Liquid crystal display device comprising reflecting portions for reflecting light beams and focusing them on circumferences of electrode portions of linear light sources

A direct type backlight unit used in a liquid crystal display device is provided which can suppress lowering of luminance at an electrode portion of a linear light source. A reflecting plate is formed on a side wall of a box-shaped reflector close to an end of a linear light source. The reflector reflects light beams from the linear light source to be guided toward a liquid crystal panel. The reflecting plate on the side wall has at least two inclined surfaces. The inclined surfaces may have a stepped shape or a convex ridge shape. According to this arrangement, it is possible to reduce or eliminate decrease of the luminance level at ends of an effective display area of a liquid crystal panel.

INCORPORATION BY REFERENCE

The present application claims priorities from Japanese applications JP2007-146610 filed on Jun. 1, 2007, JP2008-022270 filed on Feb. 1, 2008, the contents of which are hereby incorporated by reference into this application.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to a liquid crystal display device, and more particularly, to a direct type backlight unit used in a liquid crystal display device and a liquid crystal display device having the same.

(2) Description of Related Art

As a liquid crystal panel used in liquid crystal display devices, a passive matrix type panel and an active matrix panel using thin film transistors (TFT) are known. However, such liquid crystal panels are not of an emissive type and therefore require an additional illumination light source to visualize images formed on the liquid crystal panels.

Therefore, a liquid crystal display device includes a liquid crystal display panel having a drain driver and a gate driver arranged at its circumference and a backlight unit (hereinafter, sometimes referred to as BLU) for irradiating the liquid crystal display panel.

The BLU is classified into a side-light type BLU and a direct type BLU. In recent years, liquid crystal display devices are becoming bulky and larger in screen size. In such bulky and large-screen liquid crystal display devices, a direct type BLU is suitable because it can provide high luminance output. A liquid crystal display device using the direct type BLU is disclosed in JP-A-2006-259750 and JP-A-11-084377, for example.

SUMMARY OF THE INVENTION

A direct type BLU includes one or plural linear light sources (for example, cold cathode fluorescent lamp), an optical element including a diffusion plate on which light beams irradiated from the linear light sources are incident, and a reflector (an reflecting element) having a reflecting surface for reflecting light beams irradiated from the linear light sources onto a side opposite to a liquid crystal display panel toward the liquid crystal display panel.

In recent years, large-screen liquid crystal display devices are requested to be small in thickness. However, in order to make large-screen liquid crystal display devices small in thickness, it is necessary to make the direct type BLU small in thickness. When the direct type BLU is made small in thickness; that is, when the distance between an optical element and a reflector is decreased, there is a problem that a luminance distribution in a display surface of a liquid crystal display panel becomes uneven. Such an uneven luminance distribution is remarkable particularly at end surfaces of the liquid crystal display panel, and a decrease of the luminance level at both end surfaces in the longitudinal direction of a linear light source is problematic.

Such an uneven luminance distribution is remarkable particularly at end surfaces of the liquid crystal display panel, and a decrease of the luminance level at both end surfaces in the longitudinal direction of a linear light source (for example, EEFL (External Electrode Fluorescent Lamp)) is problematic. In addition, when an electrode portion disposed at both ends or one end in the longitudinal direction of the linear light source is located within an effective range of the BLU, since the electrode does not emit light beams, the electrode portion may appear as a dark portion, whereby luminance unevenness may occur.

The present invention has been made in view of the problems described above. The present invention provides a technology suitable to obviate or reduce a decrease of the luminance level at both ends in the longitudinal direction of a light source, thereby reducing luminance unevenness.

According to the technology of the present invention, at least an inner surface of a side wall of a frame at both ends of a linear light source is inclined outward from the frame.

In accordance with an aspect of the present invention, there is provided a liquid crystal display device, including: a liquid crystal panel; and a backlight unit mounted on a back side of the liquid crystal panel to emit illumination light, wherein the backlight unit at least includes: a frame having side walls that are erected toward the liquid crystal panel from respective pairs of parallel opposing ends of a bottom portion; a linear light source attached so as to extend in parallel to one of the paired side walls; and a light diffusion plate inserted between the linear light source and the liquid crystal panel, and wherein the inner surfaces of the paired side walls arranged perpendicular to the linear light source have a reflecting surface that is inclined from the bottom portion so as to be opened in a direction toward the liquid crystal panel.

In the above aspect of the liquid crystal display device, the backlight unit may have two or more reflecting surfaces having different inclination angles on each of the side walls arranged perpendicular to the linear light source.

In the above aspect of the liquid crystal display device, the backlight unit may have the inclined reflecting surface at both sides of electrode portions of the linear light source.

In the above aspect of the liquid crystal display device, the side walls arranged perpendicular to the linear light source of the backlight unit may be constructed by at least one reflecting surface having a curved surface shape.

In the above aspect of the liquid crystal display device, the side walls arranged perpendicular to the linear light source of the backlight unit may be constructed by a plurality of reflecting surfaces having a stepped shape.

In the above aspect of the liquid crystal display device, the side walls arranged perpendicular to the linear light source of the backlight unit may be constructed by a plurality of reflecting surfaces of which the inclination angle gradually increases from the bottom portion of the frame.

In the above aspect of the liquid crystal display device, the side walls arranged perpendicular to the linear light source of the backlight unit may be constructed by a plurality of reflecting surfaces of which the inclination angle gradually decreases from the bottom portion of the frame.

In accordance with another aspect of the present invention, there is provided a liquid crystal display device, including: a liquid crystal panel; a plurality of linear light sources disposed on a rear surface side of the liquid crystal panel to irradiate light beams to the liquid crystal panel; and a rectangular frame disposed on a rear surface side of the linear light sources, wherein reflecting portions for reflecting light beams from the linear light sources to be irradiated to the liquid crystal panel are provided on inner wall surfaces of the frame, wherein the linear light sources are provided on a side surface of the frame so as to extend in a horizontal direction of the liquid crystal panel, wherein valleys are provided in portions of the reflecting portions provided on the side surfaces of the frame so as to surround the portions where the linear light sources are provided, and wherein the valleys form reflecting portions at the circumferences of the portions where the linear light sources are provided.

The valleys may be semi-elliptical when the side surfaces of the frame are observed from a display surface side of the liquid crystal panel. The cross-sections of the valleys that are perpendicular to a display surface of the liquid crystal panel or parallel to a horizontal direction of the liquid crystal panel may be curved surfaces. In the cross-sections perpendicular to a display surface of the liquid crystal panel or parallel to a horizontal direction of the liquid crystal panel, an angle between a tangential line of the curved surface of the valleys and a straight line parallel to the horizontal direction of the liquid crystal panel may differ depending on the position of the curved surface. The angle may gradually increase from a bottom surface of the frame toward the liquid crystal panel.

In addition, reflecting elements may be provided to the valleys so as to cover electrode portions of the linear light sources. The cross-sections of the reflecting elements that are perpendicular to a display surface of the liquid crystal panel or parallel to a vertical direction of the liquid crystal panel may be substantially arch shaped. The upper surfaces of the arch-shaped reflecting elements may have curved surfaces on cross-sections that are perpendicular to a display surface of the liquid crystal panel or parallel to a vertical direction of the liquid crystal panel.

In addition, the interfaces of the reflecting portions on the side surfaces of the frame and the valleys may be chamfered. The valleys may be provided to correspond to the plurality of linear light sources, and the shape of the interfaces of adjacent valleys face the center of the frame may be designed into a straight line shape or an arc shape as viewed from a display surface of the liquid crystal panel.

DETAILED DESCRIPTION OF THE EMBODIMENT

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.FIG. 1is a schematic diagram for explaining an exemplary structure of a liquid crystal display device having a direct type backlight unit. Specifically,FIG. 1Ais a development perspective view showing only a backlight unit;FIG. 1Bis a partly cross-sectional view for explaining the state where the backlight unit ofFIG. 1Ais mounted on a liquid crystal panel, taken along a direction perpendicular to a linear light source; andFIG. 1Cis a partly cross-sectional view taken along a direction parallel to the linear light source ofFIG. 1A.

As shown inFIG. 1A, a direct type backlight unit1at least includes a frame2having side walls2band2cthat are erected toward a liquid crystal panel from respective pairs of parallel opposing ends of a rectangular bottom plate2a, linear light sources3attached so as to extend in parallel to one of the paired side walls2bof an inner bottom portion of the bottom plate2aof the frame2, and a light diffusion plate4inserted between the linear light sources3and the liquid crystal panel. In this manner, the frame2according to this embodiment has a rectangular shape or a box-like shape.

The linear light sources3are cold cathode fluorescent lamps, for example, and inFIG. 1A, the light sources are provided along the bottom surface2ato extend over the two side walls2cin parallel to the other side walls2b.

FIGS. 1B and 1Cshow the state where the backlight unit1is mounted on a rear side of a liquid crystal panel5. The liquid crystal panel5is constructed such that a liquid crystal layer5eis sandwiched between two transparent substrates (glass substrates)5aand5band polarization plates5cand5dare laminated on the outer surfaces of the substrates5aand5b. The liquid crystal panel may be of a passive matrix type or an active matrix type, and an additional optical compensation film or the like may be laminated according to the type used. In the drawing, the area denoted by the arrow A is an effective display area of the liquid crystal panel5of a liquid crystal display device.

As shown inFIG. 1B, the bottom plate2aand the side walls2bthat are parallel to the longitudinal direction of the linear light sources3have reflecting surfaces on at least their inner surfaces so that light beams emitted from the linear light sources3are reflected on the reflecting surfaces toward the liquid crystal panel5, whereby light is efficiently utilized.

On the other hand, as shown inFIG. 1C, electrodes3afor applying an electrical voltage are provided at both ends of the linear light sources3, and light beams are not emitted from the electrodes3a. Therefore, it is inevitable that the luminance at the ends of a liquid crystal panel is lower than that at the central portion thereof. However, the effective display area of the liquid crystal panel5is within the range denoted by the arrow A. That is, the effective display area extends above the portions of the electrodes3. Such a low luminance problem may be resolved by forming the electrodes3aoutside the effective display area. However, recent liquid crystal display devices are becoming thinner and are also requested to have narrower frames. To meet such size requirements in a future liquid crystal display device, it is necessary to dispose the electrodes3ainside the effective display area.

In order to cover the size requirements, like the side walls2bofFIG. 1B, at least the inner surfaces of the side walls2cof the frame2perpendicular to the linear light sources3are formed as a reflecting surfaces so that the reflecting surfaces function as a reflector that reflects light beams emitted from the linear light sources3at an oblique angle with respect to the liquid crystal panel5toward the liquid crystal panel5, thereby efficiently utilizing the light.

FIGS. 2A-2Care diagrams for explaining a luminance distribution on a region adjacent to an end of the effective display area of the left side wall2cofFIG. 1C. Specifically,FIG. 2Ais a schematic cross-sectional view showing the positional relationship between the linear light source3, the electrode3a, the left side wall2c, and the bottom plate2a.FIG. 2Bis a graph for explaining qualitatively a luminance level of the liquid crystal panel5in a direction parallel to the linear light source3ofFIG. 2A. InFIG. 2B, the horizontal axis represents a position (distance) in a direction parallel to the linear light source3from an end d0of the effective display area toward the inside of the effective display area, and the vertical axis represents a luminance level.FIG. 2Cis shown to refer to the relationship between a corresponding position and the electrode3aof the linear light source3and is a schematic view showing that the bottom plate2aand the left side wall2cform reflector having an inclination angle θ with respect to each other. In this invention, a side wall perpendicular to the linear light source3is referred to as a reflector and is distinguished from other reflecting surfaces.

In the graph ofFIG. 2B, it can be seen that the luminance level P decreases as the position moves closer to the end d0from the inside of the effective display area. More specifically, the luminance level P scarcely decreased at positions from the inside of the liquid crystal panel5to the electrode3a; while the luminance level P decreased remarkably from the position d1(luminance level P1) of the electrode3aand reached P0at the end d0of the effective display area. It has been known that, if the side wall2chad not a reflecting function as a reflector, the luminance level P0at the end d0of the effective display area would have been decreased further to reach substantially zero.

As shown inFIG. 2B, the side wall2chas an inclination angle θ with respect to the bottom plate2aand is constructed as a reflecting surface to form a reflector in order to suppress decrease of a luminance level at the effective display area above the electrode3aof the linear light source3where light beams are not emitted. However, the luminance level at the area above the electrode3ais still insufficient.

Next, another embodiment of the present invention will be described with reference toFIG. 3.FIG. 3is a diagram for explaining an embodiment of the reflector of the present invention. The reflector has the same structure as that ofFIG. 2and has a side wall2c0having a shape different from that of the side wall2cof the reflector shown inFIG. 2.

In the embodiment ofFIG. 3, the reflecting surface of the side wall2c0is a reflector having at least two inclination angles. Alternatively, the reflecting surface is a reflector having at least two reflecting surfaces.

That is, as shown in the side wall2c0ofFIG. 3Aor3C, the reflector of the embodiment ofFIG. 3has at least two different inclination angles or at least two inclined surfaces. Here, the inclined surface refers to two inclined surfaces f1and f2which constitute the reflector of the side wall2c0shown inFIG. 3C. For example, the reflector of the embodiment ofFIG. 3may have three inclined surfaces; and among these inclined surfaces, the two, upper and lower surfaces have the same inclination angle that is different from the inclination angle of an intermediate inclined surface. InFIG. 3B, the broken line represents the luminance level corresponding to that ofFIG. 2and the solid line represents the luminance level corresponding toFIG. 3Aor3C. According to this embodiment, as shown inFIG. 3B, the luminance level at the end d0of the effective display area increased to P0′.

In the embodiment ofFIG. 3, the height at which the inclination angle of the reflector changes is lower than an axial center3xof the linear light source3. However, the inclination angle changing height may be located higher than the axial center3xof the linear light source3. In addition, the inclination angle changing height may be set in terms of a tube diameter of the linear light source3rather than the height of the axial center3xso as to be above or below the tube diameter. In either case, the interface of the bottom plate2aand the side wall2c0is located at an inner side of the electrode3a.

Next, another embodiment of the present invention will be described with reference toFIG. 4.FIG. 4is a diagram for explaining an embodiment of the reflector of the present invention.

Similar toFIG. 2Cor3C,FIG. 4is a schematic view showing a simplified shape of the reflector of the present invention and the bottom plate2a, as viewed from a transversal direction. In the drawing, the one-dot-chain line is the axial center3xof the linear light source3.

FIG. 4shows a cross-section of the reflector perpendicular to the display surface of the liquid crystal panel5and parallel to a horizontal direction (i.e., the longitudinal direction of the linear light source3) of the liquid crystal panel. The reflector (side wall) ofFIG. 4is an embodiment wherein the number of inclined surfaces is four. The inclined surfaces h1to h4are formed by line segments that touch the interior of a curve (not shown) such as a parabola (hereinafter, referred to curve used as a reference). Therefore, the inclination angles of the inclined surfaces h1to h4, . . . , and hn, that is, the angles between the inclined surfaces and a straight line parallel to the display surface of the liquid crystal panel5satisfy the following relationship.
θh1<θh2<θh3<θh4< . . . <θhn  Formula (1)

When the number of inclined surfaces is increased to infinite, the surfaces will be curve. Therefore, the figure of the inclined surface of the side wall (reflector) of the present invention may include a curve. In addition, as shown inFIG. 5, a curve such as a parabola may be reversed upside down so that the inclination angles satisfies the following relationship.
θh1>θh2>θh3>θh4> . . . >θhn  Formula (2)

In this case, the inclined surfaces are formed by line segments that touch the exterior of a curve such as a parabola.

The number of curves used as a reference may be more than one, and a plurality of identically or differently shaped curves may be used.

In addition, all the edges of the corner portions at interfaces of the inclined surfaces may be cut smooth so as to form a curve.

In addition, a curve may be divided at a predetermined proportion so as to form stepped side walls. In this case, the curve may be divided at a uniform proportion in both the height direction and the transversal direction and may be divided at mutually different proportions in the height and transversal directions. For example, when the angle between a tangential line of a curve and the bottom plate2ais small, the proportion of division may be increased.

Next, another embodiment of the present invention will be described with reference toFIG. 5.FIG. 5is a diagram for explaining an embodiment of the reflector of the present invention.

Similar toFIG. 2Cor3C,FIG. 5is a schematic view showing a simplified shape of the reflector of the present invention and the bottom plate2a, as viewed from a transversal direction. In the drawing, the one-dot-chain line is the axial center3xof the linear light source3.FIG. 5shows an embodiment wherein the curve such as a parabola used as a reference is reversed upside down from that ofFIG. 4. That is, the inclination angles satisfy the following relationship.
θm1>θm2>θm3>θm4> . . . >θmn  Formula (3)

Next, another embodiment of the present invention will be described with reference toFIG. 6.FIG. 6is a diagram for explaining an embodiment of the reflector of the present invention.

Similar toFIG. 2Cor3C,FIG. 6is a schematic view showing a simplified shape of the reflector of the present invention and the bottom plate2afrom a transversal direction.

As shown inFIG. 6, when a reflector has three or more inclined surfaces, the inclination angles of the inclined surfaces satisfy the following relationship, in which the inclined surfaces are denoted, in order from the bottom surface (bottom plate2a), by q0, . . . , qk, qk+1, qk+2, . . . , qn (n and k are integer, 0≦k<n).
θk<θk+1 and θk+1>θk+2  Formula (4); or
θk>θk+1 and θk+1<θk+2  Formula (5)

That is, in the embodiment ofFIG. 4or5, the inclination angles of the reflecting surfaces of the reflector are increased or decreased monotonously as they went upward.

However, in the embodiment ofFIG. 6, the inclination angles of the reflecting surfaces of the reflector are composed of irregular inclination angles rather than increasing or decreasing monotonously. Therefore, the reflector is formed by uneven or irregular surfaces.

In addition, the edges of the uneven portions at interfaces of the reflecting surfaces may be cut smooth so as to form a curve.

Next, another embodiment of the present invention will be described. In the embodiments described above, all the reflectors were constructed by a plurality of inclined reflecting surfaces having a plurality of inclination angles with respect to the longitudinal direction of the linear light source. However, in another embodiment of the present invention, an inclined structure is provided so that it inclines perpendicularly with respect to the linear light source at a side surface thereof.

FIG. 7is a diagram showing a reflector portion of the embodiment ofFIG. 4, as viewed from the above. For the sake of explanation, the liquid crystal panel portion is not shown. In addition, only two linear light sources and the left end portions are shown.

FIG. 7is a schematic view of the reflector shown inFIG. 4, as viewed from the above. The inclined surfaces h1to h4are erected from the bottom plate2aand reach the liquid crystal panel. In the drawing, h0represents a portion of the liquid crystal panel in contact with a frame portion (outside the effective display area).

Next, another embodiment of the present invention will be described with reference toFIGS. 8and9.FIGS. 8 and 9are diagrams for explaining an embodiment of the reflector of the present invention.

Unlike the reflector of the embodiments described above wherein an inclined structure is provided so as to reflect light beams in the longitudinal direction of the linear light source; in the embodiment ofFIGS. 8 and 9, however, an inclined structure is provided so as to reflect light beams in a direction perpendicular to the longitudinal direction of the linear light source.

InFIG. 8, a triangular pyramid-shaped reflector is provided on the side wall2cin parallel to and between the two parallel, linear light sources3. In addition, inFIG. 8, for the sake of explanation, only two linear light sources are shown, and the bottom plate2aand the reflector b1are shown up to intermediate portions thereof.

The number of linear light sources3and the number of reflectors b1are arbitrary. In addition, the reflector b1may extend to the other end (not shown) or may extend only to an intermediate position.

In the reflector ofFIG. 9, an inclined structure in a direction parallel to the linear light sources3is provided on the inclined surface of the one of the above-mentioned embodiments, e.g. the embodiment shown inFIG. 4.

By providing such an inclined structure, light beams emitted from the linear light sources can be effectively reflected in a direction perpendicular to the longitudinal direction of the linear light source3in addition to in the longitudinal direction. As a result, the luminance level at the end of the effective display area can be increased further.

Incidentally, inFIG. 9, although only one linear light source3is shown for easy understanding of the structure of the reflector b2, it is needless to say that an identical linear light source3is provided on the left side. Similarly, the bottom plate2aand the linear light source3are shown up to intermediate portions thereof.

The number of linear light sources3and the number of reflectors b2are arbitrary. In addition, the reflector b2may extend to the other end (not shown) or may extend only to an intermediate position.

In this way, according to the embodiments ofFIGS. 4 to 9, the luminance level at the ends of the effective display area can be increased close to the luminance level in the inside thereof; therefore, it is possible to reduce or eliminate the decrease of the luminance level at the ends of the liquid crystal panel.

That is, in a thin liquid crystal display device, a decrease of the luminance level of the liquid crystal panel at both ends in the longitudinal direction of the linear light source can be reduced, thereby improving the light emission quality. In addition, frames can be narrowed.

In the embodiments described above, the reflector has the same shape over the entire portions of the liquid crystal panel. However, the reflector may have different shapes in a direction perpendicular to the axial direction of the linear light source so that the shape in a central portion of the liquid crystal panel is different from the shape at both ends of the liquid crystal panel. In addition, the shape of the reflector may change in an alternating manner or in a specified order.

In the embodiments described above, the reflecting surface of the reflector is usually subjected to surface treatment such as mirror-finishing or polishing in order to increase reflection efficiency. However, the surface may be roughened by means of blaster for the purpose of providing both light reflection and diffusion properties so that the luminance distribution of the liquid crystal panel becomes more uniform. In this case, after roughening the surface, a reflecting film may be formed thereon to increase reflectance.

While embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and the invention is not limited by the embodiments. It will be apparent to those persons skilled in the art that various changes can be made therein without departing from the spirit and scope of the present invention.

Next, another embodiment of the present invention will be described with reference toFIG. 10.FIG. 10is a diagram showing an embodiment of the reflector of the present invention as viewed from the side of an irradiation surface of a backlight unit (i.e., from the display surface of the liquid crystal panel5). In this embodiment, the reflecting portion2c0is provided in the side surface2cof the frame2and valleys2c1are formed in the reflecting portion2c0. The valleys2c1are formed in the reflecting portion2c0provided in the side surface2cof the frame2so as to surround the portions where the electrode portions3aof the linear light sources3are provided. In this embodiment, the valleys2c1(hereinafter, referred to as valley-shaped reflecting portions) are provided to correspond to each of the plural linear light sources3. As is obvious fromFIG. 10, the valley-shaped reflecting portions2c1are semi-elliptical as viewed from the display surface side of the liquid crystal panel5. In other words, in this embodiment, the circumferences of the reflecting portions2c0, provided in the side surface2cof the frame2, around the electrode portions3aof the linear light sources3are bent three-dimensionally.

The valley-shaped reflecting portion2c1can provide a light focusing effect thanks to its bent shape so that light beams are focused to the circumferences of the electrode portions3a. The shape of the valleys2c1may be a spheroid, a paraboloid, or a cylinder, for example. The valleys2c1may also be formed by combining these plural shapes or approximating any one of these plural shapes by plural planes. According to this embodiment, light beams emitted from the linear light sources3are incident to the valley-shaped reflecting portions2c1and focused onto the circumferences of the electrode portions3a, whereby it is possible to prevent lowering of the luminance level at the electrode portions3a.

Next, another embodiment of the present invention will be described with reference toFIG. 11.FIG. 11is a diagram showing an embodiment of the reflector of the present invention. Specifically,FIG. 11Ais a view viewed from an irradiation surface of a backlight unit (i.e., from the side of the display surface of the liquid crystal panel5).FIG. 11Bis a view viewed from the side surface of the backlight unit and shows a cross-section of the reflector perpendicular to the display surface of the liquid crystal panel5or parallel to the horizontal direction (the longitudinal direction of the linear light source3) of the liquid crystal panel, taken along the central axis of the linear light source3. In this embodiment, in addition to the arrangement of the embodiment ofFIG. 10, convex-shaped reflecting elements2c2is provided above the electrode portions3aof the linear light sources3. The convex-shaped reflecting elements2c2are provided at portions of the valley-shaped reflecting portions2c1corresponding to the upper portions of the electrode portions3aof the linear light sources3and are convex toward the liquid crystal panel5.

The convex-shaped reflecting elements2c2can provide an effect of recovering the luminance level at the circumferences of the electrode portions3aby reflecting light beams to an irradiation surface around the electrode portions3a. The shape of the convex-shaped reflecting elements2c2is formed by at least one flat surface or at least one curved surface, for example. The convex-shaped reflecting elements may be inclined with respect to the bottom portion2aand may be curved surfaces having an inflection point. The convex-shaped reflecting elements2c2may have a thickness of 0.3 mm or more in order to maintain strength. A gap between the electrode portion3aand the reflecting element2c2may be 0.2 mm or more in order to prevent collision of the linear light sources3and the convex-shaped reflecting elements2c2, thereby preventing damage of the linear light sources3or the valley-shaped reflecting portions2c1. The convex-shaped reflecting elements2c2can reflect light beams emitted from the linear light sources3toward above the electrode portions3a, thereby preventing lowering of the luminance level due to the electrode portions3a.

Next, another embodiment of the present invention will be described with reference toFIG. 12.FIGS. 12A and 12Bare diagrams showing an embodiment of the reflector of the present invention as viewed from the side surface of the backlight unit and shows a cross-section of the reflector perpendicular to the display surface of the liquid crystal panel5and parallel to the horizontal direction (the longitudinal direction of the linear light source3) of the liquid crystal panel, taken along the central axis of the linear light source3.FIG. 12Cshows a cross-section of the reflector perpendicular to the display surface of the liquid crystal panel5or parallel to the vertical direction (a direction vertical to the longitudinal direction of the linear light source3) of the liquid crystal panel. In this embodiment, arch-shaped reflecting elements2cA are provided in the reflecting portions2c0so as to cover the electrode portions3aof the linear light sources3. As is obvious fromFIG. 12C, the arch-shaped reflecting element2cA has an arch-shaped or trapezoidal cross-section that is perpendicular to the display surface of the liquid crystal panel5and parallel to the vertical direction of the liquid crystal panel. The arch-shaped reflecting element2cA has an upper surface2cA1and side surfaces2cA2.

The arch-shaped reflecting elements2cA can provide an effect of recovering the luminance level at the circumferences of the electrode portions3aby reflecting light beams incident from the sides of the electrode portions to an irradiation surface. The arch-shaped reflecting elements2cA can reflect light beams emitted from the linear light sources3and incident to the electrode portions3atoward above the circumferences of the electrode portions3a, thereby preventing lowering of the luminance level at the circumferences of the electrode portions3a. To prevent the luminance level at both ends of the backlight unit from lowering, it is necessary to set the inclination of the reflecting portion2c0to about 30 degrees to about 80 degrees. However, if the inclination is too steep, there is a problem that the electrode portions3aare visible. Conventionally, in order to prevent the electrodes from entering the effective display area, the linear light source3is made long for example; however, this raises a problem that the size of the backlight unit will be longer. According to this embodiment, when the backlight unit has a thickness of 10 mm or more, even if the electrodes3aare exposed to the outside from the arch-shaped reflecting elements2cA by a length of about 3 mm, it is possible to keep uniform luminance.

As shown inFIG. 12B, the arch-shaped reflecting elements2cA have a curved, upper surface2cA1viewed in a cross-section that is perpendicular to the display surface of the liquid crystal panel5and parallel to the horizontal direction of the liquid crystal panel. In this embodiment, the upper surface2cA1has a reclined S-shape. As shown inFIG. 12C, the arch-shaped reflecting elements2cA have an arch shape or a trapezoidal shape, and the side surfaces2cA2are inclined with respect to the bottom portion2aof the frame2. The shape of the arch-shaped reflecting elements2cA is formed by at least one flat surface or at least one curved surface, for example.

A gap between the arch-shaped reflecting element2cA and the linear light source3may be 0.2 mm or more in order to prevent collision of the linear light sources3and the reflecting elements2c2, thereby preventing damage of the linear light sources3or the valley-shaped reflecting portions2c1and/or the reflecting portions2c0on the side surfaces2cof the frame. In addition, it is possible to prevent interference due to thermal expansion of the valley-shaped reflecting portions2c1and/or the reflecting portions2c0. Furthermore, since the arch-shaped reflecting elements2cA are inclined, incident light beams can be effectively reflected toward above the electrode portions3a, thereby preventing lowering of the luminance level at the electrode portions3a.

Next, another embodiment of the present invention will be described with reference toFIG. 13.FIG. 13is a diagram showing an embodiment of the reflector of the present invention as viewed from an irradiation surface of the backlight unit. As shown in the drawing, an interface2cB between the reflecting portion2c0on the frame side surface2cand the valley-shaped reflecting portion2c1and an interface2cB between adjacent valley-shaped reflecting portions2c1are chamfered to form chamfered portions R, and to connect these portions smoothly. The interfaces may be connected smoothly to form a part of a spherical surface, a cylindrical surface, or other curved surfaces. According to the places, the chamfered portions R may have a radius of curvature of about 0.3 mm to about 5 mm. However, the radius of curvature of the chamfered portions R is not limited to this range. If the interface2cB of the reflecting portion2c0on the frame side surface2cand the valley-shaped reflecting portion2c1and the interface2cB of adjacent valley-shaped reflecting portions2c1are not smoothly formed, the luminance distribution of the reflecting light beams may change abruptly at these interfaces. As a result, these interfaces2cB are visible on the irradiation surface. According to this embodiment, by forming these interfaces2cB smoothly, it is possible to prevent abrupt change of the luminance level on the irradiation surface, thereby preventing occurrence of luminance unevenness. Therefore, in this embodiment, it is possible to provide improved luminance evenness when images displayed on the display surface of the liquid crystal panel5are observed by the human eyes.

Next, another embodiment of the present invention will be described with reference toFIG. 14.FIG. 14is a diagram showing an embodiment of the reflector of the present invention as viewed from an irradiation surface of the backlight unit and is a schematic view showing a simplified shape of the reflector of this embodiment. In the embodiments described above, there is a possibility that sharp edges may be formed at intersection of the adjacent valley-shaped reflecting portions2c1. Therefore, when an operator mounts the reflecting portions2c0by hand of the operator during assembly of a backlight unit, there is a danger that the sharp edges may hurt the operator. In this embodiment, the sharp edges are cut to have a flat surface, thereby ensuring safety of the operator. That is, in this embodiment, the shape of the intersection of the adjacent valley-shaped reflecting portions2c1face the central portion of the frame2is designed into a straight line shape2c4as viewed from the display surface side of the liquid crystal panel5. In the example ofFIG. 14, the intersection is shaped as straight line shaped; however, the intersection may be designed into an arc shape that is convex to the center of the frame2. In addition, the intersection may be chamfered to form chamfered portions R.

In the embodiments described above, the valley-shaped reflecting portions2c1and the arch-shaped reflecting elements2cA have the same shape over the entire portions of the liquid crystal panel. However, they may have different shapes in a direction perpendicular to the axial direction of the linear light source so that the shape in a central portion of the liquid crystal panel is different from the shape at both ends of the liquid crystal panel. In addition, the shape of the reflecting portions and elements may change in an alternating manner or in an arbitrary order.

In the embodiments described above, the valley-shaped reflecting portions2c1and the arch-shaped reflecting elements2cA are usually constructed by a reflective diffusion sheet or coat in order to increase reflection efficiency. However, the surface may be subjected to surface treatment such as mirror-finishing or polishing for providing a high glossiness or roughened by means of blaster for the purpose of providing light diffusion properties so that the luminance distribution of the liquid crystal panel becomes more uniform. In this case, after roughening the surface, a reflecting film may be formed thereon to increase reflectance.