JPH071427U - Surface light source - Google Patents

Abstract

(57) [Abstract] [Purpose] The present invention is used as a backlight of a liquid crystal display plate, etc., and enables a bright image to be observed in either a direction perpendicular to the display plate or an oblique direction. An object is to provide a surface light source device. According to the surface light source device of the present invention, a first prism sheet in which long prisms having a triangular cross section are arranged side by side and a second prism sheet in which prisms having a cylindrical lens shape are arranged side by side in the longitudinal direction of the prism are provided on the exit side thereof. The feature is that they are arranged so as to cross each other.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a surface light source device used for a backlight of a liquid crystal display device.

[0002]

[Prior art]

 FIG. 2 shows a conventional surface light source device using a light guide, in which a linear light source 1 is arranged near the end face of the light guide 2, and a diffusion member 3 is provided on the surface of the light guide 2. The reflecting member 4 is arranged on the back surface.

In this surface light source device, light from the light source 1 enters the light guide 2 through the incident end face 2a and is transmitted. Here, by changing the direction of the light reflected by the back surface or the reflecting member 4 by forming a rough surface or forming fine irregularities on the back surface of the light guide body 2, A part of the light transmitted inside is emitted from the surface 2b of the light guide. The light emitted from the light guide 2 passes through the diffusion member 3 to become diffused light, which illuminates the liquid crystal display panel 5, for example.

FIG. 3 shows a conventional surface light source device, which is of a type using a reflecting member. In this surface light source device, a linear light source 1 is arranged inside a reflecting member 6 having a cross-sectional shape as shown in the drawing, and diffuses light emitted from the light source 1 directly or after being reflected by the reflecting member 6. The light is made incident on the liquid crystal display panel 5 as diffused light through the member 3 and illuminated.

The conventional surface light source device as described above, whether using the light guide shown in FIG. 2 or using the reflecting member shown in FIG. As a result, the light becomes divergent and does not enter the liquid crystal display panel 5, causing a loss of light and making it difficult to perform bright illumination. In particular, since the light incident on the liquid crystal display plate 5 is diffused light that travels in all directions, when observing from a direction perpendicular to the liquid crystal display plate, for example, there is light that does not enter the eyes of the observer, and a bright image is observed. I can't do it.

In order to solve the above-mentioned drawbacks of the conventional surface light source device, the diffusion sheet 3 and the liquid crystal display plate 5 are provided with a prism sheet 7 having a prism surface having a shape in which prisms 7a are arranged side by side as shown in FIG. It is known that a bright image can be observed by arranging the diffused light from the diffusing member 3 so as to direct the diffused light from the diffusing member 3 as close to the direction perpendicular to the liquid crystal display plate 5 as possible.

[0007]

[Problems to be solved by the device]

 When the prism sheet 7 as shown in FIG. 4 is arranged on the diffusion member of the surface light source device as described above, when observing from a direction substantially perpendicular to the liquid crystal display plate 5, a bright image can be observed. It is possible, but on the contrary, when viewed from an oblique direction, the image becomes dark and almost unobservable.

In order to avoid such a defect, the prism sheet 8 shown in FIG. 4 having the corner portions of the prism sheet shown in FIG. 4 as curved surfaces is arranged between the diffusion member 3 and the liquid crystal display panel 5. Thus, there is one that makes it possible to observe a bright image from an oblique direction by including light with a spread. However, in this case, the amount of light that does not enter the liquid crystal display plate 5 also increases, causing a loss of the amount of light, and the screen of the liquid crystal display plate 5 becomes a dark screen as a whole. Of course, when the diffusing member 3 is not used, the directivity of the emitted light is extremely strong and it is difficult to use it as a surface light source device.

The present invention is a surface light source device capable of illuminating the entire screen brightly with less loss of light quantity, and being able to observe a relatively bright image when observing not only in a direction perpendicular to the screen but also in an oblique direction. To provide.

[0010]

[Means for Solving the Problems]

 The surface light source device of the present invention is provided with a diffusing member and emits it as light diffused light from the light source. The first prism sheet with a square cross-section and the second prism sheet with curved corners such as prisms are arranged so as to cross each other, and the overall brightness is large, and it is possible to observe from an oblique direction. Is.

[0011]

【Example】

 Next, an embodiment of the surface light source device of the present invention will be described with reference to the drawings.

FIG. 1 is a perspective view of an embodiment of the present invention, in which 1 is a light source, 2 is a light guide, 3 is a diffusing member, and 4 is a reflecting member, which are the same as those of the surface light source device shown in FIG. . The surface light source device of this embodiment further comprises a first prism sheet 7 having the shape shown in FIG. 4 and a second prism sheet 8 shown in FIG.

As a result, the diffused light emitted from the diffusing member 3 is directed by the first prism sheet 7 in a direction perpendicular to the diffusing plate 3, and is slightly refracted by the second prism sheet 8. As a result, most of the light is incident on the display plate such as a liquid crystal display plate so that a bright image can be observed, and it is also possible to observe in an oblique direction.

In the above-mentioned embodiment, two prism sheets are arranged in the surface light source device using the light guide, but the diffusion plate of the surface light source device using the reflecting member as shown in FIG. 3 is used. It is also possible to arrange two similar prism sheets on the emitting side.

[0015]

[Effect of device]

 The surface light source device of the present invention comprises a first prism sheet having a prism having a long rectangular cross section on the exit side of the diffuser plate, and a corner portion of the prism in which the prism and the longitudinal direction of the prism are crossed to form a curved surface. By arranging two prism sheets, it is possible to observe with a bright image as a whole, even in a diagonal direction, and it is suitable for illumination of liquid crystal display panels.

[Brief description of drawings]

FIG. 1 is a perspective view of an embodiment of the present invention.

FIG. 2 A surface light source device using a conventional light guide

FIG. 3 is a surface light source device using a conventional reflecting member.

FIG. 4 is a perspective view of a prism sheet.

FIG. 5 is a perspective view of another prism sheet.

[Explanation of symbols]

 1 Linear light source 2 Light guide 3 Diffusing member 4 Reflecting member 7 First prism sheet 8 Second prism sheet

Claims (1)

[Scope of utility model registration request] 1. A surface light source device for converting diffused light through a diffusing plate arranged on the surface of a light source part, and a first prism sheet having a shape in which a large number of prisms having a triangular cross section are arranged side by side on the exit side of the diffusing plate. , A second prism sheet in which a large number of cylindrical lens-shaped prisms are arranged side by side and the joint portion of each prism is a curved surface is arranged, and these two prism sheets are arranged so that the longitudinal directions of the prisms intersect with each other. Surface light source device.