JP4014026B2 - Surface light source device, image display device, and light guide plate - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention provides a portable telephone, portable electronic terminal device, electronic notebook, car navigation device, video camera, digital camera, VTR device, etc., with a liquid crystal display panel or other image display panel (illuminated member) on the back side. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface light source device used as a backlight or the like that illuminates in a planar manner, and an image display device provided with the surface light source device, and also relates to a light guide plate used in these surface light source devices and image display device It is.
[0002]
[Prior art]
For example, a liquid crystal display device as an image display device is used for a mobile phone, a video camera, or the like. As the liquid crystal display device, a surface light source device that illuminates a liquid crystal display panel as an illuminated member in a planar shape from the back side is used.
[0003]
In the surface light source device, a rod-like fluorescent lamp is disposed so as to face one side of the light guide plate, and the light of the fluorescent lamp is taken into the inside from one side of the light guide plate, and the surface facing the liquid crystal display panel of the light guide plate Planar illumination light is emitted from the (exiting surface). However, in recent years, a surface light source device has been developed in which a plurality of LEDs (light emitting diodes) are arranged in a line instead of a fluorescent lamp and the LEDs are used as a light source in order to reduce the thickness and life of the surface light source device. .
[0004]
In such a surface light source device using an LED as a light source, since the LED of the point light source has directivity, the luminance is more likely to vary than when a fluorescent lamp as a linear light source is used as the light source. Therefore, for example, as disclosed in Japanese Patent Application Laid-Open No. 10-260404, by arranging a curved lens on the portion of the light guide plate facing the LED, and devising the size and shape of the curve, A technique has been developed in which the light emission luminance of light emitted from the emission surface is made uniform by adjusting the intersection position of the emission boundary lines of adjacent LEDs.
[0005]
Further, for example, as disclosed in Japanese Patent Application Laid-Open No. 2001-23423, the shape of the incident surface (one side surface) side of the light guide plate is a substantially triangular shape, and an LED is arranged at the apex portion, so that the light from the LED The light propagates inside the light guide plate by making the light incident on the inside of the light guide plate equally and forming a number of substantially semicircular reflective surfaces (vertical grooves) on the incident surface and diffusing the light on the reflective surface. A technology has been developed that eliminates the directivity of the light and makes the light emitted from the light exit surface of the light guide plate uniform.
[0006]
[Problems to be solved by the invention]
However, such a conventional surface light source device is effective for making the luminance of the light emitted from the exit surface of the light guide plate uniform, but for the user, the central portion of the exit surface of the light guide plate is the other part. It may be easier to see the lighter than the brighter. In such a case, the conventional surface light source device only for the purpose of uniforming the luminance of the emitted light cannot sufficiently satisfy the user's request.
[0007]
Accordingly, the applicant of the present application aims to make the light emitted from the substantially central portion of the exit surface of the light guide plate brighter than the light emitted from other portions by devising the shape of the light guide plate. It is said.
[0008]
[Means for Solving the Problems]
The invention of claim 1, along at least one side surface of the light guide plate by arranging a plurality of LED, the inside of the light guide plate propagates after the light from the plurality of LED is incident inside the light guide plate, this the angle of incidence on the exit surface of the light guide plate in the process of propagation is related to which surface light source device so that the light falls below the critical angle to exit from the exit surface of the light guide plate. In this invention, the side facing the LED disposed in the central portion of the one side is a plane formed along the thickness direction of the light guide plate and along the one side. In addition, a side surface that faces the LEDs disposed at both ends in the direction along the one side surface with the LED disposed at the center portion is a curved surface formed so as to surround the light emitting portion of the LED. The opening angle of the light incident on the inside of the light guide plate from the curved surface is larger than the opening angle of the light incident on the inside of the light guide plate from the plane.
[0009]
According to a second aspect of the present invention, there is provided an image display device comprising: the surface light source device according to the first aspect of the present invention; and an illuminated member that is illuminated in a planar shape by light emitted from the surface light source device. It is characterized by that.
[0010]
According to a third aspect of the present invention, a plurality of LEDs are arranged along at least one side surface, and among the light from the plurality of LEDs, the incident angle with respect to the emission surface becomes less than the critical angle in the process of propagating inside. The present invention relates to a light guide plate that emits light from the exit surface. In the present invention, the side surface facing the LED disposed at the central portion of the one side surface is a plane formed along the thickness direction and along the one side surface. In addition, a side surface that faces the LEDs disposed at both ends in the direction along the one side surface with the LED disposed at the center portion is a curved surface formed so as to surround the light emitting portion of the LED. The opening angle of light incident on the light guide plate from the curved surface is made larger than the opening angle of light incident on the light guide plate from the plane.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0012]
[First Embodiment]
1 to 2 show a surface light source device 1 according to an embodiment of the present invention. Among these, FIG. 1 is a plan view of the surface light source device 1. 2 is a cross-sectional view taken along line AA in FIG.
[0013]
In these drawings, the surface light source device 1 includes a light guide plate 2 and a plurality of LEDs (light emitting diodes) 4 a to 4 d as light sources arranged in a line on the side surface 3 side of the light guide plate 2. Among these, the light guide plate 2 is formed using a material having excellent light transmission properties such as PMMA (polymethyl methacrylate), PC (polycarbonate), and cycloolefin resin material, and faces the LEDs 4a to 4d. The cross section is formed in a substantially wedge shape so that the plate thickness becomes thinner as it goes away from the side surface 3 (see FIG. 2), and the planar shape is formed in a substantially rectangular shape (see FIG. 1).
[0014]
Further, the light guide plate 2 has a substantially semicircular recess 6 formed such that side portions facing the LEDs 4a and 4d at both ends of the plurality of LEDs 4a to 4d surround the light emitting portions 5a and 5d of the LEDs 4a and 4d. , 6 are curved surfaces 7, 7. The curved surface 7 serves as an incident surface of light from the opposing LEDs 4a and 4d, and relaxes the directivity of light emitted from the light emitting portions 5a and 5d of the LEDs 4a and 4d so as to diffuse light. To work.
[0015]
In addition, the light guide plate 2 has a rectangular concave portion in which a side portion facing the other LEDs 4b and 4c (hereinafter referred to as central LEDs 4b and 4c for convenience) except the LEDs 4a and 4d at both ends accommodates the LEDs 4b and 4c. 8 is the deepest plane 10. The plane 10 is an incident surface of light from the opposing LEDs 4b and 4c, and is a direction (width direction of the light guide plate 2) orthogonal to the plate thickness direction of the light guide plate 2 (vertical direction in FIG. 2). It is a plane extending in the direction. In addition, the light emission parts 5b and 5c of LED4b and 4c are accommodated in the recessed part 8. FIG.
[0016]
Moreover, the inclined surface 11 of the shape cut off diagonally is formed in the both ends by the side of LED4a-4d of the light-guide plate 2. As shown in FIG. The inclined surface 11 has a function of reflecting the light reaching the inclined surface 11 out of the light propagating through the light guide plate 2 to the central portion side of the light guide plate 2.
[0017]
And such a surface light source device 1 is accommodated in the case outside a figure so that light may radiate | emit only from the output surface 12 side of the light-guide plate 2, and uses the light from LED4a-4d for illumination effectively. It is like that.
[0018]
The surface light source device 1 configured as described above is directed when light from the LEDs 4a and 4d at both ends is incident from the curved surfaces 7 and 7, as schematically shown in FIG. On the other hand, the directivity is not relaxed when the light from the central LEDs 4b and 4c is incident from the plane 10. That is, when the opening angle θ1 of the light incident from the curved surfaces 7 and 7 is compared with the opening angle θ2 of the light incident from the plane 10, the opening angle θ1 of the light incident from the curved surfaces 7 and 7 is incident from the plane 10. The light opening angle θ2 becomes larger (θ1> θ2), and the amount of light propagating through the central portion of the light guide plate 2 increases. The light from the LEDs 4a to 4d incident on the inside of the light guide plate 2 is emitted when the incident angle with respect to the output surface 12 of the light guide plate 2 is less than the critical angle in the process of propagating through the inside of the light guide plate 2. 12 is emitted. As a result, the luminance of emitted light from the exit surface 12 of the light guide plate 2 is higher on the center side than on the end side, and the substantially center portion of the exit surface 12 of the light guide plate 2 is brightly emphasized.
[0019]
Such a surface light source device 1 illuminates a liquid crystal display panel 13 as a member to be illuminated arranged in a plane so as to face the light exit surface 12 of the light guide plate 2. At least the surface light source device 1 of this embodiment and the liquid crystal display panel 13 constitute a liquid crystal display device 14 as an image display device.
[0020]
A diffusion sheet for diffusing the light emitted from the light guide plate 2 is disposed between the light emission surface 12 of the light guide plate 2 and the liquid crystal display panel 13, and the light emitted from the light guide plate 2 is transmitted to the light guide plate 2. You may make it arrange | position the prism sheet collected near the radiation direction of the output surface 12 of this. Further, a reflective sheet is disposed on the lower surface (surface opposite to the emission surface) 15 side of the light guide plate 2 so as to face the lower surface 15 of the light guide plate 2, and light emitted from the lower surface 15 of the light guide plate 2 is emitted. The light may be reflected by the reflection sheet and returned to the inside of the light guide plate 2.
[0021]
[Second Embodiment]
FIG. 4 is a plan view of the surface light source device 1 according to the second embodiment of the present invention. Note that the same components as those of the surface light source device 1 according to the first embodiment described above are denoted by the same reference numerals, and redundant description is omitted.
[0022]
In the present embodiment, a partition wall 16 that partitions adjacent LEDs 4b and 4c in the center is formed. That is, in the present embodiment, rectangular recesses 17 and 17 are formed corresponding to the LEDs 4b and 4c in the center, and flat surfaces 18 and 18 serving as incident surfaces are formed at the deepest portions of the recesses 17 and 17. ing. The concave portions 17 and 17 can surround at least the light emitting portions 5b and 5c of the LEDs 4b and 4c with a gap.
[0023]
In the surface light source device of the present embodiment, when the divergence angle of light emitted from the light emitting portions 5b and 5c of the LEDs 4b and 4c is large, the side surface of the partition wall 16 can also be a light incident surface. The light taken from 16 can also be used effectively for illumination.
[0024]
[Third Embodiment]
FIG. 5 shows a plan view of a surface light source device 1 according to a third embodiment of the present invention. Note that the same components as those of the surface light source device 1 according to the first embodiment described above are denoted by the same reference numerals, and redundant description is omitted.
[0025]
In the present embodiment, the light guide plate 2 has concave portions 6 and 6 formed with curved surfaces 7 and 7 similar to those of the first embodiment described above only on the side portions facing the LEDs 4a and 4d at both ends. Has been. On the other hand, the concave portions 8, 17 and 17 as in the first and second embodiments described above are not formed in the side surface portions facing the LEDs 4b and 4c in the center of the light guide plate 2, and The flat surface 20 of the side surface 3 is used as the incident surface of light from the LEDs 4b and 4c as it is.
[0026]
As described above, the LEDs 4b and 4c in the central portion are arranged so as to be shifted to the left in FIG. 5 with respect to the LEDs 4a and 4d at both ends, so that the boundary line L1 of the incident light from the LEDs 4b and 4c in the central portion and The position of the intersection 21a with the boundary line L2 of the incident light from the LEDs 4a and 4d, and the position of the intersection 21b of the boundary line L1 of the incident light from the central LED 4b and the boundary line L1 of the incident light from the central LED 4c However, the position is shifted closer to the one side surface 3 of the light guide plate 2 than the positions of the intersections 22a and 22b in the first embodiment (see FIG. 1). As a result, in the light guide plate 2 of the present embodiment, a region where a difference in brightness is less likely to spread is spread toward one side as compared to the light guide plate 2 of the first embodiment. In FIGS. 5 and 1, the right part of the figure from the intersections 21a, 21b, 22a, and 22b is a region where the difference in brightness is less likely to occur in the emitted light luminance, and the difference in brightness is less likely to occur. Is possible.
[0027]
[Other embodiments]
In each of the above-described embodiments, the mode in which the four LEDs 4a to 4d are arranged on the side surface 3 side of the light guide plate 2 is illustrated. However, the present invention is not limited to this. For example, as shown in FIG. , 24b, 24c are arranged on the side surface 3 side of the light guide plate 2, the incident surfaces of the LEDs 24a, 24c at both ends are the curved surfaces 7 of the substantially semicircular recesses 6, and the incident surface of the central LED 24b is a rectangular shape. The flat surface 26 of the recess 25 may be used. Further, five or more LEDs are arranged on one side of the light guide plate, and light from the LEDs arranged at both ends of at least one side is formed in a substantially semicircular recess formed on one side of the light guide plate. The light from a plurality of LEDs at the center may be incident from the plane of one side of the light guide plate.
[0028]
In each of the above-described embodiments, a plurality of LEDs are arranged only on the side surface 3 side of the light guide plate 2. However, the LEDs may be arranged on a plurality of side surfaces of the light guide plate 2, respectively.
[0029]
Further, as shown in FIG. 2, each of the above-described embodiments exemplifies the light guide plate 2 having a substantially wedge-shaped cross section. However, the present invention is not limited to this, and the thin plate-shaped guide having a substantially rectangular cross section is not limited thereto. The light plate 2 may also be used, and the present invention can be applied to a substantially V-shaped light guide plate whose cross-sectional shape is thin at a substantially central portion.
[0030]
Further, light diffusion processing is performed on the lower surface 14 or the emission surface 12 of the light guide plate 2, or fine particles having a refractive index different from that of the material of the light guide plate 2 are mixed in the light guide plate 2 to propagate through the light guide plate 2. Light may be diffused to promote light emission. Further, the light diffusivity at the lower surface of the light guide plate or the substantially central portion of the exit surface is made higher than the other portions, and the light emission from the lower surface of the light guide plate or the substantially central portion of the exit surface is promoted. Combined with the function and effect of the embodiment, it is possible to increase the luminance of emitted light from the substantially central portion of the light guide plate more effectively.
[0031]
In each of the above-described embodiments, the gap size between the LED and the curved surface, the shape of the curved surface (size and curvature), the gap size between the LED and the flat surface, etc. are the performance of the LED, the size of the light guide plate 2, etc. The best numerical value is appropriately determined according to the various conditions.
[0032]
【The invention's effect】
As described above, the present invention relaxes the directivity of light from the LED by causing light from the LEDs arranged on both ends of the light guide plate to enter from the curved surface that is the side surface of the light guide plate. The light from the LEDs arranged between the LEDs at both ends is made incident from the plane which is the side surface of the light guide plate, so that the directivity of the light from the LEDs is not impaired, and the light on the center side of the light guide plate Can be increased, and the luminance of the emitted light from the center of the exit surface of the light guide plate can be increased.
[Brief description of the drawings]
FIG. 1 is a plan view of a surface light source device according to a first embodiment of the present invention.
2 is a cross-sectional view taken along line AA in FIG.
FIG. 3 is a partial plan view of a surface light source device showing a part of FIG. 1 in an enlarged manner.
FIG. 4 is a plan view of a surface light source device according to a second embodiment of the present invention.
FIG. 5 is a plan view of a surface light source device according to a third embodiment of the present invention.
FIG. 6 is a plan view of a surface light source device according to another embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Surface light source device, 2 ... Light guide plate, 3 ... One side surface, 4a-4d ... LED, 5a-5d ... Light-emitting part, 7 ... Curved surface 10, 18, 20, 26 ... Plane , 12 ... emitting surface, 13 ... liquid crystal display panel (illuminated member), 14 ... liquid crystal display device (image display device)

Claims (3)

Along at least one side surface of the light guide plate by arranging a plurality of LED, the inside of the light guide plate propagates after the light from the plurality of LED is incident into the light guide plate, the light guide plate in the process of this propagation in of which the surface light source device adapted to light incident angle becomes equal to or less than the critical angle is emitted from the emission surface of the light guide plate for emitting surface,
The side surface facing the LED disposed in the central portion of the one side surface is a plane formed along the thickness direction of the light guide plate and along the one side surface,
The side surface facing the LEDs disposed at both ends in the direction along the one side surface with the LED disposed at the center portion being a curved surface formed so as to surround the light emitting portion of the LED,
The opening angle of light incident on the inside of the light guide plate from the curved surface is larger than the opening angle of light incident on the inside of the light guide plate from the plane.
A surface light source device.   An image display device comprising: the surface light source device according to claim 1; and an illuminated member that is illuminated in a planar shape by light emitted from the surface light source device. A plurality of LED disposed along at least one side, of the light from the plurality of LED, the light incident angle becomes equal to or smaller than the critical angle for the exit surface in the process of propagating inside is emitted from the exit surface In the light guide plate,
The side surface facing the LED disposed in the central portion of the one side surface is a plane formed along the thickness direction and along the one side surface,
The side surface facing the LEDs disposed at both ends in the direction along the one side surface with the LED disposed at the center portion being a curved surface formed so as to surround the light emitting portion of the LED,
The opening angle of light incident on the light guide plate from the curved surface is larger than the opening angle of light incident on the light guide plate from the plane.
A light guide plate characterized by that.

Images