JPH06250024A - Surface light source device - Google Patents

Abstract

PURPOSE:To improve the availability of a light obtained from a tubular light source. CONSTITUTION:A reflection mirror 14 for light source is made to be a semi- elliptical shape in the cross-sectional view, a transmitted light from the tubular light source 13 is prevented from returning to the tubular light source 13 again after reflecting by the reflection mirror 14 for light source. The rear reflection surface 22 of a light transmission plate 12 is formed to have a curvature where the larger the oblique angle becomes the far it is separated from the tubular light source 13 and the light exit angle from the front surface 23 is uniformized. The front light exit surface 23 of the light transmission plate 12 is formed to be a sawtooth shape in the cross-sectional view by means of many prisms 25 and the transmitted light is made to approach the normal direction of the front light exit surface 23. The vertex angle of the prism 25 is made acuter as the prism is separated farther from the tubular light source 13 and the final light is made to approach the normal direction of the front light exit surface 23 with the angle conformed with the respective optical paths of various light rays radiated within the light transmission plate 12.

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 used as a backlight for a liquid crystal display device or the like.

[0002]

2. Description of the Related Art A conventional surface light source device is constructed as shown in FIG. In FIG. 16, 1 is a tubular light source, 2 is a light source reflecting mirror, 4 is a light guide plate, 5 is a roughened surface of the exit surface which is the front surface of the light guide plate 4, and 6 is attached to the reflection surface which is the rear surface of the light guide plate 4. It is a rear reflector that is worn.

As shown in FIG. 16, the light emitted from the tubular light source 1 enters the light guide plate 4 directly or after being reflected by the light source reflecting mirror 2.

The light incident on the light guide plate 4 propagates inside the light guide plate 4 while being reflected by the rear surface reflecting mirror 6 and the like.

Further, the emission surface, which is the front surface of the light guide plate 4, does not emit to the outside unless the angle is equal to or more than the total reflection angle. Therefore, in order to emit the light forward, as shown in FIG. 16, the emission surface is subjected to the rough surface treatment 5, or a prism is provided to enhance the light in the direction normal to the emission surface,
A diffusion sheet may be applied to make the surface light source more uniform.

Further, the reflecting surface (rear reflecting mirror) 6 which is the rear surface of the light guide plate 4 may be roughened, or the reflecting surface 6 may be inclined in a curved shape as shown in FIG.

[0007]

In the conventional example, in order to propagate the light from the tubular light source 1 to a position away from the tubular light source 1, total reflection is repeated in the light guide plate so that the amount of light on the display surface is reduced. It is necessary to devise the shape of the reflecting surface or the way of roughening the surface so that it becomes uniform.

However, repeating the total reflection in this way causes a light loss. In addition, making the reflecting surface a rough surface causes a decrease in light transmittance. For these reasons, the light efficiency has been significantly deteriorated in the past.

Further, the light source reflecting mirror 2 for making the light from the tubular light source 1 incident on the light guide plate 4 simply covers the tubular light source, but since a thin white film is used as the material thereof, its shape is However, the light source reflecting mirror 2 was brought into contact with the tubular light source 1 as much as possible to stabilize its shape in a substantially circular shape. However, in that case, the number of bonding surfaces between the light source reflecting mirror 2 and the tubular light source 1 increases. Then, even when the light from the tubular light source 1 strikes this contact surface, it is reflected to the light guide plate 4 side as attenuated light, and the original illuminance characteristic of the tubular light source 1 cannot be fully utilized.

In view of the above problems, it is an object of the present invention to provide a surface light source device capable of improving the utilization efficiency of light obtained from a tubular light source.

[0011]

As shown in FIGS. 1 and 2, a means for solving the problems according to the present invention is a translucent light guide plate 12 for illuminating an object to be illuminated from behind in a planar manner, and one of the light guide plates 12. The light guide plate 12 is provided with a tubular light source 13 arranged at a side end portion, and a light source reflecting mirror 14 arranged around the tubular light source 13 and reflecting light diverging from the tubular light source 13 to the light guide plate 12 side.
Is an end incidence surface 21 on which light from the tubular light source 13 is incident at one end, a rear reflection surface 22 that reflects rearward light inside toward the front, and a rear reflective surface 22 that reflects internal light forward. In a surface light source device having a front emission surface 23 that emits light to the illuminated side, the light source reflecting mirror 14 is formed in a semi-elliptical shape in cross section with an oblateness of more than 1, and the light guide plate 1 is provided.
The rear reflecting surface 22 is formed in a parabolic shape so that the inclination angle becomes larger as the distance from the tubular light source 13 increases, and a large number of prisms 25 of the tubular light source 13 are provided on the front exit surface 23 of the light guide plate 12. The prisms 25 are formed in a saw-tooth shape in a cross section in a direction orthogonal to the tube axis, and each prism 25 has a light transmitting surface 27 that obliquely emits light from the tubular light source 13 and a light transmitting surface 27 that obliquely emits the light. And a light-reflecting surface 28 for reflecting the reflected light forward are arranged so as to be inclined with respect to each other with the apex angle θ interposed therebetween.
The apex angle θ of the prism 25 is formed so as to be farther from the tubular light source 13.

[0012]

In the above means for solving the problems, when the light source reflecting mirror 14 has a semi-elliptical shape in cross section, the light emitted from the tubular light source 13 is radiated in a relatively widening direction, and therefore the rate of returning to the tubular light source 13 is high. Less. Moreover, the light source reflector 1
Since the light reflected at 4 enters the end incident surface 21 of the light guide plate 12 at a relatively acute angle, the tubular light source 1 is disposed inside the light guide plate 12.
Light can easily reach areas farther than 3.

Further, since the rear reflection surface 22 of the light guide plate 12 is formed in a parabolic shape so that the inclination angle becomes larger as it is farther from the tubular light source 13, the more it is reflected from the tubular light source 13, the more the reflection of light becomes. The angle becomes an acute angle, and the light is emitted at an angle close to vertical emission with respect to the front emission surface 23.

Further, the front emission surface 23 of the light guide plate 12 is
A plurality of prisms 25 are formed in a saw-tooth shape in cross section, one surface of each prism 25 functions as a light transmitting surface 27, and the other surface reflects the obliquely emitted light from the light transmitting surface 27 forward. Since it functions as 28, the final light reflected by the light reflecting surface 28 can be brought close to the normal direction of the front emission surface 23.

Since the apex angle θ of the prism 25 is formed so as to be farther away from the tubular light source 13, the light guide plate 1 is formed.
At an angle according to each optical path of various rays emitted in 2
The final light can be brought close to the normal line direction of the front emission surface 23.

These light source reflecting mirror 14 and light guide plate 12
The direct light from the tubular light source 13 and the reflected light from the rear reflection surface 22 can reach the front emission surface 23 relatively uniformly only by devising the shape of. Thereby, the brightness homogeneity of the illumination surface can be increased.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A surface light source device according to an embodiment of the present invention is, as shown in FIG. 1, a translucent light guide plate 12 for illuminating a liquid crystal panel as an object to be illuminated planarly from the rear side, and a light guide plate 12 of the light guide plate 12. It is provided with a tubular light source 13 arranged at one end, and a light source reflecting mirror 14 arranged around the tubular light source 13 and reflecting light diverging outward from the tubular light source 13 toward the light guide plate 12 side.

The light guide plate 12 is made of polymethylmethacrylate (PMMA) or the like and has a thickness of 15 m, for example.
The end incident surface 21 on which the light from the tubular light source 13 is incident at one end is formed by a metal mold having a length of m and a length of 111 mm.
And a rear reflection surface 22 that reflects the light to the inside rearward to the front by the rear surface, and a front emission surface 23 that emits the internal light to the front side of the illuminated body.

The end entrance surface 21 is formed orthogonally to the end of the front exit surface 23, and is elongated in correspondence with the tube diameter of the tubular light source 13.

The rear reflecting surface 22 is the tubular light source 13.
It is formed in a parabolic shape so that the angle of inclination increases with increasing distance from. This is because in order to prevent the brightness of the front emission surface 23 from decreasing as the distance from the tubular light source 13 decreases, the reflection angle of the reflected light is set to an acute angle and approaches the normal direction of the front emission surface 23 to improve the light emission efficiency. Is.

As shown in FIG. 2, on the front emission surface 23, a large number of prismatic prisms 25 projecting forward are formed in a saw-tooth shape in cross section in a direction perpendicular to the tube axis of the tubular light source 13. ing.

Here, of the two surfaces 27, 28 projecting forward of each prism 25 having a triangular prism shape, the surface 27 on the side farther from the tubular light source 13 is incident on the end portion by setting the inclination angle ψ in FIG. It is arranged at a tilt angle that is closer to a right angle with respect to the light traveling in the light guide plate 12 through the surface 21. In other words, they are arranged at an inclination angle that allows light to be emitted more easily.

On the other hand, of the two surfaces 27, 28 projecting forward of the prism 25 having a triangular prism shape, the surface 28 closer to the tubular light source 13 is opposite to the surface 27 farther from the light guide plate 12.
It is arranged at an inclination angle that is more parallel to the light traveling inside. In other words, they are arranged at an inclination angle that makes it more difficult to emit light. However, it can be said that the surface 28 on the near side is arranged at a position where the light obliquely emitted from the surface 27 on the far side of the adjacent prism 25 is easily reflected forward, as shown in FIG.

In consideration of this, the surface 27 of each prism 25 having a triangular prism shape on the side far from the tubular light source 13 has a tubular light source 1.
The surface 28 on the side closer to the tubular light source 13 functions as a light transmitting surface that obliquely emits the light from 3 and the light emitted obliquely from the light transmitting surface 27 (the surface on the far side) of the adjacent prism 25 is forward. It functions as a light-reflecting surface that reflects light.

The light reflecting surface 28 may be formed into a mirror surface by, for example, forming a metal pattern, but the surface of PMMA, which is the material of the light guide plate 12, is used as it is without any special processing. However, since sufficient light reflection is obtained, it is not necessary to perform a different surface treatment as compared with the light transmitting surface 27.

Assuming that the apex angle between the light transmitting surface 27 and the light reflecting surface 28 of the prism 25 is θ, the apex angle θ
Are formed so as to be farther from the tubular light source 13. This is because the light traveling in the light guide plate 12 is a tubular light source 13.
Considering that the light traveling direction becomes closer to the front emission surface 23 in parallel to the front emission surface 23, the light transmission surface 27 of the prism 25 is inclined at a right angle to the front emission surface 23 as it is separated from the tubular light source 13. This is because the light transmission efficiency is increased by arranging the corners.

The tubular light source 13 is a cold cathode fluorescent lamp (C
CFT) or hot cathode tube (HCFT) is used, and is arranged near the end incident surface 21 of the light guide plate 12. The tubular light source 13 has a diameter of 6 mm, for example.
The distance from the center of 3 to the end incident surface 21 of the light guide plate 12 is, for example, 3.1 mm.

The light source reflecting mirror 14 is made of, for example, a mirror-finished sheet material made of aluminum or the like, and is formed in a semi-elliptical shape in cross section with a flatness ratio larger than 1, as shown in FIG. Here, as a means for holding the light source reflecting mirror 14 in a semi-elliptical shape in cross section, for example, a resin protective cover or the like formed by a mold so that the inner circumference has a semi-elliptical shape in cross section may be used.

In the surface light source device having the above structure, of the light from the tubular light source 13, the light emitted toward the light guide plate 12 directly reaches the end incident surface 21 of the light guide plate 12.

On the other hand, the light emitted from the tubular light source 13 toward the outside hits the light source reflecting mirror 14 and is reflected.

At this time, the light source reflecting mirror 14 has an aspect ratio of 1
Since it is larger, the reflected light spreads so as to avoid the tubular light source 13, and reaches the end incident surface 21 of the light guide plate 12. Therefore, as compared with the conventional example shown in FIGS. 16 and 17, the rate at which the light reflected by the light source reflecting mirror 14 is returned to the tubular light source 13 again decreases, and the light loss can be reduced.

Moreover, the light reflected by the light source reflecting mirror 14 enters the end entrance surface 21 of the light guide plate 12 at a relatively acute angle, so that the light easily reaches a position apart from the tubular light source 13 in the light guide plate 12. .

Next, the light that has reached the end incident surface 21 is refracted to some extent and enters the light guide plate 12.

Of these, the light refracted relatively backward is
The rear reflection surface 22 is reached.

At this time, the tubular light source 13 of the rear reflection surface 22
Since the inclination angle of the portion close to is small, the incident angle of light to this portion can be made larger than the critical angle, total reflection becomes easy, and light loss at the time of reflection can be reduced.

Further, since the inclination angle of the portion of the rear reflecting surface 22 which is separated from the tubular light source 13 is large, the reflection angle of the reflected light at this portion becomes an acute angle. It can be reflected in the line direction. Therefore, the light emission efficiency of the front emission surface 23 can be improved.

From these facts, the amount of light traveling toward the front emission surface 23 in the light guide plate 12 can be made relatively uniform.

Of the light entering the light guide plate 12 from the end entrance surface 21, the light refracted relatively forward advances directly to the front exit surface 23.

In this way, the light reflected by the rear reflection surface 22 or directly traveling from the end entrance surface 21 reaches the front emission surface 23.

At this time, the light is reflected by the prism 2 as shown in FIG.
The light is emitted to the light transmitting surface 27 of No. 5 at an angle close to vertical emission. Therefore, as compared with the conventional example in which the light transmitting surface 27 is not formed on the front emission surface 23, the light reflection at the time of emission can be reduced and the light loss here can be reduced.

The light emitted from the light transmitting surface 27 hits the light reflecting surface 28 as shown in FIG. 2, and is reflected in the direction normal to the front emission surface 23. Then, the liquid crystal panel as the object to be illuminated is illuminated planarly from behind. At this time, the illumination light is
Since the illumination is performed in the direction normal to the front emission surface 23, the brightness when the liquid crystal panel is viewed from the front is improved.

Here, when the light traveling in the light guide plate 12 reaches the front emission surface 23, the farther it is from the tubular light source 13, the closer the light traveling direction becomes parallel to the front emission surface 23. Therefore, if the front emission surface 23 is formed uniformly depending on the position as in the conventional example, the amount of emitted light on the front emission surface 23 may vary.

However, in the present embodiment, the apex angle θ of the prism 25 is formed so as to be sharper as it is farther from the tubular light source 13, so that the farther the light transmitting surface 27 is from the tubular light source 13, the more the front emitting surface 23 is. Therefore, the emitted light can be emitted at an angle close to vertical emission at any position. The angle emitted here hits the light reflection surface 28 and is corrected in the direction of the normal line of the front emission surface 23 as described above. Therefore, the light transmission efficiency is adjusted while adjusting the directivity angle on the front emission surface 23. Can be increased.

In reality, it is impossible to design the apex angle θ of the prism 25 so as to ideally emit light as described above in consideration of all kinds of light. If designed, most of the light in the light guide plate 12 operates as described above. That is, first, in FIG.
As described above, the front emission surface 23 is divided into n. The area closest to the tubular light source 13 is the first area Ra1, and the farthest area is the nth area Ran. next,,
The tilt angle ψ and the apex angle θ of the light transmitting surface 27 are determined with respect to the average incident angles of the respective lights reaching the first area Ra1 and the nth area Ran. Then, the areas Ra2 to Ra9 located between the first area Ra1 and the nth area Ran.
It is preferable that the inclination angle ψ and the apex angle θ are designed to gradually change linearly. Further, the inclination angle of the light reflecting surface 28 may be adjusted so that the light emitted from the light transmitting surface 27 can be reflected in the front direction, but it is difficult to strictly adjust each prism 25. The inclination angle may be the same as the inclination angle ψ of the light transmitting surface 27. Then, the prism 25 becomes an isosceles triangle and can be accurately formed.

Here, a ray tracing simulation until reaching the front emission surface 23 was carried out in several kinds of surface light source devices having different configurations. The simulation conditions are as follows.

Simulation by Two-Dimensional Model The tubular light source 13 has a perfect cylindrical shape, and is 3 degrees apart from the center by 1 degree.
It radiates with an intensity of 1 in all directions at 60 degrees.

When the light reflected by the light source reflecting mirror 14 returns to the tubular light source 13, it is considered that all the light is absorbed by the tubular light source 14. Moreover, the light loss at the light source reflecting mirror 14 is not considered.

Reflected light rays (light loss) generated at the end incident surface 21 of the light guide plate 12 and light rays reaching the end surface 21a opposite to the end incident surface 21 of the flat light guide plate 12 shown in FIGS. No secondary tracking is performed.

The diameter of the tubular light source 13 is 6 mm, and the light guide plate 12 is
Is 15 mm, the length of the light guide plate 12 is 111 mm, and the distance from the center of the tubular light source 13 to the end incident surface 21 of the light guide plate 12 is 3.1 mm.

The refractive index is air 1.0 and the light guide plate 1.49.

Here, in FIG. 3, the light source reflecting mirror 14 has a semicircular shape with a sectional radius of 7.5 mm, and the rear reflecting surface 2 of the light guide plate 12 is shown.
2 is formed in parallel with the front emission surface 23 (P in FIG. 3).
When the point o is the origin, the rear reflection surface 22 has y = -7.5.
4 is a diagram showing the measurement result in this case.

In FIG. 5, the light source reflecting mirror 14 has a sectional radius of 7.5.
When the rear reflection surface 22 of the light guide plate 12 is inclined at a constant inclination angle (when the Po point in FIG. 5 is the origin, the rear reflection surface 22 is y = 0.13513514x).
6 is a diagram showing the measurement results in this case.

In FIG. 7, the light source reflecting mirror 14 has a sectional radius of 7.5.
When the rear reflection surface 22 of the light guide plate 12 is inclined in a parabolic shape with a semi-circular shape of mm (when the Po point in FIG. 7 is set as the origin, the rear reflection surface 22 has y = 0.0012174336x).
² becomes a quadratic curve represented by 2-7.5), and FIG. 8 shows the measurement results in this case.

FIG. 9 shows a case where the light source reflecting mirror 14 has a semi-elliptical cross section (vertical diameter 15 mm, flatness ratio 1.1) and the rear reflecting surface 22 of the light guide plate 12 is formed parallel to the front emitting surface 23 (FIG. The rear reflection surface 22 becomes a straight line represented by y = -7.5 when the Po point in 9 is the origin), and FIG. 10 is a diagram showing the measurement result in this case.

FIG. 11 shows a case where the light source reflecting mirror 14 has a semi-elliptical cross section (longitudinal diameter 15 mm, flatness ratio 1.1), and the rear reflection surface 22 of the light guide plate 12 is inclined at a constant inclination angle (FIG. 11).
When the Po point in the inside is set as the origin, the rear reflection surface 22 is y =
0.13513514x−7.5), and FIG. 12 shows the measurement results in this case.

FIG. 13 shows a case where the light source reflecting mirror 14 has a semi-elliptical cross section (longitudinal diameter 15 mm, flatness ratio 1.1), and the rear reflecting surface 22 of the light guide plate 12 is inclined in a parabolic shape (see FIG. 13). When the Po point is the origin, the rear reflecting surface 22 has y = 0.0.
012174336x a quadratic curve represented by ² -7.5), FIG. 14 shows a measurement result in this case.

In FIGS. 3, 5, 7, 9, 11, and 13,
The front emission surface 23 is shown by a broken line because the prism 25 is not taken into consideration.

Further, FIGS. 4, 6, 8, 10, 12, 14
(A) shows the relative light intensity of each area when the front emission surface 23 is divided into n areas, the area closest to the tubular light source 13 is the first area Ra1, and the farthest area is the nth area Ran. The maximum intensity (MAX) of the distribution is 100. Also, (b) is an area number, (c) is the number of reaching rays, (d) is the reaching light quantity,
(E) shows "90 ° -the average incident angle of the reaching light beam", (f) shows "90 ° -the maximum incident angle of the reaching light beam", and (g) shows "the minimum incident angle of the reaching light beam". In addition, in these simulations, the function of the prism 25 is not considered at all.

FIG. 4 and FIG. 10, FIG. 6 and FIG. 12, or FIG.
14A to 14G, the light source reflecting mirror 14 has a higher ellipticity than the circle to reach the front emission surface 23, and the light source reflecting mirror 14 arrives relatively uniformly. I understand.

Further, by comparing FIGS. 4 and 6 and 8 or FIGS. 10 and 12 and FIGS. 14A to 14G, the shape of the rear reflection surface 22 of the light guide plate 12 is parallel. It can be seen that a straight line or a quadratic curve has a higher efficiency of reaching the front emission surface and a relatively uniform arrival than the straight line.

By the way, since these states do not take the prism 25 into consideration, a method for determining the apex angle θ of the prism 25 will be described with reference to FIG.

As shown in FIG. 15, first, the front emission surface 23 is divided into ten, the apex angle θ ₁ of the prism 25 in the first area Ra1 is 61.1 degrees, and the inclination angle ψ ₁ of the light transmission surface 27 is 61.1. The apex angle θ ₁₀ of the prism 25 in the tenth area Ra10 is 55.5 °, and the inclination angle ψ ₁₀ of the light transmitting surface 27 is 21.0. Also, from the second area Ra2 to the ninth area Ra
Apex angles θ _{2 to} θ 9 of the prism 25 of ₉ and the light transmitting surface 27
The inclination angles ψ _{2 to} ψ ₉ are set to linearly change between (θ ₁ , ψ ₁ ) and (θ ₁₀ , ψ ₁₀ ), respectively.

In the surface light source device shown in FIG. 15, the thickness of the light guide plate 12 and the shapes of the rear reflection surface 22 and the like are as shown in FIG.
The conditions are the same as those shown in.

According to the configuration of FIG. 15, the ratio of the total luminous flux of the front emission surface 23 of the light guide plate 12 to the total luminous flux of the tubular light source 13 (hereinafter referred to as light efficiency), the intensity distribution of the front emission surface 23,
Also, the exit angle when the normal to the exit surface is 0 degree and the direction tilting away from the tubular light source is positive is approximately calculated as follows.

Light efficiency = 69.1% Intensity distribution ≧ 50% Emission angle = + 30 ° to −30 ° The present invention is not limited to the above-mentioned embodiments, but is within the scope of the present invention. Of course, many modifications and changes can be made.

For example, the above-mentioned surface light source device is merely an example, and if the tube diameter of the tubular light source 13 and the thickness of the light guide plate 12 are changed, the shape of the light guide plate 12 and the semi-elliptical shape of the light source reflecting mirror 14 may be changed. Change.

A sheet having a high reflectance may be attached to the rear reflecting surface 22 or a white light scattering material such as TiO ₂ may be applied.

[0068]

As is apparent from the above description, according to the present invention, since the light source reflecting mirror has a semi-elliptical shape in cross section, the light emitted from the tubular light source is radiated in a relatively widening direction, and therefore, again. Less likely to be returned to the tubular light source. Moreover, the light reflected by the light source reflecting mirror enters the end incident surface of the light guide plate at a relatively acute angle, so that the light easily reaches a position apart from the tubular light source in the light guide plate.

Further, since the rear reflection surface of the light guide plate is formed in a parabolic curve so that the inclination angle becomes larger as it is farther from the tubular light source, the reflection angle of light becomes sharper as it is farther from the tubular light source. At any position, light can be emitted at an angle close to vertical emission with respect to the front emission surface.

Further, the front emission surface of the light guide plate is formed in a sawtooth shape in cross section by a large number of prisms, one surface of each prism functions as a light transmitting surface, and the other surface is obliquely projected from the light transmitting surface. Since it functions as a light reflecting surface that reflects the emitted light forward, the final light reflected by the light reflecting surface can be brought close to the normal direction of the front emission surface.

Since the apex angle of the prism is formed so as to be farther from the tubular light source, the final light is directed to the front emission surface at an angle according to each optical path of various light rays emitted in the light guide plate. It can be close to the line direction.

The direct light from the tubular light source and the reflected light from the rear reflection surface can be made to reach the front emission surface relatively uniformly only by devising the shapes of the light source reflection mirror and the light guide plate. . This has an excellent effect that the brightness homogeneity of the illumination surface can be increased.

[Brief description of drawings]

FIG. 1 is a schematic explanatory diagram of a surface light source device according to an embodiment of the present invention.

FIG. 2 is an enlarged view of a main part of a surface light source device according to an embodiment of the present invention.

FIG. 3 is a side view of a surface light source device in which a light source reflecting mirror has a semicircular cross section and a rear reflection surface of a light guide plate is parallel to a front emission surface.

FIG. 4 is a diagram showing various measurement results of a surface light source device in which a light source reflection mirror has a semicircular cross section and a rear reflection surface of a light guide plate is parallel to a front emission surface.

FIG. 5 is a side view of a surface light source device in which a light source reflector has a semicircular cross section and a rear reflection surface of a light guide plate is inclined at a constant inclination angle.

FIG. 6 is a view showing various measurement results of a surface light source device in which a light source reflecting mirror has a semicircular cross section and a rear reflecting surface of a light guide plate is inclined at a constant inclination angle.

FIG. 7 is a side view of a surface light source device in which a light source reflecting mirror has a semicircular cross section and a rear reflecting surface of a light guide plate is inclined in a parabolic shape.

FIG. 8 is a diagram showing various measurement results of a surface light source device in which a light source reflecting mirror has a semicircular cross section and a rear reflecting surface of a light guide plate is inclined in a parabolic shape.

FIG. 9 is a side view of a surface light source device in which the light source reflecting mirror has a semi-elliptical cross section and the rear reflection surface of the light guide plate is parallel to the front emission surface.

FIG. 10 is a diagram showing various measurement results of a surface light source device in which a light source reflecting mirror has a semi-elliptical cross section and a rear reflection surface of a light guide plate is parallel to a front emission surface.

FIG. 11 is a side view of a surface light source device in which a light source reflecting mirror has a semi-elliptical cross section and a rear reflection surface of a light guide plate is inclined at a constant inclination angle.

FIG. 12 is a diagram showing various measurement results of a surface light source device in which a light source reflecting mirror has a semi-elliptical cross section and a rear reflection surface of a light guide plate is inclined at a constant inclination angle.

FIG. 13 is a side view of a surface light source device in which a light source reflecting mirror has a semi-elliptical cross section and a rear reflecting surface of a light guide plate is inclined in a parabolic shape.

FIG. 14 is a diagram showing various measurement results of a surface light source device in which a light source reflecting mirror has a semi-elliptical cross section and a rear reflecting surface of a light guide plate is inclined in a parabolic shape.

FIG. 15 is a diagram illustrating a front emission surface of a surface light source device according to an embodiment of the present invention.

FIG. 16 is a side view of a conventional surface light source device in which a rear reflection surface of a light guide plate is parallel to a front emission surface.

FIG. 17 is a side view of a conventional surface light source device in which a rear reflection surface of a light guide plate is curved.

[Explanation of symbols]

 12 light guide plate 13 tubular light source 14 light source reflecting mirror 21 end incident surface 22 rear reflecting surface 23 front emission surface 25 prism 27 light transmitting surface 28 light reflecting surface θ apex angle

Claims (1)

[Claims] 1. A translucent light guide plate for illuminating an object to be illuminated in a planar manner from the rear, a tubular light source arranged at one end of the light guide plate, and a tubular light source arranged around the tubular light source. From a light source reflecting mirror that reflects the light diverging outward from the light guide plate side, the light guide plate, the end incident surface on which the light from the tubular light source is incident at one side end, In a surface light source device having a rear reflection surface that reflects light forward on a rear surface and a front emission surface that emits internal light to the front side of the object to be illuminated, the light source reflection mirror has an aspect ratio of 1 It is formed in a larger semi-elliptical shape in cross section, and the rear reflection surface of the light guide plate is formed in a parabolic shape so that the inclination angle becomes larger as the distance from the tubular light source increases, and the front emission surface of the light guide plate is formed. The multiple saws are connected in the direction perpendicular to the tube axis of the tubular light source, Each of the prisms has a light-transmitting surface that obliquely emits the light from the tubular light source and a light-reflecting surface that reflects the light that is obliquely emitted from the light-transmitting surface forward with the apex angle sandwiched. 2. The surface light source device according to claim 1, wherein the prisms are inclined with respect to each other, and the apex angle of the prisms is formed so as to be more distant from the tubular light source.