JPH10172318A - Surface light emitting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase a quantity of light to be emitted outside of a light guide plate separated from a light source by continuously forming an elliptical base having a protrusion formed in such a manner as to have a first dimension along a normal of an incident face greater than a second dimension along a widthwise direction of a light guide member and tilted faces extending with an angle tilted from the base, and forming a top parallel to the base. SOLUTION: A base of a protrusion 6 is formed into an ellipse having a dimension along a normal of an incident side face greater than that along a widthwise direction of a light guide member 1. Tilted faces are formed with a tilt angle from the base. The tilted faces 6a, 6b, 6c, 6d form a predetermined angle with respect to the respective normals from the back face of the light guide member 1. In this protrusion 6, incident light which enters at a predetermined critical angle or less is first reflected on a top 6k, before it is oriented toward and entirely reflected on the tilted faces 6,a 6b, 6c, 6d, and then, light L1, L2, L3, L4 are oriented toward a diffusion plate 5. Consequently, it is possible to increase luminance as a whole.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to a surface light emitting device used for illuminating a CD (liquid crystal display device) or the like from the back.

[0002]

2. Description of the Related Art When illuminating an LCD or the like having a predetermined area from the back, the first point to be considered is that light generated from a light source is made uniform over all portions of the LCD having a predetermined area. It is mentioned.

[0003] Therefore, conventionally, a light source is arranged on the side of a light guide member formed of a material having high light transmittance, and the light from the light source is guided in the surface direction of the light guide member to form a light guide member. When configured to scatter light emitted from the light emitting surface of the light guide member for the light emitting member arranged in parallel to the light emitting surface,
A large number of protrusions are formed on the side opposite to the light emitting surface of the light guide member, and while these protrusions reflect light from the light source, light is emitted such that more protrusions are formed in portions far from the light source. Many surface light emitting devices having a uniform surface brightness have been put to practical use.

According to the surface light emitting device constructed as described above, the light guide member is mass-produced by injection molding using, for example, an acrylic resin material having high light transmittance. The mold provided with the cavity is mainly processed by chemical etching.

FIGS. 10A and 10B are an enlarged sectional view of a conventional light guide plate 10 and an enlarged sectional view of an injection mold 201 used for injection-molding the light guide plate 10.

First, in FIG. 10B, when a mold recess 202 for forming the projection 16 of the light guide plate 10 is formed by chemical etching using an injection mold 201, the bottom surface of the cavity of the mold is formed. A resist film 20 in which portions are provided with opening holes 203a having a predetermined pitch and a predetermined opening area.
3 and then introduce an etchant to open the opening 20.
After the surface contacting via 3a is formed by excavating by erosion, the cavity of the injection mold 201 is formed by removing the resist film 203.

[0007] The injection molding die 2 thus processed and formed.
As shown in FIG. 10B, a light guide plate 10 having a thickness H and having a large number of projections 16 formed by injection molding is used to form the light guide member 10 as described above. Light emitting surface 1
At 0a, while the light from the light source is reflected, more projections 16 are formed in a portion far from the light source so that the brightness on the light emitting surface becomes uniform.

[0008]

However, when the mold cavity is machined by chemical etching as described above, the opening hole portion 203a becomes hemispherical when it is a small-diameter dot, and has a pot bottom shape when it is a large-diameter dot. Is known to be.

If so-called over-etching occurs during the chemical etching process, over-etching 202a as shown in FIG. 10B is formed. The diameter d of the projection 16b is, for example, Φ0.5.
mm or less and the arrangement pitch is 1 mm
If the width becomes narrower below, the communication portion 202b may be formed. Therefore, the defective portions 16a, 1
6b will be formed.

As a result, the light L from the light source is not reflected irregularly at the defective portion 16a of the projection 16, or cannot be directed toward the light emitting surface 10a after being reflected by the projection 16, so that light can be efficiently emitted. In addition, it is not possible to select a shape that normally guides the light guide plate away from the light source, so that desired performance cannot be obtained.

Furthermore, in the chemical etching process, it is particularly difficult to control the concentration of the chemical solution, the temperature, and the like. In the case where the density of the projections is provided steplessly, it is very difficult to prevent the occurrence of variation depending on the location. It was difficult. For this,
It is necessary to increase the interval between the adjacent protrusions 16,
The arrangement density of the projections could not be increased, and there was naturally a limit, and there was a limit in increasing the amount of light emitted to the outside of the light guide plate to increase the luminance.

[0012] Therefore, the present invention has been made in view of the above-described problems, and when the density of the projections provided on the light guide plate is steplessly varied, the variation in the shape of the projections depending on the location may occur. The distance between adjacent projections can be reduced to increase the arrangement density of the projections, and the amount of light emitted outside the light guide plate away from the light source can be increased. It is another object of the present invention to provide a surface light emitting device capable of increasing the overall luminance.

[0013]

Means for Solving the Problems The above-mentioned problems are solved,
In order to achieve the object, according to the present invention, a light source is disposed on a side or both sides of a light-transmitting plate-shaped light guide member, and light from the light source is incident on the light guide surface of the light guide member. In order to illuminate the light by guiding the light into the inside and scattering the light with a diffusion member arranged in parallel with the light emitting surface of the light guide member, the rear surface of the light guide member is approximately at a distance from the light incident surface. A surface light-emitting device in which a large number of protrusions are formed at a proportionally high density to make the brightness of the diffusion member uniform over the entire surface, wherein the shape of the protrusions is a first line along a normal to the light incident surface. Is larger than the second dimension along the width direction of the light guide member, an oblong base extending from the oblong base at an oblique angle, and continuously formed from the oblique surface. In addition, by forming it from a top part that is substantially parallel to the oval base part, it can enter at a critical angle β or more determined by the resin material. It is characterized by reflecting the the incident light by the projection unit.

Further, a light source is disposed on the side or both sides of the light-transmitting plate-shaped light guide member, and light from the light source is guided inside from the light incident surface of the light guide member. A large number of protrusions are formed on the back surface of the light guide member at a high density substantially proportional to the distance from the light entrance surface in order to scatter light and perform illumination by a diffusion member provided in parallel on the light emitting surface of the light guide member. Forming a surface emitting device to make the brightness of the diffusion member uniform over the entire surface,
It is determined from the resin material by forming the shape of the protrusion from a circular base, an inclined surface extending from the circular base with an inclination angle, and a top continuously formed from the inclined surface. The incident light incident at a critical angle β or more is reflected by the projection.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a cross-sectional view of a surface-emitting device used for a backlight of a liquid crystal having no self-luminous ability, for example. FIG. 2 is a sectional view taken along the line XX of FIG.

In both figures, a light source unit 4 is formed by bonding a high-brightness light emitting diode (LED) on a substrate 5 and then
It is formed so as to be sealed with a silicon resin or an epoxy resin or the like, so that the electrode section of the substrate 5 is exposed to the outside as shown in the figure and the electrode section is connected to a power supply section (not shown) so that lighting can be performed. Thus, it is possible to manufacture and supply the surface light emitting device alone.

On the other hand, the flat light guide plate 1 has substantially the same shape and area as the flat display surface 15 of the liquid crystal, and the light receiving side surface 1f has a shape for accommodating the pair of light source sections 4 described above. A part is formed, and a transparent acrylic resin, a polycarbonate (PC) resin, or the like is used as the material, and injection molding is performed. Further, the light emitting surface 1a, the left and right side surfaces 1d, 1e and the opposite surface 1c and the back surface 1b of the light guide plate 1 are formed so as to be mirror surfaces, respectively, and countless projections 6 are regularly formed on the back surface 1b. .

As shown in FIG. 2, the arrangement of these protrusions 6 is such that the horizontal pitch Pw and the vertical pitch P
While d is arranged to be in a sparse state, the horizontal pitch Pw and the vertical pitch Pd gradually become denser as the distance from the light source 4 increases, and furthermore, the staggered shape as shown in the drawing. By arranging the projections 6, the projections 6 are arranged based on a simulation analysis so that the light from the light source 4 can reach the adjacent projections 6 reliably.

On the other hand, the reflection frame 3 formed in a box shape as shown in the figure is formed so as to have a size and a shape for accommodating the above-mentioned light guide plate 1 with almost no gap. The reflection frame 3 is formed by, for example, injection molding from a white resin or by electroless plating, which is a reflection inner surface 3a which is a reflection surface.
3b, 3c, and 3d are provided so that the light reflected on each reflection inner surface is directed to the diffusion plate 2. The above is the schematic structure of the surface light emitting device, the dimensions of which are appropriately determined according to the size of the liquid crystal. good.

When the backlight is horizontally long,
The apparatus shown in FIGS. 1 and 2 may be provided symmetrically in such a manner that a pair of parts are opposed to each other, and the projections 6 are arranged so as to be in a dense state at the central portion.

FIG. 3A is a schematic diagram showing the state of reflection of light L entering the light guide plate 1, and FIG. 3B is a main part showing the state of reflection of light L on the projection 6. It is sectional drawing.

First, in FIG. 3A, light L emitted from the light source 4 and shown by a broken line in the figure is a critical angle β due to the refractive index n = 1.49 of the acrylic resin. 4
The angle is 2.16 °, and total reflection occurs when incident on each surface at an incident angle of 42.16 ° or more. That is, light incident on the light guide plate 1 at an angle α formed by the normal line from the light guide plate 1 is refracted at the critical angle β, but the refractive index n = s.
In the relational expression of inα / sinβ, α is 90 °,
42. The critical angle β from sinβ = sin (90 °) / n
16 ° will be obtained.

Similarly, in the case of PC resin, since n = 1.59, the critical angle is 38.97 ° and the incident angle is 38.97 ° on each surface.
When incident at an angle of 97 ° or more, total reflection occurs.

Therefore, the light L incident from the light incident side surface 1f of the light guide plate 1 formed of an acrylic resin has an angle β of 42.16 ° or less, the light emitting side surface 1a,
d, 1e and the incident angle 4 at portions other than the protrusion 6 on the back surface 1b.
Above 7.84 ° the critical angle is exceeded and all are totally reflected.
Similarly, in the case of PC resin as well, all the light incident from the incident side surface 1f is totally reflected.

The light that reaches the opposite surface 1c while repeating the above-described total reflection is emitted from the light guide plate 1 to the outside, is reflected by the reflection inner surface 3b of the reflection frame 3, and then is returned again. Will be incident.

Next, the projection 6 which is the most characteristic feature of the present invention.
Is formed on the back surface 1b as shown in FIG. 3 (b), and is totally reflected if the incident angle of the projection 6 with respect to the reflection surface 6a is equal to or larger than the critical angle β. When the incident angle on the light emitting surface 1 a is equal to or smaller than the critical angle β, the light is refracted out of the light guide plate 1 without reflection, reaches the diffusion plate 2, and is diffused by the diffusion plate 2. If the incident angle with respect to the light emitting surface 1a is equal to or larger than the critical angle β, the light is totally reflected and guided inside the light guide plate.

On the other hand, light that has entered the rear surface 1b at a critical angle β or less exits from the rear surface 1b, and
Of the light guide plate 1
And directed to the light emitting surface 1a. Light incident on the back surface 1b at a critical angle β or more is totally reflected by the back surface 1b, directed to the light emitting surface 1a, and directed to the left side of the drawing.

The light diffused by the diffusion plate 2 as described above forms a surface light source, and in the case of a liquid crystal backlight, passes through the LCD transmission pattern 15 and is displayed.

The projection 6 is formed to project conically from the back surface 1b of the light guide plate 1 as shown in the figure.
While the tip has a spherical shape with a radius r, the apex angle θ is 110
It is formed so as to be in the range of ° to 150 °. By forming the projections 6 in this manner, light that has entered the rear surface 1b at a critical angle β or more and is originally light
The light to be totally reflected by the surface is totally reflected by the reflection inclined surface 6a of the projection 6 and directed to the light emitting side surface 1a so that the incident angle with respect to the light emitting side surface 1a is equal to or less than the critical angle β. The light can be emitted from 1a.

As the projection 6 formed as described above is separated from the light source 4 as described above, the horizontal pitch Pw gradually increases.
And the vertical pitch Pd is arranged in a dense state, and furthermore, arranged so as to be staggered as much as possible, so that light from the light source 4 can surely reach the opposite surface 1c.

Various experiments were carried out with the apex angle θ of the projection 6 changed, and it was confirmed that the efficiency was the best around 120 °, and the height h of the projection 6 was 0.05 mm and the diameter d was 0 mm. .
A good result could be obtained by narrowing the horizontal pitch Pw and the vertical pitch Pd to 0.3 mm in the region where the projections 6 are provided with the highest density at 25 mm and near the opposite surface 1c.

Next, FIG. 4 is a schematic view showing a manufacturing step (a) and a molding end step (b) of a mold for a light guide plate injection-molded as described above. First, in FIG. 4A, the mold concave portion 102 serving as a cavity for forming the above-mentioned protrusion 6 can be cut by the cutting tool 30 having the above-mentioned apex angle θ at the tip end portion.

For this reason, the mold member 101 having the cavity C which is preliminarily processed to have the outer shape of the light guide plate 1.
Is set on the automatic machine 200. The bottom surface of the cavity C is mirror-finished, and thereafter, while the cutting tool 30 is relatively automatically fed in the up / down Z direction, the front / rear X direction, and the left / right Y direction as shown in the drawing, the cutting tool 30 is rotated a predetermined amount to a predetermined position. The mold recess 102 is cut with a cutting feed amount of.

In this cutting step, a high density portion (lateral pitch Pw) of the mold concave portion 102 for forming the projection 6 is formed.
And the vertical pitch Pd is, for example, 0.3 mm or less)
Since there is a possibility that the shape of the mold recess 102 to be machined from now on may be affected by the mold recess 102 processed before the cutting process and may be deformed, the cutting process is performed in order from the mold recess 102 farther from the light source 4. Accordingly, the unavoidable shape distortion generated at the time of processing can be limited to only the side of the reflection slope 6 b (FIG. 3B) of the light source in the projection 6.

That is, since the reflective inclined surface 6a that contributes to the reflection as described above is processed by the cutting tool 30 at an accurate apex angle θ on the surface of the protruding portion 6 on the side far from the light source 4, the protruding portion 6a is processed. It is possible to minimize the effect of reflecting light in the section 6.

Referring again to FIG. 4B, the light guide plate 1 is formed by injection molding under predetermined conditions using an acrylic resin material by using the mold member 101 having the mold concave portion 102 cut as described above. Obtainable.

Here, when the light sources 4 are provided on both sides of the light guide plate 1 and the light-entering surfaces 1f are provided on both side surfaces, cutting is performed in order from the center of the cavity C in the left-right direction. Needless to say. In addition, although the cutting density of the same shape of the mold concave portion 102 is changed by one cutting tool 30, the light source 4 side is shallow and distant with the same cutting tool 30 by changing the cutting depth in a plurality of steps. You may process so that a side may become deep.

The same effect can be obtained by performing similar machining with a plurality of cutting tools having different machining depths or a plurality of different cutting tools having different conical portion areas by changing the radius r of the tip spherical portion. Further, it is possible to change both the density and the depth to greatly change the amount of emitted light without increasing the pitch of the protrusions 6. Can realize a surface light source device having uniform brightness without being noticeable via the diffusion plate 2.

Referring again to FIG. 3B, the reflection slope 6b
Not only does not contribute to the reflection, but also may be an obstacle to ensure that the light L from the light source 4 reaches the reflecting slope 6a. Therefore, as shown in FIG. 5, the mold concave portion 102 of the mold member 101 is cut so that the cutting tool 30 having the apex angle θ indicated by the broken line is inclined toward the light source 4 by the angle B.

According to the projection formed from the mold member obtained in this way, the light L1 and L2 from the light source 4 can surely reach the reflecting slope 6a without being obstructed by the reflecting slope 6b, and can be guided. It is now possible to set the angle of the reflection slope that increases the light emission component in the vertical direction of the light plate,
Brightness can be further increased.

Further, in FIG. 6, the light sources 4 are disposed on both sides of the light guide plate 1 as described above,
When f is provided on both side surfaces, the mold concave portion 102 of the mold member 101 is cut so that the cutting tool 30 having the apex angle θ shown by the broken line is inclined by the angle B. According to the projection formed from the mold member 101 obtained in this way, the light L1 and L2 from the light sources 4 on both sides can be directed to the light emitting surface.

As a result of comparative measurement of the light guide plate 10 obtained by using the mold by the conventional chemical etching and the light guide plate 1 formed by the above embodiment, the light guide plate 1 shows that the light guide plate 1 is further away from the light source 4. It can be seen that light can be transmitted to the light guide plate 10, while the light guide plate 10 reflects almost half-moon-like light, and the amount of light emitted to the outside of the light guide plate at the protrusion is found to be very small.

As described above, the die member for forming the light guide plate is directly machined to freely and efficiently set the apex angle of the conical portion of the protrusion and the size of the tip r.
Further, since the processing variation of the die member is small, the protrusion 6
Can be narrowed, and the amount of light emitted from the light guide plate can be increased, so that the brightness can be increased about 1.5 times that of the conventional chemical etching. In addition, since the mold member is directly cut with a cutting tool, the machining depth of the mold member can be arbitrarily changed, or it can be machined with a plurality of cutting tools. Can be set arbitrarily, and the output light amount can be set large.

The light guide plate 1 is used for a liquid crystal backlight for a portable telephone, a notebook personal computer or a car navigation device having a larger display screen, and an L-shaped fluorescent lamp as its light source. It can exhibit very excellent performance for liquid crystal backlights used when it is desired to minimize power consumption. Furthermore, the above-mentioned light guide plate can be applied in various other ways, and a light source and a reflection frame are appropriately designed according to the purpose of use of the surface light emitting device using the light guide plate.

Next, FIG. 7 shows a state in which a cutting process is performed on the mold concave portion 102 serving as a cavity for forming the protruding portion 6, and as shown in FIG.
And the tapered portion 30a and the blade tip 3
0b is set to θ2 so that the cutting tool 30
As shown in the figure, a mold concave portion 102 serving as a cavity for the protrusion 6 is cut in the state of being inclined at an angle B during resin injection molding. In addition, the tip apex angle θ1 can be adopted from 100 degrees to 150 degrees, and 130 degrees is the best.

By using the cutting tool 30 having the cutting edge as described above, it becomes possible to perform machining by setting the inclination angle arbitrarily. In this state, the cutting tool 30 can be moved in the front-rear X direction as shown in the figure. By cutting the mold concave portion 102 with a predetermined cutting feed amount while relatively automatically feeding, a cavity for a projection portion described later can be formed.

FIG. 8A is a front view showing the shape of the projection 6, FIG. 8B is a sectional view taken along the line AA of FIG. 8A, and FIG. It is sectional drawing in the BB arrow of a).

In this figure, the base of the protrusion 6 has an oblong shape whose dimension along the normal line of the light incident side surface 1f shown in FIG. 1 is larger than the dimension along the width direction of the light guide member 1. An inclined surface is formed at an inclination angle from the base. As shown in FIGS. 8 (b) and 8 (c), each inclined surface is a light guide member 1.
Inclined surfaces 6a and 6 whose angle with respect to the normal from the back surface of
b, 6c and 6d. Also, the protrusion 6
Are formed as shown. In order to obtain such a shape, the cutting described with reference to FIG. 7 is suitably adopted. The angle γ was best at 25 degrees.

In the projection 6 formed as described above, the incident light which is incident at the critical angle β or less is first applied to the top 6.
After reflecting at k, the inclined surfaces 6a, 6b, 6c, 6d
, Then totally reflected and light L1, L2, L3, L4
As a result, the light is directed to the diffusion plate 5, so that the overall brightness can be increased.

Next, FIG. 9A is a front view showing another shape of the projection 6, FIG. 9B is a sectional view taken along the line AA of FIG. 9A, and FIG. FIG. 10 is a sectional view taken along line BB of FIG.

8, the same components as those already described in FIG. 8 are denoted by the same reference numerals, and the description thereof will be omitted. If the configuration is limited to the configuration in which the protrusions 6 are different from each other, the configuration will be described. Although the inclined surface is formed, of each inclined surface, the light incident side surface 1
inclined surfaces 6c and 6d formed along the normal line of f
The angle between the light guide member 1 and the normal line from the back surface is
a and 6b are formed to be half of the angle γ.
The top 6k of the projection 6 is formed so as to approach a substantially circular shape as shown.

According to the projections 6 formed as described above, the incident light having an angle of less than the critical angle β is first applied to the top 6.
After reflecting at k, the inclined surfaces 6a, 6b, 6c, 6d
, Then totally reflected and light L1, L2, L3, L4
To the diffusion plate 5. Here, since the inclined surfaces 6c and 6d are orthogonal to the light incident side surface 1f, the amount of light is smaller than that of the inclined surfaces 6a and 6b. Since the projections 6 can be provided together, the brightness can be further increased.

According to the above embodiment, the case of the protrusion 6 having the same shape has been described. However, the present invention is not limited to this.
The height of the top 6k of the projection 6 may gradually increase as the distance from the light source increases. Further, by changing the taper angle of the cutting edge of the cutting tool 30, the inclined surface 6
The area of the conical portion formed by a and 6b may be changed.

[0055]

As described above, according to the present invention,
In the case where the density of the projections provided on the light guide plate is steplessly varied, it is possible to prevent the occurrence of variations in the shape of the projections depending on the location, and to reduce the distance between the adjacent projections to reduce the projections. Can increase the installation density of
A surface light emitting device that can increase the amount of light emitted to the outside of the light guide plate away from the light source and can increase overall luminance can be provided.

[0056]

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a surface light emitting device.

FIG. 2 is a sectional view taken along line XX of FIG. 1;

FIG. 3A is a schematic diagram illustrating a state of reflection of light L entering a light guide plate 1; FIG. 2B is a cross-sectional view of a main part showing a state of reflection of light L on the protrusion 6.

FIG. 4 (a) is a manufacturing process diagram of a mold for a light guide plate to be injection molded. (B) is a schematic view showing a molding end step.

FIG. 5 is a view showing a cutting process of a mold for a light guide plate.

FIG. 6 is a view showing a cutting process of a mold for a light guide plate.

FIG. 7 is a cutting diagram of a mold for a light guide plate.

FIGS. 8A and 8B are a plan view showing the shape of the projection, a sectional view taken along the line AA, and a sectional view taken along the line BB.

FIG. 9A is a plan view showing another shape of the protruding portion, and FIG.
It is arrow sectional drawing (b), BB arrow sectional drawing (c).

FIG. 10A is an enlarged sectional view of a conventional light guide plate 10 and FIG. 10B is an enlarged sectional view of an injection mold 201 used for injection-molding the light guide plate 10.

[Explanation of symbols]

 Reference Signs List 1 light guide plate, 1f light incident side surface 2 diffuser plate, 3 reflection frame, 4 light source, 5 substrate 6 projection, 6a, 6b, 6c, 6d inclined surface, 6k top, 30 cutting tool, 101 type member, 102 type concave part β Critical angle

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Keiichiro Tomosai 2-16-20 Shimura, Itabashi-ku, Tokyo Stock company copal (72) Inventor Norimichi Kato 2-16-20 Shimura, Itabashi-ku, Tokyo Inside Copal Co., Ltd.

Claims (6)

[Claims] 1. A light source is disposed on a side or both sides of a light-transmitting plate-shaped light guide member, and guides light from the light source from a light incident surface of the light guide member to the inside. In order to illuminate by scattering light with a diffusion member arranged in parallel to the light emitting surface of the light guide member, a large number of protrusions are formed on the back surface of the light guide member at a high density substantially proportional to the distance from the light entrance surface. A surface emitting device that forms a portion and makes the luminance of the diffusion member uniform over the entire surface, wherein the shape of the protrusion is a first dimension along a normal to the light incident surface, and the light guide member is An oblong base larger than a second dimension along a width direction of the oblong base, an inclined surface extending from the oblong base at an inclination angle, and being formed continuously from the inclined surface and substantially formed on the oblong base. By forming from the parallel tops, the incident light incident at a critical angle β or more determined from the resin material is projected to the protrusions. Area light emitting device characterized by reflection. 2. The surface light emitting device according to claim 1, wherein the inclination angles of the inclined surfaces are all formed at the same angle. 3. The oblique base according to claim 1, wherein the oblique angle of the oblique base is smaller than the oblique angle of the oblong base along the longitudinal direction. The surface emitting device according to claim 1. 4. When the inclination angle of the inclined surface with respect to the longitudinal direction of the oval base is defined as γ, the inclination angle of the inclined surface with respect to the lateral direction of the oval base is formed to be approximately γ / 2. The surface emitting device according to claim 1, wherein: 5. The surface light emitting device according to claim 3, wherein the top is formed so as to approach a substantially circular shape. 6. A light source is disposed on a side or both sides of a light-transmitting plate-shaped light guide member, and guides light from the light source from a light incident surface of the light guide member to the inside. In order to illuminate by scattering light with a diffusion member arranged in parallel to the light emitting surface of the light guide member, a large number of protrusions are formed on the back surface of the light guide member at a high density substantially proportional to the distance from the light entrance surface. A surface light emitting device that forms a portion and makes the luminance of the diffusion member uniform over the entire surface, wherein the shape of the protrusion is a circular base, and an inclined surface extending from the circular base with an inclination angle. And a top formed continuously from the inclined surface, so that incident light incident at a critical angle β or more determined from the resin material is reflected by the projection.