JP2011198479A - Surface light source and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface light source capable of suppressing luminance unevenness and a liquid crystal display device using this surface light source.SOLUTION: The surface light source includes: a plurality of light-emitting elements (110) mounted on a mounting surface of a mounting substrate (20); and a plurality of lenses (100) each of which has a light-incident surface and a light-outgoing surface and is mounted on the mounting surface so that each light-emitting surface of the light-emitting elements is covered with the incident surface. The plurality of the lenses are so mounted on the mounting surface as to reduce variance in the distance between the light-emitting surface and the incident surface due to the variance in the height from the mounting surface to the light-emitting surface in the plurality of light-emitting elements.

Description

  The present invention relates to a surface light source used as a backlight of a liquid crystal display device, for example, and a liquid crystal display device using the surface light source.

  In the backlight of a conventional large liquid crystal display device, a large number of cold cathode fluorescent lamps are arranged directly under the liquid crystal panel. These cold cathode tubes have been used together with members such as a diffusion plate and a reflection plate. In recent years, light emitting diodes have been used as light sources for backlights. Light-emitting diodes have been improved in efficiency in recent years, and are expected as light sources with low power consumption instead of fluorescent lamps. Further, since the light emitting diode is a point light source, the brightness of the light emitting diode can be controlled according to the image by arranging the light emitting diode in a two-dimensional manner. According to such a configuration, it is possible to increase the contrast of the video and reduce the power consumption of the liquid crystal display device.

  In a backlight using a light emitting diode as a light source, uniform brightness can be obtained on the surface of the backlight by using a large number of light emitting diodes. However, since a large number of light emitting diodes are required, there is a problem that cannot be made inexpensive. On the other hand, efforts are being made to increase the output of one light-emitting diode and reduce the number of light-emitting diodes used. For example, Patent Document 1 proposes a surface light source in which a lens for expanding the directivity of a light emitting diode is arranged.

Japanese Patent No. 3875247

  However, when the light emitting diode is disposed on the mounting substrate, the mounting height mainly varies in the optical axis direction depending on the soldering conditions and the like. Along with this, when the orientation is widened by the lens, the individual luminance distribution varies. Therefore, when a surface light source is constituted by a plurality of light emitting diodes, it becomes a factor of luminance unevenness.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a surface light source and a liquid crystal display device capable of suppressing luminance unevenness even when the mounting positions of light emitting diodes vary in the optical axis direction. And

  In order to solve the above problems, a surface light source of the present invention includes a plurality of light emitting elements mounted on a mounting surface of a mounting substrate, a light incident surface, and a light emitting surface. A plurality of lenses attached to the mounting surface so as to cover the incident surface, and the plurality of lenses are the light emitting surface due to variations in height from the mounting surface to the light emitting surface in the plurality of light emitting elements. And the mounting surface so as to reduce the variation in the distance between the surface and the incident surface.

  The liquid crystal display device according to the present invention includes a liquid crystal panel that modulates light emitted from the back surface to display an image, and the surface that is disposed on the back side of the liquid crystal panel and that emits light to the liquid crystal panel. And a light source.

  ADVANTAGE OF THE INVENTION According to this invention, even if the attachment position of a light emitting diode varies in the optical axis direction, the surface light source and liquid crystal display device which can suppress brightness nonuniformity can be provided.

The perspective view which shows schematic structure of the surface light source 1 which concerns on Embodiment 1 of this invention. Partial sectional view of surface light source 1 Enlarged view of the vicinity of the light emitting device Diagram for explaining lens height adjustment Enlarged view of the vicinity of the light emitting device according to the modification. The figure which shows the luminance distribution of the surface light source when the height of the lens is not adjusted The figure which shows the luminance distribution of the surface light source when the height of the lens is adjusted Diagram showing staggered arrangement of light emitting devices The perspective view which shows the structure of the liquid crystal display device which concerns on Embodiment 2 of this invention.

(Embodiment 1)
The surface light source according to Embodiment 1 of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view showing a schematic configuration of a surface light source 1 according to Embodiment 1 of the present invention. FIG. 2 is a partial cross-sectional view including the light emitting device 10 of the surface light source 1.

  The surface light source 1 includes a plurality of light emitting devices 10, a mounting substrate 20, a reflection plate 30, and a diffusion plate 40.

  The light emitting device 10 includes a light emitting element 110 and a lens 100. The light emitting devices 10 are arranged in a matrix on the mounting substrate 20. The light emitting device 10 spreads the white light emitted from the light emitting element 110 with the lens 100 and irradiates it toward the diffusion plate 40.

  The diffusion plate 40 is disposed to face the mounting substrate 20. The diffuser plate 40 receives white light emitted from the light emitting device 10. The diffusion plate 40 diffuses the incident white light inside and emits it from the front surface. Thereby, planar white light is emitted from the surface light source 1.

  The reflection plate 30 has an opening in a corresponding portion of the light emitting device 10 and is attached onto the mounting substrate 20 so that the light emitting device 10 is exposed. The reflection layer 30 reflects the light emitted from the light emitting device 10 and reflected by the diffusion plate 40 or the like back to the diffusion plate 40 side again. The reflective layer 30 has a white diffuse reflection surface.

  FIG. 3 is an enlarged view for explaining a mounting state of the light emitting device 10. The light emitting element 110 is attached on the mounting surface 21 of the mounting substrate 20. The light emitting element 110 includes a blue LED 111 that emits blue light, and a phosphor layer 112 that is formed to cover the blue LED 111. The phosphor layer 112 generates white light from the blue light emitted from the blue LED 111 by converting a part of the blue light emitted from the blue LED 111 into yellow light. The light emitting element 110 emits white light from the light emitting surface 113 by the action of the blue LED 111 and the phosphor layer 112.

  The blue light emitted from the blue LED 111 preferably has a peak wavelength in the wavelength range of 400 to 520 nm, and more preferably has a peak wavelength in the wavelength range of 450 to 500 nm. The yellow light emitted from the phosphor layer 112 preferably has a peak wavelength in the wavelength range of 550 to 610 nm, and more preferably has a peak wavelength in the wavelength range of 570 to 590 nm.

  The lens 100 has an incident surface 101 on which light emitted from the light emitting surface 113 is incident, and an output surface 102 on which incident light is emitted. The incident surface 101 preferably has a shape in which an air layer is sandwiched between the light emitting element 110. The entrance surface 101 and the exit surface 102 are axisymmetric with respect to the optical axis A of the lens 100. The incident surface 101 has a concave shape formed continuously from the center including the optical axis. Further, the emission surface 102 has a convex shape formed continuously from the central portion including the optical axis.

  Light that enters the lens 100 from the incident surface 101 is emitted from the emission surface 102. The light that has entered the lens 100 from the incident surface 101 is spread by the action of the emission surface 102 and reaches a wide range of the diffusion plate 40. The dotted arrows shown in FIG. 2 indicate the state of light that is spread and emitted by the action of the emission surface 102.

  The light emitting element 110 has directivity. Specifically, the intensity of light decreases as the angle increases from the direction of the optical axis A. Thus, the light emitting element 110 has directivity, and it is necessary to expand the directivity with the lens 100 in order to illuminate a wide range.

  The lens 100 is made of a transparent material having a predetermined refractive index. The refractive index of the transparent material is, for example, about 1.40 to 1.53. As such a transparent material, an epoxy resin, a silicon resin, an acrylic resin, a resin such as polycarbonate, or a rubber such as silicon rubber can be used. In particular, it is preferable to use an epoxy resin or silicon rubber.

  The lens 100 is attached to the mounting surface 21 of the mounting substrate 20. Here, in mounting the light emitting element 110, the mounting height mainly in the direction of the optical axis A varies depending on the soldering conditions and the like. Therefore, when the lens 100 is attached to the mounting substrate 20, the distance between the light emitting surface 113 and the incident surface 101 varies. The lens 100 is designed so as to have optimum light distribution characteristics when the distance between the light emitting surface 113 and the incident surface 101 is a predetermined value. Therefore, when the distance between the light emitting surface 113 and the incident surface 101 varies, the light distribution of the light emitted from the lens 100 varies. As a result, luminance unevenness occurs in the surface light source 1.

  In order to reduce such luminance unevenness, the lens 100 is mounted on the mounting surface so as to reduce the variation in the distance d2 between the light emitting surface 113 and the incident surface 101 due to the variation in the height d1 from the mounting surface 21 to the light emitting surface 113. 21 is attached. That is, the lens 100 in the surface light source 1 is provided for each light emitting device 10 so that the distance d2 between the light emitting surface 113 and the incident surface 101 is not as varied as possible (so that d2 is kept constant even if d1 varies). It is installed with the height adjusted.

  In the present embodiment, the mounting substrate 20 has a plurality of recesses 22 on the mounting surface 21. The recess 22 may be an opening that penetrates the mounting substrate 20. The recess 22 is a cylindrical recess that opens to the mounting surface 21 side. The lens 100 has a cylindrical convex portion 103 that fits into the concave portion 22. The convex portion 103 is formed on the bottom surface of the lens 100 located on the mounting surface 21 side. The convex portion 103 is provided about 2 to 4 places around the optical axis of the lens 100. The convex portion 103 is inserted into the concave portion 22 and fixed with an adhesive or the like (not shown). The depth of the concave portion 22 is preferably deep enough to allow at least all the convex portions 103 to be inserted. In the present embodiment, the lens 100 can reduce the variation in the distance d2 between the light emitting surface 113 and the incident surface 101 by adjusting the insertion amount of the convex portion 103 with respect to the concave portion 22.

  FIG. 4 is a diagram for explaining the height adjustment of the lens 100. Here, light emitting devices 10a and 10b each including light emitting elements 110a and 110b that are adjacent light emitting devices and have different light emitting surfaces are shown. The height d1 of the light emitting surface is d1a and d1b, respectively, and d1a is larger. At this time, when the lenses 100a and 100b are attached to the mounting surface substrate 20 without adjusting the height, a difference is caused in the distance d2 between the light emitting surface and the incident surface. That is, the distance d2 between the light emitting surface and the incident surface varies. As shown in FIG. 4, the lens 100a of the light emitting device 10a is set to have a height corresponding to d1a-d1b so that there is no difference in the distance d2 between the light emitting surface and the incident surface.

  Similarly, luminance unevenness of the surface light source 1 can be reduced by adjusting the height of the lens 100 so that d2 of the light emitting device 10 in the surface light source 1 is as constant as possible.

  The height adjustment of the lens 100 is not limited to the height adjustment by the concave portion 22 and the convex portion 103. In short, any other configuration may be used as long as it can be adjusted in the height direction. For example, as shown in FIG. 5, a configuration in which a jig 60 for adjusting the lens height is separately provided may be used. In the configuration of FIG. 5, the adjustment jig 60 is mounted on the mounting substrate 20. The lens 100 is attached to the jig 60 so that the position in the height direction can be adjusted. However, if the lens height is adjusted by the concave portion 22 and the convex portion 103 as in this embodiment, the lens height can be adjusted relatively easily and at low cost.

  Next, the effect of reducing luminance unevenness in the surface light source 1 of the present embodiment will be described using a graph.

  FIG. 6 is a comparative example, and is a diagram illustrating a luminance distribution on the diffusion plate 40 when the lens 100 is mounted without adjusting the mounting height. FIG. 7 is a diagram showing a luminance distribution on the diffusion plate 40 in the present embodiment. 6 and 7, it is assumed that the light emitting element 110 has a mounting variation (a variation in height d1 from the mounting surface 21 to the light emitting surface 113). The degree of variation is the same in FIGS.

  Thus, it can be seen that the luminance unevenness is reduced in FIG. 7 compared to FIG. That is, it can be seen that even if there is a variation in height in the optical axis direction that occurs when the light emitting element 110 is attached to the substrate 20, luminance unevenness at the diffusion plate 40 can be reduced by adjusting the height of the lens 100. . As a result, luminance unevenness as the surface light source 1 can be reduced.

  In the present embodiment, a difference is not generated in the distance d2 between the light emitting surface 113 and the incident surface 101, but it is difficult to completely eliminate the variation in all the light emitting devices. Substantially, when the target design value of the distance d2 between the light emitting surface 113 and the incident surface 101 is d and the difference between d2 and d in each light emitting device 10 is Δd, Δd is | Δd / d | < It is preferable to satisfy 0.1. In this way, the illuminance distribution emitted from the light emitting device is sufficiently uniformed, and uneven brightness can be further reduced.

  The basic aspect of the surface light source 1 according to the first embodiment has been described above, but a preferable aspect of the surface light source 1 will be described below.

  Lens 100 preferably has a refractive index greater than 1.40 and less than 1.52. When the refractive index of the lens 100 is 1.52 or more, the refracting action on the emission surface 102 becomes strong, and the wide alignment of the light beam becomes insufficient. When the refractive index of the lens 100 is 1.40 or less, the refracting action on the exit surface 102 becomes weak, and the tolerance becomes severe if the shape of the exit surface 102 is changed in order to sufficiently align the luminous flux.

Furthermore, when the pitch of the light emitting device 10 is P and the distance from the light emitting element 110 to the diffusion plate 40 is H, the surface light source 1 preferably satisfies the following expression.
0.2 <H / P <0.6
Here, the “pitch P of the light emitting devices 10” refers to the distance between the optical axes of the light emitting devices 10 in the direction in which the light emitting devices 10 are arranged, and the direction in which the light emitting devices 10 are arranged is a matrix arrangement as shown in FIG. In this case, there are two directions of vertical and horizontal directions orthogonal to each other. As shown in FIG. 8, in the case of an arrangement in which the positions of the light emitting elements for each row are shifted in the row direction (staggered arrangement), the horizontal and diagonal directions are two. Direction. Note that the pitches in these two directions do not necessarily match, but preferably match.

  If H / P is 0.6 or more, the distance from the light emitting device 10 to the diffuser plate 40 becomes larger with respect to the pitch P of the light emitting device 10, so that the surface light source becomes larger. When H / P is 0.2 or less, it becomes difficult to ensure the uniformity of the illuminance distribution on the back surface of the diffusion plate 40, resulting in uneven brightness.

  In the present embodiment, phosphor layer 112 may be formed of an RG phosphor that emits red light and green light when receiving blue light. According to such a configuration, the blue light transmitted through the phosphor layer 112 and the red light and the green light excited by the phosphor layer 112 are mixed to generate white light.

  Furthermore, in the present embodiment, the blue LED 111 that emits blue light is used, but an ultraviolet LED that emits ultraviolet light can also be used. In this case, the phosphor layer 112 may be made of an RGB phosphor that emits red light, green light, and blue light when receiving ultraviolet light.

(Embodiment 2)
Next, a liquid crystal display device according to Embodiment 2 of the present invention will be described with reference to FIG.

  FIG. 9 is a perspective view of a liquid crystal display device 2 using the surface light source 1 shown in FIG. The liquid crystal display device 2 includes a liquid crystal panel 50 that displays light by modulating light emitted from the back surface, and a surface light source 1 that is disposed on the back side of the liquid crystal panel 50 and that emits light to the liquid crystal panel 50. It has.

  The diffuser plate 40 is illuminated by the plurality of light emitting devices 10 arranged in a plane. The back surface of the diffusion plate 40 is irradiated with white light with uniform illuminance, and the white light is diffused by the diffusion plate 40 to illuminate the liquid crystal panel 50.

  Although not shown, an optical sheet such as a diffusion sheet or a prism sheet is disposed between the liquid crystal panel 50 and the diffusion plate 40. The light from the light emitting device 10 is scattered by the diffusion plate 40 and returns to the light emitting device side or passes through the diffusion plate 40. The light that returns to the light emitting device side and enters the reflection plate 30 is reflected by the reflection plate 30 and then enters the diffusion plate 40 again. The light transmitted through the diffusion plate 40 is further diffused by the optical sheet to illuminate the liquid crystal panel 50.

  The present invention is suitable as a liquid crystal display device with reduced luminance unevenness and a surface light source as a backlight used in the liquid crystal display device.

DESCRIPTION OF SYMBOLS 1 Surface light source 2 Liquid crystal display device 10 Light-emitting device 20 Mounting board 21 Mounting surface 22 Recessed part 30 Reflecting plate 40 Diffusion plate 50 Liquid crystal panel 60 Jig 100 Lens 101 Incident surface 102 Output surface 103 Convex part 110 Light emitting element 111 Blue LED
112 phosphor layer 113 light emitting surface

Claims (4)

A plurality of light emitting elements mounted on the mounting surface of the mounting substrate;
A plurality of lenses that have a light incident surface and an output surface, and are attached to the mounting surface such that each light emitting surface of the light emitting element is covered by the incident surface;
The plurality of lenses are attached to the mounting surface so as to reduce variation in distance between the light emitting surface and the incident surface due to variation in height from the mounting surface to the light emitting surface in the plurality of light emitting elements. ing,
Surface light source device. When the target interval between the incident surface and the light emitting surface on the optical axis of the light emitting element is d and the amount of deviation from the target interval is Δd, the plurality of lenses satisfy the following expression (1). Attached to the mounting surface to
The surface light source according to claim 1.
| Δd / d | <0.1 (1) The mounting substrate has a plurality of recesses or openings on the mounting surface,
Each of the lenses has a convex portion that fits into the concave portion or the opening,
The plurality of lenses reduce variation in distance between the light emitting surface and the incident surface by adjusting an insertion amount of the convex portion with respect to the concave portion or the opening portion.
The surface light source according to claim 1. A liquid crystal panel that modulates the light emitted from the back and displays an image;
The surface light source according to claim 1, which is disposed on a back side of the liquid crystal panel and irradiates light to the liquid crystal panel.
Liquid crystal display device.

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