JP2006134661A - Planar light source and liquid crystal display device using this - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a planar light source capable of obtaining uniform illumination light even if using a point light source element as a light source, having high illuminance, capable of realizing reduction of size and weight of a device by reducing an invalid area in a light guide plate, and being applicable to a light guide system provided with a scattering means in an emitting surface of the light guide plate, and to provide a liquid crystal display device using this. <P>SOLUTION: A light source part 10 has a plurality of point light source elements 2 arranged along an incidence plane 1a of the light guide plate 1. The light guide plate 1 transmits light introduced from the incidence plane 1a to the entire surface while totally reflecting it between facing principal surfaces and changes the light path with a light path modification member provided in the inside to emit flat light from the emitting surface 1b. A value of d/p which is a quotient of the distance d between the point light source elements 2 and the incidence plane 1a of the light guide plate 1 divided by an arrangement interval p of the point light source elements 2 is 0.2 or more and less than 1. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a planar light source and a liquid crystal display device using the planar light source. More specifically, incident light from a light source unit is introduced into a light guide plate, and planar light is emitted from the main surface of the light guide plate. The present invention relates to a planar light source that emits light and a liquid crystal display device using the same.

  Liquid crystal display devices (liquid crystal displays) capable of displaying images are used for personal computer monitors, television receivers, mobile phones, and the like. Liquid crystal display devices are thin and light, and are rapidly spreading because of the recent reduction in price and higher image quality due to progress in manufacturing technology.

  Since the liquid crystal display device itself is non-self-luminous, a transmissive liquid crystal display device having a light source called a backlight on the back side of the liquid crystal panel is generally used. In a transmissive liquid crystal display device, an image is formed by spatially modulating illumination light from a light source with a liquid crystal panel. There are various types of backlights, but edge-lighted backlights that introduce light from the side of the light guide plate and convert it into a uniform surface light source are suitable for thinning and miniaturization. Widely used. In general, a cold cathode tube (hereinafter referred to as CCFL), which is a linear light source, has been used as a light source of an edge light type backlight, but in recent years, a light emitting diode (hereinafter referred to as an LED) having high luminous efficiency. With the development of, demands for using LEDs are increasing.

  8 shows a configuration of a planar light source used as an edge light type backlight using an LED as a light source, and FIG. 8A is a cross-sectional view of the planar light source as viewed from the side. (B) is a top view of a planar light source. 8A and 8B, the planar light source 70 includes the light guide plate 1 and the light source unit 10. The light source part 10 is arrange | positioned at the side part of the light-guide plate 1, and has LED2, the board | substrate 3, and the reflecting plate 4 as a light source. In addition, illustration of the reflecting plate 4 is abbreviate | omitted in FIG.8 (b).

  The light guide plate 1 is made of a transparent resin having a large refractive index, such as polycarbonate resin or methacrylic resin, and has an incident surface 1a on the side and an output surface 1b on one side of the opposing main surface. The light source unit 10 includes a plurality of LEDs 2, and these LEDs 2 are mounted on the substrate 3 at equal intervals along the incident surface 1a. The LED 2 and the substrate 3 are covered with a reflector 4 made of a white resin sheet or the like having a high reflectance.

  In the planar light source 70 configured as described above, incident light introduced from the incident surface 1a of the light guide plate 1 repeatedly undergoes total reflection between opposing main surfaces as indicated by arrows in FIG. Propagate while. At this time, it is general to form a reflection surface 1c by forming a diffuse reflection layer, a reflection groove, or the like having a specific density distribution or size on the surface facing the emission surface 1b. By setting it as such a structure, the propagating light can be efficiently radiate | emitted from the output surface 1b. In addition, by appropriately setting the shape, density distribution, etc. of the diffuse reflection layer and the reflection grooves provided on the reflection surface 1c, substantially uniform illumination over the entire surface of the liquid crystal panel when used as a backlight of a liquid crystal display device Can give light. Further, since the light source unit 10 is configured to arrange a large number of LEDs 2 and directly introduce light into the incident surface 1a of the light guide plate 1, a light emission amount that can be used as a backlight of the liquid crystal display device is obtained. be able to.

  However, if the backlight is configured by using the LED 2 that is a point light source, unevenness in brightness and darkness is likely to occur in the vicinity of the incident surface, and the LED 2 is opposed to the LED 2 on the incident surface 1a of the light guide plate 1 as shown in FIG. Although the incident surface 1a at the position is bright, the dark portion 5 tends to be generated between the adjacent LEDs 2. Therefore, various methods as described below have been proposed so as to eliminate such dark portions 5 and ensure the uniformity of illumination light to such an extent that no problem occurs in actual use in the effective illumination region.

That is, a method of forming a diffusing element such as a prism array on the incident surface 1a of the light guide plate 1 (for example, Patent Document 1), or a method of forming a hole in a portion facing the LED 2 in the vicinity of the incident surface 1a of the light guide plate 1 (For example, patent document 2) etc. are proposed. Further, as a method of promoting light diffusion in the direction along the incident surface 1a of the light guide plate 1, a method of using a certain distance from the incident surface 1a of the light guide plate 1 as a space for uniformization (for example, Patent Documents). 3) etc. have been proposed.
JP 10-199316 A JP 2000-149635 A JP-A-9-34371

  However, since the method of forming the diffusing element or the hole in the light guide plate 1 as described above is based on the premise that a certain invalid area is generated inside the light guide plate 1, a liquid crystal display device using CCFL as a light source Compared to the above, there is a problem that the light guide plate 1 is larger and heavier and hinders downsizing of the apparatus.

  Further, the method of providing a diffusing element such as a prism or a lenticular lens on the incident surface 1a of the light guide plate 1 has a certain effect in the conventional light guide method in which the output surface 1b of the light guide plate 1 and the back surface thereof are flat. There is a problem in that the light guide method in which a prism whose longitudinal direction is perpendicular to the incident surface 1a is formed on either the exit surface 1b or the back surface of the light guide plate 1 has little effect. This is presumably because the propagation direction of light in the direction orthogonal to the prism extending direction is suppressed by the action of the prism formed on the light guide plate 1. In recent years, a light guide system in which a prism is directly formed on the light guide plate 1 is becoming mainstream. This light guide method has the effect of concentrating light in a direction perpendicular to the direction of extension of the prism to improve the front brightness, and can reduce one prism sheet installed on the light exit surface 1b of the light guide plate 1, Since the prism provided on the light guide plate 1 serves as a light guide and the propagation of light in the lateral direction is hindered, sufficient uniformity of illumination light cannot be ensured.

  Furthermore, the method of using a certain distance from the incident surface 1a of the light guide plate 1 as a space for homogenization can obtain a certain degree of illumination light uniformity, but still provides sufficient illumination light uniformity. It cannot be secured.

  Therefore, the object of the present invention is to obtain uniform illumination light even when a point light source element is used as a light source, high illuminance, and reducing the ineffective area in the light guide plate, thereby reducing the size and weight of the device. Another object of the present invention is to provide a planar light source that can be realized and can also be applied to a light guide method in which a diffusing means is provided on the exit surface of a light guide plate, and a liquid crystal display device using the same.

  The present invention is directed to a planar light source. The planar light source introduces light from a light source unit having a plurality of point light source elements and an incident surface facing the light source unit, and opposes the introduced light. A light guide plate that emits planar light from the light exit surface by propagating to the entire surface while being totally reflected between the main surfaces and changing the light path by an optical path changing member provided inside.

  Here, the surface light source of the present invention is characterized in that d / p, which is a value obtained by dividing the distance d between the point light source element and the incident surface of the light guide plate by the arrangement interval p of the point light source elements, is 0.2. This is in the point of being less than 1. With such a configuration, uniform illumination light can be obtained even when a plurality of point light source elements are used as the light source, and the ineffective area in the light guide plate can be reduced, and the apparatus can be reduced in size and weight.

  In the present invention, the plurality of point light source elements may be arranged at equal intervals, or at least partially arranged at unequal intervals. In the latter case, the arrangement interval p is the maximum arrangement interval between adjacent point light source elements.

  Moreover, you may make it include in any one of the main surfaces of a light-guide plate the structure which has a periodic structure in the direction parallel to an incident surface by making a direction perpendicular | vertical to an incident surface into a longitudinal direction. Even in such a light guide system, light in a sufficiently uniform state is incident on the light guide plate, so that the uniformity of illumination light may be impaired even if there is no lateral propagation of light inside the light guide plate. And can be suitably used.

  The point light source element is preferably a light emitting diode. By using a light emitting diode with high luminous efficiency, high illuminance can be obtained.

  The present invention is also directed to a liquid crystal display device. The liquid crystal display device includes a liquid crystal panel in which liquid crystal is sealed between a pair of glass substrates, and a backlight disposed on the back side of the liquid crystal panel. The backlight introduces light from a light source unit having a plurality of point light source elements and an incident surface facing the light source unit, and propagates the introduced light to the entire surface while totally reflecting between the opposing main surfaces. And a light guide plate that emits planar light from the exit surface by changing the optical path by the optical path changing member provided in.

  Here, the liquid crystal display device of the present invention is characterized in that d / p, which is a value obtained by dividing the distance d between the point light source element and the incident surface of the light guide plate by the arrangement interval p of the point light source elements, is 0.2 or more. A planar light source set to be less than 1 is used as a backlight. With such a configuration, the planar light source constituting the backlight can reduce the ineffective area in the light guide plate and reduce the size and weight of the device. Therefore, the liquid crystal display device as a whole can be reduced in size and weight. Can be realized. In addition, since the backlight can give uniform illumination light to the liquid crystal panel, a liquid crystal display device with good display characteristics can be obtained.

  As described above, according to the planar light source of the present invention, by setting the interval between the light source unit and the light guide plate and the arrangement pitch of the light sources constituting the light source unit to appropriate values, a plurality of point light source elements can be used as the light source. Even if it is used, light can be guided to the light guide plate in a state in which the non-uniformity of the illumination light is mitigated, thereby reducing light and darkness near the incident end of the light guide plate, and making it possible to emit light with uniform and high illuminance. . In addition, since the ineffective area of the light guide plate can be reduced, the apparatus can be reduced in size and weight. Therefore, the liquid crystal display device using the planar light source of the present invention as a backlight has good display characteristics, and can be small and lightweight.

(First embodiment)
The planar light source according to the first embodiment of the present invention will be described below. FIG. 1 shows a configuration of a planar light source according to the present embodiment, FIG. 1 (a) is a cross-sectional view of the planar light source viewed from the side, and FIG. 1 (b) is a plan view of the planar light source. FIG. 1A and 1B, the planar light source 15 includes a light source unit 10 and a light guide plate 1.

  The light source unit 10 includes an LED 2 that is a point light source element, a substrate 3, and a reflection plate 4. A plurality of LEDs 2 are used, and are mounted on the substrate 3 with an arrangement interval p along the incident surface 1a of the light guide plate 1 as will be described later. The reflection plate 4 is made of a white resin sheet or the like having a high reflectance, and is configured to surround the LED 2 and the substrate 3 in order to efficiently guide light from the LED 2 to the light guide plate 1. In addition, illustration of the reflecting plate 4 is abbreviate | omitted in FIG.1 (b). The light source unit 10 having such a configuration is disposed on the side surface side of the light guide plate 1.

  The light guide plate 1 is formed of a transparent resin having a large refractive index, such as polycarbonate resin or methacrylic resin. The light guide plate 1 has a light incident surface 1a on one side surface and an optical path changing member (not shown) inside. Then, as indicated by an arrow in FIG. 1A, the light incident from the incident surface 1a propagates to the entire surface of the light guide plate 1 while being totally reflected between the exit surface 1b and the reflecting surface 1c, and the optical path is changed. By changing the optical path by the member, the propagated light is emitted from the emission surface 1b to emit planar light. Examples of the optical path changing member include a scattering pattern such as a groove portion and unevenness having a predetermined pattern formed on the main surface, a diffusion sheet diffusion material, and the like. In addition, the incident surface 1a of the light guide plate 1 is at a position facing the substrate 3 on which the LEDs 2 are mounted, and the distance between each LED 2 and the incident surface 1a of the light guide plate 1 is a constant distance d.

  The characteristic part according to the present embodiment is that the distance d between the LED 2 and the light guide plate 1 and the arrangement interval p of the LEDs 2 are set to appropriate values. Hereinafter, the distance d between the LED 2 and the light guide plate 1 is referred to as “light source-light guide plate distance d”, and the arrangement interval p of the LEDs 2 is referred to as “light source pitch p”. Here, the light source pitch p will be described more specifically. FIG. 2 is a plan view showing a state where the LED 2 is mounted on the substrate 3. The plurality of LEDs 2 may all be arranged at equal intervals, or at least partially arranged in a state where they are not equally spaced. In the latter case, the light source pitch p is the maximum arrangement interval. To explain with a specific example, as shown in FIG. 2A, if all the LEDs 2 are arranged at equal intervals, the distance between the adjacent LEDs 2 is all constant. p1. As shown in FIG. 2B, when the plurality of LEDs 2 are arranged at different intervals (p2 and p3), the light source pitch p is p2 which is the maximum arrangement interval. As shown in FIG. 2C, when the LEDs 2 are arranged in a plurality of columns, the light source pitch p is the maximum arrangement interval in consideration of the interval p4 between the rows and the interval p5 between the columns. p4 is the light source pitch.

  In the present embodiment, the light source-light guide plate distance d and the light source pitch p defined as described above are set to the following values. That is, d / p, which is a value obtained by dividing the distance d between the light source and the light guide plate by the light source pitch p, is set to 0.2 or more and less than 1. In other words, the distance d between the light source and the light guide plate is set in a range of 0.2 times or more and less than 1 time the light source pitch p. Since such a relationship is established between the distance d between the light source and the light guide plate and the light source pitch p, even when a plurality of LEDs 2 having high luminous efficiency are used as the light source, the light from the light source is reduced in non-uniformity. Thus, light can be introduced into the light guide plate 1. Thereby, the brightness and darkness in the vicinity of the incident surface 1a of the light guide plate 1 can be reduced, and uniform illumination light can be realized with high illuminance. In addition, by introducing the light into the light guide plate 1 after making the light uniform in advance, the same effect can be obtained in a smaller space as compared with the case where the light is made uniform inside the light guide plate 1 as in the conventional example. Thus, the apparatus can be reduced in size and weight.

  When d / p, which is a value obtained by dividing the distance d between the light source and the light guide plate by the light source pitch p, is less than 0.2, significant light and darkness occurs in the vicinity of the incident surface 1a of the light guide plate 1. As such a planar light source, the planar light source 70 shown in FIG. On the other hand, when d / p, which is a value obtained by dividing the distance d between the light source and the light guide plate by a light source pitch p, exceeds 1, the brightness in the vicinity of the incident surface 1a is eliminated, but the light source unit 10 and the light guide plate 1 Unnecessary invalid spaces are created between them, which hinders downsizing and weight reduction of the device. Therefore, in this embodiment, it is more preferable that d / p, which is a value obtained by dividing the distance d between the light source and the light guide plate by the light source pitch p, is 0.2 or more and less than 0.8, 0.5 to 0 More preferably, it is in the range of .8.

  Hereinafter, the reason why such an effect is obtained will be described in more detail. First, the reason why it is more efficient to make the light uniform before being introduced into the light guide plate 1 is to make the light uniform inside the light guide plate 1 will be described. FIG. 3 is a schematic diagram showing a locus of incident light incident on the light guide plate 1 from the air. In FIG. 3, the incident light a1 is incident from the air having a refractive index n1 of 1 toward the light guide plate 1 having a refractive index n2 of 1.5 in a state almost parallel to the incident surface 1a. . Here, the maximum angle θmax of θ2 that the incident light a2 incident on the light guide plate 1 can take from the normal S of the incident surface 1a is obtained as about 41.8 ° from the following equation (1). Therefore, θ2 is less than 41.8 °.

  On the other hand, the maximum angle θmax of θ1 that the incident light a1 traveling from the air toward the light guide plate 1 can take from the normal S of the incident surface 1a is close to approximately 90 °, and is clearly larger than θ2. In order to make the light uniform, it is effective to obtain light diffusion in the horizontal direction on the incident surface 1a of the light guide plate 1. Therefore, in the above example, the normal line of the incident surface 1a of the light guide plate 1 is used. It means that in the air having a larger angle from S, the light homogenization efficiency is larger than the inside of the light guide plate 1 having a small angle from the normal S.

  Since the planar light source 15 according to the present embodiment aims to equalize the light before being introduced into the light guide plate 1 as described above, the light is uniformed inside the light guide plate 1 as in the above-described conventional example. Compared with the planar light source to be achieved, higher light uniformity efficiency can be obtained. As a result, the same effect can be obtained in a smaller space, and the apparatus can be reduced in size and weight.

  In addition, the planar light source 15 according to the present embodiment has a periodic structure on one of the main surfaces of the light guide plate 1 in a direction parallel to the incident surface 1a with the direction perpendicular to the incident surface 1a as a longitudinal direction. The structure which has can be included. Such a structure has a function of converging incident light, and specifically, a prism array or a prism sheet in which a plurality of prisms, more preferably a plurality of fine prisms are arranged in a fixed periodic structure. Etc. By adopting such a light guide method, the front luminance of the planar light source 15 can be further improved. In addition, since the planar light source 15 according to the present embodiment is intended to make the light before introduction into the light guide plate 1 uniform, the direction orthogonal to the extending direction of the diffusing member even if such a light guide method is adopted. The direction of light propagation to the light is suppressed, and the light homogenization efficiency is not hindered.

  Note that, even in the method of making the light uniform inside the light guide plate 1 like the planar light source 70 described in the conventional example, θ2 can be obtained by providing a structure such as a prism on the incident surface 1a of the light guide plate 1. Since a component having an angle equal to or larger than θmax is generated, it is possible to improve the light uniformity efficiency. However, if the conventional planar light source 70 employs a light guide method in which a prism is formed on the exit surface 1b or the back surface 1c of the light guide plate 1 to increase the front luminance, light propagation in the incident surface direction within the light guide plate 1 is prevented. It will be suppressed. Therefore, in the conventional planar light source 70, even if a structure such as a prism is provided on the incident surface 1a, the light uniformization efficiency cannot be increased as in the planar light source 15 of the present embodiment.

  Next, the reason for defining the light source-light guide plate distance d and the light source pitch p will be described. First, the illumination state on the incident surface 1a of the light guide plate 1 was calculated, and the relationship with the positional relationship with the LED 2 was examined. FIG. 4 is a schematic diagram for calculating the illumination state on the incident surface 1 a of the light guide plate 1. In FIG. 4, the straight line L <b> 1 indicates the position where the LEDs 2 are arranged, and the straight line L <b> 2 represents the incident surface 1 a of the light guide plate 1. The distance between the straight line L1 and the straight line L2 is represented by d. Points K1 to K4 arranged on the straight line L1 schematically represent the LEDs 2 having the same luminous intensity, and are arranged at a constant interval p. A point M is a calculation point for examining the illuminance state, and is on the straight line L2.

  In an actual light source arrangement, it is common to use more than four point light sources. However, in the planar light source 15 according to the present embodiment, it is assumed that d / p is relatively small. Therefore, the influence of the light source located far from the calculation point M is small. Therefore, even if the influence of the light source located far from the calculation position M is ignored, it is sufficient to obtain a quantitative prospect. Here, four light sources K1 to K4 near the calculation position M are taken as an example. Will be described. Also, the illuminance at each point is displayed as a function of the distance x from the point that opposes the second light source K2 (more precisely, the intersection of L2 with a straight line passing through K2 and perpendicular to L1).

The illuminance at the calculated position M is represented by the sum of the illuminances S1 to S4 from the light sources K1 to K4. The illuminances S1 to S4 are calculated based on the distance between the calculated position M and the light sources K1 to K4 and the calculated position M. K1 to K4 depend on the desired angles θ1 to θ4. First, angles θ1 to θ4 at which the light sources K1 to K4 are desired from the calculated position M are expressed by the following equations (2) to (5). In the following formulas (2) to (5), x is the distance between the calculated position M and the point S facing the second light source K2. More specifically, the point S is a point passing through K2 and perpendicular to the straight line L1 intersecting the straight line L2.

  The illuminances S1 to S4 from the light sources K1 to K4 at the calculation position M are intended for illuminance in a planar shape along the straight line L2, and therefore, the vertical incidence is used as a reference, and the inclination is an angle θ from this reference. The illuminance is proportional to cos (θ). In general, the illuminance decreases in inverse proportion to the square of the distance from the light source. However, in FIG. 4, as shown in FIG. 1, it is assumed that propagation in one direction is restricted by the reflector 1c. Therefore, the illuminances S1 to S4 are inversely proportional to the distances T1 to T4 from each light source. Here, the distances T1 to T4 from the respective light sources are defined by T1 = d / cos (θ1), T2 = d / cos (θ2), T3 = d / cos (θ3), depending on d and angle θ defined above. It can be expressed as T4 = d / cos (θ4). Accordingly, the illuminance S1 is proportional to cos (θ1), the illuminance S2 is proportional to cos (θ2), the illuminance S3 is proportional to cos (θ3), and the illuminance S4 is proportional to cos (θ4). It is proportional to the square of cos (θ1) to cos (θ4). Thereby, when a proportional multiplier is set to A, illumination intensity S1-S4 is represented by following (6)-(9) Formula.

  Accordingly, θ1 to θ4 are calculated by substituting x and p into the above equations (2) to (5), and S1 to S4 are calculated by substituting the obtained values into the above equations (6) to (9). The illuminance at the calculation point M is obtained by taking the sum of S1 to S4.

  FIG. 5 is a graph showing the relationship between the incident position and the relative illuminance at the calculation point M, where d / p, which is a value obtained by dividing the distance d between the straight line L1 and the straight line L2 by the light source pitch p, is 0.1. , 0.2, 0.3, 0.4, 0.6, 0.8, and 1.0, and the illuminance distribution in each state is calculated. In addition, the incident position of the light to the calculation point M is represented by x / p, and the relative illuminance is illuminance normalized by the maximum illuminance in each setting of d / p.

  In FIG. 5, each graph shows that the relative illuminance is maximum at a point where x / p = 0 and x / p = 1 where the light source and the calculation point M face each other, and x / p = 0 to x / p = At the point 1, a downwardly convex curve is drawn so that the relative illuminance is minimum at the point x / p = 0.5. Each graph has a larger curvature as the d / p value is smaller, and a gentle curvature as the d / p value is larger.

  FIG. 6 shows the calculation result in FIG. 5 in relation to the illuminance ratio (maximum illuminance / minimum illuminance) and d / p which is a value obtained by dividing the distance d between the light source and the light guide plate by the light source pitch p. . In FIG. 6, when d / p is 0.1, the illuminance ratio is extremely large, approximately 12 times. However, when d / p becomes 0.2, the illuminance ratio rapidly decreases to 3.5 times, and d / p When the value becomes 0.3, the illuminance ratio decreases to twice. As a result, it is clear that the illuminance ratio tends to rapidly decrease as d / p increases from 0.1. Moreover, when visual evaluation was also performed, in the state where d / p where the illuminance ratio was 3.5 times or less was larger than 0.2, the dark portion on the incident surface 1a of the light guide plate 1 was remarkably eliminated. The effect was confirmed, and when d / p was larger than 0.3, it was confirmed that the light / dark pattern on the incident surface 1a of the light guide plate 1 was at a level that could hardly be recognized.

(Second Embodiment)
FIG. 7 is a side view showing the configuration of the liquid crystal display device according to the second embodiment of the present invention. In FIG. 7, the liquid crystal display device 60 includes a liquid crystal panel 50 and a backlight 55. The backlight 55 has the same configuration as the planar light source 15 described in the first embodiment.

  Although not shown here, the liquid crystal panel 50 includes a liquid crystal cell in which liquid crystal is sealed between a pair of glass substrates, a polarizing plate, a color filter, and the like. The planar light source 15 serving as the backlight 55 is disposed so that the light exit surface 1 b of the light guide plate 1 is on the back side of the liquid crystal panel 50. By inserting an optical sheet such as a prism sheet, a polarizing reflection film, and a diffusion film between the backlight 55 and the liquid crystal panel 50, the directivity of the illumination light can be strengthened and the luminance in the front direction can be increased. In addition to this, it is possible to increase the polarization component transmitted through the liquid crystal panel to increase the brightness, and further to expect effects such as reduction of fine unevenness and moire due to diffusion.

  Since the liquid crystal display device 60 configured as described above can reduce the size of the planar light source 15 as the backlight 55 as described above, the liquid crystal display device 60 as a whole can be reduced in size. Further, even if the planar light source 15 is downsized, it can supply uniform and bright light, so that the liquid crystal display device 60 with good display characteristics can be realized.

  In each of the above-described embodiments, the LED 2 is described as an example of the point light source element. However, the present invention is not limited to this, and a point light source element such as a semiconductor laser is also applicable.

  The surface light source of the present invention is a liquid crystal display device using the same, and does not provide a space or structure for uniformizing light on the light guide plate, and can emit light with uniform and high luminance while using a plurality of point light sources. Therefore, since the device can be downsized, it can be suitably used for a backlight of a liquid crystal display device.

Sectional drawing and top view which show the structure of the planar light source which concerns on the 1st Embodiment of this invention The top view which shows the mounting state of LED which concerns on the same embodiment The figure which shows the locus | trajectory of the light which injects into a light-guide plate from an air layer Schematic diagram for calculating the illumination state on the incident surface of the light guide plate Graph showing the result of calculating the illuminance distribution A graph showing the result of calculating the light / dark ratio (maximum illuminance / minimum illuminance) Side view of the liquid crystal display device according to the second embodiment of the present invention. Sectional view and plan view showing the configuration of a conventional planar light source

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light guide plate 1a Incident surface 1b Output surface 1c Reflective surface 2 LED
3 Substrate 4 Reflecting plate 10 Light source unit 15 Planar light source 50 Liquid crystal panel 55 Backlight 60 Liquid crystal display device

Claims (6)

A light source unit having a plurality of point light source elements;
By introducing light from the incident surface facing the light source unit and propagating the introduced light to the entire surface while totally reflecting between the opposed principal surfaces, and changing the optical path by an optical path changing member provided inside, A light guide plate for emitting planar light from the emission surface,
D / p, which is a value obtained by dividing the distance d between the point light source element and the incident surface of the light guide plate by the arrangement interval p of the point light source elements, is 0.2 or more and less than 1. , Planar light source.   The planar light source according to claim 1, wherein the plurality of point light source elements are arranged at equal intervals.   The plurality of point light source elements are arranged at unequal intervals at least in part, and the arrangement interval p is the maximum arrangement interval between adjacent point light source elements. Item 2. A planar light source according to Item 1.   2. The structure according to claim 1, wherein one of the main surfaces of the light guide plate includes a structure having a periodic structure in a direction parallel to the incident surface with a direction perpendicular to the incident surface as a longitudinal direction. The surface light source described.   The planar light source according to claim 1, wherein the point light source element is a light emitting diode. A liquid crystal panel in which liquid crystal is sealed between a pair of glass substrates;
A backlight disposed on the back side of the liquid crystal panel,
The backlight is
A light source unit having a plurality of point light source elements;
By introducing light from the incident surface facing the light source unit and propagating the introduced light to the entire surface while totally reflecting between the opposed principal surfaces, and changing the optical path by an optical path changing member provided inside, A light guide plate for emitting planar light from the emission surface,
A surface set so that d / p, which is a value obtained by dividing a distance d between the point light source element and the incident surface of the light guide plate by an arrangement interval p of the point light source elements, is 0.2 or more and less than 1. A liquid crystal display device characterized by being a light source.

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