Backlight and frontlight, intermediate light guide, cover member, and liquid crystal display

A backlight is disposed on a rear surface side of a subject to be irradiated and illuminates the subject to be irradiated from the rear surface side. The backlight includes: a light guide plate; an intermediate light guide disposed along an end surface on one side of the light guide plate; and a light source disposed to an end portion of the intermediate light guide. One surface side of the light guide plate is formed into a reflection surface on which a concavoconvex shape is formed so as to reflect light propagating inside thereof. The other surface side of the light guide plate is formed into an exit surface that outputs the light reflected by the reflection surface. The reflection surface includes a plurality of grooves that are formed of a gentle slope portion and a steep slope portion. The subject to be irradiated is disposed outside of the exit surface.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a structure preferable as a backlight or a frontlight for use in a liquid crystal display device, and a liquid crystal display device provided with the backlight or the frontlight.

2. Description of the Related Art

FIG. 20is a diagrammatic sectional view showing one example of an existing transmissive liquid crystal display device, and a liquid crystal display device100in the example comprises a liquid crystal display unit120and a backlight110disposed at a rear surface side of the liquid crystal display unit120.

The backlight110is constituted so that light from a long light source113may be allowed to enter into a light guide plate112from one end surface (incidence surface112a) thereof and to exit from one side surface (exit surface112b) that faces the liquid crystal unit120in the light guide plate112. On the other side surface112con a side that faces the exit surface112bof the light guide plate112, a prism sheet114and a white sheet115are disposed in this order. Furthermore, in order to integrally hold constituent components of the backlight110, a cover-like holding member116that can accommodate in one lump the long light source113, the light guide plate112, the prism sheet114and the white sheet115is disposed. Furthermore, the white sheet115that is disposed on a rear surface side of the light guide plate112has light diffusion properties and light reflection properties, still furthermore between the light guide plate112and the white sheet115the prism sheet114is disposed, and thereby light diffusion properties and uniformity of a brightness distribution are improved. Furthermore, as the long light source113, a cold cathode tube has been used.

However, in a backlight of a smaller display device such as an information terminal device and so on, since the cold cathode tube, requiring an inverter and so on, is too large in the power consumption and results in largely consuming a battery, instead of the cold cathode tube a light source that uses an EL (electro-luminescence) element has been widely adopted.

However, when an EL element is used as a light source of this kind of a display device, in order to obtain brightness of substantially several Cd/m2, power consumption such large as 4 to 5 mW/cm2is necessary, accordingly there is a problem in that despite of larger power consumption, the brightness is low.

Furthermore, in the EL element, in order to allow the element itself to emit, an inverter is necessary in an amplitude circuit, and a problem results in that the inverter becomes a noise source of a liquid crystal display device. So far, as a countermeasure to the inverter noise, it has been necessary to provide the liquid crystal display device with a noise countermeasure circuit and noise shield means, resulting in higher cost. Furthermore, the inverter, in view of a circuit, is disadvantageous in raising the cost.

Furthermore, since the EL element has disadvantages in that the emission life is relatively short, for a longer use, component replacement and maintenance are necessary. For instance, in the case of an ordinary EL element, in terms of a half decay time when brightness becomes one half the initial brightness, the emission life is substantially 5000 h at the longest and substantially 2500 h at the shortest. Accordingly, a light source that has increased lifetime is in demand.

The present invention provides a backlight that is lower in power consumption, exhibits higher brightness, has a longer lifetime and generates less noise, and a liquid crystal display device provided therewith.

SUMMARY OF THE INVENTION

In order to overcome the above problems, a backlight according to the invention is a backlight that is disposed on a rear surface side of a subject to be irradiated and illuminates the subject to be irradiated from the rear surface side, the backlight including a light guide plate, an intermediate light guide disposed along an end surface of one side of the light guide plate, and a light source disposed to the intermediate light guide, one surface side of the light guide plate being formed into a reflection surface on which a concavoconvex shape is formed to reflect light traveling inside thereof, the other surface side of the light guide plate being formed into an exit surface that lets exit light reflected by the reflection surface, on the reflection surface a plurality of grooves that are formed of a gentle slope portion and a steep slope portion that has an angle of inclination steeper than that of the gentle slope portion being continuously formed in stripe, outside of the exit surface the subject to be irradiated being disposed.

Since the light exited from the light source can be reflected at the steep slope portion and irradiated from the exit surface of the light guide plate onto the subject to be irradiated, the subject to be irradiated can be illuminated from a rear side thereof, resulting in allowing functioning as a backlight.

In order to overcome the above problems, in a backlight according to the invention, the light source is made of a light-emitting diode having any one of green, bluish green, blue, orange, red, and yellowish green color.

When the light-emitting diode having any one color of green, bluish green, blue, orange, red, and yellowish green color is used as a light source, the light-emitting diode can be cheaply obtained, resulting in contributing to cost reduction as the light source. Furthermore, in comparison with a structure that uses an EL element as the light source, since there is no need of noise countermeasures, a shield and a noise reduction circuit are not needed, resulting in contributing to the cost reduction.

Furthermore, since the light-emitting diode having one of these colors is higher in the obtained brightness relative to the power consumption, a brighter backlight can be cheaply provided.

In order to overcome the above problems, in the backlight according to the invention, a cover member having at least a reflection surface cover portion that covers a side end portion on a reflection surface side of the light guide plate, a light guide cover portion that covers the intermediate light guide, and an exit surface cover portion that covers a side end portion on the exit surface side of the light guide plate is attached so as to cover at least the intermediate light guide and the side end portion of the light guide plate.

When the cover member is disposed on front and rear sides of a side end portion of the light guide plate and a periphery side of the intermediate light guide, light leakage from a side end portion side of the light guide plate and the periphery side of the intermediate light guide can be reduced, light introduced into the light guide plate can be increased, resulting in an improvement in the brightness as the backlight.

In order to overcome the above problems, in the backlight according to the invention, a reflection surface is formed on an inner surface of the cover member.

When the reflection surface is formed on an inner surface of the cover member, an amount of light that is reflected inside of the intermediate light guide and input into the light guide plate side can be increased, resulting in an improvement in the brightness as the backlight.

When a semi-transmissive liquid crystal display unit or a transmissive liquid crystal display unit is applied as the subject to be irradiated of the backlight according to the invention, a liquid crystal display unit of brighter display can be provided.

In order to overcome the above problems, a liquid crystal display device according to the invention includes a light guide plate, an intermediate light guide disposed along an end surface of one side of the light guide plate, and a light source disposed to an end portion of the intermediate light guide, one surface side of the light guide plate being formed into a reflection surface on which a concavoconvex shape is formed to reflect light traveling inside thereof, the other surface side of the light guide plate being formed into an exit surface that lets exit light reflected by the reflection surface, on the reflection surface a plurality of grooves that are formed of a gentle slope portion and a steep slope portion that has an angle of inclination steeper than that of the gentle slope portion being continuously formed in stripe, and outside of the exit surface a transmissive or semi-transmissive liquid crystal display unit being disposed.

Since light exited from the light source can be reflected at the steep slope portion and irradiated from the exit surface of the light guide plate onto the subject to be irradiated, the transmissive or semi-transmissive liquid crystal display unit can be illuminated from a rear side thereof.

In order to overcome the above problems, in the liquid crystal display device according to the invention, the liquid crystal display unit is a transmissive or semi-transmissive black-and-white display type.

In order to overcome the problems, in the liquid crystal display device according to the invention, the light source is formed of a light-emitting diode having any one color of green, bluish green and blue color.

When the light-emitting diode is used as a light source, in comparison with an EL element, the power consumption is smaller, and higher brightness relative to the power consumption can be obtained. Furthermore, the light-emitting diode having any one color of green, bluish green and blue color can be easily obtained and is cheap, resulting in contributing to the cost reduction. Furthermore, when the light-emitting diode having any one color of these colors is used as a light source, although colored light illuminates from a rear surface side the liquid crystal display unit, there is no problem when the liquid crystal display unit is not a color display type but a black-and-white display type transmissive or semi-transmissive type, resulting in obtaining a liquid crystal display unit having brighter display mode at low cost.

The steep slope portion and the gentle slope portion that form the groove are preferably disposed alternately.

Since the light outputted from the light source can be reflected at the steep slope portion and irradiated from the exit surface of the light guide plate onto the subject to be irradiated, the subject to be irradiated can be illuminated from a rear side thereof, thereby allowing functioning as a backlight, resulting in obtaining a liquid crystal display unit having a brighter display mode.

In order to overcome the above problems, in the liquid crystal display device according to the invention, a cover member having at least a reflection surface cover portion that covers a side end portion on a reflection surface side of the light guide plate, a light guide cover portion that covers the intermediate light guide, and an exit surface cover portion that covers a side end portion on the exit surface side of the light guide plate is attached so as to cover at least the intermediate light guide and the side end portion of the light guide plate.

When the cover member is disposed on front and rear sides of a side end portion of the light guide plate and a periphery side of the intermediate light guide, light leakage from a side end portion side of the light guide plate and the intermediate light guide side can be suppressed, and light introduced into the light guide plate can be increased, resulting in an improvement in the brightness as the backlight, and further resulting in providing a liquid crystal display unit having a brighter display mode.

In order to overcome the above problems, in the liquid crystal display device according to the invention, a reflection surface may be formed on an inner surface of the cover member.

Since the light is further reflected at the inner surface of the cover member and light leakage at the intermediate light guide portion can be reduced, an amount of light that is input from the intermediate light guide into the light guide plate side can be increased, resulting in an improvement in the brightness as the backlight, further resulting in providing a liquid crystal display unit having a brighter display mode.

A frontlight according to the invention is a frontlight that is disposed on a front surface side of a subject to be irradiated and illuminates the subject to be irradiated from a front surface side, the frontlight including a light guide plate, an intermediate light guide disposed along an end surface on one side of the light guide plate, and a light source disposed to the intermediate light guide, one surface side of the light guide plate being formed into a reflection surface on which a concavoconvex shape is formed to reflect light traveling inside thereof, the other surface side of the light guide plate being formed into an exit surface that lets exit light reflected by the reflection surface, on the reflection surface a plurality of grooves that are formed of a gentle slope portion and a steep slope portion that has an angle of inclination steeper than that of the gentle slope portion being continuously formed in stripe, and the light source being formed of a light-emitting diode having any one color of green, bluish green, blue, orange, red and yellowish green color.

Since the light exited from the light source can be reflected at the steep slope portion and irradiated from the exit surface of the light guide plate onto the subject to be irradiated, the subject to be irradiated can be illuminated from a rear side thereof, resulting in functioning as a frontlight. When a light-emitting diode having any one color of green, bluish green, blue, orange, red, and yellowish green color is used as a light source, the light-emitting diode can be cheaply obtained, resulting in contributing to cost reduction as the light source. Furthermore, in comparison with a structure that uses an EL element as the light source, since there is no need of noise countermeasures, a shield and a noise reduction circuit are not needed, resulting in a reduction in cost.

Furthermore, since the light-emitting diode having one of these colors is higher in the obtained brightness relative to the power consumption, a brighter frontlight can be cheaply provided.

In the frontlight according to the invention, a cover member having at least a reflection surface cover portion that covers a side end portion on a reflection surface side of the light guide plate, a light guide cover portion that covers the intermediate light guide, and an exit surface cover portion that covers a side end portion on the exit surface side of the light guide plate is attached so as to cover at least the intermediate light guide and a side end portion of the light guide plate.

When the cover member is disposed on front and rear sides of a side end portion of the light guide plate and a periphery side of the intermediate light guide, light leakage from a side end portion side of the light guide plate and the periphery side of the intermediate light guide can be made less, light introduced into the light guide plate can be increased, resulting in an improvement in the brightness as the frontlight.

In the frontlight according to the invention, the cover member is made of a metal plate, and on an inner surface side thereof a reflection surface is formed.

When a reflection surface is formed on an inner surface of the cover member, an amount of light that is reflected inside of the intermediate light guide and input into the light guide plate side can be increased, resulting in an improvement in the brightness as the frontlight.

In the frontlight according to the invention, the subject to be irradiated is a black-and-white display reflective liquid crystal display unit.

When the light-emitting diode having one of the previous colors is used as the light source, although colored light illuminates the liquid crystal display unit from a rear surface side, there is no particular problem when the liquid crystal display unit is not a color display type but a black-and-white display reflective type, resulting in obtaining at cheap cost a liquid crystal display unit having a brighter display mode.

A liquid crystal display device according to the invention includes a frontlight including a light guide plate, an intermediate light guide disposed along an end surface on one side of the light guide plate, and a light source disposed to an end portion of the intermediate light guide, one surface side of the light guide plate being formed into a reflection surface on which a concavoconvex shape is formed to reflect light traveling inside thereof, the other surface side of the light guide plate being formed into an exit surface that lets exit light reflected by the reflection surface, on the reflection surface a plurality of grooves that are formed of a gentle slope portion and a steep slope portion that has an angle of inclination steeper than that of the gentle slope portion being continuously formed in stripe, and the light source being formed of a light-emitting diode having any one color of green, bluish green, blue, orange, red and yellowish green color; and a liquid crystal display unit disposed outside of the exit surface of the frontlight.

In the liquid crystal display device according to the invention, the liquid crystal display unit is a reflective black-and-white display type.

Furthermore, when the light-emitting diode having one of the previous colors is used as the light source, although colored light illuminates the liquid crystal display unit from a rear surface side, there is no particular problem when the liquid crystal display unit is not a color display type but a black-and-white display reflective type, resulting in obtaining at cheap cost a liquid crystal display unit having a brighter display mode.

In the liquid crystal display device according to the invention, a cover member having at least a reflection surface cover portion that covers a side end portion on a reflection surface side of the light guide plate, a light guide cover portion that covers the intermediate light guide, and an exit surface cover portion that covers a side end portion on the exit surface side of the light guide plate is attached so as to cover at least the intermediate light guide and the side end portion of the light guide plate.

When the cover member is disposed on front and rear sides of a side end portion of the light guide plate and a periphery side of the intermediate light guide, light leakage from a side end portion side of the light guide plate and the periphery side of the intermediate light guide can be made less, light introduced into the light guide plate can be increased, resulting in an improvement in the brightness as the frontlight.

In the liquid crystal display device according to the invention, the cover member is made of a metal plate, and on an inner surface thereof a reflection surface is formed.

When a reflection surface is formed on an inner surface of the cover member, an amount of light that is reflected inside of the intermediate light guide and input into the light guide plate side can be increased, resulting in an improvement in the brightness as the frontlight.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, embodiments of the invention will be explained with reference to the drawings. However, the present invention is not restricted only to the following embodiments. Furthermore, in the respective drawings, scales of the respective constituent members are appropriately altered for the sake of illustration convenience.

FIG. 1is a sectional block diagram of a transmissive or semi-transmissive liquid crystal display device provided with a backlight (a planar light-emitting device) that is a first embodiment of the present invention,FIG. 2is a perspective view of the backlight, andFIG. 3is a side view showing with part of the backlight enlarged. A section direction inFIG. 1is a direction along a I—I line inFIG. 2.

A liquid crystal display device A according to the embodiment comprises a liquid crystal display unit20and a backlight10that is disposed at a rear surface side of the liquid crystal display unit20and illuminates the liquid crystal display unit20from the rear surface side.

The liquid crystal display unit20in this mode is a transmissive type or a semi-transmissive type, and is roughly constituted by connecting and integrating, with a sealing member24, a transparent first substrate21and a transparent second substrate22that are made of glass or the like and face each other with a liquid crystal layer23interposed therebetween. On the liquid crystal layer23sides of the first substrate21and the second substrate22, display circuit layers26and27are formed, respectively.

The display circuit layers26and27contain, though not shown in the drawing, an electrode layer made of a transparent conductive film for driving the liquid crystal layer23, an alignment film for controlling alignment of the liquid crystal layer23and so on. Furthermore, in the display circuit layers26and27, when a driving mode of a liquid crystal is a simple matrix type, a transparent electrode and an alignment film are disposed, however when a liquid crystal driving mode is an active matrix type, in addition to pixel electrodes, pixel driving thin film transistors or thin film diodes are disposed, and various kinds of wirings for driving these are disposed. However, the driving mode of the liquid crystal is not made any particular distinction in the invention.

The liquid crystal display unit20according to the embodiment is a black-and-white display type liquid crystal display unit that is not provided with a color filter for color display.

The backlight10comprises a transparent light guide plate12and light source device13. In the backlight10, the light source device13is disposed on an end surface12aside of a side therefrom light is introduced into the light guide plate12.

The light guide plate12is disposed on a rear surface side (outside of the substrate22) of the liquid crystal display unit20and irradiates the light inputted from the light source device13onto the liquid crystal display unit20, and is formed of a planar transparent acrylic resin plate and so on. As shown inFIGS. 2 and 4, on an end surface12a(hereinafter, in some cases, referred to as an incidence surface12a) of one side of the light guide plate12, the light source device13is disposed, and light outputted from the light source device13is introduced through the incidence surface12ainto the light guide plate12. A bottom surface of the light guide plate12(a surface on a side opposite to the liquid crystal display unit20side) is formed in a prism surface (reflection surface)12c, and a top surface on the opposite side (a surface on the liquid crystal display unit20side) from the prism surface12cis formed into a planar exit surface12b.

As a material that constitutes the light guide plate12, other than the acrylic resin, transparent resin materials such as polycarbonate resin and epoxy resin, and glass can be used. Furthermore, when specific examples are cited, though not particularly restricted thereto, ARTON (trade name: manufactured by JSR Corporation) or ZEONOA (trade name: manufactured by Nippon Zeon Co., Ltd.) can be preferably cited.

The exit surface12bof the light guide plate12is a surface that is disposed facing the liquid crystal display unit20and from which light for illuminating the liquid crystal display unit20is outputted, and is formed into a smooth surface whose surface roughness (Ra) is, for instance, 10 nm or less.

On the prism surface12c, in order to reflect light that propagates the inside of the light guide plate12and to change a propagation direction thereof, a plurality of grooves14having substantial V-shape in section is formed with a predetermined pitch so as to form a stripe-like pattern two-dimensionally. The groove14is asymmetrically formed of a gentle slope portion14aformed inclined to the exit surface12band a steep slope portion14bthat is formed continuously with the gentle slope portion14aand at an angle of inclination steeper than that of the gentle slope portion14a, and the formation directions of the respective grooves14are aligned so as to extend in parallel with the incidence surface12aof the light guide plate12. A direction of the light guide plate12is preferably constituted so that as the gentle slope portion14abecomes distant from the light source device13, a thickness may gradually increase. That is, when the steep slope portion14bis disposed so as to be gradually thinner as departs from the light source device13, efficiency with which light outputted from the light source device13is reflected by the steep slope portion14band outputted from the exit surface12bcan be improved.

FIG. 3is a side view showing with part of the light guide plate12enlarged. Reference numeral19inFIG. 3shows an example of propagation paths of light that propagates the inside of the light guide plate12. The light19outputted from the light source device13that is disposed on a left side from the drawing propagates the inside of the light guide plate12with reflections repeating at an inner surface of the light guide plate12, and part thereof exits from the exit surface12bof the light guide plate12.

The light that is input from the light source device13into the light guide plate12side is not restricted to parallel light shown inFIG. 3, and light having various components of angle of incidence is input.

The propagation path of the light in the inside of the light guide plate12can vary depending on an angle of inclination theta1of the gentle slope portion14athat constitutes the groove14, an angle of inclination theta2of the steep slope portion14b, and a pitch PTof the groove14. Accordingly, by properly setting these angles of inclination theta1and theta2and the pitch PT, uniformity of an amount of exit light in a plane of the exit surface12bcan be improved, and a bright line can be inhibited from being generated on the prism surface12cside of the light guide plate12.

For instance, when an angle (visual angle) at which a display screen of a liquid crystal display device1being obtained can be seen most brightly when the display screen is observed from various angles, that is, a visual angle at which brightness in the display screen becomes the maximum, would like to be set in the range ±10 degree with respect to a normal line of the display screen, it is preferable to set the angle of inclination theta2of the steep slope portion14bat 40 degree or more and 50 degree or less, for instance at substantially 43 degree. Similarly, the angle of inclination theta1of the gentle slope portion14ais preferably set in the range of 1.8 to 2.5 degree, for instance at substantially 2 degree.

Furthermore, the smaller the pitch PTof the grooves14is, the lower the amount of exit light from the backlight10becomes, that is, the lower the brightness of the liquid crystal display device1becomes. On the other hand, when the pitch PTis too large, the bright line is generated in the light guide plate12, and unevenness of the brightness as the backlight10unfavorably tends to be generated. Accordingly, the pitch PTof the grooves14is preferably set in the range of 120 μm or more and 250 μm or less.

The light source device13, as shown inFIGS. 2 and 4, is constituted of a quadratic intermediate light guide13A made of acrylic resin or polycarbonate resin and a light source (light emitting element)13B formed of an LED disposed at one end of a longer direction of the intermediate light guide13A. Among side surfaces of the intermediate light guide13A, on a surface on an opposite side from the light guide plate12, a prism surface13dhaving a triangular concavoconvex is formed. The light introduced from the light emitting element13B into the intermediate light guide13A is reflected by the prism surface13dto change a propagation direction toward the light guide plate12, and thereby the light from the light emitting element13B is efficiently irradiated onto the incidence surface12aof the light guide plate12. The prism surface13dis preferably covered with a light reflection film so as to improve a light reflection efficiency.

InFIG. 4, since up and down relationship of the light guide plate12is shown from a direction reversed from that ofFIGS. 1 through 3, inFIG. 4the grooves14are drawn so as to be formed on a top surface side of the light guide plate12. Accordingly, since the exit surface12bis directed downward inFIG. 4, the light is outputted downward.

As the LED (light-emitting diode) that is used as the light-emitting element13B, one capable of emitting any one color of green, bluish green, blue, orange, red, and yellowish green color can be used. The light-emitting diodes capable of emitting these colors are characterized in that the power consumption is such small as in the range of substantially 2.0 to 2.5 mW/cm2, a higher brightness such as in the range of substantially 5 to 10 cd/cm2can be easily obtained, a longer life such as 10,000 h or more can be obtained, the noise is generated with difficulty, and the cost is cheap (for instance, substantially 20 to 30 Japanese Yen a piece). The light-emitting diodes capable of emitting the light of these colors, because of coloring, cannot be applied as a backlight of a color display type liquid crystal display unit. However, these can be applied to a black-and-white display type liquid crystal display unit20like the embodiment without problems. Accordingly, when the light-emitting diode having one of the respective colors is used, a backlight that is low in the power consumption and has a brighter display mode with respect to the low power consumption can be obtained. Furthermore, among these, when the brightness is further demanded, a green light-emitting diode may be altered to one of yellowish green color. Still furthermore, in order to give fashionability to the display, it is effective to use a light-emitting diode having a red color or orange color.

Although in the embodiment, as the light source device13, one that is provided with the light-emitting element13B formed of the light-emitting diode is used, as the light source device13, any one of the light source devices that can irradiate the light uniformly on the incidence surface12aof the light guide plate12can be preferably used. However, one that is formed of the light-emitting diode that is less in the power consumption, excellent in the emission efficiency, and cheap is preferable.

In the backlight10having the configuration shown inFIGS. 1 through 4, the light of green, bluish green or blue color outputted from the light-emitting element13B is guided through the intermediate light guide13A toward the light guide plate12side, reflected by the gentle slope portion14binside of the light guide plate12and outputted from the exit surface12btoward the liquid crystal display unit20followed by passing through the transmissive or semi-transmissive liquid crystal display unit20, and further followed by illuminating the liquid crystal display unit20from a rear side. The light-emitting diodes capable of emitting the light of these colors, because of coloring, cannot be applied as a backlight of a color display type liquid crystal display unit. However, these can be applied to a black-and-white display type liquid crystal display unit20like the embodiment without problems.

Furthermore, when the light-emitting diode of one of the respective colors is used, a backlight10that is low in the power consumption and has a brighter display mode with respect to the lower power consumption can be obtained.

The light-emitting diode capable of emitting one of these colors, being low in the power consumption and easier in obtaining higher brightness, can provide a brighter transmissive or semi-transmissive liquid crystal display unit20. Furthermore, since the light-emitting diodes capable of emitting the colors, being longer in the life than the EL element and so on, more difficult to generate noise, and cheaper in the cost, permits the omission of,a noise preventive mechanism at the liquid crystal display unit20side, contributing to lowering costs of the entire liquid crystal display device that is provided with the backlight10.

FIG. 5shows a second embodiment of a backlight according to the invention, and a backlight (planar light emitting device) B according to this embodiment is formed by attaching a cover member25to part of the light guide plate12according to the former embodiment.

The cover member25according to the embodiment is, as shown inFIG. 5, a metal cover member that is disposed so as to cover a bar-like intermediate light guide13A, a light-emitting element13B on one end side thereof, and a side end portion on an intermediate light guide13A side of the light guide plate12, and has a horseshoe sectional shape.

The cover member25is constituted of a reflection surface cover portion25athat is a site disposed on a reflection surface side of the light guide plate12, an exit surface cover portion25bthat is a site disposed on the exit surface side of the light guide plate12, and a light guide cover portion25cthat is connected to the base portions and disposed facing the reflection surface13dof the intermediate light guide13A.

FIG. 6is an enlarged view for explaining a state in which the cover member25according to the embodiment is adhered to the intermediate light guide13A and the light-emitting element13B.

As shown in the drawing, in the cover member25according to the embodiment, in order to cover the light-emitting element13B projected from a side surface of the light guide plate12, an outer surface cover portion25dis formed so as to face an outer surface side (a side opposite to a surface that faces the intermediate light guide plate13a) of the light-emitting element13B, and a side surface cover portion25eis formed so as to face a side surface on the light guide plate12side of the light-emitting element13B. The outer surface cover portions25dand25eare preferably formed not so as to form a gap with the reflection surface cover portion25a, the exit surface cover portion25band the light guide cover portion25c, respectively. The cover portion25d, when the outer surface side of the light-emitting element13B is light-shielded not so as to leak light outside of the cover member25, may not be disposed.

One feature of the cover member25according to the embodiment is in that as shown inFIGS. 5 through 7, the reflection surface cover portion25ais formed more projected in length to a light guide direction (a direction forwarding from the intermediate light guide13A to the light guide plate12) than the exit surface cover portion25b, and a projection length L is set at 0.5 mm or more. By thus constituting, the backlight according to the embodiment can realize an appreciable improvement in the brightness. Furthermore, the projection length is preferably set at 0.7 mm or more, being more preferable to be 0.8 mm or more. By setting the projection length in the above range, a further improvement in the brightness can be realized. The operations thereof will be detailed in the following with reference toFIGS. 7 and 8.

FIG. 7is a partial sectional side view along a VII—VII line of the backlight shown inFIG. 5, andFIG. 8is a partial sectional side view of a cover member251that has a structure in which a length in a light guide direction of the reflection surface cover portion25aand that in the light guide direction of the exit surface cover portion25bare made the same. InFIG. 8, a reflection surface cover portion25a1whose length is made the same as the length in the light guide direction of the exit surface cover portion25bis shown.

First, in the configuration shown inFIG. 8, the cover member251having a horseshoe sectional shape grasps a side end portion of the light guide plate12from up and down with the intermediate light guide13A accommodated inside thereof, and a length in the light guide direction of the cover member251on the prism surface12cside of the light guide plate12is made substantially identical as that on the exit surface12bside. In this structure, as shown inFIG. 8, light that is reflected by an inner surface side of a tip end portion of the exit surface cover portion25band propagates within the light guide plate12is outputted through the prism surface12cof the light guide plate12below the backlight. The light, provided that the liquid crystal display unit20is disposed on a top surface side of the backlight, would not contribute to illumination of the liquid crystal display unit20and becomes waste light, resulting in not contributing to the display of the liquid crystal display unit20.

On the other hand, in the backlight10according to the embodiment shown inFIG. 7, the cover member25having a horseshoe sectional shape accommodates the intermediate light guide13A inside thereof and grasps the light guide plate12by tip ends thereof from up and down. In addition, the reflection surface cover portion25aon the prism surface12cside of the light guide plate12is formed longer in the light guide direction by the projection length L than the exit surface cover portion25bon the exit surface12bside of the light guide plate12. In the backlight10thus configured, the light outputted from the intermediate light guide13A, with reflections at an inner surface of the light guide plate12or an inner surface side of the cover member25repeating, propagates from the intermediate light guide13A side to a direction toward the light guide plate12side. In the backlight10according to the embodiment, as shown inFIG. 7, of the light that is reflected at the inner surface side of the cover member25, the light reflected at the inner surface side of the tip end portion of the exit surface cover portion25bis further reflected at the inner surface side of the tip end portion of the reflection surface cover portion25aand outputted from the exit surface12bof the light guide plate12above the backlight10. Accordingly, as shown in, for instance,FIG. 7, when the liquid crystal display unit20is disposed on a top surface side of the backlight10, the light reflected at the tip end portion of the reflection surface cover portion25aalso can be utilized as light that contributes to the display of the liquid crystal display unit20. Thus, since the backlight10according to the embodiment can increase an amount of exit light from the exit surface12bof the light guide plate12and the light from the prism surface12cof the light guide plate12can be suppressed from leaking, the backlight10according to the embodiment can realize an appreciable brightness improvement effect in comparison to the backlight having the structure shown inFIG. 8.

In the above-explained respective embodiments, a reflection film is not particularly disposed on an outer surface of the prism surface12cof the light guide plate12. However, a reflection film29high in the light reflectance such as Ag or Al may be disposed on the outer surface of the prism surface12cas shown with a two dot chain line inFIG. 1so as to further improve the light reflectance of the prism surface12c. Furthermore, on an inner surface of the cover member25, a light reflection film may be separately disposed to improve the light reflectance at the inner surface of the cover member25. Still furthermore, although, in the above embodiment, an entire cover member25is made of a metal plate, the entire cover member25may be formed, not of a metal plate, but of a light reflection film.

Still furthermore, in the invention, a cover-type reflector member28having a horseshoe sectional shape such as shown inFIG. 9may be attached at an end portion of the light guide plate12separately from the above cover member25so that light may be reflected by a light reflection surface disposed on an inner surface portion of the reflector member28and thereby exit light from the exit surface12bof the light guide plate12may be increased. The reflector member28may be formed of the identical material as the cover member25.

When the reflector member28is separately attached to the end portion side of the light guide plate12, the light that may leak outside of the end portion side of the light guide plate12can be re-reflected and returned to the inside of the light guide plate12. As a result, an amount of light that can be reflected at the steep slope surface portion14bof the prism surface12ccan be increased, and thereby the brightness as the backlight10can be improved.

FIG. 10is a partial perspective view showing a configuration of a frontlight (planar light-emitting device) that is a second embodiment of the invention. Furthermore,FIG. 11is a partial perspective view showing a state in which a cover member58described later is removed from the frontlight50shown inFIG. 10. The frontlight50shown in these drawings is constituted including a tabular light guide plate52made of a transparent resin material; a rod-like bar light guide (light guide)53disposed at a side end portion (one end portion on a shorter-side side of a rectangular light guide plate52) on a side end surface52aside of the light guide plate52; light-emitting elements (light source)55,55disposed at both end portions in a length direction of the bar light guide53; and a cover member58that is adhered so as to cover the bar light guide53and the light-emitting elements55,55, as well as a side end portion on the bar light guide53side of the light guide plate52.

The light guide plate52, as shown inFIG. 11, is a transparent tabular member in which a side end surface52athat faces the bar light guide53is an incidence surface, and a top surface thereof is a reflection surface52cin which projection portions54that are substantially in parallel with the side end surface52aand have an wedge-like side view are formed in stripe in parallel with each other is a reflection surface52c. The light guide plate52is structured so that the light introduced from the side end surface52ainto the inside thereof is reflected at the reflection surface52c, changed in its direction of propagation, and outputted from a surface (bottom surface in the drawing) on an opposite side of the reflection surface52c.

Furthermore, the light guide plate52can be manufactured according to a method in which a resin material such as transparent acrylic resin is injection-molded in a tabular shape. Still furthermore, as the material constituting the light guide plate52, the identical materials as that for the light guide plate12according to the previous embodiment can be selected.

The bar light guide53and the light-emitting elements55in this example are ones the same as that used in the first embodiment, and, as shown inFIG. 15, on a side surface of the light guide53wedge-like grooves56are formed to form a reflection surface53b. The bar light guide53reflects the light that is outputted from the light-emitting elements55,55and introduced into the inside at a surface that constitutes these grooves56, changes a propagation direction of the light toward the light guide plate52, and irradiates the light onto the side end surface52aof the light guide plate52. The light introduced from the bar light guide53into the light guide plate52travels inside of the light guide plate52, is reflected at the surface that constitutes the projections54formed on the reflection surface52c, changed in its direction of propagation, and outputted from an exit surface (bottom surface in the drawing) of the light guide plate52.

The cover member58, as shown inFIG. 10, is a metal member that has a horseshoe sectional shape and is disposed with the bar light guide53, the light-emitting elements55,55at both ends thereof and a side end portion on the bar light guide13side of the light guide plate52covering. The cover member58is constituted including a reflection surface cover portion58athat is a site disposed on the reflection surface side (top surface side in the drawing) of the light guide plate52; an exit surface cover portion58bthat is a site disposed on the exit surface side (bottom surface side in the drawing) of the light guide plate52; and a light guide cover portion58cthat is connected to the base portions and disposed facing the reflection surface53bof the bar light guide53.

Furthermore,FIG. 12is an enlarged explanatory view for explaining a state in which the cover member58according to the embodiment is adhered to the bar light guide53and the light-emitting element55.

As shown in the drawing, in the cover member58according to the embodiment, in order to cover the light-emitting element55projected from a side surface of the light guide plate52, an outer surface cover portion58dis formed so as to face an outer surface side (surface on a side opposite to a surface that faces the bar light guide53) of the light-emitting element55and a side surface cover portion58eis formed so as to face a side surface on the light guide plate52side of the light-emitting element55.

One feature of the cover member58according to the embodiment is in that as shown inFIG. 10, the reflection surface cover portion58ais formed more projected in a light guide direction (direction forwarding from the bar light guide53to the light guide plate52) than the exit surface cover portion58b, and a projection length L1thereof is set at 0.5 mm or more. By thus constituting, the frontlight50according to the embodiment can realize a remarkable improvement in the brightness. Furthermore, the projection length L is preferable to be set at 0.7 mm or more, being more preferable to be set at 0.8 mm or more. By setting in the above range, a further improvement in the brightness can be realized. The operations thereof will be detailed in the following with reference toFIGS. 13 and 14.

FIG. 13is a partial sectional side view of a frontlight50shown inFIGS. 10 through 12, andFIG. 14is a partial sectional side view of a frontlight in which the reflection surface cover portion68aand the exit surface cover portion68bare the same in the length.

First, in the existing configuration shown inFIG. 14, the cover member68having a horseshoe sectional shape is constituted by grasping a side end portion of the light guide plate52from up and down with the bar light guide53accommodated inside thereof, and lengths in the light guide direction of the cover member68are made substantially identical on the reflection surface52cside of the light guide plate52and on the exit surface52bside thereof. In this structure, as shown inFIG. 14, light that is reflected at an inner surface side of a tip end portion of the exit surface cover portion68band propagates within the light guide plate52is outputted from the reflection surface52cof the light guide plate52above the frontlight. The light, provided that a reflective liquid crystal display unit70is disposed on a bottom surface side of the frontlight, reaches a user without going through the liquid crystal display unit70. The light not only does not contribute to the display of the liquid crystal display unit70but also causes blushing on the reflection surface52cof the light guide plate52, resulting in causing the deterioration of the visibility.

On the other hand, in the frontlight50according to the embodiment shown inFIGS. 10 through 13, the reflection surface cover portion58ais formed longer in the light guide direction by a projection length L′ than the exit surface cover portion58bin the light guide direction.

In the configuration like this, the light outputted from the bar light guide53, with reflections at an inner surface of the light guide plate52or an inner surface side of the cover member58repeating, propagates from the light guide53side to a direction toward the light guide plate52. In the frontlight50according to the embodiment, the light reflected at the inner surface side of the tip end portion of the exit surface cover portion58bis further reflected at the inner surface side of the tip end portion of the reflection surface cover portion58aand outputted. Accordingly, as shown in, for instance,FIG. 13, when a reflective liquid crystal display unit70is disposed on a bottom surface side of the frontlight50, the light reflected at the tip end portion of the reflection surface cover portion58aalso can be utilized as light that contributes to the display of the liquid crystal display unit70. Thus, since the frontlight50according to the embodiment can increase an amount of exit light from the exit surface52bof the light guide plate52and also can suppress the light from the reflection surface52cof the light guide plate52from leaking, a frontlight that can realize an appreciable brightness improvement in comparison with an existing frontlight, can cause the blushing with difficulty, and is excellent in the visibility can be formed.

In the bar light guide53of the frontlight50according to the embodiment, as shown inFIG. 16, in the grooves56formed on the reflection surface53b, an angle that slope portions56a,56bform is made in the above range, and depths D of the grooves shown inFIG. 16are also constituted controlled at predetermined depths. The depths D of the grooves56will be detailed in the following with reference toFIG. 17.FIG. 17is a graph that shows relationship between the depths D of the grooves56formed on the reflection surface53bof the light guide53and distances between the light-emitting element55and the respective grooves56.

InFIG. 17, the depths of the grooves56from a center of the light guide53to one light-emitting element55are shown. Relationship between the distances up to the other light-emitting element55and the depths D of the grooves is symmetrical with respect to the center of the light guide53. That is, the depths D of two grooves56that are equally distanced from the center of the light guide53are the same.

The depths D of the grooves56in the frontlight50according to the embodiment, as shown inFIG. 17, are formed differently between a region1that is the neighborhood of the center portion of the light guide53and a region2from the outside of the region1to the light-emitting element55. That is, in the region1that is the center portion side of the light guide53, the depths D of the grooves56are formed constant at a depth d2, and in the region2, the depth of the groove56nearest to the light-emitting element55is set at d1and the closer to the center of the light guide53the groves56are, the deeper the grooves56are formed. In the region2, the relationship between the distance from the light-emitting element55to the groove56and the depth D of the groove56is formed according to a quadratic function or an exponential function. That is, a depth D of a groove56, with a distance t from the light-emitting element55, can be expressed by a relational expression D=a×t2+b×t+d1(a and b are constants) or D=c×et+d1(c is a constant), and constants contained in the relational expressions may be appropriately adjusted to the best values according to a dimension such as the length of the light guide53and so on.

More specifically, when the length of the bar light guide53is substantially 40 to 100 mm, the groove depths d1and d2shown inFIG. 17are set at substantially 20 μm and 50 μm, respectively, and in the region2the groove depths D are preferably formed so as to sequentially increase according to the quadratic-function or exponential function from 20 μm at the light-emitting element55side to the center of the bar light guide53.

Thus, the frontlight50according to the embodiment, since the bar light guide53thereof is constituted controlled as mentioned above, can increase an amount of light that is introduced from the bar light guide53into the light guide plate52and can improve the uniformity thereof. Thereby, an increase in the amount of light outputted from the exit surface of the light guide plate52and an improvement in the uniformity of the exit light can be realized. In addition, owing to the disposition of the cover member58having the above configuration, light can be suppressed from leaking from a top surface (reflection surface52c) of the light guide plate52, and the light that has leaked so far to the top surface can be outputted toward a bottom surface of the light guide plate52, resulting in realizing an improvement in the brightness of the frontlight.

In the next place, an example of a liquid crystal display device provided with the frontlight50according to the embodiment will be explained.FIG. 18is a perspective view showing one example of a liquid crystal display device equipped with the frontlight50shown inFIG. 10, andFIG. 19is a schematic sectional view along a XIX—XIX line shown in FIG.18. The liquid crystal display device shown in the drawings comprises the frontlight50according to the embodiment and a reflective black-and-white liquid crystal display unit70disposed at a rear side thereof.

The liquid crystal display unit70is, as shown inFIG. 19, constituted by connecting and integrating with a sealing material74a first substrate71and a second substrate72that face each other with a liquid crystal layer73interposed therebetween. On the liquid crystal layer73side of the first substrate71, a display circuit77that includes an electrode layer and an alignment film and drives and controls the liquid crystal layer73is formed, and on the liquid crystal layer73side of the second substrate72, a reflection film75that reflects the light incident on the liquid crystal display unit70and a display circuit76that includes an electrode layer and an alignment film and drives and controls the liquid crystal layer73are sequentially laminated. Furthermore, the reflection film75may be formed with a concavoconvex shape on a surface thereof to diffuse the reflected light.

In the liquid crystal display device according to the above configuration, the light outputted from the light-emitting element55is firstly introduced into the bar light guide53followed by being reflected at the reflection surface53bof the bar light guide53to change its propagation direction, and is introduced into the light guide plate52from a side end surface of the light guide plate52disposed facing the exit surface of the bar light guide53. The light traveling inside of the light guide plate52is reflected at the slope portion54aof the reflection surface52cof the light guide plate52, thereby the propagation direction thereof is changed, and the light that illuminates the liquid crystal display unit70is outputted from the exit surface52bof the light guide plate52.

Subsequently, the light inputted into the liquid crystal display unit70goes through the first substrate71, the display circuit77, the liquid crystal layer73, and the display circuit76and reaches the reflection film75, is reflected by the reflection film75, and returned again to the liquid crystal layer73side. The reflected light is outputted from a top surface side of the liquid crystal display unit70, transmits through the light guide plate52and reaches a user. Thus, the liquid crystal display device according to the invention, when the frontlight50according to the invention is used as a light source of a reflective liquid crystal display unit70, allows seeing the display even in a dark place where sufficient ambient light cannot be obtained. Furthermore, when the liquid crystal display unit70is provided with the frontlight50according to the invention, an amount of light to be irradiated to the liquid crystal display unit70can be increased, resulting in obtaining brighter display. Still furthermore, since the light is suppressed from leaking to a top surface side of the frontlight50, the lowering of the visibility due to the blushing can be suppressed.

Furthermore, similarly to the case of the previous embodiment, the LED (light-emitting diode) used as the light-emitting element55can be any one that is capable of emitting green color, bluish green color, blue color, orange color, red color, or yellowish green color.

Furthermore, among these, in the case of more brightness being demanded, the green emitting light-emitting diode may be changed to the yellowish green emitting one. Still furthermore, in order to endow the display with the fashionability, the red- or orange-emitting light-emitting diode may be effectively used.

The light-emitting diodes capable of emitting these colors are characterized in that the power consumption is such small as substantially in the range of 2.0 to 2.5 mW/cm2, a higher brightness such as substantially 5 to 10 cd/cm2can be easily obtained, a longer life such as 10,000 h or more can be obtained, the noise is generated with difficulty, and the cost is cheap (for instance, substantially 20 to 30 Japanese Yen a piece). The light-emitting diodes capable of emitting these colors, because of coloring, cannot be applied as a frontlight of a color display type liquid crystal display unit. However, these can be applied, without problems, to a black-and-white display type liquid crystal display unit70such as one according to the embodiment. Accordingly, when the light-emitting diode having one of the respective colors is used, a frontlight display liquid crystal display device70that is low in the power consumption and has a brighter display mode with respect to the low power consumption can be obtained.

As explained above, the invention is constituted including a light guide plate; a light guide provided to one side end portion thereof; and a light source; wherein one surface side of the light guide plate is formed into a concavoconvex reflection surface; the other surface side of the light guide plate is formed into an exit surface; the reflection surface is provided with a plurality of stripe-like grooves formed of a gentle slope portion and a steep slope portion; and a subject to be irradiated is disposed outside of the exit surface. Accordingly, light outputted from the light source is reflected at the steep slope portion and can be irradiated from the exit surface of the light guide plate onto the subject to be irradiated. Thus, the subject to be irradiated can be illuminated from a rear side thereof, resulting in allowing functioning as a backlight.

In the backlight according to the invention, the light source is formed of a light-emitting diode of any one color of green, bluish green, and blue color. Since the light-emitting diode having one of these colors can be cheaply obtained, it contributes to the cost reduction as the light source. Furthermore, in comparison with a structure where an EL element is used as the light source, since the light-emitting diode generates less noise, there is no need of noise countermeasure, that is, there is no need of shield or a noise reduction circuit, resulting in contributing to the cost reduction.

Furthermore, since the light-emitting diode having one of these colors is higher in the brightness relative to the power consumption, a brighter backlight can be cheaply provided.

In the backlight according to the invention, the steep slope portion that constitutes the groove is disposed on a side closer to the light source side than the gentle slope portion. Accordingly, the steep slope portion assuredly guides the light from the exit surface of the light guide plate to a side of the subject to be irradiated. As a result, a brighter backlight can be easily obtained.

In the backlight according to the invention, the cover member having at least the reflection surface cover portion that covers the side end portion on the reflection surface side of the light guide plate, the light guide cover portion that covers the light guide, and the exit surface cover portion that covers the side end portion on the exit surface side of the light guide plate is adhered so as to cover the light guide and the side end portion of the light guide plate. Accordingly, light leakage from the side end portion side of the light guide plate and the light guide side can be made smaller and the light introduced into the light guide plate can be increased, resulting in an improvement in the brightness as the backlight.

In the backlight according to the invention, since the reflection surface is formed on an inner surface side of the cover member, an amount of light that is reflected inside of the light guide and inputted into the light guide plate side can be increased, resulting in an improvement in the brightness as the backlight.

Since the liquid crystal display device according to the invention is provided with the backlight in which the light outputted from the light source is reflected at the steep slope portion and can be irradiated from the exit surface of the light guide plate onto the object to be irradiated, the transmissive or semi-transmissive liquid crystal display unit can be illuminated from a rear side thereof.

In order to overcome the above problems, in the liquid crystal display device according to the invention, the liquid crystal display unit is a black-and-white display type and the light source is made of the light-emitting diode having any one color of green, bluish green and blue color. When the light-emitting diode is used as the light source, in comparison with the EL element, the power consumption is smaller, and higher brightness relative to the power consumption can be obtained. Furthermore, the light-emitting diode having any one color of green, bluish green and blue color can be easily obtained and cheap, resulting in contributing to the cost reduction. Furthermore, in comparison with a structure where the EL element is used as the light source, the light-emitting diode is less in the noise generation. Accordingly, since there is no need of noise countermeasure, there is no need of shield and noise reduction circuit, resulting in contributing to the cost reduction.

Furthermore, the light-emitting diodes having these colors are higher in the obtained brightness relative to the power consumption, resulting in cheaply providing a brighter backlight.

Still furthermore, when one of the light-emitting diodes having these colors is used as the light source, colored light illuminates the liquid crystal display unit from the rear surface side thereof. However, when the liquid crystal display unit is not a color display type but a black-and-white display type, there is no particular problem, and a brighter display mode can be cheaply obtained.

In order to overcome the above problems, in the liquid crystal display device according to the invention, the steep slope portion that constitutes the groove is disposed closer to the light source side than the gentle slope portion, and the light outputted from the light source is reflected by the steep slope portion and can be irradiated from the exit surface of the light guide plate onto the subject to be irradiated. Accordingly, the subject to be irradiated can be illuminated from the rear side thereof, and thereby allowing functioning as a backlight. Thus, a liquid crystal display having transmission mode display or semi-transmission display mode that utilizes illumination light from the rear surface side can be obtained.

In the liquid crystal display device according to the invention, the cover member is disposed on front and rear sides of the side end portion of the light guide plate and a periphery side of the light guide, thereby the light leakage from the side end portion side of the light guide plate and the light guide side can be made smaller, and the light introduced into the light guide plate can be increased. Accordingly, the brightness as the backlight can be improved, resulting in providing a liquid crystal display unit of brighter display.

In order to overcome the above problems, in the liquid crystal display device according to the invention, a reflection surface may be formed on an inner surface side of the cover member. Since the liquid crystal display device is provided with a brighter backlight, a liquid crystal display unit of brighter display can be provided.

In the frontlight according to the invention, the light source includes a light-emitting diode of any one color of green, bluish green, blue, orange, red and yellowish green color. Since the light-emitting diode having one of these colors can be cheaply obtained, it contributes to the cost reduction as the light source. Furthermore, in comparison with a structure where an EL element is used as the light source, since the light-emitting diode generates less noise, there is no need of noise countermeasure, that is, there is no need of shield or a noise reduction circuit, resulting in contributing to the cost reduction.

Furthermore, since the light-emitting diode having one of these colors is higher in the obtained brightness relative to the power consumption, a brighter frontlight can be cheaply provided.

In the frontlight according to the invention, the steep slope portion that constitutes the groove is disposed on a side closer to the light source side than the gentle slope portion. Accordingly, the steep slope portion assuredly guides the light from the exit surface of the light guide plate to a side of the subject to be irradiated. As a result, a brighter frontlight can be easily obtained.

Furthermore, when the liquid crystal display device is provided with the frontlight, since higher brightness can be obtained relative to the power consumption, a brighter liquid crystal display device can be cheaply provided.