JP2006031941A - Planar light source unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a planar light source unit in which uniform emission of light is realized on an emitting surface without making the size larger than the size of a liquid crystal panel as much as possible. <P>SOLUTION: The planar light source unit 10 comprises a light guide body 1, a cylindrical lens 7, a plurality of white LEDs 4, a reflecting mirror 8, and a light diffusion member 11. The light guide body 1 is of plate shape and has an emitting surface 29 for emitting light. The cylindrical lens 7 is arranged at one end face 27 extending in a direction crossing the emitting surface 29 in the light guide body 1 and condenses light in the direction crossing the emitting surface 29 of the light guide body 1 (for example, in thickness direction of the light guide body). The white LED 4 is arranged as as to face one end face 27 of the light guide body 1 through the cylindrical lens 7. The reflecting mirror 8 is arranged so as to face the other end face 28 located on the opposite side to the one end face 27 in the light guide body 1. The light diffusion member 11 is arranged at the rear face side located on the opposite side to the emitting surface 29 in the light guide body 1. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a planar light source unit, and more particularly to a planar light source unit used as a backlight mechanism in a display device having a backlight mechanism.

  2. Description of the Related Art In recent years, a liquid crystal display device having a thin backlight and a highly visible backlight mechanism has been used as a display device for a laptop or notebook computer or a liquid crystal television (for example, see Patent Document 1). .

  FIG. 12 is a schematic perspective view of a planar light source unit constituting the conventional backlight mechanism disclosed in Patent Document 1. 13 is a schematic cross-sectional view taken along line XIII-XIII in FIG. A conventional planar light source unit will be described with reference to FIGS.

As shown in FIGS. 12 and 13, the conventional planar light source unit 110 is disposed as a backlight mechanism on the back surface of the liquid crystal panel 106 via a light directing sheet 103, and has a light guide 101 and a linear shape. A light source 104, a light diffusing reflector 102, and a light diffusing member 111 are provided.
For the light guide body 101, a substance that allows light to pass therethrough can be used as its constituent material. For example, methacrylic resin or polycarbonate resin can be used as the material of the light guide body 101. A linear light source 104 is disposed so as to face the end face of the light guide 101. A light reflecting mirror 105 is disposed so as to surround the linear light source 104. The light reflecting mirror 105 is a reflecting mirror for causing the light from the linear light source 104 to efficiently enter the end face of the light guide 101.

  On the back side of the light guide 101 (the surface opposite to the light exit surface), the light diffusion member 111 is arranged in a dot shape. For the light diffusing member 111, for example, a pigment having a high refractive index and a large diffuse reflectance as compared with the material of the light guide 101 can be used. Specifically, a paint containing titanium white as such a pigment, printing ink, or the like can be used as the light diffusing member 111. Further, such a light diffusing member 111 prints the above-described printing ink or the like in a dot shape on the back surface of the light guide 101 by a method such as screen printing. Instead of forming the light diffusing member 111, using a technique such as roughening the back surface of the light guide 101, or forming a small hole on the back surface, or providing a small protrusion on the back surface, Light diffusibility can be imparted to the light guide 101. As can be seen from FIG. 13, the light diffusion reflection plate 102 is disposed under the light diffusion member 111. The light diffusing reflector 102 is used to efficiently return the light emitted from the light guide 101 to the light guide 101 and use the light efficiently.

  As the linear light source 104, an array of fluorescent tubes, tungsten incandescent tubes, optical rods, LEDs, or the like can be used. Further, a light directing sheet 103 is disposed on the light exit surface of the light guide 101. The light directing sheet 103 is made of a light-transmitting material, and makes light emitted from the light guide 101 enter the front liquid crystal panel 106 as effective parallel light.

  FIG. 14 is a schematic plan view showing a planar light source unit when a plurality of LEDs 104 are used as the linear light source 104. With reference to FIG. 14, the problem of the conventional planar light source unit will be described.

  The conventional planar light source unit shown in FIG. 14 uses a plurality of LEDs 104 arranged on the substrate 112 as a linear light source as described above. The LED 104 is mounted on the substrate 112 by a technique such as soldering. As shown in FIG. 14, in the case where a plurality of LEDs 104 are used as a linear light source, in order to emit light with less unevenness as a linear light source, a countermeasure of narrowing the interval between the LEDs 104 can be considered. However, when such a method is employed, the number of necessary LEDs 104 increases, which increases the manufacturing cost and power consumption of the planar light source unit. Therefore, it is preferable that the number of LEDs used is as small as possible. For this reason, it is conceivable to reduce the necessary number of LEDs 104 by using LEDs 104 having a relatively large directivity angle.

  Here, the light beam 113 emitted from the LED 104 having a large directivity angle enters the light guide 101 from the end face of the light guide 101. When the light beam 113 enters the light guide 101, it spreads into the light guide 101 at an angle according to Snell's formula. For example, when the light emission angle from the LED 104 is 40 ° and the refractive index n of the light guide 101 is 1.5, the light (light ray 113) incident on the light guide 101 has an emission angle of about 25. Spread at °. FIG. 14 shows the spread of the light beam 113 in the horizontal direction in the light guide 101 at this time.

  However, when a plurality of LEDs 104 (for example, a plurality of white LEDs) are used in this way, as shown in FIG. 14, a light quantity deficient portion 115 that is an area where the lights from adjacent LEDs 104 do not interfere with each other occurs. As a result, local brightness gradation occurs in the diffused light emitted from the upper surface (outgoing surface) of the light guide 101 (specifically, the brightness of the light from the light quantity deficient portion 115 is other than It becomes darker than the brightness of the light emitted from the part).

  In addition, when the LEDs 104 of three colors (red (R), green (G), and blue (B)) are used as the plurality of LEDs 104, white light is guided by mixing all the lights from the LEDs 104 of the three colors. There is a mixed color emission part 121 emitted from the body 101. On the other hand, on the LED 104 side from the mixed color emitting portion 121, only two colors of the light from these three colors of LEDs 104 are mixed or not mixed at all. There is a non-white light emitting portion 119 that exits from the light guide 101. As a result, color unevenness occurs in the light emitted from the light guide body 101.

Various techniques have been proposed in the past in order to improve the density and color unevenness of light emitted from the light guide 101. For example, in Patent Document 2, a reflective sheet is disposed on the back surface of the light guide body 101, and the reflective sheet is partially bonded to the light guide body 101 in the vicinity of the LED 104. It is supposed to emit light uniformly. Further, in Patent Document 3, LEDs of different colors exhibit the same illumination distribution in the light guide 101 by arranging LEDs of different colors in the vertical direction (vertical) and arranging them at the same position in a plane. Therefore, color unevenness is not generated. In Patent Document 4, one or a small number of LEDs are arranged on the end face of the light guide body 1010, and incident light from the LEDs is distributed to the light guide body 101 to the left and right, and a hole having a function of allowing a part to pass therethrough. By providing a planar light source unit that can uniformly emit light at low cost by uniformly spreading light from the light source by efficient optical path conversion and making it non-directional like a linear light source Can provide.
JP-A-6-342161 JP-A-9-92886 JP 11-353920 A JP-A-6-342161

  However, in the above-described conventional technique, the light intensity deficiency portion 115 shown in FIG. 14 and other portions are reduced to some extent, but the light amount deficiency portion 115 still exists, and the display of the liquid crystal display device In order to maintain the quality at a high level, it is necessary to arrange such a light quantity deficient portion 115 in a region that does not overlap with the liquid crystal panel 106 (see FIG. 13). As a result, the width of the light guide 101 is larger than the width of the liquid crystal panel 106 by at least the distance L1.

  Further, the light incident on the inner end face of the light guide body 101 from the LED with a wide directivity angle has an angle exceeding the critical angle determined by the refractive index of the light guide body 101 and the external air, and the inner end face of the light guide body 101. , The light is transmitted through the end face of the light guide 101. For this reason, the light quantity of the light radiate | emitted from the output surface of the light guide 101 was to fall.

  Further, when the three-color LED 104 is used as the LED 104, the non-white light emitting portion 119 that is wider than the light quantity deficient portion 115 is formed as described above. Therefore, considering the display quality of the liquid crystal display device, this non-white light emitting portion 119 is used. Must be arranged in a region that does not overlap the liquid crystal panel 106. As a result, the width of the light guide 101 needs to be larger than the width of the liquid crystal panel 106 by the distance L2.

  Here, in general, in a liquid crystal display device, it is desired to make the periphery of the display surface (that is, a portion called a frame) as narrow as possible. For this reason, it is not preferable that the width of the light guide 101 is larger than the width of the liquid crystal panel 106. In addition, although it is possible to make the structure of the light guide body 101 bent so as to be larger than the size of the liquid crystal panel 106, such a structure is complicated. There is a problem in that light leaks to the outside and light utilization efficiency decreases. Therefore, such a bent structure is considered to be insufficient as a practical measure.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to make uniform light emission on the emission surface without making the size larger than the size of the liquid crystal panel as much as possible. It is providing the planar light source unit which can implement | achieve.

  The planar light source unit according to the present invention includes a light guide, a lens, a plurality of light sources, a reflecting mirror, and a light diffusing member. The light guide has a plate shape and has an emission surface for emitting light. The lens is disposed on one end surface of the light guide that extends in a direction intersecting the emission surface, and condenses light in a direction intersecting the emission surface of the light guide. The plurality of light sources are arranged so as to face one end surface of the light guide through the lens. The reflecting mirror is arranged in the light guide so as to face the other end surface located on the opposite side to the one end surface. The light diffusing member is disposed on the other surface side of the light guide that is located on the side opposite to the emission surface.

  Here, when light having a certain emission angle is incident on the light guide as it is from one end face of the light guide, a direction substantially perpendicular to the light emission surface of the light guide (thickness direction of the light guide) The light incident at a certain angle or more with respect to the light is not reflected in the light guide, and the light is emitted from the emission surface while the light (color) from the plurality of light sources is not sufficiently mixed. Is done. As a result, so-called shading and color unevenness occur in the light emitted from the emission surface of the planar light source unit.

  However, in the planar light source unit according to the present invention, by arranging the lens, the angle of the light traveling direction with respect to the direction parallel to the exit surface of the light guide can be set to a value within a predetermined range. For this reason, the angle of the light can be adjusted so that the light incident on the light guide is reflected a sufficient number of times within the light guide to sufficiently mix the light (color). . As a result, it is possible to emit uniform light with little color unevenness and light and shade, in which light from a plurality of light sources is sufficiently mixed, from the exit surface of the light guide.

  Further, by disposing the reflecting mirror on the other end surface of the light guide, the light emitted from the other end surface of the light guide can be made incident again on the light guide by reflecting the light with the reflecting mirror. As a result, the light emitted from the other end surface of the light guide can be used for mixing the light inside the light guide and emitting the light from the emission surface. Therefore, it is possible to improve the uniformity and the amount of light emitted from the emission surface.

  In addition, since the uniformity of the light emitted from the light exit surface of the light guide can be improved, the conventional light quantity deficient portion is almost eliminated. Therefore, when the planar light source unit according to the present invention is applied to a liquid crystal display device, it is not necessary to dispose the insufficient light amount portion at a position where it does not overlap with the liquid crystal panel as in the prior art (that is, almost the entire surface of the planar light source unit is liquid crystal). Can be used as a backlight to supply light to the panel). Therefore, the size of a so-called frame portion (portion around the liquid crystal display portion) in the liquid crystal display device can be reduced.

  In the planar light source unit, the traveling direction of the light emitted from the lens and incident on the light guide includes one of a direction substantially parallel to the light exit surface of the light guide and a direction of focusing inside the light guide. Thus, it is preferable that the characteristics of the lens are determined.

  In this case, the light incident on the light guide can be reliably reflected inside the light guide as many times as necessary to sufficiently mix the light (color). Here, the direction substantially parallel to the exit surface of the light guide 1 refers to a direction in which an inclination angle with respect to the extending direction of the exit surface is ± 10 ° or less, more preferably ± 5 ° or less.

  In the planar light source unit, the lens may be either a convex lens or a Fresnel lens.

  In this case, by using a general convex lens or Fresnel lens, the planar light source unit according to the present invention can be easily manufactured without using a special lens.

  Further, if a Fresnel lens having a relatively small thickness is used as the lens, the periphery of the display surface in the liquid crystal display device using the planar light source unit can be easily reduced.

  In the planar light source unit, the lens preferably emits light so as to be focused inside the light guide. In the above planar light source unit, the distance between the focal point where the light is focused by the lens and the one end surface of the light guide is such that the light from the plurality of light sources does not interfere with each other and does not interfere with each other. Preferably it is larger than the width of the region to be released.

  In this case, the distance between the focal point and the one end surface of the light guide is too small (the focal length of the lens is too small), and the incident angle of light with respect to the inner side surface of the light guide becomes large. It is possible to reduce the probability of occurrence of a phenomenon in which the number of reflections of light within the light body is insufficient. As a result, it is possible to reduce the possibility that the uniformity of the light emitted from the light exit surface of the light guide body is lowered due to the insufficient number of times of light reflection.

In the planar light source unit, the reflecting mirror has a central portion in a direction intersecting with the exit surface of the light guide (for example, a direction substantially perpendicular to the exit surface) from the other end surface of the light guide. It is preferable to be bent so as to protrude. The bending angle θ of the bent portion of the reflecting mirror is 90 ° + θ ₁ <θ <120 ° + 2 when the incident angle of light from the lens to the light guide with respect to the direction parallel to the exit surface is θ ₁ × so as to satisfy the relational expression theta _1/3, the reflecting mirror is preferably formed.

  In this case, the light reflected by the reflecting mirror can be efficiently reincident on the light guide.

  In the planar light source unit, the lens may be integrally formed with the light guide.

  In this case, since it is not necessary to prepare a lens as a separate part, the number of parts of the planar light source unit can be reduced. As a result, the manufacturing cost of the planar light source unit can be reduced.

  In the planar light source unit, the light source may be a white LED or a combination of LEDs of three colors including red, green, and blue.

  In this case, a planar light source unit that emits white light from the emission surface can be realized.

  In addition, if a combination of LEDs of three colors consisting of red, green, and blue is used, when the luminance of the white LED is insufficient, it is sufficient to use three LEDs of high luminance. Light with high brightness can be easily obtained.

  As described above, according to the present invention, by arranging the lens and the reflecting mirror, the light incident on the light guide is necessary to sufficiently mix the light (color) inside the light guide. Since the light incident on the light guide can be reflected as many times as possible, it is possible to realize a planar light source unit that emits uniform light without color unevenness from the exit surface.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and description thereof will not be repeated.

  FIG. 1 is a schematic plan view of a planar light source unit according to the present invention. 2 is a schematic cross-sectional view taken along line II-II shown in FIG. FIG. 3 is a schematic cross-sectional view showing another example of the cross section taken along line II-II shown in FIG. The planar light source unit 10 according to the present invention will be described with reference to FIGS.

  As shown in FIG. 1, a planar light source unit 10 according to the present invention includes a plurality of white LEDs 4 that are light sources, a cylinder lens 7, a light guide 1, a reflecting mirror 8, and a light diffusing member 11. The plurality of white LEDs 4 are arranged in a straight line on the substrate 12. As shown in FIGS. 2 and 3, the light guide 1 is disposed so as to face the white LED 4. The light guide 1 has a plate-like outer shape, and the white LED 4 is disposed at a position facing the side surface (one end face 27) having a relatively small surface area of the plate-like light guide 1. That is, the plurality of white LEDs 4 are arranged along the one end face 27 of the light guide 1. A cylinder lens 7 is arranged between the light guide 1 and the white LED 4 so as to face the side surface of the light guide 1.

  Further, on the side surface (the other end surface 28) opposite to the side surface (the one end surface 27) facing the cylinder lens 7 in the light guide 1, a reflecting mirror 8 having a cross-sectional shape as shown in FIG. Is arranged. A plurality of light diffusing members 11 are arranged on the surface (lower surface or back surface) located on the opposite side of the light emitting surface 29 (see FIG. 2), which is the upper surface of the light guide 1. In addition, the distance between the adjacent light-diffusion members 11 is set so that it may become large as it leaves | separates from white LED4.

  Such a planar light source unit 10 is used, for example, as a backlight of a liquid crystal display device 20 as shown in FIG. FIG. 4 is a schematic cross-sectional view showing a liquid crystal display device to which the planar light source unit according to the present invention is applied. As shown in FIG. 4, the liquid crystal display device 20 to which the planar light source unit 10 according to the present invention is applied has a structure in which the liquid crystal panel 6 is disposed on the emission surface 29 (upper surface) of the planar light source unit 10. . As the liquid crystal panel 6, for example, a transmissive liquid crystal panel can be used.

  Next, the operation when light is emitted from the emission surface in the planar light source unit 10 shown in FIGS. 1 to 3 will be briefly described.

  As shown in FIGS. 1 to 3, the cylinder lens 7 has no lens curvature in the horizontal direction (the direction parallel to the paper surface in FIG. 1). Therefore, in the horizontal direction, the light rays 13 emitted from the white LEDs 4 travel so as to spread radially from the individual white LEDs 4 as in the case where the cylinder lens 7 does not exist. That is, the light beam 13 proceeds so as to spread around the white LED 4 inside the light guide 1. The spread light beam 13 is light that travels straight toward the reflecting mirror 8 and a side end face of the light guide 1 (for example, an end face that extends in a direction crossing the exit face 29 or the back face, and one end face of the light guide 1. 2 and two end faces connecting the other end face 28) and light traveling toward the other end face 28. The light traveling toward the side end face of the light guide 1 is reflected on the side end face (the inner peripheral side) of the light guide 1 and changes its traveling direction. Then, any component of the light beam 13 is finally emitted from the other end face 28 of the light guide 1 and obtained in the reflecting mirror 8. The light beam 13 is reflected by the reflecting mirror 8, and most of it is incident on the light guide 1 again.

  Further, as shown in FIGS. 2 and 3, in the vertical direction of the light guide 1, since the cylinder lens 7 exists, the traveling direction of the light emitted from the white LED 4 is changed by the curvature of the cylinder lens 7. The For this reason, the quantity of light incident on the light guide 1 is greater than when the cylinder lens 7 is not present. The incident light is reflected by the side surfaces (upper surface and lower surface) of the light guide 1 as shown in FIGS. 2 and 3, and finally part of the light reaches the reflecting mirror 8, and the reflecting mirror. The light is reflected at 8 and enters the light guide 1 again. And it is radiate | emitted from the output surface 29 (upper surface) of the light guide 1 by being scattered in the light-diffusion member 11 installed in the back surface side of the light guide 1. FIG.

  2 and 3 show the locus of the light beam 13 when the curvature of the cylinder lens 7 is different. That is, FIG. 2 shows the locus of the light beam 13 when the light beam 13 travels in a substantially horizontal direction (a direction substantially parallel to the upper surface, which is the output surface of the light guide 1). ing. On the other hand, FIG. 3 is a case where the curvature of the cylinder lens 7 is larger than the curvature of the cylinder lens 7 shown in FIG. 2, and the light beam 13 emitted from the cylinder lens 7 is focused at a predetermined distance. The trajectory is shown.

  Here, as the white LED 4, a fine surface light source represented by a high-brightness LED having a flip chip structure is used. Therefore, it is difficult to obtain completely parallel light or to focus on one point (focal point). Accordingly, one object of the present invention is to obtain the light beam 13 that minimizes the spread of the light beam. Therefore, any one of the modes shown in FIGS. 2 and 3 may be used, and the planar light source unit may be configured so that both of the trajectories of the light beam 13 shown in FIGS. 2 and 3 are mixed. 10 may be configured.

  As shown in FIG. 2, in the case where the light beam 13 is a light having a small spread (parallel light substantially parallel to the exit surface 29 of the light guide 1), the light spreads at the half-value angle of the cylinder lens 7. The distance D1 from the position 30 where the light beam 13 is incident on and reflected from the side surface (upper surface or lower surface) of the light guide 1 to the end of the light guide 1 is larger than the distance L1 shown in FIG. It is preferable to use a configured cylinder lens 7 (having a predetermined half-value angle). Here, FIG. 5 is a schematic plan view of the liquid crystal display device for explaining the characteristics of the cylinder lens, and the light guide body 1 constituting the planar light source unit of the liquid crystal display device is not interposed via the cylinder lens. The case where the light from the white LED 4 is directly incident is shown. In FIG. 5, the plurality of white LEDs 4 are arranged in a state separated by a predetermined interval.

  At this time, as shown in FIG. 5, the light emitted from each white LED 4 enters the light guide 1 while spreading around the white LED 4. In the region located between the white LEDs 4 in FIG. 5, the light quantity deficient portion 15 in which the light quantity of the light emitted from the emission surface in the light guide 1 is relatively small is formed. That is, the light quantity deficient portion 15 is a region where light from the white LED 4 does not reach sufficiently when the cylinder lens 7 (see FIG. 1) and the reflecting mirror 8 are not present, and the portion on the exit surface of the light guide 1. The amount of light emitted from the light guide 1 is smaller than the amount of light emitted from the other exit surface portion of the light guide 1. And the distance L1 mentioned above respond | corresponds to the width | variety of the part in which this light quantity insufficient part 15 exists.

  Further, as shown in FIG. 3, when the curvature of the cylinder lens 7 is relatively large and the light emitted from the cylinder lens 7 (at a half-value angle) is focused light that is substantially focused at a certain focal length, The characteristics such as the curvature of the cylinder lens 7 are set so that the distance D2 from the position 31 (focal point) where the light emitted from the lens 7 converges to the end of the light guide 1 is larger than the distance L1 described above. decide. In this way, substantially uniform light can be emitted from the exit surface of the light guide 1 over the entire surface.

  Moreover, in the planar light source unit 10 in the present invention, as shown in FIGS. 1 to 3, it faces the end surface (the other end surface 28) of the light guide 1 on the side opposite to the side where the white LED 4 is arranged. In addition, a reflecting mirror 8 is installed. The inventor has found that there is an appropriate numerical range for the bending angle θ of the reflecting mirror 8 (see FIG. 6). Hereinafter, this will be specifically described with reference to FIG. FIG. 6 is a schematic cross-sectional view for explaining the bending angle of the reflecting mirror constituting the planar light source unit according to the present invention.

  As shown in FIG. 6, the light beam 13 emitted from the white LED 4 (see FIG. 2) enters the end surface of the light guide 1 via the cylinder lens 7. At this time, the incident light beam 13 is refracted according to Snell's law. The light beam 13 incident on the light guide 1 spreads inside the light guide 1. Part of the spread light beam 13 goes straight to the other end face 28 on the reflecting mirror 8 side, and part of the light ray 13 enters the side surface (upper surface or lower surface) of the light guide 1. A part of the light beam 13 incident on the lower surface enters the light diffusing member 11 as described above, is scattered and reflected, and becomes diffused light and is emitted from the emission surface 29 (upper surface) of the light guide 1. Further, in a portion where the light diffusing member 11 is not disposed, mutual reflection is repeated, and finally enters the reflecting mirror 8 together with the component of the light beam 13 traveling straight to the other end face 28 described above. The light beam 13 is reflected by the reflecting mirror 8 and is incident on the light guide 1 again.

The behavior of the light beam 13 in the reflecting mirror 8 is as follows. That is, as shown in FIG. 6, the light beams 13a to 13c emitted from the end face of the light guide 1 on the reflecting mirror 8 side are guided at the same angle θ ₁ as the emission angle θ ₁ of the cylinder lens 7 according to Snell's law. 1 is emitted from one end face. The emitted light beams 13a to 13c are reflected by the reflecting mirror 8, respectively. The reflecting mirror 8 has a symmetrical shape about the center line 25. The center line 25 passes through the center of the light guide 1 in the thickness direction and extends in a direction parallel to the emission surface 29. Also, the light rays 13a to 13c shown in FIG. 6 are typical light, and are light rays that enter the light guide 1 from the lower side of the cylinder lens 7 (light rays when the emission angle of the cylinder lens is −θ _1). ) Also behaves symmetrically about the center line 25 of the reflecting mirror 8. In order to make the light beams 13a to 13c reflected by the reflecting mirror 8 enter the light guide 1 again more efficiently, the reflecting mirror 8 preferably has the following conditions.

Hereinafter, for the sake of explanation, the angle formed by the reflecting surface of the reflecting mirror 8 and the end surface of the light guide 1 is defined as the reflecting mirror angle θ ₂ . In order to make the light beams 13a to 13c reenter the light guide 1 more efficiently as described above, first, the number of reflections of the light beams 13a to 13c on the reflecting surface of the reflecting mirror 8 is first reduced. Therefore, it is necessary to minimize the reflection loss. That is, when the light is reflected at the reflecting mirror 8 a plurality of times like the light ray 13b, the reflection loss at the time of reflection at the reflecting mirror 8 is larger than the light ray 13a reflected at the reflecting mirror 8 only once. There's a problem. Therefore, it is considered to reduce the number of times the light is reflected by the reflecting mirror 8 (to prevent the light from being reflected twice by the reflecting mirror 8 like the light beam 13b). Specifically, the light reflected once by the reflecting mirror 8 may be reflected in a direction parallel to the reflecting surface of the reflecting mirror 8 or in a direction toward the light guide 1 side.

More specifically, the angle θ ₃ shown in FIG. 6 needs to be larger than the angle θ ₂ . The angle θ ₃ can be expressed by an equation of 90 ° − (2 × θ ₂ + θ ₁ ). That is, a relationship of 90 ° − (2 × θ ₂ + θ ₁ )> θ ₂ is established between the angle θ ₁ (directivity angle) and the angle θ ₂ of the incident light (the light beam 13 incident on the light guide 1). do it. Rearranging this equation, it becomes _{θ 2 <30 ° -θ 1/} 3.

In order to emit light more efficiently from the exit surface of the light guide 1, as a second condition, light incident on the light guide 1 is reflected on the upper surface and the lower surface of the light guide 1. It is necessary to increase the number of times (increase the number of mutual reflections). As described above, in order to repeat the reflection of the light reflected by the reflecting mirror 8 and incident on the light guide 1 again on the upper surface and the lower surface of the light guide 1 in the light guide 1, the angle described above is used. It is necessary that θ ₃ be greater than 0 °. Specifically, it is necessary to satisfy the equation 90 ° − (2 × θ ₂ + θ ₁ )> 0. If this formula is arranged, the formula θ ₂ <45 ° −θ _1/2 is obtained.

In each of the above relational expressions, when the angle θ ₁ that is the directivity angle is approximately 0 °, the reflector angle θ ₂ is 30 ° <θ ₂ <45 °. As a result, the range of the bending angle θ of the reflecting mirror 8 that satisfies the above-described conditions is 90 ° <θ <120 °.

  By disposing the reflecting mirror 8 having such a bending angle θ, the reflected light from the reflecting mirror 8 can be incident on the light guide 1 again more effectively. The light diffusing member 11 is arranged on the back side of the light guide 1 as described above. The light diffusing members 11 are arranged densely toward the white LED 4 which is a point light source, and are arranged so as to become sparse toward the reflecting mirror 8 (graded arrangement). The light beam 13 (see FIG. 2) enters the light diffusing member 11 having such an arrangement and is scattered and reflected, so that the light beam 13 is diffused so that the entire exit surface of the light guide 1 is uniformly brightened. That is, it looks as if the light source exists on the reflecting mirror 8 side, and as a result, uniform luminance can be obtained on the exit surface of the light guide 1.

  Here, the light diffusing member 11 may be configured by partially applying a light diffusing substance having a high diffuse reflectance to the back side of the light guide 1. However, as a method for diffusing the light beam 13, another method may be used. May be used. For example, the light beam 13 is scattered and reflected by using a technique such as roughening the side surface (back surface) of the light guide 1, forming a small hole on the back surface, or forming a small protrusion on the side surface. Also good. Although not particularly shown, the light diffused and reflected by the light guide 1 and transmitted to the back side is reflected on the lower part of the back surface of the light guide 1 where the light diffusing member 11 is disposed. It is preferable to provide a light diffusing reflector for making it incident on the light guide 1.

  FIG. 7 is a schematic plan view showing a first modification of the planar light source unit according to the present invention. With reference to FIG. 7, the 1st modification of the planar light source unit by this invention is demonstrated.

  The planar light source unit 10 shown in FIG. 7 basically has the same structure as the planar light source unit 10 shown in FIGS. 1 to 3, but the type of light source is different. That is, the planar light source unit 10 shown in FIG. 7 includes three color LEDs 17a, 17b, 16, and 18. The LED 16 is an LED (red LED) that emits red light. The LEDs 17a and 17b are LEDs (green LEDs) that emit green light. The LED 18 is an LED (blue LED) that emits blue light. By arranging such three-color LEDs and mixing the light emitted from the respective LEDs 16, 17a, 17b, 18, white light can be obtained.

  Further, in the planar light source unit shown in FIGS. 1 to 3, regarding the characteristics of the cylinder lens 7, the light quantity deficient portion 15 (as a distance L1 which is a reference value for the distances D1 and D2 shown in FIGS. Although the width L1 (see FIG. 5) of FIG. 5 is used, when the three-color LEDs 16, 17a, 17b and 18 as shown in FIG. 7 are used, the distance L1 as the reference value is shown in FIG. As shown, it is preferable to adopt the distance to the position where the region where the light from the three color LEDs 16 to 18 is completely mixed becomes the entire surface of the light guide 1. FIG. 8 is a schematic diagram for explaining the characteristics of the cylinder lens 7 constituting the planar light source unit shown in FIG. FIG. 9 is a schematic cross-sectional view of the planar light source unit shown in FIG.

  As shown in FIG. 8, the light emitted from the three color LEDs 16 to 18 is in a state in which the respective lights are completely mixed at a part away from the LEDs 16 to 18 to some extent. In such a region (mixed color emitting portion 21), white light (mixed color light 23 (see FIG. 9)) is emitted from the exit surface of the light guide 1. Further, since light is not sufficiently mixed in the portion closer to the LEDs 16 to 18, the light from the LEDs 16 to 18 or light that is not sufficiently mixed (monochromatic light 22 (see FIG. 9)) is a light guide. 1 exits from the exit surface. Such a portion from which the monochromatic light 22 is emitted is referred to as a non-white light emitting portion 19. And the distance L1 as a reference value in the case of using such three-color LEDs 16 to 18 adopts the width of the non-white light emitting portion 19 (distance L1 in FIG. 8). As shown in FIG. 9, the monochromatic light 22 is emitted from the non-white light emitting unit 19, and the mixed color light 23 (that is, white light) is emitted from the mixed color emitting unit 21 (see FIG. 8). Even in such a configuration, light can be efficiently and uniformly emitted from the light guide 1 as in the planar light source unit shown in FIGS.

  FIG. 10 is a schematic cross-sectional view showing a second modification of the planar light source unit according to the present invention shown in FIGS. A second modification of the planar light source unit according to the present invention will be described with reference to FIG.

  The planar light source unit 10 shown in FIG. 10 basically has the same structure as that of the planar light source unit 10 shown in FIGS. 1 to 3, but does not include an independent cylinder lens 7 but a guide. The difference is that the convex lens portion 9 is formed by partially processing the light body 1. Even if such a convex lens portion 9 is formed at the end of the light guide 1 and disposed so as to face the white LED 4, the same effect as the planar light source unit 10 shown in FIGS. Can do. Moreover, since the volume which a lens part occupies can be made small rather than the case where the cylinder lens 7 which is another components shown in FIGS. 1-3 is used, size reduction of the planar light source unit 10 can be achieved. Furthermore, since the light guide 1 and the lens are integrated, the number of parts of the planar light source unit 10 can be reduced from the number of parts of the planar light source unit 10 shown in FIGS. The manufacturing cost of the planar light source unit can be reduced.

  FIG. 11 is a schematic cross-sectional view showing a third modification of the planar light source unit according to the present invention shown in FIGS. With reference to FIG. 11, the 3rd modification of the planar light source unit by this invention is demonstrated.

  The planar light source unit 10 shown in FIG. 11 basically has the same structure as that of the planar light source unit 10 shown in FIG. 10 except that the end portion of the light guide 1 is not a convex lens unit 9 but a Fresnel lens unit. The difference is that 14 is formed. As described above, even when the Fresnel lens portion 14 having different refraction angles in a stepwise manner is formed at the end portion of the light guide 1, the same effect as the planar light source unit shown in FIG. 10 can be obtained. Further, since the thickness of the Fresnel lens portion 14 is thinner than that of the convex lens portion 9 shown in FIG. 10, the planar light source unit 10 can be further reduced in size. In addition, the convex lens part 9 shown in FIG. 10 and the Fresnel lens part 14 shown in FIG. 11 can each be suitably selected from workability.

  To summarize the characteristic configuration of the above-described planar light source unit 10 according to the present invention, the planar light source unit 10 includes a light guide 1 and a cylinder lens 7 (or a convex lens unit 9 or a Fresnel lens) as a lens. Unit 14), white LEDs 4 or three-color LEDs 16, 17a, 17b, 18 as a plurality of light sources, a reflecting mirror 8, and a light diffusing member 11. The light guide 1 is plate-shaped and has an emission surface (upper surface) for emitting light. In the light guide 1, the cylinder lens 7 is disposed on one end surface 27 extending in a direction intersecting with the emission surface, and intersects with the emission surface 29 of the light guide 1 (for example, the thickness direction of the light guide 1). To collect the light. The white LED 4 or the three color LEDs 16, 17 a, 17 b, 18 are arranged so as to face the one end face 27 of the light guide 1 through the cylinder lens 7. The reflecting mirror 8 is disposed in the light guide 1 so as to face the other end face 28 located on the opposite side of the one end face 27. The light diffusing member 11 is disposed on the other surface side (rear surface side) located on the opposite side to the emission surface 29 in the light guide 1.

  Here, when the light beam 13 having a certain emission angle is incident on the light guide 1 as it is from one end surface 27 (end surface on which the cylinder lens 7 or the like is disposed) of the light guide 1, the light guide 1. The light beam 13 incident at a certain angle or more with respect to the direction substantially perpendicular to the light exit surface 29 (upper surface) (the thickness direction of the light guide 1) is insufficient in the number of reflections inside the light guide 1. Mixing of light (color) from the white LED 4 or the three color LEDs 16, 17 a, 17 b, and 18 as a plurality of point light sources becomes insufficient. When the color mixing is insufficient as described above, so-called shading and color unevenness occur in the light beam 13 emitted from the emission surface of the planar light source unit 10.

  However, in the planar light source unit 10 according to the present invention, by arranging the cylinder lens 7 and the like, the angle of the traveling direction of the light beam 13 with respect to the direction parallel to the emission surface 29 of the light guide 1 is within a predetermined range. Can be a value. For this reason, the angle of the light beam 13 (light beam) is reflected so that the light beam 13 incident on the light guide body 1 is reflected as many times as necessary to sufficiently mix the light (color) within the light guide body 1. 13 incident angles with respect to the light guide 1 can be adjusted. As a result, the light from the plurality of LEDs 4 or the three-color LEDs 16, 17 a, 17 b, and 18 can be emitted from the light exit surface of the light guide 1, with uniform color with little color unevenness and shading.

  Further, by disposing the reflecting mirror 8 on the other end face 28 side of the light guide 1, the light beam 13 emitted from the other end face 28 of the light guide 1 is reflected by the reflecting mirror 8, thereby again guiding the light guide 1. Can be made incident. As a result, the light emitted from the other end face 28 of the light guide 1 and then incident on the light guide 1 again can be used for mixing light inside the light guide 1 and emitting light from the emission face 29. Therefore, the uniformity and the amount of light emitted from the emission surface 29 can be improved.

  Moreover, since the uniformity of the light emitted from the light exit surface 29 of the light guide 1 can be improved, the conventional light quantity deficient portion 115 (see FIG. 14) is almost eliminated. Therefore, when the planar light source unit 10 according to the present invention is applied to the liquid crystal display device 20 as shown in FIG. 4, it is not necessary to dispose the light quantity deficient portion 115 at a position that does not overlap with the liquid crystal panel 6 as in the prior art (that is, The almost entire surface of the light guide 1 of the planar light source unit 10 can be used as a backlight for supplying light to the liquid crystal panel 6). Therefore, the size of a so-called frame portion (portion around the liquid crystal display portion) in the liquid crystal display device 20 can be reduced.

  In the planar light source unit 10, the traveling direction of the light emitted from the cylinder lens 7 and incident on the light guide 1 is substantially parallel to the emission surface 29 of the light guide 1, as shown in FIG. It is preferable that the characteristics of the cylinder lens 7 are determined so as to include one of the directions of focusing inside the light guide 1 as shown in FIG.

  In this case, the light incident on the light guide 1 can be reliably reflected inside the light guide 1 as many times as necessary to sufficiently mix the light (color). Here, the direction substantially parallel to the exit surface 29 of the light guide 1 refers to a direction in which an inclination angle with respect to the extending direction of the exit surface 29 is ± 10 ° or less, more preferably ± 5 ° or less.

  In the planar light source unit 10, the lens may be either a convex lens such as the convex lens unit 9 shown in FIG. 10 or a Fresnel lens such as the Fresnel lens unit 14 shown in FIG. In this case, the planar light source unit 10 according to the present invention can be easily manufactured by using a general convex lens or Fresnel lens without using a special lens.

  Further, if the Fresnel lens portion 14 having a relatively small thickness is used as a lens, the periphery (frame portion) of the display surface in the liquid crystal display device using the planar light source unit 10 can be easily reduced.

  In the planar light source unit 10, the cylinder lens 7 as an example of the lens preferably emits the light beam 13 so as to be focused inside the light guide 1 as shown in FIG. 3. As shown in FIG. 3, in the planar light source unit 10, the distance D <b> 2 between the focal position 31 where the light beam 13 is focused by the cylinder lens 7 and the one end surface 27 of the light guide 1 is a plurality of light sources. It is preferable that the light from the white LEDs 4 is larger than the width L1 of the region (that is, the light quantity deficient portion 15 shown in FIG. 5) emitted from the emission surface 29 of the light guide 1 without interfering with each other.

  In this case, the distance D2 between the focal point position 31 and the one end surface 27 of the light guide 1 is too small (the focal length of the cylinder lens 7 is too small), and the light beam 13 is incident on the side surface inside the light guide 1. As a result, the probability of occurrence of a situation in which the angle increases and as a result the number of reflections of the light beam 13 within the light guide 1 is insufficient can be reduced. As a result, since the number of reflections of the light beam 13 within the light guide 1 is insufficient, the possibility that the uniformity of light emitted from the emission surface 29 of the light guide 1 is reduced can be reduced.

In the planar light source unit 10, the reflecting mirror 8 has a central portion in the direction intersecting the exit surface 29 of the light guide 1 (for example, a direction substantially perpendicular to the exit surface 29). The body 1 is preferably bent so as to protrude from the other end face 28 (so that the central portion of the reflecting mirror 8 has a convex shape moving away from the other end face 28). The bending angle θ (see FIG. 6) of the bent portion of the reflecting mirror 8 is set such that the incident angle of light from the cylinder lens 7 to the light guide 1 with respect to the direction parallel to the emission surface 29 is θ ₁ . 90 ° + θ ₁ <θ <so as to satisfy the relationship of _{120 ° + 2 × θ 1/} 3 expression, it is preferable that the reflecting mirror 8 is constructed. Further, when the incident angle θ ₁ can be approximated to 0 °, the reflecting mirror 8 may be configured to satisfy the relational expression of 90 ° <θ <120 °. In this case, the light reflected by the reflecting mirror 8 can be efficiently incident on the light guide 1 again.

  In the planar light source unit 10, the convex lens portion 9 or the Fresnel lens portion 14 as a lens may be integrally formed with the light guide 1 as shown in FIG. 10 or FIG. In this case, since it is not necessary to prepare a lens as a separate part, the number of parts of the planar light source unit 10 can be reduced. As a result, the manufacturing cost of the planar light source unit 10 can be reduced.

  In the above planar light source unit, the light source is either the white LED 4 shown in FIG. 1 or the like, or a combination of three colors LEDs 16, 17 a, 17 b, and 18, which are red, green, and blue as shown in FIG. May be. In this case, the planar light source unit 10 that emits white light from the emission surface 29 can be realized. In addition, if the combination of LEDs 16, 17 a, 17 b, and 18 of three colors consisting of red, green, and blue is used, when the luminance of the white LED 4 is insufficient, the high-luminance three-color LEDs 16, By using 17a, 17b, 18 light with sufficient luminance can be easily obtained.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above-described embodiment but by the scope of claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

It is a plane schematic diagram of the planar light source unit according to the present invention. It is a cross-sectional schematic diagram in line segment II-II shown in FIG. It is a cross-sectional schematic diagram which shows the other example of the cross section in line segment II-II shown in FIG. It is a cross-sectional schematic diagram which shows the liquid crystal display device to which the planar light source unit by this invention is applied. It is a plane schematic diagram of the liquid crystal display device for demonstrating the characteristic of a cylinder lens. It is a cross-sectional schematic diagram for demonstrating regarding the bending angle of the reflective mirror which comprises the planar light source unit by this invention. It is a plane schematic diagram which shows the 1st modification of the planar light source unit by this invention. It is a schematic diagram for demonstrating the characteristic of the cylinder lens 7 which comprises the planar light source unit shown in FIG. It is a cross-sectional schematic diagram of the planar light source unit shown in FIG. It is a cross-sectional schematic diagram which shows the 2nd modification of the planar light source unit by this invention shown in FIGS. 1-3. It is a cross-sectional schematic diagram which shows the 3rd modification of the planar light source unit by this invention shown in FIGS. 1-3. It is a perspective schematic diagram of the planar light source unit which comprises the conventional backlight mechanism. It is a cross-sectional schematic diagram in line segment XIII-XIII of FIG. It is a plane schematic diagram which shows the planar light source unit at the time of using several LED as a linear light source.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Light guide, 4 White LED, 6 Liquid crystal panel, 7 Cylinder lens, 8 Reflective mirror, 9 Convex lens part, 10 Planar light source unit, 11 Light diffusing member, 12 Substrate, 13, 13a-13c Light beam, 14 Fresnel lens part , 15 Light quantity deficient part, 16, 17a, 17b, 18 LED, 19 Non-white light emitting part, 20 Liquid crystal display device, 21 Mixed color emitting part, 22 Monochromatic light, 23 Mixed color light, 25 Center line, 27 One end face, 28 The other end face, 29 exit face, 30, 31 position.

Claims (7)

A light guide that is plate-shaped and has an exit surface that emits light; and
In the light guide, a lens that is disposed on one end surface that extends in a direction that intersects the exit surface, and that collects light in a direction that intersects the exit surface;
A plurality of light sources arranged to face one end face of the light guide through the lens;
In the light guide, a reflecting mirror disposed to face the other end surface located on the opposite side to the one end surface;
A planar light source unit, comprising: a light diffusing member disposed on the other surface side located on the opposite side to the emission surface in the light guide.   The traveling direction of the light emitted from the lens and incident on the light guide includes either one of a direction substantially parallel to the light exit surface of the light guide and a direction of focusing inside the light guide. The planar light source unit according to claim 1, wherein characteristics of the lens are determined.   The planar light source unit according to claim 1, wherein the lens is one of a convex lens and a Fresnel lens. The lens emits light so as to be focused inside the light guide,
The distance between the focal point where the light is focused by the lens and the one end surface of the light guide is such that light from the plurality of light sources is emitted from the exit surface of the light guide without interfering with each other. The planar light source unit according to claim 1, wherein the planar light source unit is larger than a width of the region. The reflecting mirror is bent so that a central portion in a direction intersecting the exit surface of the light guide projects from the other end surface of the light guide,
The bending angle θ of the bent portion of the reflecting mirror is set such that the incident angle of light from the lens to the light guide with respect to the direction parallel to the emission surface is θ ₁ .
_{90 ° + θ 1 <θ <} 120 ° + 2 × θ 1/3
The planar light source unit according to claim 1, wherein the reflecting mirror is configured to satisfy the relational expression:   The planar light source unit according to claim 1, wherein the lens is integrally formed with the light guide.   The planar light source unit according to any one of claims 1 to 6, wherein the light source is one of a white LED or a combination of LEDs of three colors including red, green, and blue.

Images