JP2009181883A - Backlight device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a backlight device for suppressing luminance irregularity when surface-emitting the whole light-emitting face while controlling luminance in light-emitting regions with no sense of discomfort. <P>SOLUTION: The vertical type backlight device 1 includes a diffusion sheet 8 having the light-emitting face 12 set on the outer face side, a mounting board 5 having a mounting face 5a opposed to the inner face side of the diffusion sheet 8, a plurality of LEDs 6 mounted on the mounting face 5a, and a frame 7 surrounding the group of LEDs 6 to form a cavity 10 between the diffusion sheet 8 and the mounting board 5. A reflection factor R1 of the mounting face 5a is set smaller than a reflection factor R2 of an inner peripheral face 7a of the frame 7. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a so-called direct-type backlight device in which light emitting elements of a plurality of light emitting diodes are opposed to each other on the inner surface side of an optical member such as a diffusion plate forming a light emitting surface.

  2. Description of the Related Art Conventionally, in backlight devices used in liquid crystal display devices, so-called direct type backlight devices in which a plurality of cold cathode fluorescent tubes (CCFLs) are arranged as light sources on the inner surface side of a diffusion plate or the like are widely used. It has been adopted. In general, this type of backlight device is configured to emit white light with uniform brightness by mixing light emitted from each CCFL in a space (air layer) to the light emitting surface.

  Also, in recent years, backlight devices have responded to the demands for improving the image quality of liquid crystal display devices with the spread of televisions using liquid crystal display devices, and controlled the lighting of each CCFL in synchronization with the cell operation of the liquid crystal panel. Technology has been developed. For example, Patent Document 1 discloses a technique for improving image quality of a liquid crystal display device by suppressing blurring when displaying a moving image by blinking and lighting CCFLs in synchronization with a frame period of a liquid crystal panel.

  In direct type backlight devices, light emitting diodes (LEDs) are used as light sources instead of CCFLs in order to control the luminance and chromaticity of the light emitting surface for each subdivided area. A technique for individually controlling the lighting of LEDs for each set light emitting region has been proposed.

  On the other hand, when a plurality of LEDs are arranged directly below as described above, the emitted light from each LED affects each other over a wide range, and as a result, for example, when trying to cause the entire light emitting surface to emit light In addition, there is a risk of uneven brightness such that the brightness at the center is relatively higher than that at the periphery. In addition, when trying to control the luminance or the like for each light emitting area, there is a possibility that leakage light between the light emitting areas may unnecessarily affect areas other than the desired light emitting area.

To cope with this, for example, Non-Patent Document 1 discloses a technique in which a partition is provided around each LED and the light emitting region is divided using the partition.
JP 2004-252127 A SID 06 DIGEST 1520-1523 44.4 / T.Shirai

  However, when a partition is provided as in the technique disclosed in Non-Patent Document 1 described above, the partition appears as a dark line on the light-emitting surface, or the light-emitting section becomes too clear, and the image is displayed near the boundary of the light-emitting region. There is a risk that it may be difficult to smoothly control the emission intensity of the light.

  An object of the present invention is to provide a backlight device that can suppress luminance unevenness or the like when the entire light emitting surface is caused to emit light, and can perform luminance control for each light emitting region without a sense of incongruity. .

  The present invention includes an optical member having a light emitting surface set on the outer surface side, a mounting substrate having a mounting surface opposed to the inner surface side of the optical member, a plurality of light emitting elements mounted on the mounting surface, and the light emitting device. A frame body that surrounds the element group and forms a gap between the optical member and the mounting substrate, and the reflectance of the mounting surface is set smaller than the reflectance of the inner peripheral surface of the frame body It is characterized by.

  According to the backlight device of the present invention, it is possible to suppress luminance unevenness and the like when the entire light emitting surface is subjected to surface light emission, and to perform luminance control for each light emitting region without a sense of incongruity.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The drawings relate to an embodiment of the present invention, FIG. 1 is an exploded perspective view showing a main part of the backlight device, FIG. 2 is a plan view of the backlight device, and FIG. 3 is a main part taken along line III-III in FIG. It is sectional drawing.

  1 to 3, reference numeral 1 denotes a backlight device suitable for a liquid crystal television or the like. The backlight device 1 includes a light source unit 2. The light source unit 2 has a flat mounting substrate 5, and a plurality of light emitting diodes (LEDs) 6 are mounted as light emitting elements on a mounting surface 5 a set on one surface side of the mounting substrate 5. The part is composed. In this light source unit 2, a frame body 7 surrounding the group of LEDs 6 on the mounting surface 5a is fixed, and a diffusion plate 8 as an optical member is disposed at the end of the frame body 7. Then, the bezel 9 is crowned on the edge of the diffusion plate 8 and the frame body 7, so that the diffusion plate 8 is separated from the mounting substrate 5 with a predetermined gap (air layer) 10. 7 is held.

  The mounting board 5 is configured by a circuit board having a substantially rectangular shape in plan view. The mounting substrate 5 is, for example, a flame retardant grade FR-4 printed wiring board, a composite laminated substrate (CEM-3 substrate) using a glass nonwoven fabric, a glass cloth, and an epoxy resin, or an aluminum substrate. It is configured. Further, the mounting surface 5a side of the mounting substrate 5 is constituted by a low reflection surface having a reflectance R1 of 20% or less, preferably a reflectance R1 of 5%, for example, by sticking a black PET sheet. Yes. The reflectance R1 on the mounting surface 5a side may be adjusted by, for example, the color of the resist used for the mounting substrate 5.

  Each LED 6 is composed of, for example, a surface-mounted white LED in which a yellow phosphor is added to a blue light emitter. In the present embodiment, 64 LEDs 6 are mounted on the mounting surface 5a, and these LEDs 6 are arranged at equal intervals to form an 8 × 8 matrix on the mounting surface 5a. .

  Here, a single-convex lens 6 a is fixed to the emission surface of the LED 6. The optical characteristics of the one-convex lens 6a are appropriately set by, for example, simulation based on the output characteristics and arrangement state of the LEDs 6, and thereby the emission state of the emitted light having the normal direction of each LED 6 as the optical axis, etc. Has been optimized.

  In addition, as LED6, it replaces with the above-mentioned white LED, for example, you may use LED which consists of R, G, B each single-color light-emitting body, Furthermore, R, G is used for the light-emitting body which contains an ultraviolet-ray in emitted light. , B may be added with phosphors that emit light.

  The frame body 7 is composed of a rectangular annular member that is provided so as to protrude from the mounting surface 5 a along the edge portion of the mounting substrate 5. In this frame 7, for example, a white reflective sheet is attached to the inner peripheral surface 7 a surrounding the gap 10 between the mounting substrate 5 and the diffusion plate 8 (that is, the inner peripheral surface 7 a including the LED 6 group). As a result, the reflectance R2 is 80% or more, and preferably, the reflectance R2 is 95%. Here, the inner peripheral surface 7a is more preferably a mirror surface.

  The diffusing plate 8 is composed of a flat plate member having a substantially rectangular shape in plan view that is substantially the same shape as the mounting substrate 5. A plurality of optical sheets 11 made of a lens sheet or the like are attached to the outer surface side of the diffusion plate 8, and the outer surface of the optical sheet 11 positioned at the outermost position is set as the light emitting surface 12.

  As described above, the backlight device 1 of the present embodiment is configured by a so-called direct-type backlight device in which a plurality of LEDs 6 are opposed to each other as a light source on the inner surface side of the diffusion plate 8. In order to cause the backlight device 1 to emit light in a region, for example, as shown in FIG. 2, 4 × 4 light emitting regions 12 a that are equally divided are set on the light emitting surface 12. Further, corresponding to these light emitting regions 12a, the LEDs 6 on the mounting substrate 5 are grouped into small groups of 2 × 2 adjacent to each other. Then, each LED 6 is independently driven for each group by the lighting circuit 15 (see FIG. 1) connected to the mounting substrate 5, so that the backlight device 1 can obtain a desired luminance for each light emitting region. It is possible. Here, each group of LEDs 6 is driven by, for example, PWM control. In this case, it is desirable that the PWM signal for each group is feedback-controlled based on signals from a photo sensor and a color sensor (not shown) with reference to the temperature characteristics of the LED 6 and the like.

  In the backlight device 1 having such a configuration, when the lighting circuit 15 controls the lighting of the LEDs 6 for each group, most of the emitted light from each LED 6 in the lighting-controlled group is adjusted by the single convex lens 6a. By being illuminated, the light advances in the gap 10 within a predetermined radiation angle with respect to the normal direction of the LED 6. These lights reach the diffusion plate 8 while being mixed in the gap 10, and contribute mainly to the light emission of the corresponding light emitting region 12 a and also to the light emission of a predetermined region around it. On the other hand, a part of light emitted at a large radiation angle with respect to the normal direction of the LED 6 without being appropriately dimmed by the single convex lens 6a, a part of light reflected by the diffusion plate 8, and the like are mounted on the mounting surface 5a. Most of these lights are absorbed as they are. That is, since the reflectance R1 of the mounting surface 5a is set to a small reflectance (for example, R1 = 5%), most of the light reaching the mounting surface 5a is absorbed as it is. Therefore, the light emitted from each LED 6 is accurately prevented from being diffused over a wide range more than necessary in the gap 10, and the luminance control for each desired light emitting region 12a can be realized without a sense of incongruity.

  Similarly, even when all the LEDs 6 are controlled to be turned on by the lighting circuit 15 so that the light emitting surface 12 emits light entirely, the emitted light from each LED 6 is similarly diffused in the gap 10 over a wide range more than necessary. It contributes mainly to the light emission of the corresponding light emitting region 12a, and also contributes to the light emission of a predetermined region around it. Thereby, the light from LED6 of the adjacent light emission area | region 12a complements mutual light emission, and generation | occurrence | production of the brightness nonuniformity in the boundary vicinity of each light emission area | region 12a is suppressed. Here, since there is no adjacent light emitting region 12a at the end (edge) on the light emitting surface 12, complementation from the surrounding LED 6 cannot be expected, but the reflectance R2 of the inner peripheral surface 7a of the frame 7 is Since the large reflectance (for example, R2 = 95%) is set, a part of the light from the LED 6 located at the end is reflected by the inner peripheral surface 7a and emitted from the end of the self light emitting region 12a. To complement. Thereby, it is possible to suitably suppress luminance unevenness when the light emitting surface 12 emits light over the entire area.

  Here, FIG. 4 shows light emission when the above-described backlight device 1 in which the reflectance R1 of the mounting surface 5a is set to 5% and the reflectance R2 of the inner peripheral surface 7a is set to 95% (non-mirror surface) is caused to emit light entirely. 7 is a simulation result of the luminance distribution over the entire surface 12, and a broken line A in FIG. 7 is a simulation result of the luminance distribution of the backlight device 1 along the line III-III in FIG.

  Further, FIG. 5 shows the entire area of the light emitting surface 12 when the above-described backlight device 1 having the mounting surface 5a having a reflectance R1 of 5% and the inner peripheral surface 7a having a mirror surface having a reflectance R2 of 95% emits light. The broken line B in FIG. 7 is the simulation result of the luminance distribution of the backlight device 1 along the line III-III in FIG.

  On the other hand, FIG. 6 shows the above-described backlight device 1 when the reflectance R1 of the mounting surface 5a is maintained at 5% and the reflectance R2 of the inner peripheral surface 7a is changed to 5% to emit light entirely. FIG. 7 shows a simulation result of luminance distribution over the entire light emitting surface 12 as a comparative example, and a broken line C in FIG. 7 shows the line III-III in FIG. 2 of the backlight device 1 after changing the reflectance R2. The simulation result of the luminance distribution along is shown as a comparative example.

  As apparent from these comparisons, the reflectance R1 of the mounting surface 5a is set to a low reflectance, and the reflectance R2 of the inner peripheral surface 7a is relatively higher than the reflectance R1 of the mounting surface 5a. By setting to, it is possible to suppress the occurrence of a dark portion at the end portion of the light emitting surface 12, and to emit light with high brightness uniformity over the entire region. Furthermore, by using the inner peripheral surface 7a as a mirror surface, it is possible to further improve the luminance uniformity when the entire light emitting surface 12 emits light.

  By the way, in the above-described backlight device 1, 8 × 8 LEDs 6 are evenly arranged, and each light emitting region 12 a on the light emitting surface 12 divided into 16 equal parts is caused to emit light using 2 × 2 LEDs 6. However, the number of the LEDs 6 for each light emitting area 12a, the arrangement of the LEDs 6, the shape of the light emitting area 12a, the number of the light emitting areas 12a, etc. are arbitrarily determined depending on the size and resolution of the liquid crystal display device to be applied. It is possible to change.

  For example, as shown in FIGS. 8 and 9, 10 × 10 LEDs 6 can be used, and each light emitting region 12 a on the light emitting surface 12 divided into 25 equal parts can be emitted using 2 × 2 LEDs 6. It is.

  Further, for example, the interval d2 between the LEDs 6 adjacent to each other in the group corresponding to the light emitting region 12a can be set relatively larger than the interval d1 between the LEDs 6 adjacent in the same group. With this configuration, for example, when only one light emitting area 12a of the backlight device 1 emits light, the amount of direct “leakage light” from the LED 6 with respect to another adjacent light emitting area 12a is suppressed. be able to. Thereby, it becomes possible to make the brightness area control by the lighting control of each LED 6 clear.

  On the other hand, when it is desired to suppress excessive clarification of the light emitting section, the light for causing the peripheral region of the corresponding light emitting region 12a to emit light can be supplemented by setting the reflectance R1 of the mounting surface 5a high. . And the utilization efficiency of the light radiate | emitted from LED6 can be improved by raising the reflectance R1 of the mounting surface 5a in this way. Even in this case, the relationship between the reflectances of the mounting surface 5a and the inner peripheral surface 7a is set to R1 <R2 in order to suppress luminance unevenness when the entire light emitting surface 12 emits light. Of course.

  According to such a configuration, for example, as indicated by a broken line in FIG. 10, the relative luminance characteristics (FIG. 10) when all the LEDs 6 are evenly arranged while improving the utilization efficiency of the light emitted from the LEDs 6. It is possible to obtain a relative luminance characteristic substantially equivalent to that indicated by a solid line.

  In the above-described embodiment, an example in which an LED is used as a light emitting element has been described. However, the present invention is not limited to this, and for example, an organic EL or the like can also be used as a light emitting element.

An exploded perspective view showing the main part of the backlight device Plan view of backlight device Cross-sectional view of essential parts along the line III-III in FIG. Explanatory drawing which shows typically the simulation result of the luminance distribution when the backlight apparatus which set the reflectance of the mounting surface to 5% and the reflectance of the inner peripheral surface is set to 95% is caused to emit light entirely. Explanatory drawing which shows typically the simulation result of the luminance distribution when the backlight apparatus which set the reflectance of the mounting surface to 5% and the inner peripheral surface is set to a mirror surface having a reflectance of 95%, and emits light entirely. As a comparative example, an explanatory view schematically showing a simulation result of luminance distribution when the backlight device having the reflectance of the mounting surface and the reflectance of the inner peripheral surface set to 5% emits light over the entire surface. Explanatory drawing which shows the simulation result of each luminance distribution along the III-III line | wire of FIG. 2 when a backlight apparatus is made to light-emit the whole surface. The top view which shows the modification of a backlight apparatus Cross-sectional view of essential parts along the line IX-IX in FIG. Explanatory drawing which shows the simulation result of the luminance distribution along the IX-IX line of FIG. 8 when the backlight device emits a region.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Backlight apparatus, 2 ... Light source unit, 5 ... Mounting board, 5a ... Mounting surface, 6 ... Light emitting diode (light emitting element), 6a ... Single convex lens, 7 ... Frame, 7a ... Inner peripheral surface, 8 ... Diffusing plate (Optical member)), 9 ... bezel, 10 ... gap, 11 ... optical sheet, 12 ... light emitting surface, 12a ... light emitting region, 15 ... lighting circuit, R1 ... reflectance (reflectance of mounting surface), R2 ... reflectance (Reflectance of inner peripheral surface), d1... Interval (interval of light emitting elements in a group), d2... Interval (interval of light emitting elements between groups)

Claims (4)

An optical member having a light emitting surface set on the outer surface side;
A mounting substrate whose mounting surface is opposed to the inner surface of the optical member;
A plurality of light emitting elements mounted on the mounting surface;
A frame that surrounds the light emitting element group and forms a gap between the optical member and the mounting substrate;
The backlight device characterized in that the reflectance of the mounting surface is set smaller than the reflectance of the inner peripheral surface of the frame.   The backlight device according to claim 1, wherein an inner peripheral surface of the frame is a mirror surface.   The backlight device according to claim 1, wherein the plurality of light emitting elements are grouped for each of a plurality of regions set on the light emitting surface, and lighting control is performed for each group.   The backlight device according to claim 3, wherein an interval between the light emitting elements in the group is set to be relatively smaller than an interval between the light emitting elements between the adjacent groups.

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