JP2006040639A - Plane light source and display device equipped with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase polarizing anisotropy of irradiation light of a backlight as much as possible. <P>SOLUTION: The backlight 10 is provided with a light source part 60, and a light guide plate 13 uniformly irradiating incident light of the light source 60 from an irradiating face. The light source part 60, provided with a plurality of LED light sources 60a, is so structured to increase polarizing anisotropy of the light irradiated from the light guide plate 13 as compared with the case of irradiation of non-polarized light, by irradiating the polarized light having a polarized polarity in a thickness direction of the light guide plate 13 from each LED light source 60a. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a surface light source device that emits uniform light from an emission surface and a display device including the same.

  2. Description of the Related Art In recent years, liquid crystal display devices (Liquid Crystal Display) have been widely used for OA equipment such as personal computers, portable information equipment, and camera-body-type VTRs equipped with a liquid crystal monitor, taking advantage of the thin and low power consumption characteristics. ing.

  As such a liquid crystal display device, for example, a transmissive liquid crystal display device excellent in visibility is known. A transmissive liquid crystal display device includes a surface light source device (hereinafter also referred to as a backlight) provided on the back side of a liquid crystal display element (liquid crystal display panel), and modulates the light of the backlight by the liquid crystal display element. Thus, the display is performed. In addition to a transmissive display using light from a backlight, a transflective liquid crystal display device that performs a reflective display using ambient ambient light is also generally known.

  As the backlight applied to the transmissive liquid crystal display device and the transflective liquid crystal display device, a so-called edge light system is becoming mainstream as the liquid crystal display device becomes thinner and lighter (for example, Patent Document 1 and Patent Document 2).

  Here, a conventional edge light type backlight will be described with reference to FIG. The edge light type backlight 120 is disposed on the back side (lower side in FIG. 8) of the liquid crystal display element 130 having a pair of polarizing plates 132 and 133, and a light guide plate 125 that is a light control member, and the light guide plate 125. And a linear light source 116 provided on the side surface of the main body. Then, light incident on the light guide plate 125 from the light source 116 is homogenized by the light guide plate 125, and is emitted toward the liquid crystal display element 130 from the emission surface on the front side (upper side in FIG. 8) of the light guide plate 125. Yes.

  That is, the light emitted from the light source 116 enters the light guide plate 125 directly or indirectly by being reflected by the reflector 115. The light incident on the light guide plate 125 is repeatedly reflected and refracted inside the light guide plate 125, and a part of the light is emitted from the front exit surface, and the other light is emitted from the rear exit surface. A dot pattern is formed on the reflection surface and the emission surface of the light guide plate 125 by molding or printing. Further, a reflection sheet 126 is disposed on the back side of the light guide plate 125, and the emitted light on the back side is reflected to the front side by the reflection sheet 126.

  The light emitted to the front side of the light guide plate 125 is supplied to the liquid crystal display element 130 via the light control member. The light control member includes a first diffusion sheet 124, a first prism sheet 123, a second prism sheet 122, and a second diffusion sheet 121, which are arranged in order from the back side to the front side. ing.

  On the front surface of the first prism sheet 123, a plurality of fine prism patterns extending in a direction substantially orthogonal to the end surface of the light guide plate 125 on which the light from the light source 116 is incident are formed. A plurality of prism patterns orthogonal to the prism pattern of the first prism sheet 123 are formed on the front surface of the second prism sheet 122. Thus, the backlight 120 is configured as a planar light source device with high luminance efficiency, and bright display by the liquid crystal display device is enabled.

  However, in recent years, there has been a demand for higher brightness, and the method of arranging two prism sheets orthogonally as described above has a limit in light use efficiency, and it is difficult to greatly improve the brightness efficiency. There is a problem.

  In order to solve the above problems, it is known to form a prism pattern on the light guide plate itself of the backlight (see, for example, Patent Document 3). This backlight will be described with reference to FIG.

  In the backlight 101, the light emitted from the light source 116 disposed on the end surface of the light guide plate 113 is incident on the light guide plate 113 directly or reflected by the reflector 115. The light guide plate 113 has an emission surface from which light in the light guide plate 113 is emitted on the front side, and a reflection surface that reflects light in the light guide plate 113 on the back side. That is, on the back surface of the light guide plate 113, a part of the light is reflected to the front surface side by the reflection surface, and the other light is transmitted through the reflection surface and emitted to the back surface side.

  A fine prism pattern extending in a direction substantially orthogonal to the end surface on which the light from the light source is incident is formed on the light exit surface of the light guide plate 113 or the reflective surface on the back surface side. The prism pattern is repeatedly formed in a direction substantially parallel to the end surface of the light guide plate 113. Further, a reflection sheet 114 is provided on the back side of the light guide plate 113.

  A prism sheet 112 as a light control member is disposed on the front side of the light guide plate 113. A plurality of prism patterns that are substantially orthogonal to the prism pattern of the light guide plate 113 are formed on the rear surface side of the prism sheet 112. Further, a diffusion sheet 111 is disposed on the front side of the prism sheet 112. With the above configuration, the luminance of the backlight 101 is further increased.

Further, it has been conventionally known that a cold cathode tube is applied to the linear light source 116. In recent years, an LED array in which a plurality of light emitting diodes (LEDs), which are point light sources, are arranged in a line is often applied as a linear light source. This is because the LED has an advantage that it has lower power consumption than a cold cathode tube and can be reduced in thickness. A backlight including such an LED array as a linear light source is suitably used for a liquid crystal display device such as a mobile phone or a portable information terminal.
JP-A-8-68997 JP 2001-166302 A Japanese Patent Laid-Open No. 11-224516

  Incidentally, a display device such as a liquid crystal display device having a display panel sandwiched between polarizing plates has a predetermined transmission axis. Therefore, when the light from the surface light source device that irradiates the display panel does not have sufficient polarization, a polarization loss occurs in the display panel, and the light from the light source incident on the light control member can be used effectively. It will disappear.

  Therefore, as in Patent Document 2, a prism sheet is disposed between the light guide plate and the polarizing plate of the display panel, and the prism sheet makes the maximum intensity direction of the light emitted from the light guide plate in the transmission axis direction of the polarizing plate. It is known to swivel. This makes it possible to increase the amount of the polarized light component that passes through the polarizing plate.

  However, in practice, there is a limit to increase the polarization component of light incident on the display panel by the prism sheet. As a result, there is a problem that the light amount of the light source cannot be used effectively.

  The present invention has been made in view of such various points, and an object thereof is to increase the polarization anisotropy of the emitted light of the surface light source device as much as possible.

  In order to achieve the above object, in the present invention, the light source itself that makes the light incident on the light control member emits polarized light.

  Specifically, the surface light source device according to the present invention is a surface light source device including a light source and a light control member that uniformly emits light of the incident light source from an output surface, and the light source is polarized light Is configured to increase the polarization anisotropy of the light emitted from the light control member as compared with the case of emitting non-polarized light.

  The light control member may be composed of a light guide plate.

  The polarization polarity direction of the light emitted from the light source is preferably the thickness direction of the light guide plate.

  The light source is preferably composed of a plurality of point light sources.

  The light source may be composed of a light emitting diode.

  The semiconductor chip of the light-emitting diode includes an active layer that contributes to light emission, and the active layer preferably has a quantum wire structure or a quantum dot structure.

  A display device according to the present invention includes the surface light source device and a display element that is disposed to face the surface light source device and includes a pair of polarizing plates.

  The display element may be a liquid crystal display element.

-Action-
Next, the operation of the present invention will be described.

  The inventors of the present invention have made extensive studies on the characteristics of the emitted light of the planar light source device, and as a result, applied the light source that emits polarized light as the light source that supplies the light to the light control member. The fact that it can influence the polarization of the emitted light at has been found.

  That is, the polarized light emitted from the light source enters the light control member. The light incident on the light control member is uniformly reflected from the light exit surface of the light control member over the entire light exit surface by repeating reflection and refraction inside the light control member. This makes it possible to increase the polarization anisotropy of the light emitted from the light control member.

  Further, the light control member is constituted by a light guide plate, and the polarization anisotropy of the light emitted from the light guide plate is further increased by defining the polarization polarity direction of the light emitted from the light source in the thickness direction of the conductive plate. It becomes possible.

  By the way, it can be said that the light emitting diode includes a semiconductor chip that emits light, a phosphor, and the like. The semiconductor chip has an active layer that contributes to light emission. In general, the active layer has a bulk structure in which the light emitting layer does not exhibit a quantum effect, or exhibits a quantum confinement effect only in a one-dimensional direction. It has a quantum well structure. Light emitted from a light emitting diode having an active layer having a bulk structure or a quantum well structure hardly exhibits polarization.

  On the other hand, the active layer structure emits in the plane direction of the semiconductor chip by forming a quantum wire structure having a high light emission efficiency with a quantum confinement effect in a two-dimensional direction and a quantum dot structure having shape anisotropy. It becomes possible to increase the polarization property with respect to the light to be transmitted. In this case, when the semiconductor chip is packaged as a light emitting diode, the polarization direction can be adjusted.

  Therefore, as in the present invention, the light source is composed of a light emitting diode that is a point light source, and the structure of the active layer of the light emitting diode is a quantum wire structure or a quantum dot structure, so that polarization in a desired polarization direction can be achieved. Can be emitted.

  As described above, since the polarization anisotropy of the emitted light of the surface light source device is increased, the polarization loss in the display element having a pair of polarizing plates is effectively reduced. As a result, since the light of the light source incident on the light control member is effectively used, the luminance of the image displayed on the display device can be efficiently increased.

  According to the present invention, since the light source that makes light incident on the light control member emits polarized light, the polarization anisotropy of the emitted light of the surface light source device can be increased as much as possible. It can be used effectively.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The present invention is not limited to the following embodiment.

Embodiment 1 of the Invention
1 and 2 show an embodiment of a backlight and a display device including the backlight according to the present invention. In the following embodiments, the upper side in FIG. 1 is referred to as “front side”, and the lower side is referred to as “back side”. That is, the observer observes the display on the front side of the display device.

  As shown in FIG. 1, which is a perspective view, the liquid crystal display device S of the present embodiment is a backlight 10 that is a backlight and a liquid crystal display that is a display element disposed to face the front side of the backlight 10. A liquid crystal display device including the element 30. The liquid crystal display device S is a known transmissive liquid crystal display device, and displays light by modulating the light emitted from the backlight 10 by the liquid crystal display element 30.

  The liquid crystal display element 30 typically includes a pair of substrates 31 and a liquid crystal layer (not shown) provided between the substrates 31. Further, the liquid crystal display element 30 has a pair of polarizing plates 32 and 33 provided with the pair of substrates 31 sandwiched therebetween. The absorption axes of the polarizing plates 32 and 33 are substantially orthogonal to each other.

  The backlight 10 includes a light source unit 60, a light guide plate 13 that is a light control member, an optical sheet 12, and a reflection sheet 14.

  The light source unit 60 includes a plurality of light sources 60a. The light source 60a is composed of a light emitting diode (hereinafter referred to as an LED light source 60a) that is a point light source. The light source unit 60 is configured by an LED array in which a plurality of LED light sources 60a are arranged in a line at predetermined intervals along the end face (incident surface on which light from the light source 60a is incident) 13a. . The light source unit 60 is mounted on a flexible substrate (not shown).

  As shown in FIG. 1, the light guide plate 13 is made of a resin such as polycarbonate or polymethyl methacrylate, and is formed as a plate-like member. One side surface of the light guide plate 13 is an incident surface 13a on which light from the light source unit 60 is incident, while the front surface of the light guide plate 13 is an output surface 13b from which light inside the light guide plate 13 is emitted. Further, the back surface of the light guide plate 13 is an anti-light emitting surface 13c that reflects part of the light in the light guide plate 13 to the front side and emits the other part to the back side.

  It is preferable to apply a prism shape or a dot pattern to one or both of the exit surface 13b and the counter-exit surface 13c. Although not shown, a prism structure having a substantially triangular cross section having a ridge line in a direction substantially orthogonal to the incident surface 13a is repeatedly formed on the back side of the light guide plate 13 in the present embodiment.

  The optical sheet 12 is disposed on the front side of the light guide plate 13 and improves the brightness of display light by bringing the traveling direction of light from the exit surface 13b closer to the normal direction of the display surface of the liquid crystal display element 30. It is configured to let you.

  The optical sheet 12 is formed using polyethylene terephthalate as a base material, and a prism structure having a substantially triangular cross section is formed on the back side thereof by an ultraviolet curable resin. The ridge line direction of the prism structure is substantially perpendicular to the ridge line direction of the prism structure of the light guide plate 13.

  The reflection sheet 14 is disposed on the back side of the light guide plate 13, reflects the light emitted from the non-emission surface 13 c of the light guide plate 13 to the back side, and again enters the light guide plate 13 on the front side. It is configured as follows. The reflection sheet 14 is formed using polyethylene terephthalate as a base material, and is provided with, for example, a white diffusion layer or a metal vapor deposition layer.

  And although illustration is abbreviate | omitted, the said LED light source 60a is comprised by the white light emitting diode (white LED). The white LED has a semiconductor chip made of InGaN or the like and emits blue light, and a yellow phosphor typified by YAG or the like, and thereby emits white light.

  The semiconductor chip includes an active layer that contributes to light emission, and the active layer has a quantum wire structure (a structure that exhibits a quantum confinement effect in a two-dimensional direction and high light emission efficiency) or a quantum dot structure (having shape anisotropy). Structure). Thus, the LED light source 60a is configured to emit polarized light. Note that the polarization anisotropy of the emitted light can be adjusted when the semiconductor chip is incorporated as an LED.

  Furthermore, the polarization polarity direction of the light emitted from the LED light source 60a is preferably the same direction as the thickness direction of the light guide plate 13 as shown in FIG. Accordingly, the backlight 10 is configured to increase the polarization anisotropy of the light emitted from the light guide plate 13 as compared with the case where non-polarized light having no polarization is emitted from the light source unit 60. .

  With the above configuration, the light having polarization emitted from each LED light source 60a of the light source unit 60 enters the light guide plate 13 through the incident surface 13a. The polarized light that has entered the light guide plate 13 is repeatedly reflected and refracted inside the light guide plate 13 so that a part of the light is emitted directly from the light exit surface 13b of the light guide plate 13 to the front side, and the other Light exits from the opposite exit surface 13 c of the light guide plate 13 to the back side. The light emitted to the back side is reflected by the reflection sheet 14 and again enters the light guide plate 13, and then exits from the exit surface 13 b of the light guide plate 13 to the front side.

  As a result, all the light is uniformly emitted from the emission surface 13b of the light guide plate 13 over the entire emission surface 13b. Thereby, the polarization anisotropy of the light emitted from the light guide plate 13 can be sufficiently increased.

  The light emitted from the light guide plate 13 passes through the optical sheet 12 and enters the liquid crystal display element 30 after the light traveling direction is brought close to the normal direction of the display surface of the liquid crystal display element 30.

  In the liquid crystal display element 30, light efficiently transmitted through the polarizing plate 33 on the back side passes through a liquid crystal layer (not shown) and selectively transmits through the polarizing plate 32 on the front side according to the driving state of the liquid crystal. As a result, display with high luminance is performed.

  Therefore, according to this embodiment, since the LED light source 60a incident on the light guide plate 13 emits polarized light, the polarization anisotropy of the emitted light of the backlight 10 compared to the conventional one that emits non-polarized light. Can be increased.

  Furthermore, since the emitted light of the backlight 10 has sufficient polarization, the polarization loss in the liquid crystal display element 30 can be reduced by applying the backlight 10 to a liquid crystal display device. As a result, the light quantity of the LED light source 60a can be used effectively, so that the brightness of the display image can be dramatically increased while reducing power consumption.

(Example)
Next, an embodiment in which the present invention is implemented will be described with reference to FIGS.

  In this example, the luminance change rate of the backlight with respect to the relative angle when the polarization anisotropy of the LED light source 60a was changed with respect to the backlight 10 described in the above embodiment was experimentally measured.

  FIG. 3 is an explanatory view showing an experimental method. In order to measure the luminance of the light emitted from the backlight 10, the luminance measuring device 42 was installed horizontally on the front side of the backlight 10. Furthermore, in order to measure the luminance of the polarized light, a polarizing filter 41 is provided at the lens tip of the luminance measuring device 42.

  In addition, the center of the lens of the luminance measuring device 42 was set so as to be aligned with the center of the backlight 10 of the sample to be measured, and focusing was performed at a height position of about 40 cm from the surface of the backlight 10. Then, the luminance was measured while rotating the backlight 10 by 5 ° counterclockwise while maintaining the horizontal state. At this time, as shown in FIG. 3, the state in which the polarization direction 41a of the polarizing filter 41 and the direction in which the LED light source 60a is provided coincides with 0 °.

  The following four types of measurement samples were performed. As shown in FIG. 2, a sample in which the light emitted from the LED light source 60a has polarization anisotropy and is inclined by 90 ° with respect to the horizontal plane with the optical axis of the LED light source 60a as a base axis is taken as an example. As shown in FIG. 4, a sample that is similarly inclined by 45 ° is referred to as Comparative Example 1. In addition, as shown in FIG. Further, as shown in FIG. 6, a sample in which the emitted light is not given polarization anisotropy is referred to as Comparative Example 3.

  The graph which shows the measurement result of the said Example and each Comparative Examples 1-3 is shown in FIG. In FIG. 7, the solid line indicates Example 1, the one-dot chain line indicates Comparative Example 1, the two-dot chain line indicates Comparative Example 2, and the broken line indicates Comparative Example 3. Moreover, the measured numerical value is relativized, and the place having the highest polarity was defined as 100%.

  From the graph of FIG. 7, the polarization anisotropy of the light incident on the light guide plate 13 is not inclined with respect to the horizontal plane (the substrate surface of the light guide plate 13) when the optical axis of the LED light source 60a is used as the base axis (the light guide). From the case of having a polarity in the longitudinal direction on the incident surface 13a of the light plate 13: from Comparative Example 2), when it is perpendicular to the horizontal plane (with the optical axis of the LED light source 60a as the base axis, the inclination is 90 ° with respect to the horizontal plane In some cases, it can be seen that the polarization anisotropy increases as the process proceeds to Example.

  From these results, when the light emitted from the light source unit 60 has a polarization anisotropy polarity in the substantially thickness direction of the light guide plate 13, the polarization anisotropy polarity in the emitted light of the backlight 10. It becomes clear that the light of the light source unit 60 can be used more efficiently.

  As described above, the present invention is useful for a surface light source device that emits uniform light from an exit surface and a display device including the same, and increases the polarization anisotropy of the exit light of the surface light source device. Suitable for

It is a disassembled perspective view which shows a backlight and a liquid crystal display device typically. It is a perspective view which shows the polarization anisotropy of the emitted light of the LED light source of Example 1. FIG. It is a perspective view which shows the method of measuring the polarization anisotropy of the emitted light of a backlight. 6 is a perspective view showing a comparative example 1. FIG. It is a perspective view which shows the comparative example 2. FIG. 10 is a perspective view showing a comparative example 3. FIG. It is a graph which shows the measurement result of an Example and each comparative example. It is a disassembled perspective view which shows the conventional surface light source device and a display apparatus. It is a disassembled perspective view which shows the conventional surface light source device and a display apparatus.

Explanation of symbols

S Liquid crystal display device (display device)
10 Backlight (surface light source device)
13 Light guide plate (light control member)
13b Emission surface 30 Liquid crystal display element (display element)
60 Light source (light source)
60a LED light source (point light source)

Claims (8)

A surface light source device comprising a light source and a light control member that uniformly emits light from the incident light source from an emission surface,
The light source is configured to increase polarization anisotropy of light emitted from the light control member by emitting polarized light as compared with a case of emitting non-polarized light. Light source device. In claim 1,
The surface light source device, wherein the light control member is formed of a light guide plate. In claim 2,
A surface light source device, wherein a polarization polarity direction of light emitted from the light source is a thickness direction of the light guide plate. In claim 1,
The surface light source device, wherein the light source is composed of a plurality of point light sources. In claim 4,
The surface light source device, wherein the point light source is constituted by a light emitting diode. In claim 5,
The semiconductor chip of the light emitting diode includes an active layer that contributes to light emission,
The surface light source device, wherein the active layer has a quantum wire structure or a quantum dot structure. A surface light source device according to claim 1;
A display device, comprising: a display element disposed opposite to the surface light source device and having a pair of polarizing plates. In claim 7,
The display device is a liquid crystal display device.

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