JPH1123850A - Surface light emission device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To actualize the liquid crystal display device which can convert the lover part of light made incident on the polarizing plate of a liquid crystal cell into one polarized light, has high luminance, gives a feeling of superior picture quality. SOLUTION: This device is equipped with a light guide body 1 which has an interface between two kinds of material having mutually different refractive indexes and separates unpolarized light into an S and a P wave, a linear light source 2 which is arranged nearby the incidence surface of the light guide body 1, and a 1/4-wavelength plate and a mirror 5 which are arranged nearby the opposite end surface of the light guide body 1 from its incidence surface to convert the majority of the light made incident on the polarizing plate of the liquid crystal display device into one polarized light uniformly, thereby suppressing the absorption of the light by the polarizing plate. Further, a reflection preventing means is arranged on the light projection surface 1b of the light guide body 1 to reduce the reflection loss on the interface between the light guide and air. Further, the uniformity of a light projection distribution in a plane is increased by devising the arrangement density of the interface between the two kinds of material of the light guide body 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a planar light emitting device using non-polarized light as a light source, such as output light from a fluorescent lamp, and more particularly, to a planar light emitting device used for a backlight of a liquid crystal display device. Related to the device.

[0002]

2. Description of the Related Art Conventionally, output light of a backlight of a liquid crystal display device is diffused and condensed by a light diffusion sheet, a prism sheet, or the like. I have.

[0003] However, the light emitted from the backlight does not directly enter the viewer of the screen, but is absorbed when passing through a polarizing plate or a liquid crystal cell. Therefore, there is a large difference between the amount of light between the backlight and the light seen through the screen.

In particular, when passing through a polarizing plate, only one of the P wave and the S wave which are orthogonal to each other is transmitted, and the other is absorbed by the polarizing plate. Of light.

In order to solve this problem, conventionally, by using a polarization splitting means and a phase converting means and preliminarily polarizing light to be incident on a polarizing plate, the light transmittance of the polarizing plate is increased and the light use efficiency is improved. Techniques for improving have been proposed.

As one example, Japanese Patent Application Laid-Open No. 7-64085 discloses that a dielectric interference film is provided on the uneven surface of a prism array.
There has been proposed a structure in which a polarization separator is formed by laminating a plurality of layers, and the polarization separator is arranged on the light emitting surface side of the light guide. According to this technique, the light emitted from the light guide is S-wave and P-wave at the interface between the prism array and the dielectric interference film, and at the interface between the dielectric interference film and the dielectric interference film laminated thereon. Separated into waves and
One of the polarizations (P wave) is transmitted through the polarization separator,
The other polarized light (S-wave) repeats total reflection and returns to the light guide side, and the returned light again strikes the light diffusion sheet or the dot printing portion of the light guide and is diffused. And reused. Therefore, in this proposed technique, although the separation of the S wave and the P wave is not perfect, one of the polarized lights is emitted in a large amount, so that the amount of light transmitted through the polarizing plate can be increased.

Further, Japanese Patent Application Laid-Open No. 6-27420 discloses that
The incident light is separated into an S wave and a P wave by a polarizing beam splitter, and the S wave is converted into a P wave by passing through a half-wave plate, and then combined with the original P wave by a condenser lens. There has been disclosed a technology in which a concave mirror is used to make the light enter a liquid crystal cell. According to this, S included in the incident light
Since the wave is converted into a P-wave and combined with the original P-wave before being incident on the liquid crystal cell, the ratio of the polarization (P-wave in this case) that is effectively used can be increased.

As described above, according to these proposed technologies, when the light emitted from the backlight passes through the light guide, only the polarized light of either the P wave or the S wave is transmitted, and the other polarized light is absorbed. In this method, the light incident on the polarizing plate is previously unified into P-waves or S-waves, or most of the light is incident on the polarizing plate as one polarized light, so that the conventionally absorbed light can be effectively used. And high brightness and low power consumption.

[0009]

By the way, among the above-mentioned proposed technologies, in the technology described in Japanese Patent Application Laid-Open No. 7-64085, light emitted from a light guide is vertically incident on a prism array. Is assumed, but in practice,
Light that has passed through the diffusion sheet disposed between the light guide and the prism array is diffused light, and many of the diffused light are not incident perpendicularly to the prism array. Bad. Further, the separation of the S-wave and the P-wave at the interface depends on the refractive index difference of the medium. That is, it is not possible to sufficiently separate the S wave and the P wave by repeating the reflection and transmission only a few times.

On the other hand, in the technique described in Japanese Patent Application Laid-Open No. 6-27420, the S wave and the P wave are separated, and the S wave is
Although it can be converted to a wave and synthesized with the original P wave, it is necessary to secure a certain distance between the concave mirror and the condenser lens, and between the concave mirror and the liquid crystal cell, respectively, as well as a beam splitter and a condenser. Since expensive optical components such as lenses are required, they are not suitable for a backlight of a liquid crystal display device. In addition, since the polarization shifts when reflected by the concave mirror, a phase plate for correcting the polarization shift is required for practical use.

Further, according to these techniques, the unpolarized light is S
When passing through a medium after being separated into a wave and a P-wave, there is a problem that the S-polarized wave and the P-wave, which are linearly separated light, become elliptically polarized light or circularly polarized light due to a phase difference in the medium.

The present invention has been made in view of such circumstances, and is capable of converting most of light incident on a polarizing plate of a liquid crystal cell into one polarized light, thereby providing high brightness and excellent image quality. It is an object of the present invention to provide a planar light emitting device capable of realizing a liquid crystal display device.

[0013]

Means for Solving the Problems In order to achieve the above object, the planar light emitting devices according to the invention of the present application are characterized in that they are configured as follows.

First, in the planar light emitting device according to the first invention (the invention described in claim 1), the thickness of the interface between the two types of materials having different refractive indexes is adjusted so that the Brewster condition is satisfied with respect to incident light. Many are arranged at an angle of 30 ° to 60 ° with respect to the direction, and one end surface is an incident surface, and one of the surfaces orthogonal to the incident surface is a light emitting surface. The incident light from the incident surface is efficiently separated into first and second polarized lights whose polarization planes are orthogonal to each other, the first polarized light is emitted from the light exit surface, and the second polarized light is Is a light guide that travels toward the opposite end face side, a light source disposed near the incident surface of the light guide, a reflector that covers the light source, and two side end faces that are parallel to the light traveling direction. The rotated mirror and the polarization plane of the second polarized light transmitted through the light guide are rotated by 90 °,再 wavelength plate disposed on the side end face opposite to the light source, a mirror disposed outside the 波長 wavelength plate, It is characterized by having anti-reflection means arranged on the exit surface.

Further, in the planar light emitting device according to the second invention (the invention according to claim 5), the thickness of the interface between the two materials having different refractive indices is such that the interface satisfies the Brewster condition with respect to incident light. Many are arranged at an angle of 30 ° to 60 ° with respect to the direction, and one end surface is an incident surface, and one of the surfaces orthogonal to the incident surface is a light emitting surface. The incident light from the incident surface is efficiently separated into first and second polarized lights whose polarization planes are orthogonal to each other, the first polarized light is emitted from the light exit surface, and the second polarized light is Is a light guide that travels toward the opposite end face side, a light source disposed near the incident surface of the light guide, a reflector that covers the light source, and two side end faces that are parallel to the light traveling direction. The rotated mirror and the polarization plane of the second polarized light transmitted through the light guide are rotated by 90 °, In order to re-enter the light into the light guide, a て い る wavelength plate disposed on the side end face opposite to the light source, and a mirror disposed outside the 波長 wavelength plate, The configuration is such that the arrangement density of the interface between the two materials of the light guide gradually increases from the entrance surface of the light guide and the opposite side end surface facing the light guide toward the center. Characterized by

In the planar light emitting device of each invention of the present application, it is possible to improve the brightness by disposing a mirror such as a reflection sheet or a reflection plate on the bottom surface corresponding to the back surface of the light emitting surface of the light guide. Preferred above.

Here, the light guide used in each invention of the present application functions as a main part of polarization separation means for separating natural polarized light (non-polarized light) incident from the light source into S wave and P wave.
The quarter-wave plate functions as polarization conversion means for converting one of linearly polarized lights orthogonal to each other to the other. Further, the anti-reflection means may be configured to reduce the loss due to reflection at the lower surface when the outgoing light component of one of the S wave or the P wave (S wave) passes through the interface between the resin constituting the light guide and the air and is output. It is arranged for the purpose of reducing.

Next, these will be described in more detail. (1) Light guide The light guide used in the present invention is an image of a sidelight type backlight, and is composed of two or more transparent media, for example, acrylic, acrylic resin, polycarbonate, polysulfone, PET, or silicon. It is made of transparent resin such as resin. Further, in terms of shape, 2 having different refractive indexes from each other.
A sheet-like or rectangular parallelepiped light guide in which a plurality of types of continuous substantially W-shaped transparent resin layers are alternately laminated to form a flat light emission surface by filling the outermost irregularities, or a cross-sectional outline on one surface A pair of resin sheets on which a large number of triangular irregularities are formed are arranged to face each other so that the irregularities of the two sheets are engaged with each other at a certain interval, and the sheet is different from the same sheet. A light guide formed by filling a transparent resin having a refractive index, or a light guide having a different refractive index.
In order to arrange a large number of interfaces made of different kinds of materials at an inclination of 30 ° to 60 ° with respect to the thickness direction so as to satisfy the Brewster condition with respect to incident light, the above two kinds of materials are arranged in the thickness direction of the light guide. And a sheet-shaped or rectangular parallelepiped light guide formed by alternately stacking a large number of them in a state inclined with respect to the light guide, and a light guide obtained by stacking a plurality of these layers in the thickness direction.

Next, the principle of polarization separation by the light guide will be described. Although the light guide of the first invention will be described below as an example, the principle of polarization separation by the light guide of the second invention is basically the same as that of the first invention.

First, when naturally polarized light is perpendicularly incident on the medium A, the incident light is incident on the interface with the medium B on a slope arranged at an angle of 30 ° to 60 ° with respect to the thickness direction so as to satisfy the Brewster condition. Reflected at or transmitted through the interface. Although the reflected light reflected at the interface is about several percent, only the S-polarized light is reflected toward the light exit surface if the angle at the interface satisfies the Brewster condition.

On the other hand, the transmitted light transmitted through the interface between the mediums A and B is naturally polarized light containing both S-waves and P-waves whose S-waves are slightly reduced. Only the S wave is separated by several percent and reflected on the lower surface side, and is reflected again on the exit surface side by the lower mirror. By repeating this, only the S-wave is emitted in the direction perpendicular to the light emitting surface, and the transmitted light gradually reduces the S-wave at the interface between the medium A and the medium B. , And remain on the side end surface of the light guide (the end surface opposite to the incident surface on which light from the fluorescent tube is incident). Thus, the S wave and the P wave can be completely separated.

The Brewster angle refers to the angle at which only S waves of incident light are reflected when light enters from one medium to another medium, and the angle is determined by the refractive index of the medium. That is, when light is incident on the medium B from the medium _A , assuming that the refractive index of the medium A is n _A and the refractive index of the medium B is n _B , the following expression (Brewster angle φ) is obtained between these refractive indexes and Brewster angle φ The relationship of 1) is established.

Tan φ = n _A / n _B (1) Here, in the present invention, the inclination angle of the interface between the two media of the light guide is 30 ° to 60 °. The reason is that since the light from the fluorescent tube, which is the light source, is light having a spread, the angle at which the Brewster angle becomes one cannot be determined. However, the angle at which the most light from the fluorescent tube enters the light guide is the direction perpendicular to the plane of incidence, and the angle of inclination of the interface between the media A and B is 45 to emit light in the vertical direction of the display. ° is desirable.

Further, the Brewster angle is 4
The refractive index difference between the two types of media, which is 5 °, is 0, but in this case, no interface exists. Therefore, there is a method of reducing the refractive index difference as much as possible. However, since the light from the fluorescent tube is diffused light with a certain degree of spread, the incident angle is 30 ° or more.
A refractive index difference Δn <0.6 that can realize polarization separation of 80% or more in the range of 60 ° is sufficient, and it is desirable to do so. (2) Quarter-Wave Plate In the present invention, a quarter-wave plate is used as polarization conversion means in order to align the light finally incident on the incident-side polarizing plate of the liquid crystal display device to either an S-wave or a P-wave. Used.

In general, a half-wave plate may be used to convert one of the S wave and the P wave into the other. In the present invention, the S wave is emitted from the light emitting surface of the light guide, and Since it is necessary to make the light incident on the polarizing plate of the liquid crystal display device provided on the light emitting surface side, a quarter-wave plate is attached to the side end surface of the light guide opposite to the incident surface, and a mirror is arranged outside the end surface. Structure.

In this way, the P-waves sequentially transmitted through the interface between the mediums A and B, which are the polarization separation layers, are reflected by the mirror after passing through the quarter-wave plate, and the reflected light is again reflected by the quarter-wave plate. , And eventually passes through a half-wave plate.

The light converted into the S-wave by the quarter-wave plate is re-entered into the light guide from the side end face of the light guide on the quarter-wave plate side. Since only the S wave is present, the light is reflected at the interface between the two media A and B by several percent and is emitted directly from the light emission surface, or is reflected by the mirror on the back surface of the light guide opposite to the light emission surface. Then, the light is emitted from the light emitting surface.

Here, in the present invention, if a prism sheet (reflection sheet) having an apex angle of about 90 ° is used as a mirror disposed on the back surface of the light guide, absorption loss is smaller than that of a mirror made of metal. Since only a small amount is required, more light can be emitted from the light emission surface. If the vertex angle of the prism sheet is slightly larger than 90 °, the emission angle distribution of the emitted light can be widened, and the viewing angle as a display element can be widened. (3) Anti-reflection means The anti-reflection means is used when the output light component finally adjusted to one polarized light (S wave) passes through the interface between the resin constituting the light guide and air and exits. It is arranged for the purpose of reducing loss due to reflection at the interface. For example, if a layer in which the refractive index changes continuously from the refractive index of the resin constituting the light guide to the refractive index of the air layer can be formed on the light exit surface of the light guide, light can be recognized as an interface. Since there is no layer, it is possible in principle to extract all the light directed in the emission direction.

In practice, a layer made of a fluorine-based acrylic resin having a refractive index of 1.3 to 1.4 is the uppermost layer in the light emitting direction,
Forming a layer having a refractive index gradually changing in the thickness direction from the refractive index of the resin constituting the light guide toward the light guide as the antireflection layer is considered to be one of effective means in practice.

Further, it is also possible to use a pseudo-gradient refractive index which appears when using a geometrical shape with a pitch equal to or less than the wavelength of light as shown in FIG. At this time, in the case of the same wavelength as the wavelength used, that is, in the visible light range, about 0.5
The effect appears from μm. More effectively, it is desirable that the wavelength be 1/4 or less of the shortest wavelength used. By doing so, it is possible to effectively prevent reflection without causing scattering and diffraction.
Therefore, the geometrical shape (triangle unevenness) pitch is 0.5 μm
Or less, more preferably 0.1 μm or less. In addition, due to problems in processing technology and cost, 0.05μ
A pitch less than m is not practical. From the above, the pitch of the geometric shape is in the range of 0.05 μm to 0.5 μm,
More preferably, the range is 0.05 μm to 0.1 μm.

For reference, the principle of obtaining a gradient refractive index with the geometrical shape shown in FIG. 1 will be briefly described. First,
When light travels on a one-dimensional periodic structure smaller than the wavelength, the light does not cause diffraction or scattering for that period,
It is generally known to behave as though it passes through a medium having a homogeneous refractive index. For example, when the triangular shape forms a periodic structure continuously as in the present invention, for light oscillating in a direction perpendicular / parallel to the ridge line, an approximate refractive index of each light is estimated. be able to.

Here, as shown in the model of FIG.
Assuming that the thickness of the medium constituting the periodic structure and the thickness of the space corresponding thereto change stepwise, the refractive index felt by the light at that time can be calculated for each step, and the respective refractive indices are shown in FIG. As shown in FIG. 1A, it is as if an optical medium in which thin layers having different refractive indexes are laminated.

Since the actual system has a periodic structure in which triangular shapes are continuous as shown in FIG. 1 (b), light is like a medium whose refractive index changes gradually and continuously. Is eliminated, and as a result, 100% of the incident light can be transmitted without reflection loss. (4) Others In order to use the planar light emitting device as a backlight of a liquid crystal display device, it is necessary to make the distribution of light emitted from the light emitting surface of the light guide as uniform as possible. Preferably, the luminance difference between the end or the peripheral part and the central part of the light emitting surface is 10%.
Within.

In the case of the first invention, the reflectance at the interface between the two media A and B is constant, and the S-wave decreases as the distance from the incident surface side of the light guide increases. Decrease. On the incident surface of the light guide and on the opposite side, when the light emitted from the light guide is reflected by the mirror and returns to the light guide again, it passes through the quarter-wave plate in going and returning. Since the waves are converted into S waves, the S waves increase again and become brighter, but become darker as approaching the light source side incident surface. Therefore, the light emitted from the light exit surface of the light guide is light traveling toward the opposite side end surface from the light incident surface of the light guide (going light) and reflected by the mirror to the light incident surface side. The return light (return light) is synthesized, and the light emission characteristic has a distribution as shown in the graphs of FIGS. 2 and 3 where the center is darker than the end of the light exit surface.

In order to solve this problem, in the second invention, as described above, the arrangement density of the interface between the medium A and the medium B provided in the light guide is adjusted by changing the arrangement density of the light guide into the light incident surface and the opposite side facing the light guide. A uniform light emission distribution is obtained by adopting a configuration in which the height is increased from the side end surfaces toward the center.

As a specific means, as shown in FIG. 12, the interface between the two types of media 110a and 110b is not continuously and uniformly arranged, but a region having no inclined surface is provided in the middle. , The number of interfaces between the regions,
A configuration in which the number of interfaces increases stepwise from both side end surfaces 101a and 101c of the light guide 101 toward the center, or an interface group having a predetermined number of interfaces (four interfaces) as one unit as illustrated in FIG. The light guide 20 is arranged so as to sandwich a region having no inclined surface, and the pitch between the interface groups is adjusted.
1 is gradually narrowed from both side end surfaces 201a and 201c toward the center. <Operation> Light from a light source is incident on the medium A of the light guide, and impinges on the interface with the medium B having a Brewster angle approximately. As a result, about several percent of the S-polarized light out of the light that hits the interface is reflected toward the light exit surface side of the light guide, and is emitted toward the front of the light exit surface, while the remaining S polarized light is emitted. P-polarized light passes through the interface. Then, at the next interface between the medium A and the medium B, part of the S-polarized light is reflected again by the mirror on the back surface of the light guide, and the reflected light is emitted from the light emission surface in the front direction.
By repeating this, the S-polarized light is emitted from the light emitting surface toward the front direction, and the transmitted light is only the P-polarized light.
This P-polarized light passes through a quarter-wave plate, is reflected by a mirror, and then passes through a quarter-wave plate again to be converted into S-polarized light to pass through both media A and B in the light guide. It penetrates.
At this time, a part of the S-polarized light is emitted in the front direction of the light emission surface, and finally, only the polarized light (S wave) of the specific component whose polarization axis is aligned in the front direction of the light emission surface. The Rukoto. In this way, since only light that can pass through the polarizing plate can be supplied to the polarizing plate provided on the incident side of the liquid crystal display device, the amount of light conventionally absorbed by the polarizing plate can be reduced. Therefore, the light use efficiency is improved accordingly.

Further, by arranging the antireflection means having the above-mentioned function on the light exit surface side of the light guide, finally, the light emission component aligned to one polarized light (S wave) is guided. Loss due to reflection at the interface when light is emitted through the interface between the resin constituting the light body and air can be reduced.

Further, the arrangement density of the interface between the medium A and the medium B of the light guide is configured so as to increase from the entrance surface of the light guide and the side end surface opposite thereto to the center. Thereby, the light emission distribution on the light emission surface of the light guide can be made uniform. In this case, by further arranging the antireflection means having the above-described function on the light emitting surface side of the light guide, the light emission component finally aligned with one polarized light (S-wave) can be obtained. When light is emitted through the interface between the resin constituting the light guide and air, loss due to reflection at the interface can be reduced.

As described above, the planar light emitting device of the present invention can make most of the light incident on the polarizing plate as S-polarized light without using expensive optical components such as a beam splitter and a condenser lens. Becomes

[0040]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 4 is a schematic sectional view showing the configuration of the first embodiment of the present invention.

The light guide 1 used in the planar light emitting device shown in FIG. 4 has two types of substantially W-shaped transparent resin layers 10a and 10b (medium A and medium B) alternately having different refractive indexes. A rectangular parallelepiped laminate in which a plurality of layers are laminated and the outermost irregularities are smoothed by filling a transparent resin (medium A), and one side end face 1
a is a light incident surface, and one of four surfaces orthogonal to the light incident surface 1a is a light emitting surface 1b.

In the vicinity of the light incident surface 1a of the light guide 1, a fluorescent tube 2 is arranged as a linear light source. The fluorescent tube 2 is covered by a lamp reflector (silver sheet) 3. A quarter-wave plate 4 is disposed near the side end surface 1c of the light guide 1 opposite to the incident surface 1a, and a reflection sheet (silver sheet) 5 is disposed outside the quarter-wave plate 4. Have been. A prism sheet 6 having a vertex angle of about 90 ° is disposed as a reflection sheet on a bottom surface 1d corresponding to the back surface of the light exit surface 1b of the light guide 1, and further, other prisms 6 parallel to the light traveling direction. A reflection sheet (not shown) is disposed on the side end surface.

An antireflection sheet (for example, a fluorine-based acrylic resin film) 7 whose refractive index continuously changes from the light guide 1 toward the air layer is disposed on the light emitting surface 1b of the light guide 1. ing. Further, the incident surface 1a of the light guide 1 and the fluorescent tube 2
In between, two lens sheets 8 mainly made of polycarbonate, each having irregularities having a triangular cross section with a vertex angle of 90 °, are shaped so that each irregular surface faces the light guide 1 side, and The ridge lines are arranged orthogonal to each other (see FIG. 5).

FIG. 6 is a schematic sectional view showing the structure of another embodiment of the first invention. In the planar light emitting device shown in FIG. 6, a continuous triangular shape having a pitch of 0.5 μm or less and a vertex angle and a base angle of 45 ° is used as an antireflection sheet 17 provided on the light emitting surface 1 b of the light guide 1. The difference from the embodiment of FIG. 4 is that a transparent resin sheet having irregularities is used.

Here, as the light guide used in the planar light emitting device of the first invention, various structures other than those illustrated in FIGS. 4 and 6 can be considered. Such examples are shown in FIGS.

In the light guide 21 shown in FIG. 7, the number of interfaces and the number of laminations of two types of transparent resin layers 20a and 20b having different refractive indexes are determined.
5 shows an example in which the number of light guides is larger than that of the light guide 11 shown in FIG.

In the light guide 31 shown in FIG. 8, two types of strip-shaped resin plate materials 30a and 30b (medium A and medium B) having different refractive indices are inclined at 45 ° with respect to the thickness direction. The layers are alternately laminated while holding the shape, and processed into a rectangular parallelepiped shape as a whole.

The light guide 41 shown in FIG. 9 has a pair of transparent resin sheets 40 each having a large number of irregularities having a substantially triangular cross section on one surface.
a are arranged so as to face each other so that the irregularities of the two sheets are engaged with each other at a certain interval, and the sheet is filled with a transparent resin 40b having a refractive index different from that of the same sheet. It is.

The light guide 51 shown in FIG. 10 has two types of substantially W-shaped transparent resin layers 50a and 50b having different refractive indexes.
(Medium A and Medium B) have a structure in which a plurality of layers are alternately laminated, and the feature is that the top of the W-shape is formed in a round shape instead of a square shape.

In the light guide 61 shown in FIG. 11, the interface between the two transparent resin layers 60a and 60b (medium A and medium B) is
The feature is that it is formed in a substantially saw blade shape instead of a letter shape.
Next, an embodiment of the second invention will be described below with reference to the drawings.

FIG. 12 is a schematic sectional view showing the structure of the second embodiment of the present invention. The light guide 101 used in the planar light emitting device shown in FIG. 12 has two types of substantially W-shaped transparent resin layers 110a having different refractive indices, as in FIG.
And 110b (medium A and medium B) are alternately laminated in multiple layers,
It is a rectangular parallelepiped laminate in which the outermost unevenness is smoothed by filling a transparent resin (medium A), but the interface between the two types of media is not arranged continuously and uniformly, but an inclined surface is formed in the middle. It is characterized in that a non-existent region is provided and the number of interfaces between the regions is increased stepwise from both side end surfaces 101a and 101c of the light guide 101 toward the center.

Also in this example, similarly to the embodiment of FIG. 4, the fluorescent tube 2 and the lamp reflector 3 are arranged near the light incident surface 101a of the light guide 101, and the light guide A side end surface 1 of the side 101 opposite to the incident surface 101a
A quarter-wave plate 4 and a reflection sheet 5 are arranged near 01c. Further, a prism sheet 6 is disposed on a bottom surface 101d corresponding to the back surface of the light exit surface 101b of the light guide 1, and a reflection sheet (not shown) is disposed on the other two end surfaces. Further, two lens sheets 8 are arranged between the incident surface 101 a of the light guide 101 and the fluorescent tube 2.

FIG. 13 is a schematic sectional view showing another embodiment of the second invention. The surface light emitting device shown in FIG. 13 differs from that of FIG. 12 in the structure of the light guide.

That is, in the light guide 201 of this example, 4
An interface group having one interface as one unit is arranged across a region having no inclined surface, and the pitch between the interface groups is stepwisely increased from both side end surfaces 201a and 201c of the light guide 201 toward the center. The feature is that it is narrow.

The light guide used in the planar light emitting device of the second invention has the same structure as the light guide shown in FIGS. 7 to 11 in addition to the above-described structure. A light guide having a form as shown in FIG. 12 or FIG. 13 may be applied.

[0056]

EXAMPLES Examples of the first invention will be described below together with comparative examples. In this embodiment, ten types of light guides shown below are used, and as shown in FIG.
A fluorescent tube (tube diameter: 2.6 mm) 2 is arranged outside one end face, and this is covered with a lamp reflector 3. A に は wavelength plate 4 is provided on a side end surface opposite to the side end surface on which the fluorescent tube 2 is disposed.
And a silver reflection sheet 5 (not shown) on the two end faces parallel to the light traveling direction of the light, and a silver reflection sheet (not shown) between the fluorescent tube 2 and the light guide. Two lens sheets 8 are arranged. [Example 1-1a] First, a rectangular polycarbonate (PC) plate of 5.0 mm × 16 cm (n = 1.5865)
In, 6 sheets of 1.0 mm thickness, 19 sheets of 0.5 mm, 26 sheets of 0.2 mm, 45 sheets of 0.1 mm, 26 sheets of 0.2 mm, 19 sheets of 0.5 mm and 6 sheets of 1.0 mm were prepared (total 1).
47), these are arranged in the listed order, and a polymethyl methacrylate (PMMA) film is interposed between the PC boards as a spacer. However, this PMM
It is assumed that the thickness of the A film generally satisfies the following expression (2) by a casting method.

[0057]

(Equation 1)

Here, d _{PC and} d _PMMA are PC
Plate, thickness of PMMA film, N: (1 ≦ N ≦ 146)
Represents the N-th layer of the laminate. In this way, the plate material and the spacer, which were alternately arranged, were fixed to a jig which can be held while being inclined at an angle of 45 °, and both ends on the short side were fixed by heat fusion to obtain a 45 ° interface. After that, the spacer film was removed, and a silicone thermosetting resin (Shin-Etsu Chemical Co., Ltd.,
n = 1.4125). The PC board is put in a vacuum oven together with the silicon resin layer, and the pressure is reduced to fill the gap between the PC boards with the silicon resin. This work also serves as degassing of the resin.

Thereafter, the sample was placed in an oven at 100 ° C.
Heat for 5 hours to cure the resin. This is 16cm × 10
A rectangular parallelepiped of 3 cm × 3 mm is cut out and finished to a plate thickness of 2.5 mm while being mirror-polished on six sides.
8) is applied and light irradiation is performed, and when the reaction rate reaches about 50%, the light irradiation is temporarily stopped, and then a fluorine-based acrylic photocurable resin (refractive index at the time of curing 1.37) is applied. After being left for a while, an anti-reflection film whose refractive index continuously changes from 1.48 to 1.37 from the light guide to the air layer by photo-curing was formed.

A planar light emitting device using the light guide (with an antireflection film) manufactured as described above was designated as Example 1-1a. [Example 1-1b] A transparent acrylic sheet was prepared by arranging a large number of triangular prisms having a cross section of a right-angled isosceles triangle having three sides of 1 mm, 1 mm, √2 mm and a vertex angle of 90 ° on one side. Another sheet-like material formed of resin (refractive index: 1.49) and having a large number of triangular prisms having the same shape as the triangular prisms arranged on one side is placed on a transparent photo-curable resin (refractive index of the light guide body is changed). From the incident surface (side end surface on the fluorescent tube side) to the opposite side end surface (side end surface on the 波長 wavelength plate side), 1.50 (side end) → 1.53 (center) → 1.50 ( Side end)), and the two triangular prisms of the two resin sheet-like materials are projected upward (△) and the other is projected (▽). And placed alternately in a state of engagement, width 16.5 cm, length 21.5 cm,
After producing a single plate-like object having a thickness of 1 / √2 mm, the slopes of both side ends (both ends extending along the length direction of the triangular prism) of the plate-like object are formed on the surface of the plate-like object. By processing the slope part so that it has a vertical end surface shape,
One light guide was produced.

Further, two light guide plates are laminated in the thickness direction, and finally, an acrylic photo-curing resin (refractive index at the time of curing 1.48) is applied to the surface of the light-emitting surface to irradiate light.
When the reaction rate becomes about 50%, the light irradiation is temporarily stopped,
Next, a fluorine-based acrylic photocurable resin (refractive index of 1.37 at the time of curing) is applied, and after being left for a while, photocured so that the refractive index from the light guide toward the air layer is 1.48.
From 1.37 to 1.37.

A planar light emitting device using the light guide (with an antireflection film) produced as described above was designated as Example 1-1b. [Example 1-1c] A pair of sheet-like objects each having a large number of triangular prisms each having a cross-sectional shape of a right-angled isosceles triangle having three sides of 1 mm, 1 mm, √2 mm and a vertex angle of 90 ° are arranged on one side, respectively. Another transparent resin which is formed of a transparent acrylic resin (refractive index: 1.49) and fills the gap between the sheet-like materials is made of a photo-curable resin (refractive index of the light incident surface of the light guide (fluorescent tube). 1.50 (side end surface) → 1.5 from the side end surface on the side) to the opposite side end surface (side end surface on the の wavelength plate side).
3 (central part) → stepwise changed to 1.50 (side end part)), width 16.5 cm, length 2
One plate having a size of 1.5 cm and a thickness of 1 / √2 mm was prepared. Thereafter, the slope portions at both ends of the plate-like object are processed into a vertical end surface shape to produce one light guide, and two of the light guides are laminated in the thickness direction. An acrylic photocurable resin (refractive index at the time of curing 1.48) is applied to the surface of the surface and irradiated with light, and the reaction rate is about 50%.
The light irradiation is temporarily stopped at the time when the light-sensitive material is applied, and then a fluorine-based acrylic light-curing resin (refractive index at the time of curing is 1.37) is applied. An antireflection film whose refractive index continuously changes from 1.48 to 1.37 was formed.

A planar light emitting device using the light guide (with an antireflection film) manufactured as described above was designated as Example 1-1c. [Example 1-1d] A prism sheet mainly composed of an ultraviolet curable resin having a refractive index of 1.53 (vertical angle 90 °, pitch 50)
0 μm and a sheet thickness of 550 μm) are arranged on a glass mold having the same uneven surface as that of the sheet via a curable resin composition mainly composed of an ultraviolet curable resin having the following refractive index nA. Then, while maintaining a uniform distance of 10 μm between the mold and the prism sheet, light is applied from the glass mold side to cure the glass sheet, thereby forming a substantially continuous W having a refractive index nA on the prism sheet having the following refractive index nB. A letter-shaped second prism layer was formed.

Similarly, a third prism layer having a refractive index of n B is formed so as to have a thickness of 500 μm, and a refractive index of n is formed thereon.
A fourth prism layer is formed. These were alternately laminated seven times, and finally the uppermost uneven surface was filled with a resin having a refractive index of nB and smoothed to form a light-emitting surface, thereby obtaining a nine-stage laminated body as a whole.

After that, the end is cuboid (100 mm × 15
(0 mm × approximately 1 mm) and polished so that the end face becomes an optical mirror surface. Finally, an acrylic photocurable resin (refractive index at the time of curing 1.48) on the light exit surface
Is applied and light irradiation is performed. When the reaction rate reaches about 50%, the light irradiation is temporarily stopped, and then a fluorine-based acrylic photocurable resin (refractive index at the time of curing 1.37) is applied and left for a while. After that, an antireflection film whose refractive index continuously changes from 1.48 to 1.37 from the light guide to the air layer by photocuring was formed. Refractive index nA: 1.49 Refractive index nB: [From the incident surface of the light guide (side end surface on the fluorescent tube side) to the opposite side end surface (side end surface on the quarter wavelength plate side), 1.50 (side) (End) → 1.53 (center) → 1.5
The value was changed stepwise such as 0 (side end).

A planar light emitting device using the light guide (with an antireflection film) manufactured as described above was designated as Example 1-1d. [Example 1-1e] The prism pitch was set to 200 μm, and the thickness of the refractive index nA layer and the refractive index nB layer alternately laminated was 5 μm for the refractive index nA layer and 100 μm for the refractive index nB layer. The thickness of the light guide to be manufactured is about 1.
The layers were alternately laminated 17 times so as to have a thickness of 0 mm, and finally the uppermost concave and convex surface was filled with a resin having a refractive index of nB and smoothed to form a light emitting surface. The lowermost prism sheet used had a refractive index nB, a vertex angle of 90 °, a pitch of 200 μm, and a sheet thickness of 120 μm. Otherwise, a light guide was produced in the same manner as in Example 1-1d.

A planar light emitting device using the light guide (with an antireflection film) manufactured as described above was designated as Example 1-1e. [Example 1-2a] A transparent resin having a continuous triangular unevenness having a pitch of 0.1 μm and a vertical angle and a bottom angle of 45 ° with respect to the light emitting surface of the light guide prepared in Example 1-1a. An antireflection layer was obtained in the same manner as in Example 1-1a, except that a sheet (refractive index: 1.47) joined using an acrylic photocurable resin (refractive index at the time of curing: 1.48) was used as an antireflection layer. The obtained planar light emitting device was designated as Example 2-1a. [Example 1-2b] A transparent resin having a continuous triangular unevenness with a pitch of 0.1 μm and a vertical angle and a bottom angle of 45 ° with respect to the light emitting surface of the light guide prepared in Example 1-1b. An antireflection layer was obtained in the same manner as in Example 1-1b, except that a sheet (refractive index: 1.47) bonded using an acrylic photocurable resin (refractive index at the time of curing: 1.48) was used as an antireflection layer. The obtained planar light emitting device was designated as Example 2-1b. [Example 1-2c] A transparent resin having a continuous triangular unevenness having a pitch of 0.1 μm and a vertical angle and a bottom angle of 45 ° with respect to the light emitting surface of the light guide produced in Example 1-1c. An antireflection layer was obtained in the same manner as in Example 1-1c, except that a sheet (refractive index: 1.47) bonded using an acrylic photocurable resin (refractive index at the time of curing: 1.48) was used as an antireflection layer. The obtained planar light emitting device was designated as Example 2-1c. [Example 1-2d] A transparent resin having a continuous triangular unevenness having a pitch of 0.1 μm and a vertical angle and a bottom angle of 45 ° with respect to the light emitting surface of the light guide prepared in Example 1-1d. A sheet (refractive index: 1.47) was obtained in the same manner as in Example 1-1d, except that a sheet (refractive index of 1.48) cured by using an acrylic photocurable resin was used as an antireflection layer. The obtained planar light-emitting device was designated as Example 2-1d. [Example 1-2e] A transparent resin having a continuous triangular concavo-convex pattern having a pitch of 0.1 μm and a vertex angle and a bottom angle of 45 ° with respect to the light emitting surface of the light guide produced in Example 1-1e. An antireflection layer was obtained in the same manner as in Example 1-1e, except that a sheet (refractive index: 1.47) bonded using an acrylic photocurable resin (refractive index at the time of curing: 1.48) was used as an antireflection layer. The obtained planar light emitting device was designated as Example 2-1e. [Comparative Example 1-1] Dot print pattern, diffuse reflection sheet, fluorescent tube and reflector, and acrylic light guide (100
mm × 150 mm × thickness 1 mm), a light diffusion sheet (bead coating type) and two prism sheets each having an apex angle of approximately 90 ° were attached to a conventional backlight (plane light emitting device) having respective ridge lines. They were arranged in an orthogonal state, and this was designated as Comparative Example 1-1. [Comparative Example 1-2] The acrylic light guide described in Comparative Example 1-1 having a thickness of 2 mm was used as Comparative Example 1-2. [Comparative Example 1-3] A polarizing element described in JP-A-7-64085 was used, and its size was 100 mm x 100 mm.
Comparative Example 1 using a planar light-emitting device using a size of × 1 mm
-3. <Evaluation> The above Examples 1-1a to 1-1e and 1-2a
The following items were evaluated for the surface light-emitting devices for liquid crystal display devices obtained in Comparative Examples 1-1 and 1-3 and Comparative Examples 1-1 and 1-3.

Luminance This luminance was evaluated by placing a polarizing plate on each planar light emitting device for a liquid crystal display device with the optical axes aligned, measuring the luminance of light transmitted through the polarizing plate at the center of the screen, and evaluating the luminance. went.

Transmitted Light In the same manner, a polarizing plate is placed on each planar light emitting device for a liquid crystal display device with the optical axis aligned, and the amount of light transmitted through the polarizing plate is measured. It was evaluated whether only light was transmitted.

S / P Ratio The ratio of the S-wave and the P-wave in the front direction of each planar light emitting device for a liquid crystal display device, that is, S / (S + P) * 100 (%) was obtained, and how much S-wave could be extracted. Was evaluated.

In-plane uniformity 15 points in the plane of each planar light emitting device for a liquid crystal display device (FIG. 14)
) Was measured, and (maximum luminance / minimum luminance) × 100 (%) was obtained.

Table 1 shows the results of these evaluations.

[0073]

[Table 1]

From the above results, it is found that the embodiment 1-1a of the present invention
-1-1e and 1-2a-1-2e show that the light can be more effectively used than in the comparative example (prior art). This is because the diffused light emitted from the fluorescent tube is collected by the lens sheet, more light is guided toward the front of the display, and a bright and good screen is obtained. Loss due to reflection at the interface when the light output component aligned to the S wave passes through the interface between the resin constituting the light guide and the air and is emitted is reduced, and the light reflected at the slope of the light guide ( This is because the absorption of light by the polarizing plate arranged to transmit most of the S-wave component) is suppressed.

In Comparative Example 1-1, the light was brightest before the light passed through the polarizing plate, but more than half of the light was absorbed because the polarization directions were not uniform. Brightness is low. In Comparative Example 1-2, since the angle component of the light hitting the inclined surface for polarization separation is very diversified, the loss of light that does not match the Brewster angle is large, and the effect as expected cannot be obtained.

Next, an embodiment of the second invention will be described together with a comparative example. First, the light emission characteristics of the planar light emitting device are such that the central portion is darker than the end portion of the light emitting surface because the number of interfaces between the two media of the light guide is uniform in the light guide. The brightness of the light reflected from each interface is as shown in the graph of FIG. 3, and the light emission characteristics are as shown in FIGS. 2 and 3.

Therefore, in this embodiment, the number of interfaces between the two media A and B of the light guide is changed according to the following rules. Assuming 1/11 of the total number of interfaces as one unit, the amount of transmitted light T _{S (N)} at the _Nth interface is determined from the reflectance R _S of S-polarized light determined from the refractive indices of the two media A and B. The difference from the transmitted light amount T _{S (N−1)} at the immediately preceding interface is defined as the emitted light amount I _{S ( N)} at the N-th interface.

I _{S (N)} = T _{S (N−1)} −T _{S (N−1)} (1−R _{S (N)} ) ² (1) One unit at the center of the light guide irradiating intensity I the amount of light emitted from both sides of the two units of the average value of _S and the light guide incident surface and the side end face (the side end face of the fluorescent tube side) (side end surface of the 1/4 wavelength) I _S
And the difference between them is calculated as [(11-1) /
2] Divide equally, and increase the arrangement density of the interface from the incident surface of the light guide and the side end surface on the reflection side facing the light guide sequentially toward the center so as to correspond to the amount of emitted light corresponding thereto.

It is to be noted that the number of interface divisions is preferably 11 units or more. If the number of interface divisions is 10 units or less, there arises a problem that in-plane luminance cannot be uniform. In this embodiment, the following four types of light guides are used, and a fluorescent tube (tube diameter of 2.6 mm) 2 is arranged outside one end face of the light guides as illustrated in FIG. And
This is covered with a lamp collector 3. A quarter-wave plate 4 is arranged on the side end surface opposite to the side end surface on which the fluorescent tube 2 is arranged, and a silver reflecting sheet 5 is arranged outside the quarter-wave plate 4, and silver end surfaces are arranged on the two end surfaces parallel to the light traveling direction. Place a reflective sheet (not shown)
Further, two lens sheets 8 are provided between the fluorescent tube 2 and the light guide.
Place. [Example 2-1a] A sheet shape in which a large number of triangular prisms having a cross section of a right-angled isosceles triangle having three sides of 1 mm, 1 mm, √2 mm and a vertex angle of 90 ° are arranged side by side in accordance with the rule of the above formula (3). Object, transparent acrylic resin (refractive index 1.49)
Formed. In addition, another sheet-like material in which a large number of triangular prisms having the same shape as the triangular prism are arranged on one side in accordance with the rule of the above formula (3) is used as a transparent light-curing resin (refractive index 1.
53), and these two resin sheet-like materials are arranged in such a manner that the triangular prisms are alternately engaged with each other such that one is convex upward (柱) and the other is convex downward (▽). 16.5 cm wide, 21.5 cm long, 1 / √ thick
After making one plate-like object, the slope portions of both side ends (triangular prisms) extending along the length direction of this plate-like object) are perpendicular to the surface of the plate-like object. One light guide plate was produced by processing the slope portion so as to have an appropriate end surface shape. Further, two light guides were laminated in the thickness direction. The planar light emitting device using the light guide produced as described above was designated as Example 2-1a. [Example 2-1b] A large number of triangular prisms each having a cross section of a right-angled isosceles triangle having three sides of 1 mm, 1 mm, and √2 mm and a vertex angle of 90 ° are arranged side by side in accordance with the rule of the above formula (3). Is formed of a transparent acrylic resin (refractive index: 1.49), and another transparent resin to be filled in the gap between the sheet-shaped materials is formed of a photocurable resin (refractive index: 1.53). Formed, width 16.5 cm, length 21.
After preparing one sheet of 5 cm and a thickness of 1 / √2 mm, the slopes at both ends of the sheet are processed into a vertical end face to form one light guide, and further, Two light guides were stacked in the thickness direction.

A planar light emitting device using the light guide produced as described above was designated as Example 2-1b. [Example 2-1c] A prism sheet (vertical angle 90 °, pitch 500 μm, sheet thickness 550 μm) mainly composed of an ultraviolet curable resin having a refractive index of 1.53 and having irregularities according to the rule of the above formula (3) was used. Placed on a glass mold having the same uneven surface as that of the sheet via a curable resin composition mainly composed of an ultraviolet curable resin having a refractive index of 1.49,
By irradiating and curing light from the glass mold side while maintaining the distance between the mold and the prism sheet uniformly at 10 μm,
A continuous substantially W-shaped second prism layer having a refractive index of 1.49 was formed on a prism sheet having a refractive index of 1.53.

Similarly, a third prism layer having a refractive index of 1.53 is formed so as to have a thickness of 500 μm, and a prism layer having a refractive index of 1.49 is formed thereon. These are alternately laminated seven times, and finally the uppermost uneven surface is filled with a resin having a refractive index of 1.53 and smoothed to form a light emitting surface. Insert the end of the body into a rectangular parallelepiped (100 mm
(× 150 mm × about 1 mm), and polished so that the end surface thereof was an optical mirror surface.

A planar light emitting device using the light guide produced as described above was designated as Example 2-1c. [Example 2-1d] The thickness of a layer having a refractive index of 1.49 and a layer having a refractive index of 1.53, which have irregularities in accordance with the rule of the above formula (3), are alternately stacked at a prism pitch of 200 μm, and are alternately stacked. Each of the layers having a refractive index of 1.49 is 5 μm and the refractive index is 1.5.
3 is 100 μm, and the light guide to be produced is alternately laminated 17 times so as to have a thickness of about 1.0 mm. Finally, the uppermost uneven surface is filled with a resin having a refractive index of 1.53 and smoothed. The light emitting surface was formed to form a laminate having 19 steps as a whole.
The lowermost prism sheet used had a refractive index of 1.53, a vertex angle of 90 °, a pitch of 200 μm, and a sheet thickness of 120 μm. Otherwise, the light guide was produced in the same manner as in Example 2-1c.

A planar light emitting device using the light guide produced as described above was designated as Example 2-1d. [Comparative Example 2-1] Dot print pattern, diffuse reflection sheet, fluorescent tube and reflector, and acrylic light guide (100
mm × 150 mm × thickness 1 mm), a light diffusion sheet (bead coating type) and two prism sheets each having an apex angle of approximately 90 ° were attached to a conventional backlight (plane light emitting device) having respective ridge lines. They were arranged in an orthogonal state, and this was designated as Comparative Example 2-1. [Comparative Example 2-2] Comparative Example 2-2 was made by changing the thickness of the acrylic light guide described in Comparative Example 2-1 to 2 mm. [Comparative Example 1-3] A polarizing element described in JP-A-7-64085 was used, and its size was 100 mm x 100 mm.
Comparative Example 2 using a planar light emitting device having a size of × 1 mm
-3. <Evaluation> With respect to the planar light emitting devices for liquid crystal display devices obtained in the above Examples 2-1a to 2-1d and Comparative Examples 2-1 to 2-3, the same items 1 and 2 were evaluated.

Table 2 shows the evaluation results.

[0085]

[Table 2]

From the above results, it was found that the embodiment 2-1a of the present invention
According to 2-1d, it can be seen that the light can be more effectively used than the comparative example (prior art). This is because most of the light reflected on the inclined surface of the light guide is only the S wave component,
This is because the absorption of light by the polarizing plate arranged to transmit the wave most is suppressed. In addition, it was confirmed that the in-plane uniformity of the light exit surface of the light guide was improved.

In Comparative Example 2-1, the light was brightest before transmission through the polarizing plate, but more than half of the light was absorbed because the polarization directions were not uniform, and as a result, after passing through the polarizing plate. Brightness is low. In Comparative Example 2-2, since the angle component of the light hitting the inclined surface for polarization separation is very diversified, the loss of light that does not match the Brewster angle is large, and the expected effect cannot be obtained.

[0088]

As described above, according to the planar light emitting devices of the first and second aspects of the present invention, light with uniform polarization can be emitted from the light guide. The ratio of the light absorbed by the polarizing plate on the side can be reduced.
Accordingly, light can be effectively used without using expensive optical components such as a beam splitter and a condenser lens, and light emission with high luminance and excellent image quality can be realized.

Further, in the planar light emitting device of the first invention, since the antireflection means is provided on the light exit surface of the light guide, the light output component aligned to one polarized light constitutes the light guide. The reflection loss at the interface when light is emitted through the interface between the resin and air can be reduced, and the luminance can be further increased.

In the planar light emitting device according to the second aspect of the present invention, the arrangement density of the interface between the two types of media provided in the light guide for polarization separation is gradually increased toward the center of the light guide. Therefore, the uniformity of the light emission distribution in the plane can be improved.

[Brief description of the drawings]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory view of the principle that an inclined refractive index appears when one surface of an antireflection sheet has a shape in which irregularities having a triangular cross section are continuous.

FIG. 2 is a graph showing an example of light emission characteristics of a light guide used in the planar light emitting device of the first invention.

FIG. 3 is a graph showing another example of the light output characteristics of the light guide.

FIG. 4 is a schematic sectional view showing the configuration of the first embodiment of the present invention.

FIG. 5 is a view taken in the direction of arrow X in FIG. 4;

FIG. 6 is a schematic sectional view showing a configuration of another embodiment of the first invention.

FIG. 7 is a schematic view showing a modification of the light guide used in the planar light emitting device of the first invention.

FIG. 8 is a schematic view showing a modification of the light guide.

FIG. 9 is a schematic view showing a modification of the light guide.

FIG. 10 is a schematic view showing a modified example of the light guide.

FIG. 11 is a schematic view showing a modification of the light guide.

FIG. 12 is a schematic cross-sectional view showing a configuration of an embodiment of the second invention.

FIG. 13 is a schematic sectional view showing the configuration of another embodiment of the second invention.

FIG. 14 is a diagram showing measurement points of in-plane front luminance.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Light guide 1a Incident surface 1b Light emitting surface 2 Fluorescent tube (light source) 3 Lamp reflector 4 1/4 wavelength plate 5 Reflection sheet 6 Reflection sheet (mirror) 7 Antireflection sheet 8 Lens sheet

Claims (5)

[Claims] 1. A large number of interfaces made of two kinds of materials having different refractive indices are arranged at an inclination of 30 ° to 60 ° with respect to a thickness direction so as to satisfy Brewster conditions with respect to incident light. Is an incident surface, and one of the surfaces orthogonal to the incident surface is a light emitting surface, and the incident light from this incident surface is converted into first and second light beams whose polarization planes are orthogonal to each other. And a light guide for emitting the first polarized light from the light exit surface and traveling the second polarized light toward the end surface opposite to the incident surface, and the light guide. A light source disposed in the vicinity of the light incident surface, a reflector covering the light source, a mirror disposed on two side end faces parallel to the light traveling direction, and a polarization plane of the second polarized light transmitted through the light guide. 90
A quarter-wave plate disposed on the side end face opposite to the light source to rotate the light and re-enter this light into the light guide;
A planar light emitting device comprising: a mirror disposed outside a four-wavelength plate; and antireflection means disposed on a light exit surface of a light guide. 2. The planar light emitting device according to claim 1, wherein a mirror is disposed on a bottom surface corresponding to a back surface of the light exit surface of the light guide. 3. The planar light emission according to claim 1, wherein the refractive index of the outermost surface on the light emission side of the antireflection means is smaller than all the members constituting the light guide. apparatus. 4. The anti-reflection means having a pitch of 0.1.
4. The planar light emitting device according to claim 1, wherein a sheet having continuous unevenness of 5 μm or less is used. 5. A large number of interfaces made of two kinds of materials having different refractive indexes are arranged at an angle of 30 ° to 60 ° with respect to a thickness direction so as to satisfy Brewster conditions with respect to incident light. Is an incident surface, and one of the surfaces orthogonal to the incident surface is a light emitting surface, and the incident light from this incident surface is converted into first and second light beams whose polarization planes are orthogonal to each other. And a light guide for emitting the first polarized light from the light exit surface and traveling the second polarized light toward the end surface opposite to the incident surface, and the light guide. A light source disposed in the vicinity of the light incident surface, a reflector covering the light source, a mirror disposed on two side end faces parallel to the light traveling direction, and a polarization plane of the second polarized light transmitted through the light guide. 90
A quarter-wave plate disposed on the side end face opposite to the light source to rotate the light and re-enter this light into the light guide;
The light guide is constituted by a mirror arranged outside the four-wavelength plate, and the arrangement density of the interface of the two kinds of materials is
A planar light emitting device comprising: a light-guiding body; and a surface light-emitting device which is configured so as to sequentially increase in height from a light incident surface and a side end surface opposite to the light guide toward a central portion.