权利要求：
1. Alighting device for emitting light comprising:
a base chassis;
a reflection sheet provided on the base chassis;
an optical element arranged at a predetermined distant position away from the reflection sheet in a direction in orthogonal to a light emitting surface of the lighting device;
a plurality of LEDs arranged in one row in a space between the reflection sheet and the optical element so as to emit light in a direction in parallel with the light emitting surface of the lighting device; and
an optical sheet provided on the light emitting surface side of the optical element,
wherein a light shielding pattern is provided at a position corresponding to each of the LEDs on the light emitting surface side of the optical element, and
the light shielding pattern is configured by stacking a plurality of light shielding layers in which a light shielding layer positioned closest to the optical element side among the light shielding layers has a ratio of white color higher than a ratio of white color of at least one of the other light shielding layers.
2. The lighting device
according to claim 1,
wherein the LED contains a phosphor, and has a configuration for emitting white light by excitation of the phosphor.
3. The lighting device according to claim 1,
wherein the light shielding layer positioned closest to the optical element side among the plurality of light shielding layers is made of a white ink, and at least one of the other light shielding layers is made of a mixed color ink of white and blue, or a mixed color ink of white, blue and black.
4. The lighting device according to claim 1,
wherein the light shielding pattern includes at least three light shielding layers, and, when it is assumed that the three light shielding layers are defined as a first layer, a second layer and a third layer sequentially from the optical element side toward the optical sheet side, the first layer is made of a white ink, and either one of the second layer and the third layer is made of a white ink, and the other one is made of a mixed ink of white and blue, or a mixed ink of white, blue and black.
5. The lighting device according to claim 1,
wherein the light shielding pattern includes at least two light shielding layers, and one light shielding layer positioned closest to the optical element among the two layers is made of a white ink, and the other light shielding layer is made of a mixed color ink of white and blue, or a mixed color ink of white, blue and black.
6. The lighting device according to claim 5,
wherein the light shielding pattern includes: a first pattern having an oval or elliptical shape provided correspondingly right above the LED; and a second pattern configured of a plurality of dots provided on periphery of the first pattern and configured so that a density of the dots per a unit area is lower as being distant away farther from the first pattern, and
one light shielding layer made of the white ink and positioned closest to the optical element includes the first pattern and the second pattern, and the other light shielding layer made of the mixed ink includes the first pattern.
7. The lighting device according to claim 1,
wherein the optical element is a diffusion plate.
8. The lighting device according to claim 7, further comprising:
an LED substrate on which the plurality of LEDs arranged in one row are mounted, a plurality of the LED substrates being arranged along a light emitting direction of the LED,
wherein one or a plurality of the diffusion plates are provided so as to correspond to the LED substrates, respectively.
9. The lighting device according to claim 8,
wherein a plurality of prisms are formed on a surface on the LED side of each of the diffusion plates.
10. The lighting device according to claim 9,
wherein each of the prisms has a triangular-shaped cross-sectional surface in orthogonal to the light emitting direction of the LED and is formed so as to extend in the light emitting direction of the LED, or has a triangular-shaped cross-sectional surface in parallel with the light emitting direction of the LED and also orthogonal to a surface of the optical element and is formed so as to extend in a direction orthogonal to the light emitting direction of the LED.
11. The lighting device according to claim 9,
wherein a roughened surface, a mirror surface or a taper surface is formed on an end surface or an end portion of the diffusion plate on the light emitting direction side of the LED.
12. The lighting device according to claim 9,
wherein a surface of the diffusion plate on which the prism is not formed is an crimped surface or a glossy surface.
13. Alighting device for emitting light comprising:
a base chassis;
a reflection sheet provided on the base chassis;
an optical element arranged at a predetermined distant position away from the reflection sheet in a direction in orthogonal to a light emitting surface of the lighting device;
a plurality of LEDs arranged in one row in a space between the reflection sheet and the optical element so as to emit light in a direction in parallel with the light emitting surface of the lighting device;
an optical sheet provided on the light emitting surface side of the optical element; and
an LED substrate on which the plurality of LEDs arranged in one row are mounted,
wherein a light shielding pattern is provided at a position corresponding to each of the LEDs on one surface of the diffusion plate, and a light propagation groove extending in a direction in parallel with a light emitting direction of the LED is formed on the other surface thereof.
14. The lighting device according to claim 13,
wherein the one surface of the diffusion plate is the light emitting surface of the diffusion plate, the other surface thereof is a light incident surface of the diffusion plate, the light shielding pattern is provided on the light emitting surface of the diffusion plate, and the prism for use in forming the light propagation groove is provided on the light incident surface of the diffusion plate.
15. The lighting device according to claim 14,
wherein, when it is assumed that an array pitch of the light propagation groove in a direction orthogonal to a light emitting direction of the LED is P, that a width in a longitudinal direction of the light emitting surface of the LED is La, that an array pitch of the LED is Lp, and that the number of the light propagation grooves within the width La is Na, a relation of “Lp/P≧Na≧Lp/La (note that Lp>La and Lp>P)” is satisfied.
16. The lighting device according to claim 14,
wherein, when it is assumed that a height of the prims is a, and that a distance between the light emitting surface of the diffusion plate and the incident surface of the optical sheet is h, a relation of “h≧a” is satisfied.
17. The lighting device according to claim 14,
wherein the light shielding pattern includes a plurality of dots, and, when it is assumed that an array pitch of the light propagation groove in a direction orthogonal to the light emitting direction of the LED is P, and that the minimum size of the dots of the light shielding pattern is Da, a relation of “3×Da>P≧Da/100” is satisfied.
18. The lighting device according to claim 14,
wherein the light shielding pattern includes a plurality of dots, and, when it is assumed that an array pitch of the light propagation groove in a direction orthogonal to a light emitting direction of the LED is P, that the minimum pitch of the dots of the light shielding pattern is Pd, and that the minimum space distance between the dots of the light shielding pattern is Ps, in a case of a transmittance Tr of the light shielding pattern in a range of 0.1%≦Tr<50%, a relation of “Pd≧P≧Ps” is satisfied.
19. The lighting device according to claim 14,
wherein two LEDs having different light emitting directions from each other are alternately arranged in one row, and the reflection sheet is provided with such a slope as tilting in the light emitting direction of the lighting device.
20. A video display device using the lighting device according to claim 1 as a backlight,
wherein light from the backlight is emitted to a liquid crystal panel so as to display video images.
具体实施方式：
[0037]Hereinafter, one embodiment of the present invention will be described in detail with reference to the accompanying drawings. Note that the following explanation will be made for explaining one embodiment of the present invention, and does not limit the scope of the present invention. Therefore, those who skilled in the art can apply an embodiment in which each component or all the components are replaced by a component(s) equivalent to the component(s), and these embodiments are included within the scope of the present invention.
[0038]Note that, in the following explanation of the embodiments, components having the same function/configuration are denoted by the same reference symbols throughout each drawing, and the repetitive description thereof will be omitted.
First Embodiment
[0039]FIG. 1 shows a developed perspective view showing a video display device and a lighting device according to a first embodiment of the present invention. The video display device of FIG. 1 is provided with a liquid crystal panel 10 serving as a display panel and a lighting device 100, and the lighting device is provided with a light source unit 11, a light shielding unit 12 and an optical sheet unit 13. The lighting device 100 is operated as a backlight for irradiating the liquid crystal panel 10 with light from the back surface of the liquid crystal panel 10. On the liquid crystal panel 10, light transmittance of each liquid crystal pixel is controlled by an input video signal, and light from the lighting device is spatially modulated in each liquid crystal pixel whose light transmittance has been controlled, so that video images are displayed thereon.
[0040]In the lighting device 100 according to the present embodiment, a light emitting diode (LED) for emitting white light is used as its light source. This white color diode has a configuration having, for example, yellow phosphor and an LED chip for emitting blue light for emitting white light by exciting the yellow phosphor by a part of the blue light from the LED chip, emitting light, and mixing yellow light from the yellow phosphor and the blue light from the LED chip. The LED to be applied to the present embodiment is not limited to have this configuration but may have any configuration as long as the LED emits light of a desired color by utilizing a phosphor.
[0041]Hereinafter, each component of the lighting device 100 will be described. However, prior to the description, each direction in FIG. 1 is defined as follows. A light emitting direction of the lighting device 100 is defined as a light emitting surface side of the lighting device 100, and an opposite direction to this direction is defined as a back surface side of the lighting device 100. Note that the light emitting surface of the lighting device 100 is defined as a front surface (light emitting surface) of each of various sheets forming the optical sheet unit 13. Moreover, an upward direction of the liquid crystal panel 10 or the lighting device 100 from which light of the LED2 is emitted is defined as a “+z” direction, and an opposite direction to this direction (that is, a downward direction of the liquid crystal panel 10 or the lighting device 100) is defined as a “−z” direction, a direction which goes from the back surface side (light source unit side) toward the light emitting side (optical sheet unit side) and which is also orthogonal to the “z” direction is defined as a “+y” direction; and an opposite direction to this direction (that is, a direction going from the light emitting surface side toward the back surface side) is defined as a “−y” direction. That is, the y direction is equal to the direction orthogonal to the light emitting surface of the lighting device 100, and the +y direction is referred to as a light emitting surface side direction, and the −y direction is referred to as a back surface side direction in some cases. Moreover, a direction which is orthogonal to a “yx” plane and which is a leftward direction when viewed from the light emitting surface side of the lighting device 100 is defined as a “+x” direction, and an opposite direction to this direction is defined as a “−x” direction. Hereinafter, the present embodiment will be explained by using this coordinate system, unless otherwise specified. Note that, when simply described as “light emitting surface side”, this indicates the light emitting surface side of the lighting device 100.
[0042]The light source unit 11 includes: an LED 2 serving as a light source, an LED substrate 3 serving as a light source substrate on which a plurality of the LEDs 2 are mounted; a reflection sheet 4; and a base chassis 7. As the LED 2, a white LED of a side-view type whose light emitting direction is in parallel with an electrode surface is used in the present embodiment, and is mounted on the LED substrate 3 so as to emit white light in the +z direction. That is, the light emitting direction of the LED is a direction in parallel with the light emitting surface of the lighting device, and, at the same time, is an upward direction of the orthogonal direction to the liquid crystal panel 10 or the lighting device 100 (a short-length direction or a longitudinal direction, which is an upward direction on a sheet of FIG. 1).
[0043]The LED substrate 3 includes a circuit element and a wiring for supplying power to the LED 2, and is a printed board made of, for example, a glass epoxy resin. Moreover, the LED substrate 3 has a laterally-elongated rectangular shape which extends in the x direction. That is, a longitudinal direction of the LED substrate 3 is equal to a horizontal direction of the liquid crystal panel 10 or the lighting device 100 (longitudinal direction or lateral direction, which is a right-and-left direction on a sheet of FIG. 1). A plurality of the LEDs 2 are arranged in one row along the longitudinal direction of the LED substrate 3. When the plurality of LEDs arranged in one row is assumed as an LED row, the LED substrate 3 can be also referred to as being formed so as to correspond to each of the LED rows. Moreover, an electric current to be supplied to each LED 2 is controlled by various circuits mounted on the LED substrate 3.
[0044]The base chassis 7 is made of metal having a high thermal conductivity, such aluminum or iron, and has a “masu (in Japanese)” (measuring box) shape or a box shape which is opened on the liquid crystal panel 10 side. Moreover, a plurality of the LED substrates 3 each having an inner surface (the light emitting side) with the plurality of LEDs 2 arranged thereon are arranged so as to have a predetermined interval in the z direction, and are fixed. In this manner, the plurality of LED rows are arranged along the light emitting direction (z direction) of the LED 2.
[0045]The reflection sheet 4 is used for directing the light traveling toward the back surface side to the light emitting surface side, and configured of, for example, a white plate-shaped resin sheet. The reflection sheet 4 is attached to an inner surface (light emitting surface side) of the base chassis 7 so as to be positioned closer to the back surface side than the LED 2. For example, the base chassis 7 is attached so as to, for example, sandwich the reflection sheet 4 by the base chassis 7 and the LED substrate 3. At this time, the front surface (surface on the light emitting surface side) of the LED substrate 3 is subjected to a reflection coating such as a white coating in order to enhance the reflection efficiency. Moreover, the LED substrate 3 is attached to the base chassis 7, a reflection sheet 4 provided with a hole corresponding to the LED 2 is covered above them, and the reflection sheet 4 may be attached to the base chassis 7 in a state in which the LED 2 is exposed on the hole of the reflection sheet 4. In this case, the front surface of the LED substrate 3 is covered with the reflection sheet 4, and therefore, the reflection coating onto the surface of the LED substrate 3 is unnecessary. However, it is preferred to form a step difference portion or a bent portion also on the reflection sheet 4 so as to correspond to a step difference between the LED substrate 3 and the base chassis 7. Moreover, the reflection sheet 4 may be individually provided on each of the inner surface (light emitting surface side) of the base chassis 7 and the front surface of the LED substrate 3.
[0046]The light shielding unit 12 contains the optical element 1 and the ink 6 serving as a light shielding pattern. The optical element 1 is a diffusion plate (hereinafter, this diffusion plate is referred to as “light-shielding-unit diffusion plate”) that is formed by mixing light diffusing particles or beads with a transparent resin such acrylic resin, polycarbonate, or polystyrene or by performing a surface roughening treatment on the light emitting surface or the back surface or both of the surfaces of a transparent resin. In this manner, the spatial light luminance uniformity on the light emitting side can be improved. Moreover, the ink 6 serving as the light shielding pattern has an optical function for reflecting or absorbing the light traveling toward the +y direction from the LED 2 so as to reduce the luminance of the light traveling toward the +y direction.
[0047]The optical sheet unit 13 is configured of one or a plurality of optical sheets 5. This optical sheet 5 is configured of one of a diffusion plate, a diffusion sheet, a u-lens sheet, a prism sheet having a light-converging effect and a luminance improving sheet that transmits predetermined polarization light while reflecting polarization components except for the polarization light, or configured of any combination of them. By using this optical sheet 5, light from the light shielding unit 12 is diffused and/or a component of the light traveling toward the light emitting surface side is increased, so that the spatial luminance uniformity and luminance on the light emitting side can be improved.
[0048]Here, the explanation will be further made for the ink 6 serving as the light shielding pattern in the light shielding unit 12. As described above, the LED 2 emits light in the +z direction on the side view-type LED, and the light is leaked upward (in the +y direction) from the package of the LED 2, and besides, the emitted light from the LED 2 is directed toward the +y direction by the reflection sheet 4 which is the closest to the light emitting side of the LED 2. Therefore, a so-called light spot (hot spot) is caused, the light spot being a portion in vicinity of a position of the LED 2 which is locally brighter than other position when viewed from the light emitting surface side of the lighting device 100. By a user, the hot spot is visually recognized as luminance unevenness. In order to prevent the luminance unevenness, by using the ink 6 serving as the light shielding pattern, the light quantity in the vicinity of the position of the LED 2 is reduced on the light emitting surface of the optical element 1 so that the brightness of the hot spot is reduced.
[0049]For this reason, the ink 6 is provided on positions corresponding to arrangement positions of the optical element (light-shielding-unit dispersion plate) 1 and the LED 2 and the peripheral positions (more particularly, on the light emitting side of the LED 2) thereof. The ink 6 is provided on the light emitting surface side (that is, the optical sheet unit 13 side) of the optical element 1 in the present embodiment. However, the ink may be provided on the back surface side (that is, the light source unit 11 side) of the optical element 1, or on both of the sides.
[0050]Details of the configuration of the ink 6 will be described with reference to FIGS. 2 and 3. FIG. 2 is an enlarged perspective view showing the LED 2 and the LED substrate 3 of the light source unit 11, and besides, a portion containing an optical unit agent 1 and the ink 6 serving as the light shielding pattern of the light shielding unit 12, when viewed from the -z direction side. Moreover, FIG. 3 is a front view showing the light-shielding-unit diffusion plate 1 of the light shielding unit 12 and a portion containing the ink 6 serving as the light shielding pattern when viewed in the +y direction (light emitting surface side), and is a view showing one example of the printed pattern of the ink 6.
[0051]The ink 6 serving as the light shielding pattern in the present embodiment includes: a first pattern 61 having an oval or elliptical shape whose longitudinal direction is the x direction and which has such a size as to cover the entire one LED 2 from the light emitting surface side; and a second pattern 62 having a fine dot which is arranged on the LED 2 on the light emitting direction side in the periphery of the first pattern 61.
[0052]Such a light shielding pattern is formed as, for example, shown in FIG. 3. In the enlarged view of the optical element 1 shown on the right side of FIG. 3, a plurality of fine squares shown in a left-and-down end region indicate virtual unit blocks. A density of the dot-shaped ink 6 in this unit block is changed depending on a position of the unit block as shown in, for example, an enlarged view of four unit blocks on the left side of FIG. 3. In the unit block in which the first pattern 61 is formed, a ratio (density) occupied by the ink 6 is 100% (that is, the unit block is solidly painted with the ink 6). A ratio (density) occupied by the ink 6 in a unit block in which the second pattern 62 is formed is changed depending on a distance from the first pattern 61 within a range from 80 to 10%. For example, as the distance from the first pattern 61 becomes larger or as it is farther separated therefrom, the density of the ink 6 in the unit block in which the second pattern 62 is formed is gradually made to be lower.
[0053]In this manner, a light shielding pattern having such a characteristic as to have the lowest light transmittance at a portion corresponding to the LED 2, and also as to gradually increase the light transmittance as separating further from the LED 2 in the light emitting direction of the LED 2 can be obtained. The light intensity of the above-described hot spot has such a characteristic as to be gradually decreased as further separating from the LED 2. Therefore, by configuring the light transmittance characteristics of the light shielding pattern so as to be matched with the characteristics of the hot spot as described above, the brightness of the hot spot can be favorably reduced. Note that the above-described unit block is virtual, and does not appear on the optical element 1. Furthermore, a size of the unit block and a size of the dot of the ink 6 can be appropriately changed depending on the combination of the optical configuration of the light source unit 11, the light emitting characteristics of the LED 2, the distance from the optical element 1 to the optical sheet unit 5, and the optical sheet.
[0054]In the lighting device having such a configuration, the present embodiment has the feature that the ink 6 serving as the light shielding pattern has a multi-layered structure obtained by stacking a plurality of light shielding layers (ink layers). The feature of the present embodiment will be described with reference to FIGS. 4 to 7.
[0055]FIG. 4 is a cross-sectional view in parallel with a “y-z” plane showing the stacked structure of the ink 6 serving as the light shielding pattern, more particularly, the first pattern of the first embodiment. In FIG. 4, the LED substrate 3 is arranged on the reflection sheet 4, and, for example, a white paint is applied onto the surface of the LED substrate 3. As described above, the configuration of the reflection sheet 4 is not limited to this. The optical element 1 (light-shielding-unit diffusion plate) is arranged with a predetermined distance in the +y direction so as to be opposed to the reflection surface of the reflection sheet 4 or the surface of the LED substrate 3. Therefore, between the reflection sheet 4 and the optical element 1, a space having the predetermined distance is formed. The LED 2 is arranged in this space, and the LED 2 emits light toward the +z direction in this space. That is, the optical axis of the LED 2 is in parallel with the surface of the reflection sheet 4 or the optical element 1 and with the z direction. The light emitted with a predetermined light emitting angle from the LED 2 in the +z direction is repeatedly reflected between the reflection sheet 4 and the optical element 1, and propagates in the +z direction in the space while the light is partially transmitted through the optical element 1. FIG. 4 illustrates only the light from the LED which directly travels toward the optical element 1 by using an arrow.
[0056]The light that directly travels from the LED toward the optical element 1 is partially reflected on a boundary surface between the optical element 1 and the ink 6 and on a boundary between the layers of the multi-layered ink 6, and returned toward the LED 2 side. In this case, the ink 6 has a structure of three layers which are defined as a first layer, a second layer and a third layer in an order from the optical element 1 side or the LED 2 side toward the optical sheet 5 side. Here, as the colors of the respective layers of the ink 6, the first layer has a white color, the second layer also has a white color, and the third layer has a mixed color of white and blue. In other words, the layer (first layer) positioned so as to be closest to the optical element side has a higher ratio of the white color (white purity) than a ratio of at least one of the other layers. In the present embodiment, the ratio of the white color in the first layer is 100%, that is, the first layer is made of only the white ink without mixing the other color therewith. However, the ratio is not always required to be 100%. For example, other color such as blue or black may be mixed therewith at a ratio smaller than a mixed ratio of blue ink or black ink in a mixed ink described later. Hereinafter, an optical function of each of the light shielding layers will be explained.
[0057]First, the optical function of the white ink of the first layer will be explained. Here, a case that the ink 6 having a high absorptivity is used will be considered. As one example, it is assumed that the transmittance of the optical element 1 is 80%, that the transmittance and the absorptivity of each of the ink layers are 30% and 10%, respectively, that a dimension of the ink 6 extending in the +z direction from the light emitting side of the LED 2 is 10 mm, and that a distance in the +y direction between the center of the light emitting surface of the LED 2 and the optical element 1 is 3.4 mm. In such a configuration, if light of 27.1% of the entire light quantity is light that directly impacts on the ink surface of the first layer, and if light of 10% of the light of 27.1% is absorbed by the first layer, light of 2.7% becomes a loss. Moreover, the loss of the light is further increased also in consideration of light which is reflected on the first layer of the ink 6, which is again reflected on the reflection sheet 4, and then, which impacts again on the ink 6. In consideration of the loss of the light due to the absorption, it is required to use an ink having a low absorptivity, and therefore, it is effective to use a white ink having low absorption as the ink 6. In general, ink containing a color tone such as blue ink or black ink has a high absorptivity. For this reason, in the present embodiment, the absorbed light quantity is suppressed to the minimum by using the white ink, so that the light quantity reflected on the first layer, and propagated in the z direction is increased. In this manner, the efficiency of light usage can be improved.
[0058]The ink of the second layer is similarly made of white ink in order to suppress the absorption relative to the transmitted light (8.1% of the entire light quantity) from the first layer.
[0059]As described above, the ink of the first layer and the ink of the second layer have a function for improving the utilization efficiency of light.
[0060]Subsequently, an optical function of the ink of the third layer will be described. However, prior to the description, an optical influence caused by the reflected light from the ink 6 and chromaticity change of the light transmitted from the ink 6 will be described with reference to FIGS. 5 and 6.
[0061]FIG. 5 shows the optical influence caused by the reflected light from the ink 6. As shown in the diagram, the light reflected from the ink 6 is partially made incident to the LED 2, and the phosphor of the LED 2 is again excited by this incident light. At this time, by the color of the phosphor of the LED 2, the chromaticity of light (hot spot) right above the LED is changed. In the present embodiment, since a white LED having a yellow phosphor is used as the LED 2, light generated by the re-excitation of the yellow phosphor contains strongly yellow- to red-color tone components. Therefore, the chromaticity of the light (hot spot) right above the LED changes in a direction to yellow to red color.
[0062]Meanwhile, the light transmitted through the first layer and the second layer of the ink 6 is also changed in the chromaticity by the optical property of the ink 6. As shown in FIG. 6, a general-use white ink has such a wavelength-transmittance property (transmission spectrum) as to have a high transmittance on the long wavelength side. For this reason, light in the vicinity of the LED 2 particularly having the intense light quantity is changed in the chromaticity in the direction to the yellow- to red-color more than that on the periphery thereof.
[0063]In this manner, the light right above the LED 2 is largely shifted toward the long wavelength side or changed in the chromaticity by adding the chromaticity change in the yellow to red color direction caused by the re-excitation of the phosphor of the LED 2 with the chromaticity change of the transmitted light caused by the optical property of the white ink, with the result that the chromaticity is greatly shifted or changed. When such chromaticity change occurs, color unevenness locally occurs right above the LED 2, and degradation in the spatial color uniformity within the light emitting surface of the lighting device 100 occurs. That is, the hot spot caused in the vicinity of the portion right above the LED 2 is locally higher in the luminance than the periphery thereof, and besides, is locally different in the color more than the periphery thereof, and therefore, contains particularly the strong yellow-color tone or red-color tone component.
[0064]In the present embodiment, in order to reduce such degradation in the color uniformity, ink obtained by mixing white and blue colors (hereinafter, referred to as “blue mixed ink”) is used for the third layer of the ink 6 as shown in FIG. 4. As shown in FIG. 7, the blue mixed ink has such a wavelength-transmittance (transmission spectrum) property as to absorb more light on the long wavelength side without absorbing light of the blue wavelength band on the short wavelength side. Therefore, in the light that has transmitted through the first layer and the second layer in the vicinity of the portion right above the LED 2 having the strong yellow- or red-color tone component, the yellow- or red-color tone component of the transmitted light is absorbed in the third layer by using the blue mixed ink for the third layer of the ink 6. That is, the light having the strong yellow or red tone that has transmitted through the first layer and the second layer is corrected by the third layer so as to be returned to white. The amount of the chromaticity adjustment in the third layer can be set by, for example, changing a composition amount of the blue ink in the blue mixed ink with taking the chromaticity of the emitted light of the lighting device as a target chromaticity. In the blue mixed ink according to the present embodiment, a mixed ratio of the blue ink with respect to the white ink is set in, for example, a range of about 0.1 to 0.4% in weight ratio.
[0065]In this manner, the blue mixed ink of the third layer has a function for adjusting or correcting the chromaticity of light on the portion right above the LED 2.
[0066]As described above, according to the present embodiment, the ink 6 serving as the light shielding pattern formed on the optical element has the multi-layered structure obtained by stacking the plurality of light shielding layers, and the light shielding layer (first layer in the present embodiment) positioned so as to be the closest to the back surface side (LED 2 side) is made of the white ink, and at least one (third layer in the present embodiment) of the other light shielding layers is made of the blue mixed ink, and therefore, the chromaticity change due to the phosphor of the LED 2 and the white ink in the first layer can be reduced while reducing the light intensity of the hot spot in the vicinity of the portion right above the LED 2. Therefore, according to the present embodiment, a lighting device with the improved spatial luminance uniformity and color uniformity of the emitted light can be provided. Moreover, by using the lighting device according to the present embodiment as a backlight of a liquid crystal display device, high quality images with the high spatial luminance uniformity and color uniformity can be displayed.
[0067]The brightness of the hot spot can be further reduced as the thickness of the light shielding pattern becomes thicker. For this reason, in the present embodiment, in order to ensure the thickness of the light shielding pattern, the light shielding pattern is formed so as to have the three-layered structure. However, the structure is not limited to this. If the film thickness of each layer can be made thicker, the structure may be achieved by two layers. Of course, it is also needless to say that the structure is a four-layered structure. Moreover, in the above-described embodiment, the first pattern 61 has been explained. However, it is clear that the second pattern 62 may similarly have the multi-layered structure. Furthermore, the first pattern 61 may have the multi-layered structure, and the second pattern 62 may have a one-layer structure.
Second Embodiment
[0068]With reference to FIG. 8, a second embodiment of the present invention will be explained. Since the present embodiment is different from the first embodiment only in the composition of the ink in the third layer, explanation except for those of the ink in the third layer will be omitted.
[0069]As shown in FIG. 8, in the ink 6 according to the present embodiment, the third layer is made of an ink obtained by mixing white, blue and black colors (hereinafter, referred to as “blue and black mixed ink”). By this ink, the hot spot is favorably reduced in the less printing processes.
[0070]In order to suppress the hot spot right above the LED 2, it is required to provide a film thickness of about 16 μm for the light shielding pattern. However, in order to reproduce a fine pattern by a printing process, it is required to decrease a mesh number of the printing plate. However, the decrease in the mesh number of the printing plate means that the film thickness formed by the printing process at one time becomes thinner. Practically, when it is desired to form a dot having a size of 0.47 μm, it is required to use a printing plate having the mesh number of “350×350”. The film thickness formed by the printing process at one time in such a printing plate is about 4 μm to 5 μm. Therefore, in order to obtain a film thickness of 16 μm, it is required to perform the printing process 3 to 4 times. The increase in the number of printing processes increases a printing cost. For this reason, in order to achieve both of the fine pattern and the decrease in the number of printing processes, a new devisal for suppressing the hot spot is required.
[0071]Therefore, in the present embodiment, by using the blue and black mixed ink as the ink of the third layer, the light absorptivity in the third layer is increased. In this manner, the light can be further absorbed while correcting the chromaticity of light transmitted through the first layer and the second layer, so that the chromaticity change can be suppressed while reducing the light intensity of the hot spot even in a thin film thickness of the light shielding pattern. In the blue and black mixed ink according to the present embodiment, the mixed ratios of the blue ink and the black ink with respect to the white ink are set to, for example, about 0.1 to 0.4% in the weight ratio, respectively.
[0072]When the blue and black mixed ink is used for the first layer, the light utilization efficiency is reduced since the light quantity absorbed in the first layer increases so that the light is reflected on the first layer, which results in decrease in the light quantity propagating in the z-direction. However, in the present embodiment, the blue and black mixed ink is used for the third layer, and therefore, the decrease in the light quantity propagating in the z direction can be suppressed. That is, according to the present embodiment, the further reduction of the light intensity of the hot spot while suppressing the chromaticity change of the light in the vicinity of the portion right above the LED 2 can be achieved in the light shielding pattern having the thin film thickness (that is, in the less number of printing processes).
[0073]As similar to the first embodiment, also in the present second embodiment, the light shielding pattern may have the two-layered structure or the four-layered structure.
Third Embodiment
[0074]With reference to FIG. 9, a third embodiment of the present invention will be explained. Since the third embodiment is different from the first embodiment and second embodiment in a layer configuration of the ink and a method of forming the ink but the same as them in others, explanations for others except for the method of forming the ink will be omitted.
[0075]As shown in FIG. 9, in the present embodiment, the light shielding pattern 6 has a two-layered structure in which the first layer is made of the white ink and the second layer is made of the blue and black mixed ink. The first layer made of the white ink is printed by using a gradation printing plate, and the second layer made of the mixed color ink (blue mixed ink or blue and black mixed ink) is printed by using a solid printing plate.
[0076]In the gradation printing plate, the white ink is printed on the optical element 1 so as to make a pattern area smaller as separating further from the LED 2, that is, so as to make a dot density per unit block as shown in FIG. 3 lower. The absorption by the white ink is small as described above. Therefore, by applying this to a wide area, an optimal light shielding performance can be achieved, and a desired luminance uniformity can be achieved.
[0077]On the other hand, in the solid printing plate, the blue mixed ink or the blue and black mixed ink is printed only on the hot spot portion right above the LED 2, such as only on the portion of the first pattern 61 of FIG. 2.
[0078]At this time, if the sufficient light shielding effect can be achieved by the ink of the first layer printed in the gradation printing plate, there is no problem in the increase in the coating area of the solid printing plate. However, if the sufficient light shielding effect cannot be achieved by the first layer, the increase in the coating area of the second layer by the use of the mixed ink increases the amount of absorption in the second layer for the light transmitted through the first layer.
[0079]Therefore, in the present embodiment, in order to cover the wide area on the gradation printing plate, the first layer is formed by printing the first pattern 61 and the second pattern 62 of FIG. 2 by the use of the white ink, and the second layer is formed by printing only the portion right above the LED, that is, only the portion of the first pattern 61 on the solid printing plate by the use of the mixed color ink. That is, in the present embodiment, the first layer formed on the gradation printing plate by using the white ink has both of the first pattern 61 and the second pattern 62, and the second layer formed on the solid printing plate by using the blue mixed ink or the blue and black mixed ink only has the first pattern 61. That is, the first pattern 61 has the multi-layered structure, and the second pattern 62 has the s