Light guide plate, display device, and electronic apparatus with display

Disclosed herein is a light guide plate including: a side end face on which light from a light source is incident; an incoming part which forms the side end face and by which the light coming in through the side end face is guided; a principal surface which is formed in a direction perpendicular to the side end face and through which the light guided by the incoming part is let go out; and a main body part which forms the principal surface and which is continuous with the incoming part on the opposite side from the side end face.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light guide plate by which light being incident from a light source is let go out in a direction perpendicular to the direction of incidence, a display device, and an electronic apparatus with a display. More particularly, the invention relates to a technology by which the light guide efficiency of a light guide plate can be enhanced.

2. Description of the Related Art

Hitherto, there has been known a light guide plate which receives light incident from a light source, guides the incident light and lets the light go out in a direction perpendicular to the direction of incidence. Besides, such a guide plate has been widely used, for example, as an illuminating section (back light, etc.) in a liquid crystal display device.

FIG. 14is a side view of a liquid crystal display device101using a light guide plate121according to related art.

As shown inFIG. 14, the liquid crystal display device101includes a light source191, an LCD (liquid crystal display)111in which the contents being displayed on the front side (the upper side inFIG. 14) thereof is made clearly visible by irradiation with the light of the light source191, and a light guide plate121by which the light from the light source191is guided to the back side (the lower side inFIG. 14) of the LCD111. Incidentally, a polarizing plate113is disposed on the front side of the LCD111, and a polarizing plate114is disposed on the back side of the LCD111. In addition, a lens sheet116and a diffuser118are sequentially arranged between the polarizing plate114and the light guide plate121. Further, a back reflector194is disposed on the back side of the light guide plate121.

In the liquid crystal display device101as above, the light source191is disposed to face a side end face131aof an incoming part131of the light guide plate121. Therefore, upon incidence on the side end face131a, the light from the light source191is guided through the incoming part131into a main body part132, and is let go out from a flat principal surface132atoward the back surface of the LCD111. In other words, the light guide plate121constitutes a back light for the LCD111.

Here, for making the liquid crystal display device101smaller in size, the light guide plate121is reduced in thickness at the main body part132located on the back side of the LCD111. On the other hand, for securing a sufficient amount of light, the thickness of the incoming part131is set large on the side of the side end face131a, in conformity with the light source191which is comparatively large in size. Therefore, the front surface of the incoming part134has an inclined front surface133awhich is inclined from the side end face131atoward the principal surface132a. In addition, the back surfaces of the incoming part131and the main body part132constitute a flat back surface133b.

Thus, in the light guide plate121according to the related art, the thickness of the incoming part131on the side of the side end face131ais greater than the thickness of the main body part132, and both the parts are connected to each other through the inclined front surface133aand the flat back surface133b. Therefore, there has been a problem that light leaks through the inclined front surface133a, whereby the light guide efficiency of the light guide plate121is lowered.

FIGS. 15A and 15Billustrate the conditions of generation of light leakage due to the light guide plate121in the related art.

Incidentally,FIG. 15Aschematically illustrates the path of a ray of light coming from the light source191and entering the light guide plate121, whereasFIG. 15Billustrates simulational determination of various paths of rays of light from the light source191.

As shown inFIG. 15A, when a ray of light coming from the light source191and being incident on the incoming part131of the light guide plate121(a ray of light parallel to the principal surface132aof the main body part132) passes through the side end face131aand impinges on the inclined front surface133a(set at angle θ against the principal surface132a), the ray of light is reflected (at reflection angle θ) on the inclined front surface133a, and is then reflected (at reflection angle2θ) on the flat back surface133b. Thereafter, the ray of light impinges again on the inclined front surface133a; in this instance, if the angle of impingement on the inclined front surface133ais greater than a critical angle for total reflection, the light would leak through the inclined front surface133a.

FIG. 15Bshows the simulationally determined conditions of light leakage. As is seen from the figure, if the incoming part131is configured to have the inclined front surface133aand the flat back surface133b, much light leaks through the inclined front surface133a. According to the simulation results, it is seen that when the plate thickness at the side end face131ais 0.5 mm and the thickness of the main body part132is 0.25 mm, 26% of the incident light is lost through the inclined front surface133abefore reaching the principal surface132a, and the total light guide efficiency determined taking other losses also into account is as low as 64%. Incidentally, on the side of the flat back surface133b, the back reflector194for reflecting the leaking light is arranged, so that light leakage does not occur on this side.

In view of the foregoing, the present applicant has already proposed a technology by which the light guide efficiency of a light guide plate can be enhanced. In the technology, an incoming part, at a side end face opposed to a light source, of a light guide plate is split into a plurality of portions stacked in the thickness direction, these split portions are mutually staggered sideways along a direction parallel to a principal surface of the light guide plate by lateral light guide parts and flat light guide parts, and light is bent in the thickness direction and guided to a main body part of the light guide plate by a bent light guide part of which plain surfaces on opposite sides are substantially parallel to each other (refer to, for example, Japanese Patent Laid-Open No. 2006-351511, hereinafter referred to as Patent Document 1).

SUMMARY OF THE INVENTION

Even according to the technology disclosed in Patent Document 1, however, the leakage of light from the bent light guide part cannot be prevented perfectly, and, therefore, a further enhancement of the light guide efficiency of light guide plates is being requested.

Accordingly, there is a need for a technology by which the light guide efficiency of a light guide plate can be further enhanced.

According to one embodiment of the present invention, there is provided a light guide plate including: a side end face on which light from a light source is incident; an incoming part which forms the side end face and by which the light coming in through the side end face is guided; a principal surface which is formed in a direction perpendicular to the side end face and through which the light guided by the incoming part is let go out; and a main body part which forms the principal surface and which is continuous with the incoming part on the opposite side from the side end face; wherein the incoming part is so formed as to have a thickness on the side end face side greater than the thickness of the main body part, and has a bent light guide part by which the light coming in through the side end face outside the range of thickness of the main body part is guided into the range of thickness of the main body part while being changed in direction, the bent light guide part has an inclined front surface which is so inclined that a surface in a direction perpendicular to the side end face is continuous with the principal surface, and an inclined back surface inclined on the opposite side from the inclined front surface so as to be parallel to the inclined front surface; and a reflecting member is provided which is disposed along the outside of at least one of the inclined front surface and the inclined back surface and by which the light leaking from the bent light guide part is reflected toward the bent light guide part or the main body part.

According to another embodiment of the present invention, there is provided a display device including the above-mentioned light guide plate, a light source, and a display in which the contents being displayed are made clearly visible by irradiation (illumination) with the light of the light source.

According to a further embodiment of the present invention, there is provided an electronic apparatus with a display, including the above-mentioned light guide plate, a light source, a display in which the contents being displayed are made clearly visible by irradiation (illumination) with the light of the light source, and an electronic controller operable to electronically controlling the light source and the display.

Since the incoming part of the light guide plate is so formed that its thickness on the side of the side end face is greater than the thickness of the main body part of the light guide plate. Therefore, the thickness of the main body part opposed to the display can be made thinner, and the display device can be reduced in size, while securing a sufficient amount of light entering the incoming part through the side end face.

In addition, the bent light guide part has the inclined front surface which is so inclined that a surface in the direction perpendicular to the side end face is continuous with the principal surface of the main body part, and the inclined back surface inclined on the opposite side from the inclined front surface so as to be parallel to the inclined front surface. Therefore, the light reflected inside the bent light guide plate is unlikely to leak to the exterior of the bent light guide part.

Further, the light guide plate is provided with the reflecting member which is disposed along at least one of the inclined front surface and the inclined back surface and by which the light leaking from the bent light guide part is reflected toward the bent light guide part or the main body part. Therefore, the light leaking from the bent light guide part is reflected by the reflecting member, to enter the bent light guide part or the main body part. The light is thereafter let go out through the principal surface toward the display.

Thus, according to the embodiments of the present invention, the display device can be made smaller in size, and it is ensured that the light reflected in the bent light guide part of the light guide plate is unlikely to leak to the outside of the bent light guide part. Therefore, a light guide plate with an enhanced light guide efficiency can be realized. Further, the light leaking from the bent light guide part is reflected by the reflecting member, to again enter the bent light guide part or to enter the main body part. Accordingly, the light guide efficiency of the light guide plate is further enhanced.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, embodiments of the present invention will be described below referring to the drawings.

FIG. 1is a side view of a back irradiation type liquid crystal display device1(corresponding to the display device in the present invention) using a light guide plate21according to a first embodiment of the invention.

As shown inFIG. 1, the back irradiation type liquid crystal display device1has an LCD (liquid crystal display)11(corresponding to the display in the present invention) in which liquid crystals are sealed between a pair of glass plates. A polarizing plate13and a polarizing plate14are disposed on the front side (the upper side inFIG. 1) and the back side (the lower side inFIG. 1) of the LCD11.

In addition, a lens sheet16(corresponding to the lens member in the present invention) in which lenses being ridge-shaped in section are arrayed in the width direction is disposed so as to face the polarizing plate14. Further, a diffuser18is disposed on the back side of the lens sheet16, and a transparent light guide plate21for constituting a back light for the LCD11is disposed on the back side of the diffuser18. Furthermore, light sources91including LEDs (light emitting diodes) are disposed on the side of a side end face31aof the light guide plate21.

Here, the light guide plate21includes an incoming part31which forms the side end face31aand by which light coming in through the side end face31ais guided, and a main body part32which forms a principal surface32aand which is continuous with the incoming part31on the opposite side from the side end face31a. The thickness of the incoming part31on the side end face31aside is larger than the thickness of the main body part32; specifically, in the light guide plate21in the first embodiment, the thickness thereof on the side end face31aside is two times the thickness of the main body part32. In addition, the incoming part31has a bent light guide part33by which the light coming in through the side end face31aoutside the range of thickness of the main body part32is guided into the range of thickness of the main body part32while being changed in direction, and a flat light guide part35by which the light coming in through the side end face31awithin the range of thickness of the main body part32is guided into the range of thickness of the main body part32.

Therefore, the light from the light sources91enters the light guide plate21through the side end face31aof the light guide plate21, and is guided into the main body part32by the bent light guide part33and the flat light guide part35which constitute the incoming part31. Then, the light guided into the main body part32is let go out toward the LCD11through the principal surface32aformed in the direction perpendicular to the side end face31a. Incidentally, the perpendicular direction is not limited to the case where the angle formed between the side end face31aand the principal surface32ais 90°, and means a situation in which the side end face31aand the principal surface32aare in such a positional relationship that, for example, the light coming in from a lateral direction (through the side end face31a) is let go out in an upward direction (through the principal surface32a).

Thus, the light guide plate21of the first embodiment is so configured that the light coming from the light sources91disposed to face the side end face31aof the incoming part31is let go out through the principal surface32aof the main body part32while being changed in direction by about 90° from the direction of incidence. In addition, the thickness of the incoming part31on the side end face31aside is twice the thickness of the main body part32. Specifically, since the thickness of the incoming part31is set large on the side of the side end face31aon which the light from the light sources91is incident, it is possible to secure a large quantity of light entering the incoming part31through the side end face31a.

Further, the bent light guide part33has an inclined front surface33awhich is so inclined that a surface in the direction perpendicular to the side end face31ais continuous with the principal surface32a, and an inclined back surface33bwhich is inclined on the opposite side from the inclined front surface33aso as to be parallel to the inclined front surface33a. Therefore, the light entering the bent light guide part33is reflected between the inclined front surface33aand the inclined back surface33b, and is unlikely to leak to the exterior of the bent light guide part33. To be more specific, the light coming in through the side end face31aoutside the range of thickness of the main body part32is guided by the bent light guide part33into the main body part32while being changed in direction from the incidence direction into the range of thickness of the main body part32. On the other hand, the light coming in through the side end face31awithin the range of thickness of the main body part32is guided by the flat light guide part35into the range of thickness of the main body part32while remaining unchanged in direction.

Besides, near the bent light guide part33of the light guide plate21, a front reflecting member81(corresponding to the reflecting member in the present invention) is disposed along the outside of the inclined front surface33a. Therefore, the light leaking from the inclined front surface33ais reflected by the front reflecting member81toward the bent light guide part33or the main body part32. Furthermore, a back reflector94is disposed on the back side of the main body part32, so that the light leaking from the back surface of the main body part32is reflected by the back reflector94toward the main body part32.

Therefore, according to the liquid crystal display device1shown inFIG. 1, the light of the light sources91coming in through the side end face31ais guided into the main body part32at good light guide efficiency by the bent light guide part33, the flat light guide part35and the front reflecting member81of the light guide plate21, and is let go out through the principal surface32a. Consequently, the light let go out through the principal surface32aadvances in the direction perpendicular to the side end face31a(upwards inFIG. 1), and is radiated onto the LCD11through the diffuser18and the lens sheet16. Then, this provides a back light for the LCD11, whereby the contents being displayed on the LCD11are made to be clearly visible.

Besides, since the main body part32opposed to the LCD11is small in thickness, the liquid crystal display device1can be reduced in size (reduced in thickness). Therefore, by electronically controlling the LCD11and the light sources91by an electronic controller (not shown) so that various images, characters and the like can be displayed on the LCD11, the liquid crystal display device1is made to be suitable for mobile apparatuses (corresponding to the electronic apparatus in the present invention) such as mobile phones.

FIG. 2is a side view of a front irradiation type liquid crystal display device2using the light guide plate21according to the first embodiment.

As shown inFIG. 2, for the front irradiation type liquid crystal display device2, an LCD12is used which has liquid crystals sealed therein and which has an inner reflective layer12aat the inner surface of a glass plate on one side. In addition, a phase difference plate19is disposed on the front side (the upper side inFIG. 2) of the LCD11, and a polarizing plate15is arrange on the further front side of the phase difference plate19. Besides, a transparent light guide plate21which is the same as that in the liquid crystal display device1shown inFIG. 1is disposed, upside down, on the front side (the frontmost side) of the polarizing plate15.

Here, even though disposed upside down, the light guide plate21guides the light from light sources91coming in through a side end face31ato a principal surface32aof a main body part32. Specifically, the light coming in through the side end face31aoutside the range of thickness of the main body part32is guided by a bent light guide part33into the main body part32while being changed in direction from the incidence direction into the range of the thickness of the main body part32. In addition, the light leaking on the side of an inclined front surface33aof the bent light guide plate33is reflected by a surface reflecting member81toward the bent light guide part33or the main body part32. Further, the light coming in through the side end face31awithin the range of thickness of the main body part32is guided by a flat light guide part35into the range of thickness of the main body part32while remaining unchanged in direction.

According to the liquid crystal display device2as above, the light of the light sources91disposed so as to face the side end face31aof the light guide plate21is guided through an incoming part31into the main body part32at a good light guide efficiency, and is let go out through the principal surface32a. Then, the light let go out from the principal surface32aadvances in the direction perpendicular to the side end face31a(downwards inFIG. 2), to enter the LCD12through the polarizing plate15and the phase difference plate19.

Besides, the light entering the LCD12is reflected by the inner reflective layer12aprovided inside the LCD12, and is let go out upward this time. Then, it is possible to see the light let go out through the transparent light guide plate21, so that the contents displayed on the LCD12is made to be clearly visible. In addition, the side end face31awhere the light guide plate21is thick makes it possible to secure a sufficient quantity of light coming into an incoming part31, and the main body part32which is thin makes it possible for the liquid crystal display device2to be smaller in size (smaller in thickness).

FIG. 3is a front-side perspective view showing a main part of the light guide plate21in the first embodiment shown inFIGS. 1 and 2.

In addition,FIG. 4is a back-side perspective view showing a main part of the light guide plate21in the first embodiment shown inFIGS. 1 and 2.

Incidentally, while the condition where the front reflecting member81is separated from the bent light guide part33is shown inFIG. 3for convenience of description, in the actual assembly the front reflecting member81is arranged along the outside of the inclined front surface33aas indicated by arrows.

The light guide plate21according to the first embodiment can operate so that the light from three light sources91(seeFIGS. 1 and 2) is radiated onto the LCD11(seeFIG. 1) or the LCD12(seeFIG. 2). Therefore, as shown inFIGS. 3 and 4, the light guide plate21includes three side end faces31apermitting incidence of light from the light sources91, an incoming part31which forms the side end faces31aand which guides the light coming in through the side end faces31a, a principal surface32a(seeFIG. 3) which is formed in the direction perpendicular to the side end faces31aand through which the light guided by the incoming part31is let go out, and a main body part32which forms the principal surface32aand which is continuous with the incoming part31on the opposite side from the side end faces31a. Besides, the main body part32is formed to be greater in width than the side end faces31a.

Here, the incoming part31is formed to be thicker on the side of the side end faces31athan at the main body part32. In addition, the incoming part31has a bent light guide part33by which the light coming in through the side end faces31aoutside the range of thickness of the main body part32is guided into the range of thickness of the main body part32while being changed in direction. Besides, the bent light guide part33is formed to spread in the width direction of the main body part32, and has an inclined front surface33awhich is so inclined that a surface in the direction perpendicular to the side end faces31ais continuous with the principal surface32a, and an inclined back surface33bwhich is so inclined as to be parallel to the inclined front surface33aon the opposite side from the inclined front surface33a.

Further, the incoming part31is provided in the bent light guide part33with V-shaped lateral light guide parts36(seeFIG. 3) by which the light coming in through the side end faces31ais guided while being changed in direction along the width direction of the main body part32. Besides, the lateral light guide part36is disposed within the range for facing each light source91(seeFIGS. 1 and 2) in such a manner that its V-shaped base portion side is directed toward the light source91.

Furthermore, the incoming part31has flat light guide parts35(seeFIG. 4) by which the light coming in through the side end faces31awithin the range of thickness of the main body part32is guided into the range of thickness of the main body part32. Besides, the flat light guide part35is disposed within the range for facing each light source91(seeFIGS. 1 and 2). Therefore, within the range for facing each light source91, each side end face31ais formed by the bent light guide part33on the upper side and the flat light guide part35on the lower side. Incidentally, since the flat light guide part35is absent, for example, between the side end faces31a, the inclined back surface33bside of the bent light guide parts33forms space parts38(seeFIG. 4).

Thus, the light guide plate21according to the first embodiment includes the bent light guide parts33on the front side of the incoming part31, the lateral light guide parts36(seeFIG. 3) in the bent light guide part33, and the flat light guide parts35(seeFIG. 4) on the back side. Therefore, the light coming in through the side end faces31aoutside the range of thickness of the main body part32is guided by the bent light guide parts33into the range of thickness of the main body part32, and is guided by the lateral light guide parts36into the main body part32on both sides of the flat light guide parts35. In addition, the light coming in through the side end faces31awithin the range of thickness of the main body part32is guided by the flat light guide parts35into the main body part32while remaining unchanged in direction.

Accordingly, the light guided mainly by the flat light guide parts35(seeFIG. 4) comes into the main body part32facing the side end face31a, whereas the light guided mainly by the belt light guide parts33and the lateral light guide parts36(seeFIG. 3) comes into the main body part32facing the portions between the side end faces31a. As a result, the light coming in through the side end faces31ais diffused throughout the main body part32, and is let go out through the whole area of the principal surface32a.

Besides, the bent light guide part33has a front reflecting member81(seeFIG. 3). The front reflecting member81is formed from a material having a light-reflecting function (for example, a silver sheet, a white polyethylene terephthalate resin, etc.), and has a shape conforming to the inclined front surface33aside of the bent light guide part33(e.g., a shape obtained by bending so as to conform to the inclined front surface33a). Therefore, by disposing the front reflecting member81along the outside of the inclined front surface33aas indicated by arrows inFIG. 3, the light leaking from the bent light guide parts33can be reflected toward the bent light guide parts33or the main body part32. As a result, leakage of light from the bent light guide parts33is prevented, so that the light guide efficiency of the light guide plate21is enhanced. Incidentally, the material of the front reflecting member81is not limited to the silver sheet and the white polyethylene terephthalate resin, and may be any material that has a light-reflecting function. The use of such a material is not only applicable to the light guide plate21in the first embodiment but also similarly applicable in other embodiments.

FIGS. 5A and 5Billustrate a light leakage preventing action of the bent light guide part33in the light guide plate21according to the first embodiment shown inFIGS. 3 and 4.

Incidentally,FIG. 5Aschematically illustrates the path of a ray of light coming from the light source91and entering the light guide part21, whileFIG. 5Billustrates various paths of rays of light coming from the light source91which are determined by simulation.

As shown inFIG. 5A, when a ray of light coming from the light source91and being incident on the incoming part31of the light guide plate21(a ray of light parallel to the principal surface32aof the main body part32) passes through the side end face31aand impinges on the inclined front surface33a(inclined at angle θ against the principal surface32a), the ray is reflected (at reflection angle θ) on the inclined surface33a, and is then reflected (at reflection angle θ) on the inclined front back surface33b. In this case, since the inclined back surface33bis inclined on the opposite side from the inclined front surface33aso as to be parallel to the inclined front surface33a, the ray of light reflected by the inclined back surface33badvances toward the main body part32in parallel to the principal surface32a. Therefore, there is little leakage of light through the bent light guide part33. Incidentally, the inclination of the inclined back surface33bso as to be parallel to the inclined front surface33ais not limited to the case where the extension of the inclined front surface33aand the extension of the inclined back surface33bwill never intersect, but means that the inclined surfaces are in such a positional relationship that the light reflected by the inclined back surface33badvances toward the main body part32.

FIG. 5Bshows paths of rays of light in the bent light guide part33which are determined by simulation. As is seen from the figure, leakage of light is substantially prevented, since the inclined front surface33aand the inclined back surface33bare inclined to be parallel to each other. In addition, the rays of light having leaked are reflected from the front reflecting member81, which is disposed along the outside of the inclined front surface33a, toward the bent light guide part33or the main body part32. Incidentally, a back reflector94for reflecting the leaking light is disposed on the back side of the main body part32, so that there is no leakage of light on this side.

Therefore, loss of light being guided into the main body part32is minimized (light is let go out through the principal surface32a, without leaking through the inclined front surface33a), and a very high light guide efficiency is obtained. According to the results of such a simulation, in contrast to a final light guide efficiency of the light guide plate21of 80% in the case where the front reflecting member81is not used, the light guide efficiency is enhanced to 84% in the case where a silver sheet is used as the front reflecting member81, and the light guide efficiency is enhanced to 83% in the case where a white polyethylene terephthalate resin is used as the front reflecting member81.

FIG. 6is a front-side perspective view showing a main part of a light guide plate22according to a second embodiment of the present invention.

Besides,FIG. 7is a back-side perspective view showing a main part of the light guide plate22in the second embodiment.

Incidentally, inFIGS. 6 and 7, for convenience of description, a front reflecting member82(seeFIG. 6) and a back reflecting member85(seeFIG. 7; corresponding to the reflecting member in the present invention) are illustrated in the state of being separated from a bent light guide part33. Actually, however, the front reflecting member82is arranged along the outside of an inclined front surface33a, and the back reflecting member85is arranged along the outside of an inclined back surface33b, as indicated by arrows.

As shown inFIGS. 6 and 7, the light guide plate22in the second embodiment, like the light guide plate21(seeFIGS. 3 and 4) in the first embodiment, permits the light from three light sources91(seeFIGS. 1 and 2) to enter the light guide plate22. Therefore, the light guide plate22includes three side end faces31a, an incoming part31for guiding the light entering through the side end faces31a, a principal surface32a(seeFIG. 6) through which the light guided by the incoming part31is let go out, and a main body part32formed to be wider than the width of the side end faces31a, with these components having the same shapes as those of the light guide plate21in the first embodiment.

In addition, a bent light guide part33(an inclined front surface33a, an inclined back surface33b) being spread in the width direction of the main body part32, V-shaped lateral light guide parts36(seeFIG. 6) formed in the bent light guide part33, a flat light guide part35(seeFIG. 7) forming the side end faces31atogether with the bent light guide part33, and space parts38(seeFIG. 7) present, for example, between the side end faces31a, which are formed in the incoming part31, also have the same shapes as those of the light guide plate21(seeFIGS. 3 and 4) in the first embodiment.

Here, the light guide plate22in the second embodiment has a front reflecting member82(seeFIG. 6) different from that in the first embodiment, and back reflecting members85(seeFIG. 7) which have not been provided in the first embodiment. Specifically, the front reflecting member82, which is disposed along the outside of an inclined surface33aof the bent light guide part33, is three-dimensionally molded from a white polyethylene terephthalate resin having a light-reflecting function, unlike that in the first embodiment. The front reflecting member82is not only formed in a bent shape conforming to the inclination of the inclined front surface33abut also provided on it back side with V-shaped projected parts82a(seeFIG. 6) conforming to the inside recesses of lateral light guide parts36.

Therefore, when the front reflecting member82is arranged on the bent light guide part33as indicated by arrows while conforming the projected parts82aof the front reflecting member82to the lateral light guide parts36, as shown inFIG. 6, the front reflecting member82is set along the outside of the inclined front surface33a, and the projected parts82aare fitted into the lateral light guide parts36. As a result, the light leaking on the inclined front surface33aside of the bent light guide part33is reflected by the back side of the front reflecting member82toward the bent light guide part33or the main body part32. In addition, the light leaking through the lateral light guide parts36is reflected by the projected parts82atoward the lateral light guide parts36.

Further, as shown inFIG. 7, the back reflecting members85are arranged on the side of flat light guide parts35and in the ranges where the flat light guide parts35are absent (in four space parts38). Specifically, the back reflecting members85include three kinds (for left end, for center, and for right end) of back reflecting members85a,85b,85cwhich are three-dimensionally molded from a white polyethylene terephthalate resin having a light-reflecting function, like the front reflecting member82, and which have shapes and sizes conforming to the four space parts38. When arranged in the space parts38as indicated by arrows, the back reflecting members85a,85b,85care set along the outside of the inclined back surface33b. As a result, the light leaking on the inclined back surface33bside of the bent light guide part33is reflected by the back reflecting members85(85a,85b,85c) toward the bent light guide part33or the main body part32.

Thus, the light guide plate22according to the second embodiment has the front reflecting member82(seeFIG. 6) and the back reflecting member85(seeFIG. 7) which are arranged respectively on the outside of the inclined front surface33aand the inclined back surface33band by which the light leaking through the bent light guide part33is reflected toward the bent light guide part33or the main body part32. Therefore, loss of light being guided into the main body part32is minimized, and a very high light guide efficiency is obtained.

Specifically, as contrasted to a final light guide efficiency of 80% in the case where the front reflecting member82(seeFIG. 6) and the back reflecting member85(seeFIG. 7) are not used, the light guide efficiency is enhanced to 89%, as determined by simulation, in the case of the light guide plate22using both the front reflecting member82and the back reflecting member85. Incidentally, in the case where only the front reflecting member82is used, the light guide efficiency is 87%. Therefore, the front reflecting member82molded three-dimensionally and provided with the projected parts82a(seeFIG. 6) is higher in light guide efficiency than the front reflecting member81shown inFIG. 3. In addition, in the case where only the back reflecting member85is used, the light guide efficiency is 82%. Thus, even when only the back reflecting member85is used, the light guide efficiency is enhanced.

FIGS. 8A and 8Bare a perspective view (FIG. 8A) and a side view (FIG. 8B) illustrating a main part of a light guide plate23according to a third embodiment of the present invention.

As shown inFIGS. 8A and 8B, the light guide plate23in the third embodiment has an incoming part41of which the thickness on the side of side end faces41ais greater than the thickness of a main body part42, specifically, three times the thickness of the main body part42. Therefore, in the case where the thickness at the side end faces41ais set to be equal to the thickness at the side end faces21aof the light guide plate21in the first embodiment shown inFIG. 1(namely, set to be twice the thickness of the main body32), the thickness of the main body part42can be reduced more (can be reduced to a value of ⅓ times the thickness of the side end faces41aand the side end faces21a, instead of being reduced to a value of ½ times the thickness of the side end faces41a,21a).

Here, in the light guide plate23in the third embodiment, the main body part42is formed to be wider than the width of the side end faces41a. In addition, an incoming part41has two bent light guide parts43,44by which the light coming in through the side end faces41aoutside the range of thickness of the main body part42is guided into the range of thickness of the main body part42while being changed in direction. Specifically, the light guide plate23has the two bent light guide parts43,44which are adjacent to each other along the thickness direction of the incoming part41. The bent light guide part43on the upper side has a lateral light guide part46by which the light coming in through the side end face41ais guided while being changed in direction along the width direction (in the rightward direction inFIG. 8) of the main body part42. On the other hand, the bent light guide part44on the lower side guides the light, coming in through the side end face41a, into the main body part42without changing the direction of the light in the width direction. Consequently, the bent light guide part43on the upper side and the bent light guide part44on the lower side are so arranged as not to overlap with each other in the width direction of the main body part42, due to the presence of the lateral light guide part46of the bent light guide part43.

Further, the incoming part41has a flat light guide part45by which the light coming in through the side end face41awithin the range of thickness of the main body part42is guided into the range of thickness of the main body part42while remaining unchanged in direction. In addition, the flat light guide part45has a lateral light guide part47by which the light coming in through the side end face41ais guided while being changed in direction along the width direction (in the leftward direction inFIG. 8) of the main body part42. Consequently, the flat light guide part45and the bent light guide part44are so arranged as not to overlap with each other in the width direction of the main body part42, due to the presence of the lateral light guide part47of the flat light guide part45.

Therefore, while the light guided by the bent light guide parts43,44and the flat light guide part45enters the main body part42, the light in the bent light guide part43is changed in direction toward the rightward direction of the bent light guide part44by the lateral light guide part46, and the light in the flat light guide part45is changed in direction toward the leftward direction of the bent light guide part44by the lateral light guide part47. As a result, the light coming in through the side end face41ais diffused throughout the main body part42, to be let go out from the whole area of the principal surface42a.

In addition, since the side end face41ais trisected due to the presence of the bent light guide parts43,44and the flat light guide part45and the thickness of the main body part42is ⅓ times the thickness at the side end face41a, the liquid crystal display device1(seeFIG. 1) can be further reduced in size (reduced in thickness). In addition, an increase in the number of the bent light guide parts43leads to an increase in the number of divisions, n, of the side end face41a, whereby the thickness of the main body part42can be reduced to 1/n times the thickness at the side end face41a. Besides, the thinning of the main body part42in this manner is not only applicable to the light guide plate23in the third embodiment but also similarly applicable in other embodiments.

Further, a front reflecting member83is arranged along the outside of inclined front surfaces43a,44aof the bent light guide parts43,44. The front reflecting member83is three-dimensionally molded from a white polyethylene terephthalate resin having a light-reflecting function. Specifically, the front reflecting member83is not only formed in a recessed and projected shape conforming to the step between the bent light guide part43and the bent light guide part44but also formed in a bent shape conforming to the inclinations of the inclined front surfaces43a,44a.

Therefore, when the front reflecting member83is arranged on the bent light guide parts43,44as indicated by arrows, as shown inFIG. 8, the front reflecting member83is set along the outside of the inclined front surfaces43a,44a. As a result, the light leaking on the side of the inclined front surfaces43a,44aof the bent light guide parts43,44is reflected by the front reflecting member83toward the bent light guide parts43,44or the main body part42. Therefore, leakage of light from the bent light guide parts43,44is prevented, and the light guide efficiency of the light guide plate23is enhanced. Accordingly, loss of light being guided into the main body part42is minimized, and a very high light guide efficiency is obtained.

FIGS. 9A and 9Bare perspective views of a light guide plate24according to a fourth embodiment of the present invention.

Incidentally,FIG. 9Ashows the front side of the light guide plate24, andFIG. 9Bshows a part on the back side of the light guide plate24. InFIG. 9B, a light source92is omitted, for convenience of description.

As shown inFIGS. 9A and 9B, the light guide plate24in the fourth embodiment has an incoming part51having a shape the same as or similar to that in the light guide plate21(seeFIGS. 3 and 4) in the first embodiment. Specifically, the incoming part51is formed to be thicker on the side of a side end face51athan at a main body part52. In addition, the incoming part51has a bent light guide part53formed to be spread in the width direction of the main body part52. The bent light guide part53includes an inclined front surface53a, and an inclined back surface53bwhich is inclined on the opposite side from the inclined front surface53aso as to be parallel to the inclined front surface53a. Further, the incoming part51is provided with a V-shaped lateral light guide part56in the bent light guide part53. Furthermore, the incoming part51has a flat light guide part55.

Here, the light guide plate24in the fourth embodiment has the incoming part51arranged in a corner portion of the main body part52in the state of being oriented diagonally. In addition, back reflecting members86are arranged along the outside of an inclined back surface53bof the bent light guide part53. Incidentally, the back reflecting members86include a left-right pair of back reflecting members86a,86bwhich are three-dimensionally molded from a white polyethylene terephthalate resin having a light-reflecting function.

Therefore, at the incoming part51arranged in the corner portion of the main body part52, the light leaking on the side of the inclined back surface53bof the bent light guide part53is reflected by the back reflecting members86toward the bent light guide part56or the main body part52. Therefore, leakage of light through the inclined back surface53bis prevented, and the light guide efficiency of the light guide plate24is enhanced. In addition, the light of the light source92coming in through the side end face51ais reflected in the left-right direction of the main body part52by lateral light guide parts56, so that the light coming in through the side end face51ais diffused throughout the main body part52. As a result, loss of light being guided into the main body part52is minimized, a very high light guide efficiency is obtained, and, further, it is possible to realize a one-light-in-corner back light which can be reduce in thickness efficiently.

FIGS. 10A and 10Bare a front-side perspective view (FIG. 10A) and a back-side perspective view (FIG. 10B) showing an incoming part61of a light guide plate25according to a fifth embodiment of the present invention.

As shown inFIGS. 10A and 10B, the light guide plate25in the fifth embodiment has a bent light guide part33and an incoming part61having shapes the same as or similar to those in the light guide plate21(seeFIG. 3) in the first embodiment. At each of side end faces61aof the incoming part61, lenses being ridge-shaped in section are arrayed in the thickness direction. Such a lens array structure ensures that, in the light guide plate25in the fifth embodiment, the luminous intensity distribution of the light coming in through the incoming part61is broadened, and, particularly, irregularities of color in the case where high color reproduction LEDs are used as light sources91(seeFIG. 1) can be reduced. Incidentally, the formation of the side end face61ato have the lens array structure is not only applicable to the light guide plate25in the fifth embodiment but also similarly applicable in other embodiments.

In addition, the same front reflecting member81as that in the light guide plate21(seeFIG. 3) in the first embodiment is arranged on the front side of the bent light guide part33, and the same back reflecting member85as that in the light guide plate22(seeFIG. 7) in the second embodiment is arranged on the back side of the bent light guide part33. Therefore, the light leaking to the front side of the bent light guide part33is reflected by the front reflecting member81, and the light leaking to the back side of the bent light guide part33is reflected by the back reflecting member85.

Here, the luminous intensity distribution of the light entering the light guide plate25through the incoming part61is broadened in the horizontal direction by the side end faces61ahaving the lens array structure. In this case, the bent light guide part33is present on both sides of each of the side end faces61a, and, further, the back reflecting members85are arranged on both sides. Therefore, the light leaking through the lower half of the side end face61awhere the light does not enter the bent light guide part33is reflected by the back reflecting members85toward the incoming part61. As a result, loss of light entering the incoming part61is minimized, and a very high light guide effect can be obtained.

FIG. 11is a side view of a back irradiation type liquid crystal display device3using a light guide plate26according to a sixth embodiment of the present invention.

As shown inFIG. 11, the liquid crystal display device3includes an LCD11, a polarizing plate13, a polarizing plate14, light sources91, and a back reflecting plate94which are the same as or similar to those in the back irradiation type liquid crystal display device1shown inFIG. 1. On the other hand, a lens sheet17used here is different from the lens sheet16(seeFIG. 1).

This lens sheet17has a shape as if the lens sheet16(seeFIG. 1) has been reversed upside down. The lens sheet17is a prism sheet in which prisms are formed from a photo-curing resin (photopolymer) on the lower side of a highly transparent polyester film. With the lens sheet17arranged with its lenses (prisms) on the side of a principal surface32a, the need for a diffuser18(seeFIG. 1) is eliminated. Therefore, a further reduction in size (reduction in thickness) can be achieved.

In addition, the light guide plate26in the sixth embodiment includes an incoming part31, side end faces31a, a main body part32, the principal surface32a, a bent light guide part33, an inclined front surface33a, an inclined back surface33b, and a flat light guide part35of which the shapes are the same as or similar to those in the light guide plate21(seeFIG. 1) in the first embodiment. On the other hand, a front reflecting member84here is different from the front reflecting member81(seeFIG. 1).

The front reflecting member84has a shape obtained by extending the front reflecting member81(seeFIG. 1) in the direction of the main body part32. To be more specific, in the liquid crystal display device3shown inFIG. 11, the diffuser18(seeFIG. 1) is absent, so that the gap between the light guide plate26and the lens sheet17can be enlarged. In view of this, the front reflecting member84is so extended as to cover an end portion (at a position for overlapping with the lens sheet17as viewed in the perpendicular direction) of the principal surface32ain addition to the inclined front surface84of the incoming part31, whereby it is ensured that the light let go out through the principal surface32aenters the lens sheet17reliably.

FIG. 12is a side view of a back irradiation type liquid crystal display device4using a light guide plate27according to a seventh embodiment of the present invention.

As shown inFIG. 12, the liquid crystal display device4is obtained by adapting the back irradiation type liquid crystal display device1shown inFIG. 1for both-side display. Specifically, LCDs11a,11b, polarizing plates13a,13b, polarizing plates14a,14b, lens sheets16a,16b, diffusers18a,18bwhich are the same as or similar to those in the liquid crystal display device1are arranged on both the upper and lower sides of a main body part72of the light guide plate27.

Here, the light guide plate27in the seventh embodiment has a principal surface72aand a principal surface72b, for emitting light from both surfaces of the main body part72. In addition, since the main body part72is located at the center of side end faces71aof an incoming part71, a bent light guide part73is provided so that the side end faces71aare continuous with the principal surface72a, and a bent light guide part74is provided so that the side end faces71aare continuous with the principal surface72b. Besides, due to the presence of the bent light guide part73and the bent light guide part74, the thickness at the side end faces71aof the light guide plate27is greater than the thickness at the side end faces31aof the light guide plate21in the first embodiment shown inFIG. 1. Therefore, further larger light sources93can be arranged, and sufficient amounts of light for functioning as back lights for the LCDs11a,11bcan be secured.

In addition, front reflecting members81a,81bthe same as or similar to the front reflecting member81in the light guide plate21in the first embodiment shown inFIG. 1are arranged at the bent light guide parts73,74. Therefore, the light leaking from the bent light guide part73is reflected by the front reflecting member81atoward the bent light guide part73or the main body part72, and the light leaking from the bent light guide part74is reflected by the front reflecting member81btoward the bent light guide part74or the main body part72.

Therefore, according to the liquid crystal display device4shown inFIG. 12, by the bent light guide parts73,74of the light guide plate27and the front reflecting members81a,81b, the light of the light sources93coming in through the side end faces71ais efficiently guided into the main body part72, and is let go out through the principal surfaces72a,72b. Accordingly, the light emitted from the principal surfaces72a,72badvances in the directions perpendicular to the side end faces71a(upwards and downwards inFIG. 12), and is emitted to illuminate the LCDs11a,11bthrough the diffusers18a,18band the lens sheets16a,16b. This provides back lights for the LCDs11a,11b, whereby the contents being displayed on the LCDs11a,11bare made to be clearly visible.

FIG. 13is a side view of a back irradiation type liquid crystal display device5using a light guide plate28according to an eighth embodiment of the present invention.

As shown inFIG. 13, the liquid crystal display device5is obtained through adaptation for both-side display, like the back irradiation type liquid crystal display device shown inFIG. 12. Specifically, LCDs11a,11b, polarizing plates13a,13b, polarizing plates14a,14b, and light sources93which are the same as those in the liquid crystal display device4are arranged on both the upper and lower sides of a main body part72of the light guide plate27. On the other hand, lens sheets17a,17bprovided here are different from the lens sheets16a,16b(seeFIG. 12).

The lens sheets17a,17bare prism sheets the same as the lens sheet17shown inFIG. 11, and are arranged with the lenses (prisms) on the side of principal surfaces72a,72b, whereby the need for the diffusers18a,18b(seeFIG. 12) is eliminated. Therefore, a further reduction in size (reduction in thickness) can be achieved.

In addition, the light guide plate28in the eighth embodiment includes an incoming part71, side end faces71a, a main body part72, the principal surfaces72a,72b, and bent light guide parts73,74which have the same shapes as those in the light guide plate27(seeFIG. 12) in the seventh embodiment. On the other hand, front reflecting members84a,84bprovided here are different from the front reflecting members81a,81b(seeFIG. 12).

The front reflecting members84a,84bare obtained by extending the front reflecting members81a,81b(seeFIG. 12) in the direction of the main body part72. Specifically, in the liquid crystal display device5shown inFIG. 13, the diffusers18a,18b(seeFIG. 12) are absent, so that the gaps between the light guide plate28and the lens sheets17a,17bcan be enlarged. In view of this, the front reflecting members84a,84bare extended so as to cover end portions (at positions for overlapping with the lens sheets17a,17bas viewed in the perpendicular direction) of the principal surfaces72a,72bfrom the incoming part71, whereby it is ensured that the light emitted from the principal surfaces72a,72benters the lens sheets17a,17breliably.

While some embodiments of the present invention have been described above, the invention is not limited to these embodiments, and various modifications are possible. For example, combinations of layouts of the bent light guide parts33, the flat light guide parts35and the lateral light guide parts36of the light guide plate21in the first embodiment and the like factors can be modified, as occasion demands. In addition, application of the light guide plate21is not limited to the application as the back light in the liquid crystal display device1; the light guide plate is widely applicable as a surface light source in a variety of displays.

The present application contains subject matter related to that disclosed in Japanese Priority Patent Application JP 2008-103688 filed in the Japan Patent Office on Apr. 11, 2008, the entire content of which is hereby incorporated by reference.