JP2000331519A - Surface light source device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface light source device using scattered light of high luminance and directivity obtained by a light extracting mechanism comprising a roughened surface and attempting further improvement of a front luminance. SOLUTION: A light source 12 is arranged on one or both of at least one pair of opposing side end parts of a light guide body 11 wherein one surface is considered as a light emitting surface 11a and a light extracting mechanism is formed on both of this one surface and another surface 11c opposing thereof. A reflector 13 is arranged so as to cover the light source 12 for emitting light emitted from the light source 12 from an end face of a side end part 11b to an interior of the light guide body 11. The light extracting mechanism is composed of a multiplicity of dots 14a, 14b, 14c,... and 15a, 15b, 15c,... formed from roughened surfaces. These multiplicity of roughened surface dots are composed so that a quantity of light emitting onto the light emitting surface 11 a is uniform for the whole surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a surface light source device,
More specifically, the present invention relates to a technique for mainly improving luminance in a surface light source device suitably used as a backlight of a liquid crystal display device or the like.

[0002]

2. Description of the Related Art In recent years, a transmissive liquid crystal display (display) device has been frequently used as a display device of a word processor, a personal computer or the like. Such a liquid crystal display device is generally configured by arranging a planar illumination device, that is, a backlight, on the back surface of a liquid crystal element. This backlight has a mechanism for converting a linear light source such as a cold cathode discharge tube into planar light.

[0003] Specifically, a conventional backlight has a light source disposed directly below the back surface of a liquid crystal element, or a light source provided on a side surface thereof, and a surface light source is obtained using a light guide such as an acrylic plate. Is typical (side light method),
In particular, in the case of the latter sidelight method, an optical element such as a prism array is disposed on the light emitting surface of the light guide to obtain desired optical characteristics.

That is, a conventional sidelight type backlight (surface light source device) comprises a cold cathode discharge tube or the like at one end 1b of a light guide 1 made of an acrylic plate or the like as shown in FIG. A tubular light source 2 is provided, and this is
On the other hand, a scattering reflection portion composed of white ink dots 4a, 4b, 4c, 4d,... Is formed on the surface 1c on the side opposite to the light emitting surface 1a by a printing technique. The reflection sheet 5 made of a diffuse reflection material such as foamed polyethylene was arranged.

The large number of white ink dots 4a, 4a
, b, 4c, 4d,... are patterns arranged vertically and horizontally at a predetermined interval from each other, and are formed so that the area of each dot increases as the distance from the light source 2 increases. The emitted light amount is made to be as uniform as possible over the entire surface.

The conventional surface light source device having such a configuration has a problem that a sufficient luminance value cannot be obtained due to its structural characteristics. However, recently, the performance required for such a backlight is becoming more and more advanced. In particular, in a portable personal computer or a TV monitor using a color liquid crystal display device, the color liquid crystal cell itself is extremely high. Due to the low light transmittance, the luminance value required for the backlight light source is inevitably high.

[0007] For this reason, in the backlight of the sidelight type, it is inevitable to secure the front luminance by an optical condensing action by using a sheet composed of a prism array or the like frequently. However, although the use of a sheet made of a prism array or the like is effective for securing the front luminance, there is a problem in that the viewing angle characteristics are narrowed and the cost is greatly increased.

The most effective solution to such a problem is to disperse high-luminance, highly directional scattered light generated from a rough surface as disclosed in Japanese Patent Application Laid-Open No. 6-18879. It is an attempt to use. That is, as shown in FIG. 5, a large number of rough dots 6a, 6b, 6c, 6d,... Are formed on the other surface 1c opposite to the light emitting surface 1a to emit strong directional scattered light. Thus, a surface light source device has been proposed.

Even in the case of the surface light source device shown in FIG. 5, a large number of rough surface dots 6a, 6b, 6c,... Are formed in a pattern arranged vertically and horizontally at a constant pitch with a predetermined interval therebetween. In addition, the respective areas are formed so as to increase as the distance from the light source 2 increases, so that the amount of light emitted on the light emitting surface 1a is made as uniform as possible over the entire surface.

[0010]

However, even when such a surface light source device using directional scattered light is used as a backlight of a display device such as a word processor or a personal computer, the brightness is limited. When it is necessary to increase the luminance, it is considered that another measure such as increasing the output of the light source is required.

However, increasing the output of the light source has a problem in that the power consumption increases, and the size of the surface light source device and the manufacturing cost increase. Therefore, development of a surface light source device capable of improving luminance without depending on an increase in the output of the light source has been awaited.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned conventional problems, and utilizes scattered light having high luminance and high directivity obtained by a light extraction mechanism having a rough surface or the like, and further improving the efficiency. An object of the present invention is to provide a surface light source device that improves front luminance.

[0013]

SUMMARY OF THE INVENTION The present invention is a surface light source device, and is configured as follows to solve the above-mentioned technical problem. In other words, the surface light source device of the present invention has a light guide in which one surface is a light emission surface, and a light extraction mechanism is formed on both the one surface and the other surface opposed thereto.
A light source disposed at at least one side end of the light guide, and a reflector covering the light source so that light emitted from the light source is incident on the inside of the light guide from an end face of the side end; It is characterized in that the take-out mechanism is constituted by a pattern composed of translucent directional scattered light generating means.

<Specific Configuration of the Present Invention> The surface light source device of the present invention is composed of the above-mentioned essential components. However, the present invention is established even when the components are specifically as follows. The additional constituent element is that the light emitting surface of the light guide and the directional scattered light generating means formed on the other surface facing the light guide are composed of a large number of rough dots, and the rough dots are a light source. It is configured to increase its area as the distance from the camera increases.

In the surface light source device according to the present invention, the directional scattered light generating means formed on the light emitting surface of the light guide and the other surface facing the light guiding surface is composed of a large number of rough surface dots. Dots are formed in the same area or different areas,
The disposition density of these rough dots can be increased as the distance from the light source increases.

Further, in the surface light source device of the present invention, the light source further includes a light control sheet disposed above the light exit surface of the light guide, and the light source is formed of a tubular light source elongated in a direction along a side end of the light guide. The dimming sheet is composed of a prism array,
This prism array is characterized in that the apex is directed to the light emitting surface side of the light guide and the tubular light source and the generatrix of each prism are arranged in parallel.

Further, in the surface light source device of the present invention, a large number of rough surface dots formed on one of the light emitting surface of the light guide and the other surface facing the light guide are arranged on the light source. It is preferable to form the light guide from a position exceeding about one-third of the length from the side end of the light guide to the other side end opposite to the other side.

According to the surface light source device of the present invention configured as described above, a light beam entering the inside of the light guide from the light source installed at the side end of the light guide is defined as a light exit surface according to a conventional method. The light is scattered toward the light emitting surface by a directional scattered light generating means including a large number of rough surface dots as a light extraction mechanism provided on the opposite surface.

At the same time, the light beam incident on the light guide from the light source is scattered by the directional scattered light generating means composed of a large number of rough surface dots formed on the light emitting surface and emitted from the light emitting surface. I do. Thus, in the surface light source device of the present invention, the light incident on the light guide is sufficiently utilized effectively without increasing the output of the light source, and the brightness of the light emitted from the light exit surface of the light guide is increased. be able to.

[0020]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a surface light source device according to the present invention. FIG. 1 shows a surface light source device 10 according to one embodiment of the present invention. The surface light source device 10 according to this embodiment has one surface 1
A light guide 11 has a light emitting surface 1a, and a light source 12 is provided at a side end 11b.

As the light source 12, a fluorescent tube, an LED array or the like can be used, but it is not particularly limited to these light sources. As the light source 12 used in the surface light source device 10 of the present invention, it is most preferable to use a cold cathode tube having excellent light source luminance.

The surface light source device 10 of the embodiment shown in FIG.
As a typical example, is a so-called one-lamp type in which one cold-cathode tube is provided as a light source 12 only at one (light incident end) 11b of a pair of opposed side ends. . But,
In addition to such a configuration, a so-called two-lamp type, in which one cold-cathode tube is provided as a light source 12 at both of a pair of opposed side ends of the light guide 11, four sides of the light guide 11 A four-lamp type in which a cold cathode tube is provided as a light source 12 at all ends, or
It is also possible to use a lamp in which a cold cathode tube of a lamp is provided at one or both side end portions of the light guide 11 facing each other.

A reflector 13 is provided around each light source 12 so that the emitted light can be transmitted to the light guide 1 with as little waste as possible.
It is configured to be incident on one light incident end 11b. The reflector 13 includes a light source 12 disposed inside.
The shape is not particularly limited as long as it can effectively reflect the light from the light source and enter the light guide 11 from the opening, and various shapes can be used.

In the surface light source device 10, the light emitting surface 11a of the light guide 11 and the surface 11c opposed to the light emitting surface 11a are formed as a light extraction mechanism from a rough surface or the like as a light extraction mechanism for extracting scattered light having high intensity and excellent directivity. Large number of dots (rough surface dots) 14
a, 14b, 14c, 14d,... and 15a, 15
.. are formed as patterns composed of translucent directional scattered light generating means.

At this time, it is preferable to adjust the degree of the rough surface, the area occupied by the rough surface, and the like to make the luminance distribution uniform. Such uniform luminance on the light emitting surface is one of the characteristics required for the surface light source device. As the light-transmitting directional scattered light generating means, a light-transmitting paint or ink containing light-scattering fine particles such as silica or light-reflecting fine particles can also be used.

In the surface light source device 10 shown in FIG.
Light emitting surface 11a and rough surface dots 14a, 14b, 14c,..., And 1 provided on surface 11c opposed thereto.
5a, 15b, 15c,... Are representative examples, and are formed in a predetermined pattern, for example, a pattern arranged vertically and horizontally at a predetermined interval from each other.

The rough surface dots 14a, 14b, 1
4c,... And 15a, 15b, 15c.
The area of each dot is configured to increase as the distance from the light source 2 increases, and the amount of light emitted on the light emitting surface 11a is made as uniform as possible (uniform brightness distribution) over the entire surface.

Further, from the viewpoint of making the luminance distribution on the light emitting surface, that is, the light emitting surface 11a, the arrangement density of the rough dots having the same area or different areas increases as the distance from the light source increases. The same effect can be obtained.

Further, in the surface light source device 10, as shown in FIG. 1, the length from the light incident end 11b of the light guide 11 on which the light source 12 is arranged to the other side end facing the light guide 11 is set. Assuming that L, rough surface dots 15a, 15b, 15c, 15d,... Formed on the light exit surface 11a of the light guide 11 are:
It is formed on the surface from the position about L / 3 from the light incident end 11b to the other side end.

Therefore, the increase in the area of the rough surface per unit area on both surfaces of the light emitting surface 11a of the light guide 11 and the other surface 11c opposed thereto is shown in a graph as shown in FIG. Explaining this graph, the curve K
Is a light emitting surface 11a of the light guide 11 and another surface 11c opposed thereto in the surface light source device 10 according to the embodiment shown in FIG. 1 when the luminance is made uniform over the entire light emitting surface.
5 is a curve showing an increase in the area of the rough surface occupying a unit area on both surfaces, and a curve J represents light emission of the light guide 1 when the luminance in the surface light source device shown in FIG. It is an area increase curve of the rough surface occupying per unit area in the other surface 1c facing the surface 1a.

Here, the luminance on the light emitting surface 11a, that is, the magnitude of the light energy emitted from the light guide has a relationship substantially proportional to the area of the rough surface occupying a unit area, and therefore, extends over the entire light emitting surface. Under the constraint that the luminance is kept constant, the conventional method shown by the curve J has a limit on the light energy emitted from the light guide. That is, by providing a dot pattern on both sides as shown by the curve K and keeping the area of the rough surface occupying a unit area sufficiently large, it is possible to effectively extract the light rays entering the light guide without loss. .

In the surface light source device 10 according to this embodiment,
Rough surface dots 14a, 14b, 14 as light extraction mechanism
The reflection sheet 16 is arranged on the entire surface of the light guide 11 on the entire surface thereof in the vicinity of the other surface 11c on which the light guides c,... are formed. It is preferable that the reflection sheet 16 is formed of a normal reflection material such as silver or a diffuse reflection material such as luminescent polyester.

Furthermore, the surface light source device 1 according to the present embodiment
0, the light source 1 is composed of, for example, a triangular prism array having an apex angle of 60 to 70 degrees, and the apex portion is directed to the light emitting surface 11a side.
2 includes a light control sheet 17 disposed so that the generatrix of each prism is parallel to each other. The light control sheet 17 changes the direction of the emitted light and takes out the light.

In addition, a sheet made of a triangular prism array having an apex angle of 70 to 120 degrees, preferably 80 to 100 degrees, is set so that the apex angle is directed to the side opposite to the light exit surface 11a.
A mode for obtaining desired light-collecting characteristics is also typical. When using this mode, it is preferable to dispose a diffusion sheet between the light emitting surface 11a and a sheet made of a triangular prism array.

According to the surface light source device 10 configured as described above, the light rays from the light source 12 incident from the one side end 11b propagate in the light guide 11 according to the total reflection condition based on Snell's law. This light beam is a rough dot 14a,
When reaching the light extraction mechanism composed of 14b, 14c,..., A scattering phenomenon occurs, and the light rays are emitted without staying in the light guide 11 any longer.

On the other hand, the light rays entering the light guide 11 from the light source 12 are also scattered by the rough dots 15a, 15b, 15c,... Formed on the light exit surface 11a of the light guide 11, and the scattered light is also The light exits from the light exit surface 11a. Thereby, the scattered light emitted from the light emission surface 11a of the light guide 11 is consequently generated by the rough surface dots 14a, 14b, 14c,
Are combined with the scattered light due to the rough dots 15a, 15b, 15c,... Formed on the light emitting surface 11a, and as a result, the luminance is improved.

In the surface light source device 10 according to this embodiment, as described above, the brightness on the light emitting surface 11a of the light guide 11 is improved.
The following effects can also be obtained. That is, in the surface light source device 10, light beams directly emitted from the light guide 11,
There is a light beam or the like emitted through reflection by the reflection sheet 16 provided on the surface 11c of the light guide 11 opposite to the light emission surface 11a, and in any case, the light scattering state schematically shown in FIG. As is clear from the explanatory diagram, the scattered light distribution 14A-1,... With high intensity and high directivity due to the rough surface dots 14a, 14b, 14c,.
1A, the light is refracted at the critical surface with the air, and the direction of the emitted light beam is the light emission surface 11a as indicated by reference numeral 14A-2.
Greatly deviates from the normal direction of.

On the other hand, the distribution of the scattered light at the rough surface dots 15a, 15b, 15c,... Formed on the light exit surface 11a of the light guide 11 is as shown in FIG. The light is emitted as a scattered light distribution 15A along the normal direction than 14a-2. Accordingly, when viewed as a whole of the light emitting surface 11a of the light guide 11, the viewing angle distribution 18 (?) In the direction orthogonal to the light source 12 is appropriately expanded, and a practically preferable viewing angle distribution can be obtained. There is.

Thus, the light emitting surface 11 of the light guide 11
The light beam emitted from the light-modulating sheet 17 is, for example, deflected by a dimming sheet 17 composed of a triangular prism array in which a vertex is directed toward the light-emitting surface 11a and the light source 12 and the generatrix of each prism are arranged in parallel. Then, the luminance peak position is directed in the normal direction of the light emitting surface 11a.

As described above, the light guide 1 is used as the light extraction mechanism.
The rough dots 14a, 14b, 14c,..., And 15 are formed on both surfaces of one light emitting surface 11a and the other surface 11c opposed thereto.
a, 15b, 15c,..., can be formed to provide highly directional scattered light having a viewing angle characteristic suitable for use as a surface light source device, and to further increase the luminance value. Can be enhanced.

In the surface light source device 10 of the above-described embodiment,
Rough surface dot 1 formed on light emitting surface 11a of light guide 11
, 5a, 15b, 15c,..., When the length from the light incident end 11b of the light guide 11 to the opposing other side is L, the position is approximately L / 3 from the light incident end 11b. Light incident end 11
In the area between the light source 12 and the other side opposite to the area b, the area is gradually increased as the distance from the light source 12 increases, and the mutual pitch is gradually decreased.

However, the surface light source device of the present invention is not limited to this, and as shown in FIG.
The rough surface dots formed on the light exit surface 11a of the first
Needless to say, it may be formed from the vicinity of 1b.

Except for these components, they are substantially the same as the surface light source device 10 of the embodiment shown in FIG. 1, and the same or corresponding components are denoted by the same reference numerals in FIG. The description is omitted.

Regarding the light control sheet 17 disposed on the light exit surface 11a of the light guide 11, in addition to the prism having a triangular cross section, a prism having a polygonal cross section, a prism having a curved top, a cylindrical lenticular lens, A light control sheet formed of a group of pyramids having a polygonal cross section, a microlens array, a diffractive optical element array, or the like and having a shape designed to satisfy the above-described functions can also be suitably used.

In a preferred embodiment of the surface light source device of the present invention, each of the light guide 11 and the light control sheet 17 is formed of a resin material. In particular, an acrylic resin, a polycarbonate resin, a polyester resin, or a cyclic polyolefin resin is preferably used, and a group of optical elements formed on the surface of the light control sheet 17 is a known thermosetting represented by an acrylic resin or the like. What is formed with a property or a photocurable resin is preferable.

The light source as the light supply means in the surface light source device of the present invention is not particularly limited, but includes a fluorescent tube (cold cathode tube, hot cathode tube), a tungsten incandescent bulb, an optical rod, an LED array and the like. Representative. In particular,
It is most preferable to use a cold cathode tube as a linear light source that can be easily reduced in size and increased in luminance.

[0047]

As described above, according to the surface light source device of the present invention, high-luminance highly directional scattered light generated from a rough surface as a light extraction mechanism is applied to the light exit surface of the light guide. By taking out even the formed rough surface dots, it is possible to provide a surface light source device whose luminance value is very high as compared with the conventional one and whose structure is simple and easy to produce. These features respond to the demand for optical characteristics of illumination light for backlights of liquid crystal display devices, which have recently become more sophisticated.

[Brief description of the drawings]

FIG. 1 is a fragmentary sectional view schematically showing a surface light source device according to a first embodiment of the present invention.

FIG. 2 is a configuration explanatory view schematically showing a light scattering state in the surface light source device shown in FIG.

3 is a characteristic diagram showing a ratio of a rough surface formed on a light guide in the surface light source device shown in FIG. 1 and the surface light source device shown in FIG.

FIG. 4 is a fragmentary sectional view schematically showing a surface light source device according to another embodiment of the present invention.

FIG. 5 is a partial cross-sectional view schematically showing one surface light source device proposed to solve the drawbacks of the conventional surface light source device.

FIG. 6 is a cross-sectional view schematically showing a conventional typical surface light source device.

[Explanation of symbols]

Reference Signs List 10 surface light source device 11 light guide 11a light emitting surface of light guide 11b one side end (light incident end) of light guide 11c surface opposite to light emitting surface of light guide 12 light source 13 reflector 14a, 14b, 14c, 14d, rough dot (light extraction mechanism) 15a, 15b, 15c, 15d rough dot 16 reflective sheet 17 light control sheet (prism array)

Claims (5)

[Claims] 1. A light guide having one surface serving as a light emitting surface, and a light extraction mechanism formed on both one surface and the other surface facing the light guide, and at least one side end of the light guide. A light source disposed in the portion, and a reflector that covers the light source so that light emitted from the light source is incident on the inside of the light guide from the end face of the side end portion, wherein the light extraction mechanism is transparent. A surface light source device characterized by comprising a pattern composed of a directional scattered light generating means. 2. The directional scattered light generating means formed on the light emitting surface of the light guide and the other surface facing the light emitting surface comprises a large number of rough surface dots, and the rough surface dots are:
2. The surface light source device according to claim 1, wherein the area is increased as the distance from the light source increases. 3. The directional scattered light generating means formed on the light emitting surface of the light guide and the other surface facing the light emitting surface comprises a large number of rough dots, and the rough dots have the same area. 2. The surface light source device according to claim 1, wherein an arrangement density of the plurality of rough surface dots is increased as the distance from the light source is increased. 4. The surface light source device further includes a dimming sheet disposed above the light exit surface of the light guide, and the light source is elongated in a direction along the side end of the light guide. The light control sheet is formed of a prism array, and the prism array has a vertex directed toward the light exit surface side of the light guide, and the tubular light source and the generatrix of each prism are parallel to each other. The surface light source device according to any one of claims 1 to 3, wherein the surface light source device is arranged so as to be arranged as follows. 5. The light guide wherein a large number of rough surface dots formed on one of the light exit surface and the other surface facing the light guide are arranged on the light source. 5. The structure according to claim 2, wherein the second end is formed from a position exceeding about one third of the length from the side end to the other end opposite thereto to the other side. A surface light source device according to any one of the above.