JP2009277388A - Surface light source device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface light source device capable of making directivity of light distribution different, without deteriorating the display quality and brightness, at low price. <P>SOLUTION: The surface light source device 100 is equipped with a light guide plate 30, having a light reflecting face 33 in which a first and a second inclined faces 36a, 36b asymmetrical in a light introduction direction are formed; and a first and a second light sources 10, 20 arranged opposed to mutually opposing side faces 31, 32 of the light guide plate 30. The light introduced inside of the light guide plate 30 from the first light source 10 has directivity in a perpendicular direction and is emitted from the surface light source device 100, and the light introduced inside the light guide plate 30 from the second light source 20 has directivity in the three directions of the perpendicular direction and in the inclined directions, respectively to the right and left from the perpendicular direction, and is emitted from the surface light source device 100. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a surface light source device, for example, particularly to a surface light source device used as a backlight of a liquid crystal display of a portable electronic device such as a notebook computer or a mobile phone.

  A surface light source device used as a backlight of a liquid crystal display or the like is generally a side edge type in which a light source is disposed facing a side surface of a light guide plate. In this light guide plate, a light incident surface is a side surface on which light is incident from a light source extending in a longitudinal direction so as to face, and a part of the light introduced into the inside from the light incident surface is a surface. To release from. Then, on the light emission surface side of the light guide plate, an optical sheet such as a prism sheet or a diffusion sheet is arranged according to the use in order to adjust the traveling direction of the light emitted from the light emission surface.

  As disclosed in Patent Documents 1 to 3, a general light guide plate has a prism that extends in the light introduction direction on the light emission surface thereof. The light reflecting surface that reflects the light introduced into the light guide plate and directs it toward the light emitting surface is used as the back surface. A dot pattern (dotted pattern of minute recesses or protrusions) is formed on the light reflecting surface. Has been. Thereby, the brightness | luminance of the light emitted from a surface light source device is equalized over the whole surface, and bright surface emission is obtained. In addition, in the surface light source device, in order to improve the visibility in the left-right direction of the liquid crystal display, the light output direction is widely distributed in the left-right direction centering on the direction perpendicular to the light-emitting surface, and has a wide-angle directivity. It has optical characteristics. The light distribution characteristic of the surface light source device is single and does not change when the light source is turned on.

There are cases where portable electronic devices such as notebook computers and mobile phones that use such a surface light source device as a backlight of a liquid crystal display are handled in public places such as public transportation. In this case, since the visibility in the left-right direction is wide, there is a risk that the highly confidential content displayed on the liquid crystal display may be read by being seen by a third party adjacent to the seat. Therefore, a light control film (trade name, manufactured by Sumitomo 3M Co., Ltd.) that restricts the light distribution in a specific direction can be applied to the surface of the liquid crystal panel to limit the visibility in the horizontal direction to the depression angle. is there. There is also a surface light source device that can vary light distribution characteristics by using two liquid crystal panels having different light distribution characteristics in an overlapping manner.
JP 2000-221329 A Japanese Patent Laid-Open No. 2002-50219 JP 2005-108803 A

  However, the light distribution film is not made in conformity with the resolution and polarization characteristics of the liquid crystal display to be attached. For this reason, striped patterns generated due to interference between the arrangement pitch of the light distribution elements of the light distribution film and the cell arrangement pitch of the liquid crystal panel, and reflection of the reflected image generated between the light distribution film called the ghost and the liquid crystal panel There is a problem that the display quality of the liquid crystal display is deteriorated. In addition, since the light distribution film physically blocks light emitted from the outermost surface of the liquid crystal display, there is a problem that the brightness of the liquid crystal display is lowered. In addition, there is a problem that the surface light source device using two liquid crystal panels in an overlapping manner is expensive.

  In view of the circumstances described above, an object of the present invention is to provide a surface light source device that can change the directivity of the light distribution without lowering the display quality and brightness at a low price.

  In the surface light source device of the present invention, the first and second light incident surfaces which are a pair of side surfaces facing each other, the surface in the thickness direction, and introduced into the inside from the first or second light incident surface. A light guide plate comprising: a light emitting surface for emitting light; a light reflecting surface that is a back surface in the thickness direction and reflects light introduced into the light emitting surface toward the light emitting surface; and A first light source extending in the longitudinal direction and disposed opposite the first light incident surface; and extending in a longitudinal direction of the second light incident surface; A second light source disposed opposite to the light source; and a prism sheet disposed such that the light emitting surface and the surface on which the prism is formed are opposed to each other, and the second light is transmitted from the first light incident surface. A first inclined surface inclined in a direction in which the thickness decreases toward the incident surface, and the first light incident surface from the first light incident surface. A second inclined surface that is inclined in a direction in which the thickness decreases toward the incident surface and is asymmetrical to the first light incident surface is formed on the light reflecting surface. The light introduced into the light guide plate through the light incident surface is reflected by the light reflecting surface and emitted from the light emitting surface, and is perpendicular to the light emitting surface from the prism sheet. Light is emitted with directivity in three directions: a direction inclined from the vertical direction to the first light incident surface side and a direction inclined from the vertical direction to the second light incident surface side. To do.

  According to the surface light source device of the present invention, when the first light source is turned on, the light is emitted from the prism sheet with directivity in the direction perpendicular to the light emission surface (the direction toward the person viewing from the liquid crystal display). The Therefore, in a liquid crystal display equipped with a surface light source device, visibility that is drooping in the left-right direction can be obtained. Therefore, when handling a portable electronic device such as a laptop computer or a mobile phone in a public place, by turning on the first light source, the highly confidential content displayed on the liquid crystal display can be read by a third party or the like who sits next to it. Can be easily eliminated. On the other hand, when the second light source is turned on, the prism sheet is perpendicular to the light emitting surface, the direction inclined from the vertical direction to the first light incident surface side, and from the vertical direction to the second light incident surface side. Light is emitted with directivity in three directions of the inclined direction. Therefore, in a liquid crystal display equipped with a surface light source device, light is emitted with directivity in a total of three directions including a vertical direction and a direction inclined from the vertical direction to the left and right directions. The human eyes perform a wide range of display recognition by capturing a bright part of one of the three independent peaks to supplement a part with little light. Therefore, by the pseudo wide angle using the visual perception of the human eye, the wide-angle visibility in the left-right direction can be ensured as in the conventional surface light source device. As described above, it is possible to change the directivity of the light distribution of the light emitted from the surface light source device simply by switching the lighting of the first or second light source, and a liquid crystal equipped with the surface light source device. It is possible to select that the visibility in the left-right direction on the display is a depression angle or a wide angle.

  Furthermore, unlike the light distribution film, the surface light source device can appropriately form the light reflecting surface of the light guide plate according to the liquid crystal display on which the surface light source device is mounted. It is possible to prevent the display quality of the liquid crystal display from being deteriorated. Furthermore, unlike the light distribution film, the surface light source device does not physically block the light emitted from the outermost part of the liquid crystal display, so that the brightness of the liquid crystal display on which the surface light source device is mounted decreases. Can be prevented. Further, the surface light source device needs to use only one liquid crystal panel as compared with a surface light source device that uses two liquid crystal panels stacked on top of each other. It becomes possible.

  Further, in the surface light source device of the present invention, the first inclined surface is inclined from 1 degree to 8 degrees toward the light emitting surface side from the direction from the first light incident surface to the second light incident surface, The second inclined surface is preferably inclined by 36 to 60 degrees toward the light emitting surface from a direction from the second light incident surface toward the first light incident surface.

  In this case, the light distribution of the light emitted from the surface light source device has a directivity that is narrow in one direction when only the first light source is turned on, and is 3 when only the second light source is turned on. It has directivity separated in the direction.

  Moreover, the surface light source device of this invention WHEREIN: It is preferable to provide the light absorption sheet arrange | positioned so as to oppose the said light reflection surface.

  In this case, since the light absorption sheet absorbs light leaking from the light reflection surface to the outside of the light guide plate, the light reflected and scattered by the member located below the light reflection surface of the light guide plate is again inside the light guide plate. By entering the light, it is possible to improve that unintended light is mixed in the direction emitted from the surface light source device.

  An embodiment of the present invention will be described with reference to FIGS.

  First, the overall configuration of the surface light source device 100 of the present embodiment will be described.

  Referring to FIG. 1, the surface light source device 100 of this embodiment includes a first light source 10, a second light source 20, a light guide plate 30, a light absorbing sheet 40, and a prism sheet 50.

  Both the first light source 10 and the second light source 20 are LED arrays in which a plurality of LEDs (Light Emitting Diodes) are arranged in an array in one column. However, a linear light source such as a cold cathode fluorescent tube or a hot cathode fluorescent tube may be used as the first light source 10 or the second light source 20.

  The first light source 10 and the second light source 20 are lit by independent lighting circuits (not shown). Note that a portable electronic device such as a notebook computer, a mobile phone, a PDA (Personal Digital Assistant), a portable TV / DVD, or a bank equipped with a liquid crystal display that uses the surface light source device 100 of the present embodiment as a backlight. The ATM terminal or the like is provided with light source selection means (not shown) for selecting which of the first light source 10 or the second light source 20 is turned on. The light source selection means includes, for example, a changeover switch, a changeover button, or a key assigned in a predetermined state to a touch panel or a keyboard.

  The light guide plate 30 has a rectangular plate shape in general outline, and is formed of a light-transmitting material such as acrylic resin or polycarbonate resin. One side surface 31 of the pair of side surfaces 31, 32 facing each other of the light guide plate 30 serves as a first light incident surface 31 through which light enters the light guide plate 30 from the first light source 10. . The first light source 10 is arranged so that its longitudinal direction coincides with the longitudinal direction of the first light incident surface 31 so as to face the first light incident surface 31. Almost all the emitted light is introduced into the light guide plate 30 through the first light incident surface 31. The other side surface 32 is a second light incident surface 32 through which light is incident from the second light source 20 into the light guide plate 30. The second light source 20 is disposed so as to face the second light incident surface 32 with its longitudinal direction coinciding with the longitudinal direction of the second light incident surface 32. Almost all the emitted light is introduced into the light guide plate 30 through the second light incident surface 32. The first light incident surface 31 and the second light incident surface 32 opposite to the first light incident surface 31 are flat surfaces parallel to each other.

  In the following description, as shown in FIGS. 1 and 2, the direction perpendicular to the first and second light incident surfaces 31 and 32 is the X-axis direction, and 2 orthogonal to each other on a plane orthogonal to the X-axis direction. Let the axial direction be the Y-axis direction and the Z-axis direction. These X-axis direction, Y-axis direction, and Z-axis direction are three-axis directions orthogonal to each other. In this case, the Y-axis direction is the longitudinal direction of the first and second light incident surfaces 31, 32 (longitudinal direction of the first and second light sources 10, 20), and the Z-axis direction is the thickness direction of the light guide plate 30 (FIG. 1 is the vertical direction). Then, the direction from the first light incident surface 31 toward the second light incident surface 32, in other words, the light introduction direction from the first light source 10 to the light guide plate 30 is generally the X-axis positive direction. . The direction from the second light incident surface 32 side toward the first light incident surface 31, that is, the direction of introducing light from the second light source 20 to the light guide plate 30, which is the opposite direction, is X Axis negative direction. Further, the direction from the back surface 34 side of the light guide plate 30 toward the front surface 33, in other words, the direction from the light guide plate 30 side toward the prism sheet 50 is defined as a positive Z-axis direction. The direction from the front surface 33 side to the back surface 34 of the light guide plate 30, which is the opposite direction, in other words, the direction from the light guide plate 30 side to the light absorbing sheet 40 is defined as the negative Z-axis direction.

  The light guide plate 30 has a light emitting surface 33 whose surface (upper surface in the drawing) 33 in the thickness direction emits light introduced into the light emitting plate 30 to the outside. The back surface (the lower surface in the figure) 34 in the thickness direction of the light guide plate 30 is a light reflecting surface 34 that reflects the light introduced into the light guide plate 30 and directs it toward the light emitting surface 33. The light emitting surface 33 and the light reflecting surface 34 facing the light emitting surface 33 are flat surfaces whose reference planes are parallel to each other. In the present embodiment, the length of the light guide plate 30 in the X-axis direction is, for example, 168 mm, but may be 150 mm to 300 mm, and is not limited.

  A plurality of prisms 35 extending in parallel with each other in the X-axis direction are continuously formed on the light emitting surface 33 so as to protrude from the reference plane in the Z-axis positive direction. Each prism 35 has a substantially isosceles triangular cross section (cross section orthogonal to the X axis direction), in other words, a substantially triangular prism shape extending in the X axis direction. The prism 35 is formed integrally with the light guide plate 30 by injection molding or the like. The reference plane of the light emitting surface 33 is a surface defined by the four end points of the light emitting surface 33 on the light absorbing sheet 40 side. In the present embodiment, the width of each prism 35 in the Y-axis direction is, for example, 50 μm, and the apex angle of each prism 35 is, for example, 90 to 120 degrees. The width and apex angle of the prism 35 in the Y-axis direction are appropriately adjusted according to directivity required in the Y-axis direction of the backlight. The shape of the cross section of the prism 35 is not limited to a shape in which isosceles triangles are continuous, and may be a trapezoidal shape, a trapezoidal shape, a corrugated shape, or the like with a flat top, and further, these shapes. It may have a flat surface between them. Further, the shape of the cross section of the prism 35 may be changed in a similar manner continuously in the Z-axis direction, or the interval between the prisms 35 in the Y-axis direction may not be constant.

  On the light reflecting surface 34, a plurality of concave ridge portions 36 linearly extending in parallel to each other in the Y-axis direction are continuously formed so as to be depressed in the positive direction of the Z-axis from the reference plane. Each concave line portion 36 is a triangular depression whose cross section (cross section perpendicular to the Y-axis direction) is flat. The concave portion 36 is formed integrally with the light guide plate 30 by injection molding or the like. The reference plane of the light reflecting surface 34 is a surface defined by the four end points on the light absorbing sheet 40 side of the light reflecting surface 34.

  The concave portion 36 is directed in the Z-axis positive direction (the direction in which the thickness of the light guide plate 30 decreases from the first light incident surface 31 toward the second light incident surface 32) toward the X-axis positive direction. The inclined first inclined surface 36a and the positive direction of the Z-axis toward the negative X-axis direction (the thickness of the light guide plate 30 decreases from the second light incident surface 32 toward the first light incident surface 31). And the second inclined surface 36b inclined in the direction) constitutes two oblique sides having a triangular shape with the reference plane as the base. The first inclined surface 36a is a gently inclined surface that inclines very gently from 1 degree to 8 degrees from the X axis positive direction to the Z axis positive direction side (light emission surface 31 side). In other words, the first inclined surface 36a has a reflection surface angle with an opening angle from the reference plane of 1 degree to 8 degrees. On the other hand, the second inclined surface 36b is a steeply inclined surface that inclines sharply from 36 degrees to 60 degrees from the X-axis negative direction to the Z-axis positive direction side (light emission surface 31 side). In other words, the second inclined surface 36b has a reflection surface angle with an opening angle from the reference plane of 36 degrees to 60 degrees. Thus, the first and second inclined surfaces 36a, 36b of the concave portion 36 have their own reflection surface angles, and the light reflection surface 34 is provided with an optical pattern configured in an asymmetric shape. ing. In the present embodiment, the width of each concave strip 36 in the Z-axis direction is, for example, 1 μm.

  The first and second inclined surfaces 36a and 36b of the concave portion 36 are respectively flat mirror surfaces, and the light incident on the inside of the light guide plate 30 is totally reflected by this mirror surface, and is on the light emission surface 33 side. Head for. Here, the mirror surface may be a simple flat surface in the state of the light guide plate 30 at the time of injection molding. The portion where the first inclined surface 36a and the second inclined surface 36b are connected is rounded due to the limitations of mold accuracy and molding transfer accuracy related to pattern shape reproducibility. The part leaks out from the light reflecting surface 34 and becomes a loss. Of course, it is preferable that the roundness of the portion where the first inclined surface 36a and the second inclined surface 36b are connected is smaller in order to reduce optical loss.

  On the light reflection surface 34 side of the light guide plate 30, a light absorption sheet 40 is disposed so as to face and cover the light reflection surface 34. The light absorbing sheet 40 is a black or gray resin sheet and absorbs light leaking from the light reflecting surface 34 to the outside of the light guide plate 30. As a result, the light reflected and scattered by the member positioned in the negative Z-axis direction (downward) of the light guide plate 30 is incident on the light guide plate 30 again, and the prism sheet 50 side from the light emitting surface 33 of the light guide plate 30. This prevents the direction of light emitted from the light from becoming unintended. In addition, when the roundness of the part which the 1st inclined surface 36a and the 2nd inclined surface 36b of the above-mentioned concave part 36 connect is small, the light absorption sheet 40 does not need to be provided. In this case, a reflective sheet may be provided to reflect the light leaking from the light reflecting surface 34 and return it to the inside of the light guide plate 30.

  On the light emission surface 33 side of the light guide plate 30, a prism sheet 50 is disposed so as to face and cover the light emission surface 33. A horizontal flat surface of the surface in the thickness direction of the prism sheet 50 is a light exit surface 51 from which light is emitted from the surface light source device 100. In the prism sheet 50, a plurality of prisms 52 extending in parallel with each other in the Y-axis direction protrude in the negative direction of the Z-axis on the back surface in the thickness direction, that is, the surface on the light emitting surface 33 side of the light guide plate 30. Is formed. Such a prism sheet 50 is generally called a downward prism sheet. Each prism 52 has a substantially isosceles triangle shape in cross section (cross section perpendicular to the Y-axis direction), in other words, a substantially triangular prism shape extending in the Y-axis direction. There may be a flat surface between the prisms 52. In the present embodiment, the width of each prism 52 in the X-axis direction is, for example, 50 μm, and the apex angle of each prism 52 is, for example, 68 degrees. The prism sheet 50 having such a prism 52 changes the direction of light emitted from the light emitting surface 33 of the light guide plate 30 to the outside and adjusts the direction of light emitted from the light emitting surface 51.

  Although not shown in the drawings, the surface light source device 100 has first and second light incident surfaces 31 and 32 at the end portions thereof in a state where the light absorbing sheet 40 is superimposed on the light reflecting surface 34 side of the light guide plate 30. The first and second light sources 10 and 20 are assembled, and the prism sheet 50 is superimposed on the light emission surface 33 side of the light guide plate 30 and assembled inside the frame. The surface light source device 100 configured as described above is emitted from the surface light source device 100 so as to face the surface side of the surface light source device 100, that is, the side where the prism sheet 50 is disposed, although not shown. A liquid crystal panel that displays an image by controlling transmitted light is disposed and used as a backlight of a liquid crystal display. At this time, the surface light source device 100 is arranged such that the first and second light sources 10 and 20 are arranged on both sides in the left and right directions where human eyes viewing the contents displayed on the liquid crystal display are arranged. Is mounted on the LCD.

  Next, the effect of the surface light source device 100 of this embodiment is demonstrated.

  When the first light source 10 is turned on and the second light source 20 is turned off by the light source selection means, the first light is incident on the inside of the light guide plate 30 as schematically shown on the right side of FIG. Light is introduced only from the first light source 10 via the surface 31. The light introduced from the first light source 10 into the light guide plate 30 through the first light incident surface 31 is substantially reflected by the first inclined surface 36a of the light reflecting surface 34, and has a similar angle. Is incident on the light emitting surface 33. A part of the light incident on the light emitting surface 33 is emitted from the light emitting surface 33 to the prism sheet 50 side, and the direction of the prism 52 of the prism sheet 50 is changed substantially in the positive direction of the Z-axis, whereby the surface light source device. The light exits from 100 light exit surfaces 51 in the vertically upward direction. Accordingly, by turning on only the first light source 10, the light output direction of the light from the surface light source device 100 is narrowly limited to the vertically upward direction from the light output surface 51, and a light distribution having unidirectional directivity can be obtained. .

  For this reason, in the liquid crystal display equipped with the main light source device 100, when only the first light source 10 is turned on by the light source selection unit, the visibility in the horizontal direction of the liquid crystal panel can be obtained. Therefore, when a portable electronic device such as a laptop computer or a mobile phone is handled in a public place, the light source selection unit turns on only the first light source 10 so that the highly confidential content displayed on the liquid crystal panel is adjacent to the seat. The possibility of being read by a third party or the like can easily be eliminated.

  FIG. 3 shows a simulation result showing the light emission angle as the light distribution characteristic of the surface light source device 100 by changing the inclination angle of the first inclined surface 36a. The inclination angle of the second inclined surface 36b is 44 degrees. The light exit angle means an angle from the vertically upward direction (Z-axis positive direction) of the light emitted from the light exit surface 51. The positive light emission angle means that light is emitted from the vertically upward direction to the counter light incident side, that is, the second light source 20 side, and that the light output angle is negative means that the light output angle is negative from the vertical upward direction. It means that light is emitted at an inclination toward the first light source 10 side. FIG. 3 shows that the light emission angle is limited to a range of approximately 10 to 15 degrees, and a light distribution having a directivity narrowly limited in the vertical upward direction can be obtained. It can be seen that as the inclination angle of the first inclined surface 36a increases, the vertical luminance (the luminance of the light emitted vertically upward) decreases. For example, when the inclination angle of the first inclined surface 36a is changed from 2 degrees to 6 degrees and 8 degrees, the vertical luminance is reduced to approximately two thirds and half, respectively. Therefore, from the viewpoint of vertical luminance, it is preferable that the inclination angle of the first inclined surface 36a is as gentle as possible. However, the gentler the angle of inclination of the first inclined surface 36a, the smaller the number of concave portions 36 made up of the first and second inclined surfaces 36a, 36b, which is not preferable for uniformity in the X-axis direction. Influence. Considering these, the inclination angle of the first inclined surface 36a is 1 to 8 degrees, preferably 1 to 4 degrees, and more preferably 2 to 4 degrees.

  On the other hand, when the second light source 20 is turned on by the light source selection unit and the first light source 10 is turned off, as schematically shown on the left side of FIG. Light is introduced only from the second light source 20 through the light incident surface 32. A part of the light introduced from the second light source 20 into the light guide plate 30 through the second light incident surface 32 is reflected by the first inclined surface 36a of the light reflecting surface 34, and the like. The light is incident on the light emitting surface 33 at an angle. A part of the light incident on the light emitting surface 33 is emitted from the light emitting surface 33 to the prism sheet 50 side, and the direction of the prism 52 of the prism sheet 50 is changed substantially in the positive direction of the Z-axis, whereby the surface light source device. The light exits from 100 light exit surfaces 51 in the vertically upward direction. Therefore, the light reflected by the first inclined surface 36a has a light distribution having a directivity in which the light output direction from the surface light source device 100 is narrowly limited to the vertically upward direction from the light output surface 51. The other part of the light introduced from the second light source 20 into the light guide plate 30 through the second light incident surface 32 is reflected by the second inclined surface 36b of the light reflecting surface 34, and is almost the same. The light is incident on the light emitting surface 33 vertically. The light incident on the light emitting surface 33 is emitted from the light emitting surface 33 to the prism sheet 50 side, and the direction is changed by the prism 52 of the prism sheet 50 in a direction inclined in the positive / negative direction of the X axis. Light is emitted from 100 light exit surfaces 51 in a direction inclined in the positive and negative directions of the X axis from the vertically upward direction. Therefore, the light reflected by the second inclined surface 36 b is narrowly limited in two directions in which the light output direction from the surface light source device 100 is inclined in the X-axis positive / negative direction from the vertical direction to the light output surface 51. The light distribution has a characteristic. Therefore, by turning on only the second light source 20, the light output direction of the light from the surface light source device 100 is narrowly limited to the vertically upward direction from the light output surface 51 and the direction inclined in the X-axis positive / negative direction from the direction, A light distribution having directivity in three directions is obtained.

  Therefore, in the liquid crystal display equipped with the surface light source device 100, when only the second light source 20 is turned on by the light source selection means, the vertical direction in the liquid crystal panel (the direction toward the person viewing from the liquid crystal panel) and the direction. The light is separated and emitted in a total of three directions that are inclined in both the right and left directions, and luminance peaks appear in the three directions. The light emission directions of these three directions are narrow, but there is no portion where light is not emitted between them, and the light is continuously distributed. The human eyes perform a wide range of display recognition by capturing a bright part of one of the three independent peaks to supplement a part with little light. Therefore, when only the second light source 20 is turned on by the light source selection means by the pseudo wide angle using the visual cognitive ability of the human eye, as in the conventional surface light source device, the wide-angle visibility in the left-right direction. Can be secured.

  4A to 4C show simulation results showing the light emission angle as the light distribution characteristic of the surface light source device 100 by changing the inclination angle of the second inclined surface 36b. The inclination angle of the first inclined surface 36a is 2 degrees. Note that a positive light emission angle means that light is emitted from the vertically upward direction to the light incident side, that is, the first light source 10 side, and that light is emitted, and that the light output angle is negative means that light is incident from the vertical upward direction. This means that the light is emitted at an inclination toward the second light source 20 side. From FIG. 4A to FIG. 4C, when the inclination angle of the second inclined surface 36b is in the range of 40 degrees to 52 degrees, the light emission angle is substantially vertically upward in the range of −10 degrees to 10 degrees. It can be seen that there is a peak in each of three directions, that is, the direction and two directions in the vicinity of positive and negative 30 degrees, and a light distribution with directivity separated in the three directions is obtained. Also, the more positive and negative the symmetry is, the better the display unevenness. Considering that it is preferable to have clear peaks in three directions and to be positively and negatively symmetric, when the concave portions 36 of the light reflecting surface 34 are arranged in a single shape, the second inclined surface 36b. Is preferably 40 to 52 degrees, more preferably 40 to 48 degrees. On the other hand, when the inclination angle of the second inclined surface 36b is 36 degrees, 56 degrees, or 60 degrees, a peak appears only in two directions. Therefore, it is also possible to combine the second inclined surfaces 36b having different inclination angles, such as alternately providing the concave strip portions 36 having two second inclined surfaces 36b having inclination angles of 36 degrees and 54 degrees. Therefore, the inclination angle of the second inclined surface 36b may be 36 degrees to 60 degrees.

  Note that, as described above, the portion where the first inclined surface 36a and the second inclined surface 36b are connected is rounded due to the limit relating to the reproducibility of the pattern shape. As this part is rounded, the luminance decreases at the light emission peak in the left-right direction and the slope of the light distribution waveform on the anti-incident side tends to become gentler. For this reason, it is preferable that the roundness of the portion where the first inclined surface 36a and the second inclined surface 36b are connected is smaller.

  As described above, in the liquid crystal display equipped with the surface light source device 100 of the present embodiment, the light source selection unit simply selects the light source to be turned on from the first or second light source 10 or 20, and the liquid crystal display The visibility in the left-right direction can be switched between the depression angle and the wide angle. Therefore, the first light source 10 is selected by the light source selection means when a portable electronic device such as a notebook computer, a mobile phone, a PDA, or a portable TV / DVD is handled in a public place or when an ATM terminal of a bank is operated alone. By turning on only the light, it is possible to easily eliminate the possibility that the highly confidential content displayed on the liquid crystal panel can be read by a third party or the like who is sitting next to it. On the other hand, when the portable electronic device is handled in a private place or when the bank ATM terminal is operated while consulting by a plurality of people, the second light source 20 is turned on by the light source selection means, thereby the liquid crystal panel. In this case, it is possible to ensure wide-angle visibility in the left-right direction, and it is possible to obtain good operability as in the conventional case.

  Further, unlike the light distribution film, the surface light source device 100 of the present embodiment can appropriately form the shape of the light reflecting surface 34 of the light guide plate 30 according to the liquid crystal display on which the surface light source device is mounted. It is possible to prevent the display quality of the liquid crystal display on which the surface light source device 100 is mounted from being deteriorated. In addition, unlike the light distribution film, the surface light source device 100 does not physically block the light emitted from the outermost portion of the liquid crystal display, and thus the brightness of the liquid crystal display on which the surface light source device 100 is mounted. Can be prevented from decreasing. In addition, the surface light source device 100 is provided at a low price because it requires only one liquid crystal panel and is similar in structure to the conventional one, as compared with a surface light source device that uses two liquid crystal panels stacked on top of each other. It becomes possible to do.

  In addition, in the surface light source device 100 of this embodiment mentioned above, the case where only one of the 1st or 2nd light sources 10 and 20 was lighted by the said light source selection stage was demonstrated. However, both the first and second light sources 10 and 20 may be turned on. For example, the first and second light sources 10 and 20 are turned on with appropriately adjusted amounts of light, and the light incident on the light guide plate 30 from the first and second light sources 10 and 20 is synthesized. Further, it becomes possible to emit light having a more appropriate light distribution from the surface light source device 100.

  Moreover, the case where the several recessed strip part 36 formed in the light reflection surface 34 of the light-guide plate 30 was the same was demonstrated. However, the plurality of concave portions 36 may be different from each other. For example, the inclination angles of the first or second inclined surfaces 36a, 36b of the concave portion 36 are different from each other within the respective angle ranges described above, and such concave portions 36 exist in a plurality of sets. May be. As described above, by forming the light reflecting surface 34 by appropriately combining the concave portions 36 with abundant variations, it is possible to emit light having a more appropriate light distribution from the surface light source device 100.

  Further, a case has been described in which the plurality of concave portions 36 formed on the light reflecting surface 34 of the light guide plate 30 are linearly extended in parallel with each other in the Y-axis direction. However, it is only necessary that the plurality of concave portions 36 extend substantially in the Y-axis direction. For example, the concave strip 36 may extend in the approximate Y-axis direction while meandering or skewing. Further, there may be a flat surface between the concave strip portions 36. In particular, when the emission area is large, such as 17 inches wide, or when the thickness is extremely thin, such as 0.6 mm or less, it is necessary to reduce the overall density (reflection area). It is necessary to provide a flat surface. Furthermore, the present invention is not limited to the case where a flat surface is positioned at the lower end portion where the first inclined surface 36a and the second inclined surface 36b are connected, and the flat surface may be positioned at the upper end portion where the first inclined surface 36a and the second inclined surface 36b are connected. .

  Moreover, the case where the cross section of the recessed strip part 36 formed in the light reflection surface 34 of the light guide plate 30 is the same in the Y-axis direction has been described. However, the light reflecting surface 34 of the light guide plate 30 may be formed in any shape having two inclined surfaces whose inclined surfaces are inclined by the two predetermined ranges of angles described above. For example, the light reflecting surface 34 of the light guide plate 30 has four inclined surfaces with an inclination angle in the positive Z-axis direction of 1 to 8 degrees and an inclined surface with an inclination angle in the negative Z-axis direction of 36 to 60 degrees. The thing of the shape which extended the top part of the pyramid or the quadrangular pyramid may be formed.

The disassembled perspective view of the surface light source device in one Embodiment of this invention. The vertical cross-section explanatory drawing of a surface light source device. The graph which shows the simulation result of the light distribution characteristic of the surface light source device which changed the inclination-angle of the 1st inclined surface. (A)-(c) is a graph which shows the simulation result of the light distribution characteristic of the surface light source device which changed the inclination-angle of the 2nd inclined surface.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... 1st light source, 20 ... 2nd light source 30 ... Light guide plate, 31 ... 1st light incident surface (side surface), 32 ... 2nd light incident surface (side surface), 33 ... Light emission surface (front surface) 34 ... Light reflecting surface (back surface), 35 ... Prism, 36 ... Recess, 36a ... First inclined surface, 36b ... Second inclined surface,
40 ... light absorption sheet, 50 ... prism sheet, 51 ... light exit surface, 52 ... prism,
100: Surface light source device.

Claims (3)

A first and second light incident surfaces which are a pair of side surfaces facing each other; a light emitting surface which is a surface in the thickness direction and emits light introduced into the inside from the first or second light incident surface; A light guide plate having a light reflecting surface that is a back surface in the thickness direction and reflects light introduced inside and faces the light emitting surface;
A first light source that extends in a longitudinal direction of the first light incident surface and is disposed to face the first light incident surface;
A second light source that extends in the longitudinal direction of the second light incident surface and is disposed to face the second light incident surface;
A prism sheet disposed so that the light emitting surface and the surface on which the prism is formed are opposed to each other;
A first inclined surface inclined in a direction in which the thickness decreases from the first light incident surface toward the second light incident surface; and the first light incident from the second light incident surface. A second inclined surface that is inclined in a direction in which the thickness decreases toward the surface and is asymmetric to the first light incident surface is formed on the light reflecting surface;
The light introduced from the first light source into the light guide plate through the first light incident surface is reflected by the light reflecting surface and emitted from the light emitting surface, and is emitted from the prism sheet from the prism sheet. Light is emitted with directivity in the direction perpendicular to the light emission surface,
The light introduced from the second light source into the light guide plate through the second light incident surface is reflected by the light reflecting surface and emitted from the light emitting surface, and the light is emitted from the prism sheet from the prism sheet. Directivity in three directions: a direction perpendicular to the light emitting surface, a direction inclined from the vertical direction to the first light incident surface side, and a direction inclined from the vertical direction to the second light incident surface side. The surface light source device is characterized in that the light is emitted.   The first inclined surface is inclined from 1 degree to 8 degrees toward the light emitting surface from the direction from the first light incident surface to the second light incident surface, and the second inclined surface is the first inclined surface 2. The surface light source device according to claim 1, wherein the surface light source device is inclined by 36 to 60 degrees toward the light emitting surface from a direction from the second light incident surface toward the first light incident surface.   The surface light source device according to claim 1, further comprising a light absorbing sheet disposed so as to face the light reflecting surface.

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