DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] The preferred embodiment of the present invention will be described below with reference to the accompanying drawings. Throughout the figures, the same reference numerals or characters may be used to refer to identical or similar elements.

[0035] Reference is first made to FIGS. 1 - 3 illustrating a liquid crystal display (LCD) X 1 according to a first embodiment of the present invention. As shown in FIGS. 1 and 2 , the LCD X 1 includes a liquid crystal display panel 1 , a light guide 2 , a point light source 3 and a wiring board 4 . The upper (front) surface of the liquid crystal display panel 1 is entirely covered by the light guide 2 , while the lower (rear) surface of the panel 1 is attached to the board 4 . The light source 3 is mounted on the board 4 .

[0036] As shown in FIG. 2 , the LC panel 1 includes a first glass plate 10 a, a second glass plate 10 b, a sealing member 11 , liquid crystal 12 , a first polarizing plate 13 a, a second polarizing plate 13 b, and a reflector 14 . The liquid crystal 12 is contained between the first and the second glass plates 10 a, 10 b by the sealing member 11 . The first polarizing plate 13 a is held in contact with the front surface of the first glass plate 10 a, while the second polarizing plate 13 b is held in contact with the rear surface of the second glass plate 10 b. The reflector 14 is held in contact with the rear surface of the second polarizing plate 13 b.

[0037] As shown in FIG. 3 , the first glass plate 10 a is provided, in its rear surface, with a plurality of first transparent electrodes 15 a each of which extends in D 1 -direction. The transparent electrodes 15 a are arranged at regular intervals in D 2 -direction perpendicular to the D 1 -direction. Similarly, the second glass plate 10 b is provided, at its front surface, with a plurality of second transparent electrodes 15 b each of which extends in the D 2 -direction. The second electrodes 15 b are arranged at regular intervals in the D 1 -direction. Thus, the first and the second transparent electrodes 15 a, 15 b cross each other, thereby providing a plurality of pixels for displaying desired images (“passive matrix”). As shown in FIG. 2 , the first electrodes 15 a are covered by a first alignment layer 16 a, while the second electrodes 15 b are covered by a second alignment layer 16 b.

[0038] The first and the second polarizing plates 13 a, 13 b allow the passage of light only when the light oscillates in a particular direction. For instance, the first polarizing plate 13 a may allow the passage of light oscillating in a horizontal direction, while the second polarizing plate may allow the passage of light oscillating in a vertical direction.

[0039] The light guide 2 , as shown in FIGS. 1 and 2 , includes a main body 20 and a light inlet section 21 , wherein the former entirely covers the front surface of the panel 1 , while the latter partially covers a side surface of the panel 1 . The main body 20 and the light inlet section 21 is formed integral with each other by molding a transparent resin material such as polycarbonate or polymethyl methacrylate (PMMA).

[0040] The main body 20 is provided with a flat, rear surface 23 and a non-flat front surface 24 . The front surface 24 is formed with a plurality of undulations 25 each of which uniformly extends in a direction (in FIG. 1 , Y-direction). Each undulation 25 is defined by two surfaces: a first slant surface 25 a and a second slant surface 25 b which is steeper than the first slant surface. Thus, as shown in FIG. 2 , each undulation 25 has a generally triangular cross section.

[0041] The light inlet section 21 , as stated above, partially covers a side surface of the panel 1 , thereby projecting toward the board 4 beyond the rear surface 23 of the main body 20 (see FIGS. 1 and 2 ). The inlet section 21 is provided with a slant surface 21 a facing the board 4 , and with three side surfaces perpendicular to the board 4 , namely, a first side surface 21 b, a second side surface 21 d and a third side surface 21 e. The first side surface 21 b is arranged in parallel to the third side surface 21 e. As viewed vertically in FIG. 1 , the length of the first side surface 21 b is greater than that of the third side surface 21 e. The second side surface 21 d has a generally trapezoidal configuration.

[0042] The slant surface 21 a of the inlet section 21 is formed with a plurality of grooves 21 c for reflecting light. Each groove 21 c extends perpendicularly to the longitudinal direction of the slant surface 21 a. In the illustrated example, the groove 21 c has a V-shaped cross section. The intervals between the grooves 21 c are not constant, but become shorter as the grooves 21 c are arranged closer to the third side surface 21 e.

[0043] In the illustrated embodiment, the grooves 21 c are formed only in the slant surface 21 a. However, they may also be formed in the second side surface 21 d or third side surface 21 e. Further, instead of the grooves 21 c, cone-shaped or spherical recesses or protrusions may be formed. Alternatively, the side surfaces 21 a, 21 d and 21 e may be entirely covered by a single reflecting layer, or partially covered by a plurality of reflecting pieces. Such a reflecting layer or reflecting pieces may be provided by applying white paint to the above-mentioned side surfaces.

[0044] The light source 3 is provided with a light emitting surface 3 a facing the first side surface 21 b of the light inlet section 21 . The light source 3 includes a light-emitting diode (LED) for example.

[0045] Though not illustrated in the figures, the wiring board 4 is provided with circuits necessary for driving the LCD panel 1 and the light source 3 . The circuits may include drive ICs, a connector, etc.

[0046] According to the first embodiment described above, the LCD panel 1 and the light source 3 are mounted on the same wiring board 4 . In this manner, advantageously, there is no need to prepare an additional wiring board used specifically for mounting the light source 3 . Another advantage is that the circuit for the light source 3 and the circuit for the LCD panel 1 can be simultaneously formed on the board 4 .

[0047] The function of the LCD X 1 will now be described. In operation, the light source 3 emits light from the light emitting surface 3 a. This light enters the light inlet section 21 of the light guide 2 via the first side surface 21 b. Then, the light propagates through the inlet section 21 , during which the light may be reflected on the surfaces 21 a, 21 d and 21 e. When the light strikes upon the slant surface 21 a, it may be reflected by the grooves 21 c and directed in the forward direction of the LCD X 1 (Z-direction in FIG. 1 ). Then, the forward light will reach the rectangular reflecting surface 26 arranged above the slant surface 21 a. The reflecting surface 26 directs the forward light to the main body 20 of the light guide 2 .

[0048] In the LCD X 1 , as shown in FIG. 1 , the slant surface 21 a of the light inlet section 21 is held in non-parallel relation to the normal direction of the light emitting surface 3 a of the light source 3 . In addition, the space or pitch between the light-reflecting grooves 21 c formed in the surface 21 a is made shorter as the grooves are positioned farther from the light source 3 . Due to these features, the light from the light source 3 is reflected forward (Z-direction) less frequently by the grooves 21 c at places closer to the light source than at places farther from the light source. However, the amount of light reaching the closer places is greater than the amount of light reaching the farther places. Thus, the amount of light reflected forward by the grooves 21 c can be substantially equalized over the slant surface 21 a. As a result, the light emitted from the light source 3 is uniformly led into the main body 20 from the light inlet section 21 .

[0049] After entering the main body 20 , the light will propagate through the main body 20 toward the side surface 27 (see FIG. 2 ) which is opposite to the reflecting surface 26 . During the travel to the side surface 27 , as shown in FIG. 2 , the light may be totally reflected by the rear surface 23 or the front surface 24 . However, when the light strikes on the rear surface 23 at an angle smaller than the critical angle, the light passes through the surface 23 and reaches the first polarizing plate 13 a of the LCD panel 1 . The polarizing plate 13 a filters the light. Specifically, the polarizing plate 13 a may allow the passage of only the horizontally oscillating light.

[0050] Thereafter, the direction of the oscillation of the light is changed by 90° by the twist in the liquid crystal 12 , which may render the light to oscillate vertically. This light passes through the second polarizing plate 13 b and is reflected on the reflector 14 . Then, the light passes through the second polarizing plate 13 b again, and is rotated through 90° by the liquid crystal 12 , to become horizontally oscillating light. Then, the light passes through the first polarizing plate 13 a and the main body 20 , thereby going out from the LCD Xl in Z-direction shown in FIG. 1 .

[0051] To display a desired image, voltage is applied to the selected pixels (intersections of the first electrodes 15 a and the second electrodes 15 b ). When a voltage is applied to a pixel, the oscillating direction of the light passing the pixel does not change. As a result, the light filtered by the first polarizing plate 13 a cannot pass through the second polarizing plate 13 b, and the light filtered by the second polarizing plate 13 b cannot pass through the first polarizing plate 13 a. In either way, the light passing the voltage-applied pixel will not go out of the LCD 1 , which causes the pixel to appear black.

[0052] FIG. 4 shows an LCD X 2 according to a second embodiment of the present invention. The LCD X 2 is basically similar to the LCD X 1 of the first embodiment except for the following differences.

[0053] Specifically, in the LCD X 2 , use is made of two light sources 3 located at the respective longitudinal ends of a light inlet section 51 of the light guide 2 . Accordingly, the inlet section 51 has a configuration different from that of the inlet section 21 of the first embodiment. As shown in FIG. 4 , the inlet section 51 has an elongated rear surface 51 a whose central portion is spaced from the wiring board 4 to a greater extent than any other portion. As proceeding from the central portion toward the longitudinal ends, the rear surface 51 a comes closer to the board 4 , to finally touch the board 4 at the ends. This design divides the rear surface 51 into two symmetrical slopes each of which is formed with a plurality of light-reflecting grooves 51 c. In each slope, the grooves 51 c are arranged more densely as they are closer to the central portion of the rear surface 51 a, so that uniform illumination is obtained over the rear surface 51 a.

[0054] FIGS. 5 and 6 show an LCD X 3 according to a third embodiment of the present invention. In the LCD X 3 , use is made of a light guide 2 consisting of separately prepared main body 20 and light inlet section 61 . The main body 20 and the inlet section 61 may be made of the same transparent material (polycarbonate, PMMA, etc.) or different transparent materials. The inlet section 61 , as shown in FIG. 5 , has a uniformly elongated configuration having a rectangular cross section. The inlet section 61 includes four rectangular side surfaces 61 a, 61 d, 61 e and 61 f, and two rectangular end surfaces 61 b and 61 g. The end surface 61 b is held in facing relation to the light emitting surface 3 a of the light source 3 . The light emitted from the light source 3 may be reflected on the above-mentioned side surfaces or end surface, and is eventually led into main body 20 from the inlet section 61 via the side surface 61 f. To achieve efficient and uniform guiding of the light into the main body 20 , the side surfaces 61 a, 61 d, 61 e and the end surface 61 g may be covered by a reflective layer. This layer may entirely or partially cover each of these surfaces. Instead of using such a reflective layer, light reflecting recesses or projections may be formed in the above surfaces.

[0055] FIGS. 7 and 8 show an LCD X 4 according to a fourth embodiment of the present invention. As illustrated, the light guide 2 includes a main body 20 , a light inlet section 71 and a connecting section 72 . The inlet section 71 , arranged on the wiring board 4 , is a uniformly elongated transparent bar having a rectangular cross section. The connecting section 72 extends obliquely with respect to the board 4 (see FIG. 8 ) to connect the light inlet section 71 to the main body 20 which is located ahead of (or above, in FIG. 8 ) the inlet section 71 . The LCD X 4 includes three light sources 3 whose light emitting surfaces 3 a are held in facing relation to a side surface 71 d of the inlet section 71 . As shown in FIG. 8 , the light emitted from the light sources 3 is led to the main body 20 from the inlet section 71 via the connecting section 72 . The three light sources 3 may be replaced by a single elongated light source such as a cold cathode tube.

[0056] FIG. 9 shows an LCD X 5 according to a fifth embodiment of the present invention. The light guide 2 of the LCD X 5 is a hybrid of the light guide 2 of the LCD X 1 ( FIG. 1 ) and the light guide 2 of the LCD X 4 ( FIG. 7 ). Specifically, as seen from FIGS. 9 and 1 , the light inlet section 81 of the LCD X 5 is substantially the same as the light inlet section 21 of the LCD X 1 , though their postures relative to the wiring board 4 are different. As seen from FIGS. 9 and 7 , the connecting section 82 and the main body 20 of the LCD X 5 are similar to the counterparts of the LCD X 4 .

[0057] As shown in FIG. 9 , the light inlet section 81 of the LCD X 5 includes a slant surface 81 a formed with a plurality of light-reflecting grooves 81 b. The slant surface 81 a is held in non-facing relation to the board 4 . The inlet section 81 has a rectangular end surface to be held in contact with the light source 3 .

[0058] In the above-described first to fifth embodiments, the light source 3 is mounted on the wiring board 4 together with the LCD panel 1 for achieving cost reduction and improving production efficiency. The present invention, however, is not limited to such a “one-board design.” As will be described below, the light source 3 may be detached from the board 4 .

[0059] FIGS. 10 and 11 show an LCD X 6 according to a sixth embodiment of the present invention. The LCD X 6 includes an LCD panel 1 , a light guide 2 , a light source 3 and a wiring board 4 . The LCD panel 1 is mounted on the board 4 . The panel 1 , as in the previously described LCDs, includes a first glass plate 10 a, a second glass plate 10 b, a sealing member 11 , liquid crystal 12 , a first polarizing plate 13 a, a second polarizing plate 13 b, and a reflector 14 . The first glass plate 10 a is provided, in its rear surface, with a plurality of first transparent electrodes 15 a, while the second glass plate 10 b is provided, at its front surface, with a plurality of second transparent electrodes 15 b. The first electrodes 15 a are covered by a first alignment layer 16 a, while the second electrodes 15 b are covered by a second alignment layer 16 b.

[0060] The light guide 2 includes a main body 20 and a light inlet section 21 which is formed integral with the main body 20 . The front surface 24 of the main body 20 is provided with a plurality of triangular projections 25 each of which is defined by a relatively gentle slope 25 a and a relatively steep slope 25 b. The light inlet section 21 , as opposed to the counterparts of the LCD X 1 -X 5 , is completely spaced from the board 4 . Accordingly, the light source 3 , which is held in contact with the inlet section 21 (see FIG. 3 ), is detached from the board 4 . Though not illustrated, the light source 3 is mounted on a wiring board which is prepared separately from the depicted board 4 .

[0061] As shown in FIG. 11 , the light inlet section 21 includes a slant surface 21 a, an end surface 21 b contacting the light-emitting surface 3 a of the light source 3 , and a trapezoidal front surface 21 d. The inlet section 21 also includes a trapezoidal rear surface (not shown) which is opposite and identical to the front surface 21 d . The slant surface 21 a and the end surface 21 b intersect at a predetermined angle θ smaller than 90°. The slant surface 21 a is formed with a plurality of light-reflecting grooves 21 c. In this embodiment again, the density of the grooves 21 c is rendered greater as the distance from the light source 3 becomes greater.

[0062] FIGS. 12 - 15 show examples of a modified light inlet section 21 . The light inlet section 21 of FIG. 12 is substantially the same as the light inlet section 51 shown in FIG. 4 . The light inlet section 21 of FIG. 13 includes a smooth slant surface 21 a upon which a plurality of light-reflecting pieces 22 a are provided in place of light-reflecting grooves as shown in FIG. 12 . The light inlet section 21 of FIG. 14 is formed with a plurality of semi-spherical light reflecting recesses 22 b in the slant surface 21 a. The light inlet section 21 of FIG. 15 is formed with a plurality of light reflecting projections 22 c in the slant surface 21 a.

[0063] Reference is now made to FIG. 16 showing a color LCD X 7 according to a seventh embodiment of the present invention. The LCD X 7 includes an LCD panel 1 , a light guide 2 and a light source 3 . The light guide 2 is attached to the front surface of the panel 1 . The light source 3 may be held in facing relation to the light inlet surface 27 a of the light guide 3 . The light source may be provided with a single or plurality of LEDs, or a single cold-cathode tube.

[0064] As shown in FIG. 16 , the LCD panel 1 includes a first transparent plate 10 a, a second transparent plate 10 b, a sealing member 11 , liquid crystal 12 , a first polarizing plate 13 a, a second polarizing plate 13 b and a reflector 14 . The first transparent plate 10 a is provided with three kinds of color filters 8 ( 8 R, 8 G, 8 B) and a black matrix 9 . Further, the first transparent plate 10 a is provided with first transparent electrodes 15 a and a first alignment layer 16 a. Likewise, the second transparent plate 10 b is provided with second transparent electrodes 15 b and a second alignment layer 16 b. The illustrated LCD panel 1 employs the active matrix, in which each liquid crystal cell is provided with a thin film transistor (TFT) for maintaining the voltage applied to the cell.

[0065] In the light guide 2 of the seventh embodiment again, the rear surface is flat, whereas the front surface is formed with a plurality of projections 25 each of which defined by a first and a second slopes 25 a, 25 b. The distance (or pitch) between the most retreated points 19 in the front surface of the light guide 2 is constant (about 300 μm or less).

[0066] In each of the first to the sixth embodiments described above, all the projections 25 of the light guide 2 are made identical. In the seventh embodiment, however, the respective projections 25 have different configurations so that light will be reflected differently by the projections 25 , thereby being uniformly distributed over the front surface of the LCD panel 1 . Specifically, as shown in FIG. 16 , the depression angles θ1−θn associated with the respective projections 25 are determined such that θ1<θ2< . . . <θn, whereby the second slopes 25 b of the respective projections 25 become steeper as they are located closer to the second side surface 27 b than to the first side surface (light inlet surface) 27 a.

[0067] In the above embodiment, the depression angles θ1−θn become greater gradually. The present invention, however, is not limited to this. For instance, the depression angles may be determined such that θ1=θ2<θ3=θ4<. . . <θn−1=θn.

[0068] FIG. 17 shows an example of a modified light guide 2 used for the LCD X 7 . In the illustrated light guide 2 , the depths D 1 -Dn of the valleys defined between the projections 25 are determined such that D 1 <D 2 <. . . <Dn−1<Dn (the single-dot chain line H is a reference line parallel to the rear surface of the light guide 2 ). With such an arrangement, the light emitted from the light source 3 can properly strike upon not only the slopes of the projections 25 near the light source 3 , but also the slopes of the projections 25 which are relatively far from the light source 3 . Consequently, the emitted light will be uniformly reflected toward the LCD panel 1 (see FIG. 16 ).

[0069] In the example shown in FIG. 17 , the apexes of the projections 25 are spaced from the imaginary reference line H by different degrees except for the projection 25 closest to the light source 3 . According to the present invention, however, all the apexes of the projections 25 may touch the reference line H, while the depths D 1 -Dn maintain the above-mentioned relation.

[0070] FIG. 18 shows another example of a modified light guide 2 used for the LCD X 7 . In the illustrated guide 2 , the pitches between the most retreated points 19 on the front surface of the guide 2 are determined such that P 1 >P 2 >. . . >Pn, which causes the density of the projections 25 to increase as the projections 25 are located closer to the second side surface 27 b than to the light inlet surface 27 a of the guide 2 . With the use of such a light guide 2 , the light emitted from the light source 3 is properly led to the LCD panel 1 , to uniformly illuminate the panel 1 .

[0071] The present invention being thus described, it is obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the present invention, and all such modifications as would be obvious to those skilled in the art are intended to be included within the scope of the following claims.