KR20010062504A - Light guide plate, surface light source apparatus, and liquid crystal display - Google Patents

Abstract

PURPOSE: To improve utilization efficiency of illuminating light compared with a conventional one with respect to a light transmission plate, a surface light source device and a liquid crystal display device, especially constitution wherein an optical path of illuminating light made incident from the rear surface side of the light transmission plate is bent by an optical path bending surface to propagate it. CONSTITUTION: A projection 16K formed by a pair of inclinations 16I, 16J extending in the thickness direction is formed right over the light emitting point of at least the primary light source of the optical path bending surface 16C.

Description

Light guide plate, surface light source device and liquid crystal display device {LIGHT GUIDE PLATE, SURFACE LIGHT SOURCE APPARATUS, AND LIQUID CRYSTAL DISPLAY}

The present invention relates to a light guide plate, a surface light source device and a liquid crystal display device, and in particular, a light guide plate improved to perform light input efficiently by using an optical path bending surface, a surface light source device using the improved light guide plate, and the surface light source. A liquid crystal display device using the device for illumination of a liquid crystal display panel. The present invention is applied to, for example, a liquid crystal display device attached to a mobile telephone, a surface light source device and a light guide plate used therein.

It is well known that the liquid crystal display panel of the liquid crystal display device is illuminated by the surface light source device. In general, the surface light source device includes a light guide plate and a primary light source for supplying primary light to the light guide plate. Conventionally, rod-shaped fluorescent lamps (cold cathode tubes) have been widely used as primary light sources, but in recent years, those using point-like or local light emitting sources such as LEDs (light emitting diodes) have been adopted.

In particular, in a relatively small liquid crystal display device attached to a mobile telephone, this is becoming mainstream.

8 shows an exploded perspective view of an example of a liquid crystal display device in which a liquid crystal display panel is illuminated by a conventional surface light source device using a local light emitting source. 9, the cross-sectional structure of the surface light source device is shown.

Referring to the drawings, the liquid crystal display device 1 has a liquid crystal display panel 2 which is illuminated by the surface light source device 3. The surface light source device 3 includes a light guide plate 6, an LED (point light source 8), and a reflection sheet 5. The light guide plate 6 has a substantially wedge shaped cross section, one major surface providing an exit surface 6B, and the other major surface providing a rear surface 6A. In addition, the light guide plate 6 has a shape cut at an inclination of approximately 45 degrees so as to connect the exit surface 6B and the back surface 6A at the end on the thick side thereof. This inclined surface provides the optical path bending surface 6C.

The reflective sheet 5 is made of, for example, a white PET film, reflects the light leaked from the back surface 6A and returns it to the light guide plate 6 to prevent the loss of light. In addition, light is generated in various propagation directions by the diffuse reflection to promote the emission from the emission surface 6B.

One or more LEDs 8 are arranged according to the required brightness, and constitute the primary light source as a whole. In this example, four LEDs are arranged at equal intervals. As can be seen from the drawing in FIG. 9, the LED 8 is disposed almost immediately under the optical path bent surface 6C, and supplies primary light toward the optical path bent surface 6C through the incident surface 6D.

Here, the incident surface 6D is a band-shaped surface region provided by the edge portion of the back surface 6A, and meets the optical path bent surface 6C at the tip of the edge portion to form one edge line.

When the LED 8 is turned on, light is introduced into the light guide plate 6 through the incident surface 6D. Most of the introduced light is internally incident on the optical path bending surface 6C. Subsequently, a substantial portion of the internal incident light is internally reflected at the optical path bent surface 6C, whereby a direction change of approximately 90 degrees is achieved. The light internally reflected at the optical path bent surface 6C propagates in the light guide plate 6 along the direction falling away from the optical path bent surface 6C to the edge as a whole.

As is well known, in this process the exit surface 6B while experiencing the back surface 6A, the internal reflection by the exit surface 6B, the reflection by the reflecting sheet 5 (after leakage from the back 6A), and the like. Emission slowly occurs from). This output light (light output) is used for illumination of the liquid crystal display panel 2.

A problem in the conventional liquid crystal display device or the surface light source device described above is that some light leaks to the outside without internal reflection upon internal incidence at the optical path bending surface 6C.

This is because the total reflection condition is broken for some input light during internal reflection to the optical path bending surface 6C. That is, although the advancing direction of the light supplied from the LED 8 is comparatively provided, it cannot be denied that there is a slight angular spread.

As is well known, if the light guide plate 6 is a conventional resin material (e.g. PMMA: methyl methacrylate: refractive index 1.492), under the condition of setting the angle of the optical path bending surface 6C to almost 45 degrees, the critical angle is almost 42 degrees. Therefore, the light which internally injects into the optical path bending surface 6C at an incident angle of 45 degrees from immediately below in FIG. 9 is totally reflected. However, a part of light that is inclined by a few degrees (incidence angle is less than the critical angle) leaks to the outside.

The light leakage can be reduced by changing the inclination angle of the optical path bending surface 6C and the material (refractive index) of the light guide plate 6. However, the inclination angle of the optical path bent surface 6C cannot be largely changed at 45 degrees. In addition, inexpensive light guide plate materials are limited, and a large refractive index is not preferable.

Accordingly, it is an object of the present invention to provide a surface light source device, a liquid crystal display device and an improved light guide plate used therein which solve the above problems. Specifically, the present invention is to provide a light guide plate with an improved optical path bending surface so as to perform a redirection of the optical path with respect to the light input from the light emitting light source, a surface light source device and a liquid crystal display device using the same.

FIG. 1 is an exploded perspective view schematically illustrating an entire arrangement of a liquid crystal display device according to a first embodiment of the present invention.

FIG. 2 is a plan view (A) and a side view (B) of the optical path bending surface of the light guide plate employed in the embodiment shown in FIG. 1.

3 is a plan view showing an optical path bent surface with respect to the light guide plate employed in the second embodiment.

4 is a plan view (A) and a side view (B) showing the optical path bending surface of the light guide plate employed in the third embodiment.

FIG. 5 is an enlarged view of the periphery of the primary light source with respect to the light guide plate employed in the fourth embodiment.

FIG. 6 is an enlarged view of the periphery of the primary light source with respect to the light guide plate employed in the fifth embodiment.

FIG. 7 is a plan view showing the optical path bent surface of the light guide plate employed in the sixth embodiment.

Fig. 8 is an exploded perspective view showing the outline of the entire arrangement of a liquid crystal display device having a conventional surface light source device using a local light source.

FIG. 9 is a diagram showing a cross section of the surface light source device shown in FIG. 8. FIG.

Explanation of symbols on the main parts of the drawings

1, 11... Liquid crystal display device 2. LCD panel

3, 13... Surface light source devices 6, 16, 26, 36, 46; Light guide plate

6A, 16A, 26A, 36A, 46A... Back of light guide plate

6B, 16B, 26B, 36B, 46B. Exit face of light guide plate

6C, 16C, 26C, 36C, 46C... Optical path

6D, 16D, 26D, 36D, 46D... Incident surface of light guide plate

16K, 26K, 36K, 46K... spin

16I, 16J, 26I, 26J, 36I, 36J... Slope of the projection

According to the present invention, first, an emission surface for outputting light, a rear surface oriented with the emission surface, an entrance surface formed at an edge portion of the rear surface for inputting light, and light input through the entrance surface It is applied to a light guide plate having an optical path bending surface for directing in a direction away from the surface.

An essential point of the improvement of the present invention is to form at least one protrusion on the optical path bent surface of the light guide plate of this type. This projection is provided with a pair of slopes extending in the direction connecting the exit surface and the rear surface. This protrusion is formed to have a function of bending an optical path by two internal reflections.

At least one of the protrusions is formed at a position corresponding to a position (generally, a position immediately above each light source.

By this basic feature, the optical path bending surface can perform the direction change of the optical path with respect to the light input from the light emitting light source. Because of the presence of projections with slopes as described above, in the case of internal incidence into each slope, the internal incidence angle becomes larger as compared with the case of internal incidence only into a flat surface (no projection) as in the prior art, and the total reflection condition is hardly broken. Because it becomes.

That is, the large internal incident angle, of course, facilitates total reflection and reduces light leakage. As a result, the amount of light propagated in the optical path bending surface is transmitted, and the brightness of the exit surface is also improved. When applied to a liquid crystal display device, the display screen becomes bright.

Here, in consideration of the case where the spacing of the light sources is narrow, and even if not a small amount even at a position slightly away from the light source, the protrusions are preferably formed along the edges.

In addition, the valley formed between the neighboring protrusions may become shallow as it approaches the exit surface, or may be interrupted in front of the exit surface.

Next, the surface light source device according to the present invention includes at least one primary light source and a light guide plate. The light guide plate includes an emission surface for outputting light, a rear surface oriented with the emission surface, an incident surface formed at an edge portion of the rear surface for inputting light supplied from the primary light source, and the incident surface. The optical path bending surface for directing the light input through the direction away from the incidence surface, and the above-described improvement to the optical path bending surface.

That is, at least one projection is formed on the optical path bent surface,

The projection is provided with a pair of slopes for performing optical path bending by two internal reflections. Each slope pair extends in the direction which connects the said emission surface and the said back surface. At least one of the protrusions is formed at a position corresponding to the position (one or more) at which the main light input is made in the incident surface.

Also in the surface light source device, it is preferable that the projection is formed repeatedly along the edge portion.

In addition, valleys formed in adjacent stone periods may become shallower as they approach the exit surface, or may be interrupted just before the exit surface.

Further, when the improved surface light source device is arranged for illumination of the liquid crystal display panel, the liquid crystal display device according to the present invention can be obtained.

(Example)

Next, embodiments of the present invention will be described with reference to FIGS. 1 to 7. In addition, in order to understand easily in each figure, the dimension, shape, etc. of each element are exaggerated and shown suitably. In addition, the code | symbol common is attached | subjected about the element used in common with FIG. 8, FIG. 9, and the overlapping description is abbreviate | omitted suitably.

First embodiment

Referring to Fig. 1, the schematic structure of the liquid crystal display device of this embodiment is shown.

The liquid crystal display device 11 includes a surface light source device 13 for illuminating the liquid crystal display panel 2 from behind.

The surface light source device 13 includes a light guide plate 16, an LED (point light source 8), and a reflection sheet 5. The light guide plate 16 is a translucent member made of, for example, an acrylic resin, and has a substantially wedge-shaped cross section, one major surface providing an exit surface 16B, and the other major surface providing a rear surface 16A. do.

The light guide plate 16 is equipped with the optical path bending surface 16C which connects the emission surface 16B and the back surface 16A at the thick end part. This optical path bent surface 16C has protrusions 16K repeatedly formed along an imaginary surface inclined almost 45 degrees with respect to the exit surface 16B. In other words, this imaginary surface provides the general surface (the plane left in the case of the projection 16K except for the projection 16K) of the optical path bending surface 16C.

As shown by enlarged drawing B in FIG. 1, each projection 16K is equipped with a pair of slopes 16I and 16J. Each slope pair 16I, 16J extends in the direction which connects the emission surface 16B and the back surface 16A.

Incidentally, each pair of slopes 16I and 16J are inclined in opposite directions with respect to the general surface of the optical path bent surface 16C to form a triangular roof-shaped prism cut. The intersection of each pair of slopes 16I and 16J corresponds to the ridge line of each prism cut. Note that this ridgeline (intersection of slope pairs) is inclined almost 45 degrees with respect to the exit surface 16B.

In addition, the repeat pitch (interval between neighboring roofs) of the projection 16K is, for example, 50 µm. Correspondingly, the size of the projections 16K is also a minute of the same degree. For this reason, the valley bottom part formed between mutually adjacent protrusions 16K produces | generates strong reflection linearly, and this prevents it from appearing on the exit surface 16B. This is a kind of so-called "recruitment" and is likely to appear when the size of the projection 16K is increased to some extent.

Next, the behavior of the light in the liquid crystal display device 11 thus configured will be described. Regarding the operation of the optical path bending surface 16C, reference is made to FIG. 2. FIG. 2: shows the optical path bending surface 16C with the top view (A) and the side view (B).

When the LED 8 is turned on, light is introduced into the light guide plate 16 through the incident surface 16D. Most of the introduced light enters the optical path bent surface 16C internally. What is important here is that the optical path bent surface 16C is not flat unlike the conventional one (see Figs. 8 and 9), and the projections composed of the slope pairs 16I and 16J are repeatedly formed.

Thereby, internal incidence is made with respect to one slope of the slope pairs 16I and 16J of arbitrary projections. From the point of view of the amount of light, the main focus of the internal incident light proceeds almost immediately up from the light emitting point of any of the LEDs 8, and passes to the one of the pair of slopes 16I and 16J via the incident surface 16D. It is the light to reach. 2 (A) and 2 (B) show examples of a general optical path. Here, the angle at which the optical path bending surface 16C (exactly, the ridgeline of the prism cut, to the general surface representing the surface 16) becomes the back surface 16A is represented by generalizing by the reference sign θ, and from the LED 8 The direction of incidence on the incident surface 16D is also slightly inclined at vertical incidence.

In both figures, it progresses upward (nearly perpendicular to the surface) from the light emitting point of the LED 8 shown by the code | symbol P, and internally injects into one slope 16I. The light internally reflected at the slope 16I is again internally incident to the other slope 16J and is again reflected internally.

Here, the incidence angle at the time of two internal incidences is the case (45 degrees around and around) of the conventional optical path bending surface 16C (see Figs. 8 and 9) which has been redirected by almost 90 degrees with only one internal reflection. It is very small in comparison. That is, in this embodiment according to the characteristics of the present invention, as shown by the arrows in the figure, the change of direction of almost 90 degrees is achieved by dividing into two internal reflections.

The incidence angle of each internal incidence on the slopes 16I and 16J is much smaller than 45 degrees, which will be easily understood as an advantage. In addition, even if the order of internal incidence to the slopes 16I and 16J is in the order of slopes 16I to 16J, or the slopes 16J to 16I, the direction of the direction change is not particularly changed. Do not.

Here, the fact that the incidence angle of each internal incidence on the slopes 16I and 16J is sufficiently small means that the total reflection condition is satisfied with margin. Therefore, the total reflection condition is not easily broken at the time of internal incidence to the slopes 16I and 16J even for the light component whose incidence angle to the incidence surface 16D is inclined from the considerably vertical direction. This provides a fundamental difference from the prior art (flat optical path bending surface 6C).

In this way, almost all of the internally incident light to the optical path bending surface 16C is successively internally reflected (total reflection) on the slopes 16I and 16J, so that at the optical path bending surface 16 (i.e., at the edge portion or the incident surface ( 16D) is converted into light L propagating in the falling direction.

The above operation is not particularly changed from the conventional one. That is, as is well known, in the process of internal propagation, while experiencing the back reflection 16A, the internal reflection by the exit surface 16B, the reflection by the reflection sheet 5 (after leakage from the back 16A), and the like. From the exit surface 16B, emission gradually occurs. This output light (light output) is used for illumination of the liquid crystal display panel 2.

Incidentally, the angle θ at which the optical path bent surface 16C (the normal surface) forms the back surface 16A is typically around 45 degrees, but is selected by design in a fairly large range, for example, in the range of 10 degrees to 70 degrees. It is possible. It should be noted, however, that the optimum prism normal angle (angle formed by the slopes 16I and 16J) also naturally changes with the angle θ.

In addition, when the light guide plate 16 is thin, it should be noted that if the angle θ is made too large, the width that can be set to the incident surface 16D is narrowed. On the contrary, when angle (theta) is made small, the width which can be set to the incident surface 16D becomes wide. This wide degree of freedom in selecting the angle θ is an advantage of the present invention.

It should be noted that in the conventional optical path bending surface 6C (Figs. 8 and 9), the inclination angle was selected only in a narrow range centered on 45 degrees. For example, the inclination angle of the optical path bent surface 6C is only a few degrees below 45 degrees, and the total reflection condition is hardly satisfied, and the amount of light leakage from the optical path bent surface 6C increases rapidly. In the present invention, even if the inclination angle θ is made small, the total reflection condition is not easily broken.

In addition, the direction of the optical path L after the change of direction is also adjustable through the design of the angle (normal angle of the prism cut) formed by the slopes 16I and 16J. The actual selection range of the stationary angle corresponding to the above range 10 degrees to 70 degrees of the angle θ is about 60 degrees to 120 degrees.

Moreover, it is preferable that the direction of the main optical path L after reorientation is designed to be suitable for uniform emission from the emission surface 16B. In general, when the main optical path L is parallel to the exit surface 16B, the light tends to be sent far from the entrance surface 16D, and when it is tilted, the tendency is weakened.

Although the above is the outline of the first embodiment, various modifications are allowed in the form of the optical path bent surface formed on the edge portion for performing light input of the light guide plate. In the following, these examples will be described in the second to sixth embodiments.

Second embodiment

Referring to Fig. 3, the optical path bent surface 26C is shown in plan view seen from the upper side of the emission surface 26B with respect to the light guide plate 26 employed in the second embodiment. The light guide plate 26 is equipped with the optical path bending surface 26C which connects the emission surface 26B and back surface 26A (not shown) at the edge part of the thick side.

This optical path bending surface 26C has a plurality of projections 26K along an imaginary surface inclined with respect to the emission surface 26B. However, unlike the first embodiment, the projection 26K is located near the position corresponding to the light emitting point P of the LED 8 depicted by the broken line, that is, the position where the light input to the light guide plate 26 is mainly performed. It is formed only in the vicinity of. In the portion where the projections 26K are not formed (corresponding to the blank section of the LED 8), the optical path bent surface 26C forms a flat slope (near 45 degree inclination).

Each projection 26K is provided with a pair of slopes 26I and 26J. Each slope pair 26I, 26J is extended in the direction which connects the emission surface 26B and the back surface 26A (not shown). Incidentally, each pair of slopes 26I and 26J are inclined in opposite directions with respect to the general surface of the optical path bent surface 26C to form a triangular roof-shaped prism cut. The intersection of each pair of slopes 26I and 26J corresponds to the ridge line of each prism cut. The size and repeated pitch of the projections 26K may be about the same as those of the projections 16K of the first embodiment.

However, the inclination with respect to the general surface of the optical path bending surface 26C of the slopes 26I and 26J is based on the position (main light input position) corresponding to the light emitting point P with respect to the individual projections 26K. The slope on the far side is formed steeply compared to the slope on the near side. In the example of FIG. 3, in the right half, the slope 26I is steeper than the slope 26J, and in the left half, the slope 26J is steeper than the slope 26I. As shown in the figure, the difference between the inclinations is remarkable so as to fall from the position corresponding to the light emitting point P (main light input position).

The inclination difference was given to the pair of slopes twice at the position away from the light emitting point P, the internal incidence into the slope 26I or the slope 26J was performed at a slightly oblique side, correspondingly maintaining the total reflection condition twice. This is to facilitate the change of direction by reflection.

By this study, the optical path bend surface 26C efficiently achieves the redirection even with respect to the light component away from the main light (light input right next to the light emitting point P). As a result, the utilization efficiency of light is further improved.

Third embodiment

Referring to FIG. 4, the optical path bending surface 36C is shown in plan view A and side view B viewed from the upper side of the emission surface 36B with respect to the light guide plate 36 employed in the third embodiment. The light guide plate 36 is equipped with the optical-path bending surface 36C which connects the emission surface 36B and the back surface 36A (tip edge of the entrance surface 36D) to the thick end part.

This optical path bending surface 36C has a plurality of projections 36K along an imaginary surface inclined with respect to the emission surface 36B. And the depth of the valley accompanying these projections 36K falls from the position corresponding to the light emitting point P of the LED 8 depicted by the broken line, in other words, the position where the light input to the light guide plate 36 is mainly made. It is gradually becoming shallow. Then, the depth is zero just in front of the emission surface 36B and the surface is shifted to a flat surface.

Incidentally, the slopes 36I and 36J are curved surfaces that are three-dimensionally twisted and curled, and as the slope thereof approaches the emission surface 36B, the slopes 36I and 36J smoothly transition to the flat surface in response to the contact point of the valley.

This transition position (boundary) is set such that the incident angle θ1 (see FIG. 4 (B)) of light incident therein is larger than the critical angle.

Also in this embodiment, the internal reflection of the pair of slopes 36I and 36J of the projection 36K easily becomes total reflection, so that an efficient redirection is achieved.

Fourth embodiment

As shown in FIG. 5, in the fourth embodiment, a plurality of projections are repeatedly formed only in a predetermined section corresponding to the LED 8. As shown briefly, each projection forms a high peak on the back side of the light guide plate, and the height of the peak gradually decreases toward the exit surface. Then, the transition is made to the flat optical path bending surface just in front of the exit surface. The peak of each protrusion is formed in triangular shape by the intersection of two slopes. In other words, the two slopes are not curved.

As shown in the figure, the projections in this embodiment correspond to portions where peaks are formed on the flat optical path bending surface as a reference surface. Needless to say, a valley is formed between the peak and the peak, and the valley gradually becomes shallow toward the exit surface and disappears at the position where it moves to the flat surface.

Also in this embodiment, the internal reflection of the pair of slopes of the projections is easily total reflection, so that efficient redirection is achieved. Needless to say, it is preferable that such a projection forming section is formed corresponding to each LED 8.

Fifth Embodiment

As shown in Fig. 6, in the fifth embodiment, a plurality of projections are repeatedly formed only in a predetermined section corresponding to the LED 8. As shown briefly, a deep valley is formed on the back side of the light guide plate, and the depth of the valley gradually becomes shallow toward the exit surface. Then, the process shifts to the flat optical path bending surface just in front of the exit surface.

And a protrusion is formed between the valley and the valley which adjoin each other. Each protrusion is formed in triangular cross-sectional shape by the intersection of two slopes. The two slopes are not curved.

Also in this embodiment, the internal reflection of the pair of slopes of the projections is easily total reflection, so that efficient redirection is achieved. Needless to say, it is preferable that such a projection forming section is formed corresponding to each LED 8.

Sixth embodiment

As shown in FIG. 7, in the sixth embodiment, the optical path bent surface 46C of the light guide plate 46 is formed along a smoothly curved general surface. Each of the projections 46K is formed in a large number in an aspect having a pair of slopes inclined with respect to the curved general surface.

As shown, the intersections of the slope pairs form curved ridges and valleys are formed between neighboring ridges. These valleys also draw curved lines as indicated by broken lines. The depth of the valley is formed so as to gradually become shallow toward the exit surface 46B on the incident surface 46D side. Moreover, the summit angle which the pair of slopes which meet in a ridgeline becomes constant over the full length of a ridgeline. Also in this embodiment, the internal reflection of the pair of slopes of the projections is easily total reflection, so that efficient redirection is achieved.

Other variations

The various embodiments described above are not meant to limit the scope of the invention. For example, the following modifications are allowed.

(a) In each of the above embodiments, a plurality of protrusions are formed over the entire length of the edge portion or around the main input position of the light. However, in some cases, one projection may be formed per LED, or only one projection may be formed in the entirety. In this case, however, it is preferable to increase the size of the projections as necessary.

(b) The shapes of the projections or the optical path bending surfaces in the above embodiments may be used in combination. For example, the shape of FIG. 7 (6th Embodiment) which used the curved surface in FIG. 5 (4th Embodiment) or FIG. 6 (4th Embodiment) was introduce | transduced, and the peak based on the curved surface (FIG. 5) Or valleys (FIG. 6) may be formed in a defined section.

(c) In each of the above embodiments, the pair of slopes of the projections are directly connected to form a sharp ridgeline (intersection). However, it is also possible to adopt a form in which the direct connection is stopped and the ridge is rounded. It is also possible to give roundness to the entire slope to form rounded ridges and sharp ridges (intersections).

(d) Machining of the exit surface or the back surface of the light guide plate may be carried out as necessary. Processing includes, for example, promotion of emission by roughening of the emission surface or the rear surface, formation of micro projections, and the like.

(e) In order to adjust the various characteristics of the light emitted from the light guide plate, one or more additional sheets may be arranged along the emission surface. The additional sheet is, for example, a prism sheet and a light diffusion sheet.

(f) As a light guide plate, what is called a light-scattering light guide body may be employ | adopted instead of a transparent resin. A light scattering light guide is a well-known light guide which has scattering ability by microparticles | fine-particles etc. inside.

(g) Although the light guide plate in each said Example has a wedge-shaped cross section, this does not limit this invention. For example, a light guide plate having a uniform thickness may be employed as a whole, and an optical path bent surface may be formed at one end or two or more ends by the above-described method. In this case, an appropriate number of point light emitting sources and incidence surfaces are formed according to the position and number of each optical path bent surface.

(h) The present invention can also be applied to surface light source devices used for applications other than backlighting of liquid crystal display panels of liquid crystal display devices such as mobile phones and portable personal computers, and light guide plates used therein. For example, it may be applied to a surface light source device for front lighting of a liquid crystal display panel.

Further, the present invention can be widely applied to lighting devices for liquid crystal televisions and other electronic devices, liquid crystal display devices, and light guide plates used therein.

The large internal incidence, of course, facilitates total reflection and reduces light leakage. As a result, the amount of light propagated in the optical path bending surface is transmitted, and the brightness of the exit surface is also improved. When applied to a liquid crystal display device, the display screen becomes bright.

Claims (12)

An emission surface for outputting light, a rear surface oriented with the emission surface, an entrance surface formed at an edge portion of the rear surface for inputting light, and light input through the entrance surface in a direction away from the entrance surface; A light guide plate having an optical path bending surface for directing, At least one protrusion is formed on the optical path bending surface, The projection is provided with a pair of slopes extending in a direction connecting the exit surface and the rear surface to bend the optical path by two internal reflections, At least one of the projections is formed corresponding to a position at which a main light input is made in the incident surface. The light guide plate according to claim 1, wherein the protrusion is repeatedly formed along the edge portion. The light guide plate according to claim 1 or 2, wherein valleys formed in adjacent stone periods become shallower as they approach the exit surface. 4. The light guide plate according to claim 3 wherein the valley is stopped just in front of the exit surface. A surface light source device comprising at least one primary light source and a light guide plate, The light guide plate may include an emission surface for outputting light, a rear surface oriented with the emission surface, an entrance surface formed at an edge portion of the rear surface for inputting light supplied by the primary light source, and an input through the entrance surface A light guide plate having an optical path bending surface for directing the light in a direction away from the incident surface, At least one protrusion is formed on the optical path bending surface, The projection is provided with a pair of slopes extending in a direction connecting the exit surface and the rear surface to bend the optical path by two internal reflections, At least one of the projections is formed corresponding to a position at which a main light input is made in the incident surface. 6. The surface light source device according to claim 5, wherein the protrusion is repeatedly formed along the edge portion. 7. The surface light source device according to claim 5 or 6, wherein valleys formed in adjacent stone periods become shallower as they approach the exit surface. 8. The surface light source device according to claim 7, wherein the valley is stopped in front of the exit surface. A liquid crystal display device for illuminating a liquid crystal display panel using a surface light source device, The surface light source device includes at least one primary light source and a light guide plate; The light guide plate may include an emission surface for outputting light, a rear surface oriented with the emission surface, an entrance surface formed at an edge portion of the rear surface for inputting light supplied by the primary light source, and an input through the entrance surface A light guide plate having an optical path bending surface for directing the light in a direction away from the incident surface, At least one protrusion is formed on the optical path bending surface, The projection is provided with a pair of slopes extending in a direction connecting the exit surface and the rear surface to bend the optical path by two internal reflections, The liquid crystal display device according to claim 1, wherein at least one of the projections is formed corresponding to a position at which a main light input is made in the incident surface. 10. The liquid crystal display device according to claim 9, wherein the protrusion is repeatedly formed along the edge portion. The liquid crystal display device according to claim 9 or 10, wherein valleys formed in adjacent stone periods become shallower as they approach the exit surface. 12. The liquid crystal display device according to claim 11, wherein the valley is stopped in front of the exit surface.