JP2015069771A - Planar light emitting body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a planar light emitting body that has high light utilization efficiency and high uniformity of luminance distribution by arranging a light source so as to face toward the center of a light guide plate, even in the light guide plate in which light scattering elements with high productivity are made uniform.SOLUTION: A planar light emitting body 1 includes a light guide plate 2 and a plurality of light sources 3. The light guide plate 2 has a light emitting surface, and an end surface made vertical to the light emitting surface, and a luminance attenuation coefficient represents E (/m). The light sources 3 are arranged on a circumference surrounding the end surface of the light guide plate 2 and having a radius R so as to irradiate the end surface and irradiate the center of the circumference. Further, the light guide plate 2 satisfies the inequation (1).

Description

  The present invention relates to a planar light emitter.

Conventionally, a planar light emitter including a light guide plate and a light source provided at an end of the light guide plate has been used as a backlight device of a liquid crystal display device. The light guide plate consists of a transparent base material and a light diffusing element for diffusing the light incident from the light source, and connects one of the main surfaces to the light emitting surface, the other main surface to the opposite surface, and the main surface to the opposite surface. The surface to be called is called an end surface. A light source is disposed so as to face at least a part of the end face, and the end face provided with the light source facing is also referred to as an incident face.
As a configuration example of the light diffusing element, for example, a structure in which a light diffusing element is provided on at least one of the main surfaces of a transparent substrate is known. Examples of the method of providing the light diffusing element include a method of engraving irregularities or printing a light diffusing dot. In this configuration, in order to improve the uniformity of the luminance distribution in the light emitting surface, a light diffusing element (gradation light diffusing element) is provided so as to enhance the diffusion function as the distance from the light source provided at the end increases (for example, , See Patent Document 1).
As another configuration example of the light diffusing element, a configuration in which a light diffusing material having a refractive index different from that of the transparent substrate is internally added to the transparent substrate. Examples of the method of internally adding a light diffusing material in a transparent substrate include a method of extruding a resin composition in which a light diffusing material is mixed into a transparent resin into a plate shape (see, for example, Patent Document 2).

However, in the configuration in which the gradation light diffusing element is provided on at least one of the main surfaces of the transparent substrate as in Patent Document 1, engraving and printing are required while aligning the transparent substrate and the diffusion pattern for each sheet. Productivity was poor because of
Further, in the configuration in which the light diffusing material is internally added in the transparent base material as in Patent Document 2, in order to increase the uniformity of the luminance distribution in the light emitting surface, it is necessary to use the light diffusing material at a low concentration. There was a tendency for light utilization efficiency to decrease.

JP-A-57-128383 International Publication No. 94/12898

  Therefore, the present invention provides a light guide plate in which highly productive light scattering elements are uniformly prescribed, and the light source is arranged so as to face the center of the plate, so that the light use efficiency is high and the luminance distribution is highly uniform. An object is to realize a light emitter.

  The luminance attenuation coefficient E (/ m) of the light guide plate included in the planar light emitter according to the present invention is defined as R (m), where R (m) is a radius of the circumference where a plurality of light sources are disposed surrounding the end surface of the light guide plate. Equation (1) is satisfied.

More preferably, Formula (2) is satisfy | filled.

  Here, the luminance attenuation coefficient E is measured and calculated by using a rectangular parallelepiped whose main surface is cut out from the light guide plate provided in the planar light emitter of the present invention. A value calculated from the relationship between the distance from the light source on the light emitting surface of the rectangular parallelepiped light guide plate and the luminance when the rectangular parallelepiped is the light guide plate and light is incident on the end surface by the light source arranged at the center of one end surface thereof. The details will be described later.

  Moreover, one aspect | mode of the planar light-emitting body which concerns on this invention WHEREIN: It is preferable that these light sources have the same light emission intensity | strength, and are arrange | positioned on the circumference of the radius R at equal intervals. This increases the uniformity of the luminance distribution over the entire light emitting surface. Further, the light guide plate preferably has a cylindrical side surface at the end face. For example, the light emitting surface of the light guide plate is more preferably circular with a radius R.

When the luminance attenuation coefficient of the light guide plate satisfies the expression (1), the difference in luminance between the center and the periphery of the light guide plate is reduced, and the uniformity of the luminance distribution is high. Such a light guide plate has a constant luminance attenuation coefficient over the entire surface. That is, since the light diffusing element provided on the light guide plate can be arranged uniformly without depending on the distance from the light source, the productivity is higher than that of the conventional light guide plate provided with the gradation light diffusing element.
In particular, in a configuration in which a light diffusing material is internally added to a transparent substrate, productivity is high because it can be easily produced by extrusion.

  According to the present invention, even in a light guide plate in which highly productive light scattering elements are uniformly prescribed, by arranging the light source toward the center of the plate, the light use efficiency is high and the luminance distribution is uniform. A planar light emitter can be provided.

It is a figure which shows the structural example of the planar light-emitting body concerning Embodiment 1 of this invention. It is a figure explaining the measuring method of half-value angle (theta) _h . It is a graph which shows the luminance distribution on the line | wire of the semicircle of a radius of 100 mm in FIG. It is a figure which shows the method to measure a brightness | luminance. It is a figure explaining the breadth of the light from a light source. It is a figure explaining the position coordinate of a disk-shaped light-guide plate. It is explanatory drawing of a near light source. It is explanatory drawing of a far light source. It is a figure which shows an example of the calculation result of luminance distribution. It is a figure which shows another example of the calculation result of luminance distribution. It is a figure which shows another example of the calculation result of luminance distribution. FIG. 6 is a diagram showing a luminance distribution of Example 1. It is a figure which shows the luminance distribution of the comparative example 1. It is a figure which shows the luminance distribution of the comparative example 2. It is a graph which shows contrast with the normalization brightness | luminance of an Example, and the normalization brightness | luminance calculation example in embodiment.

  Hereinafter, embodiments will be described with reference to the drawings. For clarity of explanation, the following description and drawings are omitted and simplified as appropriate.

(Embodiment 1)
Hereinafter, Embodiment 1 of the present invention will be described. FIG. 1 is a front view of an example of a planar light emitter according to the first embodiment of the present invention. The planar light emitter 1 includes a light guide plate 2 having a circular light emitting surface and a plurality of light sources 3.
The light guide plate 2 has a light emitting surface (main surface) and an end surface perpendicular to the light emitting surface, and the light diffusing elements are uniformly arranged. There is no limitation on the method of arranging the light diffusing element. For example, a method of performing uniform engraving or printing on at least one of the main surfaces of the transparent substrate, or a method of mixing a light diffusing material in the transparent substrate can be employed. A method of mixing the light diffusing material into the transparent substrate is preferable in that the molding of the transparent substrate and the addition of the light diffusing material can be performed simultaneously.
The plurality of light sources 3 are provided facing and close to the end surface (incident surface) of the light guide plate 2. Specifically, the plurality of light sources 3 are arranged on the circumference of the radius R so as to surround the end face of the light guide plate 2 so as to irradiate the end face and irradiate the center of the circumference.

The light source 3 has the light spreads in the light divergence half angle theta _h. In the present invention, the light spread half-value angle θ _h (hereinafter, “light spread half-value angle” is also referred to as “half-value angle” as appropriate) is an index that is supplied from the light source 3 to the light guide plate and indicates how the luminance of the main surface is spread. is there. When the brightness of the light on the main surface is compared on a fan-shaped arc that is equidistant from the position of the light source (referred to as point O), it is the highest at one point (referred to as point A) in the front direction of the light source. The lower it is, the lower it becomes symmetrical. The light divergence half-value angle θ _h is a point (referred to as point B) indicating half the luminance of point A determined by the following measurement on a fan-shaped arc equidistant from the light source, and points O and The angle AOB formed by the point A is referred to. Note that, as described above, the point B is symmetrically lowered on the fan-shaped arc as the distance from the point A increases, so that two points B can be determined, but all the angles are equal.

<Measurement method of the optical divergence half angle theta _h of the light source 3>
A specific method for measuring the half-value angle θ _h is as follows.
FIG. 2 shows a state in which the light guide plate is cut into a 300 mm square and one light source 3 is installed in contact with the center of the end face of one side. The light source 3 is turned on, and the luminance of the light emitting surface on a semicircle having a radius of 100 mm with the end surface (point O) in contact with the light source 3 as the center is measured. In FIG. 2, a semicircle with a radius of 100 mm is indicated as R100.
When the luminance at the point where the line perpendicular to the end face passes through the light source 3 and the line with a radius of 100 mm (point A) is 1, the point where the luminance on the line with a radius of 100 mm becomes 0.5 (point B: luminance half) Point). FIG. 3 shows a luminance distribution on a line having a radius of 100 mm. Luminance half-points exist at two places on the left and right of a line perpendicular to the end face. As shown in FIG. 2, one luminance half point is a point B ₁ and the other is a point B ₂ . The angle AOB ₁ or the angle AOB ₂ is the light spreading half-value angle θ _h (radian).

Next, the luminance attenuation coefficient E will be described. The luminance attenuation coefficient E is an index indicating the attenuation of light within the light guide plate.
In the planar light emitter 1 of FIG. 1, when light is supplied from each light source 3 to the inside of the light guide plate through the end face of the light guide plate 2, the light is guided in a direction away from the light source 3 (light guide direction). Is diffused in the thickness direction of the light guide plate 2 and emitted from the light emitting surface.
FIG. 4 is a diagram illustrating a method of measuring the luminance attenuation coefficient E. The light guide plate 2 shown in FIG. 4 is a rectangular parallelepiped light guide plate made from a composition constituting the light guide plate provided in the planar light emitter of the present invention.
In FIG. 4, the upper surface of the light guide plate 2 is referred to as a light emitting surface, the lower surface is referred to as an opposite surface, and one end surface shown on the left side is referred to as an incident surface. A light source 3 is disposed so as to face and be close to the incident surface. In addition, a reflection cover 6 for efficiently using light is disposed around the light source 3.
In addition, the light-guide plate 2 is not restricted to what was mentioned above. For example, the light guide plate 2 may have a square light emitting surface. In addition, the light diffusing element may have a configuration in which light diffusing particles are internally added uniformly, or may have a configuration in which a uniform diffusion pattern print is provided on the light emitting surface and the opposite surface.
In FIG. 4, a luminance meter (CCD camera) 7 for evaluating luminance is arranged so as to face the center of the light emitting surface shown above the light guide plate 2. The fan-shaped groups shown on the light emitting surface side and the opposite surface side of the light guide plate 2 schematically show how light is emitted from the light emitting surface and the opposite surface of the light guide plate 2. Light (light guide light) incident from the light source 3 into the light guide plate 2 is guided in the light guide direction. While being guided in the light guide plate 2, part of the light is diffused by the light diffusing element and emitted from the light emitting surface and the opposite surface of the light guide plate 2 to the outside of the light guide plate 2.
In FIG. 4, an arrow shown in a direction away from the incident surface of the light guide plate 2 indicates the light guide direction.

The calculation method of the luminance attenuation coefficient is as follows.
The light guide light is emitted from the main surface by the light diffusing element while proceeding in the light guide direction. When a light source is provided with an end face on one side of a rectangular light guide plate as an incident surface, the luminance of the light emitting surface attenuates exponentially as it goes from the incident surface to the opposite end surface. For this reason, the luminance U (L) of the main surface at a distance L (m) from the incident surface theoretically follows equation (3) shown below.
In the equation, U ₀ is the luminance at the distance L = 0.
Therefore, the constant E in the equation (2) can be calculated by measuring the luminance U (L) of the light emitting surface at a distance L (m) (m: meter) from the light emitting surface.

  As described above, in the general rectangular parallelepiped light guide plate 2, the luminance of the light emitting surface attenuates exponentially as it goes from the incident surface to the opposite end surface, and thus the luminance in the normal light emitting surface is not uniform.

The planar light-emitting body of the present invention has uniform luminance on the light-emitting surface for the following reasons.
FIG. 1 shows a planar light emitter 1 in which a large number of light sources 3 are arranged around a circular light guide plate 2. Moreover, the light guide direction of each of three light sources among the light sources 3 is shown using three types of dotted lines.
Although the luminance of the main surface due to the light supplied from one light source 3 attenuates as it moves away from the light source, the light from the adjacent light sources 3 gathers as it approaches the center of the circle, so the luminance distribution in the light emitting surface is made uniform. it can.

Assuming that a disc-shaped light guide plate is used as the light guide plate, the results of calculating the present invention in detail will be described below.
Let R (m) be the radius of the light guide plate. Although the light source is disposed on a radius larger than the radius R (m), it is assumed that the light source is on the radius R (m) for the sake of simplicity.
In the disc-shaped light guide plate, the locus at a position away from the incident surface by L (m) in the light guide direction is a circle having a length (m) (RL (m)) obtained by subtracting the distance L from the radius R. . The amount of light flux per 1 m circumference on this circle is expressed as P (L) (lumen / m).
Here, lumen (lumen) which is a unit of luminous flux is a product of a unit of light intensity cd (candela) and a unit of solid angle sr (steradian). In this specification, the light flux P (L) is an amount proportional to the arrangement density and output of the light sources, and the light flux (lumen) is divided by the length (m).

The illuminance of the light emitting surface at a position away from the incident surface in the light guide direction by a distance L (m) is B (L) (lumen / m ² ). 1 lumen / m ² is equal to 1 cd · sr / m ² . Further, since the light guide light is emitted from the light emitting surface while being diffused by the light diffusing element, the reduced amount of the light guide light corresponds to the amount of light emitted from the light emitting surface. In this way, the light guide light attenuates exponentially as it advances in the light guide direction. For this reason, the illuminance B (L) of the light emitting surface is equal to a value obtained by reversing the amount of light flux P (L) differentiated by L.
The luminance of the light emitting surface at a position away from the incident surface by a distance L (m) in the light guide direction is U (L) (cd / m ² ). The illuminance B (L) on the light emitting surface is equal to the product of the luminance U (L) and the solid angle π (sr) on the complete diffusion surface.
Table 1 shows the relationship among the luminous flux P (L), the illuminance B (L), and the luminance U (L).

  A plurality of light sources 3 are arranged in contact with the end face of the light guide plate 2 having a radius R (m). The same light source 3 is used. It is assumed that the light source is a point light source in calculation and is disposed in contact with the end surface of the light guide plate 2. At this time, the center of the light emitting surface is matched with the center of the circumference where the light source is arranged.

The amount of light flux P (L) (lumen / m) per 1 m circumference is calculated according to the following approximate conditions.
The light input from each light source 3 spreads symmetrically on a line from the light source toward the center of the light guide plate 2. The luminance of the principal surface on the circumference separated from the light source by a certain distance has a maximum value on a line from the light source toward the center of the light guide plate 2. There are two positions where the half value of the maximum value is located across the symmetry line, and ½ of the angle formed by one point, the light source, and the other point is defined as the light spreading half value angle θ _h (radian). In the following calculations, for the sake of simplicity, it is assumed that light spreading within the light spreading half-value angle θ _h (radian) is a constant value, and light spreading outside the light spreading half-value angle θ _h is ignored.

  Here, in order to simplify the calculation, light loss due to reaching the end face facing the incident surface, absorbed in the light guide process, or backscattered of the light guide light is not considered.

Let P ₀ (lumen / m) be the amount of light flux from the light source on the incident surface. The light immediately after entering the incident surface from the light source is point-like, but proceeds while spreading in the range of the light spreading half-value angle θ _h (radian). Therefore, the light from the light source spreads in a fan shape with the central angle θ _h × 2 centered on the light source 3 as shown in FIG. Therefore, the light flux P (L) (lumen / m) at each point on the arc of the distance L (m) centered on the light source is inversely proportional to (2θ _h · L).
Further, since the guided light is attenuated in proportion to e- ^EL by traveling the distance L (m) from the light source, the light flux P (L) (lumen / m) excludes L = 0 (m) and its vicinity. The range can be approximated by equation (4).

Next, the illuminance of the main surface at the distance L is defined as B (L) (lumen / m ² ). Since the light that has been diffused and attenuated by the light diffusing agent corresponds to the illuminance B (L), the amount of change in the light flux P (L) corresponds to the illuminance B (L). Accordingly, the illuminance B (L) is obtained by differentiating the light flux P (L) with the distance L and reversing the positive and negative signs.
It becomes.

Substituting (4) into (5) and calculating,
It becomes.
Here, the second term is a negative value, which represents the illuminance of light that irradiates the inside of the light guide plate without exiting from the light guide plate (light returning into the light guide plate). Therefore, the second term should be ignored when discussing the illuminance of the main surface.

Therefore, the illuminance B (L) is expressed by equation (7).

Since the illuminance B (L) calculated by the equation (7) is the illuminance from the light flux P (L) from one light source 3, in order to obtain the illuminance obtained from the light source 3 of the entire circumference, (7 ) Is obtained by integrating the equation on the circumference. Here, in order to simplify the calculation, integration is performed using polar coordinates.
FIG. 6 shows coordinates on the light emitting surface. An arbitrary position of the light guide plate 2 is represented by polar coordinates with the center of the circle being 0 (zero), and a complex number Z = Xe ^jφ is used. Here, X (m) is a distance from the center of the light guide plate main surface. φ is an angle coordinate of 0 to 2π (radian). According to this, when the radius of the circumference where the light source is located is R, the position of the incident end face can be expressed as Z = Re ^jφ using the complex number Z.
When the illuminance B (L) is expressed in polar coordinates, B (Z) is obtained. The illuminance obtained from the light source 3 on the entire circumference can be obtained by integrating Equation (7) from φ = 0 to 2π on the circumference. Since all the light sources are the same, the integration result is rotationally symmetric. Therefore, if integration is performed only on one line passing through the center of the circumference, the illuminance B (z) at an arbitrary point z can be obtained.

The position L on the line is L = | Re ^jφ− Xe ^j0 |, where L, R, and X are considered as vectors as shown in FIG. In this equation, the angle φ is an angle formed with respect to a straight line in the distance X direction. When this is substituted into the equation (6) and integration is performed with Rφ along the circumference, the illuminance B becomes a function of only X, and is represented by B (X) and is expressed by equation (8).

Next, in order to evaluate the illuminance uniformity within the light guide plate surface, a ratio between the illuminance near the incident surface and the illuminance at the center of the disc farthest from the light source is obtained based on the equation (8).
The illuminance B (0) at the center X = 0 of the disk is calculated by substituting X = 0 into the equation (8) and considering that the distance L and the radius R are the same length (L = R). Substituting L = | Re ^jφ −X | = R, the equation (9) is obtained.

Next, the illuminance B (X) around the incident surface X = R−ε (where ε << R) is similarly given by Equation (10) by substituting X = R−ε into Equation (8).

Here, in calculating the equation (10), the range from φ = 0 to 2π is divided into three. That is, the light source to be considered is calculated by dividing into three according to the position on the circumference.
The light source (hereinafter referred to as “near light source”) near the entrance surface periphery X = R−ε (where ε << R) and the entrance surface periphery X = R−ε (where ε << R) are the most. The light source is divided into three light sources (hereinafter referred to as “far light source”) and remote light sources (hereinafter referred to as “medium light source”).
Near the light source, the polar coordinates of phi, ranging from phi = 0 between slightly greater than 0, and corresponds to a range of up to 2 [pi from slightly less than 2 [pi, which φ = 0~φ ₁ and phi = ( 2π−φ ₁ ) to 2π. In FIG. 7, the near light source is indicated by a black circle.

Next, the far light source corresponds to a range of φ = (π−2θ _h ) to (π + 2θ _h ) in consideration of the light spread half-value angle of the polar coordinate φ. In FIG. 8, the far light source is illustrated by a black circle.
It can be considered that light in which φ is in other ranges, that is, the intermediate light source, does not reach the position X = R−ε (where ε << R) in consideration of the light spreading half-value angle. Therefore, in the range of φ corresponding to the medium light source, the integrated value of the above equation can be approximated to zero.
Therefore Equation (9), and the integral in the range of phi = 0 2 [pi of (radian), φ = 0~φ ₁ and _{φ = (2π-φ 1)} ~2π range (near the light source), phi = ([pi The approximate calculation can be performed by dividing into a range of -2θ _h ) to (π + 2θ _h ) (far light source) and another range (medium light source).

Here, the distance L from the near light source to X is
Can be approximated.

Next, the distance L from the far light source to X is
Can be approximated.

The following equation (13) is obtained when equation (10) is calculated in consideration of equations (11) and (12).

Here, the approximation of Expression (13) will be described. The illuminance obtained from the light emitted from the near light source can be approximated to the illuminance at the rectangular light guide plate.
In the case of a rectangular light guide plate, the light guide light can be expressed by Expression (14). For circular light guide plate, since the light source is arranged to face the center of the circle, the light guide light is dependent on the distance L (m) around the optical divergence half angle theta _h and the light sources of a rectangular In the case of the light guide plate, since the light sources are arranged in the same direction, it is not necessary to take them into consideration. Therefore, the light guide light of the rectangular light guide plate is expressed by equation (14). P ₀ is the amount of light flux from the light source on the incident surface, and Y is the light guide distance.

Since the light guide light and the illuminance of the light emitting surface are expressed by the equation (5), this is calculated to obtain the equation (15).

In the near light source, since Y≈0, Equation (16) is obtained.
An approximation of equation (17) holds.

Further, considering the light emitted from the far light source in the same manner, the equation (18) is obtained.

The approximation of equation (19) holds.
Therefore, the approximation of Expression (13) is established.

Therefore, the ratio of the illuminance between the center and the periphery (periphery / center illuminance ratio) is expressed by Expression (20) which is the ratio of Expression (13) and Expression (9).

In Expression (20), when the illuminance ratio at the periphery / center of the disk is 1, Expression (21) is obtained.

The closer the value of θ _h × (e ^−ER + e ^ER ) / π in Equation (20) is to 1, the closer the peripheral central illumination ratio is to 1. Therefore, if the value of θ _h × (e ^−ER + e ^ER ) / π is within a predetermined range, it can be determined that the illuminance distribution of the light guide plate 2 is uniform.
FIG. 9 shows the calculation result of the illuminance distribution when the values of θ _h × (e ^−ER + e ^ER ) / π are 1.4 and 1.2. Similarly, FIG. 10 shows the calculation results of the illuminance distribution when the values are 1.0 and 0.8, and FIG. 11 shows the calculation results of the illuminance distribution when the values are 0.6.
When the value of θ _h × (e ^−ER + e ^ER ) / π is 0.6, 0.8, 1.0, 1.2, 1.4, the minimum value of illuminance with respect to the maximum value of illuminance within the main surface The ratios are 0.73, 0.9, 0.86, 0.75, and 0.66, respectively. From this, when the value of θ _h × (e ^−ER + e ^ER ) / π is in the range of 0.8 to 1.2, a uniform illuminance distribution with an illuminance ratio in the main surface of 75% or more can be obtained. I understand. Further, in addition to the results calculated from the illuminance shown in FIG. 9 to FIG. 11, from the experimental results, when the value of θ _h × (e ^−ER + e ^ER ) / π is in the range of 0.96 to 1.04, It was confirmed that the light was emitted more uniformly, and it was found that this is a more preferable range.

The value of the light divergence half angle theta _h, depending on the refractive index of the light source and medium to be used, consisting of approximately 0.6rad the value of 0.8Rad. When θ _h is 0.6 rad and θ _h × (e ^−ER + e ^ER ) / π is in the range of 0.8 to 1.2, ER is in the range of 1.4 ≦ ER ≦ 1.8. There will be. When θ _h is 0.7 rad and θ _h × (e ^−ER + e ^ER ) / π is in the range of 0.8 to 1.2, 1.2 ≦ ER ≦ 1.6 and θ _h is 0 When .8 rad and θ _h × (e ^−ER + e ^ER ) / π are in the range of 0.8 to 1.2, 1.0 ≦ ER ≦ 1.5. When θ _h is in the range of 0.6 rad to 0.8 rad, the range of ER is expressed by Equation (1).

If more preferred range theta _h is 0.7Rad, range ER becomes Equation (2).

  Therefore, if a light guide plate having an ER (product of luminance attenuation coefficient E and radius R) within this range is used, the light source is the center of the plate even in a light guide plate in which highly productive light scattering elements are uniformly prescribed. By arranging so as to face the surface, it is possible to realize a planar light emitter having high light utilization efficiency and high uniformity of luminance distribution.

(Embodiment 2)
In the first embodiment, the case where the light emitting surface of the light guide plate 2 is circular has been described as an example, but the present invention is not limited to this.
For example, the light guide plate 2 is formed by either a curved surface or a flat surface or a combination of a curved surface and a flat surface if the region of the end surface where the plurality of light sources 3 are arranged is a position on the circumference of the radius R. May be.
The light guide plate 2 can be, for example, a regular hexagon or a regular polygon having more sides than the scope of the present invention. In this case, the regular polygon may be any shape in which the light emitting surface is inscribed in a circle having a radius R. Furthermore, when the end surface is formed by either a curved surface or a plane, or a combination of a curved surface and a plane, the shape of the light guide plate 2 is preferably inscribed in a circle having a radius R.
If the light source is arranged on the circumference of radius R so as to irradiate the end face of the light guide plate to the center of the circumference, the shape of the light guide plate is not limited, but the shape of the light emitting surface is a regular polygon or A circular shape is preferable, and a circular shape is more preferable.

By making the region of the end face where the light source 3 is arranged on the circumference of the radius R, the distance from the center of the light guide plate 2 to each light source 3 can be made uniform, and the guide satisfying the above formula (1) can be obtained. The optical plate 2 can be manufactured. Further, it is preferable that the plurality of light sources have the same emission intensity and are arranged at equal intervals on the circumference of the radius R. This increases the uniformity of the luminance distribution over the entire light emitting surface. In addition, it is preferable that the center of gravity of the main surface of the light guide plate coincides with the center of the circumference where the light source is arranged. With such a configuration, it is possible to provide a planar light emitter with high uniformity of luminance distribution.
By making the shape of the end face flexible, the shape of the light emitting surface of the light guide plate 2 can be changed according to the application. For example, when design is required, various shapes of light emitting surfaces can be realized.
In addition, although the case where the light diffusing material is mixed uniformly in the light guide plate 2 has been described in the first embodiment, a diffusion pattern engraved or printed with a uniform pattern on the main surface and / or the opposite surface may be used.

[Examples and Comparative Examples]
As the light guide plate 2, a circular shape was used in the examples, and a rectangular shape was used in the comparative examples. First, the measurement method used in an Example and a comparative example is demonstrated.
<Luminance measurement method>
Since it is difficult to measure the illuminance, the luminance proportional to the illuminance is measured. Luminance U and illuminance B have a relationship of B = π × U. In the luminance measurement, the configuration of the apparatus shown in FIG. 4 is used. A luminance meter “CA2000” manufactured by Konica Minolta Co., Ltd. is placed as a luminance meter 7 at a position 2 m away from the main surface in front of the main surface of the light guide plate 2, and the luminance (cd / m ² ) at each position on the main surface. Measure. The luminance is normalized with the maximum value being 1 for each light guide plate 2.
<Calculation method of luminance attenuation coefficient E (/ m)>
Under the conditions of Comparative Example 1 described later, the luminance (cd / m ² ) of the main surface passing through the center of the end surface where the light source 3 of the light guide plate 2 is disposed and along a line parallel to the main surface is measured. The logarithm of the measured luminance value and the distance from the end face are plotted to determine the gradient (/ m) when the luminance characteristic is expressed.
For the light guide plate 2 of the example, a light guide plate 2 having the same shape as that of Comparative Example 1 was produced, and the luminance was measured.

Examples and comparative examples are shown below.
[Example 1]
Using the resin composition described below, an optical plate was produced using an extruder. The thickness of the plate was 10 mm.
<Resin composition>
Base resin: PMMA (“Parapet” manufactured by Kuraray Co., Ltd.), Refractive index: 1.494 (nD)
Light diffusing material: Titanium oxide (“JR-1000” manufactured by Teika Co., Ltd.), refractive index: 2.72 (nD), average particle size: 1 μm
-Light diffusing agent addition concentration: 0.00075%
As a result of observing the cross section and surface of the manufactured optical plate with a microscope, the light diffusing material was uniformly added to the optical plate.
The manufactured optical plate was cut into a circular shape with a diameter of 286 mm, and the light guide plate 2 was produced. Next, a light source 3 described below was fixed to the end face of the light guide plate 2 with a transparent adhesive, and a planar light emitter was produced. The light sources 3 were evenly arranged around the light guide plate 2 at intervals of 25 mm.

<Light source 3>
Light source 3 used: “KD-11013” manufactured by New Japan Yacht Co., Ltd.
LED spacing: 25mm
Applied voltage: DC12V

[Comparative Example 1]
A light guide plate 2 was prepared in the same manner as in Example 1 except that the optical plate was cut into a 300 mm square. Next, the same light source 3 as in Example 1 was fixed to the end face of the light guide plate 2 with a transparent adhesive, and a planar light emitter was produced. The light sources 3 were evenly arranged at 25 mm intervals on the end surface of one side of the light guide plate 2.

[Comparative Example 2]
A square optical plate similar to Comparative Example 1 was manufactured, and then the same light source 3 as that of Example 1 was fixed to the end surface of the light guide plate 2 with a transparent adhesive to produce a planar light emitter. The light sources 3 were evenly arranged at 25 mm intervals on the end faces of the four sides of the light guide plate 2.

Table 2 summarizes the shapes and dimensions of the light guide plate 2 and the arrangement of the light sources 3 in the examples and comparative examples.

The light source 3 was turned on for the light guide plate 2 of Example 1 and Comparative Examples 1 and 2, and the luminance distribution of the main surface of the light guide plate 2 was measured. The results are shown in FIGS.
As can be seen from FIG. 12, in Example 1 in which the light guide plate 2 is circular, the ratio of the area of the main surface where the normalized luminance is 0.75 or more is 80%, and the in-plane luminance is uniform. .
As can be seen from FIG. 13, in Comparative Example 1 in which the light guide plate 2 is a square, the luminance decreases as the distance from the light source 3 increases. In Comparative Example 1, the ratio of the area of the main surface where the normalized luminance was 0.75 or more was 3%.
As can be seen from FIG. 14, in Comparative Example 2 in which the light guide plate 2 has a quadrangular shape, the luminance decreases as the central portion of the light guide plate is distant from any light source. The ratio of the area of the main surface where the normalized luminance is 0.75 or more was about 47%.

FIG. 15 shows a comparison between the actual measurement result of the example and the calculation result calculated in the embodiment. The Y direction is constant at the center of the plate (Y = 146 mm), and the luminance in the X direction from 0 m to 0.3 m is displayed and compared. Both tendencies agree well, and it can be understood that the light guide plate 2 having a uniform luminance distribution in the plane can be realized by applying a uniform light diffusing element according to the theory shown in the embodiment. .
The number of light sources is assumed to be innumerable in the luminance calculation, but it can be seen from the comparison result with the embodiment that the luminance distribution can be made uniform in a plane even with a finite number. As the number of light sources is reduced, the brightness of the surrounding area decreases. However, it is preferable to place at least 8 (at least 45 degrees) and at least 4 (at least 90 degrees) to display the brightness distribution. Can be made uniform within.

Above to the shape of the main surface of the light guide plate 2 is circular, the radius R of the circle, an expression that consists of light divergence half angle theta _h luminance attenuation coefficient E and the light source 3 of the light source 3 satisfy specific ranges diffusing material Uniform luminance was also obtained in the light guide plate 2 in which is uniformly added to the plate.

  In addition, this invention is not limited to embodiment shown above. Within the scope of the present invention, it is possible to change, add, or convert each element of the above-described embodiment to a content that can be easily considered by those skilled in the art.

DESCRIPTION OF SYMBOLS 1 Planar light-emitting body 2 Light-guide plate 3 Light source 6 Reflective cover 7 Luminance meter

Claims (5)

A light guide plate having a light emission surface and an end surface perpendicular to the light emission surface, the luminance attenuation coefficient being E (/ m);
A plurality of light sources arranged on the circumference of a radius R (m) surrounding the end face of the light guide plate so as to irradiate the end face and irradiate the center of the circumference;
A planar light-emitting body in which the light guide plate satisfies the formula (1).
A light guide plate having a light emission surface and an end surface perpendicular to the light emission surface, the luminance attenuation coefficient being E (/ m);
A plurality of light sources arranged on the circumference of a radius R (m) surrounding the end face of the light guide plate so as to irradiate the end face and irradiate the center of the circumference;
A planar light-emitting body in which the light guide plate satisfies the formula (2).
  The planar light-emitting body according to claim 1, wherein the plurality of light sources are arranged at equal intervals on an end surface of the light guide plate.   The planar light-emitting body according to any one of claims 1 to 3, wherein the end face of the light guide plate is a cylindrical side face.   The planar light-emitting body according to claim 4, wherein the light-emitting surface of the light guide plate is circular with a radius R.