JP2000222924A - Surface light source element having narrow angle of visibility - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize an effective lighting system while preventing the reflection by window of a liquid crystal display device in a light source side type element for reflecting the light for incidence to a side surface of a light guide plate provided with a reflecting plate in a lower surface thereof and a light source in a side surface thereof by forming the lower surface of the light guide plate with a fine groove as a light source reflecting element, and setting the half-width of the distribution of the luminance angle at a specified value or less. SOLUTION: A part of multiple fine grooves of a reflecting element 4a provided in a lower surface of a light guide plate 4 made of the transparent acrylic resin and the polycarbonate resin and provided with a reflecting plate 3 of a polyester film coated with the high reflection material along a lower surface thereof is desirably formed into a non-spherical shape such as a parabola. The groove is formed of a non-spherical part for connecting a focal point at an edge part of a light source 2 side at the incidence of the light and a straight part, and a half-width of the distribution of luminance angle is set at 30 degree or less. Whole of the lower surface of the light guide plate 4 is desirably metalized so as to omit the reflecting plate 3. A right angled isosceles triangle prism sheet or the like is provided in a side surface of the light guide plate 4 at a light source 2 side thereof so as to collimate the light for condensation in the thickness direction of the light guide plate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a field light source device used in the field of lighting (indoor lighting, interior lighting), or a backlight of a liquid crystal display device used in personal computers, car navigation systems, meters and the like.

[0002]

2. Description of the Related Art Conventionally, as a surface light source element used in a backlight or an illumination field of this kind of liquid crystal display device, a direct type in which a light source is disposed on a back surface of a light emitting surface or a light source disposed on a side surface of a light guide plate. A light source side type that emits light in a planar shape through a light guide plate is known. As the thin surface light source element, a light source side type surface light source element is mainly used.

FIG. 2 is a sectional view showing the structure of a conventional light source side surface light source element. As shown in the figure, the light source side type surface light source element includes a light guide plate 4 and a light source 2 including a cold cathode tube or the like disposed on one side of the light guide plate, a reflector 1 and a reflection disposed along the lower surface of the light guide plate 4. It is composed of a diffusion film 5 disposed on the upper surfaces of the plate 3 and the light guide plate 4 and a prism sheet 6 in which the prism directions on the upper surfaces of the diffusion films 5 are orthogonal. The light emitted from the light source 2 is directly or reflected by the reflector 1 and enters the side surface 4b of the light guide plate 4. Then, reflection is repeatedly propagated on the upper surface and the lower surface of the light guide plate 4, and emitted from the upper surface of the light guide plate 4. Further, light leaking from the lower surface of the light guide plate 4 is reflected by the reflector 3 disposed along the lower surface of the light guide plate, passes through the light guide plate 4 again, and is emitted from the upper surface of the light guide plate 4. Light emitted from the upper surface of the light guide plate 4 is made uniform by the diffusion film 5, collected by the prism sheet 6, and emitted as a surface light source element.

Here, as the light guide plate 4, generally, a transparent acrylic resin on which white dots are printed as a reflection element or a dot formed integrally with a dot shape is often used. In this case, since the light emitted from the light guide plate has almost no directivity, it is necessary to condense the light by the prism sheet 6 and enhance the directivity. However, in this method, even if two or more prism sheets are used, it is impossible to further increase the directivity when the half width of the luminance angle distribution described later is at most about 40 °. In recent years, reports and documents on a grooved light guide plate have been found, but it is difficult to control the half-value width of the luminance angle distribution to 30 ° or less simply by providing a V-groove-shaped reflection surface on the light guide plate. .

[0005]

In recent years, the application of liquid crystal display devices to car navigation systems and on-vehicle meters has become active. In these fields, a high-luminance surface light source is required in a required angle range. However, the conventional surface light source element has a problem in that a windshield of a car is reflected in a window due to a wide vertical viewing angle. In order to solve this problem, expensive viewing angle control films are provided on the surface of the liquid crystal display device, or eaves are provided on the upper part of the liquid crystal display device. ing. In the field of recent lighting, there is an increasing need to uniformly illuminate only a specific range with a surface light source element. This requirement is not satisfactory because the conventional surface light source element has a wide viewing angle, and a surface light source element having a narrow viewing angle and capable of controlling the light emission direction is required. The present invention has been made in view of such circumstances, and has as its object to provide a surface light source element having a narrow viewing angle for solving the above-described problems.

[0006]

That is, the present invention provides a light guide plate, a reflection plate provided on the lower surface of the light guide plate, a light source provided on a side surface of the light guide plate, and a light incident on the side surface of the light guide plate. A light source side type surface light source element having a reflector to be formed, a fine groove as a reflection element of the light source is formed on a lower surface of the light guide plate, and a half angle width of a luminance angle distribution has a narrow viewing angle of 30 ° or less. And a narrow viewing angle surface light source device. As a specific means for setting the half-value width of the luminance angle distribution to 30 ° or less, a part of the groove shape of the light guide plate is formed as an aspherical surface, or the light from the light source is collimated on the light source side surface of the light guide plate. Means for providing a light shaping element or metallizing the lower surface of the light guide plate are employed.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings showing embodiments. FIG. 1 is a sectional view showing an embodiment of a narrow-viewing-angle surface light source element according to the present invention. In FIG. 1, a surface light source element includes a light guide plate 4 and a light source 2 disposed on one side surface of the light guide plate, a reflector 1 covering a surface of the light source opposite to the light guide plate 4, and a light source between the light source 2 and the light guide plate 4. , And a reflector 3 arranged along the lower surface of the light guide plate 4.

[0008] Reflecting plate 3 arranged along the lower surface of light guide plate 4
Is a polyester film coated with a highly reflective material, and Ref White (trade name, manufactured by Kimoto Co., Ltd.) was used as the polyester film. In addition, as the reflection plate 3, one obtained by depositing silver or aluminum on the reflection surface may be used.

The light source 2 has an outer shape of 2 mm and a length of 260 m.
m, a cold cathode tube having a central luminance of 37000 cd / m ² was used. The size such as the tube diameter is not particularly limited, but is preferably smaller than the thickness of the light incident surface of the light guide plate 3. Also,
As a light source, a light source other than a cold-cathode tube can be used as long as light can be efficiently incident from the side surface of the light guide plate. The material of the reflector 1 is formed by molding a metal sheet and coating the inner surface with a highly reflective material. However, there is no particular limitation as long as the material has a high reflectance.

The light guide plate 4 is made of a transparent acrylic resin and has a width of 25 mm.
Those having a thickness of 0 mm, a length of 190 mm, and a thickness of 2.5 mm were used. The material of the light guide plate is not limited as long as it is a resin having high transparency, but an acrylic resin or a polycarbonate resin is generally used. There is no particular limitation on the size of the light guide plate, but it is preferable that the light guide plate is thin in terms of weight reduction. As shown in FIG. 3, the reflection structure on the lower surface of the light guide plate 4 was of a groove type and constituted by a large number of grooves 8 composed of straight portions and parabolas. The shape of the groove 8 is not particularly limited as long as the shape focuses on the light source side edge portion of the groove 8 when parallel light is incident on the aspherical portion, but an aspherical surface is preferable, and a parabolic shape is more preferable. Similar effects can be obtained even when the shape of the aspherical surface or parabolic portion is approximated by a plurality of straight lines or a plurality of Rs. Further, it is more preferable that the entire lower surface is metallized.

When the lower surface is metallized, the reflector 3
Can be omitted. As the collimator 7, a prism sheet BEF manufactured by 3M was used. The collimator is not particularly limited as long as it has a function of condensing light in the thickness direction of the light guide plate 4, but a prism sheet or a lenticular sheet having a right-angled isosceles triangle is used to reduce the weight and space. Is preferred. Incidentally, the surface light source device shown in the embodiment of the present invention shown in FIGS. 1 and 3 was measured for the angular distribution of luminance by the method described below, and when the half width was obtained, the surface light source having a narrow viewing angle of 18 ° was obtained. The device was obtained.

FIG. 4 schematically shows a method of measuring a luminance angle of a surface light source element.
It was shown to. The light emitted from the light guide plate 4 is measured by a luminance meter 9 (a color luminance meter BM7 manufactured by Topcon) at a distance of 30 cm, Field
The luminance was measured while changing the angle θ under the condition of 1.0, and a luminance angle distribution was obtained. From this result, read the maximum value of luminance,
The half width was measured from an angle that was half that value.

[0013]

(Example 1) A surface light source element except for the collimator 7 was manufactured with the member configuration described in FIG. 1 and the above-described embodiment of the present invention, and the half value width of luminance was 23 °. (Embodiment 2) A metal structure is formed on the lower surface of the light guide plate 4 with metal aluminum,
And the half-width was measured by the same method as in Example 1, and the result was 15 °. (Embodiment 3) With a structure similar to that of Embodiment 1, metallized aluminum is formed on the lower surface of the light guide plate 4, and the collimator 7 and the reflection plate 3 are removed. The measured result was 15 °. (Embodiment 4) The light guide plate 4 has the same member configuration as that of the first embodiment, the groove shape of the light guide plate 4 is an isosceles triangle, the apex angle is 120 ° V-shaped, and the lower surface of the light guide plate is metallized with metal aluminum. Example 1 with the configuration excluding the reflector 7 and the reflector 3
The half value width was measured by the same method as that described above, and the result was 29 °. (Embodiment 5) With the same member configuration as in Embodiment 1, the groove shape of the light guide plate 4 was made into an isosceles triangle and a V-shaped apex angle of 120 °, and the half width was measured by the same method as in Embodiment 1. 27 °.

(Comparative Example 1) The light guide plate 4 has the same member configuration as that of the embodiment 1 except that the groove shape is an isosceles triangle and the apex angle is 120 ° V.
The half-width was measured by the same method as in Example 1 in a configuration excluding the collimator 7 and the result was 32 °. (Comparative Example 2) When the light guide plate 4 was replaced with a printed light guide plate and the same method as in Example 1 was used to measure the same member configuration as in Example 1, the luminance angle distribution was flat and the half-value width could not be measured. Was. (Comparative Example 3) A surface light source element having the configuration shown in FIG. 2 (light guide plate 4: printed dot light guide plate, diffusion sheet 5: Kimoto 2)
000LS, prism sheet 6: BEF manufactured by 3M), and the half width was measured by the same method as in Example 1. The result was 42.
°.

[0015]

As described above, according to the present invention, it is possible to provide a narrow-viewing-angle surface light source element in which the half-value width of the luminance angle distribution is 30 degrees or less. It is useful for preventing reflection and as a lighting device.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part showing an embodiment of a surface light source element according to the present invention.

FIG. 2 is a sectional view of a main part showing an example of a conventional light source side type surface light source element.

FIG. 3 is a sectional view showing a groove shape of the surface light source element light guide plate according to the present invention.

FIG. 4 is a schematic diagram of a half-width measurement method.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Reflector 2 Light source 3 Reflector 4
Light guide plate 4a Reflecting element 4b Light incident surface 5 Diffusion sheet 6 Prism sheet 7 Collimator 8 Groove shape 9 Luminance meter

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Yosuke Kaneko, 1150 Goshomiya, Oaza, Shimodate, Ibaraki Pref.Hitachi Chemical Industry Co., Ltd. F-term in the Goshonomiya Plant of Chemical Industry Co., Ltd. (Reference) 2H038 AA52 AA55 BA01 2H042 BA04 BA14 BA20 2H091 FA21Z FA23Z FB02 FC17 FD06 LA11 LA16

Claims (4)

[Claims] 1. A light source side type comprising a light guide plate, a reflection plate provided on a lower surface of the light guide plate, a light source provided on a side surface of the light guide plate, and a reflector for entering the side surface of the light guide plate. In the surface light source device, a narrow viewing angle surface light source device having a narrow viewing angle in which a fine groove as a reflection element of the light source is formed on a lower surface of the light guide plate and a half width of a luminance angle distribution is 30 ° or less. . 2. The narrow viewing angle surface light source device according to claim 1, wherein a part of the shape of the fine groove as a reflection element of the light guide plate is aspherical. 3. An element for collimating (shaping) light from a light source on a side surface of the light guide plate on a light source side.
The narrow-viewing-angle surface light source element as described in the above. 4. The narrow-viewing-angle surface light source device according to claim 1, wherein the lower surface of the light guide plate is metallized.