Spread illuminating apparatus with plurality of light conductive bars arrayed adjacently

1. Field of the Invention

The present invention relates to a spread illuminating apparatus suitable for a display device to operate with outside light, especially a liquid crystal display heavily used in a personal computer, a mobile communications device, and the like.

2. Description of the Related Art

A liquid crystal display (hereinafter referred to as LCD) featuring low profile, small occupying volume and light weight is used in many electric devices, such as a personal computer (hereinafter referred to as PC) and a mobile phone, and is expected to continue to be increasingly demanded.

A liquid crystal of the LCD does not emit light by itself, so the LCD requires an illuminating means to irradiate the liquid crystal when used in a place where sunlight or room lighting is not fully available. Since it is very inconvenient if an illuminating means is arranged discrete from an electric device equipped with an LCD, the illuminating means is usually arranged with the LCD as a unit. And, the illuminating means is required to be low in profile and small in power consumption, when used for a PC, in particular a notebook-size PC, and a mobile phone. These requirements are filled by a spread illuminating apparatus of side light type.

FIG. 11 is a perspective exploded view of a conventional spread illuminating apparatus of this type disclosed in Japanese Patent Laid-open No. 2000-11723. As shown in FIG. 11 , a spread illuminating apparatus 1 is disposed over a front surface (upper side in the figure) F of a reflection-type liquid crystal element L, which is a main body of a reflection-type LCD. The spread illuminating apparatus 1 comprises a light conductive plate 2 made of a light-permissible material, a light conductive bar 7 , and spot-like light sources 9 , 9 such as light emitting diodes (LEDs).

The light conductive bar 7 is disposed with its side surface 13 in contact with an end surface 3 of the light conductive plate 2 , and has the spot-like light sources 9 , 9 arranged on its both end surfaces 8 , 8 , respectively. An optical path conversion means 11 adapted to direct lights from the spot-like light sources 9 , 9 toward the end surface 3 of the light conductive plate 2 is formed on a side surface 14 of the light conductive bar 7 opposite to the side surface 13 . The optical path conversion means comprises, for example, a plurality of grooves 15 substantially triangular in section and a plurality of flat portions 16 each present between adjacent grooves 15 , 15 .

In the spread illuminating apparatus 1 thus structured, lights from the spot-like light sources 9 , 9 enter the light conductive bar 7 , have their optical paths changed by the optical conversion means 11 formed on the side surface 14 of the light conductive bar 7 , and are directed toward and introduced into the light conductive plate 2 through the end surface 3 of the light conductive plate 2 . The lights introduced into the light conductive plate 2 travel toward an end surface 10 thereof opposite to the end surface 3 while repeating reflection and refraction therein, exit out meanwhile through a bottom surface thereof, and illuminate the reflection-type liquid crystal element L disposed close to a bottom surface 5 of the light conductive plate 2 , whereby the reflection-type liquid crystal element L performs an emission (indirect emission) display.

The conventional illuminating apparatus 11 has the problem that the light exiting out from the side surface 13 of the light conductive bar 7 toward the end surface 3 of the light conductive plate 2 is not uniform in intensity along the length of the side surface 13 .

FIG. 12 illustrates schematically the problem. Attention is now called to lights r 3 and r 4 which exit out orthogonally from the side surface 13 of the light conductive bar 7 in contact with the end surface 3 of the light conductive plate 2 and which are incident orthogonally on the end surface 3 . Lights r 1 and r 2 , from which the lights r 3 and r 4 originate, respectively, are parallel to each other if the grooves 15 (not shown in FIG. 12 ) formed on the light conductive bar 7 have a constant angle. This means that lights, from which the lights r 1 and r 2 originate, respectively, have respective different incidence points on the end surface 8 of the light conductive bar 7 .

The intensity of the incident light on the end surface 8 of the light conductive bar 7 differs from point to point. Specifically, the intensity is high at a point in contact with the central portion of the spot-like light source 9 , and low at a point in contact with the end portion thereof or not in contact with any portion hereof. Thus, the light r 1 has a high intensity and the light r 2 has a low intensity. Accordingly, as to the lights r 3 and r 4 exiting out from the side surface 13 of the light conductive bar 7 , the light r 3 has a high intensity and the light r 4 has a low intensity, causing non-uniformity in the intensity of incident light on the end surface 3 of the light conductive plate 2 . Further, lights r 1 ′ and r 3 ′ have a high intensity, and the lights r 2 ′ and r 4 ′ have a low intensity. FIG. 12 shows only the left end portion of the light conductive bar 7 , but this happens also at the right end portion thereof.

In a spread illuminating apparatus shown in FIG. 13 , the brightness was measured at the section taken along A-A′ on the light conductive plate 2 , and the brightness distribution α in FIG. 14 was obtained. As shown in FIG. 14 , in the conventional apparatus, the light is not uniformly distributed (the distribution is not even) along the length of the light conductive bar 7 , causing a problem that the light distribution at the light conductive plate 2 is not uniform.

The present invention has been made in the light of the above problem, and it is an object of the present invention to provide a spread illuminating apparatus, in which non-uniformity in brightness along the length of the light conductive bar is diminished, thereby rendering the surface of the light conductive plate uniformly bright.

In order to achieve the object, the spread illuminating apparatus may comprise: a light conductive plate made of a light-transmissible material; at least two light conductive bars made of a light-transmissible material, disposed with their one side surfaces facing an end surface of the light conductive plate, each having an optical path conversion mean formed on their side surfaces opposite to the one side surfaces, arrayed with their respective side surfaces facing each other, and oriented along and close to the end surface of the light conductive plate; and a spot-like light source disposed facing one end surfaces of the light conductive bars and having its light emitting surface positioned so as to cover all interfaces between adjacent light conductive bars. Here, the light conductive bars may include another spot-like light source disposed facing the other end surfaces thereof.

Further, the spread illuminating apparatus may comprise: a light conductive plate made of a light-transmissible material; at least three light conductive bars made of a light-transmissible material, arrayed with their respective side surfaces facing each other, disposed with their one side surfaces facing an end surface of the light conductive plate, and oriented along and close to the end surface of the light conductive plate; and at least two spot-like light sources, rather than one, disposed facing one end surfaces of the light conductive bars and arranged such that at least one thereof has its light emitting surface positioned so as to cover at least one interface between adjacent light conductive bars, and that each of the other(s) has its emitting surfaces positioned to cover an end surface of each of light conductive bars not covered by the at least one spot-like light source. Here the light conductive bars may include another at least two spot-like light sources symmetrically disposed facing the other end surfaces thereof.

FIG. 1 is an exploded perspective view of a spread illuminating apparatus of the present invention;

FIG. 2 is a schematic view of how non-uniformity in brightness is diminished in the illuminating apparatus of the present invention;

FIG. 3 is a top plan view of the spread illuminating apparatus shown in FIG. 1 , showing its assembled state;

FIG. 4 is a graph of brightness distribution at the section taken along B-B′ on a light conductive plate in FIG. 3 ;

FIG. 5 is a graph of brightness distributions obtained by way of light conductive bars in FIGS. 3 , 6 and 7 along the length direction of respective light conductive bars when a spot-like light source is provided only at one end surface thereof;

FIG. 6 is a top plan view of one of the light conductive bars, which produces the brightness distribution X;

FIG. 7 is a top plan view of another one of the light conductive bars, which produces the brightness distribution Y;

FIG. 8 is a top plan view of another embodiment of the present invention;

FIG. 9 is a top plan view of further embodiment of the present invention;

FIG. 10 is a top plan view of still further embodiment of the present invention;

FIG. 11 is an exploded perspective view of a conventional spread illuminating apparatus;

FIG. 12 is a schematic view of how non-uniformity in brightness is caused in the conventional spread illuminating apparatus;

FIG. 13 is a top plan view of the conventional spread illuminating apparatus shown in FIG. 11 , showing its assembled state; and

FIG. 14 is a graph of the brightness distribution at the section taken along A-A′ on a light conductive plate in FIG. 13 .

Preferred embodiments of the present invention will be described with reference to the drawings. Referring to FIG. 1 , a spread illuminating apparatus 1 is disposed over a front surface (upper side in the figure) F of a reflection-type liquid crystal element L, which is a main body of a reflection-type LCD. The spread illuminating apparatus 1 comprises a light conductive plate 2 made of a light-transmissible material, a plurality (two in this embodiment) of light conductive bars 7 a, 7 b made of a light-transmissible material and uniform in configuration and size, and a prescribed number (two in this embodiment) of spot-like light sources 9 a, 9 b, such as LEDs.

The two light conductive bars 7 a, 7 b are disposed adjacent to each other with their one side surfaces facing one end surface 3 of the light conductive plate 2 such that lights emitted from the spot-like light sources 9 a, 9 a have their respective optical paths changed at respective optical path conversion means 11 a, 11 b (to be described later) so as to be made incident on the end surface 3 of the light conductive plate 2 . One light conductive bar 7 b of the two, which is positioned closer to the light conductive plate 2 , is disposed with its side surface 13 b in contact with the end surface 3 of the light conductive plate 2 . A side surface 14 b of the light conductive bar 7 b opposite to the side surface 13 b is in contact with a side surface 13 a of the other light conductive bars 7 a of the two.

Each of the two spot-like light source 9 a, 9 a is fixedly attached to end surfaces 8 a, 8 b of the two light conductive bars 7 a, 7 b such that the center of an emitting surface 9 af thereof is positioned at the interface between the side surface 13 a of the light conductive bar 7 a and the side surface 14 b of the light conductive bars 7 b.

The light conductive bars 7 a, 7 b have the aforementioned optical path conversion means 11 a, 11 b formed on their side surfaces 14 a, 14 b, respectively. The optical path conversion means 11 a ( 11 b ) comprises a plurality of grooves 15 a ( 15 b ) substantially triangular in section and a plurality of flat portions 16 a ( 16 b ) each present between adjacent grooves 15 a, 15 a ( 15 b, 15 b ), and is adapted to guide lights emitted from the spot-like light sources 9 a, 9 a toward the end surface 3 of the light conductive plate 2 .

The light conductive plate 2 has a light reflection pattern 17 formed on its top surface 6 in parallel with the end surface 3 . The light reflection pattern 17 comprises a plurality of grooves 18 substantially triangular in section and a plurality of flat portions 19 each present between adjacent grooves 18 , 18 . The interval between the grooves 18 , 18 varies according to the distance from the end surface 3 of the light conductive plate 2 , whereby lights exit out uniformly from a major surface (bottom surface 5 in this case) of the light conductive plate 2 independent of the distance from the end surface 3 .

A light reflection member 12 , which is adapted to efficiently guide lights leaking from the light conductive bars 17 a, 17 b into the light conductive plate 2 , is disposed so as to enclose the light conductive bars 7 a 7 b, and the end part of the light conductive plate 2 positioned close to the light conductive bar 7 b such that the longitudinal surfaces of the light conductive bars 7 a, 7 b are covered except the side surfaces 13 a, 13 b of the light conductive bars 7 a, 7 b.

In the spread illuminating apparatus structured above, lights emitted from the spot-like light sources 9 a, 9 a go into the light conductive bars 7 a, 7 b, have their optical paths changed at the optical path conversion means 11 a, 11 b formed parallel to the end surface 3 of the light conductive plate 2 , and travel into the light conductive plate 2 through the end surface 3 . The lights introduced into the light conductive plate 2 travel toward the other end surface 10 of the light conductive plate 2 while repeating reflection and refraction therein, exit out partly meanwhile through the bottom surface 5 , and illuminate the reflection-type liquid crystal element L disposed close to the bottom surface 5 , whereby the reflection-type liquid crystal element L performs an emission (indirect emission) display.

In the above spread illuminating apparatus, the non-uniformity in brightness along the length of the light conductive bar 7 b at the side surface 13 b, from which lights exit out to go into the light conductive plate 2 , is diminished as illustrated in FIG. 2 . Referring to FIG. 2 , lights r 1 and r 2 (corresponding to the lights r 1 , r 2 in FIG. 12 , respectively), which go into the light conductive bars 7 a, 7 b through respective different spots at the end surfaces 8 a, 8 b, have their optical paths changed at the optical path conversion means 11 a, 11 b. Specifically, the light r 1 has its optical path changed at the optical path conversion means 11 a thereby turning into light r 3 and is incident on the end surface 3 of the light conductive plate 2 , and the light r 2 has its optical path changed at the optical conversion means 11 b thereby turning into light r 4 and is incident on the end surface 3 . Here, the lights r 3 and r 4 are aligned to each other as shown in the figure.

The intensity of incident light on the end surface 8 a, 8 b differs from spot to spot. The intensity is high at a spot positioned to the center part of the emitting surface 9 af, and low at a spot positioned to the end part of the emitting surface 9 af or positioned off the emitting surface 9 af. This means that the light r 1 has a high intensity and the light r 2 has a low intensity, accordingly the light r 3 has a high intensity and the light r 4 has a low intensity. In the conventional apparatus, the difference in incidence position of the lights r 1 and r 2 at the end surface 8 of the light conductive bar 7 carries through straight as the difference in incidence position of the lights r 3 and r 4 at the end surface 3 of the light conductive plate 2 (see FIG. 12 ), thereby causing non-uniformity in brightness with respect to the length direction of the light conductive bar 7 .

In the apparatus of the present invention, the lights r 3 and r 4 , which originate respectively from the lights r 1 and r 2 incident on different end surfaces 8 a, 8 b of the light conductive bars 7 a, 7 b, are aligned to each other to be incident on the same spot at the end surface 3 of the light conductive plate 2 as described above. Since the light r 3 has a high intensity and the light r 4 has a low intensity, the intensity of light consisting of the lights r 3 and r 4 aligned to each other is modified closer to the average intensity along the length direction of the light conductive bars 7 a, 7 b. This is the case also with lights r 1 ′ and r 2 ′, and lights r 3 ′ and r 4 ′ originating from the lights r 1 ′ and r 2 ′, respectively. In FIG. 2 , the left end part of the light conductive bars 7 a, 7 b is explained, but this applies also to the right end part thereof.

In the apparatus of the present invention assembled as shown in FIG. 3 , the brightness was measured at the section taken along B-B′ on the light conductive plate 2 , and the brightness distribution β shown in FIG. 4 was obtained. As seen from the distribution β the brightness at the side surface 13 b is almost uniform (the distribution curve is almost even) along the length of the light conductive bar 7 a, thereby realizing uniform brightness on the light conductive plate 2 with regard to the same direction (the length of the light conductive bar 7 a ).

In FIG. 5 , brightness of light incident on the end surface 3 of the light conductive plate 2 (when the spot-like light source 9 a is disposed only at the left end surfaces 8 a, 8 b of the light conductive bars 7 a, 7 b ) is shown as a function of the distance from the spot-like light source 9 a (the end surfaces 8 a, 8 b ). This also indicates that the brightness of light incident on the end surface 3 of the light conductive plate 2 is made uniform.

Referring to FIG. 5 , the chained line X shows the distribution produced by way of the light conductive bar 7 a only (see FIG. 6 ), the dashed line Y shows the distribution produced by way of the light conductive bar 7 b only (see FIG. 7 ), and the solid line Z shows the distribution produced by way of the light conductive bars 7 a, 7 b adjacently combined (see FIG. 3 ). The lines X and Y, which are produced by the light conductive bar 7 a only, and 7 b only, respectively, show a large fluctuation according to the distance from the spot-like light source 9 a, while the line Z, which is produced by the light conductive bar 7 a, 7 b adjacently combined, shows a small fluctuation. And, the apparatus of the present invention with two light conductive bars combined has an increased average brightnesss of light at the light conductive plate 2 by more than 10% compared with the conventional apparatus with one light conductive bar. Thus, the present invention with two light conductive bars combined proves to be effective also in increasing brightness.

In the present invention, the spot-like light source is not limited to an LED, and also the numbers of the light conductive bars and the spot-like light sources, and the structures of the optical conversion means and the light reflection pattern are not limited to those taken as examples in the above described embodiments. When n (n: an integer of 2 or more) pieces of spot-like light sources are provided each to cover the end surfaces of two light conductive bars, (2×n) pieces of light conductive bars may be used (see FIG. 8 ). Each of all spot-like light sources provided does not have to cover two light conductive bars, but at least one thereof may cover two light conductive bars (see FIG. 9 ) thereby improving the uniformity in the brightness distribution compared with the conventional apparatus. Further, one spot-like light source may cover three or more light conductive bars (see FIG. 10 ) instead of two, which also diminishes the unevenness in brightness compared with the apparatus provided with one light conductive bar. Note that numerical sign 2 indicates a light conductive plate, 7 a to 7 f light conductive bars, and 9 a to 9 c spot-like light sources, respectively.

The device to be illuminated by the apparatus of the present invention is not limited to the reflection-type liquid crystal display (reflection-type liquid crystal element). And the apparatus of the present invention may be disposed over the top (front) surface of the device to be illuminated, or may alternatively be disposed under the bottom (back) surface thereof. Generally speaking, the apparatus is disposed over the top (front) surface of a reflection-type device, and under the bottom (back) surface of a transmission-type device. Also, a plate-like member adapted to diffuse light (light-diffusive plate) may be disposed between the light conductive bar and the light conductive plate.

The spread illuminating apparatus structured as described above reduces the fluctuation in brightness (intensity) of the light incident on the end surface of the light conductive plate with regard to the length direction of the light conductive bars. Accordingly, the non-uniformity in brightness along the length of the light conductive bars can be diminished, and so the brightness over the light conductive plate can be made uniform, and the average brightness over the light conductive plate can be increased at the same time.