KR20020082778A - Light guide plate, surface light source device, and image display - Google Patents

Abstract

PURPOSE: To provide a surface light source apparatus, which can prevent the appearance of a bright line and can attain a bright and even surface illumination. CONSTITUTION: A fluorescent lamp 5 is disposed to face an incident face 4 of a light guide plate 3. Light from the fluorescent lamp 5 enters the light guide plate 3 via the incident face 4 and transmits through the inside of the light guide plate 3. During the light transmission, part of the light whose incident angle with respect to an emission face 6 is smaller than a critical angle is emitted from the emission face 6 of the light guide plate 3. Plural prismatic projections 13 having triangular cross-section are formed on the rear face 11 of the light guide plate 3, and the prismatic projections 13 that are located in the proximity L of the incident face of the light guide plate 3 are roughened. With such configuration, the light reflected or refracted on the prismatic projections 13 of the light guide plate 3 is diffused on the roughened surface part in the proximity L of the incident face. Thus, a bright line which appears on the emission face 6 of the light guide plate 3 in the proximity L of the incident face becomes blurred and is made inconspicuous.

Description

Light guide plate, surface light source device, and image display device {LIGHT GUIDE PLATE, SURFACE LIGHT SOURCE DEVICE, AND IMAGE DISPLAY}

The present invention provides a surface light source device and a surface light source device suitable for use as a backlight for illuminating a liquid crystal display panel (lighting member) in a plane in a portable personal computer, a navigation device, a word processor, an electronic notebook, and the like. An image display apparatus and a light guide plate used in these surface light source apparatuses or image display apparatuses.

For example, a surface light source device used in a portable personal computer arranges a fluorescent lamp as a primary light source on the side face (incident surface) of the light guide plate, and emits light from the fluorescent lamp onto the plane through the light guide plate. Then, the liquid crystal display panel is illuminated by the emitted light. Such a surface light source device constitutes an image display device together with a liquid crystal display panel.

(First Prior Art)

12 is an exploded perspective view showing a first conventional example of this type of image display device 31. The image display device 31 includes a fluorescent lamp 34 arranged along the light guide plate 32 and its entrance face 33, a first prism sheet 36 and a second prism sheet arranged on the exit face 35 side. 37 is provided. As is well known, the prism sheet 36 and the second prism sheet 37 have a function of collecting and outputting the light emitted from the exit surface 35 in a substantially front direction.

That is, the first prism sheet 36 functions to collect the outgoing light in the normal direction of the outgoing surface 35 with respect to the plane parallel to the incidence surface 33, and the second prism sheet 37 has the incidence surface 33 Function to collect the outgoing light in the normal direction of the outgoing surface 35 with respect to the in-plane perpendicular to). On the upper side of the second prism sheet 37, the protective sheet 38 and the liquid crystal display panel 39 are sequentially stacked. On the other hand, the reflection sheet 41 is arrange | positioned at the lower surface (back surface) side of the light guide plate 32. As is well known, the reflecting sheet 41 functions to return the light leaked from the back surface of the light guide plate 32 back into the light guide plate 32 to prevent loss of light.

(Second prior art)

13 shows an image display device 41 according to the second prior art. This image display device 41 is an improvement of the image display device 31 described above to achieve a thinner and lighter weight. In the image display device 41, a prism protrusion 42 having a substantially triangular cross section corresponding to the first prism sheet 36 in FIG. 12 is formed on the rear surface of the light guide plate 43. And the prism sheet 45 corresponding to the 2nd prism sheet 37 of FIG. 12 is arrange | positioned so that the exit surface 44 of the light guide plate 43 may be arrange | positioned.

The prism protrusion 42 on the rear side of the light guide plate 43 functions to collect light components in the normal direction of the emission surface 44 with respect to the in-plane parallel to the incident surface 48 among the light from the fluorescent lamp 47. Moreover, the prism sheet 45 arrange | positioned facing the exit surface 44 of the light guide plate 43 mainly functions to orient the traveling direction of the light radiate | emitted from the exit surface 44 to the normal direction of the exit surface 44. As shown in FIG.

The output light from the prism sheet 45 is supplied to the liquid crystal display panel 50 through the protective sheet 49.

Since the image display device 41 eliminates the need for the first prism sheet 36 used in the arrangement of FIG. 12, the thickness of the image display device 41 and the weight of the image display device 41 are reduced. It becomes possible.

However, in the above-described image display apparatus 41, as shown in FIG. 13, the bright line (locally bright linear part; 52) which originates in the light incident from the light source side edge part 51 of the light guide plate 43, There exists a problem that it generate | occur | produces in the vicinity of the incident surface on the exit surface 44. FIG. This problem also occurs in the image display apparatus 31, but particularly noticeable bright lines appear easily in the image display apparatus 41. This is considered to be because the light incident from the edge portion and reaching the rear surface of the light guide plate is directly reflected toward the exit surface by the prism protrusion. In such a case, it is necessary to use the illumination of the liquid crystal display panel, avoiding the portion 52 in which the bright line of the exit surface 44 is generated.

If this is not done, the part where the bright line is generated is also observed on the display panel, and display quality deteriorates. As a result, a part of the exit surface 44 cannot be effectively used for illumination, and a light guide plate of a large size must be used, which is a deterrent to the compactness of the device.

Accordingly, an object of the present invention is to provide a light guide plate, a surface light source device, and an image display device which can prevent the occurrence of bright lines on the exit surface of the light guide plate.

1 is an exploded perspective view showing a schematic structure of an image display device according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view along the line A-A in FIG. 1.

FIG. 3 is a view taken from the direction B in FIG. 2 and depicted with the reflective sheet removed.

4 is a schematic view showing a side of the light guide plate.

FIG. 5 is a partially enlarged view of the prism sheet, and an enlarged portion E of FIG. 2 is depicted.

FIG. 6 is a view for explaining a light reflection state of the prism projections, (a) shows a reflection state of light propagating inside the light guide plate, and (b) shows a reflection state of light incident from the back side of the light guide plate.

It is a figure explaining the condensing state of the emitted light by prism protrusion.

8 is a graph showing a characteristic curve of luminance levels in order to explain the effect of roughening the vicinity of the incident cross section of the prism protrusion.

Fig. 9 is a diagram illustrating the functions of the prism protrusions of the light guide plate and the prism protrusions of the prism sheet, (a) shows the function of the prism protrusions of the light guide plate, and (b) shows the function of the prism protrusions of the prism sheet.

10 is an exploded perspective view showing a schematic configuration of an image display device according to a second embodiment of the present invention.

11 is a longitudinal sectional view for explaining an image display device according to a third embodiment of the present invention.

12 is an exploded perspective view showing a schematic configuration of an image display device according to a first conventional example.

FIG. 13 is a diagram showing a luminance level curve of a longitudinal section near the incident cross section of the light guide plate and the emitted light in the image display apparatus according to the second conventional example.

* Description of the symbols for the main parts of the drawings *

1: image display apparatus 3: light guide plate

4: incident section 5: fluorescent lamp (light source)

6: exit surface 10: liquid crystal display panel (lighting member)

11: back side (side opposite to exit surface)

12: surface light source device 13: prism protrusion

L: Near the incident cross section (side side)

The present invention firstly comprises an emission surface for emitting light, a back surface positioned on the opposite side to the emission surface, a light guide plate having an incidence cross section for incidence of light, and a primary light source disposed opposite the incidence cross section. Applies to one surface light source device.

According to a feature of the present invention, a plurality of prism protrusions having a substantially triangular cross section are formed on the rear surface substantially in parallel with each other, and the surface of the prism protrusion includes a roughening area within a predetermined range near the incident cross section. Doing.

With this feature, a plurality of prism protrusions having a substantially triangular cross section formed on the rear surface of the light guide plate promotes emission from the entrance surface, and roughens at least a part of the prism protrusion surface in a predetermined range near the entrance end surface, thereby roughening the surface of the light guide plate. It is possible to prevent the luminance deviation on the bright line which tends to occur around the incident cross section.

Therefore, it is preferable that the formation density of the said roughening area | region falls as it moves away from the said incidence end surface at the edge part of the side away from the said incidence end surface of the said predetermined range. Increasingly decreasing the density of such roughened areas is desirable to make the boundary between the predetermined range and other parts inconspicuous.

The present invention provides an illumination member for displaying an image, an emission surface for emitting light, a back surface positioned on an opposite side to the emission surface, a light guide plate having an incident end surface for incidence of light, and disposed opposite to the incident end surface. The present invention is also applied to an image display device that is illuminated by a surface light source device having a primary light source.

According to a feature of the present invention, a plurality of prism protrusions having a substantially triangular cross section are formed on the rear surface substantially in parallel with each other, and the surface of the prism protrusion includes a roughened area within a predetermined range near the incident cross section. .

With this feature, roughening at least a part of the prism protrusion surface in a predetermined range in the vicinity of the incident end surface is roughened in the vicinity of the incidence cross section while facilitating the exit from the exit surface by a plurality of prism projections having a substantially triangular cross section formed on the rear surface of the light guide plate. It is possible to prevent the luminance deviation on the bright line which tends to occur around the incident cross section. As a result, the display quality of the image display device is improved.

Therefore, it is preferable that the formation density of the said roughening area | region falls as it moves away from the said incidence end surface at the edge part of the side away from the said incidence end surface of the said predetermined range. Increasingly decreasing the density of such roughened regions makes the boundary between the predetermined range and other portions inconspicuous.

In addition, the present invention is also applied to a light guide plate having an emission surface for emitting light, a rear surface located on the opposite side to the emission surface, and an incident cross section for incidence of light, and has excellent emission efficiency and thus around the incident surface on the emission surface. This is to prevent the luminance deviation on the bright line which is easy to occur at.

According to a feature of the present invention, a plurality of prism protrusions having a substantially triangular cross section are formed on the rear surface of the light guide plate substantially parallel to each other, and the surface of the prism protrusion includes a roughened area within a predetermined range near the incident end surface of the light guide plate. have. Therefore, it is preferable that the formation density of the said roughening area | region falls as it moves away from the said incidence end surface at the edge part of the side away from the said incidence end surface of the said predetermined range. Increasingly decreasing the density of such roughened regions makes the boundary between the predetermined range and other portions inconspicuous.

Embodiment

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is described in detail, referring drawings.

[First embodiment]

1 to 3 show an image display apparatus 1 according to the embodiment of the present invention. 1 is an exploded perspective view of the image display apparatus 1. 2 is a cross-sectional view taken along the line A-A in FIG. 1, and FIG. 3 is a view seen from the direction B in FIG. 2, except for the reflective sheet 2. FIG.

(Schematic Configuration of Image Display Device)

In these drawings, the image display apparatus 1 includes a light guide plate 3 and a fluorescent lamp 5 as a primary light source. The fluorescent lamp 5 is disposed opposite the incident surface 4 provided by one side end surface of the light guide plate 3. As the light control member, the prism sheet 7 and the protective sheet 8 having a slight light diffusion function are sequentially arranged so as to face the exit surface (upper surface in FIG. 1) of the light guide plate 3. And further, the liquid crystal display panel 10 as a to-be-illuminated member is arrange | positioned on the upper surface side in FIG. 1 of the protective sheet 8 further. Moreover, the reflective sheet 2 which is excellent in light reflectivity is arrange | positioned so that the back surface (lower surface in FIG. 1; 11) of the light guide plate 3 may be opposed. The fluorescent lamp 5, the light guide plate 3, the prism sheet 7, the protective sheet 8, and the reflective sheet 2 constitute a surface light source device 12 for illuminating the liquid crystal display panel 10 in a plane. do.

(Light guide plate)

The light guide plate 3 is a member made of a material having excellent light transmittance, such as PMMA (methyl polymethacrylate), PC (polycarbonate), and cycloolefin resin material. The light guide plate 3 has a substantially wedge-shaped cross section, and is thinner as it moves away from the incident end face 4 side. The shape of the exit surface 6 is substantially rectangular. On the back surface 11 of the light guide plate 3, as shown in FIG. 4, a large number of prism protrusions 13 having a substantially triangular cross section are formed. These many prism protrusions 13 extend in the direction substantially orthogonal to the incident end surface 4, and are formed in parallel with each other. These prism protrusions 13 are at least partially roughened at the surface L in a predetermined range near the incident end face 4.

In the present embodiment, the vicinity L of the incident cross section 4 means a portion in the range of 3 mm ≦ L ≦ 15 mm in FIG. 2. This corresponds to a range of 1.5 ≦ (L / T) ≦ 7.5 when the thickness of the incident end face 4 of the light guide plate 3 is T. Moreover, it is preferable that the pitch P of each prism protrusion 13 is 50 micrometers, and the right angle (theta) of the prism protrusion 13 is designed by the most suitable angle in the range of 60 degree | times-120 degree | times (refer FIG. 4). .

In order to roughen the surface of the prism protrusion 13 in a predetermined range, for example, the corresponding part of the metal mold for forming the light guide plate 3 may be roughened. That is, beads of 5 µm to 20 µm are roughened by spraying beads of a mold for molding the light guide plate 3 into the portions corresponding to the above-mentioned neighboring portion L, and injection molding is performed using this mold. Then, the roughened part of the metal mold | die is transferred to the corresponding part of the light guide plate 2 which is a molded object, and the prism protrusion roughened in the predetermined range L is obtained.

Therefore, it is preferable to make the degree of roughening in the vicinity part L into the range which does not exceed 3.8 micrometers in arithmetic mean roughness Ra. Excessive roughening is undesirable.

(Prism sheet)

The prism sheet 7 is a member formed of a material having excellent light transmittance such as PET (polyethylene terephthalate) or PMMA or PC. The size and shape are almost the same as the exit face 6 of the light guide plate 6. The input surface (lower surface in FIGS. 1 and 2) of the prism sheet 7 faces the exit surface 6, and a large number of prism protrusions 15 are formed there. These prism protrusions 15 extend in a direction substantially perpendicular to the prism protrusions 13 of the light guide plate 3, and are formed in parallel with each other. Moreover, as shown in the detailed shape in FIG. 5, the prism protrusion 15 has a shape substantially the same as the prism protrusion 13 of the light guide plate 3 shown in FIG.

(Protection Sheet)

The protective sheet 8 is a sheet member formed of a material having excellent light transmittance such as PET, PMMA, and PC. The plane shape (rectangular shape) and the size are almost the same as that of the prism sheet 7. The protective sheet 8 is imparted with weak light diffusivity by containing a light diffusing material therein or forming minute irregularities on the surface. As a result, the light emitted from the exit surface 6 is appropriately diffused to enable more uniform and easy to see surface illumination. The protective sheet 8 also has a function of protecting the prism sheet 7 and the light guide plate 3 from being damaged during transportation or handling of the surface light source device 12.

In addition, here, "the exit light from the exit surface 6" is an exit surface 6 by the action of the prism protrusion 13 of the light guide plate 3, and the action of the prism protrusion 15 of the prism sheet 7. Attention should be paid to the fact that it has a directivity towards normal. The weak light diffusivity of the protective sheet 8 serves to moderate this directivity appropriately.

(Reflective sheet)

The reflective sheet 2 is a sheet-like member formed of a material having excellent light reflectivity such as white PET. Its planar shape and size are almost the same as the back surface 11 of the light guide plate 3. The reflective sheet 2 reflects the light leaked from the back surface 11 and returns to the inside of the light guide plate 3 to prevent loss of light.

(Operation and Effect of the Present Embodiment)

The outline of the behavior of the light in the image display apparatus 1 of this embodiment is as follows.

Light emitted from the fluorescent lamp 5 is introduced into the light guide plate 3 from the incident end face 4 and becomes internal propagated light. The internally propagated light is repeatedly internally reflected at the emission surface 6 and the rear surface 11 in the propagation process. In internal reflection with respect to the exit surface 6, a part of the component whose internal incident angle became below the critical angle exits from the exit surface 6. The internal incidence to the back surface 11 is performed with respect to the prism protrusion 13 formed in the back surface 11. As described above, since the prism protrusions 13 are substantially perpendicular to the incidence end face 4, the light reflected internally by the prism protrusions 13 emits light in the plane parallel to the incidence end face 4. ) Is richly contained in the front-facing component (see FIG. 6 (a)). Some internal propagated light leaks from the back surface 11, but as described above, it is reflected by the reflective sheet 2 and returned into the light guide plate 3 to the exit surface 6. And most of them exit from exit surface 6. When reentering the light guide plate 3, the prism protrusion 13 is subjected to refraction and reflection (see, for example, FIG. 6 (b)).

Thus, the prism protrusion 13 functions to collect in-plane light components parallel to the incident end surface 4 of the light guide plate 3 in the normal direction of the exit surface 6 of the light guide plate 3 (see FIG. 7). .

However, in this embodiment, the surface of the prism protrusion 13 is roughened in the predetermined range L near the incident cross section 4. In order to explain the effect of this roughening, the prism protrusion of the same shape as this embodiment is formed in the back surface of a light guide plate, but it compares with the conventional light guide plate which is not roughened.

In such a conventional light guide plate, as shown by the dashed-dotted line in FIG. 8, the luminance distribution of the emitted light from the exit surface is noticeably high near the incident end surface of the light guide plate, and the bright line is generated. This is considered to cause the light from the fluorescent lamp 5 to enter the light guide plate from the upper and lower end edges 16 and 17 of the light guide plate incidence end face, which may be attributed to the different behavior from other incident light. That is, it is presumed that such edge transverse light is internally reflected by a prism protrusion formed on the rear surface, and is locally emitted from the incident surface 6 to form a bright line.

In contrast, in the light guide plate 3 of the present embodiment, the surface of the prism protrusion 13 is at least partially roughened in a predetermined range L near the incident end surface 4. Therefore, the internal incident light into the prism protrusions 13 within the range is subjected to the diffusion effect including the light passing through the edge. Therefore, the advancing direction toward the exit surface 6 is diversified appropriately, and the strong local exit from a specific linear portion of the exit surface 6 is avoided. That is, it is difficult for the luminance peak to be prominent in the vicinity L of the incident end face 4 (see the solid line in Fig. 8).

Thus, according to the image display apparatus 1 of embodiment, uniform and bright image display is attained and image display quality improves. Moreover, in the surface light source device 12 employ | adopted in this embodiment, the bright line is prevented from generating in the vicinity (predetermined range; L) of the light guide plate 3 incidence end surface 4 as mentioned above. Therefore, the vicinity L of the incident cross section 4, which has not been available because of the bright line in the past, can be included in the light emitting surface. As a result, the light guide plate 3, the surface light source device 12, and the image display device 1 including them can be made smaller and lighter as the effective utilization ratio of the emission surface 6 is increased.

In addition, when the light emitted from the light guide plate 3 passes through the prism sheet 7, the traveling direction is changed by the prism protrusions 13, and the light is directed to the normal direction of the exit surface 6 (Fig. 9 (b)). Reference). The output light of the prism sheet 7 is subjected to a slight diffusion effect by the protective sheet 8 to illuminate the liquid crystal display panel 10.

As described above, the light emitted from the exit surface 6 has its light component in the normal direction of the exit surface 6 with respect to the plane parallel to the incident end surface 4 by the prism projection 13 of the light guide plate 3. It collects (refer FIG. 9 (a)). And the advancing direction of the exit light from the exit surface 6 is again normal to the exit surface 6 with respect to the surface perpendicular | vertical to the incident end surface 4 by the prism protrusion 15 of the prism sheet 7. (See Fig. 9 (b)). Light condensed in these two steps is diffused in the protective sheet 8 and supplied to the liquid crystal display panel 10. Therefore, an image display apparatus 1 capable of observing a bright and easy-to-view image from almost the front direction can be obtained.

In addition, although the prism protrusion 13 of the light guide plate 3 is formed so that it may extend in the direction substantially orthogonal to the incident cross section 4, the direction inclined several degrees from the direction orthogonal to the incident cross section 4 It may be formed so as to extend.

Second Embodiment

10 shows the image display device 1 according to the second embodiment of the present invention. This embodiment is corresponded to the modification of the said 1st embodiment. In this embodiment, the direction of the prism protrusion 13 formed in the back surface 11 of the light guide plate 3 and the direction of the prism protrusion 15 formed in the prism sheet 7 are reversed. That is, the prism protrusion 13 of the back surface 11 of the light guide plate 3 is formed in parallel with each other so that it may extend in the direction substantially parallel to the incident end surface 4, as shown in FIG. On the other hand, the prism protrusions 15 of the prism sheet 7 are formed parallel to each other so as to extend in a direction substantially perpendicular to the incident end face 4.

As in the case of the first embodiment, the prism protrusions 13 are roughened at least partially in the surface in the predetermined range L in the vicinity of the incident end face 4. This is the same as the first embodiment. The effect can be obtained.

[Third Embodiment]

Fig. 11 shows an image display device 1 according to the third embodiment of the present invention. This embodiment corresponds to another modification of the first embodiment. The longitudinal cross-sectional shape of the light guide plate 3 employ | adopted in this embodiment is substantially rectangular shape unlike 1st Embodiment. Then, two opposing side end faces of the light guide plate 3 provide the incidence end faces 4 and 4, and the fluorescent lamps 5 and 5 are correspondingly arranged, respectively. The prism protrusions 13 formed on the back surface 11 of the light guide plate 3 are roughened in a predetermined range L and L in the vicinity of both incident end surfaces 4 and 4.

This embodiment is suitable for the case where the light guide plate 3 is large or when the increase in the illumination brightness is further desired. And by the roughening process performed on the surface of the prism protrusion 13 of predetermined range L and L, the effect similar to 1st Embodiment mentioned above can be acquired.

In addition to the incident end faces 4 and 4, the left and right side end faces may also be the incident end faces, and the fluorescent lamp 5 may be further arranged correspondingly. In this case, what is necessary is just to roughen the surface of the prism protrusion 13 about the predetermined range vicinity of each incident cross section.

As mentioned above, also in this embodiment, the gradation of roughening degree is given to the roughened part (predetermined range L of the vicinity of the incident cross section 4) of the prism protrusion 13, and the boundary area of the non-roughened part. Is preferred. That is, when the roughened state is gradually moved from the dense state to the coarse state as it moves away from the incidence end face 4, the illumination quality is further improved by making the boundary between the roughened part and the non-roughed part not visible from the exit surface side.

[Other Modifications]

The method of roughening of the prism protrusion surface of predetermined range L may be arbitrarily selected. That is, as mentioned above, the method which sprays a bead to the metal mold | die which forms the light-guide plate 3, roughens it, and transfers it is only an example. For example, the metal mold | die which forms the light guide plate 3 may be etched and roughened, or the metal mold | die may be roughened by electric discharge machining.

In addition, the mold for forming the light guide plate 3 is not subjected to a roughening treatment, and a light-diffusion material is sprayed onto the surface of the prism protrusion 13 in the portion (predetermined range L) near the incident end surface of the light guide plate 3. The roughening process may be performed.

Moreover, in each said embodiment, also about the surface of the prism protrusion 15 of the prism sheet 7, the part corresponding to the vicinity part (predetermined range L) of an incident cross section is roughened, and is made in the vicinity of an incident cross section. The diffusion state of the emitted light may be further adjusted.

In addition, in each said embodiment, although the longitudinal cross-sectional shape of the light guide plate 3 was made into wedge shape and rectangular shape, these are the illustrations to the last. You may employ | adopt a conventional light guide plate of various cross-sectional shapes.

As described in detail above, according to the present invention, there is provided a light guide plate which suppresses the generation of bright lines generated near the incident end surface of the exit surface, and equips the surface light source device with the luminance of the bright lines in the vicinity of the primary light source. There is provided a surface light source device having no deviation and which can effectively use an exit surface. In this improved surface light source device, there is provided an image display device having a bright display screen that is easy to see by illuminating an illumination member for image display such as a liquid crystal display device. The effective use of the emission surface contributes to the miniaturization and weight reduction of the light guide plate and the surface light source device or image display device equipped with the light guide plate.

Claims (6)

And a light guide plate having an emission surface for emitting light, a rear surface positioned on the reflection side with respect to the emission surface, a light guide plate having an incidence end surface for incident light, and a primary light source disposed opposite the incidence end surface. In On the back side, a plurality of prism protrusions having a substantially triangular cross section are formed substantially parallel to each other, And a surface of the prism protrusion includes a roughening area within a predetermined range near the incident cross section. 2. The surface light source device according to claim 1, wherein the formation density of said roughened region is reduced as it moves away from said incident end face at an end portion on the side away from said incident end face in said predetermined range. An image display apparatus having an illumination member for displaying an image and a surface light source device for illuminating the illumination member, The image display device includes an emission surface for emitting light, a back surface positioned on the opposite side to the emission surface, a light guide plate having an incident cross section for entering light, and a primary light source disposed to face the incident cross section. Doing On the back side, a plurality of prism protrusions having a substantially triangular cross section are formed substantially parallel to each other, And the surface of the prism projection includes a roughened area within a predetermined range near the incident end surface. 4. An image display apparatus according to claim 3, wherein the formation density of said roughened area is reduced as it moves away from said incident end face at an end portion on the side away from said incident end face in said predetermined range. A light guide plate having an emission surface for emitting light, a back surface positioned on the opposite side to the emission surface, and an incident cross section for entering light, On the rear surface, a plurality of prism protrusions having a substantially triangular cross section are formed substantially parallel to each other, The surface of the prism protrusion in the predetermined range in the vicinity of the incident cross section includes a roughening area. 6. The light guide plate according to claim 5, wherein the formation density of the roughening region is reduced as the distance from the incident end surface is at an end portion on the side away from the incident end surface in the predetermined range.