JP2005011549A - Surface light source device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a backlight capable of improving luminance quality of a light guide body. <P>SOLUTION: A light source surface of a light emitting diode 13a is mounted oppositely to the lower end face 21a of the light guide body 21. The guide body 21 refracts the light from the diode 13a toward its surface 21b in a planar form to convert it into a planar light source. Both sidewall surfaces 21d of the guide body 21 are tilted so as to enter the light from the diode 13a at an angle not less than a critical angle. Thus, the light entering into both of the sidewall surfaces 21d of the guide body 21 from the diode 13a is totally reflected; refraction of the light illuminated to both of the sidewall surfaces 21d of the guide body 21 can be prevented; and energy loss of the light from the surface 21b of the guide body 21 can be prevented. The luminance quality of the whole surface 21b of the guide body 21 can be improved. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a surface light source device that uses light from a light source as a planar light source.
[0002]
[Prior art]
Conventionally, a backlight as an auxiliary light source as this type of surface light source device is attached to the back surface of the display screen area of a transmissive liquid crystal panel constituting the transmissive liquid crystal display device. This backlight refracts light from a light-emitting diode (LED) as a light source, which is a small surface light source, into a planar shape by a light guide that is a rectangular plate-like planar light source converter. To convert it into a planar light source.
[0003]
In particular, when this backlight is used for applications such as mobile phones, there is a tendency to use light emitting diodes, and the light guide used in this case is a rectangular resin molded product. The front and back surfaces of the light guide have various shapes in order to efficiently irradiate light toward the screen direction of the liquid crystal panel. The front and back surfaces of the light guide are connected to the light guide. Various optical sheets that transmit or reflect incident light are attached.
[0004]
Here, a plurality of light emitting diodes are arranged along the longitudinal direction of the lower end surface which is one end surface as one side of the light guide, and the number of the light emitting diodes is determined by a desired screen quality. Moreover, in order to make the light from these light emitting diodes enter the light guide, the light emitting diode is brought into contact with the lower end surface which is the light incident surface of the light guide, or the lower end of the light guide is made thin, A light emitting diode is installed at this thin position.
[0005]
And the light which injected into these light guides from these light emitting diodes is irradiated to a liquid crystal panel through this light guide and the reflective sheet affixed on the back surface of this light guide. Therefore, this light guide realizes conversion of light from each light emitting diode to a surface light source suitable for the screen size of the liquid crystal panel.
[0006]
Furthermore, the light irradiated from the surface of the light guide is incident on the liquid crystal panel through an optical sheet attached to the surface of the light guide, and a liquid crystal display device including the liquid crystal panel is used. In addition to being visually recognized by the user, it is also recognized as screen quality such as uneven screen brightness (see, for example, Patent Document 1).
[0007]
However, in general, in the case of a backlight using light emitting diodes, a light guide for reflecting light from each light emitting diode to a surface light source suitable for the screen size of the liquid crystal panel used, a reflective sheet, or various types The light is recognized by the user through the liquid crystal panel through the optical sheet. At this time, when light enters the light guide or when light propagates through the light guide, light is absorbed or diffused by various optical sheets and liquid crystal panels. For this reason, most of the energy supplied from these light emitting diodes is lost, that is, the screen quality is lowered, and the desired screen quality may not be achieved from the viewpoint of unevenness of screen brightness.
[0008]
In general, the number of light emitting diodes is increased at the expense of power consumption to ensure screen quality, or the number of light emitting diodes is decreased to reduce power consumption and reduce costs. Screen quality may be sacrificed.
[0009]
Furthermore, the light incident on the light guide from these light emitting diodes has a strong directivity, and the light source surface method parallel to the optical axis of the light incident perpendicularly to the lower end surface of the light guide from each of the light emitting diodes. In directions inclined at an angle a or more toward the left and right and up and down directions with reference to the line direction, the energy of light emitted from each of these light emitting diodes rapidly decreases, and the light is not effectively irradiated by these light emitting diodes. It becomes. In particular, when the light from these light-emitting diodes propagates radially after entering the light guide, and reaches both side surfaces that are adjacent to the lower end surface facing each light-emitting diode of this light guide, Light is absorbed by the light diffusing as refracted light from the inner layer of the light guide to the external air layer and the light returning to the inside of the light guide as reflected light at the interfaces on both sides of the light guide. As a result, energy loss of light occurs, which is one of the screen quality such as screen brightness unevenness.
[0010]
For this reason, various methods have been proposed as methods for improving the screen quality. As a typical example, it is known to use a resin having high reflection characteristics for a holder case that surrounds and supports a light guide. However, when this method is used, the refracted light irradiated to the outside of the light guide can be returned to the inside of the light guide, but this refracted light is reflected by the surface of the holder case. Since the light is transmitted through the side surface of the light guide, only a small amount of energy of the refracted light that has been lost can be recovered, which is insufficient for improving the screen quality of the display screen area.
[0011]
Furthermore, a method of providing a highly reflective sheet in the gap between the light guide and the holder, or attaching a highly reflective sheet to the side surface of the light guide is also known. Although this method can obtain results that greatly contribute to improving the screen quality, there is a surface on which the adhesive material is applied on each of the front or back surface of the reflective sheet and the side surface of the light guide. Moreover, it is insufficient for improving the screen quality of the display screen area.
[0012]
[Patent Document 1]
JP 2002-287144 A (page 3-4, and FIGS. 3 to 5)
[0013]
[Problems to be solved by the invention]
As described above, the light incident on the light guide from each light emitting diode has a strong directivity, and in a direction inclined at an angle a or more from the normal direction of the light source surface of these light emitting diodes to the left and right and up and down directions, The energy of light supplied from each of these light emitting diodes is greatly reduced. In the first place, the cause of the deterioration of the screen quality is that when the light irradiated in the direction inclined by an angle a from the light source surface normal direction of each light emitting diode toward the left and right directions is incident on the lower end surface of the light guide, The incident angle of light irradiated in the direction of the angle a and incident on the light guide does not become a critical angle for total reflection. For this reason, when the light irradiated in the direction of the angle a is irradiated to the outside of the light guide, it becomes refracted light, and the energy loss of the light irradiated from the light guide to the liquid crystal panel is reduced. This is one of the causes of screen quality degradation.
[0014]
Therefore, in order to solve one of the factors that deteriorate the screen quality, in particular, the incident angle to the side surface of the light guide due to the light irradiated from each light emitting diode in the direction of angle a, It is required to optimize the material. And, as in the prior art, when the light guide is a rectangular flat plate, that is, when the left and right side surfaces of the light guide are parallel to the normal direction of the light source surface of each light-emitting diode, the light guide inevitably The critical angle varies depending on the material, and the light irradiated onto the side surface of the light guide is not totally reflected, so that the refracted light toward the side surface of the light guide is diffused to the outside. For this reason, the energy of the light from the light guide is lost, which is one factor that lowers the screen quality in the display screen area of the liquid crystal panel, and the luminance quality of the entire surface of the light guide is easily improved. It has a problem of not.
[0015]
This invention is made | formed in view of such a point, and it aims at providing the surface light source device which can improve the brightness | luminance quality of a planar light source converter.
[0016]
[Means for Solving the Problems]
The present invention relates to a light source and a substantially square plate-like planar light source that is disposed with one side facing the light source and refracts light from the light source toward a principal surface to convert it into a planar light source. And the side of the planar light source converter that is adjacent to the side facing the light source has a light irradiated from the light source through one end of the planar light source converter with a critical angle or more. The inclined side is incident at an angle of.
[0017]
And the side adjacent to the one side facing the light source of the planar light source converter is an inclined side where the light emitted from the light source through one side of the planar light source converter is incident at an angle greater than the critical angle. Thus, the incident angle of light incident on the side of the planar light source converter from the light source becomes a critical angle for total reflection. For this reason, since refraction of the light irradiated to the side of the planar light source converter is prevented, energy loss of light irradiated from one main surface of the planar light source converter can be prevented, and The luminance quality of the entire main surface of the planar light source converter is improved.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the configuration of an embodiment of a liquid crystal display device provided with the surface light source device of the present invention will be described with reference to FIGS.
[0019]
1 to 4, reference numeral 1 denotes a transmissive liquid crystal display device. The liquid crystal display device 1 is a transmissive liquid crystal display device used in a mobile phone or the like, for example, a thin film transistor (TFT) type such as type 2. A liquid crystal panel 2 is provided. The liquid crystal panel 2 includes a rectangular flat plate array substrate 3 and a counter substrate 4 which are arranged in a matrix on the surface of a main surface of a thin film transistor (not shown), and the array substrate 3 and the counter substrate. 4, a liquid crystal (not shown) is interposed between the two.
[0020]
On the other hand, a surface light source device as an auxiliary light source that irradiates and transmits light to the display screen area 5 of the liquid crystal panel 2 on the back side of the display screen area 5 as a display area formed in the center of the liquid crystal panel 2. It is arrange | positioned in the state which faced the surface of the backlight 11 which is. The backlight 11 includes a plurality of white light emitting diodes (LEDs) 13a, 13b, and 13c that emit white light from a light source surface 12 formed on one side surface as a small surface light source. For example, three are provided.
[0021]
The light-emitting diodes 13a, 13b, and 13c are attached to the surface of a light-emitting substrate 14 that is a flexible printed circuit board (FPC) that is driven by supplying electric energy to emit light. . The light emitting substrate 14 includes a main body portion 14a having an elongated rectangular flat plate shape on which the light emitting diodes 13a, 13b, and 13c are mounted. Then, one end of one side of the main body 14a protrudes flush from the main body 14a and is supplied to the light emitting diodes 13a, 13b, 13c mounted on the surface of the main body 14a. One end in the longitudinal direction of the elongated rectangular flat connecting piece 14b that conducts energy is integrally connected to form a substantially L shape.
[0022]
Here, these light emitting diodes 13a, 13b, and 13c are attached to the surface of the main body portion 14a of the light emitting substrate 14 in a state of being spaced apart at equal intervals along the longitudinal direction of the main body portion 14a. Further, each of the light emitting diodes 13a, 13b, 13c has a light source surface 12 on one side surface of each of the light emitting diodes 13a, 13b, 13c, and the light source surface 12 of each of the light emitting diodes 13a, 13b, 13c. Each of them is mounted on the surface of the main body portion 14 a in a state where the main body portion 14 a of the light emitting substrate 14 is aligned in the width direction.
[0023]
A light guide 21 having a substantially rectangular flat plate shape as a planar light source conversion body is formed in a state where the light emitting diodes 13a, 13b, and 13c face a lower end surface 21a as a light incident surface that is one side in the longitudinal direction. It is arranged. In the light guide 21, planar light from each of the light emitting diodes 13a, 13b, and 13c enters from the lower end surface 21a, and the planar light is planarized toward the surface 21b that is one main surface. It has a role to refract and convert it into a planar light source. On the back surface 21c of the light guide 21, a rectangular sheet-like reflective sheet 22 as an optical sheet is attached and attached.
[0024]
Here, the light guide 21 is a resin molded material formed of a heat-resistant transparent resin such as polycarbonate, acrylic, or cycloolefin polymer. Furthermore, a plurality of, for example, three sheets of various rectangular sheet-like optical sheets 23 are attached to the surface 21b of the light guide 21 in a state where they are overlapped with each other.
[0025]
Further, at the lower end where the lower end surface 21a of the light guide 21 is located, the light source surfaces 12 of the respective light emitting diodes 13a, 13b, 13c mounted on the surface of the light emitting substrate 14 are respectively placed under the light guide 21. The light emitting substrate 14 is attached in a state of facing the end surface 21a in parallel. Here, each of the light-emitting diodes 13a, 13b, and 13c mounted on the surface of the light-emitting substrate 14 has a lower end surface 21a of the light guide 21 along the longitudinal direction of the light-emitting diodes 13a, 13b, and 13c. It is attached to the center of each of the number of parts, that is, the three parts.
[0026]
Then, the light emitting substrate 14 is attached to the lower end portion of the light guide 21, each optical sheet 23 is bonded to the front surface 21 b, and the reflection sheet 22 is further bonded to the back surface 21 c to configure the backlight 11. ing. In this state, the side wall surfaces 21d and 21e, which are inclined sides as both sides in the width direction of the light guide 21 constituting the backlight 11, have a width dimension from the lower end side to the upper end side of the light guide body 21. Is inclined to gradually increase. The side wall surfaces 21d and 21e are adjacent to the lower end surface 21a of the light guide 21 facing the light source surface 12 of the light emitting diodes 13a, 13b, and 13c.
[0027]
Further, the slopes of the side wall surfaces 21d and 21e of the light guide 21 formed by the side wall surfaces 21d and 21e of the light guide 21 and the normal direction of the light source surface 12 of the light emitting diodes 13a, 13b and 13c. The angle X is set to be changed according to the directivity of each of the light emitting diodes 13 a, 13 b, and 13 c and the refractive index of light caused by the material of the light guide 21.
[0028]
That is, the inclination angle X of the both side wall surfaces 21d and 21e of the light guide 21 depends on the material of the light guide 21 and the directivity of the light emitting diodes 13a, 13b, and 13c. Light having a large amount of energy supplied from 13c is incident on the both side wall surfaces 21d and 21e of the light guide 21 through the lower end surface 21a of the light guide 21 at an angle equal to or greater than the critical angle at which total reflection occurs. It is set to enter.
[0029]
More specifically, the both side wall surfaces 21d and 21e of the light guide 21 are effective regions in which the amount of light energy supplied from the light source surface 12 of each of the light emitting diodes 13a, 13b, and 13c is large. The light emitting diodes 13a, 13b, and 13c are each in a region up to an angle a that is inclined in the longitudinal direction of the light emitting diodes 13a, 13b, and 13c with respect to the normal direction of the light source surface 12 of the light emitting diodes 13a, 13b, and 13c. , 13b, and 13c, the incident angle of the light irradiated toward the direction of the angle a with respect to the normal direction of the light source surface 12 on the side wall surfaces 21d and 21e adjacent to the light guide 21 is i. In this case, X ≧ 90−ai and i = sin ⁻¹ (1 / n) are satisfied. Note that n is a refractive index of light caused by the light guide 21 caused by the material of the light guide 21.
[0030]
In other words, the angle a is determined by the light emitting diodes 13a, 13b, and 13c from the optical axis of the light that is perpendicularly incident from the light source surface 12 of the light emitting diodes 13a, 13b, and 13c to the lower end surface 21a of the light guide 21. This is the angle up to the effective irradiation range of light. In addition, the angle X indicates the optical axis of light perpendicularly incident from the light source surface 12 of each of the light emitting diodes 13a, 13b, and 13c to the lower end surface 21a of the light guide 21, and the light guide close to the optical axis of this light. This is an angle formed by any one of the side wall surfaces 21 d and 21 e of the body 21. Further, the angle i is an incident angle of light irradiated at an angle a from each of the light emitting diodes 13 a, 13 b, and 13 c onto the both side wall surfaces 21 d and 21 e of the light guide 21.
[0031]
Then, the backlight 11 has the surface 21 b of the light guide 21 opposed to the back surface side of the display screen area 5 of the liquid crystal panel 2 through each optical sheet 23, and the display screen area 5 of the liquid crystal panel 2. It is attached to the back side. In this state, the liquid crystal panel 2 and the backlight 11 are accommodated in a rectangular frame-shaped holder case 31 and modularized to form the liquid crystal display device 1.
[0032]
Next, the operation of the first embodiment will be described.
[0033]
First, electrical energy is supplied from the light emitting substrate 14 to each of the light emitting diodes 13a, 13b, 13c, and each of the light emitting diodes 13a, 13b, 13c is caused to emit light.
[0034]
Then, the planar light emitted from the light source surface 12 of each of the light emitting diodes 13 a, 13 b and 13 c enters the lower end surface 21 a of the light guide 21.
[0035]
The light incident on the lower end surface 21a of the light guide 21 is converted into a surface shape toward the front surface by the reflection sheet 22 attached to the back surface 21c of the light guide 21, and the liquid crystal panel 2 The display screen area 5 is irradiated on the back surface.
[0036]
At this time, the light is emitted from the light source surface 12 of each of the light emitting diodes 13 a, 13 b, and 13 c and is incident from the lower end surface 21 a of the light guide 21. The light incident on 21d and 21e is incident at an angle greater than the critical angle by the inclination angle X formed on both side wall surfaces 21d and 21e, and is totally reflected by these both side wall surfaces 21d and 21e.
[0037]
Furthermore, the light irradiated to the back side of the display screen area 5 of the liquid crystal panel 2 passes through the display screen area 5 of the liquid crystal panel 2 and enters the eyes of the user, and the display screen area 5 of the liquid crystal panel 2 The image displayed at is visually recognized by the user.
[0038]
As described above, according to the embodiment, out of the light emitted from the light source surface 12 of each light emitting diode 13a, 13b, 13c of the backlight 11 and incident on the lower end surface 21a of the light guide 21, Light emitted in a direction inclined by an angle a toward the left and right and up and down directions with respect to the normal direction of the light source surface 12 of each of the light emitting diodes 13a, 13b, and 13c is emitted from the light emitting diodes 13a, 13b, and 13c. In the case where the normal direction of the light source surface 12 and both side surfaces of the light guide 21 are parallel, the energy supply amount depends on the material of the light guide 21 and the directivity of the light emitting diodes 13a, 13b, and 13c. A large amount of light enters the both side surfaces of the light guide 21 at an angle smaller than the critical angle.
[0039]
That is, when the light from the light emitting diodes 13a, 13b, and 13c is incident on the light guide 21 and propagates radially, and reaches both side surfaces of the light guide 21, both wall surfaces of the light guide 21 are obtained. Both side surfaces of the light guide 21 are reflected by the light diffusing as refracted light from the inner layer of the light guide 21 to the external air layer and the light returning to the inside of the light guide as reflected light. The energy loss of the light incident on the liquid crystal panel 2 increases, and when the planar light irradiated from the surface 21b of the light guide 21 is transmitted to the liquid crystal panel 2, the display screen area of the liquid crystal panel 2 is displayed. 5 may cause unevenness of the screen brightness, and the screen quality of the display screen area 5 of the liquid crystal panel 2 is deteriorated.
[0040]
Therefore, when the light guide 21 whose material is acrylic and the refractive index of light is 1.49 and the light emitting diodes 13a, 13b, and 13c having directivity shown in FIG. 3 are used, as shown in FIG. In addition, an effective region where the outside air temperature is 25 ° C., the input current (IF) to each of the light emitting diodes is 20 mA, and the energy supply amount of the light emitted from each of the light emitting diodes 13a, 13b, and 13c is large. Incident angles incident on both side wall surfaces 21d and 21e of the light guide 21 as regions inclined up to 50 ° horizontally and vertically with respect to the normal direction of the light source surface 12 of the light emitting diodes 13a, 13b, and 13c. Was set to be above the critical angle for total reflection.
[0041]
Specifically, both side wall surfaces 21d and 21e of the light guide 21 are formed in a trapezoidal shape inclined from the lower end side toward the upper end side, and the light source surfaces of the respective light emitting diodes 13a, 13b and 13c by the both side wall surfaces 21d and 21e. The inclination angle with respect to the normal direction of 12 was 2.2 °. As a result, when the input current (IF) to each light emitting diode is 17 mA, as shown in FIG. 4, the light guide body with respect to the normal direction of the light source surface 12 of each light emitting diode 13a, 13b, 13c. Compared with the conventional backlight 11 of the comparative example shown in FIG. 5 in which both side surfaces 21f and 21g of the light guide 21 are parallel, the screen brightness of the surface 21b of the light guide 21 is improved by 8%, and the light guide 21 The screen brightness unevenness of the surface 21b of the screen increased by 4%.
[0042]
Therefore, depending on the material of the light guide 21 or the directivity of each of the light emitting diodes 13a, 13b, 13c, light with a large amount of energy emitted from each of the light emitting diodes 13a, 13b, 13c The inclination angles X of the side wall surfaces 21d and 21e of the light guide 21 are set so as to be incident on 21d and 21e at an angle greater than the critical angle.
[0043]
More specifically, a region where the amount of light energy supplied from the light source surface 12 of each of the light emitting diodes 13a, 13b, and 13c is large, that is, the light source surface of each of the light emitting diodes 13a, 13b, and 13c. In a region up to an angle a tilted in the longitudinal direction of the light emitting diodes 13a, 13b, and 13c with respect to the normal direction of the twelve normal directions, the light source surface 12 of each of the light emitting diodes 13a, 13b, and 13c extends in the normal direction. On the other hand, the incident angle of the light irradiated toward the direction of the angle a to one of the side wall surfaces 21d and 21e adjacent to the light guide 21 is i, and the refractive index of the light by the light guide 21 is n. In this case, the inclination angles X of the side wall surfaces 21d and 21e of the light guide 21 are set so as to satisfy the relationship of X ≧ 90−ai and i = sin ⁻¹ (1 / n).
[0044]
As a result, light with a large amount of energy supplied from the light source surface 12 of each of the light emitting diodes 13a, 13b, and 13c is incident on the side wall surfaces 21d and 21e of the light guide 21 at an angle equal to or greater than the critical angle at which total reflection occurs. It becomes. For this reason, since refraction of the light irradiated to the both side wall surfaces 21d and 21e of the light guide 21 can be prevented, energy loss of the light irradiated in a planar shape from the surface 21b of the light guide 21 can be prevented, The luminance quality of the entire surface 21b of the light guide 21 can be improved. Therefore, when planar light irradiated from the surface 21b of the light guide 21 is transmitted to the liquid crystal panel 2, unevenness of screen brightness or the like hardly occurs in the display screen area 5 of the liquid crystal panel 2. The screen quality of the display screen area 5 of the liquid crystal panel 2 can be improved.
[0045]
In the above embodiment, the light guide 21 is disposed on the back surface of the display screen area 5 of the liquid crystal panel 2, and the planar light from the surface 21 b of the light guide 21 is displayed on the liquid crystal panel 2. The transmissive liquid crystal display device 1 that transmits light from the back surface side of the screen area 5 has been described. However, a certain amount of planar light from the front surface 21b of the light guide 21 is observed from the back surface side of the display screen area 5 of the liquid crystal panel 2. The liquid crystal display device 1 may be a transflective liquid crystal display device 1 that transmits light at a rate. Further, a light guide 21 is provided on the surface of the display screen area 5 of the liquid crystal panel 2, and the back surface 21 c of the light guide 21 is provided. Even in the reflective liquid crystal display device 1 having a front light that irradiates and reflects the planar light to the surface of the display screen area 5 of the liquid crystal panel 2, Has the same effect as the embodiment Can.
[0046]
Further, about three light emitting diodes 13a, 13b, and 13c are arranged to face the lower end surface 21a of the light guide 21, but the light emitting diodes 13a and 13b installed to face the lower end surface 21a of the light guide 21 are arranged. , 13c may be at least one.
[0047]
【The invention's effect】
According to the present invention, the side of the planar light source converter is an inclined side on which light irradiated from the light source through one side of the planar light source converter is incident at an angle greater than the critical angle. The light incident on the side of the planar light source converter is totally reflected, and refraction of the light irradiated to the side of the planar light source converter can be prevented, so one main surface of this planar light source converter Energy loss of the light emitted from the light source can be prevented, and the luminance quality of the entire main surface of the planar light source converter can be improved.
[Brief description of the drawings]
FIG. 1 is an explanatory view showing a part of an embodiment of a surface light source device of the present invention.
FIG. 2 is an exploded perspective view showing a liquid crystal display device provided with the upper surface light source device.
FIG. 3 is a graph showing the directivity of a light emitting diode used as a light source of the upper surface light source device.
FIG. 4 is an explanatory diagram showing luminance of one main surface of the linear light source conversion body of the upper surface light source device.
FIG. 5 is an explanatory diagram showing luminance of one main surface of a linear light source conversion body of a surface light source device of a comparative example.
[Explanation of symbols]
11 Backlights 13a, 13b and 13c as surface light source devices Light emitting diodes 21 as light sources Light guide bodies 21d and 21e as planar light source conversion bodies Side wall surfaces as inclined sides

Claims (3)

A light source;
An approximately square plate-shaped planar light source conversion body that is arranged with one side facing the light source and refracts light from the light source toward the principal surface and converts the light into a planar light source;
The side of the planar light source converter that is adjacent to the side facing the light source is an inclined side where light emitted from the light source through one side of the planar light source converter is incident at an angle greater than a critical angle. A surface light source device characterized by being. 2. The surface light source device according to claim 1, wherein the inclination angle of the inclined side of the planar light source converter is set according to at least the directivity of the light source and the refractive index of the planar light source converter. The angle from the optical axis of light perpendicularly incident on the planar light source conversion body from the light source to the light irradiable range by this light source is a,
The angle between the optical axis of light perpendicularly incident on the planar light source converter from this light source and the inclined side of the planar light source converter is X,
The incident angle of light irradiated at an angle a from the light source to the inclined side of the planar light source converter is i,
When the refractive index of light of the planar light source converter is n,
The planar light source device according to claim 1, wherein the planar light source device has a relationship of X ≧ i−90 + a and i = sin ⁻¹ (1 / n).

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