JP2005135760A - Surface light source device, and display device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To finely adjust and fix the position of individual LEDs to prevent the occurrence of deviation of light distribution inside a light guide body due to unevenness of an incident part and the position of the individual LEDs in a light pipeless method backlight. <P>SOLUTION: A surface light source device is provided with the light guide body having prisms formed on an incident part, and a cabinet to fix the light source. A positioning site having such a shape that can be fitted into the uneven parts of the prism array of the incident part is arranged on the cabinet. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a surface light source device used as a backlight for illuminating a non-self-luminous display element, and more particularly to a sidelight type surface light source device that makes light source light incident from one side surface of a light guide plate.

  As display devices for cellular phones and PDAs (personal data assistants), transmissive or transflective liquid crystal display devices are widely used. Since the liquid crystal element which is a constituent member of the liquid crystal display device does not emit light by itself, an illuminating means for observing an image is necessary. For this reason, a liquid crystal display device is usually configured by providing a planar illumination device (surface light source device) on the back surface of the liquid crystal element. This surface light source device is, for example, a mechanism that converts a line light source such as a discharge tube or a point light source such as an LED into planar light. In liquid crystal display devices for cellular phones and PDAs, thinness is one of the important requirements, and in order to realize this, surface light source devices using a light guide are often used. Specifically, a transparent resin material such as acrylic or PC (polycarbonate) is used as a light guide, one or more LED light sources are arranged on the side surface, and LED light is emitted from the entire top surface of the light guide. A method is typical, and a surface light source device using such a method is called a side light (edge light) type backlight.

  2. Description of the Related Art In recent years, with the miniaturization and colorization of images, a surface light source device with higher brightness and high contrast is required, and an contradictory demand has been made that an increase in power consumption must be avoided. Under such circumstances, various ideas have been made in terms of how to efficiently emit light from a light source in a planar manner.

  In particular, when a point light source such as an LED is used as the light source, a device for converting the point light source light into light having a uniform light emission distribution similar to that of the surface light source light and entering the light into the light guide body is required. .

  As a means for converting the point light source light into light having a uniform light emission distribution, there is a method in which a light guide means is prepared separately from the light guide and a point light source is provided therein. Light pipes are known as light guiding means for such applications. The point light source light is diffused in the light pipe and emitted from the light exit surface of the light pipe toward the light guide as light having a uniform light emission distribution (see, for example, Patent Document 1). A typical structure of such a light pipe type backlight is shown in FIG. As shown in the figure, the light pipe 203 has a rectangular parallelepiped shape, and is installed so that the light incident surface of the light guide 201 and the light exit surface of the light pipe face each other. The LED 202 is fixed to one of the short sides of the light pipe. As the light pipe 203 moves away from the LED 202, the thickness in the long side direction decreases. A diffusion prism array 204 is formed on the surface of the light pipe that faces the light exit surface. A prism array 205 is formed on the lower surface of the light guide 201, and a reflector 206 is installed below the prism array 205. The light emitted from the LED 202 travels while being totally reflected in the light pipe, and is reflected by the diffusing prism array 204 in the direction of the long side opposite to the diffusing prism array, that is, in the direction of the light exit surface of the light pipe 203. By optimizing the shape of the diffusing prism array, it is possible to emit light having a uniform light distribution from the light exit surface of the light pipe. When such a light pipe is used, the number of parts increases, leading to an increase in cost. In order to avoid such an increase in cost, a method of converting point light source light into uniform light without using a light pipe is known (for example, see Patent Document 2). FIG. 4 shows an example of a light pipe-less backlight that does not use a light pipe. An LED 302 is installed on the light incident surface side of the light guide 301, and a light incident surface prism array 304 is formed on the light incident surface of the light guide 301. A prism array 303 is formed on the bottom surface of the light guide 301. A reflector 305 is installed below the light guide 301.

Light emitted from the LED 302 is incident on the light guide 301 while being diffused by the light incident surface prism array 304. By optimizing the shape of the light incident surface prism array 304, a uniform light distribution can be obtained. Although a light beam having a large radiation angle from the LED is reflected on a flat light incident surface, this method has an advantage of high incidence efficiency because it is incident on the light guide body by the light incident surface prism array.
JP 2001-283622 A Japanese Patent No. 3344483

  The light pipeless type backlight as shown in FIG. 4 has an advantage that the production cost is lower than that of the light pipe type. However, depending on the position of the prism and the LED on the light incident surface, the light distribution inside the light guide may be biased. In order to prevent this, it is necessary to finely adjust and fix the position of each LED. Such adjustments may increase costs and offset the advantage of not requiring a light pipe.

  In order to solve the above-described problems, a surface light source device of the present invention is a light pipeless backlight in which a prism array is formed on a light incident surface of a light guide, and is provided in a housing that houses a light source such as an LED. In addition, a positioning means having a shape such as a convex portion or a concave portion is provided so as to fit into the concave and convex portions of the prism array on the light incident surface. With such a configuration, the optimum positioning of the light source can be made very simple, and a surface light source device with high luminance can be realized at low cost.

  A surface light source device of the present invention includes a light guide made of an optically transparent material, a light source that emits light to a light incident surface of the light guide, and a housing that holds the light source. The light incident surface is formed with a concave and convex prism array for diffusing light from the light source, and the housing is formed with a positioning portion shaped to fit into the irregularities of the prism array on the light incident surface. is there. Further, the housing is provided with a second positioning portion so that the positioning portion is not in contact with the prism array in a state where the positioning portion is engaged with the unevenness of the prism array. Furthermore, the positioning part and the second positioning part are formed at positions that sandwich the light source.

  Further, with the light source positioned by the positioning part, the center of the light source is made to coincide with the peak angle or the peak angle of a specific prism in the prism array. In addition, the light output surface of the light source is made substantially parallel to the light incident surface of the light guide in a state where the light source is positioned by the positioning portion.

  Furthermore, the positioning part was formed of an optically transparent material. Furthermore, a second prism array in which prisms are continuously formed is formed on either the light emitting surface of the light guide or the surface facing the light emitting surface. A light diffusion band is provided between the light surface and the second prism array of the light guide so that incident light can sufficiently diffuse.

  Further, the display device of the present invention includes such a surface light source device and a non-self-luminous display element that uses the light emitted from the surface light source device as illumination light.

  An outline of the surface light source device of this example is schematically shown in FIG. As shown in the drawing, a plurality of LEDs 102 are arranged on a side surface of a light guide body 101 made of a transparent substrate, and a prism array 103 is formed on the bottom surface of the light guide body 101. In this embodiment, three LEDs are used. The prism array 103 has a downwardly convex triangular section, and is formed such that the inter-prism pitch of the prism array 103 gradually decreases as the distance from the LED 102 increases. A reflecting plate 109 is installed below the prism array 103.

  A light incident surface prism array 104 is formed on the surface of the light guide 101 facing the LED 102, that is, the entire light incident surface. Further, the end surface prism array 105 is also formed on the end surface opposite to the light incident surface of the light guide 101. A certain interval is provided between the light incident surface prism array 104 and the first prism of the prism array 103, and this portion becomes a light diffusion band 108.

  The plurality of LEDs 102 are all housed in an LED housing 106, and a knife edge 107 having a tip shape capable of matching the valley apex angle of the light incident surface prism array 104 is formed at both ends of the LED housing 106. Yes. The LED light source 102 is positioned with high accuracy in a recess formed in the LED housing 106, and the positional relationship between the three LEDs 102 does not easily change due to vibration or temperature change.

  FIG. 2 shows a state in which the LED housing 106 is combined with the light guide 101 and fixed, and the LED 102 emits light. In this configuration, when one tip of the knife edge 107 is matched with the apex angle of the valley of the outermost prism of the light incident surface prism array 104, the tip of the other knife edge 107 is outside the light incident surface prism array 104. In contact with the flat part. When the LED housing 106 is combined with the light incident surface prism array 104 in this way, the center position of each LED fixed to the LED housing 106 matches the peak angle of the specific prism. Designed to. Furthermore, the light exit surfaces of all the LEDs are set to be parallel to the light incident surface. The other edge of the knife edge 107 is brought into contact with the flat portion outside the light incident surface prism array 104 because the knife edge 107 interferes with the light incident surface prism array 104 when the LED housing 106 expands or contracts due to a temperature change. This is because the LED housing 106 is bent and the optical axis of the LED 102 is prevented from being inclined.

  Light emitted from the LED 102 is incident on the light guide 101 while being diffused by the light incident surface prism array 104. By optimizing the shape of the light incident surface prism array 104 and the length of the light diffusion band 108, a uniform light distribution can be obtained in the vicinity of the end portion of the light diffusion band 108.

  In this way, by aligning one knife edge 107 provided on the LED housing 106 to which the LEDs 102 are fixed to one valley apex angle of the light incident surface prism array 104, the light incidents to the plurality of LEDs 102. The relative position with respect to the surface prism array 104 and the distance between the LED 102 and the light incident surface of the light guide 101 can be determined accurately and uniquely, and the conventional fine adjustment of the LED position is not required. . Therefore, an optimal setting can be performed without cost, and a surface light source device with low cost and high brightness can be realized.

  In the present embodiment, when the LED housing 106 is combined with the light incident surface prism array 104, an example in which the center of each LED 102 matches the apex angle of a certain prism in the light incident surface prism array is shown. It is also possible to set the center of the LED 102 to coincide with the apex angle of a valley of a certain prism in the light incident surface prism array 104. In addition, a transparent resin material such as acrylic (PMMA) or polycarbonate (PC) can be used for the light guide. The LED housing 106 is preferably made of the same material as the light guide 101 in view of the influence of thermal expansion, but materials other than resin can also be used.

  According to the surface light source device of the present invention, the optimum positioning of the LED can be performed very easily, and it is possible to provide a surface light source device with high brightness at low cost. Moreover, this surface light source device can be used for illumination of a display element.

It is a schematic diagram which shows the outline | summary of the surface light source device of this invention. It is the elements on larger scale which show typically the light source vicinity of the surface light source device of the present invention. It is a schematic diagram which shows an example of the conventional light pipe type backlight. It is a schematic diagram which shows an example of the conventional light pipeless type backlight.

Explanation of symbols

101 Light guide 102 LED
103 Second prism array 104 Prism array 105 Terminal surface prism array 106 LED housing 107 Knife edge 108 Light diffusion band 109 Reflector

Claims (9)

A light guide made of an optically transparent material, a light source that emits light to a light incident surface of the light guide, and a housing that holds the light source,
An uneven prism array for diffusing light from the light source is formed on the light incident surface of the light guide, and the housing has a shape that fits into the irregularities of the prism array on the light incident surface. A surface light source device in which a positioning portion is formed.   2. The second casing according to claim 1, wherein the casing is provided with a second positioning portion that does not come into contact with the prism array in a state where the positioning portion is engaged with the unevenness of the prism array. Surface light source device.   The surface light source device according to claim 2, wherein the positioning portion and the second positioning portion are formed at positions that sandwich the light source.   The center of the light source coincides with the peak angle or peak angle of a specific prism in the prism array in a state where the light source is positioned by the positioning part. 3. The surface light source device according to 3.   4. The surface light source device according to claim 2, wherein a light output surface of the light source is substantially parallel to a light incident surface of the light guide in a state where the light source is positioned by the positioning portion. 5.   The surface light source device according to claim 1, wherein the positioning portion is formed of an optically transparent material.   The surface light source device according to claim 1, wherein a plurality of light sources are held in the housing.   Either one of the light-emitting surface of the light guide or the surface facing the light-emitting surface includes a second prism array in which prisms are continuously formed, and light incident on the light guide 8. A light diffusion band is provided between the surface and the position of the second prism array so that light from the light source is sufficiently diffused. The surface light source device described.   A display device comprising: the surface light source device according to claim 1; and a non-self-luminous display element that uses light emitted from the surface light source device as illumination light.

Images