JP4482876B2 - Surface lighting device - Google Patents

Description

  The present invention relates to a sidelight type planar illumination device, and more particularly to a planar illumination device used as illumination means of a liquid crystal display device.

  A liquid crystal display device is widely used as a display means of today's electronic equipment, but since this liquid crystal display device is not a self-luminous type, there is an illumination means for ensuring visibility at night or in a dark place. Necessary. Conventionally, there is a planar illumination device as such an illuminating means, and as one form, a sidelight type planar illumination device has been widely used. The sidelight type planar illumination device is composed of a light guide plate having translucency and a bar-shaped light source or one or more point light sources arranged on a side end surface of the light guide plate. 2. Description of the Related Art In recent years, surface illumination devices including point light sources that are easy to reduce in size and save power are increasing for application to small electronic devices such as mobile phones.

  FIG. 7 is an exploded perspective view schematically showing a main part of the above-described sidelight type planar illumination device. In FIG. 7, the planar illumination device 100 includes a light guide plate 101 and a point light source 102 disposed on a light incident surface 101 c that is one end surface of the light guide plate 101. Usually, a light emitting diode (LED) is used as the point light source 102, and the light guide plate 101 is a transparent member formed by injection molding a polycarbonate resin or the like. Further, the point light source 102 is arranged so that one side surface thereof is the emission surface 102 a and the emission surface 102 a faces the light incident surface 101 c of the light guide plate 101.

  With such a configuration, the light emitted from the point light source 102 enters the light guide plate 101 from the light incident surface 101c, and is repeatedly reflected between the back surface 101b and the light output surface 101a to enter the light guide plate 101. In the process of propagation, a part of the light is emitted from the emission surface 101a to irradiate an object to be illuminated such as a liquid crystal display device.

  Here, since the light emitted from the LED normally used as a point light source includes light leaking from a side surface different from the light exit surface (hereinafter also referred to as leakage light), this leakage light also enters the light guide plate. It is desirable that the light can be incident and used as illumination light. In particular, since a large amount of leaked light leaks from the surface opposite to the light emitting surface of the LED (hereinafter also referred to as the back surface), in order to ensure sufficient brightness of the planar lighting device, the leakage from the back surface of the LED It is important to increase the light utilization efficiency. Conventionally, as a means for coping with such leakage light, a light source part including the point light source 102 is covered with a light-reflective member (see, for example, Patent Document 1).

FIG. 8 is a side sectional view showing the planar illumination device described in Patent Document 1. As shown in FIG. The planar illumination device includes a light guide plate 101 and LEDs 102, and the LEDs 102 are mounted on a substrate 106 and disposed at the edge portion of the light guide plate 101. Furthermore, in this planar illumination device, a reflection sheet 105 for reflecting the light of the LED 102 is disposed so as to surround the periphery of the LED 102.
JP 2001-43714 A (FIG. 2)

  However, in the planar lighting device shown in FIG. 8, the back surface of the LED 102 is a mounting surface on the substrate 106, and the substrate 106 is interposed between the back surface of the LED 102 and the reflection sheet 105. As a result, the leakage efficiency of the leaked light is reduced. Further, in general, in a planar illumination device using a point light source, since the emitted light from the emission surface of the point light source has a directivity to the front, the point light source near the light incident surface of the light guide plate Although it is known that uneven brightness formed by the bright area in the front and the dark area in the side occurs, the planar illumination device shown in FIG. Although the light enters the dark area, the effect is not sufficient to improve the luminance unevenness.

  The present invention has been made in view of the above problems, and by improving the utilization efficiency of leakage light from the back of a point light source, it is possible to improve luminance and improve luminance unevenness near the light incident surface. An object is to provide a planar lighting device.

In order to solve the above-described problems, a planar illumination device according to the present invention includes a light guide plate and a plurality of point light sources arranged such that an exit surface is opposed to a light incident surface of the light guide plate. In
Reflecting means for reflecting light from the point light source, the reflecting means at least partly directly facing the back of the point light source, and in the partial area of the reflecting means, It has an optical path changing means for guiding leaked light leaking from a surface different from the light exit surface of the light source to a dark area near the light incident surface of the light guide plate and formed between the adjacent point light sources .

  Furthermore, as one aspect of the present invention, the point light source is mounted on a circuit board, and the circuit board is disposed in parallel to the emission surface or the reflection surface of the light guide plate.

  According to another aspect of the present invention, the point light source is mounted on a circuit board, and the reflecting means is formed by performing a reflection process on the circuit board.

Moreover, as one aspect of the present invention, the reflecting means includes a rod-shaped light guide.

  According to the planar illumination device of the present invention, since at least a part of the reflecting means directly faces the back surface of the point light source, the light guide plate efficiently reflects the leaked light from the back surface of the point light source. It is possible to make the light incident on the light and improve the utilization efficiency of the leaked light. As a result, the luminance of the planar illumination device can be improved and the luminance unevenness generated near the light incident surface of the light guide plate can be reduced. At this time, a circuit board such as a flexible printed circuit board (FPC) on which the point light source is mounted is disposed in parallel to the light exiting surface or the reflecting surface of the light guide plate, so that the space between the back surface of the point light source and the reflecting means. A configuration without inclusions can be easily achieved.

  Further, according to the planar illumination device according to the present invention, the reflection means is formed by performing a reflection process such as white printing on the circuit board so that the back surface of the point light source becomes the mounting surface on the circuit board. Even in such an arrangement configuration, it is possible to increase the use efficiency of leakage light from the back surface and improve the luminance of the planar illumination device.

  Furthermore, according to the planar illumination device according to the present invention, since the reflecting means includes the optical path changing means, the reflection direction of the leaked light can be controlled. By making the light incident, it is possible to more effectively reduce luminance unevenness generated near the light incident surface of the light guide plate. Such an optical path changing unit can be easily formed by using a reflecting unit including a rod-shaped light guide.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. 1A and 1B are diagrams showing the main part of a planar illumination device 10 according to the first embodiment of the present invention, in which FIG. 1A is a plan view and FIG. 1B is a side view. A planar illumination device 10 according to the present embodiment includes a light guide plate 1, two point light sources 2 and 2 disposed on a light incident surface 1 c that is one end face of the light guide plate 1, and a reflection unit 5. Yes. In the present embodiment, a flexible printed circuit board (FPC) 4 which is a circuit board on which the point light sources 2 and 2 are mounted is disposed on the reflective surface 1b side of the light guide plate 1 in parallel with the reflective surface 1b, and has one side surface. Each point light source 2, 2 which is a white LED having emission surfaces 2a, 2a is mounted on the FPC 4 with a bottom surface connected to the emission surfaces 2a, 2a as a mounting surface, and the emission surfaces 2a, 2a are mounted on the light guide plate 1. It arrange | positions facing the light-incidence surface 1c. Further, the reflecting means 5 is disposed on the opposite surfaces (hereinafter referred to as rear surfaces) 2b and 2b of the point light sources 2 and 2 so as to directly face the rear surfaces 2b and 2b. ing.

  Here, the light guide plate 1 is a plate-like translucent member formed by injection molding a transparent resin, and the material thereof is an acrylic resin, a polycarbonate resin, or an amorphous material that has a good balance between moldability and optical properties. In this case, polystyrene, polyester, polyolefin, fluorine-based transparent polymer, epoxy resin, or the like can be used instead. As for its manufacturing method, injection molding is excellent in terms of productivity and product accuracy, but it is not limited to this, and various resin molding methods such as hot-press molding, extrusion molding, casting method, etc. are applied. Is possible. The reflecting means 5 is a sheet-like member having high reflectivity. For example, a white film in which a resin base material is whitened by foaming or dispersion of a white pigment is preferably used. It is also possible to use a film obtained by vapor-depositing or a metal plate such as an aluminum plate subjected to mirror finishing.

  In the planar illumination device 10, the light incident on the light guide plate 1 from the point light sources 2, 2 is combined with the light emitted from the emission surfaces 2 a, 2 a of the point light sources 2, 2 and directly incident on the light incident surface 1 c. , Leakage light that is reflected by the reflecting means 5 and leaks toward the light incident surface 1c after leaking from a surface different from the exit surfaces 2a and 2a is included. As described above, since the reflecting means 5 is disposed so as to directly face the back surface 2b without having an inclusion between the back surface 2b of the point light source 2 and particularly from the back surface 2b of the point light source 2. Can be efficiently reflected and incident on the light guide plate 1. As a result, not only the luminance of the planar illumination device 10 increases, but also a sufficiently large amount of leaked light enters the dark area formed between the two point light sources 2, 2. Luminance unevenness generated near the light incident surface is reduced.

  In the planar illumination device 10 according to the present embodiment, the FPC 4 may be disposed on the emission surface 1a side of the light guide plate 1 in parallel with the emission surface 1a. Moreover, the board | substrate which mounts a point light source is not limited to FPC, For example, the circuit board which used aluminum as the base material used when high heat dissipation is requested | required can also be applied.

Hereinafter, other embodiments of the planar lighting device according to the present invention will be described with reference to FIG. 2 to FIG. 6, and the same reference numerals are used to denote the same parts as those of the first embodiment described above. Is used.
2A and 2B are diagrams showing the main part of the planar illumination device 20 according to the second embodiment of the present invention. FIG. 2A is a plan view and FIG. 2B is a side view. FIG. 3 is a plan view showing the FPC 14 used in the planar lighting device 20. The planar illumination device 20 in this embodiment includes a light guide plate 1 and two point light sources 12 and 12 arranged on a light incident surface 1c that is one end surface of the light guide plate 1. Moreover, in this embodiment, FPC14 is arrange | positioned in parallel with the light-incidence surface 1c of the light-guide plate 1, Each point light source 12 and 12 which is white LED which makes the top surface the output surfaces 12a and 12a, The bottom surface opposite to the emission surfaces 12 a and 12 a is mounted on the FPC 14 with the mounting surface as the mounting surface, and the emission surfaces 12 a and 12 a are arranged to face the light incident surface 1 c of the light guide plate 1.

  The FPC 14 in the present embodiment is printed with a highly reflective material at least on the surface 14a on the side where the point light sources 12 and 12 are mounted, excluding the land portion 16 to which the electrodes of the point light sources 12 are soldered. The hatched portion shown in FIG. 3 corresponds to the print area. As the highly reflective material, for example, a white ink in which a white pigment such as barium sulfate or titanium dioxide is dispersed can be used. In FIG. 3, the mounting areas 17 and 17 of the point light sources 12 and 12 are indicated by broken lines. In the present embodiment, the back surface of each point light source 12, 12 corresponds to the bottom surface of the point light source 12, 12, that is, the mounting surface on the FPC 14, and each point light source 12, 12 on the mounting area 17, 17 of the FPC 14. By implementing the above, at the same time, the reflecting means made of the FPC 14 on which the high-reflecting material is printed is arranged so as to directly face the back surfaces of the respective point light sources 12 and 12.

  As described above, the planar lighting device 20 according to the present embodiment obtains the same functions and effects as those of the first embodiment described above by causing the FPC 14 to also function as the reflecting means according to the present invention. . In addition, it may replace with printing of a highly reflective material, and you may make it perform the reflection process on the surface of FPC14 by sticking reflective tapes, such as a white tape. Further, similarly to the first embodiment, a circuit board or the like based on aluminum may be used instead of the FPC 14.

  FIGS. 4A and 4B are diagrams showing a main part of the planar illumination device 30 according to the third embodiment of the present invention. FIG. 4A is a plan view and FIG. 4B is a side view. FIG. 5 is a perspective view showing a rod-shaped light guide 26 used in the planar illumination device 30. The planar illumination device 30 in the present embodiment includes the light guide plate 1, the point light sources 2, 2, the FPC 4, and the reflection means 25, but the configuration of the light guide plate 1, the point light sources 2, 2, and the FPC 4. Since this is the same as the planar illumination device 10 in the first embodiment described above, description thereof is omitted, and here, the reflection means 25 will be described.

  The reflecting means 25 in the present embodiment is composed of a rod-shaped light guide 26 and a reflective layer 27, and the rod-shaped light guide 26 has one side surface 26 a directly facing the back surfaces 2 b and 2 b of the point light sources 2 and 2. The reflective layer 27 is disposed on the opposite side surface 26b side. Here, the rod-shaped light guide 26 is a rod-shaped light-transmitting member formed of the same material as that of the light guide plate 1, and as shown in FIG. Optical path changing means 28 is formed which is composed of a multi-row triangular prism extending along the height direction h of the body 26 and arranged along the longitudinal direction l. The predetermined area where the optical path changing means 28 is formed is generated near the light incident surface 1c due to the directivity of the point light sources 2 and 2 when the reflecting means 25 is arranged on the back side of the point light sources 2 and 2. It is preferable to include a range facing a dark portion (corresponding to the region B in FIG. 4A). The reflective layer 27 is preferably made of a highly reflective white film as described above and is disposed on the side surface 26b. Silver or aluminum or the like is applied to the side surface 26b of the rod-shaped light guide 26. It may be formed integrally with the rod-shaped light guide 26 by vapor deposition.

According to the planar illumination device 30 in the present embodiment, not only the same actions and effects as the planar illumination device 10 in the first embodiment described above are obtained, but also the reflection means 25 has the optical path conversion means 28. By controlling the reflection direction of the leaked light from the back surfaces 2b and 2b of the point light sources 2 and 2 as indicated by an optical path P schematically shown in FIG. 2 can be efficiently guided to the dark area B generated between 2 and the luminance unevenness generated near the light incident surface 1c can be more effectively reduced.
The optical path changing means 28 according to the present invention is not limited to the multiple triangular prisms as described above, and may have any appropriate shape including uneven structures of various shapes such as a polygonal shape or an arc shape. can do. Further, the formation surface of the optical path changing means 28 may be a side surface 26a on the side facing the point light sources 2 and 2.

Further, as shown in FIG. 6, the reflecting means having the optical path changing means in the present embodiment is directly provided with optical path changing means 32 made of, for example, a multi-row triangular prism, on the surface 31a of the highly reflective sheet-like member 31. It may be. For example, the reflecting means 35 fixes a brightness increasing prism sheet as an optical path changing means 32 to the predetermined region of the sheet-like member 31 made of the above-described highly reflective white film with an adhesive or the like. Can be formed. Alternatively, any appropriate concavo-convex structure corresponding to the optical path changing means 32 is formed on the highly reflective sheet-like member 31 itself, or highly reflective by vapor deposition or printing on a substrate having such a concavo-convex structure. The optical path changing means 32 may be formed integrally with the sheet-like member 31 by means such as forming a film.
In the planar illumination device 30 shown in FIG. 4, instead of the reflection means 25, the reflection means 35 is arranged such that the surface 31 a directly faces the back surfaces 2 b and 2 b of the point light sources 2 and 2. The same operation and effect as the planar illumination device 30 can be obtained.

  1, 2, and 4, the components such as the light guide plate 1, the point light sources 2 and 12, and the reflection means 5 and 25 that constitute the planar illumination devices 10, 20, and 30 are illustrated for the sake of explanation. However, it is needless to say that the planar illumination device according to the present invention is not limited to the presence or absence of a space between these components.

It is a figure which shows the principal part of the planar illuminating device in the 1st Embodiment of this invention, (a) is a top view, (b) is a side view. It is a figure which shows the principal part of the planar illuminating device in the 2nd Embodiment of this invention, (a) is a top view, (b) is a side view. It is a top view which shows FPC in the planar illuminating device shown in FIG. It is a figure which shows the principal part of the planar illuminating device in the 3rd Embodiment of this invention, (a) is a top view, (b) is a side view. It is a perspective view which shows the rod-shaped light guide in the planar illuminating device shown in FIG. It is a perspective view which shows another aspect of the reflection means which has an optical path conversion means. It is a perspective view which shows the principal part of the conventional planar illuminating device. It is a sectional side view which shows the conventional planar illuminating device which has a reflection means of the leakage light from a point light source.

Explanation of symbols

1: light guide plate, 2, 12: point light source, 4: flexible printed circuit board, 5, 25, 35: reflecting means, 14: flexible printed circuit board (reflecting means), 26: rod-shaped light guide, 28, 32: optical path Conversion means

Claims (4)

In a planar illumination device having a light guide plate and a plurality of point light sources arranged with an emission surface facing the light incident surface of the light guide plate,
Reflecting means for reflecting light from the point light source, the reflecting means at least partly directly facing the back of the point light source, and in a part of the reflecting means, the point shape A surface having optical path conversion means for guiding leakage light leaked from a surface different from the light exit surface of the light source to a dark area near the light incident surface of the light guide plate and formed between the adjacent point light sources. Illuminator. The planar illumination device according to claim 1, wherein the point light source is mounted on a circuit board, and the circuit board is disposed in parallel to an emission surface or a reflection surface of the light guide plate. 2. The planar illumination device according to claim 1, wherein the point light source is mounted on a circuit board, and the reflection means is formed by performing a reflection process on the circuit board. The planar illumination device according to claim 1, wherein the reflection unit includes a rod-shaped light guide .

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