JP4274921B2 - LIGHTING DEVICE AND DISPLAY DEVICE HAVING THE SAME - Google Patents

Description

  The present invention relates to an illuminating device and a display device including the illuminating device, and more particularly to an illuminating device and a liquid crystal display device that are preferably used as an illuminating device for a liquid crystal display device.

  A non-self-luminous display device such as a liquid crystal display device performs display by modulating light emitted from a lighting device with a display panel. These illumination devices (in particular, sometimes referred to as “planar illumination devices”) include a direct type in which a light source is disposed directly under the display panel, and a light source on a side surface of a light guide plate provided directly under the display panel. It is roughly classified into the side light system (or edge light system) to be arranged. In addition, the following three types (types I, III, and III) are known as side light systems.

  Type I: An illuminating device that uses a light guide plate having diffusion portions arranged at a density such that light emitted from the light exit surface of the light guide plate is uniform.

  Type II: An illumination device in which grooves on a prism and fine lenses are formed on the light exit surface of the light guide plate and on the opposite side (for example, Non-Patent Document 1).

  Type III: A lighting device in which a light source is arranged at a corner of a light guide plate (for example, Patent Document 1 and Non-Patent Document 2).

  Since the type I illumination device uses the diffusing section to emit light from the light exit surface, the spread angle of the emitted light flux is relatively large (low directivity). On the other hand, type II and type III lighting devices have a feature of high directivity because they utilize reflection and refraction of light.

  The “directivity” referred to here indicates how much light emitted from the illumination device has directionality in a specific direction. For example, as shown in a specific example later, the evaluation is performed by the half-value width angle in the intensity distribution (light distribution) of the emitted light, and the directivity is higher as the half-value width angle is narrower.

  A type II sidelight type illumination device has different directivity of emitted light in a light propagation direction and a direction orthogonal to the propagation direction.

  With reference to FIGS. 8A and 8B, the configuration and light distribution characteristics of the illumination device 10 will be described. FIG. 8A is a plan view schematically showing the illumination device 10, and FIG. 8B is a graph showing a light distribution of the illumination device 10.

  As schematically shown in FIG. 8A, in the illumination device 10, the plurality of LEDs 12 are linearly arranged along one side surface (incident end surface) of the light guide plate 14. A cold cathode tube may be used in place of the plurality of LEDs 12, or LEDs or cold cathode tubes may be arranged on the side surfaces on both sides of the light guide plate 14.

  Light that is emitted from the LED 12 and enters the light guide plate 14 from the incident end surface of the light guide plate 14 propagates in the light guide plate 14 in the first direction (see the arrow in FIG. 8), and exits (surface parallel to the paper surface). ) To the display panel. The linear light source 12 is disposed along a second direction (see an arrow in the figure), and the first direction is orthogonal to the second direction. In general, the light guide plate 14 is a rectangle having a first direction (light propagation direction) as a longitudinal direction.

  The intensity distribution (light distribution) of the light emitted from the emission surface of the illumination device 10 has direction dependency as shown in FIG. The horizontal axis in FIG. 8B is the angle formed by the exit surface normal and the outgoing light, and the vertical axis is the outgoing light intensity. Here, the results of measurement with a capture angle of ± 60 degrees are illustrated.

  As shown in FIG. 8B, in the second direction orthogonal to the light propagation direction (in the plane orthogonal to the exit surface including the line AA ′ in FIG. 8A), The directivity (parallelism) is low, and the directivity of outgoing light is high in the first direction that is the propagation direction of light (in the plane that includes the line BB ′ in FIG. 8 and that is perpendicular to the outgoing face).

  FIG. 9 schematically shows the configuration of a type III illumination device 20. The illumination device 20 includes a light guide plate 24 and a light source 22 provided at a corner of the light guide plate 24. Light incident from the light source 24 propagates radially through the light guide plate 24. That is, the light emitted from the light source 22 propagates in the radial direction of the concentric circle 26 centering on the light source 22. The directivity of the light emitted from the light guide plate 24 is low in the radial direction that is the light propagation direction (in the plane that includes the CC ′ line in FIG. 9 and that is orthogonal to the emission surface), and the direction that is orthogonal to this direction. High in (tangential direction of concentric circles).

  In the illuminating device 10 shown in FIG. 8, since the plurality of light sources 12 are arranged in a line on the side surface (edge portion) of the light guide plate 14, the light source 12 is different at an arbitrary point (position) in the light guide plate 14. Light enters from the light source 12. That is, light having a different traveling direction, which is emitted from the light source 12 arranged at a different position, is incident on an arbitrary point in the light guide plate 14, and the distribution of incident angles is increased. Since the traveling direction of such light is changed by the prism of the light guide plate 14 and the light is emitted from the light exit surface of the light guide plate 14, the light source 12 is arranged in the direction perpendicular to the light propagation direction (that is, the light propagation direction). The directivity in the AA ′ direction in FIG. On the other hand, the illumination device 20 shown in FIG. 9 has only one light source 22 arranged at the corner of the light guide plate 14, so that the traveling direction of light incident on an arbitrary point in the light guide plate 24 ( That is, the distribution of the incident angles is narrow, and the directivity in the direction (concentric tangential direction) orthogonal to the light propagation direction (radial direction) in the light guide plate 24 is high. However, in the illuminating device 20, since the light is directed to the exit surface side by the prism 26 formed on the back surface of the light guide plate 24, the directivity of the exit light is determined by the distribution of the incident angle of the light with respect to the prism 26. It spreads in the propagation direction of light (CC ′ direction in FIG. 9).

  Here, the “propagation direction” of light in the light guide plate is a direction in the plane of the light guide plate, and the propagation direction at an arbitrary point in the light guide plate connects that point and the light source (or incident end face). The direction in which the straight line distance is the shortest will be indicated. For example, when the light source is arranged at the corner of the light guide plate, the radial direction of a circle centered on the corner is the propagation direction. When a plurality of light sources are arranged along the side surface of the light guide plate (the same applies when one linear light source is arranged), the direction orthogonal to the side surface is the propagation direction.

  The directivity of light emitted from the illumination device affects the viewing angle characteristics of the display device. In a display device using a lighting device with high directivity, a high-quality display can be observed from a specific direction, but when the observation angle goes out of a specific range, for example, the brightness decreases. The quality is degraded. Therefore, for example, a high-directivity lighting device can be suitably used for applications such as mobile phones and PDAs where the display content is not desired to be seen by others. When the display cannot be observed from the direction (for example, the front), a highly directional lighting device is not preferable.

  In recent years, mobile information terminals such as mobile phones and PDAs that are rapidly spreading are greatly limited in usage time due to power consumption. Since the power consumption of LEDs currently used as light sources accounts for a fairly large proportion of the power consumption of the entire system, there is a strong demand to reduce the power consumption of the light sources.

In order to solve the above-described problem of power consumption and viewing angle characteristics, Patent Document 2 discloses a liquid crystal display device that can be switched to a mode with a narrow viewing angle and low power consumption as required. . As schematically shown in FIG. 10, the liquid crystal display device 90 disclosed in Patent Document 2 includes a pair of lighting devices 92, a liquid crystal cell 96, and a pair of liquid crystal cells 96 arranged to face each other. It has polarizing plates 95 and 97 and an optical compensation sheet 98 disposed on the viewer side. The mode is switched by making the optical compensation sheet 98 removable. That is, when the optical compensation sheet 98 is removed, high directivity can be obtained. Therefore, when a wide viewing angle is required while ensuring brightness only in a limited viewing angle range with low power consumption, optical compensation is achieved. Directivity is lowered by attaching the sheet 98.
JP 2003-35824 A JP-A-7-104271 K. KALANTAR, IDW'02, pp. 549-552 `` Viewing Angle Control using Optical Microstructures on Light-Guide Plate for Illumination System of Mobile Transmissive LCD Module ''. M. Shinohara, et al., Optical Society of American Annual Meeting Conference Program, Vol. 10, p.189 (1998).

  However, the liquid crystal display device 90 described in Patent Document 2 has the following problems although the viewing angle (directivity) can be controlled.

  The liquid crystal cell 96 has a pair of substrates and a liquid crystal layer provided between the substrates, and an image is formed by changing the optical state of the liquid crystal layer for each pixel. On the other hand, the optical compensation sheet 98 provided for changing the directivity of light is arranged further on the observer side of the polarizing plate 97 on the observer side. Therefore, one substrate (glass substrate) and one polarizing plate 97 exist between the liquid crystal layer on which an image is formed and the optical compensation sheet 98. As a result, parallax occurs and display quality is reduced.

  Moreover, since the light in the front direction is diffused by using the optical compensation sheet 98, the luminance in the front direction is significantly reduced.

  Further, the cost is increased by the optical compensation sheet 98 and the mechanism for attaching and detaching the optical compensation sheet 98. Further, it becomes necessary to store or manage the optical compensation sheet 98 after being attached / detached while protecting the surface thereof.

  In place of the optical compensation sheet in the configuration described in Patent Document 2, a method using a polymer-dispersed liquid crystal layer capable of electrically controlling a transmission state and a scattering state has been proposed. Since the light in the front direction is also diffused in the state, the luminance in the front direction is lowered. Furthermore, in this method, it is necessary to arrange one liquid crystal cell having a polymer dispersed liquid crystal layer on the light source side of the liquid crystal display panel, which not only significantly increases the cost but also the light scattering characteristics of the polymer dispersed liquid crystal layer. Since it usually has wavelength dependency, the level of scattering differs depending on the colors of R, G, and B, coloring may occur, and the display quality may deteriorate.

  The present invention has been made in view of the above-described points, and an object thereof is to provide an illuminating device capable of switching directivity while suppressing a decrease in front luminance as compared with the prior art and a display device including the same. To do.

  The illuminating device of the present invention includes a plurality of light sources and at least one light guide plate that propagates light emitted from the plurality of light sources and emits the light from an emission surface to the outside, and a part of the plurality of light sources It is possible to switch between a first mode in which the light source is selectively lit and a second mode in which at least one of the light sources that are not lit in the first mode is lit. The directivity within a predetermined plane is characterized in that the first mode is higher than the second mode.

  Another illumination device of the present invention includes a first illumination unit including a first light source, a first light guide plate that propagates the light emitted from the first light source and emits the light from the emission surface to the outside, a second light source, A second illuminating unit including a second light guide plate that propagates the light emitted from the second light source and emits the light from the emission surface to the outside, and the first illuminating unit is observed more than the second illuminating unit. It is arranged on the person side and can be switched between a first mode in which the first light source is selectively turned on and a second mode in which the second light source is turned on.

  In one embodiment, the first illumination unit can emit light having higher directivity than the second illumination unit.

  In one embodiment, the first light guide plate has a first incident end face provided at a corner, and the first light source is arranged to emit light toward the first incident end face.

  In one embodiment, the first light guide plate has a first incident end face provided on a side surface, and the first light source is arranged to emit light toward the first incident end face.

  In one embodiment, the first illumination unit further includes a prism sheet disposed on the light exit side of the first light guide plate.

  In one embodiment, the second illumination unit further includes a diffusion sheet provided on the first illumination unit side of the second light guide plate.

  Another illumination device of the present invention includes a plurality of light sources and at least one light guide plate, and the at least one light guide plate has a plurality of prisms in which respective ridge lines are arranged substantially concentrically. The plurality of light sources includes a first light source disposed near the center of the substantially concentric circle and a second light source disposed at a position shifted from the center of the substantially concentric circle with respect to the at least one light guide plate. And switching between a first mode in which the first light source is selectively lit and a second mode in which at least one of the at least one second light source is lit.

  In one embodiment, the at least one light guide plate has a first incident end face provided at a corner and at least one second incident end face adjacent to the corner, and the first light source is the first light source. The second light source is disposed so as to emit light toward the one incident end face, and the second light source is disposed so as to emit light toward the at least one second incident end face.

  In one embodiment, the at least one light guide plate has an incident end surface provided on a side surface, and the first light source and the second light source are arranged to emit light toward the incident end surface. .

  In one embodiment, the directivity of light emitted from the light exit surface in a predetermined plane is higher in the first mode than in the second mode.

  In one embodiment, the at least one light guide plate includes: a first light guide plate having an incident end surface that receives light from the first light source; and a second light guide plate having an incident end surface that receives light from the second light source. In addition, the first light guide plate is provided on the light exit side of the second light guide plate.

  A display device according to the present invention includes any one of the illumination devices described above and a display panel disposed on an observer side of the illumination device.

  In one embodiment, the directivity of light in the first mode is higher in the horizontal direction (left-right direction) of the display panel than in the vertical direction (up-down direction).

  In one embodiment, the directivity of light in the first mode is lower in the vertical direction of the display panel than in the horizontal direction.

  An illuminating device according to the present invention includes a plurality of light sources and at least one light guide plate, a first mode in which a part of the plurality of light sources is selectively lit, and a light source that is not lit in the first mode. Directivity is switched by switching to the second mode in which at least one is lit. Therefore, if the liquid crystal display device is configured using the illumination device of the present invention, a decrease in front luminance is suppressed as compared with the method using the optical compensation sheet described in Patent Document 2. In addition, the above-described problems caused by providing an optical compensation sheet such as a reduction in display quality due to parallax do not occur.

  In the second mode, at least one of the light sources that are not turned on in the first mode may be turned on, and the light source that is turned on in the first mode may be turned on. In addition, the light source that is turned on in the second mode may be changed (selected), and more than three modes may be switched, such as preparing a third mode in addition to the first and second modes. Anyway.

  Hereinafter, an illumination device according to an embodiment of the present invention and a liquid crystal display device including the same will be described with reference to the drawings. However, the present invention is not limited to these.

(Embodiment 1)
FIG. 1A is a plan view schematically illustrating the configuration of the illumination device 100 according to the first embodiment, and FIG. 1B is a side view schematically illustrating the configuration of a liquid crystal display device 150 including the illumination device 100. It is.

  The illumination device 100 includes light sources 101A, 101B, and 101C, and a light guide plate 102 that propagates the light emitted from the light sources 101A, 101B, and 101C and emits the light from the emission surface to the outside. The plurality of light sources 101A, 101B, and 101C can be switched between a first mode in which some of them are selectively lit and a second mode in which at least one of the light sources that are not lit in the first mode is lit. It has become. Since the relative position of the light source with respect to the light guide plate 102 is different, light having different directivities is emitted by changing the light source to be turned on (some light sources may be turned on in any mode). Here, a mode with high directivity is referred to as a first mode.

  The liquid crystal display device 150 includes a lighting device 100 and a liquid crystal display panel 110 on the viewer side of the lighting device 100. The liquid crystal display panel 110 includes, for example, a lower polarizing plate 105, a liquid crystal cell 106, and an upper polarizing plate 107 in this order from the lighting device 100 side. Since the configuration other than the illumination device 100 may be the same as that of a known liquid crystal display device, detailed description thereof is omitted here. The liquid crystal display device 150 is preferably used for a mobile phone, for example, and the liquid crystal display panel 110 is, for example, a 2.4 type QVGA panel (240 × 320 dots).

  The light guide plate 102 of the illumination device 100 has a first incident end face 102a provided at a corner, and second incident end faces 102b and 102c adjacent to the corner. Of the three light sources, the light source 101A is arranged to emit light toward the first incident end face 102a. The other light sources 101B and 101C are arranged so as to emit light toward the second incident end faces 102b and 102c, respectively. As the light sources 102a, 102b, and 102c, for example, an LED including a reflector can be suitably used.

  The light guide plate 102 is, for example, a light guide plate that emits light that is emitted from the light source 101A and incident from the first incident end surface 102a and propagates radially, from the emission surface.

  Here, the configuration of a light guide plate that is preferably used as the light guide plate 102 will be described with reference to FIGS. FIG. 2A is a cross-sectional view taken along 2A-2A ′ in FIG. 1A and schematically shows how light emitted from the light source 101A propagates through the light guide plate 102. FIG. FIG. 2B is a partially enlarged view of FIG.

  The light guide plate 102 has minute prisms arranged concentrically around the light source 101A arranged at the corner (first incident end face 102a). As schematically shown in FIG. 2B, the inclined surface of the microprism 103 is arranged so as to reflect the light propagating radially from the first incident end surface 102 a to the emission surface side. The (longitudinal direction) is provided so as to extend in the tangential direction of a concentric circle centering on the light source 101A, as schematically shown in FIG. The light incident on the light guide plate 102 from the light source 101A propagates through the light guide plate 102 while repeating total reflection, and a part of the light is emitted from the emission surface. In order to return the light emitted from the back surface of the light guide plate 102 (the surface opposite to the light exit surface) to the light guide plate 102, a reflection plate 104 may be provided as shown in FIG.

  The microprism 103 is provided so that its ridgeline extends in a tangential direction of a concentric circle centering on the light source 101A. Therefore, the light propagating radially from the light source 101A in the light guide plate 102 also reaches the prism 103 in the propagation direction. It does not deflect in the orthogonal direction. Therefore, the light emitted from the emission surface has high directivity in a plane orthogonal to the light propagation direction in the light guide plate 102. On the other hand, the light emitted from the light sources 101B and 101C is reflected by the microprism 103 while propagating through the light guide plate 102, but the propagation direction of the light emitted from the light sources 101B and 101C is Since the ridgeline of the microprism 103 is not orthogonal to the extending direction, it is deflected in the direction orthogonal to the light propagation direction, and the directivity decreases.

  FIG. 3 shows the intensity distribution of light emitted from the lighting device 100 when each of the light sources 101A, 101B, and 101C is selectively turned on one by one. FIG. 3 shows an intensity distribution in a plane orthogonal to the propagation direction of light emitted from the light source 101A (radial direction of a circle centered on the light source 101A).

  As is apparent from FIG. 3, the angular distribution of the emitted light when the light source 101A is selectively turned on is narrow (half-value width angle is ± 10 ° or less) and has high directivity, and the exit surface normal direction (exit angle) = 0 °). On the other hand, the angle distribution of the emitted light when the light source 101B or the light source 101C is selectively turned on is wider (half-value width angle is about 25 °) than when only the light source 101A is turned on, and the directivity is low. Further, the direction in which the emission light intensity is maximum is deviated from the normal direction of the emission surface.

  Therefore, in the illumination device 100, if only the light source 101A is selectively turned on, light having high directivity is emitted (first mode). Further, the outgoing light intensity distribution at this time has a maximum intensity in the normal direction of the outgoing surface.

  In the first mode, since only one light source is lit, power consumption is low. Compared with the fact that currently 3 to 4 LEDs are used in the lighting device for 2.4-inch QVGA panel, the power consumption can be reduced to 1/4 to 1/3. In addition, since the light emitted from the illumination device 100 in the first mode has high directivity and has the maximum intensity in the normal direction of the emission surface, the liquid crystal display device 150 has a narrow viewing angle characteristic in the first mode. And the front luminance is high.

  Therefore, for example, when the liquid crystal display device 150 is attached to a mobile phone, if one person wants to observe the display and set the first mode, the display can be performed with low power consumption while being difficult to see from the surroundings. it can. Since mobile phones are often used in this way, normally, when the display is performed in the first mode, the usable time of the mobile phone is greatly extended. Of course, this applies not only to mobile phones but also to PDAs and mobile PCs.

  In the second mode, for example, all of the light sources 101A to 101C are turned on. Since the light sources 101B and 101C are arranged at positions different from the optimum position (position where the light source 101A is provided) with respect to the light guide plate 102, the light emitted from these light sources is the prism 103 of the light guide plate 102. The light emitted from the light sources 101B and 101C is emitted at a different angle from the light emitted from the light source 101A (in FIG. 3). Not only does the peak position differ, but also the directivity decreases (corresponding to the wide half-value width angle in FIG. 3).

  When all of the light sources 101A to 101C are turned on, light having an intensity distribution obtained by adding the emitted light intensity distributions of the three light sources in FIG. 3 is emitted. Therefore, in the second mode, the light source With the light from 101B and 101C, it is possible to loosen the directivity (lower directivity) while further increasing the front luminance compared to the first mode. The second mode is effective when the display is observed by a large number of people or when the display cannot be observed from the front.

  In the second mode, three light sources are turned on, but the power consumption does not increase as compared with the conventional method, but only at the same level. Therefore, by switching between the first mode and the second mode according to the application, a reduction in power consumption as a whole can be realized.

  Depending on the application, in the second mode, only one of the light sources 101B or 101C or only one of the light sources 101A and 101B or 101C may be turned on. Alternatively, only one of the light source 101A and the light source 101B or 101C may be turned on in the first mode, and all of the light sources 101A to 101C may be turned on in the second mode.

  In the above embodiment, the light sources 101B and 101C are disposed relatively close to the light source 101A. However, the light sources 101B and 101C may be disposed at positions away from the light source 101A, and each of the incident end faces. A plurality of light sources may be provided along 102b and 102c.

  Further, in the above-described embodiment, the light exit surface of the light source provided at the corner and a plurality of prisms having ridge lines in the direction perpendicular to the propagation direction of the light emitted from the light source provided at the corner and radially propagated Although the 1st mode which radiate | emits light with high directivity was implement | achieved by the structure provided with the light-guide plate radiate | emitted from, it is not restricted to this.

  For example, the illumination device 100 ′ illustrated in FIG. 4 can also switch between the first mode that emits light with high directivity and the first mode with low directivity.

  The illumination device 100 ′ includes light sources 101 </ b> A ′, 101 </ b> B ′, and 101 </ b> C ′, and a light guide plate 102 ′ that propagates light emitted from the light sources 101 </ b> A ′, 101 </ b> B ′, and 101 </ b> C ′ and emits the light from the emission surface to the outside.

  Three light sources 101A ', 101B' and 101C 'are arranged on the incident end face 102a' (side surface on the short side) of the light guide plate 102 '. The light source 101A ′ is disposed in the vicinity of the center in the direction (short side direction) in which the incident end face 102a ′ extends, and the light source 101B ′ and the light source 101C ′ are disposed at substantially symmetrical positions with the light source 101A ′ as the center. .

  The light guide plate 102 ′ includes a plurality of prisms 103 ′ having ridge lines in a tangential direction of concentric circles centering on the light source 101 </ b> A ′. That is, the prism 103 ′ has a ridge line in a direction perpendicular to the propagation direction of light emitted from the light source 101 </ b> A ′ and propagating radially in the light guide plate 102 ′.

  In the illumination device 100 ′ as well, as in the illumination device 100 described above, the first mode is realized by selectively lighting the light source 101A ′ disposed in the vicinity of the center of the concentric circle, and is disposed at a position shifted from the center. The second mode can be realized by turning on the light sources 101B ′ and 101C ′. Of course, in the second mode, only one of the light sources 101B 'and 101C' may be turned on, or the light source 101A 'may be turned on simultaneously.

  As described above, the illumination devices 100 and 100 ′ according to the first embodiment include at least one of the first mode in which a part of the plurality of light sources is selectively lit and the light source that is not lit in the first mode. Since the directivity can be switched by switching to the second mode to be lit, a decrease in front luminance is suppressed as compared with the method using the optical compensation sheet described in Patent Document 2. Further, the above-described problems (deterioration of display quality due to parallax, cost increase due to the optical compensation sheet and its attaching / detaching mechanism) due to the provision of the optical compensation sheet do not occur.

(Embodiment 2)
The illuminating device of Embodiment 1 has a configuration in which the directivity of emitted light is switched by selecting a light source to be lit from a plurality of light sources arranged on a plurality of incident end faces of a single light guide plate. ing. On the other hand, the illuminating device of this Embodiment 2 enables change of directivity of emitted light by the combination of a plurality of light guide plates and a plurality of light sources.

  The configuration and operation of the illumination device and the liquid crystal display device according to the second embodiment will be described with reference to FIGS.

  FIG. 5A is a cross-sectional view schematically showing the configuration of the liquid crystal display device 250 of the second embodiment. FIG. 5B is a plan view schematically illustrating the configuration of the upper layer illumination unit 210 of the illumination device 200 included in the liquid crystal display device 250, and FIG. 5C schematically illustrates the configuration of the lower layer illumination unit 220 of the illumination device 200. FIG.

  As shown in FIG. 5A, the liquid crystal display device 250 has an illumination device 200 in place of the illumination device 100 in the liquid crystal display device 150 shown in FIG. The lighting device 200 includes an upper layer illumination unit 210 and a lower layer illumination unit 220. The upper layer illumination unit 210 provided on the viewer side (the liquid crystal display panel 110 side) is configured to emit light having higher directivity than the lower layer illumination unit 220. Further, the light emitted from the lower layer illumination unit 220 passes through the light guide plate 202 of the upper layer illumination unit 210 and is emitted from the illumination device 200.

  As shown in FIG. 5B, the upper layer illumination unit 210 includes a light guide plate 202 and a light source 201 provided on a corner (first incident end surface) 202 a of the light guide plate 202. The light guide plate 202 and the light source 201 correspond to the light guide plate 102 and the light source 101A included in the illumination device 100, respectively. Therefore, as described above, the angle distribution of the emitted light is narrow (half-value width angle is ± 10 ° or less), the directivity is high, and the intensity in the normal direction of the emission surface (exit angle = 0 °) is the highest.

  As shown in FIGS. 5A and 5C, the lower layer lighting device 220 includes a light guide plate 212, light sources 211A, 211B, and 211C arranged toward the side surface (incident end surface) of the light guide plate 212, and a light guide plate. 212 has a diffusion sheet 222 and a prism sheet 224 arranged on the upper layer illumination unit 210 side. Further, a reflector 214 is provided below the light guide plate 212 as necessary.

  The lower layer illumination device 220 does not need to emit light with high directivity, but rather preferably emits light uniformly. Therefore, as illustrated in FIG. 5A, it is preferable to provide a diffusion sheet 222 on the light emitting side of the light guide plate 212 in order to diffuse the light emitted from the light guide plate 212. Further, by providing the prism sheet, the light having a large divergence angle among the light diffused by the diffusion sheet 222 is refracted by the prism surface, and is directed toward the front direction (normal direction of the display surface). Brightness can be increased.

  For example, the illumination device 200 performs switching between a first mode in which the light source 201 is selectively turned on and a second mode in which the light sources 211A to 211C are turned on together with the light source 201. In the first mode, as shown in FIG. 6, the lighting device 200 emits light with very high directivity as in the first mode of the lighting device 100 of the first embodiment. In the second mode, light having low directivity is emitted as shown in FIG. FIG. 6 is a graph showing the intensity distribution of the light emitted from the illumination device 200. The first mode and the second mode are normalized by the maximum intensity. In the second mode, since the light source 201 is also lit, the front luminance is higher than in the first mode.

  As described above, the lighting device 200 according to the second embodiment can switch the directivity of the emitted light by switching the light source to be turned on, as with the lighting device 100 according to the first embodiment. Therefore, compared with the method using the optical compensation sheet described in Patent Document 2, a decrease in front luminance is suppressed. Further, the above-described problems (deterioration of display quality due to parallax, cost increase due to the optical compensation sheet and its attaching / detaching mechanism) due to the provision of the optical compensation sheet do not occur. In addition, the combination of the light sources that are turned on in the first mode and the second mode is not limited to the above example, and various combinations are possible. Further, it is possible to select three or more modes. A certain point is the same as that of the illumination device 100 of the first embodiment. Depending on the application, a mode in which only the lower-layer illumination unit 220 is selectively lit may be used.

  Moreover, it can replace with the upper layer illumination part 210 of the illuminating device 200, and the illuminating device currently disclosed by the nonpatent literature 1 can be used suitably. For example, the upper layer illumination unit 310 shown in FIGS. 7A and 7B can be used.

  The upper layer illumination unit 310 includes a light guide plate 302 and a plurality of light sources 301 arranged along the side surface (incident end surface) of the light guide plate 302, and further includes a prism sheet 304 on the light output side of the light guide plate 302. ing. Light emitted obliquely from the emission surface of the light guide plate 302 is totally reflected by the prism surface of the prism sheet 304 and directed in the front direction. The upper layer illumination unit 310 emits light having high directivity in a direction parallel to the line B-B ′ in FIG. In the upper layer illumination device 310, light that has entered the lens unit provided on the light exit side out of the light propagating through the light guide plate 302 while repeating total reflection is emitted from the light guide plate 302. Similar to the illuminating device 10 shown, the directivity in the BB ′ direction of the light emitted from the light guide plate 302 is high, and the directivity in the AA ′ direction is low.

  When a configuration in which light with high directivity is emitted using the upper layer illumination unit 310 as shown in FIG. 7 is adopted, the direction of the emitted light with high directivity of the illumination device (liquid crystal) is arranged by the arrangement of the light source 301 and the light guide plate 302. The direction in which the viewing angle of the display device is narrow) can be easily changed according to the application. That is, in the configuration shown in FIG. 7, the light sources 301 are arranged along the short side of the rectangular light guide plate 302, and the light source 301 is oriented in a direction parallel to the long side (BB ′ direction) orthogonal to the short side. High (view angle is narrow). Therefore, when the liquid crystal display panel is arranged according to the arrangement shown in FIG. 7B, the light directivity in the first mode is higher in the horizontal direction (left-right direction) than in the vertical direction (up-down direction) of the liquid crystal display panel. . On the other hand, when the display panel is arranged by rotating the arrangement shown in FIG. 7 by 90 °, the directivity of light in the first mode is higher in the vertical direction of the liquid crystal display panel than in the vertical direction. Of course, the aspect ratio of the light guide plate can be appropriately changed according to the application.

  When the directivity in the horizontal direction is set high, the directivity in the vertical direction is low, so that the user himself / herself can be viewed without any problem even if the angle is slightly deviated, but it is difficult for the user to visually recognize it. On the other hand, if the visibility in the vertical direction is set high, the directivity in the horizontal direction is low (the viewing angle is wide), so it is suitable for, for example, an in-vehicle display device that observes the display screen from the driver seat and the passenger seat. Can be used.

  Here, an example of a configuration in which only one upper layer irradiation unit that emits light with high directivity is provided, but two upper layer irradiation units that emit light with high directivity in different directions are provided, and these are selected. It is also possible to switch the direction with high directivity by turning on the light.

  In addition, as an upper layer illumination unit having high directivity, for example, the apex portion on the prism or lens array is brought into contact with the light exit side of the light guide plate as disclosed in JP-A-8-511129, and the contact is made. A type that takes out light from a part may be used, or a lighting device in which only the light source 101A ′ is arranged in a configuration like the lighting device 100 ′ shown in FIG. 4 may be used.

  In addition, since switching between the first mode and the second mode is performed by appropriately switching a plurality of light sources according to the application, for example, it is realized by an electrical switch that switches a path for supplying power to the light sources.

  In the first and second embodiments, the configuration in which the light source is disposed along one side of the light guide plate is illustrated. However, the light source may be disposed along a pair of opposing sides. In this case, the light from the light sources arranged on the respective sides may be emitted at different angles, and each may be lit separately to switch the directivity or may be lit simultaneously. .

  In the above embodiment, the liquid crystal display device is exemplified as the non-self-luminous display device, but the present invention can be applied to a known display device such as an electrochromic display device or an electrophoretic display device. In addition, there are a simple matrix method and an active matrix method as a display device, either of which may be used.

  According to the present invention, the directivity of light emitted from the illumination device and the viewing angle dependency of the display device can be switched by selectively turning on the light source. In the mode with high directivity, the directivity is high and the intensity in the normal direction of the exit surface is the highest.

  For example, when the display device of the present invention is used for a mobile phone or the like and is observed by one person, if the mode is set to a high directivity mode, the use time is greatly reduced without deteriorating the display visibility. Can be stretched. Further, depending on the specification application, it is possible to prevent the display from being observed by surrounding third parties.

  Even when used in a mode with low directivity, the directivity can be lowered without lowering the front luminance of the display device (or backlight), so that the visibility angle in the front direction is not changed, and the visible angle is widened. This is effective when the display is observed by a large number of people or when the display cannot be observed from the front. In the mode with low directivity, the power consumption does not increase as compared with the conventional method, but only at the same level as the conventional method.

  By switching these modes according to the scene to be used, it is possible to effectively switch the display viewing angle (directivity of the lighting device), and the use time can be extended as a whole.

  Note that since the power consumption can be reduced by using the lighting device of the present invention, the lighting device is particularly preferably used for a display device for mobile use such as a mobile phone or a personal digital assistant, but other uses such as a display device for a personal computer. It can also be applied to other display devices.

(A) is a top view which shows typically the structure of the illuminating device of Embodiment 1 by this invention, (b) is a side view which shows typically the structure of the liquid crystal display device of Embodiment 1 by this invention. . (A) is sectional drawing in alignment with 2A-2A 'in Fig.1 (a), (b) is the elements on larger scale of (a). It is a graph which shows the intensity distribution of the light radiate | emitted when each of the light sources 101A, 101B, and 101C of the illuminating device of Embodiment 1 is selectively lighted one by one. It is a top view which shows typically the structure of the other illuminating device of Embodiment 1 by this invention. (A) is sectional drawing which shows typically the structure of the liquid crystal display device of Embodiment 2 by this invention, (b) is a structure of the upper layer illumination part with which the illuminating device of Embodiment 2 by this invention is equipped typically. It is a top view to show, (c) is a top view which shows typically the structure of the lower layer illumination part with which the illuminating device of Embodiment 2 by this invention is provided. It is a graph which shows intensity distribution of the light radiate | emitted from the illuminating device of Embodiment 2 by this invention. It is a figure which shows typically the structure of the other upper layer illumination part used for the illuminating device of Embodiment 2 by this invention, (a) is sectional drawing, (b) is a top view. (A) is a top view which shows typically the structure of the conventional sidelight type illuminating device (type II), (b) is a graph which shows the light distribution. It is a figure which shows typically the structure of the conventional sidelight type illuminating device (type III). It is a schematic diagram for demonstrating the problem of the conventional liquid crystal display device.

Explanation of symbols

100, 100 ′ Illumination device 101A, 101B, 101C, 101A ′, 101B ′, 101C ′ Light source (LED)
102, 102 'Light guide plate 102a First incident end face 102a' Incident end face 102b, 102c Second incident end face 103, 103 'Micro prism 104 Reflector 105 Lower polarizing plate 106 Liquid crystal cell 107 Upper polarizing plate 110 Liquid crystal display panel 150 Liquid crystal display apparatus

Claims (8)

A plurality of light sources and at least one light guide plate;
The at least one light guide plate has a plurality of prisms in which respective ridge lines are arranged substantially concentrically;
The plurality of light sources include a first light source disposed near the center of the substantially concentric circle and a second light source disposed at a position shifted from the center of the substantially concentric circle with respect to the at least one light guide plate. ,
A lighting device capable of switching between a first mode in which the first light source is selectively turned on and a second mode in which at least one of the at least one second light source is turned on. The at least one light guide plate has a first incident end face provided at a corner and at least one second incident end face adjacent to the corner;
The first light source is arranged to emit light toward the first incident end face, and the second light source is arranged to emit light toward the at least one second incident end face. The lighting device according to claim 1 . Wherein at least one of the light guide plate incident end surface provided on the side surface, the first light source and the second light source is arranged to emit light toward the incident end face, claim 1 The lighting device described in 1. Directivity in a predetermined plane of the light emitted from the light emitting surface is greater than towards the first mode is the second mode, the lighting device according to any one of claims 1 to 3. The at least one light guide plate includes a first light guide plate having an incident end surface that receives light from the first light source, and a second light guide plate having an incident end surface that receives light from the second light source,
The lighting device according to any one of claims 1 to 4 , wherein the first light guide plate is provided on a light emitting side of the second light guide plate. A lighting device according to any one of claims 1 to 5 ;
And a display panel disposed on an observer side of the illumination device. The display device according to claim 6 , wherein the directivity of light in the first mode is higher in the horizontal direction of the display panel than in the vertical direction. The display device according to claim 6 , wherein the directivity of light in the first mode is lower than the horizontal direction in the vertical direction of the display panel.

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