JP4389529B2 - Surface illumination device and light guide plate - Google Patents

Description

  The present invention relates to a light guide plate of a surface illumination device used for a liquid crystal display device and the like, and the surface illumination device.

  FIG. 10 shows an example of a surface illumination device used in a conventional liquid crystal display device. The surface irradiation device 70 includes a light source 72 and a light guide plate 71 in order to uniformly emit light 72L from the light source 72. The light guide plate 71 is a reflective surface (so-called top surface) 75 with respect to the light emitting surface (so-called top surface) so that the plate thickness d1 gradually decreases from the front end toward the back end on the light source 72 side, that is, in the light guide direction. A so-called bottom surface 76 is formed to be inclined. The light guide plate 71 has a module structure in which a reflection sheet 77 is attached to a bottom surface 76, and a diffusion sheet 78, a plurality of prism sheets 79 and 80, and a protection sheet 81 are stacked on a top surface 75. As shown in FIG. 11, the light source 72 is encapsulated in one package with a yellow phosphor layer 86 attached to the light emitting surface of a blue light emitting diode (LED), and the surface is attached with a transparent resin layer 87. The blue light emitting diode 85 and the yellow phosphor layer 86 make white light. The packaged light source 72 is mounted on a printed wiring board 89, and its light emitting surface side is attached to the front end surface of the light guide plate 71. In this surface illumination device 70, the light from the light source 72 enters from the front end 73 of the light guide plate 71 and travels toward the back end 74 as shown in FIG. 12A. The light traveling toward the far end is emitted from the entire top surface 75 by being reflected in the direction of the top surface 75 by the reflection sheet 77 installed on the bottom surface 76 of the light guide plate 71.

  As the light guide plate 71, a plate having a top surface 75 and a bottom surface 76 formed in parallel is known.

Patent Document 1 discloses an apparatus that improves the luminance of light by providing a funnel-shaped taper on a light guide plate.
Further, as described above, since the light guide plate has low luminance and luminance uniformity of light emitted from the light guide plate, it is necessary to use a luminance improvement sheet or a luminance uniformity improvement sheet (see Patent Document 2).
Various techniques for sealing the LED and the phosphor are known (see Patent Document 3 and Patent Document 4).
Japanese Utility Model Publication No. 01-152406 JP 09-35518 A JP 2002-222996 A JP 2000-77723 A

In the conventional light guide plate, the thickness is parallel between the bottom surface and the top surface, or the light source side is wide as shown in FIG. 10, so that light incident on the surface of the light guide plate at an incident angle smaller than the critical angle is guided. The light is not reflected by the surface of the light plate and is emitted outside the light guide plate. That is, as shown in FIG. 12B, the light 72L incident from the front end 73 of the light guide plate 71 is immediately incident on the top surface 75 side even if it is incident, depending on conditions such as the frequency of light from the light source, the material of the light guide plate, and the refractive index. Will be emitted.
As described above, the conventional light guide plate emits light at the front surface of the light guide plate when it travels to the light guide plate when the type of light spreading from the light source is irradiated. First, as shown in FIG. 12A, uneven brightness occurs in the surface emission, which causes a problem in the uniformity of the radioactivity and the luminance distribution.
As described above, the conventional light guide plate is a factor that complicates optical adjustment because a plurality of optical sheets of various types must be stacked to form a module structure in order to uniformly emit light. .

  In view of the above, the present invention provides a surface illumination device that uniformly emits light from a light source over the entire surface and a light guide plate used for the surface illumination device.

The light guide plate according to the present invention is a first region where light is incident, and the thickness of the first region is inclined with respect to the optical axes on both sides in the thickness direction so that the thickness of the first region gradually increases from the light source side toward the light guide direction. A first region formed with an angle within a range of 1 ° ≦ β ≦ 25 ° and a second region that emits light continuously to the first region, the thickness of the second region being the light guide direction The second region set to gradually decrease toward the surface, the prism or V-groove formed in the direction perpendicular to the optical axis on the reflecting surface of the second region, and the optical axis on the light emitting surface of the second region. Prisms or V-grooves formed along a vertical angle that is set to increase from the front end to the back end of the second region, and decreases from the center of the second region to both ends. A prism or V-groove having an apex angle set in the direction of the thickness direction of the first region And a reflecting surface formed on the surface.

  In the light guide plate of the present invention, the first region where light is incident is formed so that the thickness gradually increases in the light guide direction, and both surfaces in the thickness direction are formed as reflecting surfaces. A part of the light is reflected by the inclined reflecting surface of the first region and is incident on the light emitting surface at an angle greater than the critical angle. Thereby, the light is totally reflected on the light exit surface and travels to the back of the light guide plate.

The surface illumination device according to the present invention is a light source that emits light, and a first region in which the light emitted from the light source is incident, and the thickness of the first region gradually increases from the light source side toward the light guide direction. As shown in the figure, the first region where the tilt angles with respect to the optical axes of both surfaces in the thickness direction are each in the range of 1 ° ≦ β ≦ 25 °, and the second region that emits light continuously to the first region. A second region in which the thickness of the second region is set to be gradually reduced toward the light guide direction, and a prism or V formed on a reflection surface of the second region in a direction perpendicular to the optical axis. A groove and a prism or V-groove formed on the light exit surface of the second region along the optical axis, and an apex angle set so as to increase from the front end to the back end of the second region; , The apex angle set so as to decrease from the center of the second region to both ends A prism or V groove, a reflecting surface formed on both surfaces in the thickness direction of the first region, and has a light guide plate having.

  The surface illumination device of the present invention includes a light guide plate in which the first region where light is incident is formed so that the thickness gradually increases in the light guide direction, and both surfaces in the thickness direction are reflective surfaces. With this light guide plate, part of the light incident on the light guide plate from the light source is reflected by the inclined reflecting surface of the first region, and is incident on the light emitting surface at an angle greater than the critical angle. The light incident on the light exit surface by reflection is totally reflected by the light exit surface and travels to the back of the light guide plate. Therefore, the light travels uniformly in the light guide plate and is uniformly irradiated from the light exit surface.

  According to the light guide plate of the present invention, since incident light can be guided to the back of the light guide plate, the light radiation efficiency is improved, the luminance of the light emitted from the light guide plate is increased, and the luminance uniformity is also increased. can do. Therefore, the brightness enhancement sheet and the brightness uniformity enhancement sheet can be omitted, and the surface illumination device can be made thinner when applied to a surface illumination device (so-called surface light source). Furthermore, since the brightness improving sheet and the brightness uniformity improving sheet are not used, the cost of the light guide plate can be reduced.

  When the thickness of the second region that emits light from the light guide plate is set so as to gradually decrease toward the light guide direction, the incident light is inclined because the reflecting surface opposite to the light emitting surface is inclined. Can be uniformly reflected from the front end to the back end toward the light exit surface. Thereby, light can be uniformly emitted from the light emission surface.

  When forming a prism or V-groove in the direction perpendicular to the optical axis on the reflecting surface of the second region of the light guide plate and forming a prism or V-groove along the optical axis on the light emitting surface of the second region, The light can be efficiently reflected by the prism or the V-groove and the reflection sheet to the light emitting surface side, and the light emitted by the prism or the V-groove on the light emitting surface can be suppressed to improve the surface irradiation.

  When a prism or V-groove is formed on the reflecting surface of the second region of the light guide plate in a direction perpendicular to the optical axis, and a prism or V-groove whose apex angle changes along the optical axis is formed on the light emitting surface of the second region. Can further suppress the diverging light and further improve the surface irradiation.

  When forming a triangular prism-like cut at a portion corresponding to the adjacent light source of the light guide plate, the light immediately after the incident can be refracted and reflected by the surface of the cut portion, and the light can be advanced toward the back end of the light guide plate. And the light radiation efficiency can be improved.

  According to the surface illumination device of the present invention, since the light from the light source can be guided to the back of the light guide plate, the light emission efficiency is improved, the brightness of the light emitted from the light guide plate is increased, and the brightness is uniform. Can also be increased. Surface light emission with uniform brightness can be obtained from the entire surface of the light guide plate. The brightness improving sheet and the brightness uniformity improving sheet can be omitted, and the surface illumination device (so-called surface light source) can be made thinner. Furthermore, since the brightness improving sheet and the brightness uniformity improving sheet are not used, the cost of the surface lighting device can be reduced.

  In the light guide plate, when the thickness of the second region that emits light is set so as to gradually decrease toward the light guide direction, the reflection surface on the side opposite to the light exit surface is inclined, so that the light is transmitted to the front end. Can be uniformly reflected from the light emitting surface to the light emitting surface. Thereby, light can be uniformly emitted from the entire surface of the light guide plate.

  When the light source is composed of a blue semiconductor light-emitting element having a yellow phosphor layer, and this semiconductor light-emitting element is attached to the light guide plate or integrally formed with the light guide plate, the surface illumination device is more in comparison with the conventional surface illumination device. Thinning can be achieved. Further, since the blue light emitting diode can be directly mounted on the printed wiring board, the number of mountings can be reduced to one.

  In the light guide plate, when a prism or V-groove is formed on the reflecting surface of the second region in a direction perpendicular to the optical axis and a prism or V-groove is formed on the light emitting surface of the second region along the optical axis, the reflecting surface The light is efficiently reflected to the light exit surface side by the prism or the V groove and the reflection sheet, and the light emitted from the prism or V groove on the light exit surface is suppressed, so that the surface illumination from the light guide plate is improved. Can do.

  In the light guide plate, a prism or V-groove is formed on the reflecting surface of the second region in a direction perpendicular to the optical axis, and a prism or V-groove whose apex angle changes along the optical axis is formed on the light emitting surface of the second region. Sometimes, the diverging light can be further suppressed, and the surface irradiation from the light guide plate can be improved.

  In the light guide plate, when forming a triangular prism-like cut at a portion corresponding to between adjacent light sources, the light immediately after incidence is refracted and reflected by the surface of the cut portion, and the light is advanced toward the back end of the light guide plate. Thus, the light radiation efficiency in the surface illumination device can be improved, and the optimum luminance can be obtained.

Embodiments of the present invention will be described below with reference to the drawings.
First, the basic configuration of the light guide plate and the surface illumination device of the present invention will be described with reference to FIGS.
Figure 1 shows a basic configuration of a surface lighting device according to the present invention. A surface illumination device 10 in FIG. 1 includes a light source 2 and a light guide plate 1 that guides light from the light source 2 and emits the light in a planar shape. The light guide plate 1 has a flat plate shape, and includes a first region 7 where light is incident and a second region 8 which emits light continuously to the first region 7, and the thickness of the first region 7 ( The so-called plate thickness) t1 is set to gradually increase from the light source 2 side toward the light guide direction, and the thickness (so-called plate thickness) t1 of the second region 8 is gradually decreased from the light source 2 side toward the light guide direction. It is set to be configured. Reflective sheets 11 and 12 are deposited on both surfaces 7A and 7B in the thickness direction of the first region 7, and the both surfaces 7A and 7B are formed as reflective surfaces. The inclination angles β [β1, β2] (see FIG. 4) with respect to the optical axes of both surfaces 7A and 7B are such that the incident light L1 from the light source 2 is reflected by the surface of the first region 7 and the light exit surface of the second region 8; When the light enters the so-called top surface 5, the angle is set to a critical angle α or more, that is, an angle at which the light is totally reflected at the top surface 5. The angle β [β1, β2] is effective in the range of 1 ° ≦ β ≦ 25 °. In this example, both inclination angles β1 and β2 are set to the same angle. In this case, the first region 7 is formed in a tapered shape. The inclination angles β1 and β2 can be set to different angles. When the angle β is in the range of 1 ° ≦ β ≦ 25 °, the top surface can be set to a critical angle or more, and the light guide plate can be thinned. On the surface opposite to the top surface 5 of the second region 8, the so-called bottom surface 6, the reflective sheet 13 is deposited and the bottom surface 6 is formed as a reflective surface.

  The top surface 5 and the bottom surface 6 of the second region 8 of the light guide plate 1 are prisms for efficiently emitting light L1 incident on the light guide plate 1 from the top surface 5 as shown in FIGS. 2A to 2C. Alternatively, V-shaped grooves (hereinafter referred to as V-grooves) 25 and 26 are formed. A prism or V-groove 26 is formed on the bottom surface 6 along a direction perpendicular to the optical axis of incident light, and a prism or V-groove 25 is formed on the top surface 25 along the optical axis. Light can be applied to the top surface 5 by the prism or V-groove 26 provided on the bottom surface 6 of the light guide plate 1. On the top surface 5 side, the prism or V-groove 25 provided on the top surface 5 can emit light. Uniform surface light emission can be performed while suppressing divergence. That is, the bright and dark portions are eliminated, and the surface light emission has a uniform brightness over the entire surface.

  On the other hand, the light source 2 includes a blue light emitting diode (LED) 42 having a yellow phosphor layer 43 as shown in FIG. That is, the light source 2 is formed by forming a yellow phosphor layer 43 on a light emitting surface of a blue light emitting diode 42 and further covering a transparent resin layer 44 thereon. The unpackaged light source 2 having only light emitting elements is directly attached to the light incident end face of the first region 7 of the light guide plate 1. This light emitting element can also be formed integrally with the light guide plate 1. The blue light-emitting diode 42 having the yellow phosphor layer 43 is mounted on the printed wiring board 45.

Next, the operation of the surface illumination device 10 having the basic configuration of the present invention , particularly the behavior of the light L1 from the light source 2 in the light guide plate 1 will be described with reference to FIG.
The light L1 is incident on the light guide plate 1 from the light source 2, is reflected by the reflection surface 7A of the first region 7 at, for example, the angle β1, and is further reflected by the reflection surface 7B of the angle β2, and then the top surface 5 of the second region 8. However, the light is totally reflected by the top surface 5 and travels toward the back end of the light guide plate 1. At this time, since the light is incident on the top surface 5 at an angle equal to or greater than the critical angle α, the light is totally reflected on the top surface 5 and travels to the back end of the light guide plate 1. As the incident light L1 is repeatedly reflected in the first region 7, the incident angle with respect to the top surface 5 becomes larger, and the incident light L1 can be totally reflected and incident to the back. The light L2 that has entered the prism or V-groove 26 provided on the bottom surface 6 of the second region 8 of the light guide plate 1 is reflected by the prism or V-groove 26 and the reflection sheet 13, and is directed toward the top surface 5 side. Is done. Of the light L2 reflected toward the top surface 5, the light diverging to the periphery is suppressed by the prism or V-groove 25 formed on the top surface 5, and as a result, the entire surface is illuminated with uniform brightness. .

According to the surface illumination device 10 having the basic configuration of the present invention , the thickness of the light guide plate 1 on the light source 2 side is gradually increased in the light guide direction, and the reflection sheets 11 and 12 are formed on both surfaces in the thickness direction. By providing the one region 7, the light from the light source 2 is reflected by the surface of the first region 7 and can travel to the back of the light guide plate 1, and the light radiation efficiency is improved. Thereby, the surface can be emitted from the top surface 5 of the second region of the light guide plate 1 with uniform brightness over the entire surface. Further, a prism or V-groove 25 is formed on the top surface 5 of the second region along the optical axis, and a prism or V-groove 26 is formed on the bottom surface 6 in a direction perpendicular to the optical axis, so that The incident light is reflected from the bottom surface 6 to the top surface 5, and the light emitted to the periphery of the top surface 5 can be directed forward, and the light can be emitted more efficiently than the top surface 5.
Since the luminance of the light emitted from the light guide plate 1 is high and the luminance uniformity is also high, the luminance improving sheet and the luminance uniformity improving sheet can be eliminated, and the surface illumination device as a surface light source can be made thin. it can. Since the brightness improving sheet and the brightness uniformity improving sheet can be omitted, the cost can be reduced.
Further, as the light source 2, a blue light emitting diode 42 having a yellow phosphor layer 43 is directly attached to the light guide plate 1, or the light emitting diode 42 having such a phosphor layer 43 is integrally formed on the light guide plate 1. The light guide plate 1 can be thinned by not using the package that covers the light emitting diode 42. As a result, the surface illumination device can be thinned. Further, mounting of the light emitting diode 42 on the package is omitted, and mounting on the printed wiring board is sufficient, and the number of mountings can be reduced to one.
Therefore, it can be suitably applied to, for example, a backlight of a liquid crystal display device.

  Next, the surface illumination device according to the first embodiment of the present invention will be described using the above basic configuration.

Figure 5 shows a surface lighting equipment according to the first embodiment of the present invention. This figure particularly shows the second region portion of the light guide plate.
The light guide plate 51 constituting the surface illumination device according to the present embodiment includes a first region (not shown) that receives light from a light source and a second region 52 that emits light from the surface. The first region is configured in the same manner as described with reference to FIG. The second region 52 is formed by forming a prism or V-groove 57 along the optical axis of the top surface 55 and forming a prism or V-groove in the direction perpendicular to the optical axis, not shown, on the bottom surface 58. In this embodiment, in particular, when the prism or V groove 57 formed on the top surface 55 is the angle, that is, the prism, the apex angle increases from the front end 53 to the back end 54, It is set to become smaller as it goes from the center to both ends. That is, the apex angle becomes an obtuse angle from the front end 53 toward the back end 54, and becomes an acute angle as the distance from the center increases. In the figure, the angles increase in the order of apex angle A1-B1-C1, in the order of apex angle A2-B2-C2, and in the order of apex angle A3-C3. Moreover, an angle becomes small in order of apex angle A1-A2-A3. Further, when a point light source is arranged in the center of the front end 53, the prism (or V-groove) is formed so that the apex angles A1, B2, and C3 are the same angle on the line along the radial light trajectory. ing. That is, the top surface 55 is provided with a prism or V groove whose apex angle changes along the optical axis.
Other configurations are the same as those described with reference to FIGS.

  According to the surface illumination device provided with the light guide plate 51 according to the present embodiment, the apex angle of the top surface 55 of the second region 52 increases from the front end 53 to the back end 54 and goes from the center to both ends. Therefore, by forming a prism or V-groove that changes so as to become smaller, divergent light can be suppressed and surface irradiation can be further improved.

In the light guide plate 51 having a continuously changing apex angle described with reference to FIG. 5 , the relationship between the light emission angle and the apex angle of the prism or V-groove is as follows. When the angle θ formed with the optical axis L0 of the light L3 radiated as viewed from the (surface) side (see FIG. 6 ), the apex angle Φ (see FIG. 7 ) of the prism or V groove on the light exit surface is The relationship is shown in Here, n is the refractive index of the light guide plate 51. However, of the two surfaces forming the prism or V-groove, the surface close to the light source is a surface perpendicular to the light emitting surface (top surface). In FIG. 7 , the light L3 from the light source is refracted by a prism or V-groove provided on the top surface, and the emitted light L3 is shown.

However, it applies to the range of θ ≦ arctan (1 / n). Outside this range, no prism or V-groove is required.

FIG. 8 shows a surface illumination device according to a second embodiment of the present invention. The surface illumination device 61 according to the present embodiment includes a light source 62 and a light guide plate 63. The light source 62 is composed of a plurality of point light sources, and each point light source 62 is attached to the light guide plate 63 at a predetermined interval. In the present embodiment, in particular, a triangular prism-shaped cut portion 66 is formed from the top surface 67 to the bottom surface 68 at a portion corresponding to between the adjacent point light sources of the light guide plate 63. That is, the triangular columnar cut portions 66 are formed on both sides of the portion in contact with each point light source 62. As described above, the light guide plate 63 includes a first region 64 that receives light from the light source and a second region 65 that emits light from the surface. The first region 64 is configured in the same manner as described with reference to FIG. In the second region 65, prisms or V grooves as described in the first embodiment are formed on the top surface 67 and the bottom surface 68, respectively.

  According to the surface illumination device 61 according to the present embodiment, the light guide plate 33 is provided with the triangular prism-shaped cut portions 66 on both sides of the portion in contact with each point light source 62, so that the light 62L from each point light source 62 is The light is totally reflected by the cut portion 66 and the light 62L can be uniformly propagated to the back end of the light guide plate 33. This makes it possible to emit illumination light with uniform brightness over the entire surface. In this surface illumination device 61, the utilization efficiency of the light from the light source 62 can be improved, and since it emits uniformly, it can be set as an optimal surface illumination device.

In each of the above-described embodiments, the bottom surface of the second region of the light guide plate is inclined with respect to the top surface. However, the configuration of the first region of the present invention is also applied to a configuration in which the top surface and the bottom surface are formed in parallel. Is applicable.
In addition, the number of the reflection sheets 11, 12, and 13 attached to the light guide plate can be adjusted by the degree of both inclined surfaces of the first region, the material of the light guide plate, the refractive index, the light source, and the like.

FIG. 9 shows a surface illumination device according to a reference example . This figure particularly shows the light guide plate portion.
As shown in FIGS. 9A and 9B , the light guide plate 31 constituting the surface illumination device according to the reference example includes a first region 32 that receives light from the light source and a second region 33 that emits light from the surface. The The first region 32 is configured in the same manner as described with reference to FIG. In the second region 33, prisms or V-grooves 34 are formed on the top surface 35 so as to extend radially from the incident position of light from the light source 32, that is, along the light traveling radially, and the bottom surface 37 has an optical axis. A prism or V-groove 38 is formed in the vertical direction.
Other configurations are the same as those described with reference to FIGS.

  According to the surface illumination device provided with the light guide plate 31 according to the present embodiment, particularly when a point light source is used as a light source attached to the light guide plate 31, light incident radially from the point light source into the light guide plate 31 is emitted. Surface emission from the top surface 35 can be efficiently performed. In addition, the effect obtained by providing the first region 32 in which the plate thickness is gradually increased toward the light guide direction is the same as that of the surface illumination device of FIG.

It is a figure which shows the basic composition of the surface illumination apparatus which concerns on this invention. A is a perspective view of a light guide plate of the surface illumination device of FIG. B is a top view of FIG. 2A and a cross-sectional view taken along line AA. 2B is a bottom view of FIG. 2A and a cross-sectional view taken along line BB. It is a top view (especially block diagram which shows one Embodiment of a light source) of the surface illumination apparatus which concerns on FIG. It is an enlarged view of the principal part of the light-guide plate of FIG. It is a block diagram which shows other embodiment of the surface illumination apparatus which concerns on the 1st Embodiment of this invention, especially a light-guide plate. It is a top view of the light-guide plate used for description of this invention. It is sectional drawing of the principal part at the top | upper surface side of the light-guide plate used for description of this invention. A It is a perspective view which shows other embodiment of the surface illumination apparatus which concerns on this invention, especially a light-guide plate. B is an enlarged view of the main part of FIG. 7A. A is a perspective view showing another embodiment of a surface illumination device according to a reference example, particularly a light guide plate. B is a top view and a cross-sectional view of FIG. 9A. 9B is a bottom view of FIG. 9A and a cross-sectional view taken along line BB. It is a block diagram of the conventional surface illumination apparatus. It is sectional drawing which shows the example of the conventional light source. A, B It is explanatory drawing of the problem of the conventional surface illumination apparatus.

1, 2, 31, 41, 51, 63 ... Light guide plate, 2, 62, 72 ... Light source 3, 23, 53 ... Front end 4, 24, 34, 54 ... Back end 5, 25, 35, 55, 67 .. Top surface, 6, 26, 37, 58, 68 .. Bottom surface, 7, 32, 64 .. First region, 8, 33, 65 .. Second region 10, 31, 31, 61 ..Surface illumination device 11, 12, 13, ..Reflector plate 25, 26, 36, 37..Prism or V-groove, 66..Triangular notch 42, .Blue light emitting diode 43 .. Yellow phosphor layer, 44 ... Transparent resin, 45 ... Printed wiring board, 70 ... Surface illumination device, 71 ... Light guide plate, 72 ... Light source, 73 ... Front end, 74 ... Back end, 75 ... Top surface, 77 ... Reflector, 78 ... Diffuser sheet, 79, 80 ... Prism sheet, 81 ... Protective sheet

Claims (5)

The first region where light is incident, and the inclination angles of the both surfaces in the thickness direction with respect to the optical axis are 1 ° ≦ β ≦, respectively, so that the thickness of the first region gradually increases from the light source side toward the light guide direction. A first region formed within a range of 25 °;
  A second region that emits light continuously to the first region, the second region having a thickness that gradually decreases toward the light guide direction;
  A prism or V-groove formed on the reflecting surface of the second region in a direction perpendicular to the optical axis;
  A prism or V-groove formed along the optical axis on the light exit surface of the second region, and an apex angle set so as to increase from the front end to the back end of the second region; A prism or V-groove having an apex angle set so as to decrease from the center of the second region toward both ends;
  Reflective surfaces formed on both surfaces in the thickness direction of the first region;
  A light guide plate. Triangular prism-shaped notches are formed at portions corresponding to adjacent light sources of the light guide plate .
The surface illumination device according to claim 1. A light source that emits light;
  The first region where the light emitted from the light source is incident, and an inclination angle with respect to the optical axes of both surfaces in the thickness direction is gradually increased so that the thickness of the first region gradually increases from the light source side toward the light guide direction. First regions each formed within a range of 1 ° ≦ β ≦ 25 °;
  A second region that emits light continuously to the first region, the second region having a thickness that gradually decreases toward the light guide direction;
  A prism or V-groove formed on the reflecting surface of the second region in a direction perpendicular to the optical axis;
  A prism or V-groove formed along the optical axis on the light exit surface of the second region, and an apex angle set so as to increase from the front end to the back end of the second region; A prism or V-groove having an apex angle set so as to decrease from the center of the second region toward both ends;
  A light guide plate having a reflective surface formed on both surfaces of the first region in the thickness direction;
  A surface illumination device. The light source is composed of a blue semiconductor light emitting element having a yellow phosphor layer, and the semiconductor light emitting element is attached to the light guide plate or integrally formed with the light guide plate .
The surface illumination device according to claim 3 . Triangular prism-shaped notches are formed at portions corresponding to adjacent light sources of the light guide plate .
The surface illumination device according to claim 4.