JP2007042405A - Backlight device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a backlight device wherein use efficiency of light is improved by controlling directivity of the light of a light source in a length direction and a width direction of a backlight. <P>SOLUTION: This backlight device has: the light source disposed inside a casing wherein one side is opened; and a light guide body allowing incidence of the light irradiated from the light source, and reflecting and guiding the light to an opening direction of the casing. The light guide body has: a first light guide plate allowing the incidence of the light of the light source; and a second light guide plate superposedly disposed on the opening side of the casing to the first light guide plate, and emitting the light to the opening direction of the casing. A width in a direction orthogonal to an optical axis of the light source in the first light guide plate is set such that it becomes large as it goes away from the light source to narrow the directivity in a width direction of the light guided into the first light guide plate. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a backlight device related to a backlight device used in a liquid crystal display device.

  In recent years, display devices using liquid crystal cells are mounted on various electronic devices such as watches, telephones, and personal computers. In such an electronic device, in particular, a watch, a mobile phone, and the like are often used at night or in a dark place, and therefore, are often provided with a backlight for illuminating a liquid crystal cell. The backlight is roughly classified into a direct type in which a light source is arranged under a light diffusion plate or the like, and a side light type in which a light source is arranged on a side surface of a light guide plate. A sidelight type backlight includes a flat light guide plate made of a synthetic resin, which is approximately the same size as a liquid crystal display panel, and one side surface of which is a light incident surface facing the light incident surface. A light source is arranged.

  As described above, the sidelight type backlight has a configuration in which the light source is disposed on the side of the light guide plate. Therefore, the sidelight type backlight can be made thinner than the direct type backlight, and the light source generates heat to the liquid crystal display panel. This is advantageous in that the influence can be reduced. As the light guide plate used in such a backlight device, for example, a plate in which a plurality of V grooves are formed, or one that has been subjected to sandblasting or graining is used, and through these light guide plates, As a point light source, light incident from a light emitting diode (LED) is guided to the entire display panel (see, for example, Patent Document 1).

  A specific example of such a conventional backlight device will be described with reference to FIGS. FIG. 8 shows a backlight device in the prior art, FIG. 8A is a plan view, and FIG. 8B is a cross-sectional view taken along the line DD in FIG. 8A. FIG. 9 is a schematic diagram showing an optical path of light emitted from a light source of a backlight device in the prior art. As shown in FIGS. 8 and 9, there are four light guide plates 2 each having a substantially rectangular parallelepiped shape made of a transparent plastic member inside a box-shaped housing 1, and four side surfaces 2 a serving as light incident portions of the light guide plate 2. A light emitting diode (hereinafter referred to as LED) 3 as a light source is installed. The light emitted from the LED 3 enters the light guide plate 2 from the side surface 2 a of the light guide plate 2, and is guided while repeating total reflection inside the light guide plate 2. Further, the lower surface 2b of the light guide plate 2 is a light reflecting surface, and prisms arranged at predetermined intervals are formed. Light irradiated from the LED 3 is reflected by the lower surface 2b and directed upward. The light is emitted from the upper surface 2c, which is the second emission surface, to the outside.

  A prism sheet 5 is provided on the upper surface 2c side of the light guide plate 2. Light emitted to the outside from the upper surface 2c of the light guide plate 2 is refracted, totally reflected, and transmitted by the prism sheet 5, and a liquid crystal panel (not shown). ). A reflective sheet 4 such as a white sheet is disposed on the lower surface 2 b side of the light guide plate 2. The reflection sheet 4 reflects light leaking from the lower surface of the light guide plate 2 and returns it to the light guide plate 2 again. Thus, in the conventional backlight device, light emitted from the plurality of LEDs 3 with directivity is guided to the light guide plate 2 and totally reflected by the prism provided on the lower surface 2b of the light guide plate 2. The light is emitted from the emission surface 2c to the outside, and is refracted, totally reflected, and transmitted by the prism sheet 5, and illuminates the entire back surface of a liquid crystal panel (not shown).

JP 2002-42529 A (Page 3-4, FIG. 1)

  However, in the sidelight type backlight device according to the prior art, the LED 3 used as the light source is a point light source, and the irradiated light generally has directivity. For this reason, the directivity of the backlight has a distorted characteristic that the direction parallel to the optical axis of the LED 3 is narrow and the direction orthogonal to the optical axis is wide. FIG. 10 shows the directivity in the length direction and the width direction of the backlight, the curve 6 shows the directivity in the length direction (ZY plane), and the curve 8 shows the directivity in the width direction (XY plane). ing. The vertical axis represents the luminance ratio of the backlight, and the horizontal axis represents the light emission angle with respect to the normal of the emission surface (2c) of the backlight.

  The traveling direction and directivity of the light emitted from the LED 3 are the prism provided on the lower surface 2b of the light guide plate 2 and the prism provided on the light exit surface 2c side of the light guide plate 2 in the direction perpendicular to the light emitting surface of the LED 3. Although controlled by the sheet 5, the traveling direction and directivity of the light in the direction parallel to the light emitting surface of the LED 3 are not controlled. For this reason, the directivity in the length direction and the width direction of the backlight device is different, resulting in a problem that uneven brightness occurs in the backlight. In addition, due to the demand for uniform brightness of the backlight, the brightness of the entire backlight device is limited by the brightness of the end of the backlight, which is the part farthest from the LED 3, and the light use efficiency is reduced. was there.

(Object of invention)
The object of the present invention has been made in view of the above-mentioned problems in the prior art, controls the directivity of light in the length direction and width direction of the backlight, efficiently guides light from the light source into the light guide plate, An object of the present invention is to provide a backlight device in which light emitted from a light guide plate has a bright and uniform brightness on the light exit surface and has improved light utilization efficiency.

  In order to achieve the above object, a backlight device according to the present invention includes a light source disposed inside a housing that is open on one side, light incident from the light source, and light reflected in the opening direction of the housing. The light guide includes a first light guide plate on which light from a light source is incident, and the first light guide plate is arranged so as to overlap with the first light guide plate on the opening side of the housing. The width of the first light guide plate in the direction perpendicular to the optical axis of the light source is set to increase as the distance from the light source increases, and the light is guided into the first light guide plate. The directivity in the width direction of the emitted light is narrowed.

  In addition, the first light guide plate receives the light incident from the light source on the first light incident surface and the light incident on the end opposite to the first light incident surface from the second light guide. A first light reflecting plate for reflecting toward the light plate; and a first light emitting surface for emitting light reflected from the first light reflecting member toward the second light guide plate; Reflects the incident light from the second light incident surface and the first light guide plate at one end corresponding to the first exit surface in the direction of the other end facing the one end. It has a 2nd reflective means and the 2nd output surface which radiate | emits light toward the opening direction of the said housing | casing, It is characterized by the above-mentioned.

  Moreover, the 1st reflection sheet is provided between the 1st light guide plate and the 2nd light guide plate, It is characterized by the above-mentioned.

  Moreover, it has a some light source and a some 1st light guide plate, and each 1st light guide plate is each arrange | positioned in the position corresponding to a some light source, It is characterized by the above-mentioned.

  Further, a second reflection sheet is provided on the opposite side of the first light guide plate to the second light guide plate.

  The second light guide plate has a prism surface for reflecting and guiding the light reflected by the second reflecting means toward the opening direction of the housing on the surface facing the first light guide plate. Is characterized in that prisms having a sawtooth inclination angle are arranged at predetermined intervals.

  Further, the inclination angle of the prism is composed of a first inclination angle of the slope of the prism facing the second reflecting means and a second inclination angle of the slope of the prism on the opposite side, and the first inclination angle. Is set so as to increase as the distance from the second reflecting means increases.

  As described above, the backlight device of the present invention is arranged to overlap the first light guide plate on which light from the light source is incident and the first light guide plate on the opening side of the housing, and emits light in the opening direction of the housing. Light in the longitudinal direction and the width direction of the backlight by setting the width in the direction perpendicular to the optical axis of the light source in the first light guide plate to increase as the distance from the light source increases. It is possible to control the directivity of the light source and to effectively use the irradiation light of the light source. As a result, it is possible to provide a backlight device that stabilizes the luminance and raises the luminance and has excellent luminance characteristics.

  1 to 7 show a backlight device according to an embodiment of the present invention. The backlight device according to the present embodiment includes a housing that is open on one side, a light source that is disposed inside the housing, and a light that is incident on the light emitted from the light source and guides the light in the opening direction of the housing. It has a light body. In addition, the light guide is incident on the light source of the light source, and is arranged on the opening side of the housing with respect to the first light guide plate and the first light guide plate that are emitted to the outside, and is emitted from the first light guide plate. And a second light guide plate that emits light and emits the light in the opening direction of the housing. The width of the first light guide plate in the direction orthogonal to the optical axis of the light source is set to increase as the distance from the light source increases, and the directivity in the width direction of the light guided into the first light guide plate is narrowed. In this way, the directivity of light in the length direction and width direction of the backlight is controlled to stabilize the brightness and increase the brightness. Hereinafter, specific examples of the backlight device according to the present embodiment will be described with reference to FIGS. 1 to 7. In addition, the same number is attached | subjected to the component similar to a prior art example, and description is abbreviate | omitted.

  FIG. 1 shows a backlight device in this embodiment, FIG. 1 (a) is a plan view, FIG. 1 (b) is a sectional view taken on line AA in FIG. 1 (a), and FIG. FIG. 3 shows a first light guide plate in the present embodiment, FIG. 3 (a) is a plan view, and FIG. 3 (b) shows FIG. FIG. 4A is a cross-sectional view taken along line BB in FIG. 4A, FIG. 4 is a diagram illustrating another example of the first light guide plate in the present embodiment, and FIG. 5 illustrates the second light guide plate in the present embodiment. ) Is a plan view, FIG. 5B is a cross-sectional view taken along the line CC in FIG. 5A, and FIG. 5C is a partially enlarged cross-sectional view of a portion A in FIG. FIG. 6 is a diagram showing the directivity of the LED in this embodiment and the directivity after passing through the first light guide plate, and FIG. 7 is the directivity in the length direction and the width direction of the backlight in this embodiment. FIG.

  As shown in FIG. 1, the backlight device according to the present embodiment includes a housing 1 that is open on one side, four LEDs 3 that are light sources disposed inside the housing 1, and light emitted from the LEDs 3. And a light guide 10 that reflects and guides light in the opening direction of the housing 1. The light guide 10 is disposed so as to be superimposed on the opening side of the housing 1 with respect to the first light guide plate 11 and the first light guide plate 11 on which the light of the LED 3 is incident, and reflects the light incident from the first light guide plate 11. And a second light guide plate 12 that guides and emits light in the opening direction of the housing 1. Further, a first reflection sheet 13 such as a silver sheet is provided between the first light guide plate 11 and the second light guide plate 12, and the second light guide plate 12 of the first light guide plate 11 and A second reflection sheet 14 such as a silver sheet is provided on the opposite side. The first reflection sheet 13 reflects the light leaking from the first light guide plate 11 and the light leaking from the second light guide plate 12 and returns them to the first and second light guide plates 11 and 12 again. It is. Similarly, the second reflection sheet 14 reflects light leaking from the first light guide plate 11 and returns it to the first light guide plate 11 again. Further, a prism sheet 5 is disposed on the light guide plate 12 on the opening side of the housing 1.

  In the present embodiment, as shown in FIG. 3, four first light guide plates 11 are arranged at positions corresponding to the four LEDs 3, respectively. The first light guide plate 11 is made of a transparent resin material, and its planar shape is substantially trapezoidal, and is set so that the value of the width b in the direction orthogonal to the optical axis of the LED 3 increases as the distance from the LED 3 increases. . In the present embodiment, the width a of the end facing the LED 3 is set to a value substantially equal to the size of the LED 3. The width c of the end opposite to the LED 3 was set corresponding to the size of the light guide 10 with a value larger than the width a. Further, the side surface facing the LED 3 is a first light incident surface 11a on which the light emitted from the LED 3 is incident, and the light incident from the LED 3 on the end opposite to the first light incident surface 11a is the second light incident surface 11a. A slope 11d as a first reflecting means for reflecting toward the light guide plate 12 and a first emission surface 11e for emitting the light reflected by the slope 11d toward the second light guide plate 12 are provided. ing.

The inclined surface 11d is formed from the lower surface 11b toward the upper surface 11c so that the thickness of the first light guide plate 11 decreases as it approaches the end. The inclined surface 11d is preferably provided with a reflective film (not shown) having high reflectivity with respect to light. This reflective film reflects light leaking from the inclined surface 11d and returns it to the first light guide plate 11 again, and is preferably a metal thin film such as aluminum or chrome. The first emission surface 11 e is provided on a part of the upper surface 11 c of the first light guide plate 11. Furthermore, it is preferable to provide a reflective film (not shown) having high reflectivity with respect to light on the side surfaces 11f and 11g in the longitudinal direction of the first light guide plate 11. This reflective film reflects light leaking from the first light guide plate 11 and returns it to the first light guide plate 11 again. The reflective film is preferably a metal thin film such as aluminum or chrome. In this embodiment, the lower surface 11b of the first light guide plate 11 is a flat surface, but a prism surface in which sawtooth-shaped prisms are arranged at predetermined intervals may be used.

  FIG. 6 shows the directivity of the LED 3 and the directivity of light after passing through the first light guide plate 11. In FIG. 6, a curve 17 indicates the directivity of the light emitted from the LED 3, and a curve 18 indicates the directivity of the light after passing through the first light guide plate 11. The vertical axis represents the luminance ratio, and the horizontal axis represents the light emission angle. In this way, by setting the value of the width b of the first light guide plate 11 in the direction orthogonal to the optical axis of the LED 3 to increase as the distance from the light source increases, the directivity of the light emitted from the LED 3 is reduced. The directivity in the width direction of the light guided into the first light guide plate 11 can be reduced.

  FIG. 4 shows another example of the first light guide plate 11. In the present embodiment, the example in which the side surfaces 11f and 11g in the longitudinal direction of the first light guide plate 11 are planes has been described. However, as shown in FIG. Alternatively, as shown in FIG. 4B, it may be formed of a curved surface that curves concavely toward the inside. Moreover, as shown in FIG.4 (c), the surface which inclines with respect to the optical axis of LED3 is formed in either one side surface 11f and 11g, and the other side surface is parallel to the optical axis of LED3. It is good as a surface.

  The second light guide plate 12 is made of a transparent resin material, has a substantially rectangular parallelepiped shape as shown in FIG. 5, and the size of the plane is the size of the plane in which the four first light guide plates 11 are arranged in parallel. The size is set to be approximately equal to this. The second light guide plate 12 has an upper surface 12c that is a plane on the opening side of the housing 1 as a second emitting surface that emits light toward the opening direction of the housing 1, and an upper surface 12c that is the second emitting surface. A prism surface is formed on the lower surface 12b opposite to the first light guide plate 11 for reflecting and guiding light incident from the first light guide plate 11 in the direction of the upper surface 12c, which is the second emission surface. In addition, the second light guide plate 12 is superimposed on the first light guide plate 11, and the first light guide plate 11 is disposed at one end corresponding to the first emission surface 11 e of the first light guide plate 11. A second light incident surface 12a on which light emitted from the second light incident surface 12a is incident, and an inclined surface 12d as second reflecting means for reflecting the incident light toward the other end facing the one end. ing. The inclined surface 12d is formed from the upper surface 12c toward the lower surface 12b so that the thickness of the second light guide plate 12 decreases as it approaches the end. The inclined surface 12d is preferably provided with a reflective film (not shown) having high reflectivity for light. This reflection film reflects light leaking from the inclined surface 12d and returns it to the second light guide plate 12, and a metal thin film such as aluminum or chrome is preferable. The second light incident surface 12 a is provided on a part of the lower surface 12 b of the second light guide plate 12.

  As shown in FIG. 5C, prisms having a sawtooth shape are arranged at predetermined intervals on the prism surface provided on the lower surface 12b of the second light guide plate 12. This prism has an inclined surface 12d which is a second reflecting means, and has one prism inclined surface 16a having a first inclination angle P and the other prism inclined surface 16b having a second inclination angle Q on the opposite side. The first inclination angle P is set to increase as the distance from the inclined surface 12d as the second reflecting means increases. The first inclination angle P varies depending on the size of the backlight and is not particularly limited, but is preferably set in the range of 0.5 to 50 degrees. The prism pitch is preferably about 0.05 to 0.3 mm.

  Next, the optical path of the light emitted from LED3 of the backlight apparatus in a present Example is demonstrated based on FIG. As shown in FIG. 2, the light emitted from the LED 3 enters the inside from the first light incident surface 11a of the first light guide plate 11, and the directivity in the width direction is narrowed while being reflected and propagated inside. It reaches the end opposite to the first light incident surface 11a. The light whose directionality is narrowed is reflected by the inclined surface 11d as the first reflecting means, and is emitted from the first emission surface 11e toward the second light guide plate 12. The light emitted from the first light guide plate 11 is incident from the second light incident surface 12a of the second light guide plate 12, and the end portion on the opposite side to the slope 12d by the slope 12d as the second reflecting means. Reflected in the direction of. Thereafter, light is propagated in the direction of the end opposite to the inclined surface 12d while being repeatedly reflected by the prism surface of the lower surface 12b of the light guide plate 12. Thereafter, light whose incident angle with respect to the upper surface 12c, which is the second emission surface of the second light guide plate 12, gradually becomes smaller and smaller than the critical angle is emitted from the upper surface 12c of the second light guide plate 12 and is planarly emitted. It is configured as follows. Note that the inner wall of the housing 1 facing the inclined surfaces 11d and 12d may be provided with an inclined inner wall 1a in close contact with the inclined surface 11d and an inclined inner wall 1b in close contact with the inclined surface 12d. As the housing 1 material, it is preferable to use a material having light reflectivity. In this case, it is not necessary to provide a reflective film on the inclined surfaces 11d and 12d.

  Furthermore, the light emitted from the second light guide plate 12 enters the prism sheet 5 and is converted into light having directivity characteristics in the opening direction of the housing 1. FIG. 7 shows the directivity in the length direction and the width direction of the backlight in this embodiment. The vertical axis represents the luminance of the backlight, and the horizontal axis represents the light emission angle with respect to the optical axis of the LED 3. A curve 19 indicates the directivity in the length direction (ZY plane) and the directivity in the width direction (XY plane). The directivity in the length direction and the directivity in the width direction of the backlight in this embodiment. Are substantially the same, and are displayed by a common curve 19. Thus, the backlight device of the present embodiment is irradiated from the LED 3 by setting the width value of the first light guide plate 11 in the direction orthogonal to the optical axis of the LED 3 to increase as the distance from the light source increases. The directionality of the light in the width direction is narrowed, and the light whose width directionality is narrowed enters and propagates into the second light guide plate 12, so that the LED 3 in the length direction and width direction of the backlight The directivity of light can be controlled. As a result, as shown in FIG. 7, the directivities in the length direction and the width direction of the backlight are substantially equal as shown by the curve 19, and the luminance unevenness of the backlight is suppressed. As a result, the light emitted from the LED 3 can be efficiently guided to the light guide and the luminance of the entire backlight can be made uniform.

  As described above, the backlight device according to the present embodiment is arranged so as to overlap the first light guide plate 11 on which the light of the LED 3 enters and the first light guide plate 11 on the opening side of the housing 1. A second light guide plate 12 that emits light in the opening direction, and the width b of the first light guide plate 11 in the direction orthogonal to the optical axis of the LED 3 is set to increase as the distance from the wire 3 increases. Thus, it is possible to control the directivity of light in the length direction and width direction of the backlight, and it is possible to effectively use the irradiation light of the LED 3. As a result, it is possible to realize a backlight device that stabilizes the luminance and raises the luminance and has excellent luminance characteristics.

  In this embodiment, an example using four LEDs as a light source has been described. However, the present invention is not limited to this, and the same applies when one LED or four or more LEDs are used. The effect of can be obtained.

  Further, the backlight device of the present invention can be widely applied to various lighting devices, display devices, and the like including liquid crystal display devices.

1A and 1B show a backlight device according to an embodiment of the present invention, in which FIG. 1A is a plan view, and FIG. 1B is a cross-sectional view taken along line AA in FIG. 1A, and an optical path of light emitted from a light source FIG. It is a schematic diagram which shows the optical path of the light emitted from the light source of the backlight apparatus in the Example of this invention. The 1st light-guide plate in the Example of this invention is shown, Fig.3 (a) is a top view, FIG.3 (b) is BB sectional drawing in Fig.3 (a). It is a figure which shows the other example of the 1st light-guide plate in the Example of this invention. The 2nd light-guide plate in the Example of this invention is shown, Fig.5 (a) is a top view, FIG.5 (b) is CC sectional drawing in Fig.5 (a), FIG.5 (c) is a figure. It is a partial expanded sectional view of the A section in 5 (b). It is a figure which shows the directivity of LED in the Example of this invention, and the directivity after 1st light-guide plate permeation | transmission. It is a figure which shows the directivity of the length direction of the backlight in the Example of this invention, and the width direction. The backlight apparatus in a prior art example is shown, Fig.8 (a) is a top view, FIG.8 (b) is CC sectional drawing in Fig.8 (a). It is a schematic diagram which shows the optical path of the light emitted from the light source of the backlight apparatus in a prior art. It is a figure which shows the directivity of the length direction and width direction of the backlight in a prior art.

Explanation of symbols

1 Housing 1a, 1b Slope inner wall 3 LED
5 Prism sheet 10 Light guide 11 First light guide plate 11a First light guide plate light incident surface 11b First light guide plate lower surface 11c First light guide plate upper surface 11d First light guide plate slope 11e First 11f and 11g of the light guide plate in the longitudinal direction of the first light guide plate 12 Second light guide plate 12a Light incident surface 12b of the second light guide plate Reflective surface 12c of the second light guide plate Second light guide plate 12d The second light guide plate slope 13 The first diffusion sheet 14 The second diffusion sheet 16a The first inclination angle 16b of the prism in the second light guide plate The second inclination of the prism in the second light guide plate Corner 17 Curve 18 showing directivity of LED Curve 19 showing directivity after transmission through first light guide plate
Curve showing backlight directivity

Claims (7)

  A light source disposed inside a housing that is open at one side; and a light guide that receives light emitted from the light source and reflects and guides light in an opening direction of the housing; A first light guide plate that receives light from a light source; and a second light guide plate that is disposed on the opening side of the housing so as to overlap the first light guide plate and emits light in the opening direction of the housing. The width of the first light guide plate in the direction orthogonal to the optical axis of the light source is set to increase as the distance from the light source increases, and the direction of the light guided into the first light guide plate in the width direction is set. Backlight device characterized by narrowing the nature.   The first light guide plate receives the light incident from the light source, the first light incident surface and the light incident from the light source on the opposite end of the first light incident surface to the second light guide plate. A first reflecting means for reflecting the light toward the second light guide plate and a first light emitting surface for emitting the reflected light from the first reflecting means toward the second light guide plate. The second light incident surface and the incident light from the first light guide plate are reflected at one end corresponding to the first emission surface in the direction of the other end facing the one end. 2. The backlight device according to claim 1, further comprising: a second reflecting unit that emits light toward an opening direction of the casing.   3. The backlight device according to claim 1, wherein a first reflective sheet is provided between the first light guide plate and the second light guide plate. 4.   4. The apparatus according to claim 1, further comprising a plurality of light sources and a plurality of first light guide plates, wherein each first light guide plate is disposed at a position corresponding to the plurality of light sources. The backlight device according to any one of the above.   5. The backlight according to claim 1, wherein the second reflection sheet is provided on a side of the first light guide plate opposite to the second light guide plate. 6. apparatus.    The second light guide plate has a prism surface for reflecting and guiding the light reflected by the second reflecting means toward the opening direction of the housing on a surface facing the first light guide plate. The backlight device according to any one of claims 1 to 5, wherein prisms having a sawtooth inclination angle are arranged on the surface at a predetermined interval. The inclination angle of the prism is composed of a first inclination angle of the slope of the prism facing the second reflecting means and a second inclination angle of the slope of the prism on the opposite side, and the first inclination 7. The backlight device according to claim 6, wherein the corner is set so as to increase as the distance from the second reflecting means increases.

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