JP2008282744A - Backlight device and display device equipped with above - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize thinning of a backlight device and a display device with luminance unevenness restrained irrespective of an arrangement state of a light source. <P>SOLUTION: The backlight device is provided with a light source 11 made of a plurality of light-emitting diodes and a diffusion plate arranged in opposition to the light source 11 with a given interval onto a floodlight direction of the light source 11, and make the light emitted from the light source 11 to be diffused. The diffusion plate is provided with a dot pattern 20 with dots 21 dotted having the same areas made of ink containing white pigment formed on an opposition face to the light source 11. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a backlight device using an LED as a light source and a display device including the backlight device.

  Backlight devices used in liquid crystal display devices and the like are classified into an edge light type and a direct type depending on the arrangement position of the light source. In the edge light type backlight device, the light source is arranged at the end of the display screen. Then, surface light is emitted from the light emitted from the light source using a light guide formed of a transparent resin. On the other hand, in the direct type backlight device, the light source is arranged behind (directly below) the display screen. Then, surface light is emitted by diffusing light emitted from the light source using a diffusion plate.

  The direct type backlight device is superior to the edge light type backlight device in terms of high surface brightness and reduced product weight. For this reason, most backlight devices employed in liquid crystal display devices whose display screen size has been increasing in recent years are direct type backlight devices.

For example, Patent Documents 1 to 3 disclose direct-type backlight devices.
Specifically, Patent Document 1 discloses a backlight device including a uniform plate in addition to a diffusion plate. FIG. 13 is a perspective view of the backlight device of Patent Document 1. FIG. In this backlight device, a plurality of light emitting diodes (LEDs) 111 are arranged in a grid pattern, and a diffusion plate 112 and a uniform plate 113 are provided in this order so as to block and cover the light from the light emitting diodes 111. . The diffusion plate 112 diffuses the light of the light emitting diode 111, and the uniform plate 113 makes the illuminance of the light diffused by the diffusion plate 112 uniform on the uniform plate 113. In the backlight device, by providing the uniform plate 113, an increase in size of the device is suppressed while suppressing glare of the light source.

  Patent Document 2 discloses a backlight device that suppresses luminance unevenness (brightness / darkness) by arranging light sources in a lattice shape or a triangular shape.

Patent Document 3 discloses a backlight device in which a dimming dot pattern for making the luminance uniform is formed in the light projecting direction of the light source.
JP 2003-187605 A (published July 4, 2003) JP 2006-310043 A (published on November 9, 2006) Japanese Patent Laying-Open No. 2005-117023 (released on April 28, 2005)

  However, the backlight devices of Patent Documents 1 to 3 have a problem that the backlight device cannot be thinned while suppressing luminance unevenness regardless of the light source arrangement.

  Specifically, in the direct type backlight device, the spatial distance between the light source and the diffusion plate (see A in FIG. 13) is maintained until the luminance unevenness is reduced in order to prevent uneven luminance from occurring on the display screen. There is a need. This spatial distance varies depending on the haze value (total light transmittance) of the diffusion plate and the thickness of the diffusion plate.

  Here, if the spatial distance between the light source and the diffusion plate necessary for alleviating the luminance unevenness can be shortened, the backlight device can be thinned. If the number of light sources (LEDs) is increased, the distance between adjacent light sources is shortened, so that uneven brightness is reduced. For this reason, the spatial distance between the light source and the diffusion plate can be shortened. However, if a large number of light sources are arranged, the cost of the light source and the drive system for driving the light source is increased, so the practicality is low.

  In addition, if the haze value (total light transmittance) of the diffusion plate is reduced to sacrifice the light utilization efficiency to reduce the luminance unevenness, the luminance of the display screen is lowered. Furthermore, if the diffusion plate is made thicker, it is not possible to reduce the thickness even if the luminance unevenness can be reduced.

  On the other hand, in Patent Documents 1 and 2, luminance unevenness is suppressed by optimizing the light source arrangement (arranged at the vertices of a lattice or a triangle). For this reason, the freedom degree of the layout of a light source is very low.

In Patent Document 3, although the light source arrangement can be freely set, the luminance unevenness is not sufficiently suppressed, and the backlight device cannot be thinned. FIG. 14 is a diagram showing a dimming dot pattern in the backlight device of Patent Document 3. As shown in FIG. As shown in FIG. 14, in Patent Document 3, a dot pattern composed of a plurality of dots 123 is formed in each unit of the light source units 121a. Moreover, when the LED is used as the light source 121, one dot 123 is formed at a point immediately above the light source 121, and the area of the dot 123 is required to be 28 to 86 mm ² . For this reason, almost all of the light source 121 is covered with the dots 123. However, it has been confirmed by the present inventors that with this size of dots 123, even if a diffusion sheet is further placed on the diffusion plate 122, unevenness due to the dots 123 will be visible. That is, the dots 123 that should have been provided to suppress luminance unevenness cause luminance unevenness.

  Therefore, in order to make dot printing invisible, it is necessary to provide another spatial distance on the diffusion plate 122 on which the dot pattern is formed, and to provide another diffusion plate. As a result, the backlight device cannot be thinned. It is also difficult to freely set the distance from the light source to the diffusion plate.

  In Patent Document 3, when a fluorescent tube is used as a light source, a dot pattern is formed on the entire surface of the diffusion plate. That is, in this case, the dot pattern is formed between the fluorescent tubes where the luminance is minimized. Therefore, luminance unevenness cannot be suppressed.

  The present invention has been made in view of the above-described problems, and an object thereof is to realize a backlight device and a liquid crystal display device capable of suppressing luminance unevenness regardless of the arrangement state of light sources. . Another object of the present invention is to reduce the thickness of the backlight device and the liquid crystal display device.

  In order to solve the above-described problem, the backlight device of the present invention is disposed opposite to the light source at a predetermined interval in the light projecting direction of the light source composed of a plurality of light emitting diodes, and diffuses the light emitted from the light source. The backlight device includes a diffusing plate, and the diffusing plate has a dot pattern in which dots having the same area made of ink containing a white pigment are scattered on a surface facing the light source.

  According to the above invention, the dot pattern of the ink containing the white pigment is scattered on the back surface (the surface facing the light source) of the diffusion plate. For this reason, the light emitted from the light source is diffused and reflected in the portion where the dot is formed, and is irradiated as it is in the portion where the dot is not formed. The areas of the dots forming the dot pattern are equal to each other. Thereby, the luminance distribution of the light source is made uniform by the dot pattern. Accordingly, luminance unevenness can be suppressed regardless of the arrangement state of the light sources. Moreover, even if the spatial distance from the light source to the diffusion plate is shortened, a dot pattern can be formed according to the shortening. For this reason, the spatial distance can be freely set, and unevenness in luminance can be suppressed according to the set spatial distance. Therefore, it is possible to reduce the thickness of the backlight device.

  Note that “dots having the same area” does not only mean that all the dots have the same area, but the areas that are substantially the same as long as the luminance distribution of the light source can be made uniform. Means that

  In the backlight device of the present invention, it is preferable that the dot pattern is formed so that the dot density decreases as the distance from the point immediately above each light source increases.

  According to the above invention, the dot density is formed so as to decrease from the point immediately above the light source where the luminance of the light source becomes maximum as the luminance decreases away from the light source. Thereby, it is possible to more reliably suppress luminance unevenness.

In the backlight device of the present invention, the dots are identified by a plurality of virtual regions that are adjacent to each other and have the same width, except for the innermost region including the point immediately above each light source.
The number of dots included in each of the plurality of regions is formed so that the number of dots per unit area decreases as the region is farther from the point immediately above the light source. It is preferable that the distance between adjacent dots be equal.

  According to the above invention, a dot is identified for each of a plurality of virtual regions centered on a point immediately above each light source. The plurality of regions are adjacent to each other and have the same width. That is, each region is formed concentrically around the point on each light source.

  In addition, the number of dots per unit area included in each region decreases as the distance from the light source increases (that is, the region with relatively low luminance). In addition, the interval between adjacent dots in the same region is equal. That is, a suitable dot pattern according to the luminance distribution of the light source is formed.

  Accordingly, the dot pattern diffuses the light in the maximum luminance region of the light source (a point immediately above the light source) and irradiates the minimum luminance region with the light reflected by the dot. That is, not only the light in the maximum luminance region of the light source (the point directly above the light source) is diffused, but also the light reflected by the dots is added in the minimum luminance region. Accordingly, it is possible to more reliably suppress luminance unevenness. In addition, a reduction in luminance can be prevented.

  In the backlight device of the present invention, it is preferable to include a reflecting plate that reflects light reflected by the diffusing plate to the diffusing plate between adjacent light sources. According to the above invention, the light reflected by the dot pattern and the diffusion plate is reflected again by the reflection plate to the diffusion plate. Therefore, the light reflected to the light source side by the diffusion plate and the dots can be reused.

In the backlight device of the present invention, the dot diameter of each dot is preferably 1 mm or less. In the backlight device of the present invention, the area of each dot is preferably 0.8 mm ² or less.

According to each of the above-described inventions, by setting the diameter of each dot to 1 mm or less and / or the area of each dot to 0.8 mm ² or less, the dots themselves can be reliably prevented from becoming uneven, and more reliably. Brightness unevenness can be suppressed. The dot diameter indicates the maximum distance between two points on the dot. For example, when the dot is circular, it is literally the diameter, and when it is elliptical, it is the long diameter.

In addition, when the diameter of each dot is 1 mm or more, or the area of each dot is 0.8 mm ² or more, unevenness of the dot itself becomes noticeable, leading to a display defect.

  In the backlight device of the present invention, the light sources are preferably arranged so that the distance between adjacent light sources is the same. Thereby, the dot pattern set with respect to one certain light source can be utilized with respect to all the light sources. Therefore, luminance unevenness can be effectively suppressed and dot pattern formation can be simplified.

  The display device of the present invention includes any one of the backlight devices described above as an irradiation device for irradiation from the back side of the display screen. According to the above-described invention, since the backlight device of the present invention is provided, it is possible to provide a display device that can suppress luminance unevenness and can be thinned regardless of the arrangement state of the light source.

  As described above, the present invention has a configuration in which the diffusion plate is provided with a dot pattern in which dots made of ink containing a white pigment are scattered on the surface facing the light source. Therefore, the luminance unevenness can be suppressed regardless of the arrangement state of the light source, and the backlight device and the display device can be thinned.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 2 is a cross-sectional view of the backlight device 1 according to the embodiment of the present invention. The backlight device 1 is a surface-emitting illumination device that uses an LED as a light source, and is used in a liquid crystal display device (display device) or the like.

  As shown in FIG. 2, the backlight device 1 includes a light source 11, a diffusion plate 12, a diffusion sheet 13, a prism sheet 14, and a polarization reflection sheet 15 arranged in this order in a housing 16. Further, the polarization reflection sheet 15 is disposed on the display screen side of the liquid crystal display device. That is, the backlight device 1 is a so-called direct-type backlight device in which the light source 11 is disposed on the back surface of the display screen (liquid crystal panel).

  The light source 11 includes a plurality of light emitting diodes (LEDs), and emits light from the back surface of the display screen. In the present embodiment, the color and arrangement state of the LEDs are not particularly limited. Between the light sources 11 adjacent to each other, a reflection plate 17 that reflects light from the light source 11 in the direction of the display screen is formed. As a result, the light reflected by the diffusion plate 12 is reused as the light irradiated to the diffusion plate 12. Here, the reflecting plate 17 preferably has a high reflectance with respect to visible light. For example, an aluminum foil, a resin or the like subjected to silver plating, or a white paint applied thereto is preferably used.

  The diffusion plate 12 causes surface emission by diffusing the light emitted from the light source 11. The diffusion plate 12 diffuses the light emitted from the light source 11 in the surface direction, thereby making the luminance unevenness of the light source 11 inconspicuous. The diffusion plate 12 is made of, for example, a polycarbonate resin, an acrylic resin, or the like. The material, thickness, haze value, etc. constituting the diffusion plate 12 are not particularly limited. A dot pattern for suppressing luminance unevenness is formed on the back surface of the diffusing plate 12 (the surface facing the light source 11). The dot pattern will be described later.

  The diffusion sheet 13 is for changing the light emission angle irregularly to improve the luminance in the normal direction, and to make the luminance unevenness of the light source 11 more inconspicuous. The prism sheet 14 improves the luminance in the normal direction by regularly changing the light emission angle. The polarization reflection sheet 15 is for increasing the transmitted light of the display screen.

  In such a backlight device 1, when the spatial distance A between the light source 11 and the diffusion plate 12 is reduced (narrowed), uneven luminance (brightness / darkness of luminance) occurs on the display screen. For this reason, the spatial distance A between the light source 11 and the diffusion plate 12 needs to be maintained to such an extent that luminance unevenness is eliminated. This spatial distance A is one cause that prevents the backlight device 1 from being thinned, and hence the liquid crystal display device from being thinned.

  Therefore, in order to reduce the spatial distance A, a dot pattern is formed on the back surface of the diffusion plate 12 (the surface facing the light source 11). Thereby, while suppressing the brightness nonuniformity in the backlight apparatus 1, it becomes possible to respond | correspond to the request | requirement of thickness reduction, suppressing the fall of a brightness | luminance as much as possible.

  FIG. 1 is a diagram showing a dot pattern 20 formed on the back surface of the diffusion plate 12. The dot pattern 20 is composed of a plurality of dots 21 that do not overlap each other. In the present embodiment, the dot pattern 20 has a shape in which a plurality of dots 21 are radially scattered around the light source 11. Moreover, in this embodiment, each dot 21 is circular, and the area of each dot 21 is mutually equal. A method for setting the dot pattern 20 will be described later.

  With such a dot pattern 20, the light emitted from the light source 11 is diffused by the dots 21 and reflected toward the light source 11. On the other hand, in the area where the dots 21 are not formed, the light from the light source 11 is irradiated as it is without being diffused. As described above, the backlight device 1 includes the reflecting plate 17. For this reason, the light reflected by the dots 21 toward the light source 11 is diffused again toward the diffusion plate 12 by the reflection plate 17.

  The dot pattern 20 is set according to the luminance distribution of the light source 11. That is, the dots 21 are densely formed in the high luminance region, and the light from the light source 11 is diffused and reflected. On the other hand, the dots 21 are formed sparsely in the low luminance area, and the light from the light source 11 is irradiated as it is, and the light reflected by the dots 21 is also added, so that the light from the light source 11 is effectively used.

  The dots 21 are not particularly limited as long as they are made of ink containing a white pigment. This is because white means high reflectivity for all visible light. Further, since the dot pattern 20 is formed according to the composition of the ink, the concentration of the white pigment is not particularly limited. The ink is a white pigment composed of, for example, a reflective agent such as titanium oxide, a diffusing agent such as silica, and a fixing agent such as an organic synthetic resin. The light incident on the diffuser is reflected by the reflectivity of the ink. Moreover, if the light-shielding agent and the diffusing agent are further included, the light incident on the diffusing plate can be effectively diffusely reflected.

  Thus, since the dot 21 contains a white pigment, the light of the light source 11 incident on the dot 21 is reflected by the white pigment. That is, the white pigment is not particularly limited as long as it reflects light.

The size and area of the dots 21 are not particularly limited as long as they are set according to the composition and concentration of the ink containing the white pigment. However, as will be described later, when the dots 21 are circular, the diameter (diameter) of each dot is preferably 1 mm or less, and the area of each dot 21 is preferably 0.8 mm ² or less. . That is, the expected angle from the light source 11 is preferably about 2 ° to 4 °. Note that the prospective angle is an angle formed by a straight line connecting one point on the light source 11 and two points on the circumference of the dot 21 that is the diameter of the dot 21.

  Note that the diameter of the dot 21 may be set according to conditions such as the arrangement position of the dot 21 and the necessary density of the dot 21, for example. The diameter of the dot 21 is more preferably 0.8 mm to 1.0 mm, 0.6 mm to 0.8 mm, or 0.4 mm to 0.6 mm, depending on each condition.

  Here, a setting method of the dot pattern 20 will be described. The dot pattern 20 can be formed by printing. FIG. 3 is a light distribution characteristic diagram of an LED (a diagram representing the radiation angle dependency of luminance). As shown in FIG. 3, the LED generally has the highest luminance direction directly above the light source, and has an axially symmetric luminance distribution with the immediately upper direction as the central axis. Further, the luminance decreases as the angle from the central axis increases, and in FIG. 3, it is ½ of the optical axis direction at about 60 degrees. Further, in FIG. 3, the change in luminance is described in a polygonal shape for the convenience of drawing and actually changes smoothly. In the backlight device 1, the arrangement of the light sources 11 can be arbitrarily set and is not particularly limited. However, when the light source 11 has the light distribution characteristic as shown in FIG. 3, it is preferable to arrange the light source 11 so that the pitch between the adjacent light sources 1 (light source pitch B) is the same (equal pitch). It is more preferable that the light source 11 is arranged in a regular hexagonal shape. Thereby, luminance unevenness can be effectively suppressed and the formation of the dot pattern 20 can be simplified.

  The arrangement of the light sources 11 is not limited to the regular hexagonal shape as shown in FIG. 4, but may be a dot arrangement that takes into account the luminance ripple with the adjacent light sources 11 in the xy direction. In this case, dots are arranged not on the circumference of a perfect circle as shown in FIG. 4 but on the circumference of an ellipse.

  Here, the dot pattern 20 is formed according to the number of the light sources 11 and the distance between the adjacent light sources 11. Then, the spatial distance A between the light diffusing plate 12 on which the dot pattern 20 is formed and the light source 11 is set to such an extent that the luminance unevenness can be regarded as reduced. Thereby, the spatial distance A can be shortened compared with the case where the dot pattern 20 is not formed.

  More specifically, in the backlight device 1, the spatial distance A between the light source 11 and the diffusion plate 12 is set to such an extent that the luminance unevenness is reduced. For example, when the distance between the adjacent light sources 11 (light source pitch B) is set to 41 mm, the spatial distance (diffusion distance) A at which the luminance unevenness is reduced is 34.3 mm. 6 and 7 are graphs showing the luminance distribution when the dot pattern 20 is not formed.

  FIG. 5 is a diagram showing measurement points of the luminance distribution in FIGS. 6 and 7. Here, as shown in FIG. 4, the light source 11 is arranged in a hexagonal shape with a certain light source 11 as the center, and the luminance of each point in the vertical axis direction and the horizontal axis direction of the central light source 11 is measured. As a result, as shown in FIGS. 6 and 7, the luminance ratio when the luminance at the center of the light source 11 is 100% is 95% or more in both the vertical axis direction and the horizontal axis direction. For this reason, this state can be said to be a state in which the luminance unevenness is alleviated.

  Next, data necessary for determining the dot pattern 20 is extracted under such conditions. That is, first, the luminance distribution at the target spatial distance (diffusion distance) A is measured on the diffusion plate 12 without printing. That is, the luminance distribution in the plane is measured while the focal point is shifted little by little in the plane with the focus of the camera for luminance measurement (not shown) being focused on the plane on which the dot pattern 20 of the diffusion plate 12 is formed.

  Next, the ink to be used (this time, a general white pigment ink is used) is applied to the entire surface of the diffusion plate 12, and the luminance distribution is measured. In the measurement of the luminance distribution, the amount of light reflected by the ink toward the light source 11 and the absorption characteristics of the ink are investigated. If the ink to be used is applied to the entire surface of the diffusion plate 12, luminance data before and after the ink application can be obtained. Therefore, the ink application on the entire surface is an important factor in determining the printing pattern.

  At this time, the luminance in an annular minute area dA having a width dr at a distance r from a point immediately above the light source 11 on the dot pattern forming surface as shown in FIG. 8 is considered. The minute area dA is a hatched portion in the figure. It is assumed that the luminance is equal everywhere in the minute area dA. Here, the distance r from the point immediately above one light source 11 is changed, and the luminance value in the minute area dA for each distance r is calculated. Further, in each minute area dA, luminance comparison before and after applying ink is performed.

  Here, FIG. 9 is a diagram for explaining a luminance difference between the light sources 11. When the light source 11 having the luminance distribution as shown in FIG. 3 is arranged in a regular hexagon as in the present embodiment, the light source 11 has the maximum luminance at a point immediately above the light source 11. On the other hand, the luminance becomes the minimum value at the center of gravity 22 of the triangle formed by the three light sources 11 as shown in FIG. In addition, the luminance of the center of gravity 22 at which the luminance is a minimum value has almost no difference from the luminance in the middle 23 of the adjacent light sources 11. Accordingly, the range in which the distance r is changed is a range from a point immediately above the light source 11 to an intermediate 23 between the adjacent light sources 11.

  Then, based on the brightness comparison before and after the ink application, the dot pattern required so that the brightness (maximum brightness) of the point immediately above the light source 11 and the brightness (minimum brightness) at the center of gravity 22 are comparable. The area for forming 20 is calculated. Based on this calculation result, the layout of the dots 21 in the dot pattern 20 is determined. At this time, care is taken so that the dots 21 do not overlap.

  FIG. 10 is a diagram showing an example of the layout of the dots 21 determined based on FIG. In FIG. 10, except for the innermost region including the point immediately above the light source 11, the dot 21 has a different distance r from the point immediately above the light source 11, and is identified by a plurality of minute regions dA. Each minute region dA is formed concentrically with a point immediately above the light source 11 as the center. Further, these minute areas dA are adjacent to each other, and the width W of each minute area dA is equal. As the number of dots 21 included in each minute area dA is farther from a point immediately above the light source 11, the number of dots per unit area decreases. Moreover, when attention is focused on one minute area dA, the intervals between adjacent dots 21 in the minute area dA are equal. Note that the minute area dA indicated by the solid line in FIG. 10 is a virtual area.

  Specifically, in FIG. 10, dots 21 are formed for each minute region dA having a distance r from the light source 11 around the light source 11. Here, the diameter of the dot 21 is unified to 1 mm. For this reason, the difference in the distance r (the pitch of Δr) between the adjacent minute regions dA is set so that the dots 21 do not overlap. In addition, the dots 21 are arranged in consideration of the distance from the point immediately above the light source 11 to the adjacent light source 11. The dots 21 are arranged in the same minute area dA so that the dots 21 are neither sparse nor dense, and the distance between the dots 21 is substantially constant.

  Here, a light source 11 having a light distribution characteristic as shown in FIG. 3 is used, and each light source 11 has the same light distribution characteristic. For this reason, if the dot pattern 20 is determined for one light source 11, the dot pattern 20 can be applied to all the light sources 11.

  Strictly speaking, actually, the luminance distribution of the individual light sources 11 varies. For this reason, it is preferable to set the dot pattern 20 for each light source 11. However, even when the dot pattern 20 is determined by the light source 11 and the dot pattern 20 is applied to another light source 11, the variation in the luminance distribution of the backlight device 1 is practically negligible. Accordingly, setting of the dot pattern 20 for each light source 11 is not essential.

Further, when the dot 21 has a perfect circle shape, first, the range of each minute area dA is determined, and the diameter (diameter) of the dot 21 in each minute area dA is determined. The diameter of the dot 21 is not particularly limited because it varies depending on the difference in diffusion and reflection function depending on the type of ink, but the diameter is preferably 1 mm or less. The area of each dot 21 is preferably 0.8 mm ² or less. Thereby, it is possible to reliably prevent the dot pattern 20 (each dot 21) itself from appearing on the display screen as unevenness.

  Next, the number of dots 21 (number of circle dots) necessary for the minute area dA is determined from the area value where the dots 21 need to be formed in each minute area dA based on the determined circle diameter. If the required number of dots 21 is determined, then the central angle between the adjacent dots 21 is obtained from the expression “circumference (360 °) / number of dots 21”. And the dot 21 is arrange | positioned in the micro area | region dA so that the pitch between the adjacent dots 21 may become equal pitch. Further, here, it is preferable that the interval between adjacent minute regions dA (in the R direction in FIG. 8) is also set to an equal pitch.

  Next, the luminance distributions according to the presence / absence of the dot pattern 20 as shown in FIG. 10 determined as described above were compared. 11 and 12 are graphs showing the comparison results. Note that the measurement points of the luminance distribution are as shown in FIG. When the dot pattern 20 is formed as shown in FIGS. 11 and 12, the spatial distance A between the light source 11 and the diffusion plate 12 may be set to 23 mm, which is shorter than in the case of FIGS. The brightness unevenness could be suppressed. Therefore, a thinner backlight device could be realized. On the other hand, when the dot pattern 20 is not formed, luminance unevenness cannot be suppressed when the spatial distance is 23 mm.

  Thus, in the backlight device 1 of this embodiment, the uneven brightness can be suppressed by the dot pattern 20. Since the dot pattern 20 may be set according to the luminance distribution of the light source 11, luminance unevenness can be suppressed regardless of the arrangement state of the light source 11. In other words, since the dot pattern 20 may be set according to the spatial distance A from the light source 11 to the diffuser plate 12, the spatial distance A can be freely set, and the luminance unevenness according to the set spatial distance A. Can be suppressed. Therefore, since the spatial distance A between the light source 11 and the diffusion plate 12 can be shortened, the backlight device 1 can be thinned.

  In addition, since the dot pattern 20 is formed so that the density of the dots 21 decreases as the distance from the point immediately above the light source 11 increases, luminance unevenness can be more reliably suppressed. Furthermore, the dot pattern 20 as shown in FIG. 10 not only diffuses the light in the maximum luminance region of the light source 11 (a point directly above the light source), but also adds the light reflected by the dots 21 in the minimum luminance region. Therefore, it is possible to more surely suppress the luminance unevenness and to prevent a decrease in luminance.

  In addition, what is necessary is just to set the dot pattern 20 according to the material which comprises the diffusion plate 12, thickness, a haze value, etc., and the shape is not specifically limited. That is, the dot pattern 20 may be formed by performing dot printing so as to obtain a preferable dot density according to the diffusion plate 12.

  The haze value indicates the degree of cloudiness or the degree of diffusion, and can also be referred to as the haze value. The smaller the haze value, the more easily the transmitted light becomes visible (for example, haze value 20%: transmittance 80%), and the larger the value (for example, haze 80%: transmittance 20%), the greater the diffused light, The transmitted light becomes difficult to see. That is, it can be said that increasing the haze value increases the diffusion effect.

  Further, when such a dot printing process is performed on the surface of the diffusion plate 12 (the surface on the display screen side), the unevenness of the dot pattern 20 can be seen as it is on the display screen. This is because the light incident on the diffusing plate is reflected by the dot printing portion on the surface side of the diffusing plate, resulting in a difference in brightness where the dots are present. For this reason, the dot pattern 20 is formed on the back surface (the light source 11 side) of the diffusion plate 12.

  Note that the backlight device 1 suppresses uneven brightness by the dot pattern 20. That is, the dot pattern 20 corresponding to the luminance (brightness) of each light source 11 may be formed. Here, the luminance unevenness is a parameter different from the color unevenness. What is suppressed by the dot pattern 20 is merely luminance unevenness of the light source 11 and not color unevenness. For this reason, the color of LED which comprises the light source 11 may be the same, or may differ.

  In the present embodiment, the case where a dot pattern is formed with respect to a uniform surface light source has been described. However, if the dot arrangement state (number of dots or dot density in the minute area dA, etc.) is changed, the luminance unevenness can be controlled only at a certain place, or a special luminance distribution (luminance unevenness) can be intentionally formed. It becomes possible. Conventionally, in order to realize an arbitrary luminance distribution (special luminance distribution), it is necessary to provide independent drive circuits for a plurality of light sources so as to achieve a target luminance distribution, leading to high costs. However, in the present invention, since the luminance distribution can be arbitrarily set by the dot pattern, an independent drive circuit is unnecessary and the cost is not increased.

  The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims. In other words, embodiments obtained by combining technical means appropriately changed within the scope of the claims are also included in the technical scope of the present invention.

  The present invention can be used for lighting devices in general, including direct-type backlight devices used in liquid crystal display devices such as televisions and monitors.

It is a figure which shows the dot pattern in the backlight apparatus of this invention. It is sectional drawing which shows schematic structure of the backlight apparatus of this invention. It is a figure which shows the light distribution characteristic of a LED light source. It is a figure which shows the arrangement | positioning state of the light source in the backlight apparatus of FIG. It is a figure which shows the measurement point of the luminance distribution centering on a certain light source. It is a graph which shows the luminance distribution of the horizontal axis direction of FIG. 5 when not forming a dot pattern. It is a graph which shows the luminance distribution of the vertical axis | shaft direction of FIG. 5 when not forming a dot pattern. It is a figure explaining the setting method of a dot pattern. It is a figure explaining the brightness | luminance difference between light sources. It is a figure which shows the dot pattern set based on FIG. It is a graph which shows the luminance distribution of the horizontal axis direction of FIG. 5 at the time of forming a dot pattern. It is a graph which shows the luminance distribution of the vertical axis | shaft direction of FIG. 5 at the time of forming a dot pattern. FIG. 11 is a perspective view of a backlight device of Patent Document 1. It is a figure explaining the dot pattern for light control in the backlight apparatus of patent document 3. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Backlight apparatus 11 Light source 12 Diffusion plate 13 Diffusion sheet 14 Prism sheet 15 Polarization reflection sheet 16 Case 17 Reflection plate 20 Dot pattern 21 Dot 22 Center of gravity 23 Midpoint A Spatial distance B Light source pitch dA Minute area (virtual area)
W width

Claims (8)

A light source comprising a plurality of light emitting diodes;
A backlight device provided with a diffusion plate that is disposed opposite to the light source at a predetermined interval in the light projecting direction of the light source and diffuses light emitted from the light source,
The diffuser plate is provided with a dot pattern in which dots having the same area made of ink containing a white pigment are dotted on a surface facing a light source.   2. The backlight device according to claim 1, wherein the dot pattern is formed so that the density of the dots decreases with increasing distance from a point immediately above each light source. The dots are identified by a plurality of virtual regions that are adjacent to each other and have the same width, except for the innermost region including the point immediately above each light source,
The number of dots included in each of the plurality of regions is formed so that the number of dots per unit area decreases as the region is farther from the point immediately above the light source. The backlight device according to claim 2, wherein the intervals between adjacent dots are equal.   The backlight device according to claim 1, further comprising a reflection plate that reflects light reflected by the diffusion plate to the diffusion plate between adjacent light sources.   The backlight device according to claim 1, wherein the dot diameter of each dot is 1 mm or less. The backlight device according to claim 1, wherein the area of each dot is 0.8 mm ² or less.   The backlight device according to claim 1, wherein the light sources are arranged such that a distance between adjacent light sources is the same.   A display device comprising the backlight device according to any one of claims 1 to 7 as an irradiation device for irradiation from the back side of the display screen.

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