JP2016162616A - Surface light-emitting device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve a surface light-emitting device capable of acquiring desired brightness without requiring lamination of prism sheets or even when the number of the lamination of the prism sheets is reduced, capable of reducing the number of man-hour and material cost by reducing the number of components, and capable of achieving reduction in thickness.SOLUTION: A surface light-emitting device 101 includes: a light source 20; a light guide plate 30 for introducing light from the light source 20 and for emitting it to an emission surface 31 side; and a reflection film 50 for covering the light source 20 and a surface 32 opposing to at least the emission surface 31 of the light guide plate 30. The light guide plate 30 has a light incident part 40 which has a dent multistage concentric surface-shape that faces the light source 20, and on a cross section in a wall thickness direction T of the light guide plate 30 passing a central axis S of the light incident part 40, a difference inclination angle θ between adjacent inclined side surfaces 42, 42 of the light incident part 40 is set to be in a range of 20 degrees or greater and 45 degrees or less.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a surface light-emitting device that introduces light from a light source into a light guide plate and emits the light toward an emission surface side of the light guide plate, and an image forming apparatus.

  On the back surface of a liquid crystal display (LCD) of a mobile terminal such as a smartphone or a tablet terminal, a backlight assembly is disposed as a surface light emitting device. A conventional backlight assembly includes, for example, a light source, a light guide plate, a reflective film, and a prism sheet (see Patent Document 1). The backlight assembly of Patent Document 1 includes a light guide plate for introducing light from a light source and emitting the light to the exit surface side, and the light source is disposed on one side of the light guide plate. Conventionally, a fluorescent lamp such as a cold cathode tube has been used as a light source of a backlight assembly. In recent years, light emitting diodes (LEDs) have been used as light sources in order to save power, increase efficiency, and extend the life of backlight assemblies.

JP 2007-179060 A

  By the way, the desired brightness cannot be obtained by simply introducing light from the light source into the light guide plate, reflecting the light from the reflection film, and emitting the light toward the exit surface side of the light guide plate. Therefore, in the backlight assembly of Patent Document 1, a prism sheet is laminated on the light guide plate to increase the light emission amount. However, a sufficient amount of light cannot be obtained even if a single prism sheet is laminated on the light guide plate.

  Therefore, in a recent surface light emitting device, for example, a plurality of prism sheets composed of an X-direction prism and a Y-direction prism are crossed and stacked on a light guide plate to obtain a desired light amount. However, since a plurality of prism sheets are laminated on the light guide plate, the number of parts of the surface light-emitting device increases, and as a result, the assembly man-hour and material cost of the surface light-emitting device also increase. Furthermore, since a plurality of prism sheets are required, it has been an obstacle to reducing the thickness of the surface light emitting device.

  The present invention was devised in view of the above circumstances, and it is possible to obtain a desired brightness even if prism sheet stacking is not required or the number of prism sheet stacks is reduced. It is an object of the present invention to provide a surface light emitting device and an image forming apparatus that can reduce assembly man-hours and material costs and can be reduced in thickness.

  In order to achieve the above object, a surface light emitting device according to the present invention includes a light source, a light guide plate that introduces light from the light source and emits the light toward the exit surface, and at least the exit surface of the light source and the light guide plate. A reflective film covering the opposing surface. The light guide plate has a multi-stage concentric light incident portion that is recessed facing the light source, and the light incident portion has an incident surface in a cross section in the thickness direction of the light guide plate that passes through the central axis of the light incident portion. Is set in a range of 20 degrees or more and 45 degrees or less.

  In the configuration of the surface light emitting device, the differential inclination angle is from the center of the light incident portion toward the radially outward direction, from the radially outward direction toward the center, or from one radial direction to the other. It is preferably set so as to increase or decrease in the range of 20 degrees to 45 degrees. The differential inclination angle is set to be constant or variable.

  In addition, the reflection surface facing the emission surface may be sequentially inclined toward the emission surface side as the distance from the light source increases. Or the reflective surface facing the said output surface may be formed in the curved surface.

  Further, a phosphor may be interposed between the light source and the light incident part. Furthermore, it is preferable that the phosphor is a phosphor film disposed on the light incident part or a fluorescent paint layer applied to the light incident part. The light source is preferably a blue LED, and the phosphor is preferably a yellow phosphor that develops white color upon receiving blue light from the blue LED.

  A diffusion film may be laminated on the light guide plate.

  Further, a plurality of the light incident portions may be formed on the light guide plate, and the number of the light sources corresponding to the light incident portions may be provided. Furthermore, the light incident part may be formed on each of the opposing side faces or adjacent side faces of the light guide plate, and the light source may be provided facing each light incident part.

  An image forming apparatus according to the present invention is characterized in that a liquid crystal display is disposed on any of the surface light emitting devices described above.

  According to the surface light emitting device of the present invention, it is possible to obtain a desired brightness even if prism sheet lamination is not required or the number of prism sheet laminations is reduced. The man-hour and the material cost can be reduced, and an excellent effect that the surface light emitting device can be thinned is exhibited.

1 is a side sectional view of a surface light emitting device according to a first embodiment. It is the front view which looked at the incident part of the light-guide plate which comprises the surface emitting device which concerns on 1st Embodiment from the light source side. It is a principal part enlarged view of the incident part vicinity of the surface emitting device which concerns on 1st Embodiment. It is a figure where it uses for description of the effect | action of the light of the surface emitting device which concerns on 1st Embodiment. It is a principal part enlarged view of the incident part vicinity in an example of the surface emitting device which concerns on 2nd Embodiment. It is a principal part enlarged view of the incident part vicinity in the other example of the surface emitting device which concerns on 2nd Embodiment. It is a sectional side view of the surface emitting device concerning a 3rd embodiment. It is a top view of an example of the surface emitting device concerning a 4th embodiment. It is a top view of the other example of the surface emitting device concerning a 4th embodiment. In other embodiment, it is the front view which looked at the light-guide plate from the light source side at the time of notching in a cross-sectional polygonal substantially half square column shape along a central-axis direction, and forming a light-incidence part. In other embodiment, it is the front view which looked at the light-guide plate at the time of forming a reflective surface in a curved surface from the light source side.

  Hereinafter, embodiments of a surface light emitting device and an image forming apparatus according to the present invention will be described with reference to the drawings. However, in the drawings, the same or similar reference numerals are given to the same or similar members and parts. Further, the drawings are schematically shown and do not necessarily match actual dimensions and ratios. Furthermore, the drawings may include portions having different dimensional relationships and ratios.

[First Embodiment]
First, the configuration of the surface light emitting device according to the first embodiment will be described with reference to FIGS. 1 to 3. FIG. 1 is a side sectional view of the surface light emitting device according to the first embodiment. FIG. 2 is a front view of the incident portion of the light guide plate constituting the surface light emitting device according to the first embodiment as viewed from the light source side. FIG. 3 is an enlarged view of a main part in the vicinity of the incident part of the surface light emitting device according to the first embodiment.

  As shown in FIG. 1, the surface light emitting device 101 according to the first embodiment mainly includes a light source 20, a light guide plate 30, and a reflection film 50. Hereinafter, the surface emitting device 101 according to the first embodiment will be described for each component.

  The light source 20 is mounted on a wiring board 10 such as a printed board. A wiring pattern (not shown) is formed on the wiring board 10. The light source 20 is mounted on the wiring pattern on the surface facing the light guide plate 30 side of the wiring substrate 10. The wiring board 10 is disposed away from the light guide plate 30.

  As the light source 20, it is preferable to employ a light emitting diode (LED) in order to save power, increase efficiency, and extend the life of the surface light emitting device 101. As LED of this embodiment, chip type LED which light-emits blue light is employ | adopted, for example. As the chip type LED, for example, a high power LED having an output of 1 W / chip or more, a large light amount and high luminance may be adopted. The emission color of the LED is not necessarily limited to blue light, and may be another emission color such as red light, green light, or ultraviolet light. Moreover, LED is not limited to what is comprised by single LED, You may connect and use several LED electrically parallel or in series. Furthermore, you may use combining multiple color LED from which a wavelength differs. The light source 20 is not necessarily limited to the LED, and a light emitting element other than the LED such as an organic EL may be adopted.

  The light guide plate 30 has a rectangular column shape or a flat plate shape (flat rectangular parallelepiped shape) as a whole. The light guide plate 30 is preferably made of a transparent synthetic resin material such as acrylic (PMMA; Polymethyl methacrylate), cycloolefin polymer (COP), or polycarbonate (PC), but is limited to the exemplified synthetic resin material. Alternatively, other transparent members such as a glass material may be employed. The light guide plate 30 is preferably a colorless transparent body, but may be a colored transparent body having the same color as the light emission color of the light source 20 or the same color as the light that has passed through a phosphor 60 described later.

  On one surface of the four side surfaces along the thickness direction (front-rear direction) T of the light guide plate 30, a light incident portion 40 that is depressed facing the light source 20 is formed. In the cross section in the thickness direction of the light guide plate 30 passing through the central axis S of the light incident portion 40 shown in FIG. 1, the light incident portion 40 is formed in a substantially polygonal shape. In addition, in the front view of the light incident portion 40 viewed from the light source 20 side shown in FIG. 2, the light incident portion 40 is formed in a multistage concentric surface (in this embodiment, a multistage concentric circle). A gas layer G exists between the light source 20 and the light incident part 40. The incident surface 41 of the light incident portion 40 has a larger depression toward the inclined side surface 42 closer to the central axis S, and the distance from the light source 20 is greater. The surface side of the light guide plate 30 (the upper surface side in FIGS. 1 to 3) serves as an emission surface 31 of light introduced from the light source 20 to the light guide plate 30.

  In the cross section in the thickness direction of the light guide plate 30 passing through the central axis S of the light incident portion 40, the incident surface 41 is formed from a plurality of inclined side surfaces 42. In the present embodiment, as shown in FIG. 1, the incident surface 41 of the light incident portion 40 is formed of eight inclined side surfaces 42 in the cross section in the thickness direction. The differential inclination angle θ between the inclined side surfaces 42 and 42 adjacent to each other of the incident surface 41 constituting the light incident portion 40 is set in a range of 20 degrees to 45 degrees. In addition, the number of the inclined side surfaces 42 in FIGS. 1 and 3 is an example, and is not limited to eight in the cross section in the thickness direction. As the size of the inclination angle θ changes, the width dimension and number of the inclined side surfaces 42 also change as appropriate.

  The reason why the differential inclination angle θ between the adjacent inclined side surfaces 42 and 42 is set to 20 degrees or more is that when the differential inclination angle θ is less than 20 degrees, the light emitted from the light source 20 is inclined to the inclined side surface 42 of the light incident portion 40. This is because it is easy to totally reflect, and the ratio of light entering the light guide plate 30 from the light incident portion 40 is reduced. That is, when the differential inclination angle θ is 20 degrees or more, the light emitted from the light source 20 is difficult to be totally reflected on the inclined side surface 42 of the light incident part 40, and is incident on the light guide plate 30 from the light incident part 40. The ratio of increases. The light incident on the light guide plate 30 travels to the emission surface 31, the reflection surface (back surface) 32 facing the emission surface 31, the reflection surface 34 along the thickness direction T connecting these, and the like.

  On the other hand, the difference in inclination angle θ between the adjacent inclined side surfaces 42 and 42 is set to 45 degrees or less because when the difference inclination angle θ exceeds 45 degrees, the light emitted from the light source 20 has a diameter in the vicinity of the light incident portion 40. This is because it becomes easier to diffuse outward in the direction. That is, when the differential inclination angle θ is 45 degrees or less, the light emitted from the light source 20 is easily refracted at the inclined side surface 42, and the light diffuses radially outward in the vicinity of the light incident portion 40. It becomes difficult to do. For this reason, the light emitted from the emission surface 31 can be appropriately diffused over the entire emission surface 31.

  The light refracted toward the reflection surface 32 side of the back surface (rear surface) of the light guide plate 30 is totally reflected by the reflection surface 32 and reaches the output surface 31 side of the surface. Thus, the light incident from the incident surface 41 reaches the output surface 31 through refraction and total reflection. By setting the differential inclination angle θ within the range of 20 degrees or more and 45 degrees or less, the light incident from the incident surface 41 is appropriately diffused over the entire light guide plate 30 and forwards from the exit surface 31 to the front surface. Exit. That is, the rate of light emitted from the light guide plate 30 increases toward the front of the surface in a state where it is appropriately diffused in the direction of the emission surface 31. Further, by setting the differential inclination angle θ to 20 degrees, 25 degrees, 30 degrees, 35 degrees, or other values, light concentrated in a specific direction is emitted from the emission surface 31. Conversely, it can be diffused from the exit surface 31 over a wide range.

  In the present embodiment, the cross-sectional shape of the incident surface 41 of the light incident portion 40 has a substantially polygonal shape that is symmetrical with respect to the central axis S (see FIGS. 1 and 3). The differential inclination angle θ between the adjacent inclined side surfaces 42 of the light incident part 40 is 20 degrees or more 45 from the center of the light incident part 40 toward the radially outward direction or from the radially outward direction toward the center. It is set to increase or decrease within a range of degrees. Specifically, θ1 and θ4, θ2 and θ5, θ3 and θ6, which are differential tilt angles symmetrical with respect to the central axis S, are formed at the same angle, and θ1 (θ4), θ2 (θ5), and θ3 are formed. (Θ6) can be set to different angles. Then, as the differential inclination angles θ1 and θ4 on the opening ends 43 and 43 side of the light incident portion 40 are directed to the differential inclination angles θ3 and θ6 on the central axis S side, that is, θ1 <θ2 <θ3, θ4 <θ5 <. The differential inclination angle θ may be set to increase within a range of 20 degrees to 45 degrees so that θ6 is obtained. Or conversely, 20 degrees or more 45 so that the angle becomes smaller from the differential inclination angles θ1 and θ4 toward the differential inclination angles θ3 and θ6 on the central axis S side, that is, θ1> θ2> θ3 and θ4> θ5> θ6. You may set so that the difference inclination-angle (theta) may reduce in the range below a degree.

  When the angle increases from the outside in the radial direction toward the center of the light incident portion 40 (on the side of the central axis S), for example, the rate of increase in the differential inclination angle θ between the adjacent inclined side surfaces 42 and 42 is constant (this example) Then, the differential inclination angles θ1 and θ4 can be set to 20 degrees, the differential inclination angles θ2 and θ5 can be set to 30 degrees, and the differential inclination angles θ3 and θ6 can be set to 40 degrees. Further, by changing the increasing rate of the difference inclination angle θ between the adjacent difference inclination side surfaces 42, 42, for example, the difference inclination angles θ1 and θ4 are 20 degrees, the difference inclination angles θ2 and θ5 are 30 degrees, and the difference inclination angle. θ3 and θ6 can be set to 45 degrees.

  On the other hand, when the angle decreases from the outer side in the radial direction toward the center of the light incident portion 40 (central axis S), for example, the reduction rate of the differential inclination angle θ between the adjacent inclined side surfaces 42 and 42 is constant (this In the example, the difference inclination angles θ1 and θ4 can be 45 degrees, the difference inclination angles θ2 and θ5 can be 35 degrees, and the difference inclination angles θ3 and θ6 can be 25 degrees. Further, by changing the decreasing rate of the differential inclination angle θ between the adjacent inclined side surfaces 42, 42, for example, the differential inclination angles θ1 and θ4 are 45 degrees, the differential inclination angles θ2 and θ5 are 35 degrees, and the differential inclination angle θ3. And θ6 can be set to 20 degrees. In addition, the value of the difference inclination angle θ between the adjacent inclined side surfaces 42 and 42 is an example, and 20 from the center of the light incident portion 40 toward the radially outer side or from the radially outer side toward the center. It is sufficient that the differential inclination angle θ is increased or decreased in the range of not less than 45 degrees and not more than 45 degrees.

  The reflection film 50 is disposed so as to cover at least a surface surface (reflection surface) 32 of the light source 20 and the light guide plate 30 that faces the light emission surface 31. The reflective film 50 of the present embodiment exposes the light exit surface 31 of the light guide plate 30, and in addition to the reflective surface 32, a side surface (reflective surface) along the thickness direction T other than the one side surface having the light incident portion 40. 34 and so on. Examples of the reflective film 40 include a synthetic resin film such as polypropylene (PP) and polyethylene terephthalate (PET) filled with fillers such as titanium oxide and barium sulfate and bubbles. The material is not limited to the exemplified materials. The light introduced from the light source 20 to the light guide plate 30 passes through the light guide plate 30 or is reflected by the reflection surfaces 32 and 34 covered with the reflection film 50 and is emitted from the emission surface 31 of the light guide plate 30. .

  Further, a phosphor 60 is interposed between the light source 20 and the light incident part 40. As shown in FIGS. 1 to 3, the phosphor 60 of the present embodiment is stretched on the inner edge portion of the light incident portion 40 so as to close the opening of the light incident portion 40. A gas layer G exists between the incident surface 41 and the phosphor 60. The phosphor 60 has a circular shape, and an outer peripheral portion thereof is bonded and fixed to an inner edge portion of the light incident portion 40. The phosphor 60 of the present embodiment is formed as a circular phosphor plate or phosphor film in accordance with the opening shape of the light incident portion 40. The size of the phosphor 60 is set to a size that fits within the opening end 43 of the light incident portion 40. The phosphor 60 is not limited to being stretched on the inner edge portion or the outer edge portion of the light incident portion 40. For example, the phosphor 60 may be directly attached to the incident surface 41 of the light incident portion 40, or the incident surface 41 A fluorescent paint may be applied to the incident surface 41 and a fluorescent paint layer (not shown) may be laminated on the incident surface 41.

  As the phosphor 60 of the present embodiment, for example, a yellow phosphor that emits white color through the blue light of the blue LED that is the light source 20 is employed. The thickness of the phosphor 60 is set to a thickness sufficient for the light that has passed through the yellow phosphor film to develop a white color according to the light quantity of the blue chip LED. Moreover, it is not limited to the combination of blue LED and yellow fluorescent substance, The fluorescent substance 60 employ | adopts a suitably preferable thing according to the light emission system of the white light in the surface emitting device 101. FIG. For example, when the excitation method is adopted, a near ultraviolet LED and an RGB phosphor may be combined. In addition, when the three-wavelength method is adopted, in order to obtain white light by mixing light of RGB three colors, the phosphor 60 is combined with three kinds of phosphors of a red phosphor, a green phosphor and a blue phosphor. It may be used.

  Examples of the phosphor 60 include a mixture of a synthetic resin material such as a silicone resin or an epoxy resin and a fluorescent material such as a nitride. However, the phosphor 60 is not limited to the exemplified materials, and may be various types applied to a white LED. Material can be adopted.

  A diffusion film (not shown) may be laminated on the emission surface 31 of the light guide plate 30. By laminating a diffusion film on the emission surface 31 of the light guide plate 30, the light emitted from the emission surface 31 can be diffused and emitted more uniformly. As will be described later, in the surface light emitting device 101 according to the present embodiment, since the incident surface 41 of the light incident unit 40 functions as a prism, it is not necessary to stack a prism sheet on the light guide plate 30 or Also when the prism sheets are stacked, the number of the prism sheets stacked can be reduced.

  Next, with reference to FIGS. 1 to 4, the operation of the surface light emitting device 101 according to the first embodiment will be described. FIG. 4 is a diagram for explaining the light action of the surface light emitting device according to the first embodiment.

  As shown in FIGS. 1 to 3, when the surface light emitting device 101 according to this embodiment is turned on and the light source 20 is turned on, light is emitted from the light source 20 toward the light guide plate 30. In the present embodiment, since the blue chip LED is employed as the light source 20, blue light is irradiated toward the light guide plate 30. The blue light emitted from the light source 20 is incident on a phosphor 60 interposed between the light source 20 and the light incident portion 30. By adjusting the separation distance between the light source 20 and the light guide plate 30, the amount of blue light emitted from the light source 20 can be adjusted.

  In the present embodiment, a yellow fluorescent plate or phosphor film that is a complementary color of blue is used as the phosphor 60. Therefore, the light passing through the phosphor 60 is colored as white light obtained by combining blue light and yellow light. In addition, it is preferable that the wavelength of the blue light which passes the fluorescent substance 60 which consists of a yellow fluorescent substance film shall be the range of 350-460 nm. Further, in the case of using a combination of three types of phosphors of a red light emitting phosphor, a green light emitting phosphor and a blue light emitting phosphor by the three wavelength method, the wavelength of blue light emitted from the light source 20 is, for example, 365 nm. Is possible. Furthermore, the wavelength of light emitted from the light source 20 is not limited to blue light, and may be in the range of 420 to 440 nm or 450 to 455 nm, for example, or 460 nm.

  As shown in FIG. 4, the white light generated through the phosphor 60 passes through the gas layer G and enters the light guide plate 30 from the incident surface 41. Of the light emitted from the light source 20, the light incident on the light guide plate 30 from the incident surface 41a on the front side from the central axis S is, for example, as shown by arrows B1, B2, and B3 in FIG. The light is refracted obliquely forward at 41a. Thereafter, the light is directly or totally reflected in the light guide plate 30 and guided to the emission surface 31, and is refracted forward on the emission surface 31. As shown by arrows B1, B2, and B3 in FIG. 4, when the light enters from the incident surface 41a on the front side from the central axis S, the light source 20 approaches the incident position on the incident surface 41a closer to the central axis S side. The light is emitted from the emission surface 31 at a distant position. On the other hand, the light incident on the light guide plate 30 from the incident surface 41b on the rear side of the central axis S is refracted obliquely rearward on the incident surface 41b as shown by arrows B4, B5, and B6 in FIG. Thereafter, the light is totally reflected by the reflecting surfaces 32 and 34. Then, the light is guided to the emission surface 31 in the light guide plate 30 and refracted forward at the emission surface 31.

  As described above, the light emitted from the light source 20 is refracted diagonally forward or diagonally rearward at the incident surface 41 having a substantially polygonal cross section. As described above, the light from the light source 20 is refracted by the incident surface 41, so that the light incident on the light guide plate 30 is guided to the emission surface 31 in a properly diffused state. The light refracted obliquely rearward at the incident surface 41 b is totally reflected by the reflecting surface 32 or the like and guided to the outgoing surface 31. When the cross-sectional shape of the light incident portion 40 is a complete semicircular shape as in the prior art, the amount of light incident on the light guide plate 30 is reduced.

  In the surface light emitting device 101 according to the present embodiment, the differential inclination angle θ between the inclined side surfaces 42 and 42 adjacent to the incident surface 41 is set in a range of 20 degrees to 45 degrees. Since the differential inclination angle θ is set to 20 degrees or more, the light emitted from the light source 20 is difficult to be totally reflected at the inclined side surface 42 of the light incident part 40 and enters the light guide plate 30 from the light incident part 40. The proportion of light increases. Further, since the differential inclination angle θ is set to 45 degrees or less, the light emitted from the light source 20 is easily refracted at the inclined side surface 42, and the light is directed radially outward in the vicinity of the light incident portion 40. Difficult to diffuse. Therefore, the light emitted from the light source 20 is refracted by the incident surface 41, and a part of the light is totally reflected by the reflective surface 32, the reflective surface 34 along the thickness direction T, and the like. Is emitted. Accordingly, the light emitted from the light source 20 is appropriately diffused over the entire light guide plate 30 and is emitted forward from the emission surface 31. That is, the substantially polygonal shape of the incident surface 41 of the light incident part 40 of this embodiment functions as a prism.

  Furthermore, in the surface light emitting device 101 according to the present embodiment, the differential inclination angle θ between the inclined side surfaces 42 and 42 adjacent to each other in the light incident part 40 is directed radially outward from the center of the light incident part 40 or the diameter. It is set to increase or decrease in the range from 20 degrees to 45 degrees from the outside in the direction toward the center. By gradually increasing or decreasing the difference inclination angle θ between the adjacent inclined side surfaces 42, 42 within a range of 20 degrees or more and 45 degrees or less, the light emitted from the light source 20 is substantially over the entire light guide plate 30. The light is uniformly diffused and emitted from the emission surface 31 toward the front of the surface.

  As described above, in the surface light emitting device 101 according to the first embodiment, since the substantially polygonal shape of the incident surface 41 of the light incident unit 40 functions as a prism, the number of prism sheets stacked on the light guide plate 30 is increased. The desired brightness can be obtained even if the brightness is reduced. Alternatively, depending on the number of inclined side surfaces 42 of the incident surface 41 of the light incident portion 40, it is not necessary to stack a prism sheet on the light guide plate 30. That is, in the surface light emitting device 101 according to the first embodiment, the prism sheet is not required to be laminated or the number of prism sheets is reduced, so that the number of parts is reduced, and the number of assembling steps of the surface light emitting device 101 is reduced. Material costs can be reduced. In addition, the surface emitting device 101 can be thinned by reducing the number of prism sheets stacked.

  Further, in the surface light emitting device 101 according to the first embodiment, the incident surface 41 has a polygonal cross section formed by a plurality of inclined side surfaces 42 having a differential inclination angle θ (θ1 to θ6). For this reason, by changing the angle of the differential inclination angle θ (θ1 to θ6) and the length of the inclined side surface 42, the illuminance and the irradiation range of the light emitted from the emission surface 31 can be adjusted. In addition, the illuminance and irradiation range of the light emitted from the emission surface 31 can be adjusted by changing the differential inclination angle θ and the number of the inclined side surfaces 42. Therefore, it becomes easy to adjust the illuminance and irradiation range of the light emitted from the emission surface 31.

  Further, in the surface light emitting device 101 according to the first embodiment, in the thickness direction cross section of the light guide plate 30 passing through the central axis S of the light incident portion 40, the incident surface 41 is substantially polygonal so as to be recessed toward the light source 20. The differential inclination angle θ (θ1 to θ6) is in the range of 20 degrees to 45 degrees. Accordingly, the light emitted from the light source 20 is appropriately diffused over the entire light guide plate 30 and is emitted forward from the emission surface 31. That is, the surface light emitting device 101 according to the first embodiment can diffuse and emit light with higher illuminance over the entire emission surface 31. As a result, the luminance in the surface light emitting device 101 is improved and the quality of the product is improved.

  Furthermore, in the surface light emitting device 101 according to the present embodiment, the differential inclination angle θ between the inclined side surfaces 42 and 42 adjacent to each other in the light incident part 40 is directed radially outward from the center of the light incident part 40 or the diameter. By gradually increasing or decreasing in the range of 20 degrees or more and 45 degrees or less from the outside in the direction toward the center, a desired light amount can be obtained substantially uniformly over the entire light guide plate 30 like a fine prism. it can.

  In the surface light emitting device 101 according to the first embodiment, the light source 20 is disposed away from the phosphor 60. In addition, since the light guide plate 30 is formed with a multi-stage concentric light incident portion 40 that is recessed toward the light source 20, a gas layer G is formed between the light source 20 and the incident surface 41. Therefore, it is possible to prevent the heat generated by the light source 20 from being directly transmitted to the light guide plate 30, thereby extending the product life of the surface light emitting device 101.

  In the surface light emitting device 101 according to the first embodiment, the incident surface 41 is formed symmetrically with respect to the central axis S in the front-rear direction. For this reason, the light incident on the incident surface 41 can be diffused evenly. Therefore, variation in the amount of light emitted from the emission surface 31 can be suppressed, and product quality and stability are improved.

  Furthermore, in the surface light emitting device 101 according to the first embodiment, the phosphor 60 is interposed between the light source 20 and the light incident portion 40. For this reason, it is possible to easily change the color and type of light emitted from the emission surface 31 by changing the type of light emitted from the fluorescent material and the light source 20 included in the phosphor 60. Then, when a diffusion film (not shown) is laminated on the emission surface 31 of the light guide plate 30, the light emitted from the emission surface 31 can be diffused and radiated more uniformly.

[Second Embodiment]
Next, a surface light emitting device according to a second embodiment will be described with reference to FIGS. FIG. 5 is an enlarged view of a main part in the vicinity of the incident part in an example of the surface light emitting device according to the second embodiment. FIG. 6 is an enlarged view of a main part in the vicinity of an incident part in another example of the surface emitting device according to the second embodiment. In addition, the same code | symbol is attached | subjected about the component same as 1st Embodiment, and description is abbreviate | omitted about the overlapping content.

  As shown in FIGS. 5 and 6, in the surface light emitting device 201 according to the second embodiment, in the cross section in the thickness direction T of the light guide plate 30 passing through the central axis S of the light incident portion 40, The cross-sectional shape has an asymmetrical substantially polygonal shape above and below the central axis S. In the cross section in the thickness direction, the differential inclination angle θ between the inclined side surfaces 42 and 42 adjacent to each other in the light incident portion 40 is in the range of 20 degrees or more and 45 degrees or less from one to the other in the radial direction of the light incident section 40. Is set to increase or decrease. Specifically, in the cross section in the thickness direction, the differential inclination angles θ11 to θ17 between the adjacent inclined side surfaces 42 and 42 can be set to different angles. As shown in FIG. 5, the angle of inclination of the light incident surface 41 increases from the difference inclination angle θ11 toward θ17, that is, 20 degrees or more and 45 degrees or less so that θ11 <θ12 <θ13 <θ14 <θ15 <θ16 <θ17. The difference tilt angle θ may be set to increase within the range of. Or, conversely, as shown in FIG. 6, 20 degrees so that smaller angles of the light incident surface 41 from θ11 toward θ17, that is, θ11> θ12> θ13, θ14> θ15> θ16> θ17. The difference tilt angle θ may be set so as to decrease within the range of 45 degrees or less.

  As shown in FIG. 5, when the angle is increased from the outer side in the radial direction toward the other side in the radial direction of the light incident portion 40, for example, the difference in inclination angle θ between the adjacent inclined side surfaces 42, 42 is increased. The rate is constant (in this example, increased by 4 degrees), the differential tilt angle θ11 is 20 degrees, θ12 is 24 degrees, θ13 is 28 degrees, θ14 is 32 degrees, θ15 is 36 degrees, θ16 is 40 degrees, and θ17 can be set to 44 degrees. Further, by changing the increasing rate of the differential tilt angle θ between the adjacent differential tilt side surfaces 42, 42, for example, the differential tilt angle θ11 is 20 degrees, θ12 is 22 degrees, θ13 is 25 degrees, θ14 is 29 degrees, θ15 Can be set to 34 degrees, θ16 to 39 degrees, and θ17 to 45 degrees.

  On the other hand, as shown in FIG. 6, when the angle decreases from the outside in the radial direction to one side in the radial direction of the light incident portion 40, for example, the differential inclination angle θ between the adjacent inclined side surfaces 42, 42 is, for example. With a constant decrease rate (decrease by 4 degrees in this example), the differential inclination angle θ11 is 45 degrees, θ12 is 41 degrees, θ13 is 37 degrees, θ14 is 33 degrees, θ15 is 29 degrees, and θ16 is 25 degrees. , And θ17 can be set to 21 degrees. Further, by changing the decreasing rate of the difference inclination angle θ between the adjacent difference inclination side surfaces 42, 42, for example, the difference inclination angle θ11 is 45 degrees, θ12 is 38 degrees, θ13 is 32 degrees, θ14 is 27 degrees, θ15 Can be set to 24 degrees, θ16 to 22 degrees, and θ17 to 20 degrees. In addition, the value of the difference inclination angle θ between the adjacent inclined side surfaces 42 and 42 is an exemplification, and the difference inclination angle θ is within a range of 20 degrees or more and 45 degrees or less from one radial direction of the light incident portion 40 to the other. As long as the number increases or decreases.

  In the cross section in the thickness direction, the differential inclination angle θ between the adjacent inclined side surfaces 42, 42 of the light incident part 40 increases from one to the other in the radial direction of the light incident part 40 in the range of 20 degrees to 45 degrees. Alternatively, in order to set to decrease, it is necessary to gradually increase or decrease the inclination angle of each inclined side surface 42 of the substantially multistage concentric entrance surface 41 along the circumferential direction.

  The surface light-emitting device 201 according to the second embodiment has basically the same effects as the surface light-emitting device 101 according to the first embodiment. In particular, according to the surface light emitting device 201 according to the second embodiment, in the cross section in the thickness direction of the light guide plate 30 passing through the central axis S of the light incident portion 40, the adjacent inclined side surfaces 42, 42 of the light incident portion 40. By increasing or decreasing the difference inclination angle θ from one to the other in the radial direction of the light incident portion 40 in a range of 20 degrees or more and 45 degrees or less, the light emitted from the light source 20 is entirely transmitted through the light guide plate 30. There is an advantageous effect that it can be diffused more uniformly over a wide range.

  Also in the surface light emitting device 201 according to the second embodiment, a diffusion film (not shown) may be laminated on the emission surface 31 of the light guide plate 30. By laminating a diffusion film on the emission surface 31 of the light guide plate 30, the light emitted from the emission surface 31 can be diffused and emitted more uniformly. Further, in the surface light emitting device 201 according to the present embodiment, since the incident surface 41 of the light incident unit 40 functions as a fine prism, similarly to the surface light emitting device 101 according to the first embodiment, a desired light amount can be obtained. Therefore, it is not necessary to stack prism sheets on the light guide plate 30 or the number of prism sheets stacked can be reduced also when prism sheets are stacked. That is, in the surface light emitting device 201 according to the second embodiment, a prism sheet is not necessary or the number of prism sheets stacked is reduced, so that the number of parts is reduced, and the number of assembly steps and materials of the surface light emitting device 201 are reduced. Costs can be reduced. In addition, the surface light emitting device 201 can be thinned by reducing the number of prism sheets stacked.

[Third Embodiment]
Next, with reference to FIG. 7, the surface emitting device according to the third embodiment will be described. FIG. 7 is a side sectional view of a surface light emitting device according to a third embodiment. In addition, the same code | symbol is attached | subjected about the component same as 1st Embodiment, and description is abbreviate | omitted about the overlapping content.

  As shown in FIG. 7, the surface light emitting device 301 according to the third embodiment has a point that no phosphor is interposed between the light source 20 and the light incident portion 40, and the reflection surface 32 of the light guide plate 30 is provided. The point which inclines to the output surface 31 side sequentially as the distance from the light source 20 leaves | separates differs from the surface light-emitting device 101 which concerns on 1st Embodiment. A surface light emitting device 301 according to the third embodiment is mainly configured by a light source 20, a light guide plate 30, and a reflective film 50. In the present embodiment, since no phosphor is interposed between the light source 20 and the light incident portion 40, an LED that emits white light is employed as the light source 20. The light guide plate 30 is configured as a colorless and transparent body using the same material as in the first embodiment. The surface light emitting device 301 according to the present embodiment changes the direction of the light emitted from the light source 20 by the light guide plate 30 and emits the light forward from the emission surface 31 of the light guide plate 30 (upward in FIG. 7).

  As shown in FIG. 7, the light guide plate 30 is disposed apart from the light source 20 mounted on the wiring board 10. The light guide plate 30 has a substantially quadrangular prism shape or a substantially flat plate shape such that the thickness decreases as the distance from the light source 20 increases. That is, the reflective surface 32 on the back surface of the light guide plate 30 is sequentially inclined toward the emission surface 31 as the distance from the light source 20 increases. On one side surface of the light guide plate 30, a light incident portion 40 that is depressed facing the light source 20 is formed. In the cross section in the thickness direction T of the light guide plate 30 passing through the central axis S of the light incident portion 40, the light incident portion 40 is formed in a substantially polygonal shape. In the cross section in the thickness direction, the incident surface 41 is formed from a plurality of inclined side surfaces 42. A gas layer G exists between the incident surface 41 and the light source 32.

  As in the case of the first embodiment, the cross section of the incident surface 41 has a substantially polygonal shape composed of eight inclined side surfaces 42. Further, the differential inclination angle θ between the adjacent inclined side surfaces 42 constituting the incident surface 41 is set in a range of 20 degrees to 45 degrees. Further, the cross-sectional shape of the incident surface 41 has a polygonal shape that is symmetrical with respect to the central axis S. For this reason, the light incident from the incident surface 41a ahead of the center axis S and refracted obliquely forward (upwardly obliquely to the left in FIG. 7) is guided directly or indirectly to the emission surface 31. Refracted toward. On the other hand, the light incident from the incident surface 41b behind the central axis S and refracted obliquely backward (left obliquely downward in FIG. 7) is reflected on the reflective surface 32 of the light guide plate 30 or the reflective surface along the thickness direction. Then, the light is guided to the exit surface 31 and refracted forward at the exit surface 31. For this reason, the light emitted from the light source 20 is diffused moderately over the entire light guide plate 30 and emitted forward from the emission surface 9.

  The surface light emitting device 301 according to the third embodiment has basically the same effects as the surface light emitting device 101 according to the first embodiment. In particular, according to the surface light emitting device 301 according to the third embodiment, the reflecting surface 32 of the light guide plate 30 has a distance from the light source 20 in the cross section in the thickness direction of the light guide plate 30 passing through the central axis S of the light incident portion 40. Since it inclines to the output surface 31 side as it leaves | separates, the optical path in the position away from the light source 20 is shortened. Therefore, there is an advantageous effect that light emitted from the light source 20 can be appropriately diffused uniformly throughout the light guide plate 30.

  Further, in the surface light emitting device 301 according to the third embodiment, since the gas layer G exists between the light source 20 and the incident surface 41 as in the first embodiment, heat generated by the light source 20 is generated. Direct transmission to the light guide plate 30 can be prevented. As a result, the product life of the surface light emitting device 301 can be extended.

  Furthermore, in the surface light emitting device 301 according to the third embodiment, the cross-sectional shape of the incident surface 41 has a substantially polygonal shape that is recessed toward the light source 20, and adjacent inclined side surfaces 42 that constitute the incident surface 41, The differential inclination angle θ between 42 is set in a range of 20 degrees to 45 degrees. For this reason, the light irradiated from the light source 20 is refracted by the incident surface 41, and a part of the light is totally reflected by the reflecting surface 32 or the like and radiated forward from the emitting surface 31. Therefore, the light incident on the incident surface 41 is emitted from the emission surface 31 without leaking outward in the radial direction of the incident portion 40. For this reason, it becomes possible to diffuse and radiate light having higher illuminance from the emission surface 31 evenly.

  Also in the surface light emitting device 301 according to the third embodiment, a diffusion film (not shown) may be laminated on the emission surface 31 of the light guide plate 30. By laminating a diffusion film on the emission surface 31 of the light guide plate 30, the light emitted from the emission surface 31 can be diffused and emitted more uniformly. Further, in the surface light emitting device 301 according to the present embodiment, since the incident surface 41 of the light incident unit 40 functions as a prism, similarly to the surface light emitting device 101 according to the first embodiment, a desired light amount can be obtained, Even when the prism sheets are not required to be laminated on the light guide plate 30 or when the prism sheets are laminated, the number of the prism sheets can be reduced. That is, in the surface light-emitting device 301 according to the third embodiment, a prism sheet is not required or the number of prism sheets stacked is reduced, so that the number of parts is reduced, and the assembly man-hour and material cost of the surface light-emitting device 301 are reduced. Can be reduced. In addition, the surface light emitting device 301 can be thinned by reducing the number of prism sheets stacked.

[Fourth Embodiment]
Next, a surface light emitting device according to a fourth embodiment will be described with reference to FIGS. 8 and 9. FIG. 8 is a plan view of an example of a surface light-emitting device according to the fourth embodiment. FIG. 9 is a plan view of another example of the surface light emitting device according to the fourth embodiment. In FIGS. 8 and 9, the reflective film is omitted. Moreover, the same code | symbol is attached | subjected about the component same as 1st Embodiment, and description is abbreviate | omitted about the overlapping content.

  As shown in FIGS. 8 and 9, the surface light emitting device 401 according to the fourth embodiment has a plurality of light incident portions 40 formed on the light guide plate 30. As in the first to third embodiments, the incident surface 41 of each light incident portion 40 has a substantially polygonal shape that is recessed toward the light source 20, and adjacent inclined side surfaces 42 that constitute the incident surface 41. , 42 is set in a range of 20 degrees to 45 degrees. The differential inclination angle θ between the adjacent inclined side surfaces 42 and 42 constituting the incident surface 41 is directed from the center of the light incident portion 40 to the radially outward direction, from the radially outward direction to the center, or in the radial direction. Is set so as to increase or decrease in the range from 20 degrees to 45 degrees from one to the other (see FIGS. 3, 5 and 6). A number of light sources 20 corresponding to the light incident portions 40 are provided facing each light incident portion 40. The plurality of light sources 20 are mounted on the common wiring board 10 on each side surface of the light guide plate 30.

  In the example of the surface light emitting device 401 illustrated in FIG. 8, a plurality of light incident portions 40 are formed on the side surfaces 33 and 34 facing each other of the light guide plate 30. On each of the opposing side surfaces 33 and 34, the plurality of light incident portions 40 are arranged in parallel. A corresponding number of light sources 20 are provided facing the light incident portions 40 of the opposite side surfaces 33 and 34. In an example of the surface light emitting device 401 shown in FIG. 8, light is irradiated from a plurality of light sources 20 located at opposite positions, and light enters the light guide plate 30 from the incident surface 41 of each light incident portion 40. For this reason, the light that has entered the light guide plate 30 undergoes refraction and total reflection, and is diffused from the exit surface 31 with light of high illuminance substantially uniformly over the entire light guide plate 30. .

  In another example of the surface light emitting device 401 shown in FIG. 9, a plurality of light incident portions 40 are formed on the adjacent side surfaces 33 and 35 of the light guide plate 30. On each of the side surfaces 33 and 35, the plurality of light incident portions 40 are arranged in parallel. A corresponding number of light sources 20 are provided facing the light incident portions 40 of the adjacent side surfaces 33 and 35. In another example of the surface light emitting device 401 shown in FIG. 9, light is irradiated from a plurality of light sources 20 facing the adjacent side surfaces 33 and 35, and light enters the light guide plate 30 from the incident surface 41 of each light incident portion 40. To do. For this reason, the light incident on the light guide plate 30 is diffused from the exit surface 31 with light of high illuminance substantially uniformly over the entire light guide plate 30 through refraction and reflection.

  The surface light-emitting device 401 according to the fourth embodiment has basically the same functions and effects as the surface light-emitting device 101 according to the first embodiment. Particularly, according to the surface light emitting device 401 according to the fourth embodiment, a plurality of light incident portions 40 are formed on the light guide plate 30 and the number of light sources 20 corresponding to the light incident portions 40 is included. There is an advantageous effect that the illuminance can be greatly increased. Further, in the surface light-emitting device 401 according to the fourth embodiment, the light incident portions 40 are formed on the side surfaces 33 and 34 facing the light guide plate 30 or the adjacent side surfaces 33 and 35, respectively, and face each light incident portion 40. Since the light source 20 is included, the light emitted from the light source 20 is uniformly distributed over the entire light guide plate 30, and light having a high illuminance can be diffused from the emission surface 31 substantially uniformly. Play.

  Furthermore, in the surface light-emitting device 401 according to the fourth embodiment, the cross-sectional shape of the incident surface 41 has a substantially polygonal shape that is recessed toward the light source 20, and adjacent inclined side surfaces 42 that constitute the incident surface 41, The differential inclination angle θ between 42 is set in a range of 20 degrees to 45 degrees. For this reason, the light irradiated from the light source 20 is refracted by the incident surface 41, and a part of the light is totally reflected by the reflecting surface 32 or the like and radiated forward from the emitting surface 31. Therefore, the light incident on the incident surface 41 is emitted from the emission surface 31 without leaking outward in the radial direction of the incident portion 40. For this reason, it becomes possible to diffuse and radiate light having higher illuminance from the emission surface 31 evenly.

  And according to the surface emitting device 401 which concerns on 4th Embodiment, in the thickness direction cross section of the light-guide plate 30 which passes along the central axis S of the light-incidence part 40, between the inclination side surfaces 42 and 42 which adjoin the light-incidence part 40 mutually. The difference inclination angle θ is in the range of 20 degrees to 45 degrees from the center of the light incident portion 40 to the radially outward direction, from the radially outward direction to the center, or from one radial direction to the other. As a result, the light emitted from the light source 20 can be diffused from the light exit surface 31 more uniformly and uniformly by the light guide plate 30 throughout.

  Also in the surface light emitting device 401 according to the fourth embodiment, a diffusion film (not shown) may be laminated on the emission surface 31 of the light guide plate 30. By laminating a diffusion film on the emission surface 31 of the light guide plate 30, the light emitted from the emission surface 31 can be diffused more uniformly. Further, in the surface light emitting device 401 according to the present embodiment, since the incident surface 41 of the light incident unit 40 functions as a prism, similarly to the surface light emitting device 101 according to the first embodiment, a desired light amount can be obtained, Even when prism sheets are not required to be stacked on the light guide plate 30 or when prism sheets are stacked, the number of prism sheets stacked can be reduced. That is, in the surface light emitting device 401 according to the fourth embodiment, a prism sheet is not required or the number of prism sheets stacked is reduced, so that the number of parts is reduced, and the assembly man-hours and materials of the surface light emitting device 401 are reduced. Costs can be reduced. In addition, the surface light emitting device 401 can be thinned by reducing the number of prism sheets stacked.

[Other Embodiments]
The preferred embodiments of the present invention have been described above, but these are examples for explaining the present invention, and the scope of the present invention is not intended to be limited to these embodiments. The present invention can be implemented in various modes different from the above-described embodiments without departing from the gist thereof.

  That is, in said embodiment, the light-incidence part 40 is exhibiting the substantially multistage concentric circle shape by front view from the light source 20 side. The shape of the light incident portion 40 is not limited to a substantially multi-stage concentric circle shape, and may be formed in a multi-stage concentric rectangular shape such as a substantially multi-stage concentric polygon. As shown in FIG. 10, the light incident portion 40 may have, for example, a shape in which the light incident portion 40 is cut out into a substantially half prism shape having a polygonal cross section along the central axis S direction which is the left-right direction. In this case, the cross section cut along the Y direction shown in FIG. 10 becomes a substantially polygonal shape shown in FIG. 1 and the like, and the inclined side surface 42 is formed in a shape extending along the left-right direction (width direction) shown in FIG. . For this reason, more light emitted from the light source 20 can be refracted in the front-rear direction at the entrance surface 41 and guided to the exit surface 31. Therefore, the illuminance of the light emitted from the emission surface 31 is increased, and the luminance of the surface light emitting device 501 is improved.

  In each of the above-described embodiments, the outer shape of the light guide plate 30 is a substantially square column shape or a substantially flat plate shape. However, the outer shape of the light guide plate 30 is limited to a substantially square column shape or a substantially flat plate shape. It may be formed in other shapes such as a substantially pentagonal prism shape. Further, as shown in FIG. 11, the reflecting surface 32 facing the light exit surface 31 of the light guide plate 30 of the surface light emitting device 601 may be configured as an arcuate curved surface instead of being linear. Moreover, you may apply the structure which makes the reflective surface 32 an inclined surface as shown in FIG. 7 to other embodiment.

  Furthermore, in the above-described embodiment, the light source 20 is disposed at a position separated from the light guide plate 30. For example, the light source 20 is brought into contact with the end surface of the opening end 43 of the light guide plate 30 to place the light source 20. You may comprise so that it may arrange | position inside the light irradiation part 40, without separating from 30. FIG. Further, the phosphor 60 made of a fluorescent plate is not stretched around the inner edge or the outer edge of the light incident portion 40, but a phosphor film may be directly attached to the incident surface 41 of the light incident portion 40, or the phosphor. When the fluorescent paint layer is formed by applying 60 to the incident surface with a fluorescent paint, the light source 20 may be arranged inside the light incident part 40 without being separated from the light guide plate 30. The outer shape of the phosphor 60 can be appropriately changed to other shapes such as a quadrangle according to the opening shape of the light incident portion 40.

  In each of the above-described embodiments, the inclination angle θ is in the range of 20 degrees or more and 45 degrees or less, but in accordance with the specification or the like, a part of the difference inclination angle θ is less than 20 degrees, You may form so that it may exceed 45 degree | times. Moreover, the structure which inclines ahead as the reflective surface 32 of the light-guide plate 30 distances from the light source 20 can be employ | adopted also for the light-guide plate 30 of other embodiment other than the light-guide plate 30 of 3rd Embodiment. it can.

  An image forming apparatus such as a thin display can be configured by disposing a liquid crystal display (LCD) on the surface light emitting devices 101, 201, 301, 401, 501, and 601 according to the above embodiment (not shown). ) That is, the surface light emitting devices 101, 201, 301, 401, 501, and 601 according to the first to fourth embodiments are configured as a backlight assembly of a liquid crystal display.

  The liquid crystal display can be disposed by laminating a diffusion film and a prism sheet on the surface light emitting devices 101, 201, 301, 401, 501, 601. However, in the surface light emitting devices 101, 201, 301, 401, 501, and 601 according to the first to fourth embodiments, the incident surface 41 of the light incident portion 40 is configured by a plurality of inclined side surfaces 42, and the incident light The surface 41 functions as a prism. Therefore, a desired light amount is obtained in the surface light emitting devices 101, 201, 301, 401, 501, 601, and it is not necessary to laminate a prism sheet on the light guide plate 30, or even when a prism sheet is laminated, The number of stacked prism sheets can be reduced. That is, the image forming apparatus according to the present embodiment does not require a prism sheet or reduces the number of stacked prism sheets, thereby reducing the number of parts and reducing the assembly man-hour and material cost of the image forming apparatus. be able to. In addition, the image forming apparatus can be thinned by reducing the number of prism sheets stacked.

  As described above, the surface light emitting devices 101, 201, 301, 401, 501, and 601 according to the above-described embodiments are used as a backlight light source of a liquid crystal display, but may be used for the purpose of illuminating various displays and signs. . Further, the surface light-emitting devices 101, 201, 301, 401, 501, and 601 may be used as guide lights, indicator lights, emergency lights, or various inspection lights, and constitute the surface light-emitting devices 101, 201, 301, and 401. The present invention can be applied to various devices and apparatuses that are included as part of the elements.

20 light source,
30 light guide plate,
31 emission surface,
33, 34 opposite sides,
33, 35 adjacent sides,
40 light incident part,
41 entrance surface,
42 sloping sides,
50 reflective film,
60 phosphor,
θ differential tilt angle,
101, 201, 301, 401, 501, 601 Surface light emitting device.

Claims (12)

A light source;
A light guide plate that introduces light from the light source and emits the light toward the exit surface;
A reflective film that covers at least a surface of the light source and the light guide plate facing the emission surface;
With
The light guide plate has a multi-stage concentric light incident portion that is depressed facing the light source,
In the thickness direction cross section of the light guide plate passing through the central axis of the light incident part,
The surface light-emitting device characterized in that a differential inclination angle between adjacent inclined side surfaces constituting the incident surface of the light incident portion is set in a range of 20 degrees to 45 degrees.   The differential inclination angle is not less than 20 degrees and not more than 45 degrees from the center of the light incident portion toward the radially outward direction, from the radially outward direction toward the center, or from one radial direction to the other. 2. The surface light emitting device according to claim 1, wherein the surface light emitting device is set so as to increase or decrease within a range.   The surface light-emitting device according to claim 2, wherein the differential inclination angle is set to be constant or variable.   4. The surface light emitting device according to claim 1, wherein the reflection surface facing the emission surface is sequentially inclined toward the emission surface side as the distance from the light source increases. 5.   The surface light-emitting device according to claim 1, wherein the reflection surface facing the emission surface is formed as a curved surface.   The surface emitting device according to claim 1, wherein a phosphor is interposed between the light source and the light incident part.   The surface emitting device according to claim 6, wherein the phosphor is a phosphor film disposed in the light incident portion or a fluorescent paint layer applied to the light incident portion.   The surface light-emitting device according to claim 6, wherein the light source is a blue LED, and the phosphor is a yellow phosphor that develops white color by receiving blue light of the blue LED.   The surface light-emitting device according to claim 1, wherein a diffusion film is laminated on the light guide plate.   The surface light-emitting device according to claim 1, wherein a plurality of the light incident portions are formed on the light guide plate, and the number of the light sources corresponding to the light incident portions is included.   The surface light-emitting device according to claim 10, wherein the light incident portions are respectively formed on opposite side surfaces or adjacent side surfaces of the light guide plate, and the light sources are provided facing each light incident portion.   An image forming apparatus comprising a liquid crystal display disposed on the surface light emitting device according to claim 1.