JP2006012509A - Light guide plate and surface light emitting device using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To exhibit high in-plane uniformity for luminance, and to emit light of high luminance. <P>SOLUTION: The light guide plate 10 has a pair of main faces 10a and 10b mutually opposed and an end surface 10c receiving incoming light from a light source 1. The main face 10a has a plurality of prisms 10d to constitute a prism surface. The main face 10b is corrugated to constitute a light emitting surface. Since the light guide plate 10 has an area the thickness of which is increased toward the direction separating away from the end surface 10c, in a position relatively close to the end surface 10c of the corrugated surface 10b and an area the thickness of which is reduced toward the direction separating away from the end surface 10c, emission of light in a position relatively close to the end surface 10c is suppressed, and emission of light in a position relatively distant from the end surface 10c, where light is not relatively emitted, is promoted. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a light guide plate and a surface light emitting device using the same, which are mainly used in a display device such as a liquid crystal display device.

  2. Description of the Related Art Conventionally, a surface light emitting device that supplies light from the back side of a liquid crystal display panel toward the display surface side, for example, a backlight device, is known as a lighting device for a display device, mainly a liquid crystal display device. Conventional backlight devices usually mainly include a light source, a light guide plate that emits light from the light source to the liquid crystal display panel, and a prism sheet for efficiently supplying light from the light guide plate to the liquid crystal display panel. Composed. The light guide plate has a flat plate shape and has a pair of main surfaces facing each other and a pair of end surfaces facing each other. A liquid crystal display panel is disposed on one main surface of the pair of main surfaces, and a light source is disposed in the vicinity of one end surface of the pair of end surfaces. A reflector is disposed on the other main surface of the pair of main surfaces, and reflects light from the light source. As such a conventional backlight device, there is one disclosed in Patent Document 1.

Japanese Patent Publication No. 7-27137

  In this conventional backlight device, light emitted from the light source 20 enters the light guide plate 21 from the end surface 21a of the light guide plate 21, is reflected by the reflection plate 22 disposed on the reflection surface 21b side of the light guide plate 21, and is reflected. The light is emitted from the emission surface 21c facing the surface 21b. The light emitted from the light guide plate 21 is changed in optical path by the prism 23a of the prism sheet 23 disposed on the light emission surface side of the light guide plate 21 and travels in a substantially vertical direction with respect to the light guide plate 21, thereby the prism sheet. The light is incident on a liquid crystal display panel (not shown) disposed on 23.

  In the conventional backlight device, light is incident only from the one end face 21a side of the light guide plate 21, so that light is easily emitted from a region near the light source 20 (light source side) of the light guide plate 21. There is a tendency that light is not easily emitted from a region (on the side opposite to the light source) from the light source 20. For this reason, the luminance on the light source side of the light guide plate 21 is relatively high, and the luminance on the side opposite to the light source of the light guide plate 21 is relatively low. Therefore, the backlight device has a problem that the in-plane uniformity is low with respect to luminance.

  Further, in the conventional backlight device, since the emitted light from the light guide plate 21 has no directivity, the emitted light with high luminance cannot be supplied in the observer direction.

  The present invention has been made in view of the above points, and provides a light guide plate capable of exhibiting high in-plane uniformity with respect to luminance and emitting high-luminance light, and a surface light emitting device using the same. The purpose is to provide.

The light guide plate of the present invention is a light guide plate having a pair of main surfaces facing each other and an end surface on which light is incident from a light source, and one main surface of the pair of main surfaces has a plurality of prisms. Each of the prisms has a base angle relatively closer to the end surface than a base angle relatively far from the end surface, and the other main surface of the pair of main surfaces extends from the end surface. It has at least any one of the area | region where thickness increases in the away direction, and the area | region where thickness decreases in the direction away from the said end surface, It is characterized by the above-mentioned.

  According to this configuration, since at least one of the region where the plate thickness increases and the region where the plate thickness decreases is provided on the light exit surface of the light guide plate, it is possible to control the in-plane light amount emitted from the light guide plate. It is possible to achieve high in-plane uniformity with respect to luminance. Moreover, the directivity of the light emitted from the light guide plate can be increased by the plurality of prisms. For this reason, the direction of light can be efficiently directed to the observer by the prism sheet. As a result, it is possible to emit light with high luminance.

  In the light guide plate of the present invention, it is preferable that the region whose thickness increases in a direction away from the end face is provided at a position relatively close to the end face.

  According to this structure, the area | region where plate | board thickness increases is provided in the position relatively near an end surface. Since light is relatively easily emitted at a position relatively close to the end face, light emission can be suppressed by providing a region where the plate thickness increases. Thereby, the in-plane uniformity of the emitted light quantity can be further improved as the entire light guide plate.

  In the light guide plate of the present invention, it is preferable that the region where the thickness decreases in the direction away from the end face is provided at least at a position relatively far from the end face.

  According to this structure, the area | region where plate | board thickness reduces is provided in the position relatively far from an end surface. Since light is relatively difficult to emit at a position relatively far from the end face, light emission can be promoted by providing a region where the plate thickness decreases. Thereby, the in-plane uniformity of the emitted light quantity can be further improved as the entire light guide plate.

  In the light guide plate of the present invention, it is preferable that the region where the thickness increases in the direction away from the end surface and the region where the thickness decreases in the direction away from the end surface are configured by curved surfaces. In the light guide plate of the present invention, it is preferable that the other main surface is a wavy surface.

  The surface light-emitting device of the present invention is disposed on the other main surface side of the light guide plate, the light source disposed in the vicinity of the end surface of the light guide plate, and faces the other main surface. And a prism sheet having a plurality of prisms on the surface.

  According to this configuration, since the light guide plate with high in-plane uniformity is provided, light can be efficiently supplied to the liquid crystal display panel in a state with high in-plane uniformity.

  The liquid crystal display device of the present invention comprises the above surface light emitting device and a liquid crystal display panel disposed on the prism sheet side of the surface light emitting device.

  According to this configuration, since the light guide plate with high in-plane uniformity is provided, it is possible to provide the observer with a display with high in-plane uniformity with respect to luminance.

  According to the present invention, the light emission surface of the light guide plate is provided with at least one of a region where the plate thickness increases and a region where the plate thickness decreases, and the in-plane light amount emitted from the light guide plate is controlled. High in-plane uniformity can be exhibited.

  The present inventor can control the amount of light emitted from the light guide plate by focusing on the relationship between the increase and decrease in the thickness of the light guide plate and the critical angle, and providing a region on the light output surface of the light guide plate where the thickness increases or decreases. And led to the present invention. That is, the essence of the present invention is that by providing at least one of a region where the plate thickness increases and a region where the plate thickness decreases on the light exit surface of the light guide plate, the amount of light emitted from the light guide plate is controlled. It is to exhibit high in-plane uniformity with respect to luminance.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1A is a diagram showing a schematic configuration of a liquid crystal display device including a surface light emitting device according to an embodiment of the present invention. FIG. 1B is a diagram for explaining the prism of the light guide plate.

  In the figure, reference numeral 10 denotes a light guide plate. The light guide plate 10 has a pair of main surfaces 10 a and 10 b that face each other and an end surface 10 c that receives light from the light source 11. The main surface 10a has a plurality of prisms 10d and constitutes a prism surface. Moreover, the main surface 10b is a wave-like surface, and comprises the light-projection surface. The light guide plate 10 is made of a transparent material such as acrylic resin.

  A light source 11 is disposed in the vicinity of the end face 10 c of the light guide plate 10. The light source 11 may be disposed so as to be in contact with the end surface 10c without being disposed away from the end surface 10c. On the main surface 10 a side of the light guide plate 10, the reflection plate 12 is disposed. In addition, as a material of the reflecting plate 12, it is comprised with the material which has high reflectances, such as aluminum. On the main surface 10b side of the light guide plate 10, a prism sheet 13 having a plurality of prisms 13a on the surface facing the main surface 10b is disposed. Further, a liquid crystal display panel 14 is disposed on the prism sheet 13 side.

Each of the plurality of prisms 10d provided on the main surface (prism surface) 10a has the same shape, and specifically has a shape as shown in FIG. That is, in each prism 10d, the base angle θ ₁ on the side relatively close to the end face 10c is set to be larger than the base angle θ ₂ on the side relatively far from the end face 10c. For this reason, each prism 10d has a steep slope 10e and a gentle slope 10f. The light passing through the light guide plate 10 is reflected and propagated mainly by the gentle slope 10f. By providing the steep slope 10e and the gentle slope 10f on the prism 10d, light can be efficiently sent to the tip of the light guide plate 10 (the part farthest from the end face 10c: the opposite light source side).

  Further, by providing the prism 10d with the steep slope e and the gentle slope f as shown in FIG. 1B, the directivity of the light emitted from the light guide plate 10 can be increased. For this reason, the direction of light can be efficiently directed to the observer by the prism sheet described later. As a result, it is possible to emit light with high luminance.

  The corrugated shape provided on the main surface (wave surface) 10b is formed by increasing or decreasing the thickness of the light guide plate 10, and specifically, the thickness is increased in a direction away from the end surface 10c. And a region where the thickness decreases in a direction away from the end face 10c. Here, the region where the thickness increases in the direction away from the end surface 10c means a region where light is not easily emitted from the waved surface which is the light emitting surface, and the region where the thickness decreases in the direction away from the end surface 10c. It means a region where light is easily emitted from a wave-like surface that is a light emitting surface.

  2 and 3 are diagrams for explaining the light guide principle of the light guide plate of the present invention. In the light guide plate 15 whose thickness changes as shown in FIG. 2 (wedge shape), when light enters from the end surface 15a on the light source side, the light is reflected by the main surface of the light guide plate as indicated by an arrow. The light is emitted from the emission surface 15c. At this time, the direction of light guided through the light guide plate 15 gradually approaches perpendicular to the light exit surface 15c. Then, when the angle formed by the direction of the light and the normal line 15b becomes smaller than the critical angle, the light is emitted from the light emitting surface 15c. The light guide plate 10 having a prism surface shown in FIG. 1A is in a light guide state similar to the light guide plate 15 having a wedge shape as shown in FIG.

  Based on this light guide state, reflection and emission at the interface between air (refractive index n = 1.0) and acrylic resin (refractive index n = 1.49) will be described. As shown in FIG. 3A, in the state where the thickness of the light guide plate 15 is reduced, that is, the normal line 15b is rotated more clockwise than the vertical direction, light is easily emitted from the light emitting surface 15c ( Emission state). On the other hand, as shown in FIG. 3C, when the thickness of the light guide plate 15 increases, that is, when the normal line 15b rotates counterclockwise from the vertical direction, light is emitted from the light emitting surface 15c. Difficult (reflective state) Therefore, when the thickness of the light guide plate 15 is gradually increased as shown in FIGS. 3A to 3C, the light is changed from being emitted to being reflected at the critical angle of 42 °.

  Using this light guide principle, the light emitted from the light exit surface is controlled. That is, a region where the light is emitted from the light exit surface as much as possible is provided with a region where the thickness increases as the distance from the end surface is increased, and a region where the light is emitted from the light exit surface is increased as the distance from the end surface is increased. An area where the thickness is reduced is provided. Usually, in a region near the light source, the amount of light emitted from the light emitting surface is relatively large, and the amount of light emitted from the light emitting surface is relatively small as the distance from the light source is increased. For this reason, an area where the thickness increases in a direction away from the end face is provided at a position relatively close to the end face, and an area where the thickness decreases in a direction away from the end face is provided at a position relatively far from the end face. desirable. The corrugated surface 10b shown in FIG. 1A is designed in consideration of this. By designing the shape of the light guide plate in this way, the amount of light emitted according to the position of the light guide plate can be controlled. Therefore, it is possible to improve the in-plane uniformity regarding luminance. In addition, it is preferable that the area | region where thickness increases in the direction away from an end surface and the area | region where thickness decreases in the direction away from an end surface are comprised by the curved surface.

  The main surface 10b facing the prism surface 10a of the light guide plate 10 is not limited to a wavy surface, and a region where the thickness is increased is provided in a region where light is not emitted from the light emitting surface as much as possible, and / or If a region where the thickness is reduced is provided in a region where light is emitted from the light emitting surface, various changes can be made. For example, as shown in FIG. 4, the main surface 10b facing the prism surface 10a of the light guide plate 10 is a surface provided with a region where the thickness is reduced at the tip (on the opposite side of the light source) (only the tip side is a curved surface 10g and others) May be the flat surface 10j). That is, since the amount of light emitted from the main surface 10b is relatively small on the side farther from the end face 10c of the light guide plate 10 (on the side opposite to the light source), a region where the thickness decreases is provided to facilitate emission from the main surface 10b.

  Next, the operation of the surface light emitting device in the liquid crystal display device shown in FIG.

  Light emitted from the light source 11 is incident from the end face 10c and propagates while being reflected in the light guide plate 10. At this time, the light transmitted through the prism 10d of the prism surface 10a becomes light with high directivity. The light transmitted through the light guide plate 10 is reflected by the reflection plate 12, the optical path is changed, and is incident on the light guide plate 10 again. Since this reflected light is already less than the critical angle, it passes through the light guide plate 10 and exits from the waved surface 10b. The emitted light is changed in the direction substantially vertical by the prism sheet 13 and enters the liquid crystal display panel 14. In this way, the prism 10d having the steep slope 10e and the gentle slope 10f in the form shown in FIG. 1B gives directivity to the light emitted from the prism surface 10a, so that the light passing through the prism sheet 13 can be efficiently transmitted. Since it is directed substantially in the vertical direction, light can be supplied to the liquid crystal display panel 14 with high luminance.

  The wavy surface 10b of the light guide plate 10 is provided with a region whose thickness increases in a direction away from the end surface 10c (light source 11) at a position relatively close to the end surface 10c (light source 11), and the end surface 10c (light source 11). Since a region where the thickness decreases in a direction away from the end face 10c (light source 11) is provided at a relatively far position, the light at a position relatively close to the end face 10c is relatively easy to emit light. The emission is suppressed, and the emission of light at a position relatively far from the end face 10c where light is not emitted relatively is promoted. For this reason, light can be supplied to the liquid crystal display panel 14 in a state where the in-plane uniformity of the light emitted from the waved surface 10b is high.

Next, examples performed for clarifying the effects of the present invention will be described.
A surface light emitting device A in which the principal surface facing the prism surface as shown in FIG. 1A is a wavy surface 10b, and a surface in which the principal surface opposite to the prism surface as shown in FIG. 4 is a flat surface 10j and a curved surface 10g. A light-emitting device B and a surface light-emitting device C whose main surfaces facing the prism surface as shown in FIG. The surface light emitting device shown in FIG. 5 is a form proposed by the present inventor in Japanese Patent Application No. 2003-407392 filed on Dec. 5, 2003. This content is included here by reference.

  FIG. 6 is a characteristic diagram showing the distribution of the thickness of the light guide plate in the surface light emitting device shown in FIGS. 1 (a), 4 and 5. As can be seen from FIG. 6, in the corrugated surface (diamond) shown in FIG. 1 (a), the plate thickness decreases from the light source side to the position of 10 mm, and then increases from the light source to the position of 30 mm. The plate thickness has decreased to the side. The flat surface + curved surface (square) shown in FIG. 4 is flat from the light source to a position of 30 mm, and then the plate thickness is reduced to the side opposite to the light source. On the flat surface (triangle) shown in FIG. 5, the plate thickness is constant from the light source side to the counter light source side.

FIG. 7 is a characteristic diagram showing the distribution of the inclination of the curved surface of the light guide plate in the surface light emitting device shown in FIGS. 1 (a), 4 and 5. FIG. 7 shows the inclination of the main surface × (−1) based on the change in the respective plate thicknesses shown in FIG. As can be seen from FIG. 7, in the wavy surface, the inclination x (−1) is small at 10 to 20 mm from the light source side, and the inclination x (−1) is large toward the counter light source side. In the flat surface + curved surface, the inclination × (−1) does not change from the light source to the position of 25 mm, and thereafter the inclination × (−1) increases to the opposite light source side. On a flat surface, the inclination x (-1) is constant from the light source side to the counter light source side.

Next, the luminance distribution in the surface light emitting device shown in FIGS. 1A, 4 and 5 was measured. As for the luminance, the luminance of the liquid crystal display device was measured when each surface light emitting device was mounted on a transflective liquid crystal display device and light was emitted using two white LEDs (10 mA each) as a light source. At this time, the surface light emitting device surface was divided into 25, and the luminance of each part was measured. In addition, as a measuring device, the brightness | luminance chromaticity measuring device (Risa-Color: the product made by Highland, brand name) was used, and the distance from a measuring device to a liquid crystal display device was 500 mm.

  From the luminance values thus measured, the luminance distribution and in-plane uniformity in the light guide plate were obtained. The in-plane uniformity (%) was obtained by (minimum luminance value / maximum luminance value) × 100. FIG. 8 is a characteristic diagram showing the luminance distribution in the surface light emitting device shown in FIGS. 1 (a), 4 and 5. FIG. As can be seen from FIG. 8, on the flat surface, the luminance is highest at the portion of 15 mm from the light source that is most likely to emit light, and the luminance tends to decrease as it goes to the opposite light source side. On the flat surface + curved surface, the luminance is highest at a portion of 15 mm from the light source from which light is most easily emitted, but the luminance is higher than that of the flat surface on the side opposite to the light source where the plate thickness is reduced. On the wavy surface, the luminance at the portion of 15 mm from the light source with the plate thickness increased is suppressed, and the luminance is higher than that on the flat surface on the side opposite to the light source with the plate thickness decreased. Therefore, as can be seen from FIGS. 6 and 8, since the luminance is suppressed and improved in the portion where the thickness is increased / decreased, the shape of the surface of the light guide plate facing the prism surface is appropriately changed. Thus, it can be seen that the in-plane uniformity of luminance can be improved by controlling the amount of emitted light. Actually, the in-plane uniformity of the wavy surface was 55%, the in-plane uniformity of the flat surface + curved surface was 43%, and the in-plane uniformity of the flat surface was 40%.

FIG. 9 is a characteristic diagram showing the rate of change in luminance in the surface light emitting devices shown in FIGS. 1 (a), 4 and 5. As can be seen from FIG. 9, on the wavy surface, the rate of change is small at 10 to 20 mm from the light source side, and the rate of change is increased toward the counter light source side. On the flat surface + curved surface, the rate of change does not change much from the light source to the position of 25 mm, and then the rate of change increases to the opposite light source side. On the flat surface, the rate of change is constant from the light source side to the counter light source side. Therefore, as can be seen from FIG. 7 and FIG. 9, the inclination of the main surface × (−1) and the rate of change in luminance show the same tendency. Thereby, it turns out that the shape of the surface facing the prism surface of the light guide plate is related to the in-plane uniformity of luminance. Therefore, by specifying the shape of the surface facing the prism surface of the light guide plate based on the luminance distribution of the light guide plate, that is, a region where the plate thickness increases is provided at a position where the luminance is high, and the plate thickness is set at a position where the luminance is low. By providing the decreasing region, it is possible to realize a light guide plate and a surface light emitting device that are excellent in in-plane uniformity regarding luminance regardless of the size of the light guide plate.

As described above, in the present invention, at least one of a region where the plate thickness increases and a region where the plate thickness decreases is provided on the light exit surface of the light guide plate, and the in-plane light quantity emitted from the light guide plate is controlled. Therefore, high in-plane uniformity with respect to luminance can be exhibited.

  The present invention is not limited to the embodiment described above, and can be implemented with various modifications. For example, the dimensions, materials, and the like described in the above embodiments are examples, and can be implemented with appropriate changes.

(A) is a figure which shows schematic structure of the liquid crystal display device provided with the surface emitting device which concerns on one embodiment of this invention. (B) is a figure for demonstrating the prism of a light-guide plate. It is a figure for demonstrating the light guide principle of the light-guide plate of this invention. (A)-(c) is a figure for demonstrating the light guide principle of the light-guide plate of this invention. It is a figure which shows schematic structure of the surface emitting device which concerns on other embodiment of this invention. It is a figure which shows schematic structure of the surface emitting device which concerns on other embodiment of this invention. It is a characteristic view which shows distribution of the board thickness of the light-guide plate in the surface emitting device shown to Fig.1 (a), FIG.4, and FIG.5. It is a characteristic view which shows distribution of the inclination of the curved surface of the light-guide plate in the surface emitting device shown to Fig.1 (a), FIG.4, and FIG.5. It is a characteristic view which shows the luminance distribution in the surface emitting device shown to Fig.1 (a), FIG.4, and FIG.5. It is a characteristic view which shows the change rate of the brightness | luminance in the surface emitting device shown to Fig.1 (a), FIG.4, and FIG.5. It is a figure which shows schematic structure of the conventional surface light-emitting device.

Explanation of symbols

10, 15 Light guide plate 10a Main surface (prism surface)
10b Main surface (wavy surface)
10c, 15a End face 10d, 13a Prism 10e Steep slope 10f Slow slope 10g Plate thickness decreasing area 10h Plate thickness increasing area 10j Flat surface 11 Light source 12 Reflector 13 Prism sheet 14 Liquid crystal display panel 15b Normal line 15c Light emitting surface

Claims (7)

  A light guide plate having a pair of main surfaces facing each other and an end surface for receiving light from a light source, wherein one main surface of the pair of main surfaces has a plurality of prisms, and each of the prisms is The base angle on the side relatively close to the end surface is larger than the base angle on the side far from the end surface, and the other main surface of the pair of main surfaces increases in thickness in a direction away from the end surface. A light guide plate having at least one of a region where the thickness decreases and a region where the thickness decreases in a direction away from the end surface.   The light guide plate according to claim 1, wherein the region where the thickness increases in a direction away from the end surface is provided at least at a position relatively close to the end surface.   The light guide plate according to claim 1, wherein the region where the thickness decreases in a direction away from the end face is provided at least at a position relatively far from the end face.   The area | region where thickness increases in the direction away from the said end surface, and the area | region where thickness decreases in the direction away from the said end surface are comprised by the curved surface, The Claim 1 characterized by the above-mentioned. Light guide plate.   The light guide plate according to any one of claims 1 to 4, wherein the other main surface is formed of a waved surface.   The light guide plate according to any one of claims 1 to 5, a light source disposed in the vicinity of an end surface of the light guide plate, and the other main surface side of the light guide plate, wherein the other main surface is disposed. A surface light emitting device comprising: a prism sheet having a plurality of prisms on a surface facing the surface. A liquid crystal display device comprising: the surface light emitting device according to claim 6; and a liquid crystal display panel disposed on a prism sheet side of the surface light emitting device.

Images