JP4784110B2 - Illumination device and liquid crystal display device - Google Patents

Description

The present invention relates to a lighting device and a liquid crystal display device .

  2. Description of the Related Art Conventionally, as a backlight of a display that performs display using the polarization action of light such as a liquid crystal display panel, an illumination device as shown in Patent Document 1 that emits linearly polarized light is known.

  The illuminating device emits emitted light so that the vibration direction of the electric field, that is, the polarization plane is aligned with linearly polarized light along the transmission axis of a polarizer installed on the light incident side (back side) of the liquid crystal display panel. By doing so, the utilization efficiency of light is improved.

  In such an illuminating device, non-polarized light emitted from a surface light emitting element composed of a light source and a light guide plate is converted into linearly polarized light by a retroreflective polarizer and emitted in a planar shape toward a liquid crystal display panel. In this case, the non-polarized light emitted from the surface light emitting element has a polarization plane of the liquid crystal display panel due to the cooperative action of the retroreflective polarizer provided on the emission side and the optical rotation reflecting means provided on the back side. It is aligned with linearly polarized light along the transmission axis of the back-side polarizer, and is irradiated toward the liquid crystal display panel. Thereby, the component light absorbed by the back side polarizer of the liquid crystal display panel is reduced, and the light use efficiency is remarkably improved.

However, the use of the illumination device described above improves the light utilization efficiency and increases the overall brightness of the display surface, but the brightness in the front direction, which is most important for the viewer of the liquid crystal display panel, is insufficient. . In recent years, a liquid crystal display panel has been widely used as a display of a portable information terminal typified by a mobile phone that has been widely spread. As a display of a portable information terminal that is often used in front of the public, it is desired that the viewing angle can be limited to the vicinity of a desired front direction so that display information cannot be seen by others. In the conventional lighting device, it has been difficult to satisfy such a demand.
Japanese Patent Laid-Open No. 11-64791

An object of the present invention is to provide an illuminating device and a liquid crystal in which the viewing angle is limited within a desired limited angle range from the normal of the display surface, and a display with sufficiently high luminance at the limited viewing angle can be obtained. It is to provide a display device .

The illuminating device of the present invention faces a light emitting element, a light guide plate that emits light from the light emitting element incident from the first surface, from the second surface, and the second surface of the light guide plate. The reflective polarizing element disposed on the surface and one of the principal surfaces are formed in a concavo-convex surface in which a plurality of ridges are continuously arranged in parallel, and the reflective polarizing element is interposed between the light guide plate and the reflective polarizing element. The first prism sheet arranged as described above, and one main surface is formed in an uneven surface formed by continuously arranging a plurality of protrusions in parallel, the gap between the first prism sheet and the first prism sheet A second prism sheet disposed between the reflective polarizing element and the light guide plate so that the reflective polarizing element is interposed, and the first prism sheet is disposed on a transmission axis of the reflective polarizing element. It is arranged so as the extending direction of the protrusions is perpendicular against the second prism Sheet extending direction of the protrusion with respect to the transmission axis of the reflective polarizing element is characterized in that it is parallel.
The liquid crystal display device of the present invention includes a light emitting element, a light guide plate that emits light from the light emitting element incident from the first surface, and the second surface of the light guide plate. The reflective polarizing element disposed so as to be opposed to one another and the main surface of the reflective polarizing element is formed in an uneven surface in which a plurality of ridges are continuously arranged in parallel. A first prism sheet disposed so as to intervene, and one main surface is formed in an uneven surface formed by juxtaposing a plurality of ridges in parallel, the first prism sheet and The first prism sheet is interposed between the reflective polarizing element and the second prism sheet disposed between the reflective polarizing element and the light guide plate so that the reflective polarizing element is interposed therebetween. and a liquid crystal display panel disposed to the first prism Over DOO, the extending direction of the protrusion with respect to the transmission axis of the reflective polarizing element is disposed so as to be perpendicular, the second prism sheet, said protrusion with respect to the transmission axis of the reflective polarizing element The extending directions of are arranged in parallel .

According to the present invention, it is possible to obtain a display in which the viewing angle is limited within a desired limited angle range from the normal of the display surface and the luminance at the limited viewing angle is sufficiently high.

(First embodiment)
FIG. 1 is an exploded front sectional view showing a lighting device according to a first embodiment of the present invention, and FIGS. 2 (a) to 2 (d) are plan views showing optical arrangement configurations of main components. FIG. 1 is a cross-sectional view taken along line II of FIG. In addition, the hatching of the cross section of FIG. 1 is abbreviate | omitted for convenience of explanation.

  This lighting device is roughly a surface light emitting element composed of a cold cathode tube 1 as a light source and a light guide plate 2, a reflective polarizing plate 3 as a polarizing element disposed on the light emitting side of the light guide plate 2, and a light distribution control element. The prism sheet 4 and the light guide plate 2 are composed of a (1/4) wavelength phase difference plate 5 and a light reflection plate 6 disposed on the opposite side (rear side) of the light emission side. In addition, this illuminating device is arrange | positioned as a backlight of the liquid crystal display panel 7 by making the light-projection surface of the prism sheet 4 oppose the back surface on the opposite side to the observation side of the display of the liquid crystal display panel 7 shown with a dashed-two dotted line. The liquid crystal display panel 7 of the present embodiment is a twisted nematic liquid crystal display panel in which a pair of polarizing plates are installed before and after the liquid crystal cell.

  The light guide plate 2 is a transparent plate made of resin made of acrylic resin having a rectangular shape substantially corresponding to the liquid crystal display panel 7 to be irradiated, and has one end surface 2a as a light incident surface on which light is incident, and a pair of main surfaces. The front surface 2b on the side facing the liquid crystal display panel 7 is used as a light output surface, and the rear surface 2c opposite to the light output surface 2b is diffused to totally reflect incident light toward the light output surface 2b. The material 2d is distributed and formed in a predetermined pattern over substantially the entire surface.

  The reflective polarizing plate 3 installed on the light emitting surface 2b of the light guide plate 2 has a transmission axis 3a that selectively transmits linearly polarized light having a polarization plane parallel to a predetermined direction, and is orthogonal to the transmission axis 3a. A reflection axis 3b that selectively reflects linearly polarized light having a polarization plane orthogonal to the predetermined direction, and the polarization plane of incident light selectively transmits linearly polarized light along the transmission axis 3a. The polarization plane selectively reflects linearly polarized light along the reflection axis 3b. In the present embodiment, the reflective polarizing plate 3 is installed so that the transmission axis 3a and the reflection axis 3b orthogonal to each other form an angle of 45 ° ± 10 ° with respect to the horizontal direction (horizontal direction on the paper surface) h of the illumination device. ing.

  In the prism sheet 4, one main surface of a transparent plate having substantially the same size as the light guide plate 2 is formed on an uneven surface in which a plurality of protrusions 4 a extending in parallel in a predetermined direction are continuously arranged. ing. As in the present embodiment, the protrusion 4a is preferably formed so that the cross section is an isosceles triangle and the apex angle α is 90 ° ± 20 °. The shape of the protrusion 4a is not limited to the right isosceles triangle as in the present embodiment, but should be optimally set according to the distribution of the emitted light to be obtained.

  The prism sheet 4 formed as described above has an intersection angle β of 90 ° between the extending direction x of the protrusion 4a and the transmission axis 3a of the reflective polarizing plate 3 as shown in FIG. 2 (a). It is ± 20 °, and is arranged on the light emitting surface side of the reflective polarizing plate 3 so that the uneven surface on which the protrusions 4a are arranged side by side is the light emitting side (front side). The extending direction x of the protrusion 4a is a direction orthogonal to the transmission axis of the back side (rear side) polarizing plate (not shown) of the liquid crystal display panel 7, and therefore the transmission of the reflective polarizing plate 3 described above. The axis 3a and the transmission axis of the back side polarizing plate are parallel.

  The light guide plate 2, the reflective polarizing plate 3, and the prism sheet 4 described above are formed of a transparent plate made of a material having substantially the same refractive index, and are superposed and installed in a state of being optically and in close contact with each other.

  A (¼) wavelength phase difference plate 5 is provided on the rear surface 2c of the light guide plate 2 opposite to the light exit surface 2b. The (1/4) wavelength phase difference plate 5 is an optical element that brings a phase difference corresponding to the (1/4) wavelength to transmitted light, converts incident linearly polarized light into circularly polarized light, and emits it. The incident circularly polarized light is converted into linearly polarized light and emitted. In the present embodiment, this (1/4) wavelength phase difference plate 5 is guided so that the angle formed by the slow axis 5a and the transmission axis 3a of the reflective polarizing plate 3 is 45 ° ± 10 °. It is installed on the rear surface 2c of the optical plate 2.

  On the rear surface side of the (1/4) wavelength phase difference plate 5, a light reflection plate 6 is installed. The light reflecting plate 6 is provided to reflect the light transmitted through the (1/4) wavelength phase difference plate 5 and emitted to the rear surface side, and to enter the (1/4) wavelength phase difference plate 5 again. ing. The light reflecting plate 6 of the present embodiment is formed by vapor-depositing silver on a PET (Poly-Ethylene Terephthalate) sheet, and the reflecting surface formed by vapor-depositing the silver into a mirror surface is a (1/4) wavelength phase difference plate. 5 is installed facing the rear surface.

  Next, the function and effect of the illumination apparatus of the present embodiment configured as described above will be described with reference to FIGS.

  First, in FIG. 1, when the non-polarized light R emitted from the cold-cathode tube 1 enters the light guide plate 2 and propagates, it enters one of the diffusing materials 2d on the rear surface 2c, and the light exit surface ( Reflected toward the front surface 2b. The light R reflected by the rear surface 2c and emitted from the light exit surface 2b is incident on the reflective polarizing plate 3 installed on the light exit surface 2b, and the polarization plane of the light is linearly polarized along the transmission axis 3a. Only the component light is selectively transmitted through the reflective polarizing plate 3 and emitted.

  Here, of the light R incident on the reflective polarizing plate 3, all of the linearly polarized light components whose polarization planes are parallel to the transmission axis 3 a of the reflective polarizing plate 3 (hereinafter referred to as axial parallel linearly polarized light) are all reflected by the reflective polarizing plate 3. As shown in FIG. 5, the transmittance (reflectance) changes according to the incident angle and incident direction of the axis-parallel linearly polarized light. In FIG. 5, in the reflective polarizing plate 3 shown in FIG. 2B, the axial parallel linearly polarized light incident along a plane perpendicular to the surface of the reflective polarizing plate 3 and parallel to the transmission axis 3 a is used. The reflectance with respect to the incident angle is represented by a long broken line A, and the reflectance with respect to the incident angle of the axis parallel linearly polarized light incident along a plane perpendicular to the surface of the reflective polarizing plate 3 and orthogonal to the transmission axis 3a is represented by a short broken line. It is represented by B, and the reflectivity with respect to the incident angle is shown, but the transmissivity has a reciprocal relationship with the reflectivity.

  That is, among the axial parallel linearly polarized waves, the axial parallel linearly polarized light P0 incident from a direction along a plane perpendicular to the surface of the reflective polarizing plate 3 and parallel to the transmission axis 3a is shown in FIG. As shown, the polarization plane is incident on the reflective polarizing plate 3 as a p-wave parallel to the incident plane (plane parallel to the drawing). Most of the axis-parallel linearly polarized light that has entered the reflective polarizing plate 3 as a p-wave is transmitted light P1 and transmitted through the reflective polarizing plate 3, but part of the axial parallel linear polarized light is reflected as reflected light P2. That is, the reflectivity decreases as the incident angle of the axially parallel linearly polarized light increases, and shows a minimum value at which the reflectivity becomes almost zero when the incident angle reaches 60 ° of the Brewster angle. As the incident angle increases, the reflectance increases rapidly. This characteristic is that light having an incident angle near the Brewster angle and having a linearly polarized light component parallel to the transmission axis 3a out of light incident from an orientation parallel to the transmission axis 3a of the reflective polarizing plate 3 is It shows that it is transmitted with a high transmittance with almost no reflection. Of the light incident from the direction parallel to the transmission axis 3a, the polarization direction of the linearly polarized light S whose polarization direction is perpendicular to the incident plane is shown in FIG. 3B. Since it is perpendicular to the transmission axis 3a, it is reflected as P2 'without transmitting. The Brewster angle is an optical characteristic value that varies depending on the material of the incident medium. Since the reflective polarizing plate 3 in the present embodiment is an optical element based on an acrylic resin, the Brewster angle is about 60 °. It becomes.

  On the other hand, of the axial parallel linearly polarized light, the axial parallel linearly polarized light S0 incident from the direction along the plane perpendicular to the surface of the reflective polarizing plate 3 and perpendicular to the transmission axis 3a is shown in FIG. As shown, the polarization plane is incident on the reflective polarizing plate 3 as an s-wave perpendicular to the incident plane. Most of the axis-parallel linearly polarized light that has entered the reflective polarizing plate 3 as an s-wave is transmitted light P1 and transmitted through the reflective polarizing plate 3, but a portion is reflected as reflected light P2. That is, as the incident angle of the axis-parallel linearly polarized light increases, the reflectance gradually increases and does not show a minimum value. This characteristic is that light having a linearly polarized light component parallel to the transmission axis 3a out of light incident from the direction orthogonal to the transmission axis 3a of the reflective polarizing plate 3 has high reflectance and is transmitted with low transmittance. Show. Of the light incident from the direction orthogonal to the transmission axis 3a, the direction of vibration of the electric field, that is, linearly polarized light P whose polarization plane is parallel to the incident plane, has a polarization plane perpendicular to the transmission axis 3a. Therefore, it is reflected without transmitting.

  FIG. 6A is a light distribution showing the intensity of the emitted light for each emission angle (equal to the incident angle) in each direction of the axially parallel linearly polarized light transmitted through the reflective polarizing plate 3 as an isoluminance curve. FIG. As shown in this light distribution diagram, the brightness of the axial parallel linearly polarized light emitted from the reflective polarizing plate 3 is high in the direction along the transmission axis and low in the direction perpendicular to the transmission axis (reflection axis direction). ing. This light distribution characteristic is that the transmitted light is higher with respect to the incident light from the direction inclined from the normal direction to the direction of the transmission axis 3a with respect to the reflective polarizing plate 3, and from the normal to the direction of the reflection axis 3b. It shows that the transmittance is low for light incident from an inclined direction.

  Returning to FIG. 1, the axial parallel linearly polarized light P1 emitted from the reflective polarizing plate 3 is incident on the prism sheet 4 and is subjected to a deflecting action by the output side uneven surface 4b, whereby the emission direction is controlled. In this case, the prism sheet 4 is arranged so that the extending direction x of the ridge 4a is orthogonal to the transmission axis 3a of the reflective polarizing plate 3, so that the prism sheet 4 enters the prism sheet 4 from a direction parallel to the transmission axis 3a. The linearly polarized light P1 is refracted and emitted so as to approach the normal direction n of the prism sheet 4 on the uneven surface 4b. At this time, the emission angle θ with respect to the normal direction n is an incident angle with respect to the liquid crystal display panel 7 to be irradiated, and is an angle corresponding to the viewing angle of the observer of the liquid crystal display panel 7.

  As described above, the linearly polarized light P1 emitted from the reflective polarizing plate 3 in the direction parallel to the transmission axis 3a is condensed on the normal line n side by passing through the prism sheet 4, whereas the reflected polarized light is reflected. The linearly polarized light emitted from the plate 3 in the direction parallel to the reflection axis 3b orthogonal to the transmission axis 3a is not condensed on the normal line n side even if it passes through the prism sheet 4. That is, as shown in the light distribution of FIG. 6A, linearly polarized light that is emitted in a relatively large area along the transmission axis is actively condensed to the normal line n side by the prism sheet 4. As a result, the light distribution of the linearly polarized light emitted from the prism sheet 4 showing the intensity of the emitted light at each emission angle (equal to the incident angle) in each direction as an isoluminance curve is shown in FIG. It becomes like this.

6B, the azimuth angle is 90 ° -270 ° (corresponding to the vertical direction on the display surface of the liquid crystal display panel 7) and the azimuth angle is 0 ° -180 ° (the liquid crystal display panel 7). The respective light distributions on the surface (corresponding to the horizontal direction on the display surface) are taken out and shown as shown in the luminance characteristic diagrams of FIGS. As is apparent from these luminance characteristics, the luminance in the emission range close to the normal line where the emission angle is about 0 ° to 25 ° in both the horizontal and vertical directions is as high as about 2200 cd / cm ² or more, and the emission angle is higher than that. In the emission range of 25 ° to 60 ° where the angle is greatly inclined, the luminance is drastically reduced.

  Therefore, when the liquid crystal display panel 7 is irradiated with the emitted linearly polarized light having such a light distribution as the backlight light, the display of the liquid crystal display panel 7 can be clearly recognized because the viewing angle is 0 ° in almost all directions. Limited to a narrow range of ~ 25 °. That is, the viewing angle of the display on the liquid crystal display panel 7 is as narrow as about 25 ° in all directions, thereby effectively preventing peeping other than the front observer.

  Incidentally, as a comparative example, the luminance characteristics when the prism sheet 4 is arranged so that the extending direction x of the protrusion 4a is parallel to the transmission axis direction of the reflective polarizing plate 3 are shown in FIGS. ) Is indicated by a two-dot chain line. Also in this case, the luminance in the angular range close to the normal line where the emission angle is about 0 ° to 25 ° is larger in both the horizontal direction and the vertical direction than the luminance in the emission angle range of 25 ° to 60 ° inclined more than that. The light distribution characteristic that is remarkably high is the same as that in the present embodiment, but the luminance value in the emission angle range of 0 ° to 25 ° is about 10% lower than that in the present embodiment. Therefore, the contrast is lowered accordingly.

  Returning to FIG. 1, the linearly polarized light P2 reflected by the reflective polarizing plate 3 is transmitted through the light guide plate 2 and is incident on the (1/4) wavelength phase difference plate 5 disposed on the rear surface side. As shown in FIG. 2D, the (1/4) wavelength phase difference plate 5 has a slow axis 5a of 45 ° with respect to the reflection axis 3b of the reflective polarizing plate 3 (see FIG. 2B). The incident linearly polarized light P2 is emitted as circularly polarized light due to its birefringence action. The emitted circularly polarized light is specularly reflected by the reflecting surface finished on the mirror surface of the light reflecting plate 6, is incident again on the (¼) wavelength phase difference plate 5, is subjected to the same birefringence action as the forward path, It returns to linearly polarized light and exits. The plane of polarization of the outgoing linearly polarized light P2 is rotated by 90 ° from the direction of the plane of polarization when entering the (¼) wavelength phase difference plate 5 in the forward path. Therefore, the direction of the plane of polarization is reflected polarized light. The direction is parallel to the transmission axis 3 a of the plate 3.

  The linearly polarized light P2 emitted from the (1/4) wavelength phase difference plate 5 passes through the light guide plate 2 again and enters the reflective polarizing plate 3. The direction of the polarization plane at this time is the linearly polarized light P1 described above. Similarly to the transmission axis 3 a of the reflective polarizing plate 3. Therefore, after that, the linearly polarized light P2 also passes through the reflective polarizing plate 3 and the prism sheet 4 in the same manner as the linearly polarized light P1 and receives the same optical action. The light distribution characteristic of the linearly polarized light P1 shown in FIG.

  As a result, if the light emitted from the prism sheet 5 in which the linearly polarized light P2 is added to the linearly polarized light P1, that is, the linearly polarized light irradiated from the illumination device of the present embodiment is used as the backlight light of the liquid crystal display panel 7, it is 0 °. A display in which the brightness is extremely high in a viewing angle range as narrow as ˜25 ° and the brightness rapidly decreases in a viewing angle range larger than about 25 ° is obtained. This display can prevent peeping by a person other than the front observer, and is a display with a desired high quality with sufficiently high brightness and contrast at the limited viewing angle.

As described above, in the illumination device according to the first embodiment, the reflective polarizing plate 3 and the prism sheet 4 are arranged in this order on the front side from which the light from the surface light emitting element composed of the cold cathode tube 1 and the light guide plate 2 is emitted. Since the transmission axis 3a of the projection 4a and the extending direction x of the protrusion 4a are arranged so as to be orthogonal to each other, the distribution of light distribution that is increased in the direction of the transmission axis 3a of the linearly polarized light P1 transmitted through the reflective polarizing plate 3 is By transmitting through the prism sheet 4, the distribution of light distribution is evenly distributed over all directions, and the light distribution is increased rapidly in a narrow emission angle range of about 0 to 25 ° from the normal direction. Be controlled. Further, since the (¼) wavelength phase difference plate 5 and the light reflection plate 6 are sequentially installed on the rear side of the surface light emitting element, the polarization plane reflected by the front reflection polarizing plate 3 is orthogonal to the transmission axis 3a (reflection). The linearly polarized light P2 that is parallel to the axis 3b is rotated by 90 ° in the plane of polarization, converted into an axially parallel linearly polarized light, and returned to the reflective polarizing plate 3. Light distribution is controlled through the sheet 4 and emitted with substantially the same light distribution. Therefore, according to the illuminating device of the present embodiment, the linearly polarized light reflected by the reflective polarizing plate 3 is also used as the emitted light, so that the light utilization efficiency is remarkably improved and the backlight for the liquid crystal display panel 7 or the like is used. When used, the viewing angle is limited to a desired limited narrow range in the front direction, and a display with sufficiently high brightness and contrast at the limited viewing angle is obtained. Peeping can be effectively prevented.
(Second Embodiment)

  FIG. 8 is a front sectional view showing a lighting device as a second embodiment of the present invention in an exploded manner, and FIGS. 9A to 9D are plan views showing the optical arrangement of its main constituent members. 8 is a cross-sectional view taken along the line VIII-VIII shown in FIG. In addition, the hatching of the cross section of FIG. 8 is abbreviate | omitted for convenience of explanation. Moreover, the same code | symbol is attached | subjected about the component same as 1st Embodiment, and the description is abbreviate | omitted.

  In the illumination device according to the second embodiment, another prism sheet 8 is installed between the light guide plate 2 and the reflective polarizing plate 3 in the illumination device according to the first embodiment. Accordingly, the reflective polarizing plate 3 is sandwiched between the two prism sheets 4 and 8. In this case, the configuration of the protrusions 8a of the prism sheet 8 disposed on the rear side of the reflective polarizing plate 3 and the arrangement pitch thereof are the same as those of the prism sheet 4 used in the first embodiment on the front side. The arrangement is such that the extending direction y of the protrusions 8 a is parallel to the transmission axis 3 a of the reflective polarizing plate 3, and therefore orthogonal to the extending direction x of the protrusions 4 a of the front prism sheet 4. Other configurations are the same as those of the first embodiment.

  In the illuminating device of the second embodiment configured as described above, the extending direction y of the protrusion 8a in the rear prism sheet 8 is parallel to the transmission axis 3a of the reflective polarizing plate 3, and therefore the rear prism. The light that passes through the sheet 8 and enters the reflective polarizing plate 3 is condensed on the area side along the transmission axis 3a having a high transmittance.

  That is, as shown in FIGS. 4A and 5 for explaining the first embodiment, linearly polarized light incident from the direction orthogonal to the transmission axis 3a of the reflective polarizing plate 3, that is, from the direction of the reflection axis 3b, is incident as an s wave. Since the linearly polarized light that is incident as the s wave has a lower transmittance as the incident angle increases, the incident angle is reduced by passing through the rear prism sheet 8 to increase the transmittance. . As a result, the light distribution of linearly polarized light emitted from the reflective polarizing plate 3 is a distribution in which the light distribution in the area along the transmission axis 3a is higher than the light distribution shown in FIG. .

  When the linearly polarized light emitted from the reflective / reflective polarizing plate 3 whose light distribution is controlled as described above is transmitted through the front prism sheet 4, it receives the same light condensing action as in the first embodiment. Therefore, the light distribution of linearly polarized light emitted from the prism sheet 4 is the distribution shown in FIGS. 10 (a) and 10 (b).

  As shown in FIGS. 10A and 10B, the light distribution of the irradiated linearly polarized light emitted from the illumination device of this embodiment has a light distribution directivity more than that of the first embodiment. The brightness increases sharply in a narrow emission angle range of about 15 ° or less from the normal direction, and the maximum brightness in both the vertical, horizontal, and azimuth directions is about 10% higher than that in the first embodiment. It has become.

  As described above, in the illumination device according to the second embodiment, the front and rear pair of prism sheets 4 and 8 are provided on the front side from which the light of the surface light emitting element including the cold cathode tube 1 and the light guide plate 2 is emitted. The extending directions x and y of the protrusions 4a and 8a are arranged so as to be orthogonal to each other, the reflective polarizing plate 3 is disposed between the pair of prism sheets 4 and 8, and the extending direction of the protrusion of the rear prism sheet 8 is the transmission axis 3a. Since it is interposed in an arrangement that is parallel to y (perpendicular to the protrusion extending direction x of the front prism sheet 4), light incident on the reflective polarizing plate 3 from a direction orthogonal to the transmission axis 3a is along the transmission axis 3a. As a result, the incident angle is reduced and the transmittance is increased. Further, the linearly polarized light emitted from the reflective polarizing plate 3 collected on the area side along the transmission axis 3a is reflected on the front side. Because it is focused on the normal side by the prism sheet 4, the front The linearly polarized light emitted from the prism sheet 4, that is, the irradiation light from the present illumination device, has a sharp increase in luminance in a narrow emission angle range of about 15 ° or less from the normal direction, and the highest luminance in both vertical and horizontal directions. However, the light distribution is further increased by about 10% compared to the first embodiment, and the directivity is further enhanced. Therefore, according to the illuminating device of the present embodiment, the linearly polarized light reflected by the reflective polarizing plate 3 is recursively used as in the first embodiment, so that the light utilization efficiency is remarkably improved and the liquid crystal display is used. When used as a backlight of the panel 7 or the like, the viewing angle can be limited to 15 degrees or less, which is smaller than that of the first embodiment, and the brightness is further reduced to about 10 within the extremely narrow limited viewing angle. A display with higher quality that is increased by about% can be obtained, and peeping by persons other than the front observer can be more effectively prevented.

  The present invention is not limited to the first and second embodiments described above. For example, the present invention is not limited to the case where the sidelight type surface light emitting device using the light guide plate as in the first and second embodiments is used as the light emitting device, but a diffusion plate using a cold cathode tube or a light emitting diode as a light source. Therefore, the present invention can be widely applied to various light-emitting elements that emit diffused light in a planar shape, such as an element that emits light in a planar shape.

  The light distribution control element is not limited to the prism sheet used in the first and second embodiments, and other optical elements such as a lens having a light condensing effect can be used effectively.

  In addition, the illumination device of the present invention is not limited to the backlight of the liquid crystal display panel, but can be effectively applied as a backlight of other display panels that require linearly polarized light.

1 is an exploded front sectional view showing an exploded configuration of a lighting device as a first embodiment of the present invention. The optical arrangement structure of the main member in the said 1st Embodiment is shown, (a) is a prism sheet, (b) is a reflective polarizing plate, (c) is a light emitting element, and (d) is a (1/4) wavelength phase difference. It is each top view of a board. FIG. 6 is a schematic explanatory view showing the action of light incident from the transmission axis direction in the reflective polarizing plate of the first embodiment, wherein (a) shows the action of linearly polarized light having a polarization plane parallel to the transmission axis of the reflective polarizing plate. (B) shows the action of linearly polarized light having a polarization plane orthogonal to the transmission axis of the reflective polarizing plate. It is a schematic explanatory view showing the action of light incident from the reflection axis direction in the reflection polarizing plate of the first embodiment, (a) shows the action of linearly polarized light having a polarization plane parallel to the transmission axis of the reflection polarizing plate. (B) shows the action of linearly polarized light having a polarization plane orthogonal to the transmission axis of the reflective polarizing plate. It is a characteristic curve figure which shows the change of the reflectance with respect to the incident angle of the linearly polarized light which injects into the reflective polarizing plate in the said 1st Embodiment. FIG. 5 is a light distribution diagram showing the intensity of transmitted light at each stage as an isoluminance curve in the first embodiment, where (a) is linearly polarized light that exits a reflective polarizing plate, and (b) is linearly polarized light that exits a prism sheet. Each light distribution is shown. FIG. 4 is a luminance characteristic diagram showing a change in luminance with respect to an emission angle of light emitted from the prism sheet in the first embodiment, where (a) shows the respective characteristics in the horizontal direction of the light emission surface and (b) shows the vertical direction of the light emission surface. Is shown. It is a decomposition | disassembly front sectional view which decomposes | disassembles and shows the structure of the illuminating device as 2nd Embodiment of this invention. The optical arrangement structure of the main member in the said 2nd Embodiment is shown, (a) is a front side prism sheet, (b) is a reflective polarizing plate, (c) is a rear side prism sheet, and (d) is each light emitting element. It is a top view. FIG. 6 is a luminance characteristic diagram showing a change in luminance with respect to an emission angle of light emitted from the front prism sheet in the two embodiments, wherein (a) shows the respective characteristics in the horizontal direction of the light emission surface and (b) shows the vertical direction of the light emission surface. Is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cold cathode tube 2 Light guide plate 3 Reflective polarizing plate 3a Transmission axis 3b Reflection axis 4 (front side) Prism sheet 4a Projection 5 (1/4) Wavelength phase difference plate 6 Light reflection plate 7 Liquid crystal display panel 8 Rear side prism sheet 8a Ridge

Claims (6)

A light emitting element;
A light guide plate that emits light from the light emitting element incident from the first surface from the second surface;
A reflective polarizing element disposed to face the second surface of the light guide plate;
A first prism having one main surface formed on a concavo-convex surface in which a plurality of protrusions are arranged in parallel and arranged so that the reflective polarizing element is interposed between the light guide plate Sheet,
One of the main surfaces is formed as a concave / convex surface in which a plurality of protrusions are continuously arranged in parallel, and the reflective polarization element is interposed between the reflective prism and the first prism sheet. A second prism sheet disposed between the element and the light guide plate;
With
The first prism sheet is disposed so that the extending direction of the protrusion is orthogonal to the transmission axis of the reflective polarizing element ,
The lighting device according to claim 2, wherein the second prism sheet is arranged such that an extending direction of the protrusion is parallel to a transmission axis of the reflective polarizing element .   The first prism sheet has the other main surface formed flat and faces the light guide plate so that the other main surface is adjacent to the second surface of the light guide plate. The lighting device according to claim 1.   The lighting device according to claim 2, wherein the protrusion has an isosceles triangle shape in cross section perpendicular to the extending direction. A reflector disposed such that the light guide plate is interposed between the reflective polarizing elements;
A retardation plate in which a slow layer axis is disposed at 45 ° with respect to the reflection axis of the reflective polarizing element between the reflection plate and the light guide plate;
The illuminating device according to claim 1, further comprising: The second prism sheet has the other main surface formed flat, and faces the light guide plate so that the other main surface is adjacent to the second surface of the light guide plate. The illumination device according to any one of claims 1 to 4, wherein A light emitting element;
A light guide plate that emits light from the light emitting element incident from the first surface from the second surface;
A reflective polarizing element disposed to face the second surface of the light guide plate;
A first prism having one main surface formed on a concavo-convex surface in which a plurality of protrusions are arranged in parallel and arranged so that the reflective polarizing element is interposed between the light guide plate Sheet,
One of the main surfaces is formed as a concave / convex surface in which a plurality of protrusions are continuously arranged in parallel, and the reflective polarization element is interposed between the reflective prism and the first prism sheet. A second prism sheet disposed between the element and the light guide plate;
A liquid crystal display panel disposed so that the first prism sheet is interposed between the reflective polarizing elements;
With
The first prism sheet is disposed so that the extending direction of the protrusion is orthogonal to the transmission axis of the reflective polarizing element,
The second prism sheet is a liquid crystal display device, wherein the extending direction of the protrusions is arranged in parallel to the transmission axis of the reflective polarizing element.

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