JP2013026200A - Planar light source device and display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a planar light source device with high light utilization efficiency, the light source device using point light sources, wherein luminance unevenness generated among the point light sources is prevented.SOLUTION: The planar light source device holds point light sources 1 at an upper part 2a side in a case 2 with a cross-section shape nearly lateral-U-shaped equipped with an upper part 2a as well as a lower part 2b opposed to the former 2a, a connecting part 2c connecting the upper part 2a and the lower part 2b, and an opening part 2d at an opposite side of the connecting part 2c. A light-emitting face 1a of each point light source 1 is set in opposition to the lower part 2b of the case 2. Further, at a position opposed to the light-emitting face 1a of each point light source 1 in the case 2, a convex-shape reflective diffusion member 21 formed of a member containing a material to reflect light is formed, protruded inward into the case 2.

Description

  The present invention relates to a planar light source device that irradiates a display element or the like that displays an image from the back surface and a display device.

  Liquid crystal display devices are widely used as thin and light display devices capable of displaying images. Recently, they are widely used not only for personal computer monitors and TV monitors, but also for car navigation and convenience store cash register terminals. Has come to be. A transmissive display device is generally used for these liquid crystal display devices. The transmissive display device includes a planar light source device called a backlight, and the illumination light emitted from the planar light source device is spatially modulated by a display element to form and display an image. There are two types of planar light source devices: a direct type that directly illuminates a plurality of light sources directly under a display element, and a light guide plate type that uses a light guide plate. The direct type is a relatively large display such as a liquid crystal TV. The light guide plate method is often used for small and medium-sized monitors.

  Conventionally, a linear light source such as a cold cathode tube has been used as a light source constituting a planar light source device. However, in recent years, in order to cope with a reduction in the thickness and power consumption of a display device, A point light source is used. In a planar light source device using a general point light source, a plurality of point light sources are mounted on a wiring board in a substantially straight line and are installed facing the incident surface of the light guide plate. In a planar light source device having a plurality of point light sources, if the pitch of the point light sources arranged adjacent to each other is widened, the point light sources become unirradiated and the brightness decreases, resulting in hot on the incident surface. Luminance unevenness called a spot is easily visually recognized. In order to prevent this, it is common practice to increase the number of point light sources arranged and narrow the pitch. However, an increase in cost and power consumption are problematic. Therefore, it is required to prevent the occurrence of hot spots while suppressing an increase in cost and power consumption.

  Therefore, in the planar light source device shown in Patent Document 1, the reflection sheet 10 is disposed so as to cover the upper surface of the LED 1, and the light dispersion portions 11 are provided at a plurality of locations corresponding to the LED 1 of the reflection sheet 10. With such a configuration, the light leaked from the LED 1 is dispersed to the periphery by the light dispersing unit 11 and reflected by the reflection sheet 10 to be incident light on the light guide plate 2. Further, in the planar light source device shown in Patent Document 2, a plurality of LEDs 21 are embedded in the linearizing member 22, and the light from the LEDs 21 is made uniform while propagating through the linearizing member 22, and enters the light guide plate. I am letting.

Japanese Patent Laying-Open No. 2005-243522 (pages 4 to 6, FIGS. 1 and 3) Japanese Patent Laying-Open No. 2005-244095 (pages 5 to 7, FIGS. 3 and 5)

  The planar light source device shown in Patent Document 1 disperses the leaked light from the LED 1 to the periphery by the light dispersion unit 11, reflects it by the reflection sheet 10, and makes it incident from the incident surface of the light guide plate 2. Since this light is a light having a high luminance, a hot spot may eventually be visually recognized on the incident surface of the light guide plate 2. Although the planar light source device shown in Patent Document 2 propagates light by the linearizing member 22 to prevent hot spots, the light utilization efficiency decreases due to light absorption in the linearizing member.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to prevent luminance unevenness that occurs between point light sources in a planar light source device using a point light source. It is another object of the present invention to provide a planar light source device with high light use efficiency.

  The planar light source device and the display device of the present invention include a plurality of point light sources having a light emitting surface for emitting light, a plurality of point light sources held therein, and an upper portion, a lower portion facing the upper portion, and an upper portion and a lower portion. A plurality of point light sources, comprising: a case having a connection portion and an opening portion to be connected; a light guide plate that arranges the opening portion of the case on a side surface, propagates light incident from the side surface and emits light from the emission surface; The light emitting surface is disposed at the upper or lower portion of the case, and the case includes a convex reflection diffusing member that protrudes toward the inside of the case at a position facing the light emitting surface, and the reflection diffusing member includes a side surface of the light guide plate and A reflection surface that is inclined with respect to the light emitting surface of the point light source is provided.

  According to the planar light source device and the display device of the present invention, the light emitted from the point light source is incident on the incident surface of the light guide plate from a wide range, thereby causing uneven brightness between the point light sources on the incident surface. Can be prevented.

It is a disassembled perspective view of the display apparatus in this invention. It is a principal part enlarged view of the planar light source device in this invention. It is a principal part enlarged view of the planar light source device in this invention. It is a front view of the planar light source device in the present invention. It is a principal part enlarged view of the planar light source device in this invention. It is a front view of the planar light source device in the present invention. It is a figure which shows the light emission characteristic of a common light emitting diode. It is a top view of a general planar light source device. It is a figure which shows the characteristic of an incident angle ((theta))-reflectance in the entrance plane of the light-guide plate of this invention. It is a principal part enlarged view of the planar light source device of this invention.

  A configuration of a display device according to the present invention will be described with reference to the drawings. In addition, what uses the same code | symbol in each figure shows the substantially same structure. FIG. 1 is an exploded perspective view of a display device according to the present invention, and FIG. 2 is an enlarged view of a main part of a planar light source device according to the present invention.

Embodiment 1 FIG.
<Configuration of display device>
As shown in FIG. 1, a planar light source device 10 of the present invention has a plurality of point light sources 1 each having a light emitting surface that emits light arranged in substantially one row, and propagates light emitted from the point light source 1 over one surface. A light guide plate 3 is provided. The point light source 1 is housed in a case 2 having a substantially U-shaped cross section formed of a reflective material, and an incident surface 3a which is a side surface of the light guide plate 3 is disposed in the opening 2d. The light of the point light source 1 incident from the incident surface 3a is emitted from the emission surface 3b of the light guide plate 3 (the surface above the paper surface of the light guide plate 3 in FIG. 1). Optical sheets 4 are provided on the light exit surface 3 b side of the light guide plate 3, and the reflection sheet 5 is disposed on the side opposite to the light exit surface 3 c of the light guide plate 3 (surface below the light guide plate 3 in FIG. 1). ing. The point light source 1, the case 2, the light guide plate 3, the optical sheets 4, and the reflection sheet 5 are sandwiched between the upper frame 6 and the lower frame 7 to constitute a planar light source device 10. Note that an opening 6a is formed in the upper frame 6 at a position corresponding to the emission surface 3b of the light guide plate 3, and planar light is emitted from the opening 6a. Further, the size of the opening 6 a is designed to be inside the outer periphery of the light guide plate 3. Further, the display element 9 is disposed on the planar light source device 10 to constitute the display device 100.

<Point light source>
The point light source 1 of the present invention uses a light emitting diode as an example. FIG. 7 is a graph showing the light emission characteristics of a general light emitting diode. As shown in FIG. 7, the light emitting diode has a characteristic that directivity is strong, but since the chip size is small, the irradiation range of light maintaining the light emission intensity is quite narrow, and generally at an angle at which the light emission intensity is halved. A certain half-value angle is about 60 °.

<Light guide plate>
FIG. 8 is a plan view of a general planar light source device, in which the light emitting surface 1 a of the point light source 1 is arranged to face the incident surface 3 a of the light guide plate 3. FIG. 8A shows an optical path of light emitted from the point light source 1 when the point light source 1 is arranged, and FIG. 8B shows a state in which incident light from the point light source 1 propagates in the light guide plate 3. . As shown in FIG. 8A, when the light emitting surface 1a of the point light source 1 is arranged opposite to the incident surface 3a of the light guide plate 3, the light is emitted from the point light source 1 with respect to the perpendicular P to the incident surface 3a. The incident angle of light incident on the light guide plate 3 is θ. Since the air and the material of the light guide plate 3 have different refractive indexes, the traveling direction of the light incident on the incident surface 3a is bent. When the light guide plate 3 made of acrylic is used, the relative refractive index of air and the light guide plate 3 is generally 1.49 (refractive index of air: 1.0003, refractive index of acrylic: 1.49). When calculated using the Fresnel formula, the incident angle θ at the incident surface 3a is about 42 ° at the maximum. Therefore, light L1 having an incident angle θ of 42 ° or less among the light emitted from the point light source 1 is incident from the incident surface 3a within the irradiation range in the vicinity of the point light source 1 in FIG. 3 spreads to the inside to form an irradiation region in FIG. On the other hand, of the incident light, the light L2 having an incident angle θ larger than 42 ° is reflected by the incident surface 3a. Since such light exists, an unirradiated region is formed on the light guide plate 3.

  As described above, the irradiation area formed by the light incident within the irradiation range from the incident surface 3a in the vicinity of the point light source 1 is light having high directivity and light emission intensity. The difference in luminance from the irradiated area is significant. As described above, the cause of the uneven brightness in the light guide plate 3 is that the light whose intensity is maintained by the directivity of the point light source 1 is incident from the vicinity of the incident surface 3a on which the point light source 1 is disposed and the point light. This is because the incident light of the light source 1 is reflected by the incident surface 3 a and does not enter the light guide plate 3, and there is an unirradiated region on the incident surface 3 a of the light guide plate 3.

<Reflective diffusion member>
In the planar light source device 10 of the present invention, the point light source 1 is arranged along the incident surface 3 a of the light guide plate 3 as shown in FIG. 1, but the light emitting surface 1 a faces the incident surface 3 a of the light guide plate 3. Do not arrange to do. As shown in FIG. 2, the upper portion 2a and the lower portion 2b facing the upper portion 2a, the connecting portion 2c connecting the upper portion 2a and the lower portion 2b, and the opening 2d on the opposite side of the connecting portion 2c are substantially U-shaped. The point light source 1 is held on the upper part 2 a side of the case 2, and the light emitting surface 1 a of the point light source 1 is arranged to face the lower part 2 b of the case 2. The case 2 has an opening 2d disposed along the incident surface 3a. Further, at the position facing the light emitting surface 1 a of the point light source 1 in the case 2, a convex reflection diffusing member 21 that protrudes toward the inside of the case 2 and is formed of a member containing a material that reflects light. Is formed. The reflection diffusing member 21 includes a plurality of reflection surfaces 21a that are inclined with respect to the incident surface 3a and the light emitting surface 1a. As shown in FIG. 2, the reflection surface 21 a in the present embodiment includes two inclined surfaces, and is inclined in different directions with respect to the incident surface 3 a of the light guide plate 3. Although the point light source 1 is disposed on the upper part 2a, it may be disposed on the lower part 2b. In the case where the point light source 1 is disposed on the lower part 2b, the reflection diffusing member 21 is opposed to the light emitting surface 1a of the point light source 1. 2a. Moreover, the attenuation of light can be suppressed by using a highly reflective material for the reflection diffusing member 21. Further, it is possible to reflect and diffuse light by using a material having a high light diffusivity such as white PET (Polyethylene Terephthalate). The case 2 is also formed of a material that reflects light. Moreover, the cross-sectional shape of the case 2 may be provided with a curved surface, for example, a U-shape. Further, the upper part 2a and the lower part 2b may be inclined with respect to the incident surface 3a.

  3 is an enlarged view of a main part of the surface light source device, and FIG. 4 is a plan view. The path of light in the planar light source device of the present invention is shown using the drawings. As shown in FIG. 3, since the light emitted from the light emitting surface 1a of the point light source 1 has high directivity, most of the light reaches the reflection diffusing member 21 disposed opposite to the light emitting surface 1a without being diffused. Then, the light that has reached the reflection diffusion member 21 and whose emission intensity is maintained is reflected by the reflection surface 21a constituting the reflection diffusion member 21, and the traveling direction is changed depending on the shape of the reflection surface 21a.

  As shown in FIGS. 3 and 4, the reflection diffusion member 21 includes a reflection surface 21a having an inclination with respect to the incident surface 3a and the light emitting surface 1a, so that the traveling direction of the light reaching the reflection surface 21a is changed. At this time, part of the light reaching the reflecting surface 21a is light traveling toward the incident surface 3a of the light guide plate 3, and the traveling direction is changed to light L21 that spreads over a wide range with respect to the incident surface 3a. In this way, the light L21 that is directed toward the incident surface 3a by the reflecting surface 21a and diffuses in a wide range with respect to the incident surface 3a is changed in the traveling direction to be incident on the incident surface 3a of the light guide plate 3. The irradiation range can be expanded. Therefore, it is possible to prevent the light whose intensity is maintained from entering in a range narrower than the vicinity of the incident surface 3a where the point light source 1 is disposed. can do. In addition, since the reflective surface 21a in this Embodiment is inclined in a mutually different direction, the light which spreads more widely can be formed with respect to the entrance plane 3a.

  Of the light whose traveling direction has been changed to the incident surface 3a by the reflecting surface 21a, the light reflected by the incident surface 3a and the light L22 that goes to the inside of the case 2 without going to the incident surface 3a of the light guide plate 3 are: In the case 2, reflection / diffusion is repeated and mixed to become uniform light, and finally the traveling direction is changed and incident from the incident surface 3 a.

  As described above, according to the planar light source device 10 of the present invention, the light source surface 1a of the point light source 1 is formed inside the case 2 disposed along the incident surface 3a of the light guide plate 3, A convex reflection diffusion member 21 protruding toward the inside of the case 2 is provided. Since the reflection diffusion member 21 includes the reflection surface 21a that is inclined with respect to the incident surface 3a, it diffuses the light whose intensity is maintained among the light emitted from the point light source 1 and By being able to make it enter from a wide range, the brightness nonuniformity between the point light sources 1 in the entrance plane 3a can be prevented.

  Further, the light reflected by the incident surface 3a and the light L22 directed toward the inside of the case 2 without being directed toward the incident surface 3a of the light guide plate 3 are repeatedly reflected and diffused in the case 2 to be uniformed by the reflecting surface 21a. The incident light can be made incident from the incident surface 3 a of the light guide plate 3.

  In the first embodiment, the example in which the reflection diffusing member 21 includes the incident surface 3 a and the reflecting surface 21 a inclined with respect to the light emitting surface 1 a has been described. However, the light emitted from the point light source 1 is reflected on the light guide plate 3. Any shape that can change the traveling direction to light that spreads over a wide range with respect to the incident surface 3a can be appropriately changed, and may be a semicircular shape, a polygonal shape, or a curved surface. By using a curved surface or polygon, it is possible to change the traveling direction to light that diffuses more widely. If the reflection diffusing member 21 is formed with a three-dimensional curve or an inclination as much as possible, the light can be spread more widely. Moreover, it is also possible to obtain the said effect by changing the material of the reflective diffusion member 21 suitably, and adjusting a reflectance and a light diffusivity.

Embodiment 2. FIG.
FIG. 5 is an enlarged view of a main part of the planar light source device 10 according to the second embodiment, and FIG. 6 is a front view. The planar light source device in the first embodiment includes the reflection diffusion member 21 formed in the case 2 so as to face the light emitting surface 1a. In the second embodiment, the planar light source device is shown in FIGS. As described above, the reflectors 22 and 23 are provided in the case 2 and between the adjacent point light sources 1 or between the reflection diffusion members 21. Except for this configuration, the configuration is the same as that of the first embodiment. Except for the specific effects of the planar light source device according to the second embodiment described below, the planar light source device according to the first embodiment is the same as the first embodiment. Since the same effect is obtained, the description is omitted.

  Here, the incident angle (θ) -reflectance characteristic on the incident surface 3a of the light guide plate 3 will be described with reference to FIG. Derived from the Fresnel formula, the angle dependence of the average reflectance (average of p wave and s wave) shows an increasing tendency as the incident angle (θ) increases as shown in the graph of FIG. I understand that.

  Further, as described with reference to FIG. 8A, light having an incident angle θ of the incident surface 3a larger than 42 ° with respect to the incident surface 3a of the light guide plate 3 used in the present invention is reflected by the incident surface 3a. The case 2 is diffused and becomes uniform light, but reaches the case 2 and the reflection diffusing member 21 and repeats reflection / diffusion, so that part of the light is absorbed by the case 2 and the reflection diffusing member 21. This may reduce the light utilization efficiency. Further, the light that reaches the case 2 or the reflection diffusing member 21 and repeats reflection / diffusion is emitted from the point light source 1 and is incident on the light guide plate 3a from the reflection diffusing member 21, compared with light having a high emission intensity. The light intensity is reduced.

  According to the planar light source device 10 of the second embodiment, as shown in FIGS. 5 and 6, the reflection part 22 is provided between the adjacent point light sources 1, and the reflection part 23 is provided between the adjacent reflection diffusion members 21. ing. The reflection portions 22 and 23 include inclined surfaces that are inclined with respect to the incident surface 3 a of the light guide plate 3 and the reflection diffusion member 21. With such a configuration, the light reflected and diffused by the reflection diffusing member 21 and reflected by the incident surface 3a of the light guide plate 3 can be changed to the light L23 having an angle incident on the incident surface 3a. For this reason, since the light reflected by the incident surface 3a can be incident on the incident surface 3a, the light incident range to the light guide plate 3 can be expanded as shown in the front view of FIG. Can be suppressed.

  Also, the light that has been repeatedly reflected and diffused in the case 2 can be similarly changed to the light L23 having an incident angle on the incident surface 3a, so that the light use efficiency can be improved. In addition, by appropriately adjusting the inclination angle of the reflecting portions 22 and 23, the light incident on the incident surface 3a after being repeatedly reflected and diffused in the case 2, and the incident surface of the light guide plate 3 that is not diffused in the case 2 It is possible to adjust the incident light at 3a.

  In the second embodiment, the example in which both of the reflection parts 22 and 23 are provided has been described. However, the reflection part 22 is provided only between the point light sources 1 or only the reflection diffusion member 21 is reflected. The structure which provides the part 23 may be sufficient. As long as it is within a range where the same effect as described above can be obtained, it can be appropriately changed. Moreover, although the shape of the reflecting portions 22 and 23 is illustrated and described as an example of an inclined flat surface, similarly to the reflection diffusing member 21, a curved surface or curved surface such as a three-dimensional semicircular shape, or You may form with a polygon.

  FIG. 10 shows a modification of the planar light source device of the present invention. As shown in FIG. 10, the case 2 in the modified example includes a reflection diffusing member 21 and reflection portions 22 and 23, and a hole 25 corresponding to a position where the point light source 1 is disposed. By adopting a method in which the case 2 point light source 1 having the hole 25 is fitted into the hole 25 of the case 2, the positions of the reflection diffusing member 21 and the point light source 1 can be accurately matched. By adopting a method in which the point light source 1 is fitted into the case 2, the reflection diffusing member 21, the reflection portions 22, 23, and the like can be integrally molded, so that between the reflection light source 22 and the reflection diffusion member 21 between the point light sources 1. It becomes easy to provide the reflecting part 23 on the surface.

1 point light source, 1a light emitting surface, 2 case, 2a upper part, 2b lower part,
2c connection part, 2d opening part, 21 reflective diffusion member, 21a reflective surface,
22, 23 reflector, 3 light guide plate, 3 a incident surface, 4 optical sheets,
5 reflective sheet, 6 upper case, 6a opening, 7 lower case,
9 Display element, 10 Planar light source device, 100 Display device.

Claims (6)

A plurality of point light sources including a light emitting surface for emitting light;
A case that holds the plurality of point light sources inside and has an upper part, a lower part that faces the upper part, and a connection part and an opening part that connect the upper part and the lower part,
A light guide plate that arranges the opening of the case on a side surface, propagates light incident from the side surface, and emits the light from an output surface;
In the plurality of point light sources, a light emitting surface is disposed at the upper part or the lower part of the case,
The case includes a convex reflection diffusion member protruding toward the inside of the case at a position facing the light emitting surface,
The planar light source device, wherein the reflective diffusion member includes a reflective surface that is inclined with respect to a side surface of the light guide plate and the light emitting surface of the point light source. The planar light source device according to claim 1, wherein the reflection surface of the reflection diffusion member is formed of a plurality of flat surfaces or curved surfaces. 2. The planar light source device according to claim 1, wherein the reflection diffusing member includes at least two reflection surfaces, and each of the reflection surfaces is arranged to be inclined in different directions. The case is between the point light sources and between the reflection diffusion members,
The planar light source device according to any one of claims 1 to 3, further comprising a reflection section including a reflection surface that is inclined with respect to the side surface of the light guide plate and the reflection diffusion member. The planar light source device according to claim 4, wherein the case integrally forms the reflection diffusing member and the reflection portion. 6. A display device, wherein a display element is disposed so as to face the emission surface of the planar light source device according to claim 1.

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