JP2000106021A - Surface light source device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface light source device capable of emitting illumination light from a light source in the front and reflecting outside light coming from the front and emitting again it in the front. SOLUTION: This surface light source device has a lightguide 1 forming the front in a stairs-shaped surface 2, taking in illumination light from an incident edge surface 1a and emitting from plural differential step surfaces 2b of the stairs-shaped surface 2; an outside light reflecting surface 3a installed on plural step surfaces 2a of the stairs-shaped surface 2 of the lightguide 1 and reflecting outside light coming from the front; a light source 5 installed on the side of the lightguide 1 so as to face the incident edge surface; and a light control plate 8 arranged in the front of the lightguide 1, taken in the outside light coming from the front, emitting it to the rear, taking in the outside light reflected with the outside light reflecting surface 3a from the rear, emitting it in the front, taking in illumination light coming from the plural differential step surfaces of the lightguide 1 from the rear, scattering the light, then emitting in the front.

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 device having both a function of emitting illumination light from a light source forward and a function of reflecting external light incident from the front and emitting the light forward. .

[0002]

2. Description of the Related Art As a surface light source device used as a backlight of a display device provided with a non-light emitting type display body which controls transmission of light incident from the outside such as a liquid crystal display element, for example, a side light type is used. There is something called.

Conventionally, this sidelight type surface light source device has a light guide plate which takes in light from an end face and emits the light to the front, and an illumination light arranged on the side of the end face which takes in the light from the light guide plate. And a light source that emits light. The light source includes a straight tube fluorescent lamp or a neon tube, an EL (electroluminescence) illuminant,
An LED array or the like in which EDs (light emitting diodes) are arranged is used.

Generally, a flat transparent plate made of acrylic resin or the like is used for the light guide plate, at least one end surface of which is an incident end surface for receiving illumination light from the light source, and the entire front surface is formed. , And an emission surface of the light taken in from the incident end surface.

The light guide plate receives illumination light from the light source from the incident end face, and reflects the illumination light in the longitudinal direction of the light guide plate while totally reflecting the illumination light at the interface between the front and back surfaces of the light guide plate and the outside air (air). And emits forward from almost the entire area of the front surface.

[0006]

By the way, a display device using a surface light source device as a backlight always performs a transmissive display using illumination light from the surface light source device, and a display device such as natural light or indoor light. There is a so-called two-way display type that performs both a reflective display using external light and a transmissive display using illumination light from the surface light source device.

When the external light of sufficient brightness can be obtained, the two-way display device performs a reflection type display using the external light without emitting the illumination light from the surface light source device, and the brightness of the external light is increased. When the surface light source device is not enough, the illumination light is emitted from the surface light source device, and the reflection type display using the external light and the transmission type display using the light from the surface light source device are simultaneously performed, so that the reflection is performed. The transmissive display compensates for the lack of screen luminance due to the mold display, and performs transmissive display using light from the surface light source device when external light cannot be obtained. The device can perform display in any brightness environment, and it is not necessary to emit illumination light from the surface light source device when external light of sufficient brightness is obtained. Use the illumination light from the device. Have the advantage to be compared with performing transmissive display, requires less power consumption.

However, in the conventional surface light source device, illumination light from a light source arranged on the side of the light guide plate is taken into the light guide plate from its incident end face, and the illumination light is emitted forward from the front surface of the light guide plate. For example, in order to configure the above-described two-way display device, a semi-transmissive reflector is disposed on the back of a non-light-emitting display such as a liquid crystal display element, and behind the transflective plate. The surface light source device had to be arranged.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a surface light source device capable of emitting illumination light from a light source forward and reflecting external light incident from the front to emit the light forward. .

[0010]

According to the surface light source device of the present invention, at least one end surface is an incident end surface, and the front surface has a stepped surface having a plurality of step surfaces and a plurality of step surfaces connecting these step surfaces. And a light guide that takes in illumination light from the incident end face and exits from the plurality of step faces, and is provided on a different face from the step face of the light guide,
An external light reflecting surface that reflects external light incident from the front,
A light source arranged on the side of the light guide so as to face the incident end face, and a light source arranged on the front face of the light guide so that the back faces the light guide; external light incident from the front is taken in from the front and emitted to the back; And, while taking in the reflected light of the external light reflected by the external light reflecting surface from the rear surface and emitting it to the front surface, the illumination light emitted from the plurality of step surfaces of the light guide is captured from the rear surface, and And a light control plate that scatters light and emits the light to the front surface.

That is, in the surface light source device according to the present invention, external light which enters from the front, is taken into the light control plate from the front, and is emitted to the back of the light control plate is reflected by the external light reflection surface. Then, the reflected light is taken into the light control plate from the back surface and emitted forward from the front surface, and the illumination light from the light source is taken into the light guide from the incident end face to form a plurality of the light guides. Emitted from the step surface of, the light is taken into the light control plate from the back surface,
According to the surface light source device, the light is scattered by the light control plate and emitted forward from the front surface. According to this surface light source device, the illumination light from the light source is emitted forward, and the external light incident from the front is reflected and reflected by the front. Can be emitted.

Therefore, according to this surface light source device, when external light with sufficient brightness is obtained, only the reflected light of the external light is emitted without turning on the light source, and the brightness of the external light is insufficient. When the light source is turned on to emit both the reflected light of the external light and the illumination light from the light source, the lack of brightness of the reflected light of the external light is compensated for by the illumination light, and the external light is obtained. When not present, the illumination light from the light source can be emitted.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, a surface light source device according to the present invention comprises: a light guide which receives illumination light from an incident end face and emits the light through a plurality of step surfaces on a front surface formed in a stepped surface;
An external light reflecting surface provided on a surface different from the step surface of the light guide, a light source arranged on a side of the light guide so as to face the incident end face, and a front surface of the light guide. Arranged with the back facing, the outside light entering from the front is taken in from the front and emitted to the back, and the reflected light of the outside light reflected by the outside light reflecting surface is taken in from the back and emitted to the front, A light control plate that captures the illumination light emitted from the plurality of step surfaces of the light guide from the back surface, scatters the light, and emits the light to the front surface. Can be emitted forward, and external light incident from the front can be reflected and emitted forward.

According to this surface light source device, when external light of sufficient brightness is obtained, only the reflected light of the external light is emitted without turning on the light source, and when the brightness of the external light is insufficient. By turning on the light source and emitting both the reflected light of the external light and the illumination light from the light source, the lack of brightness of the reflected light of the external light is compensated for by the illumination light, and when the external light is not obtained. Is capable of emitting illumination light from the light source, and thus, for example, a two-way display device that performs both a reflective display using external light and a transmissive display using illumination light from a surface light source device Can be configured without using a transflective plate.

In this surface light source device, the external light reflecting surface is provided by providing a reflecting film on each of a plurality of step surfaces of the light guide, or by providing a reflecting film on the entire back surface of the light guide. It is preferable to form on the plurality of step surfaces or on the back surface of the light guide, so that most of the external light incident from the front of the light control plate is reflected without loss, and the reflected light is reflected by the light. The light can be emitted from the entire front surface of the control plate.

Further, the light control plate has, for example, a transmission axis along a direction inclined at a predetermined angle in a predetermined direction with respect to the normal line, and has a predetermined angle range from the direction along the transmission axis. It is preferable to have a selective scattering characteristic of emitting light incident at an incident angle of not scattering and scattering light incident from another direction and emitting the same.

In the light control plate, a plurality of rows of horizontally long light-transmitting layers are formed parallel to each other with a thin-film scattering layer as a boundary layer. The interface with the scattering layer is an inclined surface inclined at a predetermined angle in a predetermined direction with respect to the normal line of the light control plate, and the inclination of the interface between the both sides of the light transmitting layer and the scattering layer. The light incident on the light-transmitting layer at an incident angle within a predetermined angle range from the transmission axis direction along the direction is emitted without scattering, and the light incident on the light-transmitting layer from another direction is reflected by the scattering layer. It may have a characteristic of being scattered and emitted.

In the case where a light control plate having any of the above characteristics is used, the light control plate is provided with a plurality of stepped surfaces of the light guide, the direction of shift of the transmission axis with respect to the normal on the front surface. It is preferable to arrange the light guide toward the incident end face of the light guide with respect to the normal line.

As described above, by disposing the light control plate having any of the above-described characteristics with respect to the light guide as described above, the light guide is taken in from the incident end face of the light guide and the plurality of steps are provided. Since the illumination light emitted from the surface is incident on the light control plate in a direction intersecting the transmission axis, most of the illumination light emitted from the plurality of step surfaces of the light guide,
The light can be scattered by the light control plate and emitted forward.

Further, of the external light incident from the front surface of the light control plate, the light is incident at an incident angle within a predetermined angle range from the transmission axis direction of the light control plate and is not scattered. The light emitted to the back is reflected by the external light reflection surface and changes its direction, enters the light control plate from a direction intersecting the transmission axis thereof, is scattered by the light control plate, and is scattered by the front surface. While being emitted, external light incident from other directions is scattered by the light control plate and emitted to the back thereof, and is reflected in various directions by the external light reflection surface, and the scattering action of the light control plate is reduced. Since the light is received and emitted to the front surface, most of the external light incident from the front can be scattered and emitted forward.

Therefore, both the illumination light from the light source and the reflected light of external light entering from the front can be diffused in a wide range and emitted forward, and the luminance distribution of the emitted light can be widened.

In this surface light source device, the main emission direction of the reflected light reflected by the external light reflecting surface, scattered by the light control plate and emitted to the front surface thereof is determined by the direction of the transmission axis of the light control plate, Although determined by the angle of inclination of the external light reflecting surface, when the light control plate is disposed as described above with respect to the light guide, for example, the angle of inclination of the transmission axis with respect to the normal to the light control plate is 40 to 40. Within the range of 80 degrees, the external light reflection surface provided on a surface different from the step surface of the light guide, with respect to the back surface of the light control plate, in a direction away from the incident end surface of the light guide. If the inclination of the external light reflecting surface with respect to the normal line of the light control plate is set within a range of 60 to 80 degrees, the external light Of the reflected light with respect to the normal line of the light control plate. The incident end face of the body can be mainly emitted in a direction inclined 5 to 60 degrees to the end surface direction of the opposite side.

Further, in this surface light source device, the light source is provided with illumination brightness control means for controlling the brightness of the illumination light emitted from the light source. It is preferable to set the luminance control condition of the illumination light by the illumination luminance control means so that the luminance of the light emitted in front of the surface light source device falls within a predetermined luminance range according to the illuminance of the external environment. By doing so, even when only the reflected light of the external light is emitted without turning on the light source in an environment where external light of sufficient brightness is obtained, the light source may be used in an environment where the brightness of the external light is insufficient. When the illumination light compensates for the lack of brightness of the reflected light of the external light by emitting both the reflected light of the external light and the illumination light from the light source by turning on the light, and also in an environment where the external light cannot be obtained. From the light source Even when emitting a bright light, in accordance with the illuminance of the environment, it is possible to emit light suitable brightness for the environmental illumination.

[0024]

1 to 3 show a first embodiment of the present invention. FIG. 1 is a side view of a surface light source device, and FIG. 2 is an enlarged view of a part of FIG.

The surface light source device of this embodiment comprises a light guide 1,
The light guide 5 includes a light source 5 disposed on a side of the light guide 1 and a light control plate 8 disposed on a front side of the light guide 1.

The light guide 1 is a transparent plate made of an acrylic resin or the like, and one end surface thereof is an incident end surface 1a for receiving light from the light source 3.

The front surface of the light guide 1 is formed so as to be gradually lowered from the incident end face 1a side to the other end side (narrowing the gap with the back surface of the light guide 1). A stepped surface 2 having a fine pitch, comprising a plurality of step surfaces 2a parallel to each other and a plurality of step surfaces 2b connecting these step surfaces 2a.
And the rear surface is a flat surface.

The plurality of step surfaces 2a of the step-shaped surface 2 are substantially parallel to the back surface of the light guide 1 and are horizontally long and flat along the width direction of the light guide 1 (the length direction of the incident end face 1a). On each of the step surfaces 2a, a mirror reflection film 3 made of a deposited film of a high-reflectance metal such as aluminum or silver is provided over the entire step surface. An external light reflecting surface 3a is formed.

Further, a plurality of step surfaces 2b of the step-shaped surface are provided.
Are rising surfaces of a very small height that rise at an angle of 90 degrees or slightly larger than the step surface 2a, and these step surfaces 2b are respectively located within the light guide 1 from the incident end surface 1a. It is an emission surface of the illumination light taken into the device.

Further, on the back surface of the light guide 1, a specular reflection film 4 made of a deposited film of a high-reflectance metal such as aluminum or silver is provided over the entire back surface.

The light guide 1 receives illumination light from a light source 5 disposed on the side of the light guide 1 from the incident end face 1a, and receives the light from a plurality of step surfaces 2b of a step-shaped surface 2 on the front surface of the light guide. External light that is emitted and enters from the front is reflected toward the front by an external light reflecting surface 3a composed of a reflective film 3 provided on the plurality of step surfaces 2a of the stepped surface 2.

The light source 5 emits illumination light toward the incident end face 1a of the light guide 1. The light source 5 includes a straight tube fluorescent lamp or a neon tube, an EL (electroluminescence) light emitter, a plurality of light sources. A light-emitting body 6 such as an LED array in which LEDs (light-emitting diodes) are arranged, and a reflector 7 that reflects light emitted from the light-emitting body 6,
The light source 5 has a light incident surface 1 on the side of the light guide 1.
a.

On the other hand, the light control plate 8 disposed on the front side of the light guide plate 1 takes in external light incident from the front side and emits it to the back side, and outputs the light to the plurality of stepped surfaces 2a of the light guide body 1.
The reflected light of the external light reflected by the upper external light reflecting surface 3a is taken in from the back and emitted to the front, and the illumination light emitted from the plurality of stepped surfaces 2b of the light guide 1 is taken in from the back. Has the function of scattering the light and emitting it to the front.

FIG. 3 is a side view of a part of the light control plate 8. The light control plate 8 has a transmission axis P along a direction inclined at a predetermined angle θ in a predetermined direction with respect to a normal H thereof. With
It is made of an optical film having a selective scattering property of transmitting light incident at an incident angle within a predetermined angle range φ from a direction along the transmission axis P and scattering incident light from other directions. Hereinafter, the light control plate 8 is referred to as a selective scattering film.

The selective scattering film 8 does not only receive light that enters from one surface and exits to the other surface, but also receives light that enters from the other surface and exits to the one surface. The same selective scattering characteristic is shown, and as shown by an arrow in FIG. 3, light incident at an incident angle within a predetermined angle range φ from the direction along the transmission axis P is transmitted without scattering, and the opposite surface is formed. And scatters incident light from other directions and emits it to the opposite surface.

In this embodiment, as shown in FIGS. 1 and 2, the selective scattering film 8 is provided on the front side of the light guide 1 on a plurality of steps 2 a of the step-shaped surface 2. The back surface of the film is brought close to or in contact with the leading edge, and the direction of deviation of the transmission axis P from the normal line H at the front surface of the film is adjusted with respect to the normal line h of the plurality of step surfaces 2a of the light guide 1. It is arranged toward the incident end face 1a of the light body 1.

That is, the light guide 1 and the selective scattering film 8 are connected to an imaginary surface (not shown) passing through the leading edges of the plurality of step surfaces 2 a of the stepped surface 2 of the light guide 1. The scattering film 8 and the back surface are arranged in a positional relationship parallel to each other.

For this reason, the external light reflecting surface 3 a on the plurality of step surfaces 2 a of the light guide 1 is located away from the incident end face 1 a of the light guide 1 with respect to the back surface of the selective scattering film 8. The stepped surface 2b is inclined so as to decrease the distance from the rear surface of the selective diffusion film 8 toward the rear surface, and the stepped surface 2b rising at an angle of 90 degrees or slightly larger than the stepped surface 2a is formed by the selective diffusion. The film 8 faces the back surface of the film 8 from an oblique direction.

Further, in the surface light source device, as shown in FIG. 1, the light source 5 is provided with an illumination brightness control means 10 for controlling the brightness of the illumination light emitted from the light source 5.

The illumination luminance control means 10 includes an illuminance detector 11 for measuring the illuminance of an external environment (use environment of the surface light source device), and the light source 5 based on the environmental illuminance measured by the illuminance detector 11. And a means for controlling the luminance of the illumination light emitted by the light-emitting body 6. The means for controlling the luminance of the illumination light includes a luminance adjustment circuit 12 and a light source lighting circuit 13.

The illuminance detector 11 adjusts the light receiving surface to the front of the surface light source device (the front surface of the selective scattering film 8) so as to measure the same environmental illuminance as the illuminance of the external light incident on the surface light source device from the front. ).

Further, the brightness adjusting circuit 12 adjusts the brightness of the illumination light emitted from the light source 5 based on the environmental illuminance measured by the illuminance detector 11 to the intensity of the emitted light emitted in front of the surface light source device. The light source lighting circuit 13 adjusts the luminous body 6 of the light source 5 according to the luminance value from the luminance adjustment circuit 12 so that the luminance falls within a predetermined luminance range according to the ambient illuminance. It is driven so as to emit illumination light having the increased brightness.

In the surface light source device, the reflectance of the external light by the external light reflecting surface 3a (the reflectance of the reflective film 3) and the luminance control condition of the illumination light by the illumination luminance control means 10 are determined. The luminance of light emitted in front of the surface light source device is set to fall within a predetermined luminance range according to the illuminance of the external environment.

The above-mentioned surface light source device emits the illumination light from the light source 5 forward and reflects the external light incident from the front and emits the light forward.
The light is turned on when the emitted light having sufficient luminance cannot be obtained only by the reflected light of the external light incident from the front.

First, the emission path of the illumination light from the light source 5 will be described. As shown by the solid line in FIG. 1, the illumination light from the light source 5 is incident on the light guide 1 at its incident end face 1a. And is guided in the light guide 1 in the longitudinal direction.

Then, of the illuminating light guided in the light guide 1 in the longitudinal direction thereof, light directed directly to any one of the plurality of step surfaces 2b on the front surface of the light guide is the step surface 2b.
Out of the light guide 1 toward the front side.

Light other than the light directly traveling to the step surface 2b, ie, the light traveling toward the plurality of step surfaces 2a on the front surface of the light guide and the light traveling toward the back surface of the light guide 1, The light is reflected by the reflection film 3 on the step surface 2a and the reflection film 4 on the back surface of the light guide, changes its direction, and is repeatedly guided in the light guide 1 in the length direction. It is incident on one of them and exits from the step surface 2b.

For this reason, the light guide 1 has its incident end face 1
Most of the illumination light taken from a is emitted from the plurality of step surfaces 2b without loss.

The illumination light emitted in front of the light guide 1 is incident on the selective scattering film 8 disposed on the front face of the light guide 1 with the back face thereof from the back face.

At this time, the selective scattering film 8 is disposed such that the back surface thereof is close to or in contact with the leading edges of the plurality of step surfaces 2a of the light guide 1, and the light guide 1 is
Since the plurality of step surfaces 2b of the light guide 1 face diagonally with respect to the back surface of the selective diffusion film 8, most of the light emitted from the plurality of step surfaces 2b of the light guide 1 is selectively lost without loss. 8 is taken in from the back.

As described above, the direction of the shift of the transmission axis P with respect to the normal H on the front surface of the selective scattering film 8 is changed by the plurality of step surfaces 2 of the light guide 1 as described above.
The illumination light emitted from the plurality of step surfaces 2b of the light guide 1 is disposed toward the incident end surface 1a of the light guide 1 with respect to the normal h of the light guide a.
From the direction intersecting the transmission axis P.

The selective scattering film 8 is shown in FIG.
As shown in the figure, the light has a selective scattering characteristic of transmitting light incident at an incident angle within a predetermined angle range φ from a direction along the transmission axis P and scattering incident light from other directions. Therefore, most of the illumination light emitted from the plurality of step surfaces of the light guide 1 and incident on the selective scattering film 8 from a direction intersecting the transmission axis P is scattered by the selective scattering film 8. The light is emitted forward from the front.

Next, the outgoing path of external light entering from the front will be described. The external light entering from the front, as shown by the broken line in FIG.
Is taken in from the front.

In this case, since the external light is incident at various angles of incidence from various directions, of the external light incident from the front surface of the selective scattering film 8, a predetermined amount is determined from the direction of the transmission axis P of the selective scattering film 8. Is transmitted through the selective scattering film 8 without being scattered and is emitted to the back surface thereof, and the external light incident from other directions is reflected by the selective scattering film 8. And is emitted to the back side.

The light transmitted through the selective scattering film 8 without being scattered and emitted to the rear surface is reflected by the external light reflecting surface 3a on the plurality of step surfaces 2a of the light guide 1, and is directed in the direction. Is incident on the selective scattering film 8 from a direction intersecting the transmission axis P, and is scattered by the selective scattering film 8 and emitted to the front surface thereof.

The light incident from the other direction and scattered by the selective scattering film 8 and emitted to the back surface is not shown in the drawing, but various light is reflected by the external light reflecting surface 3a. The light is reflected in the direction, and the reflected light is emitted to the front surface thereof by the scattering action of the selective scattering film light control plate.

The light scattered by the selective scattering film 8 and emitted to the rear surface is incident on the external light reflecting surface 3a at various angles of incidence, and varies according to the angle of incidence on the reflecting surface 3a. Since the light is reflected in the direction, some of the reflected light is incident on the selective scattering film 8 at an incident angle within a predetermined angle range φ from the transmission axis P direction,
The reflected light passes through the selective scattering film 8 without being scattered and is emitted to the front surface.

In the reflection of the external light, the external light reflecting surface 3a is formed by the reflective film 3 provided on the plurality of step surfaces 2a of the light guide 1 over the entire step surface. Most of the external light incident from the front of the selective scattering film 8 is reflected without loss, and the reflected light can be emitted from the entire front surface of the selective scattering film 8.

That is, the reflection film 3 is formed on the light guide 1
Is provided only on the plurality of step surfaces 2a, but the step surface 2b between the plurality of step surfaces 2a rises at an angle of 90 degrees or slightly larger than the step surface 2a. Since the rising surface has a small height, the interval between the plurality of reflecting films 3 provided on the plurality of step surfaces 2a is extremely small. Therefore, the external light reflecting surface 3a is provided for the external light reflecting surface 3a. Most reflect.

It should be noted that some of the external light that enters from the front and is scattered by the selective scattering film 8 includes light that exits from the back surface of the selective scattering film 8 toward the step surface 2b of the light guide 1. The light is incident on the light guide 1 from the step surface 2b, and the external light incident on the light guide 1 is
Reflected by the reflective film 4 on the back surface of the light guide 1,
The light is emitted from any of the plurality of step surfaces 2b and is emitted forward together with the light reflected by the external light reflecting surface 3a.

As described above, the surface light source device transmits external light that enters from the front thereof, is taken into the selective scattering film 8 from the front side, and is emitted to the rear surface of the selective scattering film 8. External light reflecting surface 3 on a plurality of step surfaces 2b
a of the selective scattering film 8
The illumination light from the light source 5 is introduced into the light guide 1 from the incident end face 1a and emitted from the plurality of step surfaces 2b of the light guide 1. Then, the light is taken into the selective scattering film 8 from the back surface, and the selective scattering film 8
According to this surface light source device, the illumination light from the light source 5 is emitted forward, and external light incident from the front is reflected and emitted forward. be able to.

Therefore, according to this surface light source device, when external light with sufficient brightness is obtained, only the reflected light of the external light is emitted without turning on the light source 5, and the brightness of the external light is insufficient. In this case, the light source 5 is turned on to emit both the reflected light of the external light and the illumination light from the light source 5, thereby compensating for the lack of luminance of the reflected light of the external light with the illumination light. Is not obtained, the illumination light from the light source 5 can be emitted.

Further, as described above, the selective scattering film 8 has a transmission axis P along a direction inclined at a predetermined angle θ in a predetermined direction with respect to the normal H, and the transmission axis P
Has a selective scattering property of transmitting light incident at an incident angle within a predetermined angle range φ from a direction along and scattering incident light from other directions.
On the front side of the light guide 1, the direction of shift of the transmission axis P with respect to the normal line H on the front surface of the film is described.
Are arranged toward the direction of the incident end face 1a of the light guide 1 with respect to the normal line h of the plurality of step surfaces 2a, the light guide plate 1 is taken into the light guide 1 from the incident end face 1a. The illumination light emitted from the plurality of step surfaces 2b enters the selective scattering film 8 in a direction intersecting the transmission axis P thereof.

Therefore, according to the surface light source device, most of the illumination light emitted from the plurality of stepped surfaces 2b of the light guide 1 is scattered by the selective scattering film 8 and emitted forward from the front surface. Can be.

Further, of the external light incident from the front surface of the selective scattering film 8, the incident light is incident at an incident angle within a predetermined angle range φ from the transmission axis P direction of the selective scattering film 8 and is not scattered. The light emitted to the back of the selective scattering film 8 is reflected by the external light reflecting surface 3a to change its direction, and is incident on the selective scattering film 8 from a direction intersecting the transmission axis P thereof. Outside light scattered by the film 8 and emitted to the front surface thereof, and external light incident from another direction is scattered by the selective scattering film 8 and emitted to the back surface thereof, and reflected in various directions by the external light reflecting surface 3a. Then, since the light is scattered by the selective scattering film 8 and emitted to the front surface, most of the external light incident from the front can be scattered and emitted forward.

Therefore, according to the above-mentioned surface light source device, both the illumination light from the light source 5 and the reflected light of the external light entering from the front are diffused in a wide range and emitted to the front, and the luminance distribution of the emitted light is broadened. can do.

Further, according to the surface light source device, the illumination light taken into the light guide 1 from the incident end face 1a is emitted from the plurality of step surfaces 2b on the front surface of the light guide 1. Since the external light reflecting surface 3a is formed by providing the reflection film 3 on a plurality of step surfaces 2a different from the plurality of step surfaces of the light guide 1, the light guide 5 emits light from the light source 5. 1 and the reflectance of the external light reflected by the external light reflecting surface 3a can be independently selected from the illumination light emitted from the plurality of stepped surfaces 2b and the external light reflecting surface 3a. The efficiency of using the illumination light from the light source 5 is increased by increasing the light emission rate, and the external light reflecting surface 3
It is possible to increase the reflectance of the external light due to “a” and increase the use efficiency of the external light.

In the above surface light source device, the light source 5 is provided with illumination brightness control means 10 for controlling the brightness of the illumination light emitted from the light source 5, and the external light reflecting surface 3 is provided.
The reflectance of the external light by a and the luminance control condition of the illumination light by the illumination luminance control means 10 are determined in advance according to the illuminance of the external environment such that the luminance of the light emitted in front of the surface light source device is predetermined. Since the luminance is set to be in the luminance range, it is possible to emit light having a luminance suitable for the environmental illuminance in an environment of a wide illuminance range from low illuminance to high illuminance.

That is, the preferable luminance of the light emitted from the surface light source device depends on the illuminance of the external environment. Even if the luminance of the emitted light is the same, the emitted light may be too dazzling or too dark depending on the illuminance of the environment. .

Therefore, in this embodiment, the reflectance of the external light reflecting surface 3a (the reflectance of the reflecting film 3) is too dazzling even in an environment of high illuminance exceeding 100,000 lux, for example, under direct sunlight in summer. The emission luminance is set so as to obtain emission light having a suitable luminance, and the emission luminance by both the reflected light of the external light reflected by the external light reflection surface 3a and the illumination light from the light source 5 (however, When the ambient illuminance is almost 0 lux, the luminance of the illuminating light emitted from the light source 5 is changed according to the environmental illuminance so that the emission luminance due to only the illuminating light) becomes a suitable luminance according to the environmental illuminance. It is controlled by the illumination brightness control means 10.

Therefore, according to the surface light source device described above, even when only the reflected light of the external light is emitted without turning on the light source 5 in an environment where the external light of sufficient brightness can be obtained, the brightness of the external light can be reduced. When the light source 5 is turned on in an insufficient environment to emit both reflected light of external light and illumination light from the light source 5 to compensate for the lack of luminance of the reflected light of external light by the illumination, Even when the illumination light from the light source 5 is emitted in an environment where light cannot be obtained, it is possible to emit light having a luminance suitable for the environmental illuminance in accordance with the illuminance of the environment.

Moreover, the above-mentioned surface light source device emits light having a luminance suitable for environmental illuminance only by reflected light of external light without turning on the light source 5 in an environment where external light of sufficient brightness can be obtained. Also, in an environment where the brightness of the external light is insufficient, the light source 5 is turned on to emit both the reflected light of the external light and the illumination light from the light source 5, thereby reducing the reflected light of the external light. Even when the lack of luminance is compensated for by the illumination, the luminance of the illumination light emitted from the light source 5 is adjusted so that the emission luminance by both the reflected light of the external light and the illumination light becomes a luminance suitable for environmental illuminance. Since the control is sufficient, the power consumption of the light source 5 may be small.

The surface light source device is used, for example, in a two-way display device that displays both a reflection type display using external light and a transmission type display using illumination light from the surface light source device. Since this surface light source device can emit the illumination light from the light source 5 forward and reflect the external light incident from the front and emit the light forward, the two-way display device is It can be configured without using a transflective plate.

That is, when a two-way display device is constructed using the above-mentioned surface light source device, a liquid crystal display element is provided on the front side of the surface light source device as shown by a virtual line (two-dot chain line) in FIG. It is only necessary to dispose a non-light emitting type display 15 such as.

Since the two-way display device does not require a transflective plate, a bright image can be displayed by efficiently using both the illumination light from the surface light source device and the external light incident from the front. .

That is, in the two-way display device using the transflective reflector, the illumination light from the surface light source device passes through the transflector at a transmittance according to the reflection / transmission characteristics of the transflector. The external light incident on the display body from the rear surface thereof and from the front of the display body transmits through the semi-transmissive reflection plate at a reflectance according to the reflection / transmission characteristics of the semi-transmissive reflection plate. Since the light enters the display body from the back, neither the illumination light from the surface light source device nor the external light entering from the front can be used efficiently.

On the other hand, in the two-way display device using the surface light source device of the above embodiment, the surface light source device theoretically emits light from the light source 5 with almost 100% emission efficiency. Also, external light incident from the front is reflected with a reflection efficiency of almost 100%, and furthermore, since a semi-transmissive reflector is not required, both the illumination light from the surface light source device and the external light incident from the front are efficient. By using this, a bright image can be displayed.

In the two-way display device, the surface light source device emits both illumination light from the light source 5 and reflected light of external light incident from the front as light having a wide luminance distribution.
Has a wide viewing angle.

In FIG. 1, the step-shaped surface 2 of the light guide 1 is shown in a greatly enlarged manner for convenience.
The smaller the pitch of the step surface 2b, the better.

That is, for example, the non-light emitting display 15
When a dot matrix type liquid crystal display element is used, the pitch of the step surface 2b of the step-shaped surface 2 of the light guide 1 is substantially the same as the pixel pitch of the liquid crystal display element, or about several times the pixel pitch. It is preferred that

In this way, the illumination light from the light source 3 is emitted from the plurality of stepped surfaces 2b of the light guide 1 at the above-mentioned pitch, and the light is scattered by the selective scattering film 8 to provide a substantially uniform luminance distribution. Therefore, the light is emitted to all the pixel portions of the liquid crystal display element, and a good image without missing pixels can be displayed.

In the environment where external light is obtained, the two-way display device is similar to a normal reflection type liquid crystal display device. ) Is used by selecting the orientation of the screen so as to mainly take in external light from the direction inclined in the direction of (5) in the direction of the lower edge of the screen (rightward in FIG. 1) with respect to the normal of the screen. Observed from a direction inclined by 60 degrees.

Therefore, when a two-way display device is constructed using the above-mentioned surface light source device, the main light emitting direction of the reflected light (scattered light) of the external light is determined by the method of the selective scattering film 8. The surface light source device is designed so as to be inclined at an angle of 5 to 60 degrees in one direction with respect to the line H, and the main emission direction of the reflected light of the external light is directed to the viewing direction of the display of the display device. It is desirable to arrange.

That is, in the surface light source device, the selective scattering film 8 reflected by the external light reflecting surface 3a
The main emission direction of the reflected light that is scattered by and is emitted to the front surface thereof is determined by the direction of the transmission axis P of the selective scattering film 8,
It is determined by the inclination angle of the external light reflecting surface 3a.

Then, as shown in FIG. 2, the selective scattering film 8 is placed on the front surface of the selective scattering film 8.
Of the transmission axis P with respect to the normal H of the light guide 1
In the case of disposing the light guide 1 toward the incident end face 1a with respect to the normal h of the plurality of step surfaces 2a, for example, the inclination angle θ of the transmission axis P with respect to the normal H of the selective scattering film 8 In the range of 40 to 80 degrees, and the external light reflecting surface 3a composed of the reflecting film 3 provided on the plurality of step surfaces 2b of the light guide 1 The inclination of the external light reflecting surface 3a with respect to the normal line H of the selective scattering film 8 is inclined toward the direction away from the incident end surface 1a of the light guide 1 so as to reduce the distance between the selective scattering film 8 and the back surface. If α is set in the range of 60 to 80 degrees, the reflected light of the external light is reflected by the selective scattering film 8 as shown in broken line F in FIG.
Is mainly emitted in the direction of the end face opposite to the incident end face 1a of the light guide 1 with respect to the normal H, and the emission angle (the angle with respect to the normal H of the selective scattering film 8) γ is 5
It can be in the range of up to 60 degrees.

The inclination angle α of the external light reflecting surface 3a with respect to the normal H of the selective scattering film 8 is determined by the inclination angle of the external light reflecting surface 3a with respect to the back surface of the selective scattering film 8 (the inclination angle of the selective scattering film 8). Since α + β = 90 degrees with respect to the deviation angle β between the normal line H and the normal line h of the external light reflecting surface 3a, reflected light of external light is mainly emitted in the above-described direction. In this case, the selective scattering film 8 is set so that its normal H is set to 10-30 in the direction opposite to the incident end face 1a of the light guide 1 with respect to the normal h of the plurality of step surfaces 2a of the light guide 1.
° may be arranged at an angle.

Further, the surface light source device is provided with an illumination brightness control means 10 for controlling the brightness of the illumination light emitted from the light source 5 in the light source 5, so that the reflectance of the external light by the external light reflecting surface 3a and the The luminance control condition of the illumination light by the illumination luminance control means 10 is set such that the luminance of the light emitted in front of the surface light source device is within a predetermined luminance range according to the illuminance of the external environment. Therefore, the two-way display device using the surface light source device can obtain a display with a screen luminance suitable for the environmental illuminance in a use environment in a wide illuminance range from low illuminance to high illuminance. .

In the two-way display device, external light incident from the front passes through the display body 15 to enter the surface light source device, and light emitted from the surface light source device (external light is obtained). In the environment, the reflected light of the external light or both the reflected light of the external light and the illumination light from the light source 5, and the illumination light from the light source 5 in an environment where the external light cannot be obtained, pass through the display body 15. Since the light is emitted forward, the screen luminance is determined by the reflectance of external light by the external light reflecting surface 3a of the surface light source device, the luminance of illumination light from the light source 5, and the transmittance of the display 15.

Therefore, when the surface light source device is used for a two-way display device, the reflectance of the external light by the external light reflecting surface 3a and the luminance control condition of the illumination light by the illumination luminance control means 10 are set as follows. The screen brightness may be set so as to be in a predetermined brightness range according to the illuminance of the external environment.

That is, a preferable screen luminance according to the environmental illuminance is, for example, 20 to 200 nits at an environmental illuminance of 50 lux such as a street lamp at night, such as in a room when the daytime or nighttime indoor lighting is turned on. 30-300 nits at 1000 lux of ambient illuminance, 30,000 like a shade on a sunny day
Lux ambient illuminance is 400-4000 nits.

Therefore, when the surface light source device is used in a two-way display device, the luminance of the illumination light from the light source 5 is controlled by the illumination luminance control means 10 so that the screen luminance with respect to the environmental illuminance is 50 lux. 20-200 nits, 30-300 nits at 1000 lux ambient illuminance,
What is necessary is just to control according to environmental illuminance so that it may become the brightness | luminance represented by the quadratic function which respectively satisfies the range of 400-4000 nits in environmental illuminance of 30,000 lux.

In the above embodiment, the reflection film 4 is provided on the back surface of the light guide 1. However, the reflection film 4 on the back surface may be omitted. Illumination light taken into the light body 1 from the incident end surface 1a can be totally reflected at the interface between the back surface of the light guide and the outside air (air), and can be guided in the length direction of the light guide 1.

Further, in the above embodiment, the selective scattering film 8 having the selective scattering characteristic shown in FIG. 2 was used as the light control plate disposed on the front side of the light guide 1. In addition to the selective scattering film 8, external light incident from the front is taken in from the front and emitted to the back, and the reflected light of the external light reflected by the external light reflecting surface 3a is taken in from the back and emitted to the front. In addition, it is sufficient that the illumination light emitted from the plurality of stepped surfaces 2b of the light guide 1 is taken in from the back surface, and the light is scattered and emitted to the front surface.

FIG. 4 is a side view of a part of another light control plate, and this light control plate 9 is made of a louver-shaped optical film. Hereinafter, the light control plate 9 is referred to as a louver film.

The louver film 9 is formed by forming a plurality of rows of light-transmitting layers 9a extending in one direction in parallel with each other with a thin scattering layer 9b as a boundary layer. The interface between the both sides and the scattering layer 9b is at a predetermined angle θ ′ in a predetermined direction with respect to a normal H ′ of the film.
The slope is inclined. The light transmitting layer 9a
Is made of a colorless transparent resin or the like, and the scattering layer 9b
Is made of white transparent resin or the like.

The louver film 9 is formed of the light transmitting layer 9
has a transmission axis P 'along the inclination direction of the interface between the both sides of the light transmission layer 9a and the scattering layer 9b, and enters the light transmission layer 9a at an incident angle φ' within a predetermined angle range from the direction of the transmission axis P '. Of the light-transmitting layer 9 from other directions.
The light has a characteristic of being scattered and emitted by the scattering layer 9b.

The louver film 9 is the same for the light that enters from one surface and exits to the other surface and the light that enters from the other surface and exits to the one surface. As shown by the arrows in FIG. 4, the light-transmitting layer 20 has a scattering characteristic, and one edge of one of the adjacent scattering layers 9b (indicated by an arrow in FIG. 4). A straight line passing through the edge on the film front side) and the other edge of the other scattering layer 9b (edge on the film back side), and the other edge of the one scattering layer 9b (edge on the film back side); Light incident at an incident angle φ 'in an angle range formed by a straight line passing through one end edge (the edge on the film front side) of the other scattering layer 9b is transmitted without scattering and emitted to the opposite surface, and is emitted to the other surface. The incident light from the direction is scattered and emitted to the opposite surface.

In the case where the louver film 9 is used,
Similarly to the above-described embodiment, the louver film 9 is arranged such that the back surface of the film is brought close to or in contact with the leading edges of the plurality of step surfaces 2a of the stepped surface 2 on the front surface side of the light guide 1, and the The direction of deviation of the transmission axis P ′ with respect to the normal H ′ is determined by the plurality of step surfaces 2 a
May be arranged toward the incident end face 1a of the light guide 1 with respect to the normal h.

As described above, by disposing the louver film 9 with respect to the light guide 1 as described above, the light guide 1
Since the illumination light which is taken in from the incident end face 1a and emitted from the plurality of step surfaces 2b enters the louver film 9 in a direction intersecting with the transmission axis P ', a plurality of the light guides 1 Most of the illuminating light emitted from the step surface 2b can be scattered by the louver film 9 and emitted forward.

Of the external light incident from the front surface of the louver film 9, the incident light φ ′ within a predetermined angle range from the direction of the transmission axis P ′ of the louver film 9 is not scattered. The light emitted to the back of the louver film 9 is reflected by the external light reflecting surface 3a and changes its direction, and enters the louver film 9 in a direction intersecting the transmission axis P '. While being scattered by and emitted to the front surface, external light incident from another direction is scattered by the louver film 9 and emitted to the rear surface, and is reflected in various directions by the external light reflecting surface 3a, The louver film 9
Of the external light incident from the front, it can be scattered and emitted to the front.

Therefore, the illumination light from the light source 5 is also
The reflected light of the external light entering from the front can also be diffused in a wide range and emitted forward, thereby broadening the luminance distribution of the emitted light.

When the louver film 9 is used, the main emission direction of the reflected light reflected by the external light reflecting surface 3a, scattered by the louver film 9 and emitted to the front surface of the louver film 9 is Although determined by the direction of the transmission axis P 'and the inclination angle of the external light reflecting surface 3a, when the louver film 9 is arranged as described above with respect to the light guide 1, for example, the normal line of the louver film 9 is used. The inclination angle of the transmission axis P ′ with respect to H ′ is within a range of 40 to 80 degrees, and the direction in which the external light reflecting surface 3 a is away from the incident end surface 1 a of the light guide 1 with respect to the back surface of the louver film 9. And the inclination angle of the external light reflecting surface 3a with respect to a normal line H 'of the louver film 9 is reduced. If the angle is set within the range of 0 to 80 degrees, the reflected light of the external light is directed to the end surface direction opposite to the incident end surface 1a of the light guide 1 with respect to the normal line H 'of the louver film 9 to the end surface. The light can be mainly emitted in a direction inclined by up to 60 degrees.

In the first embodiment, the reflection film 3 is provided on the plurality of step surfaces 2a of the light guide 1, and the external light reflection surface 3a is formed by the reflection films 3. The external light reflecting surface may be formed on another surface as long as the surface is different from the plurality of step surfaces 2b which are the illumination light emitting surfaces of the light guide 1.

FIG. 5 is a side view of a surface light source device according to a second embodiment of the present invention.
The reflective surface is not provided on the plurality of step surfaces 2a of the step-shaped surface 2 of the above, and these step surfaces 2a are light transmitting surfaces, and the light guide 1 is made of aluminum or silver or the like on the entire rear surface. A specular reflection film 4 made of a vapor deposition film of a high reflectance metal is provided, and the reflection film 4 forms an external light reflection surface 4a.

In this embodiment, a plurality of step surfaces 2a of the light guide plate 1 are used as light transmitting surfaces, and an external light reflecting surface 4a is formed on the back surface of the light guide 1. The other configuration is the same as that of the first embodiment described above, and the light source 5 and the illumination brightness control means 10 have the same configuration as that of the first embodiment, and are further disposed on the front side of the light guide 1. Since the light control plate is also the selective scattering film 8 or the louver film 9 described above, the overlapping description is given the same reference numeral in the drawings and omitted.

According to the surface light source device of this embodiment, since the external light reflecting surface 4a is formed on the entire back surface of the light guide 1, the light control plate (selective scattering film 8 or louver film 9) can be used. Most of the external light incident from the front is reflected without further loss, and the reflected light is reflected by the light control plate 8,
9 can be emitted from the entire front surface.

Also in this embodiment, a reflection film 4 is provided on a surface (the back surface of the light guide) different from the plurality of step surfaces 2b, which are the illumination light emission surfaces of the light guide 1, and the external light reflection surface is provided. 4a
Is formed, the emission ratio of illumination light emitted from the light source 5 and guided by the light guide 1 and emitted from the plurality of step surfaces 2b, and the reflectance of external light by the external light reflection surface 4a Can be independently selected, so that the efficiency of use of the illumination light from the light source 5 is increased by increasing the emission rate of the illumination light, and the reflectance of the external light by the external light reflection surface 4a is increased. And the efficiency of use of external light can be increased.

The above-mentioned surface light source device is not limited to a two-way display device, and can be widely used as, for example, an illumination panel that uses light from a light source arranged on the side and external light incident from the front. it can.

Further, in the above embodiment, one end face of the light guide plate 1 is the incident end face 1a.
The end faces at both ends are the incident end faces, and the front face is formed as a step-shaped surface that gradually decreases from both ends toward the middle part of the light guide. It may be something.

When using a light guide having such a structure,
A light control plate in which light sources are arranged on both sides of an incident end face at both ends of the light guide plate, and which has a symmetrical scattering characteristic with respect to a front side of the light guide, with an intermediate portion in a longitudinal direction interposed therebetween. Should be arranged.

[0111]

According to the surface light source device of the present invention, there is provided a light guide which receives illumination light from an incident end face and emits the light through a plurality of step surfaces on a front surface formed in a stepped surface, and the step surface of the light guide. An external light reflecting surface provided on a different surface, and a light source arranged on the side of the light guide so as to face the incident end surface,
The light guide is arranged with the rear surface facing the front surface, takes in external light incident from the front, emits the light to the rear surface, and captures the reflected light of the external light reflected by the external light reflecting surface from the rear surface. And a light control plate for taking in the illumination light emitted from the plurality of step surfaces of the light guide from the back surface, scattering the light, and emitting the light to the front surface. Therefore, the illumination light from the light source can be emitted forward, and external light incident from the front can be reflected and emitted forward.

According to this surface light source device, when external light of sufficient brightness can be obtained, only the reflected light of external light is emitted without turning on the light source, and when the brightness of external light is insufficient. By turning on the light source and emitting both the reflected light of the external light and the illumination light from the light source, the lack of brightness of the reflected light of the external light is compensated for by the illumination light, and when the external light is not obtained. Is capable of emitting illumination light from the light source, and thus, for example, a two-way display device that performs both a reflective display using external light and a transmissive display using illumination light from a surface light source device Can be configured without using a transflective plate.

In this surface light source device, the external light reflecting surface may be provided by providing a reflection film on each of a plurality of step surfaces of the light guide, or by providing a reflection film on the entire back surface of the light guide. It is preferable to form on the plurality of step surfaces or on the back surface of the light guide, so that most of the external light incident from the front of the light control plate is reflected without loss, and the reflected light is reflected by the light. The light can be emitted from the entire front surface of the control plate.

Further, the light control plate has, for example, a transmission axis along a direction inclined at a predetermined angle with respect to a normal to the normal line, and within a predetermined angle range from the direction along the transmission axis. It is preferable to have a selective scattering characteristic of emitting light incident at an incident angle of not scattering and scattering light incident from another direction and emitting the same.

In the light control plate, a plurality of rows of light-transmitting layers extending in one direction are formed in parallel with each other with a thin scattering layer as a boundary layer. The interface with the scattering layer is an inclined surface inclined at a predetermined angle in a predetermined direction with respect to the normal line of the light control plate, and the inclination of the interface between the both sides of the light transmitting layer and the scattering layer. The light incident on the light-transmitting layer at an incident angle within a predetermined angle range from the transmission axis direction along the direction is emitted without scattering, and the light incident on the light-transmitting layer from another direction is reflected by the scattering layer. It may have a characteristic of being scattered and emitted.

When a light control plate having any of the above-mentioned characteristics is used, the direction of the shift of the transmission axis with respect to the normal on the front surface of the light control plate is adjusted by a plurality of step surfaces of the light guide. It is preferable to arrange the light guide toward the incident end face of the light guide with respect to the normal line.

As described above, by disposing the light control plate having any of the above characteristics with respect to the light guide as described above, the light control plate is taken in from the incident end face of the light guide and the plurality of steps are formed. Since the illumination light emitted from the surface is incident on the light control plate in a direction intersecting the transmission axis, most of the illumination light emitted from the plurality of step surfaces of the light guide,
The light can be scattered by the light control plate and emitted forward.

Further, of the external light incident from the front surface of the light control plate, the light enters the light control plate at an incident angle within a predetermined angle range from the transmission axis direction of the light control plate and is not scattered. The light emitted to the back is reflected by the external light reflection surface and changes its direction, enters the light control plate from a direction intersecting the transmission axis thereof, is scattered by the light control plate, and is scattered by the front surface. While being emitted, external light incident from other directions is scattered by the light control plate and emitted to the back thereof, and is reflected in various directions by the external light reflection surface, and the scattering action of the light control plate is reduced. Since the light is received and emitted to the front surface, most of the external light incident from the front can be scattered and emitted forward.

Therefore, both the illumination light from the light source and the reflected light of the external light entering from the front can be diffused over a wide range and emitted forward, and the luminance distribution of the emitted light can be widened.

In this surface light source device, the main emission direction of the reflected light reflected by the external light reflecting surface, scattered by the light control plate and emitted to the front surface thereof is determined by the direction of the transmission axis of the light control plate, Although determined by the angle of inclination of the external light reflecting surface, when the light control plate is disposed as described above with respect to the light guide, for example, the angle of inclination of the transmission axis with respect to the normal to the light control plate is 40 to 40. Within the range of 80 degrees, the external light reflection surface provided on a surface different from the step surface of the light guide, with respect to the back surface of the light control plate, in a direction away from the incident end surface of the light guide. If the inclination of the external light reflecting surface with respect to the normal line of the light control plate is set within a range of 60 to 80 degrees, the external light Of the reflected light with respect to the normal line of the light control plate. The incident end face of the body can be mainly emitted in a direction inclined 5 to 60 degrees to the end surface direction of the opposite side.

Further, in this surface light source device, the light source is provided with illumination brightness control means for controlling the brightness of the illumination light emitted from the light source, and the reflectance of the external light by the external light reflecting surface and It is preferable to set the luminance control condition of the illumination light by the illumination luminance control means so that the luminance of the light emitted in front of the surface light source device falls within a predetermined luminance range according to the illuminance of the external environment. By doing so, even when only the reflected light of the external light is emitted without turning on the light source in an environment where external light of sufficient brightness is obtained, the light source may be used in an environment where the brightness of the external light is insufficient. When the illumination light compensates for the lack of brightness of the reflected light of the external light by emitting both the reflected light of the external light and the illumination light from the light source by turning on the light, and also in an environment where the external light cannot be obtained. From the light source Even when emitting a bright light, in accordance with the illuminance of the environment, it is possible to emit light suitable brightness for the environmental illumination.

[Brief description of the drawings]

FIG. 1 is a side view of a surface light source device according to a first embodiment of the present invention.

FIG. 2 is an enlarged view of a part of FIG.

FIG. 3 is a side view of a part of a light control plate used in the surface light source device.

FIG. 4 is a side view of a part of another light control plate.

FIG. 5 is a side view of a surface light source device according to a second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Light guide 1a ... Incident end face 2 ... Stepped surface 2a ... Step surface 2b ... Step surface 3,4 ... Reflection film 3a, 4a ... External light reflection surface 5 ... Light source 8 ... Light control plate (selective scattering film) 9 ... Light control plate (louver film) 10 ... Illumination brightness control means

Claims (7)

[Claims] At least one end surface is an incident end surface, and a front surface is formed as a step-shaped surface including a plurality of step surfaces and a plurality of step surfaces connecting these step surfaces, and illumination light is transmitted from said incident end surface. A light guide that receives and emits light from the plurality of step surfaces, an external light reflecting surface provided on a surface different from the step surface of the light guide, and that reflects external light incident from the front to the front; A light source arranged on the side of the light body so as to face the incident end face, the light source is arranged with the back face facing the front face of the light guide, and external light incident from the front is taken in from the front face and emitted to the back face, While taking in the reflected light of the external light reflected by the external light reflecting surface from the back surface and emitting the light to the front surface, the illumination light emitted from the plurality of step surfaces of the light guide is captured from the back surface, and the light is captured. A light control plate that scatters and emits light to the front Surface light source device characterized by comprising. 2. The surface light source according to claim 1, wherein the external light reflecting surface is formed by a plurality of reflecting films provided on the plurality of stepped surfaces of the light guide, respectively. apparatus. 3. The surface light source device according to claim 1, wherein the external light reflection surface is formed by a reflection film provided on the entire back surface of the light guide. 4. The light control plate has a transmission axis extending in a direction inclined at a predetermined angle in a predetermined direction with respect to a normal line thereof, and has an incident angle within a predetermined angle range from the direction along the transmission axis. It has a selective scattering characteristic of emitting light incident at an angle without scattering, and scattering and emitting light incident from other directions,
The light control plate is arranged such that the direction of shift of the transmission axis with respect to the normal line on the front surface thereof is directed toward the incident end surface of the light guide with respect to the normal lines of the plurality of step surfaces of the light guide. The surface light source device according to claim 1, wherein: 5. The light control plate according to claim 1, wherein a horizontally long light-transmitting layer is formed in a plurality of rows parallel to each other with a thin-film scattering layer as a boundary layer. The interface with the scattering layer is an inclined surface inclined at a predetermined angle in a predetermined direction with respect to the normal line of the light control plate, and the inclination of the interface between the both sides of the light transmitting layer and the scattering layer. The light incident on the light-transmitting layer at an incident angle within a predetermined angle range from the transmission axis direction along the direction is emitted without scattering, and the light incident on the light-transmitting layer from another direction is reflected by the scattering layer. The light control plate has a characteristic of emitting light after being scattered, and the light control plate adjusts the direction of deviation of the transmission axis with respect to the normal at the front surface of the light control plate with respect to the normals of the plurality of step surfaces of the light guide. The surface light source according to claim 1, wherein the surface light source is arranged toward an incident end face of the light body. Location. 6. The light guide plate according to claim 1, wherein an inclination angle of the transmission axis with respect to a normal line of the light control plate is in a range of 40 to 80 degrees, and the external light reflection surface is provided with the light guide with respect to a back surface of the light control plate. The light control plate is inclined toward the direction away from the incident end surface of the body so as to reduce the distance between the light control plate and the back surface, and the inclination angle of the external light reflection surface with respect to the normal line of the light control plate is 60 to 80 degrees. The surface light source device according to claim 4, wherein the surface light source device is within a range. 7. The light source includes illumination brightness control means for controlling the brightness of illumination light emitted from the light source. The reflectance of the external light by the external light reflection surface and the illumination brightness control means determine the external light reflectance. The brightness control condition of the illumination light is set such that the brightness of light emitted in front of the surface light source device falls within a predetermined brightness range according to the illuminance of an external environment. 2. The surface light source device according to 1.