JP2009110860A - Surface light source device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface light source device capable of suppressing uneven brightness and an irregular color without increasing the distance between a light-emitting diode and the surface of the surface light source device and also without increasing the number of the light-emitting diodes. <P>SOLUTION: A plurality of fluorescent tubes 12 are disposed in parallel with one another with light-emitting devices 13 provided in the middle between the fluorescent tubes 12 in parallel with the fluorescent tubes. A diffusion plate 14 is disposed in front of the fluorescent tubes 12 and the light-emitting devices 13. The light-emitting devices comprise a plurality of aligned LEDs 15, and a light guide plate 16 which covers the front surface of each LED. The light guide plate 16 has a first optical surface on the surface thereof facing a light source for refracting light incident from the light source so that directional characteristics are expanded in the lateral direction of the light-emitting device and for totally reflecting light reflected by a surface at the opposite side. Moreover, the light guide plate 16 has a second optical surface on the surface thereof opposite to the that facing the light source, for outputting light which has been expanded in its directional characteristics in the lateral direction of the light-emitting device by reflecting part of the light incident from the light source and allowing remaining light to pass through. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a surface light source device, and specifically to a surface light source device using a fluorescent tube and a light emitting diode in combination.

(First conventional example)
As a backlight of a liquid crystal display, a backlight using a fluorescent tube is generally used. However, fluorescent tubes have poor color reproducibility compared to light emitting diodes, and in particular red color reproducibility is inferior.

  Therefore, there has been proposed a backlight in which a light emitting diode (hereinafter referred to as LED) is used in combination with a fluorescent tube to improve the color reproducibility of the fluorescent tube. Examples of such a backlight include those disclosed in Japanese Unexamined Patent Application Publication No. 2004-139976 (Patent Document 1) and Japanese Unexamined Patent Application Publication No. 2007-73290 (Patent Document 2).

  FIG. 1A is a schematic cross-sectional view showing an example of a backlight 100 using both a fluorescent tube 101 and an LED 102 as an auxiliary light source, and FIG. 1B is a front view thereof. In this backlight 100, a plurality of fluorescent tubes 101 are arranged in parallel, a plurality of LEDs 102 are arranged in a row in each gap between the fluorescent tubes 101, and a diffusion plate is placed in front of the fluorescent tubes 101 and the LEDs 102. 103 is arranged. Then, the light L2 of the LED 102 is superimposed on the white light L1 emitted from the fluorescent tube 101 to illuminate the diffusion plate 103 from the back surface side, and the backlight 100 emits white light.

  However, as shown in FIG. 1A, the fluorescent tube 101 has a low directivity and a large spread of outgoing light, while the LED 102 has a strong directivity and a narrow spread of outgoing light. Due to the difference in characteristics between the fluorescent tube 101 and the LED 102, in the backlight 100 as shown in FIGS. 1A and 1B, an area where the light of the LED 102 is easy to reach and an area where it is difficult to reach are generated. There is a problem that unevenness increases.

  In order to improve luminance unevenness and color unevenness of the backlight 100, the LEDs 102 may be densely arranged at short intervals so that the overlap of light between adjacent LEDs 102 becomes large. However, if the LEDs 102 are arranged closely, the number of LEDs 12 used increases and the cost increases.

  Another method for reducing the luminance unevenness and the color unevenness by increasing the overlap of light of the LED 102 is to increase the distance between the diffusion plate 103 and the LED 102. However, if the distance between the diffusing plate 103 and the LED 102 is increased, the thickness of the backlight 100 is increased accordingly, and the reduction in thickness is hindered.

  Further, it is known that a parasitic capacitance that changes according to the distance between the metal back member 104 on which the LED mounting substrate is installed and the fluorescent tube 101 is generated. This parasitic capacitance is generated when a capacitor is formed by the plasma in the fluorescent tube 101 and the back member 104. The parasitic capacitance increases as the separation distance between the fluorescent tube 101 and the back member 104 decreases, and decreases as the separation distance increases. For this reason, when the LED 102 is disposed rearwardly away from the fluorescent tube 101 in order to increase the distance between the diffusion plate 103 and the LED 102, the parasitic capacitance between the fluorescent tube 101 and the back member 104 is reduced, and the fluorescent tube 101 emits light. This causes a problem that the power efficiency is deteriorated.

(Second conventional example)
FIG. 2 is a schematic cross-sectional view showing the structure of the backlight disclosed in Japanese Unexamined Patent Publication No. 2007-121927 (Patent Document 3). In the backlight 110, the back plate 104 is provided with an uneven shape, and the LED 102 is housed in the recess. According to such a structure, the distance between the LED 102 and the diffusion plate 103 can be increased, the spread of the light L2 emitted from the LED 102 in the diffusion plate 103 can be increased, and the backlight 110 can be increased without increasing the number of LEDs 102. Luminance unevenness and color unevenness can be reduced.

  However, even in such a backlight 110, the unevenness in brightness and color is reduced by increasing the distance between the diffuser plate 103 and the LED 102, so that the thickness of the backlight 100 is increased accordingly, and the reduction in thickness is hindered. It is done. Furthermore, since the back member 104 must be pressed so as to have a concavo-convex shape, the shape of the back member 104 becomes complicated, leading to high costs.

  Further, in this backlight 110, the average distance between the fluorescent tube 101 and the back member 104 becomes shorter compared to the case where the LEDs 102 are arranged at the same position in the backlight 100 of the first conventional example, and the fluorescent tube is reduced. The deterioration of the power efficiency related to the light emission 101 can be suppressed. However, since the luminance unevenness and the color unevenness are reduced by increasing the distance between the diffusion plate 103 and the LED 102, the distance between the fluorescent tube 101 and the back member 104 is correspondingly increased, and the emission of the fluorescent tube 101 is affected. Power efficiency deteriorates.

Japanese Patent Laid-Open No. 2004-139876 JP 2007-73290 A JP 2007-121927 A

  The present invention has been made in view of the technical problems as described above, and an object thereof is to increase the distance between the light emitting diode and the surface of the surface light source device without increasing the distance between the light emitting diode and the surface light source device. An object of the present invention is to provide a surface light source device capable of suppressing luminance unevenness and color unevenness without increasing the number.

  The surface light source device of the present invention includes a plurality of fluorescent tubes arranged in parallel to each other and a plurality of light emitting elements arranged along the length direction of the fluorescent tubes in a region located in the middle of the fluorescent tubes when viewed from the front. A surface light source device comprising a diode and a light guide plate arranged to face the light emitting surface side of the light emitting diode, wherein the light guide plate has a long shape in the arrangement direction of the light emitting diodes, First light for refracting the light incident from the light emitting diode on the surface facing the light emitting diode so that the directivity characteristic spreads on the short side, and totally reflecting the light reflected on the opposite surface It has an optical surface and reflects a part of the light incident from the light emitting diode on the surface opposite to the surface facing the light emitting diode, and transmits the remaining light to provide a directivity characteristic toward the short side. It is characterized by having a second optical surface for emitting the wanted light.

  In the surface light source device of the present invention, the light incident from the light emitting diode is refracted so that the directional characteristics are spread on the short side, and the first light for totally reflecting the light reflected on the opposite surface is provided. The optical surface of the light-emitting diode is reflected on the surface opposite to the surface facing the light-emitting diode, and a part of the light incident from the light-emitting diode is reflected, and the remaining light is transmitted so that the directivity characteristic is reduced in the short direction side. Since the light guide plate having the second optical surface for emitting the spread light is provided on the surface facing the light emitting diode, the light emitted from each light emitting diode is guided into the light guide plate and faces the light emitting diode. The light of each light emitting diode can be uniformly spread by guiding light by repeating reflection between the surface and the opposite side surface. Furthermore, the directivity characteristic of the light emitted from the light emitting diode by the light guide plate can be expanded to the short side. As a result, in the surface light source device of the present invention, the directivity angle of the light emitting diodes is widened by the light guide plate, so that the distance between the light emitting diodes and the surface of the surface light source device can be increased without increasing the arrangement of the light emitting diodes. Luminance unevenness and color unevenness of the surface light source device can be improved without increasing the size.

  Since the distance between the light emitting diode and the surface of the surface light source device does not increase, it is possible to improve luminance unevenness and color unevenness of the surface light source device without hindering the thickness reduction of the surface light source device. Moreover, since it is not necessary to change the distance between the back member on which the LED mounting substrate is provided and the fluorescent tube, there is no possibility that the power efficiency related to the light emission of the fluorescent tube is deteriorated.

  Furthermore, unlike the conventional example 2, it is not necessary to process the back surface member, and it is not necessary to increase the number of light emitting diodes, so that the cost of the surface light source device can be reduced.

  In an embodiment of the surface light source device of the present invention, the second optical surface of the light guide plate is a cone-shaped microscopically formed in a concave shape on a surface opposite to the surface facing the light emitting diode of the light guide plate. It is constituted by a concave pattern. According to such an embodiment, the light incident from each light emitting diode can be confined and guided to spread the light over the entire light guide plate, and the light can be emitted from the front surface of the light guide plate by passing through the recess. . Further, the light can be spread in the short direction of the light emitting element by refracting the light by the concave portion. Therefore, the surface light source device can emit light uniformly with a small number of light sources.

  In another embodiment of the surface light source device of the present invention, the first optical surface of the light guide plate has a triangular prism-shaped fine convex portion whose slope is positioned in the short direction of the light guide plate. They are arranged along the hand direction. According to this embodiment, when the light emitted from the light source is incident on the light guide pattern, the light can be spread in the short direction of the light emitting element by the convex portion, and the light emitting area of the light emitting element can be widened. .

  In still another embodiment of the surface light source device of the present invention, the plurality of light emitting diodes are constituted by three types of light emitting diodes, a red light emitting diode, a green light emitting diode, and a blue light emitting diode. According to such a surface light source device, it is possible to switch the emission color such as white, red, green,... By switching the lighting state of each color light emitting diode.

  In another embodiment of the surface light source device of the present invention, an LED module divided into a plurality of areas and configured by LEDs of three primary colors is arranged in each area. According to this embodiment, the LED module can emit light in different colors for each area.

  Still another embodiment of the surface light source device of the present invention is a surface light source device in which a diffusion plate is disposed in front of the fluorescent tube and the light guide plate, and the diffusion plate has a region facing the fluorescent tube. However, the transmittance is lower than other regions. According to this embodiment, it is possible to suppress the occurrence of luminance unevenness due to the light from the fluorescent tube passing through the diffusion plate in the front direction, and the luminance of the surface light source device can be made more uniform.

  The means for solving the above-described problems in the present invention has a feature in which the above-described constituent elements are appropriately combined, and the present invention enables many variations by combining such constituent elements. .

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

(First embodiment)
FIG. 3 is a schematic cross-sectional view showing the surface light source device according to Embodiment 1 of the present invention. FIG. 4 is a schematic front view of the surface light source device with the diffusion plate removed.

  As shown in FIG. 3, the surface light source device 10 according to the first embodiment includes a reflection sheet 11, a plurality of fluorescent tubes 12, a plurality of light emitting elements 13, and a diffusion plate 14. The fluorescent tubes 12 are arranged in parallel to each other at a predetermined interval on the front surface of the reflection sheet 11. The light emitting element 13 has a planar shape that is long in one direction, and is arranged in parallel with the fluorescent tube 12 in each region located between the fluorescent tubes 12. The light emitting element 13 includes a plurality of light emitting diodes (hereinafter referred to as LEDs) 15 and a light guide plate 16 having a rectangular plate shape, and the LEDs 15 are arranged in a line at a constant pitch along the longitudinal direction of the light emitting element 13. Arranged. The LED 15 is located behind the virtual plane on which the fluorescent tube 12 is arranged. The light guide plate 16 is disposed in front of the light emitting direction of the LED 15 so as to cover each LED 15. The diffusion plate 14 is obtained by dispersing a diffusion material on a transparent resin plate, forming a diffusion pattern on the surface, or applying a diffusion material on the surface. Further, a diffusion sheet or a brightness enhancement sheet (such as a prism sheet or a polarizing film) may be stacked on the front surface of the diffusion plate 14.

  When the thickness of the surface light source device 10 is about 25 mm, the arrangement pitch of the fluorescent tubes 12 and the arrangement pitch of the light emitting elements 13 are about 30 mm, and the arrangement pitch of the LEDs 15 in the X direction is about 20 mm or less. Yes.

  The fluorescent tube 12 is a cold cathode tube or a hot cathode tube, but a cold cathode tube is generally used. As this cold cathode tube, a white fluorescent tube that emits white light may be used, and a red fluorescent tube, a green fluorescent tube, and a blue fluorescent tube are used to mix red light, green light, and blue light to generate white light. It may be what you do. Further, since the fluorescent tube 12 has particularly poor red reproducibility, the LED 12 often uses a red light emitting diode in order to improve the red reproducibility of the fluorescent tube 12. In the first embodiment, a case where a combination of a white cold cathode tube and a red light emitting diode is described.

[Light guide plate structure]
Since the light guide plate 16 is described in detail in Japanese Patent Application No. 2007-31742 filed by the applicant of the present application, the description of the Japanese Patent Application No. 2007-31742 is incorporated, and basic items will be described here. FIG. 5A is a front perspective view showing a part of the light guide plate 16 in an enlarged manner, and FIG. 5B is a rear perspective view showing a part of the light guide plate 16 in an enlarged manner. Hereinafter, the longitudinal direction of the light emitting element 13, that is, the direction in which the LEDs 15 are arranged is referred to as the X direction, the thickness direction of the light guide plate 16 is referred to as the Z direction, and the width direction of the light emitting element 13, that is, the X direction and Z direction. The orthogonal direction is sometimes referred to as the Y direction.

  The light guide plate 16 is a resin molded member formed into a plate shape with a transparent resin having a large refractive index such as polycarbonate resin (PC) or polymethyl methacrylate (PMMA). As shown in FIG. 5A, fine conical recesses 22 are densely arranged on the entire surface (second optical surface) of the light guide plate 16, and the back surface (first optical surface) of the light guide plate 16. As shown in FIG. 5B, convex portions 23 in the form of prisms having a fine triangular cross section are formed densely on the entire optical surface 1). The conical recesses 22 may be regularly arranged or randomly arranged. As shown in FIGS. 5 (a) and 5 (b), the convex portions 23 having a triangular cross section are arranged in the short direction (width direction) of the light guide plate 16 and are uniform in the longitudinal direction of the light guide plate 16. have.

  Further, although the LED 15 and the light guide plate 16 are disposed relatively close to each other, the distance between the light emitting element 13 and the diffusion plate 14 is relatively long, and the distance between the light guide plate 16 and the diffusion plate 14 is relatively long. Has enough space.

[Light emission operation of surface light source device]
6 and 7 are explanatory views of the operation of the light guide plate 16. FIG. 6 shows the behavior of light in a cross section parallel to the ZX plane, and FIG. 7 shows the behavior of light in a cross section parallel to the YZ plane. Yes. 6 and 7 show only the light L2 emitted from one LED 15, the behavior of the light L2 emitted from the other LEDs 15 is the same.

  First, the behavior of light in a cross section parallel to the ZX plane will be described. As shown in FIG. 6, the light L2 emitted from the LED 15 enters the light guide plate 16 from the back surface of the light guide plate 16, and is guided while repeating total reflection between the front surface and the back surface of the light guide plate 16. While guiding the light in the plate 16, a part of the light incident on the conical recess 22 is refracted by the conical recess 22 and emitted to the outside. Therefore, the light L2 emitted from the LED 15 is guided through the light guide plate 16 and spreads over almost the entire light guide plate 16, and the entire light emitting element 13 emits light uniformly.

  Therefore, when all the LEDs 15 emit light, the light L2 emitted from each LED 15 is uniformly mixed in the light guide plate 16 and emitted from the entire light guide plate 16. Moreover, since the light is refracted by the concave portion 22 when passing through the concave portion 22, the directivity angle in the ZX plane is widened.

  Next, the behavior of light in a cross section perpendicular to the longitudinal direction of the light guide plate 16 will be described. As shown in FIG. 7, when viewed from the X direction, the light L2 emitted from the LED 15 is refracted by passing through the convex portion 23 formed on the back surface of the light guide plate 16, and further conical. The light L2 that is also refracted when passing through the recess 22 and exiting from the light guide plate 16 and emitted from the LED 15 at an exit angle of θs with respect to the central axis of the LED 15 passes through the light guide plate 16. Thus, the light is emitted at an emission angle θt larger than θs. Therefore, when the light guide plate 16 is not used, the light L2 emitted from the LED 15 spreads only in the range of W1 on the back surface of the diffuser plate 14, but by using the light guide plate 16, the light L2 is emitted on the back surface of the diffuser plate 14. It can be expanded to the range of W2. In particular, the light L2 can be sent to the front of the fluorescent tube 12.

  Therefore, by using the light emitting element 13 provided with the light guide plate 16, the light of the LED 15 can be spread uniformly over a wide range. Further, the light L2 of each LED 15 emitted from the light emitting element 13 is uniformly mixed by passing through the space between the light emitting element 13 and the diffusion plate 14, and further diffused by the diffusion plate 14 to cause the surface light source device 10 to pass. Make it emit light.

  As a result, the diffuser plate 14 can be uniformly illuminated from the back side by the fluorescent tube 12 and the LED 15, and the surface light source device 10 emits light with high luminous efficiency by the fluorescent tube 12 and the color reproducibility of the surface light source device 10 by the LED 15. Can be improved. In addition, the light of the LED 15 can be uniformly spread by the light guide plate 16, and the luminance unevenness and the color unevenness can be reduced.

  An example of measurement and an example of simulation for explaining this effect will be described. FIG. 8 shows the measured intensity of light in the diffuser plate 14 arranged to face the light emitting element 13. The vertical axis in FIG. 8 represents the relative intensity when the maximum intensity is 1, and the horizontal axis represents the distance in the width direction (Y direction) of the diffusion plate. The solid line represents the sample of Embodiment 1 having the light guide plate, and the broken line represents the sample of the comparative example having no light guide plate. More specifically, in the sample of Embodiment 1, one row of LEDs 15 is arranged facing the central portion of the diffusion plate 14, and the light guide plate 16 is inserted between the LED 15 and the diffusion plate 14. The distance between the LED 15 and the light guide plate 16 is 2 to 3 mm, and the distance between the LED 15 and the diffusion plate 14 is 25 mm. The sample of the comparative example is obtained by removing the light guide plate from the sample of the first embodiment.

  FIG. 8 shows that the light of the LED 15 is spread by using the light guide plate 16. When the light guide plate 16 is not provided, the half-value width of the relative intensity in the diffusion plate 14 is about 30 mm. However, when the light guide plate 16 is provided, the half-value width of the relative intensity in the diffusion plate 14 is about 60 mm. By inserting the light guide plate 16, the light can be spread about twice.

  FIG. 9 shows the measured light intensity of the diffuser plate 14 disposed to face the four rows of light emitting elements 13. The vertical axis in FIG. 9 represents the relative luminance when the maximum intensity is 1, and the horizontal axis represents the distance in the width direction (Y direction) of the diffusion plate. During measurement, all the LEDs 15 are turned on and all the fluorescent tubes 12 are turned off. In the sample of Embodiment 1 indicated by a solid line, four rows of LEDs 15 are arranged facing the diffusion plate 14, and the light guide plate 16 is inserted between the LEDs 15 and the diffusion plate 14. The sample of the comparative example is obtained by removing the light guide plate from the sample of the first embodiment.

  FIG. 10A is a diagram in which the luminance distribution of the sample of the comparative example used in the measurement of FIG. 9 is simulated, and FIG. 10B is a simulation of the luminance distribution of the sample of the first embodiment used in the measurement of FIG. FIG.

  According to FIGS. 9 and 10 (a) and 10 (b), when the light guide plate 16 is not provided, the relative luminance in the diffuser plate 14 varies greatly depending on the location, whereas the light guide plate 16 is provided. It can be seen that, with the exception of both ends of the diffusion plate 14, the relative luminance in the diffusion plate 14 is substantially uniform and the luminance unevenness is small.

  The reflection sheet 11 reflects most of the light emitted from the LED 15 to the back side and the light leaked from the back side of the light guide plate 16 to enter the light guide plate 16 and reuse it. Yes.

[Effects of First Embodiment]
Since the surface light source device 10 of Embodiment 1 improves the luminance unevenness and color unevenness of the surface light source device by spreading the light of the LED 15 by the light guide plate 16, it is not necessary to arrange the LEDs 15 densely. There is no need to increase the distance between the LED 15 and the diffusion plate 14.

  Since it is not necessary to increase the distance between the LED 15 and the diffusion plate 14, the thickness of the surface light source device is not increased, and the surface light source device can be thinned. In addition, since it is not necessary to change the distance between the back member (not shown) on which the LED mounting substrate on which the LEDs 15 are mounted and the fluorescent tube 12 is changed, there is no possibility that the power efficiency related to the light emission of the fluorescent tube 12 is deteriorated.

  According to this surface light source device 10, it is not necessary to perform uneven processing on the back member as in Conventional Example 2, and it is not necessary to increase the number of LEDs 15, so that the cost of the surface light source device 10 can be kept low. It becomes possible.

  The convex portion 23 having a triangular cross section has a convex portion so that the apex angle α (see FIG. 7) is reduced to an acute angle, while the light L2 incident on the convex portion 23 is not reflected a plurality of times. It is desirable to reduce the height of 23. In addition, when the LED 15 has one kind of emission color as in the first embodiment, it is not necessary to guide and mix light of different colors with the light guide plate 16 as in the case of using a plurality of kinds of LEDs. Therefore, the apex angle β (see FIG. 7) of the recess 22 may be an obtuse angle at which total reflection hardly occurs. However, even with monochromatic light, there is a risk of variations in brightness and wavelength due to the use of a plurality of LEDs 15. Therefore, the apex angle β is such that light can be guided to some extent and averaged uniformly. It is desirable to make the luminance uniformity good in the direction in which the LEDs 15 are arranged.

(Second Embodiment)
FIG. 11 is a schematic view showing a part of a cross section of the light guide plate 16 used in the surface light source device according to Embodiment 2 of the present invention. In the second embodiment, as shown in FIG. 11, the apex angle α (= α1 + α2) of the convex portion 23 is reduced to an acute angle, the cross section of the convex portion 23 is asymmetrical, and the angle closer to the LED 15 (one side) The angle (one-side apex angle) α2 on the side farther from the LED 15 than the apex α1 is set to be larger.

  According to the second embodiment, since the one-side apex angle α1 on the side close to the LED 15 is made small, the light L2 incident on the convex portion 23 from the LED side can be greatly expanded in the width direction, and one side far from the LED 15 Since the apex angle α2 is increased, the light greatly bent by the convex portion 23 can be prevented from being reflected by the side surface far from the LED 15, and the light can be greatly spread in the width direction of the light emitting element 13. Therefore, the brightness of the surface light source device can be made more uniform by adjusting α1 and α2 to appropriate angles.

(Third and fourth embodiments)
When the apex angles α of the convex portions 23 arranged in the Y direction are the same, when the light emission angle θs from the LED 15 increases, the light emission angle θt emitted from the upper surface of the light guide plate 16 also increases. As a result, the light is greatly spread in the width direction of the light guide plate 16. However, also in this case, when the emission angle θs becomes too large, the light incident on the convex portion 23 is reflected by the convex portion 23 a plurality of times, and on the contrary, the outgoing angle θt from the upper surface of the light guide plate 16 becomes small.

  Embodiments 3 and 4 solve such problems. FIG. 12 is a schematic view showing a part of a cross section of the light guide plate 16 used in the surface light source device according to Embodiment 3 of the present invention. In the third embodiment, as shown in FIG. 12, the height H of the convex portion 23 having a triangular cross section gradually decreases as the distance from the position immediately above the LED 15 increases.

  FIG. 13 is a schematic view showing a part of a cross section of the light guide plate 16 used in the surface light source device according to Embodiment 4 of the present invention. In the fourth embodiment, as shown in FIG. 13, the one-side apex angle α <b> 2 on the side surface farther from the light source of the convex section 23 having a triangular cross section is gradually increased as the distance from the position immediately above the LED 15 is increased.

(Fifth embodiment)
FIG. 14 is a front view showing the light emitting element 13 used in the surface light source device according to Embodiment 5 of the present invention. In the light emitting element 13 of this embodiment, the density of the recesses 22 is increased near the front of the LED 15 when viewed from the front, and the density of the recesses 22 is decreased in a region away from the LED 15. In this light emitting element 13, since the density of the recesses 22 is increased near the front of the LED 15 having a high light intensity, the degree of light scattering increases, and the density of the recesses 22 is decreased in a region away from the LED 15 having a low light intensity. Therefore, the degree of light scattering is reduced. As a result, the intensity of light emitted from the light emitting element 13 can be made uniform.

(Sixth embodiment)
FIG. 15A is an enlarged perspective view of a part of the light guide plate 16 used in the surface light source device according to Embodiment 6 of the present invention, and FIG. 15B is a part of the light guide plate 16. It is a perspective view of the back surface side which expands and shows. In the sixth embodiment, fine concave portions 22 having a pyramid shape (quadrangular pyramid shape) are densely provided on the surface of the light guide plate 16, and fine convex portions 23 having a pyramid shape are densely provided on the back surface of the light guide plate 16. Provided. According to the convex portion 23 having such a shape, light can be diffused by the convex portion 23 not only in the YZ plane but also in the ZX plane (longitudinal direction of the light guide plate 16). Further, by individually adjusting the inclination angles of the inclined surfaces of the concave portion 22 and the convex portion 23, the light diffusion condition in the YZ plane and the light diffusion condition in the ZX plane can be controlled separately.

(Seventh embodiment)
FIG. 16 is a front view of the surface light source device according to Embodiment 7 of the present invention with the diffusion plate removed. FIGS. 17A and 17B are front views showing the light emission state of the surface light source device. This surface light source device is divided into four areas 26a, 26b, 26c, and 26d as viewed from the front. The fluorescent tubes 12 are arranged in parallel with each other in the entire surface light source device. Each area 26a, 26b, 26c, 26d is provided with one or a plurality of light emitting elements 13 (LED modules). Each light emitting element 13 is composed of multicolored LEDs that can emit white light by mixing colors. In general, each light emitting element 13 includes a red LED 27R, a green LED 27G, and a blue LED 27B. Here, as the red LED 27R, the green LED 27G, and the blue LED 27B, a chip that emits light of red wavelength, a chip that emits light of green wavelength, a chip that emits light of blue wavelength may be used, or blue light or ultraviolet light may be used. It may be constituted by a combination of an LED chip emitting phosphor and a phosphor.

  In this surface light source device, since each light emitting element 13 can emit light individually, the light emitting elements 13 in each area 26a, 26b, 26c, 26d are lit in white according to the image of each area. Or can be turned off. For example, in FIG. 17A, all the LEDs 27R of the light emitting elements 13 in the areas 26a, 26d are combined with the images of the areas 26a, 26b, 26c, 26d in a state where all the fluorescent tubes 12 are turned on. 27G and 27B are turned on to make the areas 26a and 26d emit light bright and bright white, and at the same time, the light emitting elements 13 in the areas 26b and 26c are turned off to make the areas 26b and 26c emit light in a relatively dark white. Thereby, the surface light source device can change the contrast and brightness for each area, and the power consumption can be reduced by lighting in accordance with the image of each area.

  Further, in this surface light source device, each light emitting element 13 can emit light in white, red, green, blue, etc., so that light is emitted from each area 26a, 26b, 26c, 26d according to the image of each area. The element 13 can be turned on and off in various colors. For example, in FIG. 17B, in a state where all the fluorescent tubes 12 are turned on, the LED 27R of the light emitting element 13 is turned on in the area 26a in accordance with the image of each area 26a, 26b, 26c, 26d. 26a emits red light, the light emitting element 13 is turned off in areas 26b and 26c, the areas 26b and 26c emit light in a relatively dark white, and the LED 27B of the light emitting element 13 is turned on in area 26d and the area 26d emits blue. I am letting. Thereby, the surface light source device can change the contrast and brightness for each area, and the power consumption can be reduced by lighting in accordance with the image of each area.

(Eighth embodiment)
When a light emitting element is simply added to the surface light source device designed for a fluorescent tube, the luminance of the surface light source device becomes excessive, and the cost increases by the amount of the light emitting element. However, if the fluorescent tubes are reduced from the original surface light source device by the luminance of the light emitting elements, luminance unevenness occurs when the fluorescent tubes and the light emitting elements are turned on.

  The eighth embodiment eliminates such problems and is manufactured based on the following design concept. FIG. 18 is a schematic sectional view showing a surface light source device 30 according to an eighth embodiment of the present invention. The surface light source device 30 is designed on the basis of a surface light source device composed of only fluorescent tubes. First, a part of the fluorescent tube 12, for example, a fluorescent tube shown by a two-dot chain line in FIG. 18 is removed. .

  Then, diffusion ink or the like is printed on the front and back surfaces of the diffusion plate 14 by dot printing or screen printing to lower the transmittance of the diffusion plate 14, and the diffusion plate 14 has a high transmittance region 28a and a low transmittance region. 28b is formed. At this time, the region directly in front of the fluorescent tube 12 is a low-transmittance region 28b, and the intermediate region (the region directly in front of the position where the reduced fluorescent tube is located) is the high-transmittance region 28a. The luminance unevenness of the surface light source device 30 due to the reduction of the tubes is improved to make the luminance of the surface light source device uniform.

  Next, a light emitting element 13 composed of LEDs of a quantity sufficient to supplement light equivalent to the brightness of the reduced fluorescent tube is installed at the position where the reduced fluorescent tube was present. At this time, the directivity characteristic of the light emitting element 13 is adjusted by the light guide plate 16 according to the transmittance distribution of the diffusion plate 14. Specifically, since the transmittance of the diffusion plate 14 is high in the front of the light emitting element 13 and the transmittance is low on both sides thereof, the directivity characteristics of the light emitted from the LED 15 are set on both sides by the light guide plate 16. Widen (directivity is made to be a heart shape), and more light is sent to the low-transmittance regions 28b on both sides than the front-transmitted region 28a.

  If the surface light source device 30 is designed in this way, it has the same luminance as the surface light source device composed only of the original fluorescent tube, and also eliminates unnecessary use of the fluorescent tube and the light emitting element, thereby reducing the cost. In addition, it is possible to obtain a surface light source device that is small in luminance unevenness and color unevenness and excellent in color reproducibility.

(Other embodiments)
Although several embodiments have been specifically described so far with reference to the drawings, the present invention can appropriately adopt the configuration disclosed in Japanese Patent Application No. 2007-31742. For example, when a red light emitting diode, a green light emitting diode, and a blue light emitting diode are used as the light emitting element, various arrangements as disclosed herein can be employed.

FIG. 1A is a schematic cross-sectional view showing an example of a backlight using both a fluorescent tube and an LED as an auxiliary light source, and FIG. 1B is a front view thereof. FIG. 2 is a schematic cross-sectional view showing the structure of a backlight in which irregularities are formed on the back member. FIG. 3 is a schematic cross-sectional view showing the surface light source device according to Embodiment 1 of the present invention. FIG. 4 is a schematic front view of the surface light source device according to Embodiment 1 with a diffusion plate removed. FIG. 5A is a front perspective view showing an enlarged part of the light guide plate, and FIG. 5B is a rear perspective view showing an enlarged part of the light guide plate. FIG. 6 is an operation explanatory view showing the behavior of light in a cross section parallel to the ZX plane. FIG. 7 is an operation explanatory diagram showing the behavior of light in a cross section parallel to the YZ plane. FIG. 8 is a diagram showing the measured intensity of light in the diffuser plate arranged to face the light emitting element. FIG. 9 is a diagram showing the measured intensity of light in the diffuser plate arranged to face the four rows of light emitting elements. FIG. 10A is a diagram in which the luminance distribution of the sample of the comparative example used in the measurement of FIG. 9 is simulated, and FIG. 10B is a simulation of the luminance distribution of the sample of the first embodiment used in the measurement of FIG. FIG. FIG. 11 is a schematic view showing a part of a cross section of a light guide plate used in a surface light source device according to Embodiment 2 of the present invention. FIG. 12 is a schematic view showing a part of a cross section of a light guide plate used in a surface light source device according to Embodiment 3 of the present invention. FIG. 13 is a schematic view showing a part of a cross section of a light guide plate used in a surface light source device according to Embodiment 4 of the present invention. FIG. 14 is a front view showing a light emitting element used in the surface light source device according to Embodiment 5 of the present invention. FIG. 15A is an enlarged perspective view of a part of the light guide plate used in the surface light source device according to Embodiment 6 of the present invention, and FIG. 15B is an enlarged view of a part of the light guide plate. It is a perspective view of the back surface side shown. FIG. 16 is a front view of the surface light source device according to Embodiment 7 of the present invention with the diffusion plate removed. FIG. 17A and FIG. 17B are front views showing the light emission state of the surface light source device of the seventh embodiment. FIG. 18 is a schematic cross-sectional view of a surface light source device according to Embodiment 8 of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10, 30 Surface light source device 11 Reflection sheet 12 Fluorescent tube 13 Light emitting element 14 Diffusion plate 15 LED
16 Light guide plate 22 Concave part 23 Convex part 26a, 26b, 26c, 26d Area 27R Red LED
27G green LED
27B Blue LED

Claims (6)

A plurality of fluorescent tubes arranged in parallel to each other, a plurality of light emitting diodes arranged along the length direction of the fluorescent tubes in a region located in the middle of the fluorescent tubes when viewed from the front, and light of the light emitting diodes A surface light source device comprising a light guide plate arranged facing the emission surface side,
The light guide plate has a shape that is long in the arrangement direction of the light-emitting diodes, and refracts light incident from the light-emitting diodes on a surface facing the light-emitting diodes so that directivity characteristics are spread on the short side. A first optical surface for totally reflecting the light reflected by the surface on the opposite side, and a part of the light incident from the light emitting diode on the surface opposite to the surface facing the light emitting diode. A surface light source device comprising a second optical surface that emits light having a directional characteristic spread toward the lateral direction side by reflecting and transmitting the remaining light.   The second optical surface of the light guide plate is constituted by a conical fine concave pattern that is recessed on a surface opposite to the surface facing the light emitting diode of the light guide plate. The light emitting device according to claim 1.   The first optical surface of the light guide plate is formed by arranging triangular convex fine protrusions whose slopes are located in the short direction of the light guide plate along the short direction of the light guide plate. The surface light source device according to claim 1.   2. The surface light source device according to claim 1, wherein the plurality of light emitting diodes are configured by three types of light emitting diodes of a red light emitting diode, a green light emitting diode, and a blue light emitting diode.   2. The surface light source device according to claim 1, wherein an LED module divided into a plurality of areas and configured by LEDs of three primary colors is disposed in each area. The surface light source device according to claim 1, wherein a diffusion plate is disposed in front of the fluorescent tube and the light guide plate.
In the surface light source device, the diffusion plate has a lower transmittance in a region facing the fluorescent tube than in other regions.

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