JP2003197015A - Flat light source - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flat light source capable of emitting a light with a high brightness in the front and a uniform brightness distribution in the flat light source provided with a little number of point light sources. <P>SOLUTION: This flat light source is provided with, at least, a single solid light emitting element 14 disposed opposed to an incident end face 11 of a light guide plate 10 whose one end surface is set to the incident end face 11 and whose front surface is formed with an emission surface 12 emitting the light incident from the incident end face 11 on the front side, and a prism sheet 15 allowing the light emitted from the emission surface 12 of the light guide plate 10 to be incident from the rear surface opposite on the light guide plate 10 and changing the direction of each incident light emitting from the front in the opposite side of the rear surface in the front surface direction, in the front side of the light guide plate 10. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface light source used as an illumination light source of a liquid crystal display device.

[0002]

2. Description of the Related Art As a surface light source used for an illumination light source of a liquid crystal display device, conventionally, an incident end face is provided at one end and
On the side of the light guide plate on which the emission surface for emitting the light incident from the incident end face to the front side is formed, facing the incident end face, a cold cathode tube having a length over the entire length of the incident end face is arranged, A configuration in which a deflecting member that refracts light emitted from the emission surface of the light guide plate toward the front surface and emits the light from the front surface is widely used on the front side of the light guide plate.

However, in this surface light source, the light emitted from the cold cathode fluorescent lamp can be made incident on the light guide plate from the entire area of the incident end face thereof, and the light having a uniform brightness distribution can be emitted from the front face of the light guide plate. However, on the other hand, since the cold cathode fluorescent lamp has a short life, the cold cathode fluorescent lamp has to be frequently replaced, and therefore the maintenance cost increases.

Therefore, recently, instead of the cold cathode tube, a surface light source having a solid-state light emitting element such as an LED (light emitting diode) having a long life and high energy efficiency has come to be used. There is.

6 and 7 show a conventional surface light source provided with a solid-state light emitting element. FIG. 6 is a side view of the surface light source, and FIG.
FIG. 6 is a bottom view of a deflecting member arranged on the front side of the light guide plate of the surface light source.

As shown in FIG. 6, this surface light source has one end face as an incident end face 2 and a plurality of elongated strips having a length over the entire width of the front face, spaced apart in the longitudinal direction thereof. A light guide plate 1 on which an emission surface 3 is formed, a solid-state light-emitting element 4 such as an LED arranged facing the center of an incident end face 2 of the light guide plate 1, and arranged on the front side of the light guide plate 1. The light guide plate 1 includes a deflecting member 5 that refracts light emitted from the plurality of elongated emission surfaces 3 in the front direction and emits the light from the front surface.

The light guide plate 1 is made of a transparent plate such as an acrylic resin plate whose rear surface is flat and whose front surface is stepped. The wide end surface of both end surfaces is incident. The end face 2 and the plurality of stepped faces of the stepped face on the front face are the elongated emission faces 3.

Further, the deflecting member 5 has the structure shown in FIGS. 6 and 7.
As shown in FIG. 5, the front surface is formed into a flat surface, and the rear surface is provided with a plurality of laterally long portions parallel to the width direction of the light guide plate 1 (the longitudinal direction of the elongated emission surface 3) at intervals in the length direction thereof. The prism sheet is formed of a prism sheet. Less than,
This deflecting member 5 is called a prism sheet.

This surface light source emits the light emitted from the solid state light emitting element 4 from the front surface of the prism sheet 5, and the light emitted from the solid state light emitting element 4 is shown in FIG.
As indicated by the arrow in FIG.
From the plurality of elongated emission surfaces 3 formed on the front surface of the light guide plate 1 and then introduced into the light guide plate 1.
Emit in the opposite direction.

The light emitted from the plurality of elongated light emitting surfaces 3 of the light guide plate 1 is incident on the plurality of horizontally elongated prism portions 6 of the prism sheet 5 from one side surface thereof, and the other side surface of these horizontally elongated prism portions 6 is formed. The light is totally reflected at the interface with the air layer which is the outside air, is refracted toward the front surface of the prism sheet 5, and is emitted from the front surface of the prism sheet 5.

In this surface light source, since the solid-state light emitting element 4 has a long life, it is almost unnecessary to replace the light emitting element 4.
Therefore, the maintenance cost can be reduced.

[0012]

However, in the above-mentioned conventional surface light source, since the light incident on the light guide plate 1 is the light emitted from the solid-state light emitting element 4 such as an LED, the entire incident end face 2 is uniform. The brightness distribution of the front brightness of the light emitted from the front surface of the prism sheet 5 which is not irradiated is not uniform.

That is, FIG. 8 is a schematic diagram showing a light emitting direction of the above-mentioned conventional surface light source.
The path of the light that is emitted from the light and enters the prism sheet 5 through the light guide plate 1 is shown by a flat horizontal plane, and the path of the light that is deflected by the horizontally long prism portion 6 of the prism sheet 5 is the width of the light guide plate 1. It is shown by a vertical plane along the direction.

As shown in this schematic diagram, the solid-state light-emitting device 4
The light emitted from the light guide plate 1 spreads radially.
Since it enters from the incident end face 2 thereof, is guided through the light guide plate 1 and is emitted from the elongated emission face 3 on the front surface thereof, the light emitted from the elongated emission face 3 is seen from the front direction of the light guide plate 1. Light that spreads radially around the arrangement portion of the solid-state light-emitting element 3.

Since the horizontally long prism portion 6 of the prism sheet 5 is formed parallel to the width direction of the light guide plate 1, the horizontally long prism portion 6 is emitted from the elongated light emission surface 3 of the light guide plate 1. The light incident on is refracted in the front direction of the prism sheet 5 by the laterally long prism portion 6 without changing its divergence angle.

Therefore, the light refracted in the front surface direction of the prism sheet 5 by the laterally long prism portion 6 is light that spreads radially in the width direction of the prism sheet 5 when viewed from the incident end face direction of the light guide plate 1, Of the light, light in the divergence angle range toward the front surface of the prism sheet 5 is emitted from the front surface of the prism sheet 5, and light having a divergence angle larger than that leaks laterally from the side surface of the prism sheet 5.

Therefore, in the conventional surface light source, the front luminance distribution of the light emitted from the front surface of the prism sheet 5 is
As shown in FIG. 9, the light emitted from the region hatched in the drawing has a non-uniform brightness distribution in which the brightness is low.

In addition, the number of the solid-state light emitting elements 4 is increased,
By arranging the light emitting elements 4 along the lengthwise direction of the incident end face of the light guide plate at close intervals, it is possible to emit light having a uniform luminance distribution from the front surface of the prism sheet 5. If you increase the number of
Power consumption will increase.

An object of the present invention is to provide a surface light source having a solid-state light emitting element, which can emit light having a high front luminance and a uniform luminance distribution with a small number of light emitting elements. It is a thing.

[0020]

SUMMARY OF THE INVENTION A surface light source according to the present invention includes a light guide plate having one end face as a light incident end face, and a light exit plate formed on a front side for emitting light incident from the incident end face, and the light guide plate. At least one point light source arranged to face the incident end surface of the light plate, and light arranged radially in front of the light guide plate, radially emitted from the point light source, and emitted from the emission surface of the light guide plate. Incident from the rear surface facing
A diverting member for diverting each incident light into a direction in which the incident light is emitted from a front surface opposite to the rear surface to a front direction.

According to this surface light source, the light emitted from the emission surface of the light guide plate in a radial manner centered on the arrangement portion of the solid state light emitting element when viewed from the front surface direction of the light guide plate is emitted,
By the deflection member arranged on the front side of the light guide plate, the light radially emitted from the point light source and emitted from the emission surface of the light guide plate is made incident from the rear surface facing the light guide plate, and each incident light is emitted. Since the light is redirected from the front surface opposite to the rear surface to the front direction, it is possible to emit light with high front brightness and uniform brightness distribution with a small number of point light sources.

In the surface light source of the present invention, as described above, one end face is the incident end face of light, and the front face of the light guide plate having the emission face formed on the front side for emitting the light incident from the incident end face is The light emitted radially from the point light source and emitted from the emission surface of the light guide plate is made incident from the rear surface facing the light guide plate, and each incident light is changed to a direction in which it is emitted from the front surface opposite to the rear surface to the front direction. By arranging the deflecting member for directing the light, it is possible to emit light having a high front luminance and a uniform luminance distribution with a small number of point light sources.

In the surface light source of the present invention, the light guide plate has a length over the entire width of the front surface on the exit surface at intervals in the longitudinal direction, and the light incident from the entrance end surface is A plurality of elongated emission surfaces that emit in the direction opposite to the incident end face are formed, and the deflection member extends on the rear surface along a plurality of concentric circles centered on the arrangement portion of the point light source. It is preferably composed of a prism sheet on which a plurality of existing prism portions are formed.

In that case, it is more preferable that the plurality of prism portions are formed in an arc shape along the concentric circles.

Further, in this surface light source, when a plurality of point light sources are arranged facing the incident end surface of the light guide plate,
It is preferable that the diverting member is formed of a prism sheet on the rear surface, in which a plurality of prism portions extending along concentric circles centering on the arrangement portions of the point light sources are formed. .

[0026]

1 to 3 show a first embodiment of the present invention. FIG. 1 is a sectional view in which hatching of a surface light source is omitted, and FIG. 2 is a front side of a light guide plate of the surface light source. It is a bottom view of the deflection member arrange | positioned at.

In the surface light source of this embodiment, one end face is an incident end face 11, and a light emitting plate 12 is formed on the front face, which has an emission face 12 for emitting the light incident from the incident end face 11 to the front side.
And one solid state light emitting device 14 arranged to face the incident end surface 11 of the light guide plate 10, and a deflection member 15 arranged on the front side of the light guide plate 10.

The light guide plate 10 is made of a transparent plate, such as an acrylic resin plate, whose rear surface is formed into a flat surface and whose front surface is formed into a stepped surface which is lowered toward the other surface from one end to the other end. Of the both end faces, the end face having a large height is defined as the incident end face 11, and a plurality of stepped faces of the front surface of the staircase face the light incident from the incident end face 11 respectively.
The elongated emission surface 12 emits light in the direction opposite to 1.

That is, the light guide plate 10 is provided on the front surface thereof at intervals in the length direction of the light guide plate 10.
Of a plurality of elongated emission surfaces 12 having a full width.

Further, a reflective film 13 is provided over the entire area of the area between the plurality of elongated emission surfaces 12 on the front surface of the light guide plate 10 (hereinafter referred to as the inter-emission area). The reflection film 13 is made of, for example, a metal film such as Al (aluminum), and is attached to the area between the emission surfaces or is vapor-deposited or plated in the area between the emission surfaces.

The structure of the solid-state light-emitting element 14 is not shown, but is an LED (light-emitting diode) molded with a transparent resin having a light diffusing property. Is set according to the application of the surface light source.

That is, the solid-state light-emitting element 14 may emit colored light or white light. The solid-state light-emitting element that emits colored light is an LED that emits colored light of a predetermined color. The solid-state light-emitting element that emits white light has a red LED that emits red light and a green LED that emits green light.
And a blue LED that emits blue light are arranged side by side, and these LEDs are molded by the transparent resin.

The solid-state light-emitting element 14 is arranged so as to face the center portion of the incident end face 11 of the light guide plate 10 in the longitudinal direction and to be slightly separated from the incident end face 11 of the light guide plate 10. .

On the other hand, the deflecting member 15 arranged on the front side of the light guide plate 10 includes a plurality of elongated emission surfaces 1 of the light guide plate 10.
It has a function of refracting the light emitted from No. 2 in the direction in which the divergence angle in the direction along the width direction of the light guide plate 10 becomes small and emitting from the front surface.

The diverting member 15 has the same lateral width as the light guide plate 10, has a flat front surface, and the rear surface facing the light guide plate 10 has the solid light emitting element 14 as the center. A plurality of curved prism portions 16 curved in an arc shape along a plurality of concentric circles are formed at predetermined intervals with a predetermined pitch. Hereinafter, this deflecting member 15 is referred to as a prism sheet.

The prism sheet 15 is made of, for example, a transparent plate made of acrylic resin or the like. Among the side surfaces of the plurality of curved prism portions 16 of the prism sheet 15, the side surface on the inner peripheral side of the arc is the An incident surface 16a for taking in light emitted from the elongated emission surface 12 of the light guide plate 10 is formed, and a side surface on the outer peripheral side of the arc diverts the light incident from the incident surface 16a toward the front surface of the prism sheet 15. It is defined as the turning surface 16b.

The incident surface 16a is a steep surface nearly perpendicular to the front surface of the prism sheet 15, and the deflection surface 16b is an angle with respect to a normal line (not shown) of the front surface of the prism sheet 15. Is an inclined surface larger than the incident surface 16a.

In addition, the rear surface of the prism sheet 15 between the plurality of curved prism portions 16 has an entrance / exit surface 1 for transmitting incident light from the front surface side and the rear surface side, respectively.
5b, and the entrance / exit surface 15b is a surface parallel to the front surface 15a of the prism sheet 15 or having an inclination close to it.

In the light guide plate 10, the virtual straight line passing through the upper ends of the plurality of elongated emission surfaces 12 on the front surface is substantially the same as the virtual straight line passing through the tops of the plurality of curved prism portions 16 of the prism sheet 15. The prism sheets 15 are arranged so as to be parallel to each other in the lengthwise direction, and the prism sheet 15 has the top portions of the plurality of curved prism portions 16 on the rear surface thereof arranged on the light guide plate 1.
It is arranged close to the surface of the reflective film 13 provided in the plurality of inter-emission surface regions of the front surface 10b of 0.

The surface light source of this embodiment is arranged behind the liquid crystal display element 17 shown by the phantom line (two-dot chain line) in FIG. 1. For convenience of illustration, the elongated light guide plate 10 is shown in FIG. Although the pitch of the emitting surface 12 and the pitch of the plurality of curved prism portions 16 of the prism sheet 15 are greatly exaggerated, the plurality of elongated emitting surfaces 12 of the light guide plate 10 are shown.
Are formed at a pitch that is the same as or smaller than the pixel pitch of the liquid crystal display element 21, and the plurality of curved prism portions 16 of the prism sheet 15 are provided at a pitch smaller than the pitch of the plurality of elongated emission surfaces 12. It is preferable.

This surface light source guides the light emitted from the solid-state light-emitting element 14 by the light guide plate 10 and the front surface 10 thereof.
The light is emitted from the plurality of elongated emission surfaces 12 of b, the light is deflected by the plurality of curved prism portions 16 of the prism sheet 15, and the light is emitted from the front side of the prism sheet 14.

That is, the light emitted from the solid-state light emitting element 14 enters the light guide plate 10 from its incident end face 11 while spreading radially, and as shown by the arrow in FIG.
The inside of the light guide plate 10 is repeated by repeating the reflection at the reflection film 13 in the plurality of emission surface areas on the front surface of the light guide plate 10 and the total reflection at the interface between the rear surface of the light guide plate 10 and the air layer as the outside air. It is guided in the length direction, and in the process, enters into any of the plurality of elongated emission surfaces 12, and from the elongated emission surface 12,
The light is emitted in the direction opposite to the incident end face 11.

The light emitted from the solid-state light-emitting element 14 (hereinafter, simply referred to as light) is a light that spreads radially, so that the light emitted from the plurality of elongated light emitting surfaces 12 of the light guide plate 10 is the light guide. The light is a light that spreads radially around the arrangement portion of the solid-state light-emitting element 14 when viewed from the front side of the light plate 10.

Then, the elongated emission surface 12 of the light guide plate 10 is formed.
The light that is emitted from and spreads in a radial direction is incident on the plurality of curved prism portions 16 of the prism sheet 15 from their incident surfaces 16a, and the deflection surfaces 16b of these curved prism portions 16 are incident.
Is totally reflected at the interface between the prism sheet 15 and the outside air (air layer), each light is deflected in the normal direction of the front surface (emission surface) of the prism sheet 15, and the light is emitted from the front surface of the prism sheet 15 in the front direction.

FIG. 3 is a schematic diagram showing the light emission direction of the surface light source of this embodiment. In the figure, the path of light emitted from the solid state light emitting element 14 and incident on the prism sheet 15 via the light guide plate 10 is shown. Is indicated by a flat horizontal plane, and the path of light deflected by the curved prism portion 16 of the prism sheet 15 is indicated by a curved vertical surface across the width direction of the light guide plate 10.

As shown in this schematic diagram, the light emitted from the elongated light emitting surface 12 (see FIG. 1) of the light guide plate 10 is disposed in the arrangement portion of the solid state light emitting element 14 when viewed from the front direction of the light guide plate 10. It is the light that spreads radially as the center.

However, since the curved prism portion 16 of the prism sheet 15 is formed in an arc shape centered on the arrangement portion of the solid state light emitting device 14, the plurality of elongated emission surfaces 12 of the light guide plate 10 The plurality of curved prism portions 16 of the prism sheet 15 allow the light emitted in a radial direction centered on the arrangement portion of the solid state light emitting elements 14 when viewed from the front surface direction of the light guide plate 10 to pass through the prism sheet 1.
The light is refracted in a direction along the normal line of the front surface of the light guide plate 5, that is, in a direction toward the front surface of the prism sheet 15 and in a direction in which the spread angle in the direction along the width direction of the light guide plate 10 decreases.

The plurality of elongated emission surfaces 12 of the light guide plate 10 are linearly formed along the width direction of the light guide plate 10, whereas the plurality of curved prism portions 16 of the prism sheet 15 are formed. The light guide plate 10 is formed in an arc shape centered on the arrangement portion of the solid state light emitting device 14.
The light emitted from the plurality of elongated emission surfaces 12 enters each of the plurality of curved prism portions 16 on the emission side of the elongated emission surface 12, and is deflected by the curved prism portion 16.

Therefore, according to this surface light source, most of the light emitted from the solid-state light-emitting element 14 does not leak to the side from the side surface of the prism sheet 15, and the entire front surface 15a of the prism sheet 15 faces the front. Therefore, it is possible to emit light with a small number of light emitting elements, energy efficiency, high front luminance, and a uniform luminance distribution.

That is, in the surface light source of this embodiment, the light guide plate 10 has a length on the front surface thereof over the entire width of the front surface at intervals in the longitudinal direction, and the light is incident from the incident end surface 11. A plurality of elongated emission surfaces 12 for emitting light in a direction opposite to the incident end surface 11 are formed, and a deflecting member 15 arranged on the front side of the light guide plate 10 is provided on the front surface of the light guide plate 10. Since the plurality of curved prism parts 16 curved along a plurality of concentric circles centering on the arrangement part of the solid state light emitting element 14 are formed on the rear surface facing each other, The light emitted and incident on the light guide plate 10 from the incident end face 11 thereof is efficiently produced without loss, and the plurality of elongated emission faces 1 are provided.
2 is emitted from the front surface of the prism sheet 15 by changing the direction of the light by a plurality of curved prism portions 16 of the prism sheet 15 so that the spread angle in the width direction of the light guide plate 10 becomes smaller. Can be emitted.

In this embodiment, since the plurality of curved prism portions 16 of the prism sheet 15 are formed in an arc shape along a concentric circle centered on the arrangement portion of the solid state light emitting device 14, Almost all of the light emitted radially from the plurality of elongated emission surfaces 12 of the light plate 10 centering on the arrangement portion of the solid state light emitting elements 14 is emitted by the plurality of curved prism portions 16 of the prism sheet 15 on the front surface of the prism sheet 15. By changing the direction to the direction along the normal line, it is possible to emit light having higher frontal luminance and more uniform luminance distribution from the front surface of the prism sheet 15.

As described above, this surface light source can emit surface light having a high front luminance and a uniform luminance distribution with a small number of light emitting elements. Therefore, this surface light source is as shown in FIG. By arranging it behind the transmissive liquid crystal display element 21, it is possible to obtain a liquid crystal display device of good display quality in which the brightness of the screen is uniform, there is no unevenness in brightness, and the front brightness is high.

Further, in the surface light source of the above-mentioned embodiment, the reflection film 13 is provided in each of the plurality of inter-emission areas on the front surface of the light guide plate 10, so that from the front side of the prism sheet 15. External light that has entered is transmitted through the prism sheet 15 in the thickness direction, and the light guide plate 1
It can be reflected by the reflection film 13 of 0, and the reflected light can be transmitted through the prism sheet 15 again in the thickness direction and emitted to the front surface thereof. Therefore, in the liquid crystal display device,
It is possible to display both reflective display using external light, which is the light of the environment of use, and transmissive display using illumination light from the surface light source.

FIG. 4 is a bottom view of the deflecting member arranged on the front side of the light guide plate according to the second embodiment of the present invention.

In the surface light source of this embodiment, the incident end face 11 of the light guide plate 10 which is the same as that of the first embodiment is approximately 3 in the length direction.
Two solid-state light-emitting devices 1 that emit colored light or white light of the same color, facing each other near each of the equally divided points.
4a and 14b are arranged, and the light radially emitted from the plurality of elongated emission surfaces 12 of the light guide plate 10 is incident on the front side of the light guide plate 10 from the rear surface facing the light guide plate, and each incident light is incident on the rear surface. The two solid-state light emitting elements 14a, 1 are provided on the rear surface facing the front surface of the light guide plate 10 as a redirecting member for redirecting light from the front surface on the side opposite to the front surface.
The prism sheet 17 is formed by forming two kinds of arc-shaped curved prism parts 18a and 18b, which are respectively curved along two kinds of concentric circles centering on the arrangement part of 4b.

In FIG. 4, for convenience, the two types of curved prism portions 18a and 18b of the prism sheet 17 are shown by the curves along the tops thereof, but the two types of curved prism portions 18a and 18b are The prism sheet 15 has a cross-sectional shape similar to that of the plurality of curved prism portions 16 shown in FIG. 1, and the portion between the two types of curved prism portions 18a and 18b on the rear surface of the prism sheet 17 is Each of them is an entrance / exit surface (a surface having an inclination parallel to or close to the front surface of the prism sheet 17) for transmitting incident light from the front surface side and the rear surface side.

In the surface light source of this embodiment, two solid state light emitting devices 14a and 14b are arranged so that the incident end face 11 of the light guide plate 10 is opposed to each other in the vicinity of a dividing point which is divided into three substantially equal parts in the lengthwise direction. On the front side of the light guide plate 10, two kinds of arc-shaped curved prism parts 18a and 18b which are respectively curved along two kinds of concentric circles centering on the arrangement parts of the two solid state light emitting devices 14a and 14b are formed. Since the prism sheet 17 is arranged, by turning on both of the two solid state light emitting devices 14a and 14b,
The lights emitted from the respective solid-state light emitting elements 14a and 14b are mixed with each other when the lights are deflected in the front direction in the prism sheet 17 and emitted. Therefore, the front brightness is high,
Moreover, the planar light having a uniform brightness distribution can be emitted from the front surface of the prism sheet 17, and the two solid state light emitting elements 14a and 14b can be turned on for both lighting and lighting of only one. By switching, the brightness of the emitted light can be adjusted in two steps. Further, even if the two solid state light emitting elements 14a and 14b have individual differences such as output brightness and color variation, the front brightness is high from the entire front surface of the prism sheet 17 regardless of the individual differences.
Moreover, it is possible to emit planar light having a uniform luminance distribution.

Further, in this embodiment, the two solid state light emitting elements 14a and 14b for emitting colored light or white light of the same color are opposed to the incident end surface 11 of the light guide plate 10. Two solid state light emitting devices 14a and 14b,
The two solid-state light emitting devices 1 emit light of different colors (colored light and colored light, or colored light and white light).
By switching the lighting of 4a and 14b to both lighting and lighting of only one, both solid-state light emitting elements 14a and 14b
The prism sheet 17 is provided with the light obtained by mixing the light from the light source 14b and the light from one of the solid state light emitting devices 14a or 14b.
The light may be emitted from the front surface of the.

FIG. 5 is a bottom view of the deflecting member arranged on the front side of the light guide plate showing the third embodiment of the present invention.

The surface light source of this embodiment faces the incident end surface 11 of the same light guide plate 10 as in the first embodiment, and colored lights of different colors, for example, red, green which are the three primary colors of light,
Three solid-state light-emitting elements 14 that emit blue colored light, respectively
R, 14G, and 14B are arranged, and the light emitted from the plurality of elongated emission surfaces 12 of the light guide plate 10 is provided on the front side of the light guide plate 10 with a small spread angle in the direction along the width direction of the light guide plate 10. As a deflecting member that is refracted in a direction and emitted from the front surface, three kinds of concentric circles centering on the arrangement portions of the three solid state light emitting devices 14R, 14G, and 14B are formed on the rear surface facing the front surface of the light guide plate 10. Three types of curved prism portions 20a, 20 that are curved in an arc shape respectively
The prism sheet 19 on which b and 20c are formed is arranged.

In FIG. 5, for convenience, the three types of curved prism portions 20a, 20b, 20 of the prism sheet 19 are shown.
c is shown by a curve along the top thereof, the three types of curved prism parts 20a, 20b, 20c have the same sectional shape as the curved prism part 16 of the prism sheet 15 shown in FIG. In addition, the three types of curved prism parts 20a, 2 on the rear surface of the prism sheet 19 are provided.
The portions between 0b and 20c are input / output surfaces (surfaces that are parallel to or near the front surface of the prism sheet 19) that transmit incident light from the front surface side and the rear surface side, respectively.

Further, in this embodiment, the three solid state light emitting devices 14R, 14G and 14B are arranged along the length direction of the incident end face 11 of the light guide plate 10, and three types of the prism sheet 19 are provided. Curved prism parts 20a, 20b,
20c to the three solid state light emitting devices 14R, 14G, 1
4B is formed in an arc shape along each of three types of concentric circles, each centering on the arranged portion.

In this surface light source, three solid state light emitting elements 14R, 14G and 14B for emitting colored lights of red, green and blue are arranged along the incident end surface 11 of the light guide plate 10,
The three solid state light emitting devices 14 are provided on the front side of the light guide plate 10.
A prism sheet 19 having three types of curved prism parts 20a, 20b, 20c each having an arc shape curved along three types of concentric circles centering on the placement parts of R, 14G, 14b, respectively, is arranged. Therefore, by turning on all of the three solid-state light emitting elements 14R, 14G, and 14B, white light obtained by mixing the colored lights of red, green, and blue with a very high front luminance and even The light can be emitted from the front surface of the prism sheet 19 with a brightness distribution.

Further, in this surface light source, the three solid-state light emitting elements 14R, 14G and 14B are sequentially turned on, whereby red, green,
Light of three colors of blue can be sequentially emitted as light having a high front luminance and a uniform luminance distribution, and thus can also be used as a surface light source of a field sequential liquid crystal display device.

In the surface light sources of the first to third embodiments, the pitches between the plurality of concentric curved prism portions are set to be equal, but the pitch is not limited to this. For example, when moire fringes are generated due to the stepwise light guide plate, or when interference fringes are generated due to the pixel pitch when combined with a display means such as a liquid crystal display element, the respective fringes are generated. In order to be able to reduce it, the pitch between the plurality of curved prism portions may be set to a plurality of types, or may be set to be non-uniform to each other, and may be optimally set according to the purpose.

Further, the surface light sources of the first to third embodiments are arranged such that the plurality of curved prism portions 16, 17a, 17b, 20a, 20b, 2 of the prism sheets 15, 17, 19 are provided.
Although 0c is formed in an arc shape, the curved prism portion may be formed in a polygonal shape along each of a plurality of concentric circles centering on the arrangement portion of the solid state light emitting elements.

Further, the deflecting member arranged on the front side of the light guide plate 10 is not limited to the prism sheets 15, 17 and 19, but is radially emitted from the point light source to enter the light guide plate 10 and its elongated emission surface. The light emitted from 12 is made incident from the rear surface facing the light guide plate, and the incident light is totally reflected in the direction in which the incident light is emitted from the front surface opposite to the rear surface to the front direction and is continuously changed. Anything can be used as long as it is provided.

Further, the light guide plate 10 is not limited to one in which the front surface is formed into a stepped surface and the plurality of step surfaces of the stepped surface are each the elongated emission surfaces 12, and one end surface is the incident end surface,
It suffices that the front surface has an emission surface for emitting the light incident from the incident end surface to the front side.

Further, as the point light source, LED or EL
The light source is not limited to a solid-state light emitting element such as (electroluminescence), and may be any light source that radially radiates light to the surroundings.

Further, the surface light source of the present invention is not limited to the illumination light source of the liquid crystal display device and can be widely used for other purposes.

[0071]

According to the surface light source of the present invention, one end surface is a light incident end surface, and a light guide plate having an exit surface formed on a front side for emitting light incident from the incident end surface, and an incident end surface of the light guide plate. And at least one point light source arranged to face the light guide plate, the light emitted from the emission surface of the light guide plate is made incident on the rear surface facing the light guide plate, and each incident light is emitted. Since it includes a deflecting member that redirects light from the front surface on the side opposite to the rear surface to the front direction, the number of point light sources is small and the front luminance is high in order to use light without waste, and It is possible to emit light having a uniform brightness distribution.

In the surface light source of the present invention, the light guide plate has a length over the entire width of the front surface on the exit surface at intervals in the length direction thereof, and the light incident from the entrance end surface is A plurality of elongated emission surfaces that emit in the direction opposite to the incident end face are formed, and the deflection member extends on the rear surface along a plurality of concentric circles centered on the arrangement portion of the point light source. Preferably, the prism sheet is formed with a plurality of existing prism portions. By doing so, the light emitted from the point light source and incident on the light guide plate from its incident end face is efficiently converted into In front of the prism sheet It can be emitted from.

In this case, it is preferable that the plurality of prism portions are formed in an arc shape along a concentric circle centered on the arrangement portion of the point light source. By doing so, a plurality of elongated light guide plates can be formed. Almost all of the light emitted from the emitting surface in a radial direction centered on the arrangement portion of the point light source is redirected in the direction along the normal line of the front surface of the prism sheet by the plurality of arc-shaped prism portions of the prism sheet, Light with higher frontal brightness and more uniform brightness distribution can be emitted from the front surface of the prism sheet.

In this surface light source, when a plurality of point light sources are arranged so as to face the incident end surface of the light guide plate, the deflecting member has the plurality of point light sources on the rear surface facing the front surface of the light guide plate. It is preferable that the prism sheet is formed of a plurality of prism portions each curved along a plurality of concentric circles having the light source arrangement portion as a center.
By doing so, even if there are individual differences in the amount of emitted light among the plurality of point light sources, it is possible to emit light having a higher front brightness and a uniform brightness distribution from the entire front surface of the prism sheet.

[Brief description of drawings]

FIG. 1 is a sectional view of a surface light source showing a first embodiment of the present invention with hatching omitted.

FIG. 2 is a bottom view of a deflecting member arranged on the front side of the light guide plate of the surface light source.

FIG. 3 is a schematic diagram showing a light emitting direction of the surface light source.

FIG. 4 is a bottom view of the deflecting member arranged on the front side of the light guide plate according to the second embodiment of the present invention.

FIG. 5 is a bottom view of the deflecting member arranged on the front side of the light guide plate according to the third embodiment of the present invention.

FIG. 6 is a side view of a conventional surface light source including a solid-state light emitting element.

FIG. 7 is a bottom view of the deflecting member arranged on the front side of the light guide plate of the conventional surface light source.

FIG. 8 is a schematic diagram showing a light emitting direction of a conventional surface light source.

FIG. 9 is a diagram showing a luminance distribution of emitted light of a conventional surface light source.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Light guide plate 11 ... Incident end surface 12 ... Elongated exit surface 13 ... Reflective films 14, 14a, 14b, 14R, 14G, 14B ... Solid-state light emitting elements 15, 17, 19 ... Transforming member (prism sheet) 15a ... Front surface 15b ... Input / output surfaces 16, 18a, 18b, 20a, 20b, 20c ... Curved prism portion 16a ... Incident surface 16b ... Deflection surface 21 ... Liquid crystal display element

Claims (4)

[Claims] 1. A light guide plate, one end surface of which is an incident end surface of light, and an emission surface is formed on a front side for emitting light incident from the incident end surface, and the light guide plate is disposed so as to face the incident end surface of the light guide plate. At least one point light source and light arranged radially in front of the light guide plate, radially emitted from the point light source and emitted from the emission surface of the light guide plate are made incident from a rear surface facing the light guide plate, and each incident light A surface light source, comprising: a diverting member for diverting the light from a front surface opposite to the rear surface in a direction of emitting light in a front direction. 2. The light exiting surface of the light guide plate has a length over the entire width of the light guide plate at intervals in the lengthwise direction, and light incident from the incident end surface of the light guide plate is opposite to the incident end surface. A plurality of elongated emission surfaces that emit in the direction are formed.On the rear surface of the deflecting member, a plurality of prism portions extending along concentric circles centering on the arrangement portion of the point light source are formed. The surface light source according to claim 1, wherein the surface light source comprises a prism sheet. 3. The surface light source according to claim 2, wherein the plurality of prism portions are formed in an arc shape. 4. A plurality of point light sources are arranged facing the incident end surface of the light guide plate, and the deflecting member is provided on the rear surface thereof with a plurality of concentric circles centering on the arrangement parts of the plurality of point light sources. The surface light source according to claim 2 or 3, wherein the surface light source comprises a prism sheet having a plurality of prism portions extending along the prism sheet.