating a concave one, the light distribution control member 83 can be manufactured easier compared to the case for providing a concave. Note that a convex can be provided more easily if an inkjet method using the surface tension of resin, etc. is used.
As shown in
While the emission surface 83b of the central portion 110A in (a) in
Since the emission surface 83b of the light distribution control member 83 is a planar shape at the central portion 110A, a beam that is projected from the downward prism sheet 82 and that has a narrow-angle light distribution is projected from the light distribution control member 83 without changing its light distribution. Because the convex 209 having the curvature radius of r3 is provided on the emission surface 83b at the intermediate portion 110B and the convex 209 is slanted by ω9 against the Z-axis in the direction of the peripheral portion of the light distribution control member 83, a distribution of a beam that is projected from the downward prism sheet 82 and that has the narrow-angle light distribution is broadened in the Y-axis direction and, at the same time, the direction of the peak component of the beam is slanted to be directed to the normal line passing through the central portion of the display surface 106b of the liquid crystal display panel 106, thereby being slanted as a whole in the direction of the central portion.
Since the convex 209 having the curvature radius of r4, which is smaller than the above-described curvature radius of r3, is provided at the peripheral portion 110C and the convex 209 is slanted by ω10, which is larger than ω9, against the Z-axis in the direction of the peripheral portion of the light distribution control member, a distribution of a beam that is projected from the downward prism sheet 82 and that has the narrow-angle light distribution is more broadened in the Y-axis direction compared to the above-described case in the intermediate portion 110B and, at the same time, the direction of the peak component of the beam is further slanted to be directed to the normal line passing through the central portion of the display surface 106b of the liquid crystal display panel 106, compared to the above-described case in the intermediate portion 110B.
As a result, the beams that are projected from the optical member 107 and that have the narrow-angle light distribution are projected from the light distribution control member 83 so that the light distributions thereof are gradually broadened as moving on from the central portion toward the peripheral portion of the liquid crystal display panel 106; the direction of the peak component of the beams is slanted to be directed to the central portion of the display surface 106b of the liquid crystal display panel 106; and the projected beams have increased component projected in the direction of the normal line passing through the central portion of the display surface 106b of the liquid crystal display panel 106 as moving on to the peripheral portion 110C of the light distribution control member 83.
Therefore, similar to the case in Embodiment 3, since the beams that are projected from the optical member 107 and that have the narrow-angle light distribution are transformed so as to have the broadened light distribution using the light distribution control member 83, and the beams are also transformed so that the direction of the peak component thereof is slanted to be directed to the normal line passing through the central portion of the display surface 106b of the liquid crystal display panel 106, the decrease in brightness at the peripheral portion can be alleviated when observed from any viewpoint located between the infinite distance and the short distance.
In the backlight in Embodiment 9, since the convex 209 is slanted against the normal direction of the display surface 106b so that the direction of the peak component of the beams projected from the light distribution control member 83 will be slanted to be directed to the normal line passing through the central portion of the display surface 106b of the liquid crystal display panel 106, the decrease in brightness at the peripheral portion can be further alleviated in addition to the effect in Embodiment 8.
While the incident surface 83a and emission surface 83b of the central portion 110A in (a) in
The convex 209 having a curvature radius of r4 is formed on the emission surface 83b at the peripheral portion 110C, and a straight line connecting the center point and the curvature center O8 of the convex 209 is parallel to the Z-axis. The slanted plane 216 opposite to the convex 209 is formed on the incident surface 83a, and the slanted plane 216 is slanted by ω12 against the X-axis and Y-axis, which are in parallel direction to the liquid crystal display panel 106, in the direction of the peripheral portion of the light distribution control member 83. The curvature radius r4 is smaller than r3, and the slant angle ω12 is larger than ω11. While configurations are shown here only at three areas, i.e. central, intermediate, and peripheral portions 110A, 110B, and 110C, the curvature radius of the convex 209 is formed to be decreasing as coming close to the peripheral portion 110C, and the slant angle of the slanted plane 216 is formed to be increasing as coming close to the peripheral portion 110C, including the other areas.
Since the incident surface 83a and emission surface 83b of the light distribution control member 83 are planar shapes at the central portion 110A, a beam that is projected from the downward prism sheet 82 and that has a narrow-angle light distribution is projected from the light distribution control member 83 without changing its light distribution. Because the convex 209 having the curvature radius of r3 is provided on the emission surface 83b and the slanted plane 216 slanted by ω11 against the X-axis and Y-axis is formed on the incident surface 83a at the intermediate portion 110B, the direction of the peak component of a beam that is projected from the downward prism sheet 82 and that has the narrow-angle light distribution is directed, by the slanted plane 216 on the incident surface 83a, to the normal line passing through the central portion of the display surface 106b of the liquid crystal display panel 106, and a distribution of the beam is broadened in the Y-axis direction by the convex 209 on the emission surface 83b.
Since the convex 209 having the curvature radius of r4, which is smaller than the above-described curvature radius of r3, is provided on the emission surface 83b and the slanted plane 216 slanted by ω12, which is larger than the above-described slant angle ω11, against the X-axis and Y-axis is formed on the incident surface 83a at the peripheral portion 110C, a beam that is projected from the downward prism sheet 82 and that has the narrow-angle light distribution is more slanted compared to the above-described case in the intermediate portion 110B by the slanted plane 216 on the incident surface 83a, and a distribution of the beam is more broadened, by the convex 209 on the emission surface 83b, in the Y-axis direction compared to the above-described case in the intermediate portion 110B. As a result, the beams that are projected from the optical member 107 and that have the narrow-angle light distribution are transformed so that the light distributions thereof are gradually broadened as moving on from the central portion toward the peripheral portion of the liquid crystal display panel 106 and that the direction of the peak component thereof is directed to the normal line passing through the central portion of the display surface 106b of the liquid crystal display panel 106, and the transformed beams are projected from the light distribution control member 83. Therefore, the decrease in brightness at the peripheral portion can be alleviated when observed from any viewpoint located between the infinite distance and the short distance.
In the backlight in Embodiment 10, since the plural convexes 209 are provided on the emission surface 83b and, at the same time, the plural slanted planes 216 opposite to the plural convexes 209 are provided on the incident surface 83a of the light distribution control member 83, and the slanted planes 216 are formed so that the direction of the peak component of the beams projected from the light distribution control member 83 will be directed to the normal line passing through the central portion of the display surface 116b of the liquid crystal display panel 116, the effect similar to that in Embodiment 9 can be obtained.
Note that, while a configuration is shown here in which the plural slanted planes 216 are provided on the incident surface 83a and the plural convexes 209 are provided on the emission surface 83b, the similar effect can be obtained when the plural convexes 209 are provided on the incident surface 83a and the plural slanted planes 216 are provided on the emission surface 83b.
The embodiments and variants thereof described above can be mutually combined.
100, 200: liquid crystal display devices; 108: backlight; 1, 16: first backlight units; 2, 17, 18: second backlight unit; 3A, 3B, 6A, 6B, 3C, 19, 60, 117A, and 117B: light sources; 60L: lens; 4, 4R, and 81: light guide plates; 40, 40R, 50, 51, and 81a: microscopic optical elements; 5D, 82: downward prism sheets (optical sheets); 107: optical member; 83: light distribution control member; 109: concave; 209: convex; 116, 216: slanted planes; 1000: optical surface; 103a: first surface; 103b: second surface; 103c: third surface; 5V: upward prism sheet; 7: light guide plate; 70: diffusion reflection structure; 8, 80: light reflection sheets; 9: optical sheet; 10, 106: liquid crystal display panels; 21, 61: casings; 22, 62: diffusion transmission plates (diffusion transmission structure): and P, Q, and R: viewing points.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2011-122217 | May 2011 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2012/001758 | 3/14/2012 | WO | 00 | 11/27/2013 |
