JPH09190716A - Surface light source device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To miniaturize an edge-light type surface light source device by enabling the uniformity of luminous quantity in the effective area of a light guide to be maintained while enclosing a fluorescent lamp inside the effective range of the light guide. SOLUTION: This light source device uses a light guide 12 as a surface light source by causing light emitted from a straight fluorescent lamp 11 placed along one side of the light guide 12 to impinge on the side end face of the light guide 12. In this case a prism plate 14 for refracting the light emitted from the fluorescent lamp 11 to make it almost uniformly impinge on the side end face of the light guide 12 is interposed between the side end face of the light guide 12 and the fluorescent lamp 11. The prism plate 15 has a number of triangular prisms aligned along the side end face of the light guide 12, with the angle of the center triangular prism 15a made greater than those of the triangular prisms 15b at each end, or with the middle triangular prism 15a made greater in size than the triangular prisms 15c at each end while making the angles of all the triangular prisms the same.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called edge light type surface light source device suitable for a backlight of a liquid crystal display device.

[0002]

2. Description of the Related Art In recent years, liquid crystal televisions and the like using liquid crystals as display devices have been put to practical use. The liquid crystal is thin, lightweight, and has low power consumption, so it is suitable for portable use. However, since the liquid crystal is a light receiving element, a backlight for illumination is necessary.
Although a fluorescent tube is conventionally used as a backlight, since the fluorescent tube has a cylindrical shape, light is emitted only from the fluorescent tube portion, and uniform light cannot be spread over the entire liquid crystal display screen.

Therefore, there is a direct type backlight in which a reflection case and a reflection sheet are provided so that the light is evenly distributed over the entire area of the liquid crystal display screen so that the linear light source emitted from the fluorescent tube is entirely distributed. In addition, for the purpose of thinning, a straight fluorescent tube is arranged on the side end surface of the transparent light guide, and an edge light type backlight using one surface as a surface light source using multiple reflection inside the light guide is also available. is there.

FIG. 4 is a perspective view showing an example of a conventional edge-light type backlight unit, and FIG. 5 is a plan view of the backlight unit. In these figures, 41 is a fluorescent tube (cooling unit) as a light source. Cathode ray tube), 41a is an end portion, 41a
Reference numeral b is a conductive wire, 42 is a transparent light guide, 43 is a metallic reflection film, and 44 is a prism plate. That is, in the conventional edge light type backlight unit, in order to keep the light quantity in the effective area of the transparent light guide 42 uniform, as shown in the figure, both ends 41a and 41a of the straight tube type fluorescent tube 41 are transparent. Light guide 42
It was projected from the effective area of each to the outside. According to this backlight unit, the light emitted from the straight tube type fluorescent tube 41 is reflected directly and by the metal reflection film 43 to be incident on the transparent light guide 42 from the side end surface, and the incident light is transparently guided. The emitted light is reflected by the metallic reflection film 43 from the back side of the optical body 42 and transmitted through a prism plate (having a triangular prism on the lower surface) 44 for light collection arranged on the front side of the transparent light guide 42. Becomes a substantially uniform surface light source and illuminates a liquid crystal display panel (not shown) substantially uniformly.

[0005]

However, since both ends 41a, 41a of the straight tube type fluorescent tube 41 are respectively projected from the effective area of the transparent light guide 42 to the outside as described above,
The protruding portions of both ends 41a, 41a of the fluorescent tube 41 are
This has been an obstacle to the miniaturization of liquid crystal display devices.

SUMMARY OF THE INVENTION An object of the present invention is to provide a surface light source device of the edge light type as described above so as to maintain the uniformity of the light quantity in the effective area of the light guide while accommodating the fluorescent tube in the effective area of the light guide. In other words, downsizing the surface light source device.

[0007]

In order to solve the above-mentioned problems, the invention according to claim 1 guides light emitted from a straight tube type fluorescent tube arranged along one side of a light guide. In a surface light source device in which the light guide is made to enter from a side end surface and the light guide is used as a surface light source, light emitted from the fluorescent tube is refracted between the side end surface of the light guide and the fluorescent tube. It is characterized in that a prism plate is provided to allow the light to enter the side end surface of the light guide substantially uniformly.

As described above, the light emitted from the fluorescent tube is refracted between the side end surface of the light guide and the straight tube type fluorescent tube arranged along the side of the light guide to the side end surface of the light guide. Since it is a surface light source device with a prism plate that allows the light to enter substantially uniformly, the two ends of the fluorescent tube do not project outside the effective area of the light guide as in the conventional case, but the fluorescent tube is inside the effective area of the light guide. Even when it is housed in the light guide, the light emitted from the fluorescent tube is refracted by the transmission of the prism plate and made to enter the side end surface of the light guide substantially uniformly, thereby ensuring the uniformity of the light amount in the effective area of the light guide. Since this can be maintained, the surface light source device can be downsized.

The invention according to claim 2 is based on claim 1.
The surface light source device according to claim 1, wherein the prism plate has a large number of triangular prisms arranged along the longitudinal direction of the side end surface of the light guide, and both ends of the prism plate are more than the angle of the triangular prism in the middle part of the prism plate. The feature is that the angle of the triangular prism of the part is enlarged.

Thus, in the prism plate according to claim 1, which has a large number of triangular prisms arranged along the longitudinal direction of the side end surface of the light guide body, the triangular prisms at both ends of the prism plate are more inclined than the angle of the triangular prism in the middle part. Since the surface light source device has a large angle, when the fluorescent tube is housed within the effective area of the light guide, the triangular prisms at both ends, which have a larger angle than the triangular prism in the middle of the prism plate Since the light emitted from the fluorescent tube can be directed and collected at the portions corresponding to both ends of the tube, the light emitted from the fluorescent tube can be made to enter the side end surface of the light guide substantially evenly. It is possible to maintain the uniformity of the amount of light in the effective area of.

The invention according to claim 3 is the surface light source device according to claim 1, wherein the prism plate has a large number of triangular prisms arranged along the longitudinal direction of the side end surface of the light guide. And, while making the angles of all triangular prisms the same,
It is characterized in that the size of the triangular prisms at both ends is larger than the size of the triangular prisms in the middle of the prism plate.

Thus, in the prism plate according to claim 1, which has a large number of triangular prisms arranged along the longitudinal direction of the side end surface of the light guide, the angles of all the triangular prisms are the same, and the intermediate portion of the prism plate is Since it is a surface light source device in which the size of the triangular prisms at both ends is larger than the size of the triangular prisms, when the fluorescent tubes are housed within the effective area of the light guide, the angle of all triangular prisms is the same between the prism plates. With the triangular prisms at both ends that are larger in size than the size of the triangular prism of the section, the light emitted from the fluorescent tube can be directed and condensed at the portions corresponding to the both ends of the fluorescent tube of the light guide, Light emitted from the fluorescent tube is made to enter the side end surface of the light guide member substantially uniformly, and the light amount in the effective area of the light guide member can be kept uniform.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a surface light source device according to the present invention will be described below with reference to FIGS. First, FIG. 1 is a perspective view showing an edge light type backlight unit for a liquid crystal display device as an example of a surface light source device to which the present invention is applied, and FIG. 2 is a longitudinal side view of a main part of the backlight unit. . In FIGS. 1 and 2, 11 is a fluorescent tube (cold cathode ray tube) as a light source, 11a is an end portion, 11b is a conducting wire, 12 is a transparent light guide, 13 is a metallic reflection film, and 14 is transparent light guide. A prism plate on the upper surface of the body 12, 15 is a prism plate on the end surface on the transparent light guide 12 side, 15a
Is a triangular prism, and 16 is an air layer.

That is, in this edge light type backlight unit, as shown in the figure, the straight tube type fluorescent tube 11 is housed within the effective area of the transparent light guide 12 even up to both ends 11a and 11a thereof. A metal reflection film 13 is attached to the back side of the transparent light guide 12, and the periphery of the fluorescent tube 11 is covered with the metal reflection film 13, while the triangular prism is provided on the front side of the transparent light guide 12 on the lower side. A prism plate 14 for collecting light is attached. And the fluorescent tube 11
And the side end surface of the transparent light guide 12 between the prism plate 15 and the triangular prism in contact with the end surface of the transparent light guide 12 side.
Is arranged to form an air layer 16 between the prism plate 15 and the fluorescent tube 11.

Here, the prism plate 15 is the transparent light guide 1.
2 has a plurality of triangular prisms arranged along the longitudinal direction of the side end surface, and as shown in FIG. 3 (a), compared with the angles of the intermediate triangular prisms 15a, 15a, 15a, ...
As shown in FIG. 3B, the triangular prisms 15 at both ends are
The angle of b, 15b, 15b, ... Is increased. Therefore, the light emitted from the light emitting portion of the fluorescent tube 11 excluding both ends 11a and 11a and the metallic reflection film 1
The light reflected by 3 enters the prism plate 15 through the air layer 16 and is refracted, so that the triangular prisms 15 a, 15
When the light is incident on the side end surface of the transparent light guide 12 after being refracted again by b, ..., Especially, as shown in FIG. 3B, the triangular prisms 15a, 15a, 15a ,. The triangular prisms 15b, 15 at both ends with a large angle
By b, 15b, ..., It is possible to focus the light on both ends 11a, 11a of the fluorescent tube 11 where the light is not emitted, and both ends of the side end surface of the transparent light guide 12 corresponding to each end.

As a result, light is substantially uniformly incident on the side end surface of the transparent light guide 12 over the entire area thereof, and the incident light is incident from the rear side of the transparent light guide 12 on the metallic reflection film 1.
In addition, the emitted light becomes a substantially uniform surface light source by being reflected by 3 and transmitted through the light collecting prism plate 14 on the front side of the transparent light guide 12, and illuminates a liquid crystal display panel (not shown) substantially uniformly. Become. As described above, since the fluorescent tube 11 can be designed to have the same length as the effective width of the transparent light guide 12, the surface light source device can be downsized as compared with the conventional one.

By the way, regarding the triangular prisms of the prism plate 15, all the triangular prisms have the same angle, and the intermediate triangular prisms 15a, 15a, 15a, ...
3C (see FIG. 3A), as shown in FIG. 3C, the triangular prisms 15c, 15c, 1 at both ends are compared.
The size of 5c, ... May be increased. The prism plate 15 also has such a configuration of the triangular prism.
When the light is incident on the side end surface of the transparent light guide 12 from FIG.
As shown in (c), the intermediate triangular prism 15a,
The triangular prisms 15c, 15c, 15c, ... At the both ends, which have the same angle as that of 15a, 15a, ...
It is possible to collect light on both ends of the side end surface of the transparent light guide 12 corresponding to 1a. Therefore, the same effect as the above can be obtained as the surface light source device.

Although the surface light source device for the backlight of the liquid crystal display device is used in the above-described embodiments, the present invention is not limited to this, and the surface light source device used for other purposes may be used. It may be. In addition, it goes without saying that specific detailed structures and the like can be appropriately changed.

[0019]

As described above, according to the surface light source device of the first aspect of the present invention, the light emitted from the straight tube type fluorescent tube is refracted by the transmission of the prism plate and the side end surface of the light guide body is refracted. Since the light is made to enter substantially uniformly, it is possible to maintain the uniformity of the amount of light in the effective area of the light guide while the fluorescent tube is accommodated in the effective area of the light guide. Therefore, it is not necessary to project both ends of the fluorescent tube from the effective area of the light guide to the outside as in the prior art, and the fluorescent tube can be housed in the effective area of the light guide, thus achieving miniaturization of the surface light source device. be able to.

According to the surface light source device of the second aspect of the invention, in the state where the straight tube type fluorescent tube is housed in the effective area of the light guide, the angle is larger than that of the triangular prism in the middle portion of the prism plate. With the triangular prisms at both ends of the fluorescent tube, the light emitted from the fluorescent tube can be directed and collected at the portions corresponding to both ends of the fluorescent tube of the light guide, so that the light emitted from the fluorescent tube can be guided. It is possible to make the light incident on the side end surface of the. Therefore, as in the first aspect of the invention, it is possible to maintain the uniformity of the amount of light in the effective area of the light guide.

According to the surface light source device of the third aspect of the present invention, the prism plate in which all the triangular prisms have the same angle in the state where the straight tube type fluorescent tube is housed in the effective area of the light guide body. With the triangular prisms at both ends that are larger than the size of the triangular prism in the middle part, the light emitted from the fluorescent tubes can be directed and condensed at the portions corresponding to both ends of the fluorescent tube of the light guide. Therefore, the light emitted from the fluorescent tube can be substantially uniformly incident on the side end surface of the light guide. Therefore, as in the first aspect of the invention, it is possible to maintain the uniformity of the amount of light in the effective area of the light guide.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an edge light type backlight unit for a liquid crystal display device as an example of a surface light source device to which the present invention is applied.

FIG. 2 is a vertical sectional side view of a main part of the backlight unit of FIG.

3A and 3B show a configuration example of a triangular prism included in the prism plate of FIG. 2, in which FIG. 3A is a partially cutaway plan view showing a triangular prism shape in an intermediate portion, and FIG. FIG. 6C is a partially cutaway plan view showing a prism shape, and FIG. 7C is a partially cutaway plan view showing a modified example of the triangular prism shape.

FIG. 4 is a perspective view showing an example of a conventional edge light type backlight unit.

FIG. 5 is a plan view of the backlight unit of FIG.

[Explanation of symbols]

 11 Fluorescent Tube 11a End 12 Light Guide 13 Reflective Film 14 Prism Plate on Top of Light Guide 15 Prism Plate on End of Light Guide Side 15a Intermediate Triangular Prism 15b, 15c Triangular Prism 16 on Both Ends 16 Air Layer

Claims (3)

[Claims] 1. A light source, which is a surface fluorescent light source, is configured such that light emitted from a straight fluorescent tube arranged along one side of the light guide is incident on the light guide from a side end surface thereof. In the surface light source device, a prism plate is interposed between the side end surface of the light guide and the fluorescent tube to refract light emitted from the fluorescent tube and make the side end surface of the light guide enter substantially uniformly. A surface light source device characterized by being installed. 2. The prism plate has a large number of triangular prisms arranged along the longitudinal direction of the side end surface of the light guide, and the triangular prisms at both ends of the prism plate are more inclined than the angle of the intermediate prism. 2. The surface light source device according to claim 1, wherein the angle is increased. 3. The prism plate has a large number of triangular prisms arranged along the longitudinal direction of the side end face of the light guide, and the triangular prisms in the middle portion of the prism plate are formed while the angles of all the triangular prisms are the same. 2. The surface light source device according to claim 1, wherein the size of the triangular prisms at both ends is larger than the size of the prisms.