JP2001266628A - Surface light source device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light-weight surface light source device, excellent in the optical characteristics with high average brightness and uniform distribution of brightness on the whole surface without local unevenness in brightness such as dark lines or bright lines. SOLUTION: In the surface light source device, rays from a light source are made to come in from the side end surface of a light guide plate 1. The light guide plate 1 has a light emitting surface 1a, a reflecting surface 1b opposite to the light emitting surface 1a, and a light incident surface 1c different from either light emitting surface 1a or the reflecting surface 1b. The reflecting surface 1b of the light guide plate 1 comprises plural flat surfaces and one or more curved surfaces, and the angles between respective plural flat surfaces and the light emitting surface 1a are different from each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight system such as a liquid crystal display, an advertising sign, and an evacuation guide light, or a surface light source device such as a lighting fixture.

[0002]

2. Description of the Related Art In recent years, liquid crystal display devices have been widely used in various fields including display devices such as personal computers, TVs, and video movies. A liquid crystal display device basically includes a backlight portion and a liquid crystal display element portion. The structure of the backlight portion includes a direct type in which a light source is provided immediately below the liquid crystal display device, and a side surface of a light guide plate. There is an edge light system with a light source provided, and in consideration of thinning, weight reduction, uniformity of brightness, etc. of the liquid crystal display device,
The edge light method is frequently used.

An edge light type surface light source device has a configuration in which a light source is arranged on a side surface of a light guide plate to emit light on the entire surface of the light guide plate.
There is one disclosed in Japanese Patent No. 7444.

In an edge light type surface light source device,
FIG. 11 shows a basic configuration example of a surface light source device using one of the four end surfaces of the light guide plate as a light incident surface.

In this surface light source device, an optically transparent light guide plate 1, a cold cathode tube 2, a lamp reflector 3 for efficiently guiding light from the cold cathode tube 2 into the inside of the light guide plate 1, and a light reflector close to the lower surface of the light guide plate 1. It comprises a reflection plate 4 arranged, a scattering plate 5 arranged close to the upper surface of the light guide plate 1, and a lens sheet 6. In this specification, the upper surface of the light guide plate 1 is referred to as a light emitting surface 1a, and the lower surface is referred to as a reflective surface 1b.

On the reflection surface 1b of the light guide plate 1, there is formed a reflection pattern for efficiently emitting the light source light guided into the inside of the light guide plate 1, and according to the distance from the light entrance surface of the light guide plate 1. By providing distributions in the size, density, scattering reflection performance, and the like of the pattern, it is devised that a uniform luminance distribution can be obtained over the entire light emitting surface 1a.

In the edge light type surface light source device, the light source can be arranged on any of the four side surfaces of the light guide plate 1. However, in a portable electronic device driven by a battery, the light source is consumed. For the purpose of minimizing the electric power, a cathode ray tube is used as a light source, and a single tube type or an L-shaped tube type is mainly used. The surface light source device shown in FIG. 11 is an example of a surface light source device using a straight tube type cold cathode tube 2.

As the performance required for the surface light source device as shown in FIG. 11, it is required to reduce the weight as well as to increase the brightness and to make the brightness uniform, and various contrivances have been devised. In particular, the light guide plate 1 is a requirement that the incident light source light needs to be efficiently emitted from the light emitting surface 1a.

However, with respect to the light guide plate 1, high brightness and light weight are conflicting requirements. To achieve high brightness, the thickness of the light guide plate 1 on the light entrance surface 1c side is increased to reduce the amount of incident light. Increasing the weight increases the weight. Conversely, if the thickness of the light guide plate 1 on the light incident surface 1c side is reduced to reduce the weight, the brightness decreases.

[0010] In order to solve such a problem, a method of increasing the amount of light source light incident from the light incident surface 1c by devising the cross-sectional shape of the light guide plate 1, particularly the shape near the light incident surface, has been known. Many proposals have been made.

For example, Japanese Patent Application Laid-Open No. 63-208001 discloses a method in which the cross-sectional shape of the reflection surface of a light guide plate is made to be a curve of second order or higher. JP-A-53111 discloses a backlight system in which the thickness is increased only in the vicinity of a light incident surface of a light guide plate. Japanese Patent Application Laid-Open No. 6-102414 discloses a backlight system in which linear light sources are arranged on two end faces of a light guide plate, and the cross section of the light guide plate has a symmetric wedge shape.

There are many other techniques for forming a pattern having a scattered reflection or total reflection function on the reflection surface of the light guide plate in order to emit light incident on the light guide plate with high efficiency and uniform distribution. It has been disclosed. For example, Japanese Patent No. 2776603 discloses a method for optimizing the distribution of a pattern formed on a reflection surface of a light guide plate.

However, in the various surface light source devices that have been conventionally proposed, the invention relating to the cross-sectional structure of the light guide plate for the purpose of reducing the thickness or weight and the reflection pattern of the light guide plate for the purpose of improving the brightness uniformity are disclosed. Have been made independently, and no invention has been made in which they are considered at the same time.

For example, Japanese Patent Application Laid-Open No. 63-208001 discloses that uniformity of in-plane luminance can be obtained only by devising the cross-sectional shape of the light guide plate. According to the method described in this publication, even if luminance uniformity is obtained, it is difficult to effectively use the light incident from the light incident surface, and it is difficult to obtain a surface light source device having a high average luminance. Met.

JP-A-4-333803, JP-A-5
According to the method described in JP-A-53111, although the amount of incident light from the light incident surface increases, the amount of light emitted near the light incident surface increases, resulting in uneven luminance. There were problems such as a decrease in uniformity.

The method described in Japanese Patent Application Laid-Open No. 6-102414 relates to a two-light type structure in which two linear light sources are arranged on two opposite side surfaces of a light guide plate, respectively. Compared with the surface light source device, it is not preferable from the viewpoint of reducing power consumption. Further, the main purpose is to provide a curved surface portion on the reflection surface of the light guide plate to reduce local luminance unevenness, and there is no study on luminance uniformity over the entire light emitting surface.

[0017]

SUMMARY OF THE INVENTION Accordingly, the present invention provides an optically transparent plate-like member having one surface other than an end surface as a light-emitting surface and the other surface facing the light-emitting surface as a reflection surface. A light guide plate having one end face as a light incident surface, and a light source disposed close to a light incident surface of the light guide plate,
An object of the present invention is to provide a surface light source device which is lightweight, has a high average luminance, has a uniform luminance distribution over the entire surface, has no local luminance unevenness such as dark lines and bright lines, and has excellent optical characteristics. I have.

[0018]

In order to achieve the above object, a surface light source device according to the present invention has the following configuration.

The surface light source device according to the present invention is a surface light source device for receiving light from a light source from a side end surface of a light guide plate, wherein the light guide plate has a light emitting surface, a reflecting surface facing the light emitting surface, A light-incident surface is formed on a surface different from the light-emitting surface and the reflective surface, and the reflective surface of the light guide plate includes a plurality of flat surfaces and one or more curved surfaces. And the light emitting surface is formed at an angle different from each other, thereby achieving the above object.

In one embodiment, the length (L) of one curved surface constituting the reflection surface of the light guide plate is represented by the following equation.

L = Δθ / 0.1 × 2 × t3 × tanψ where Δθ is the angle difference between two planes that are geometrically in contact with the curved surface, and t3 is the intersection line of the extension of the two planes and the light emission. The distance from the surface, ψ, is the critical angle of the light guide plate.

In one embodiment, the cross section of at least one or more curved surfaces constituting the reflecting surface of the light guide plate is an arc, a parabola, a hyperbola, an elliptic arc, a trigonometric curve, a chain line, a cycloid curve, a trochoid. It is a curve, an exponential curve, an involute curve, or any other curve that can be expressed mathematically.

In one embodiment, the reflection surface of the light guide plate is composed of two planes including a virtual plane and a curved surface that is in contact with the two planes, and a virtual intersection line between the two planes and the input plane of the light guide plate. The distance from the light surface is approximately L / 2 with respect to the length L of the one curved surface.
It is.

In one embodiment, a pattern is formed on the reflection surface of the light guide plate, and the pattern has a size and a density occupying a unit area according to a distance from the light entrance surface of the light guide plate. Are provided, and distribution curves representing the change in density with respect to the distance from the light incident surface are different from each other corresponding to the plurality of surfaces forming the reflection surface.

In one embodiment, the density change and the density change rate of the pattern formed on the reflection surface are continuous with respect to the distance from the light entrance surface of the light guide plate.

In one embodiment, a reflection member for guiding light from a light source to the light guide plate, a reflection plate disposed on the reflection surface side of the light guide plate, or a reflection plate disposed on the light emission surface side of the light guide plate At least one of members having functions such as deflection, polarization, and scattering is provided.

In one embodiment, the light guide plate has a shape whose thickness decreases as the distance from the light incident surface increases.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on embodiments.

First, the structure of the surface light source device according to the present invention will be described. FIG. 1 is a diagram illustrating a first embodiment of the surface light source device according to the present invention.

The surface light source device according to the present invention comprises a light guide plate 1, a cold cathode tube 2 disposed close to one end surface of the light guide plate 1, and the light of the cold cathode tube 2 incident on the light guide plate 1 efficiently. A lamp reflector 3 for guiding to the surface 1c, a reflector 4 provided on a surface (reflection surface 1b side) of the light guide plate 1 opposite to the light emitting surface 1a, a diffusion plate 5 for scattering emitted light to reduce luminance unevenness, and A lens sheet 6 for deflecting emitted light to improve front luminance.

As shown in FIG. 1, the reflection surface 1b of the light guide plate 1
Are formed from a region extending along the longitudinal direction of the light guide plate 1. The regions and are planes, and the regions are cylindrical. The reflection surface 1b of the light guide plate 1 has an area
In each case, a reflection pattern 7 having a function of reflecting light incident on the light guide plate 1 is formed.

The light guide plate 1 is generally manufactured by an injection molding method using an optically transparent material (for example, polymethyl methacrylate). Reflection pattern 7
Can be formed on the reflection surface 1b of the light guide plate 1 by a screen printing method using an ink having a scattering reflection characteristic or the like, or a predetermined pattern is formed in advance on a mold for injection molding, and A method of integrally forming with the light guide plate 1 can be adopted. When the reflection pattern 7 is formed by a printing method, a circle, a square, or the like can be adopted. When the reflection pattern 7 is formed by an injection molding method, various shapes such as a cylinder, a prism, a half cylinder, a triangular pyramid, and a pyramid are employed. It is possible. In this embodiment, a circular pattern is formed by a printing method.

Next, a method of designing the outer dimensions of the light guide plate 1 according to the first embodiment of the present invention will be described.

FIG. 5 is a perspective view of the light guide plate 1 of the surface light source device according to the first embodiment of the present invention. The plane size of the light guide plate 1 is 210 mm × 160 mm, and one end face 1c on the long side is set.
The cold-cathode tube 2 is disposed in the vicinity. The thickness (t1) of the light entrance surface 1c of the light guide plate 1 in FIG. 5 is generally determined by the diameter of the cold cathode tube 2. In order to make the light from the cold-cathode tube 2 efficiently enter the light incident surface 1c of the light guide plate 1, the thickness of the light incident surface 1c of the light guide plate 1 is preferably set to a value larger than the tube diameter. However, if the thickness of the light guide plate 1 is too large, it is not preferable because the weight of the light guide plate 1 increases. Empirically, the thickness of the light guide plate 1 is the diameter of the cold cathode tube 2 +0.4.
mm to +1.0 mm.

Many conventional light guide plates having a simple wedge-shaped cross section are employed. The thickness (t) of the end face (opposite to light incidence face 1d) of FIG.
In 2), it is desirable that the light guide plate is as thin as possible in consideration of the weight of the light guide plate. However, a light guide plate manufactured by an injection molding method using a resin material such as polymethyl methacrylate is warped due to distortion during molding and moisture absorption. . Therefore, it is empirically desirable to have a thickness of 1.0 mm or more. Therefore, in the present embodiment, the thickness (t
2) was set to 1.2 mm.

Next, a method of designing the shape of the reflection surface of the light guide plate 1 will be described.

In the present invention, after determining the angle between the two planes constituting the reflecting surface 1b and the horizontal plane, the curved surface shape is determined. First, the virtual intersection line 12 of the two planes in FIG.
(T3) between the light-emitting surface 1a and the light-emitting surface 1a is determined as follows.

In general, a light ray traveling inside the light guide plate 1 repeats total reflection and travels inside the light guide plate 1 when the incident angle on the light emitting surface 1a or the reflection surface 1b of the light guide plate 1 is larger than the critical angle. . When there is an angle difference between the reflecting surface 1b and the light emitting surface 1a of the light guide plate 1, the reflecting surface 1b
When the angle of incidence on the light emitting surface 1a or the incident surface becomes smaller in accordance with the angle difference between the light emitting surface 1a and the light emitting surface 1a, and the incident angle becomes equal to or smaller than the critical angle, the light exits the light guide plate 1. Therefore, in order to efficiently emit light from the entire surface of the light guide plate 1, it is desirable that the cross-sectional shape of the light guide plate 1 be substantially wedge-shaped such that the thickness decreases as the distance from the light incident surface 1 c increases. In FIG. 5, the thickness of each portion is preferably t2 <t3 <t1, and an arbitrary value can be set within this range. In this embodiment, t3 = 1.5 mm.

Next, when the position of the virtual intersection line 12 in FIG. 5 is determined, the outer shape of the light guide plate 1 can be determined. The method will be described below.

First, a problem when the reflecting surface 1b of the light guide plate 1 is constituted by a plurality of planes will be described.

FIG. 6A is a sectional view for explaining the behavior of light traveling in the light guide plate 1 in which the reflection surface 1b is constituted by a plurality of planes. In FIG. 6, the reflection pattern is excluded. As described above, when the light traveling inside the light guide plate 1 having the wedge-shaped cross-sectional shape is reflected by the reflecting surface 1b once, the incident angle on the light emitting surface 1a decreases, and when the incident angle becomes smaller than the critical angle, The light exits the light guide plate 1. Referring to FIG. 6A, the reflection surface 1b of the light guide plate 1 will be described.
Is composed of a single plane, passes from point A to point B,
The light that has proceeded to D is emitted outside the light guide plate 1 at point D. If the refractive index of the light guide plate 1 made of polymethyl methacrylate is 1.48, the critical angle is 42.16 °, and if θ1> θ2, it passes from point A to point B and D
The angle component α1 at point A of the light that travels inside the light guide plate 1 and exits at point D is represented by the following equation.

42.16 ° + θ1 ° <α1 <42.16 ° + 2θ1 ° (1) On the other hand, when the reflecting surface 1b is composed of two planes,
As shown in FIG. 6A, light passes from point A to B and C,
Proceeding to E, the light is emitted at the point E, and the angle component α2 at the point A of the light emitted at the point E is represented by the following equation.

42.16 ° + θ2 ° <α2 <42.16 ° + 2θ2 ° (2) Therefore, the difference between the maximum value and the minimum value of α1 is θ1,
The difference between the maximum value and the minimum value of α2 is θ2. Assuming that the light quantity has no angle dependence and that the light quantity is constant for light at any angle, the following relationship exists between the output light quantity M1 at point D and the output light quantity M2 at point E. Holds.

Θ1: θ2 = M1: M2 = 100: 100 × θ2 / θ1 (3) Here, assuming that θ1−θ2 = 0.1 °, M2 is 100 × 0 with respect to M1. .1 / θ1
% Decrease. In the first embodiment, the thickness of the light incident surface 1c is 2.5 mm, and the thickness of the anti-light incident surface 1c is 1.2 m.
m, so that referring to FIG. 6B, θ0 =
0.5 °, θ2 <θ0 <θ1, and M2 with respect to M1
Is up to 20%.

According to the experiments of the present inventors, it has been found that the uneven brightness of the entire light emitting surface 1a due to the brightness reduction of up to 20% can be suppressed by light scattering by the reflection pattern. That is, it has been found that even when there is an angle difference of θ1−θ2 = 0.1 °, the angle difference can be ignored by forming the reflection pattern.

The behavior of the light once reflected by the reflecting surface 1b of the light guide plate 1 has been described above. A curved surface 11 is added near the virtual intersection line 12 of the two planes shown in FIG. If the shape is such that the angle difference of
Even if −θ2> 0.1 °, it is possible to suppress the occurrence of dark lines. As described above, when the light ray is reflected once by the reflecting surface 1b, the angle difference of 0.1 ° is negligible.
In order to alleviate the angle difference of (θ1−θ2) °, the curved surface 1 should be reflected by (θ1−θ2) /0.1 times on the reflecting surface 1b.
The length of 1 may be determined. The length of the curved surface 11 is defined as the distance traveled when light whose incident angle to the light emitting surface 1a becomes a critical angle near the virtual intersection line 12 repeats total reflection (θ1−θ2) /0.1 times. Since it may be considered that they substantially coincide with each other, if the critical angle of the light guide plate 1 is ψ, the expression representing the length L of the curved surface 11 is as follows.

L = Δθ / 0.1 × 2 × t3 × tanψ (4) where Δθ = θ1−θ2.

Next, the relationship between the shape of the reflecting surface of the light guide plate 1 and the weight will be described.

In the first embodiment according to the present invention, in order to suppress luminance unevenness, each plane is so set that the virtual intersection line 12 of the two planes constituting the reflection surface 1b of the light guide plate 1 approaches the light entrance surface 1c. When the angle between the two planes is set, the angle difference between the two planes increases, and it is necessary to increase the length of the curved surface 11 that is in contact with the two planes. However, when the length of the curved surface 11 is increased, the weight of the entire light guide plate 1 increases. That is, reduction of the weight of the light guide plate 1 and suppression of luminance unevenness are conflicting requirements. Therefore, the virtual intersection line 12 of the two planes
And the weight of the light guide plate 1 in consideration of the length of the curved surface 11 were calculated to find an optimal solution that can suppress luminance unevenness and reduce the weight.

The calculation result shown in FIG. 7 is an example of the light guide plate 1 according to the first embodiment of the present invention. However, reflection surface 1
The curved surface 11 of b is a cylindrical surface. From the results shown in FIG. 7, it can be seen that the weight is minimized when the distance between the virtual intersection line 12 and the light incident surface 1c is about 1/5 of the length (160 mm) in the cross section of the light guide plate. Understand.

As in the embodiment of the present invention, when the reflecting surface of the light guide plate is composed of two planes including a virtual plane and a curved surface in contact with the two planes, as shown in FIG. Exists. At the minimum point of weight shown in FIG. 7, the distance (L ') between the virtual intersection and the light incident surface is 32 mm, and the length (L) of the curve is about 65 mm. That is, L '= L /
It becomes 2. According to the study by the present inventors, it has been found that this relationship does not change even when the outer dimensions of the light guide plate change. That is, in general, when L '= L / 2, the weight is minimized.

Next, the relationship between the angle between the reflection surface 1b of the light guide plate 1 and the horizontal plane and the light emission characteristics will be described.

FIG. 8 shows a light guide plate 1 having various cross-sectional shapes.
3 is a diagram for explaining the relationship between the brightness of a surface light source device using the light guide plate 1 and FIG. The measurement of the luminance in FIG.
The light guide plate 1 was replaced with various shapes by the surface light source device shown in FIG. The various dimensions of the light guide plate 1 are basically the same as those of the first embodiment according to the present invention, except that the distance between the virtual intersection line 12 and the light entrance surface 1c is variously changed. The length of the cylindrical surface of the reflecting surface 1b was changed based on the equation (4). The brightness measurement was performed without forming the reflection pattern 7 on the manufactured light guide plate 1.

According to the known art, it is known that by forming a reflection pattern on the reflection surface 1b, it is possible to improve the average luminance and the luminance uniformity. The present inventors fabricated a conventional light guide plate having a simple wedge-shaped cross section and formed an optimal reflection pattern for the purpose of improving average luminance and luminance uniformity.
cd / m ² and luminance uniformity 95%.

The various light guide plates used for measuring the luminance of the surface light source device shown in FIG. 8 do not have a reflection pattern formed on the reflection surface. The angle of the reflection surface so as not to exceed the average luminance of the light plate, that is, the virtual intersection line 12 of the two planes constituting the reflection surface
Needs to be set.

As described above, the luminance peak appearing near the light incident surface is obtained.
Is at least 1480 cd / m ^TwoMust not exceed
No. (Preferably, 1300 cd / m^TwoIf it is below
No. 8) Therefore, in FIG. 8, the distance between the virtual intersection line and the light incident surface is shown.
When (L ′) is 20 mm, the luminance uniformity is not good.
In other cases, the optimal design of the reflection pattern
Therefore, a good luminance uniformity (about 95%) comparable to that of a conventional light guide plate is obtained.
Oneness is obtained. From the results shown in FIG. 7, L ′ = 53 m
m, the weight is minimized, and the above results (brightness
L '= 53 mm
Surface light source device with minimum weight and good brightness uniformity
Can be provided.

The above-described light guide plate 1 is an embodiment of the present invention. In general, the distance between the virtual intersection line 12 and the light incident surface 1c is equal to the length in the light guide plate cross-sectional direction. On the other hand, if it is between 1/10 and 1/6, uniformity of luminance and weight reduction can be achieved at the same time.

The cross section of the curved surface may be a parabola, a hyperbola, an elliptic arc, a trigonometric curve, a chain line, a cycloid curve, a trochoid curve, an exponential function curve, an involute curve, or any other curve that can be expressed mathematically, in addition to a circular arc. possible.

Based on the design method described above, the length required for the curved surface formed in the first embodiment of the present invention is obtained.

The following numerical values: the distance (1.5 mm) between the virtual intersection line 12 of the two planes constituting the reflecting surface and the light emitting surface 1a; the angle of these two planes with respect to the horizontal plane (θ1 = 1.79 °,
When θ2 = 0.13 °); and the critical angle (42.16 °) are substituted into Equation (4) and calculated, it is necessary to form the curved surface 11 over a length of approximately 45 mm. here,
It is desirable to allow for a margin of about 20%.

In this embodiment, the curved surface 11 is a cylindrical surface,
The length of this cylindrical surface was 54 mm. Thereby, the radius of the cylindrical surface is determined geometrically. In this embodiment,
The radius of the cylindrical surface is about 2 m.

Next, a method of forming a reflection pattern formed on the reflection surface 1b of the light guide plate 1 will be described.

The light guide plate 1 according to the first embodiment of the present invention
As shown in FIG. 1, the reflecting surface 1b is composed of two planes and a curved surface 11 which is in contact with these two planes. Here, the shape of the reflection pattern is considered except for the curved surface. The reflection surface 1b of the light guide plate 1 is composed of two planes. That is, the configuration of the light guide plate 1 is divided into a hatched portion on the light entrance surface 1c side of the light guide plate 1 shown in FIG. 9A and a hatched portion on the side far from the light entrance surface 1c of the light guide plate 1 shown in FIG. (Fig. 9
(C)). When the cross section of the light guide plate 1 is a simple wedge, and the reflection pattern is a circular pattern formed by a printing method, the diameter and density are determined by the reflection characteristics of the reflection pattern and the angle formed by the reflection surface 1b with respect to the horizontal plane. , The thickness of the light incident surface 1c, and the light incident surface 1 of the light guide plate 1
It is known that it differs depending on the length of the light guide plate 1 in a direction perpendicular to c.

The present inventors experimentally obtained a density distribution curve of the reflection pattern as shown in FIG. 10 in consideration of the average luminance and the in-plane luminance uniformity.

In the first embodiment of the present invention, since the reflecting surface 1b is constituted by a total of three surfaces of two planes and one curved surface which is in contact with the two planes, the reflecting surface 1b is used in accordance with these three surfaces. The distribution of the reflection pattern on the entire reflection surface 1b can be configured such that the distribution curve of the reflection pattern on the curved surface is in contact with the distribution curve of the reflection pattern on the two planes. In the first embodiment according to the present invention, the distribution curve of the reflection pattern shown in FIG. 2 was obtained.

Next, a second embodiment of the surface light source device according to the present invention will be described.

FIG. 3 is a sectional view for explaining a second embodiment of the surface light source device according to the present invention. The components are the same as in the first embodiment shown in FIG. The light guide plate 1 includes two planes including a virtual plane, and one curved surface 11 that is in contact with the two planes.
It is composed of Here, the virtual plane is a curved surface 1
The reflecting surface 1b is a plane set for determining the shape of No. 1 and is substantially composed of a total of two surfaces: a curved surface portion of the region and a flat surface portion of the region. This imaginary plane corresponds to a contact surface of a portion near the cold cathode tube 2 in the region.

The dimensions of each part of the light guide plate 1 were designed in the same manner as in the first embodiment.

FIG. 4 is a view for explaining the distribution of the reflection pattern of the light guide plate 1 according to the second embodiment of the present invention. The setting of the distribution of the reflection pattern was designed by the same method as in the first embodiment. (Example) A light guide plate was manufactured with the following dimensions using polymethyl methacrylate. (Example 1) The surface dimensions of the light guide plate were set to 210 mm long side × 1 short side.
The thickness was 60 mm, the thickness of the light incident surface 1c was 2.5 mm, the thickness of the anti-light incident surface 1c was 1 amm, and the thickness of the virtual intersection line portion was 1.5 mm. Since the length of the cylindrical surface was 54 mm, the radius of the cylindrical surface was 2.0 m. (Example 2) The surface size of the light guide plate was set to 245 mm long side × 1 short side.
85 mm, the light incident surface 1c has a thickness of 2.5 mm, the anti-light incident surface 1c has a thickness of 1.3 mm, and the virtual intersection line portion has a thickness of 1.7 mm.
And The length of the cylindrical surface was 56 mm, and the radius of the cylindrical surface was 2.1 m. (Comparative Example 1) A simple wedge-shaped light guide plate was manufactured by setting the long side, the short side, and the thickness of the light incident surface 1c and the light incident surface 1c to the same dimensions as those of the first embodiment. (Comparative Example 2) A simple wedge-shaped light guide plate was manufactured by setting the long side, the short side, and the thickness of the light incident surface 1c and the opposite light incident surface 1c to the same dimensions as those in Example 2. (Evaluation of Optical Characteristics) A cold cathode tube 2 (diameter: 2.0 mm) was placed in close proximity to one end face 1c on the long side of the light guide plate designed and manufactured according to the above Examples and Comparative Examples, and the following optical characteristics were evaluated. Was done. 1. Average Luminance Measuring Method The luminance at 25 points in the light guide plate is measured with a luminance meter, and the average value is defined as the average luminance. 2. Luminance uniformity In the above 25 measurement points, the ratio between the maximum luminance point and the minimum luminance point (= minimum luminance / maximum luminance) is defined as luminance uniformity and expressed as a percentage.

Table 1 shows the specifications of the light guide plate. Table 2 shows the optical characteristics of the surface light source device using these light guide plates.

[0071]

[Table 1]

[0072]

[Table 2]

Table 1 shows that the weight of the light guide plate according to the present invention is reduced by about 15 to 20% compared with the conventional one. Table 2 shows that the surface light source device according to the present invention has optical characteristics equivalent to those of the related art. In the related art, when the weight is reduced, the optical characteristics are reduced. However, the present invention has made it possible to provide a surface light source device that is reduced in weight and has excellent optical characteristics. .

[0074]

According to the surface light source device of the present invention, it is lightweight, has a high average luminance, has a uniform luminance distribution over the entire surface, and has no local luminance unevenness such as dark lines and bright lines. In addition, it is possible to provide a surface light source device having excellent optical characteristics.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a first embodiment of a surface light source device according to the present invention.

FIG. 2 is a diagram illustrating a distribution of a reflection pattern of a light guide plate in the first embodiment of the surface light source device according to the present invention.

FIG. 3 is a sectional view illustrating a second embodiment of the surface light source device according to the present invention.

FIG. 4 is a diagram illustrating a distribution of a reflection pattern of a light guide plate in a second embodiment of the surface light source device according to the present invention.

FIG. 5 is a perspective view illustrating a first embodiment of the surface light source device according to the present invention.

FIG. 6A is a view for explaining the behavior of light traveling in the light guide plate, and FIG. 6B is a cross-sectional view showing the shape of the light guide plate.

FIG. 7 is a view for explaining the relationship between the position of a virtual intersection line of two planes constituting the reflection surface of the light guide plate and the weight of the light guide plate in the first embodiment of the surface light source device according to the present invention.

FIG. 8 is a diagram illustrating the shape of a light guide plate and the luminance distribution of a surface light source device using the light guide plate.

FIG. 9 is a view illustrating a basic concept of a light guide plate in the surface light source device according to the present invention.

FIG. 10 is a view illustrating a method of designing a reflection pattern of a light guide plate in a surface light source device according to the present invention.

FIG. 11 is a cross-sectional view illustrating a conventional surface light source device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Light-guide plate 2 Cold-cathode tube 3 Lamp reflector 4 Reflector 5 Diffusion plate 6 Lens sheet

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) // F21Y 103: 00 G02F 1/1335 530

Claims (8)

[Claims] 1. A surface light source device for receiving light from a light source from a side end surface of a light guide plate, wherein the light guide plate has a light emitting surface, a reflecting surface facing the light emitting surface, the light emitting surface and the reflecting surface. A light incident surface is formed on a different surface, and the reflecting surface of the light guide plate includes a plurality of planes and one or more curved surfaces,
An angle between each of the plurality of planes and the light emitting surface is different from each other. 2. The surface light source device according to claim 1, wherein the length (L) of one curved surface forming the reflection surface of the light guide plate is represented by the following equation: L = Δθ. /0.1×2×t3×tanψ where Δθ is the angle difference between two planes which are geometrically in contact with the curved surface, t3 is the distance between the intersection line of the extension of the two planes and the light emitting surface, ψ Is the critical angle of the light guide plate. 3. A cross section of at least one or more curved surfaces constituting the reflection surface of the light guide plate is an arc, a parabola, a hyperbola, an elliptic arc, a trigonometric curve, a chain line, a cycloid curve, a trochoid curve, an exponential function. The surface light source device according to claim 1, wherein the surface light source device is a curve, an involute curve, or another curve that can be expressed mathematically. 4. The reflecting surface of the light guide plate includes two planes including a virtual plane and a curved surface that is in contact with the two planes.
The distance between the virtual intersection line of the two planes and the light incident surface of the light guide plate is
The surface light source device according to any one of claims 1 to 3, wherein the length L of the one curved surface is substantially L / 2. 5. A pattern is formed on the reflection surface of the light guide plate, and the pattern has a variation in density and density, such as a size and a density occupied per unit area, according to a distance from the light entrance surface of the light guide plate. The distribution curve, which is provided and indicates the change in density with respect to the distance from the light incident surface, is different from each other corresponding to the plurality of surfaces forming the reflection surface. A surface light source device according to any one of the above. 6. The method according to claim 4, wherein the density change and the density change rate of the pattern formed on the reflection surface are continuous with respect to a distance from the light entrance surface of the light guide plate. Surface light source device. 7. A reflecting member for guiding light from a light source to a light guide plate,
Or at least one of a reflection plate disposed on the reflection surface side of the light guide plate, or a member disposed on the light emission surface side of the light guide plate and having functions such as deflection, polarization, and scattering. The surface light source device according to claim 1. 8. The surface light source device according to claim 1, wherein the light guide plate has a shape whose thickness decreases as the distance from the light incident surface increases.