JPH07270621A - Surface light source device - Google Patents

Abstract

PURPOSE:To provide a bright surface light source device capable of preventing the current from escaping and improving the utilization efficiency of light composed of a light transmission body, a cold cathode tube in the vicinity of the incident end face and a reflection body covering the cold cathode tube. CONSTITUTION:As for the surface light source device composed of the light transmission body 1, the cold cathode tube 2 arranged in the vicinity of the incident end face of the light transmission body 1 and the reflecting body covering the cold cathode tube 2, the utilization efficiency is improved by making the reflecting body a double structure providing the reflecting surfaces 6 and 7, adopting a white synthetic resin sheet as the reflecting surface 6 disposed near the cold cathode 2 and the white reflecting surface as the reflecting surface 7 disposed away from the cold cathode 2, preventing the current from escaping.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface light source device using a light guide plate.

[0002]

2. Description of the Related Art A conventional surface light source device using a light guide plate has a structure as shown in FIG. In this figure, 1 is a light guide plate made of a transparent material, 2 is a linear light source, 3 is a light diffusing member, 4 is a reflecting member, and 5 is a lamp holder.

In this surface light source device, the light from the light source 2 is made incident on the inside of the light guide plate 1, and the light is generated by the action of a pattern composed of a large number of diffusion portions provided on the surface of the light guide plate 1 on the side of the reflecting member 4, for example. The light is emitted from the emission surface on the side of the diffusing member 3 and further passes through the light diffusing member 3 to form a surface light source.

In such a surface light source device, it is important that the light passing through the light diffusing member 3 has a uniform brightness and that it can be a bright light source.

Here, in order to obtain a bright surface light source device,
It is necessary to maximize the amount of light emitted from the light source 2 and entering the light guide plate 1. Therefore, a metal foil or a film deposited with silver or the like is attached to the inner surface of the lamp holder 5 to reflect the light from the light source 2 and allow it to enter the light guide plate 1 as much as possible to increase the utilization efficiency. It is known that

As a light source of such a surface light source device,
Generally, a cold cathode tube is used. Generally, a cold cathode tube has a smaller tube diameter than a hot cathode tube, the device can be made thin, and the temperature does not rise so much. Therefore, when used as a backlight of a liquid crystal display device, for example, a liquid crystal display device is used. This is because it is easy to take heat measures to improve durability without adversely affecting the temperature.

However, the cold cathode fluorescent lamp requires a high applied voltage of about 1 to 2 KV for lighting, though it depends on the length thereof. A frequency of about 20 to 70 KHZ is generally used.

Since a high applied voltage is applied to the cold cathode tube in this way, if the inner surface of the lamp holder is made of a metal surface, a part of the current of the cold cathode tube escapes to the inner surface side of the lamp holder and the brightness of the tube itself is reduced. And a bright surface light source cannot be obtained.

When the current escapes to the lamp holder side in this way, it adversely affects the electric circuit arranged in the equipment in which the surface light source device is mounted, for example, the drive circuit of the liquid crystal display device.

Further, in order to increase the brightness lowered due to the escape of the current as described above to the original brightness, high power consumption is required.

In order to solve this point, polycarbonate or ABS commercially available as a molding material for the reflecting member.
A lamp holder is formed by using a material in which a substance such as titanium oxide is mixed with resin, and the surface of the lamp holder is used as a reflecting surface, or polyethylene terephthalate with high reflectance characteristics for reflecting members is mainly used. It is known to use a sheet as a component as a reflecting member.

However, although it is for the reflecting member, since a synthetic resin is used, a part of the light from the light source passes through the lamp holder, resulting in a loss of the light quantity, and it is not possible to obtain a bright surface light source.

There is also a surface light source device disclosed in Japanese Patent Laid-Open No. 4-269702 in which two reflecting surfaces are combined in a lamp holder. That is, in the configuration shown in FIG. 4, the lamp holder 10 is provided with a reflecting surface 11 near the light source 1 and another reflecting surface 12 outside the reflecting surface 11 with an air layer 13 therebetween, and The surface 11 is a metal reflective surface having a high reflectance, and the reflective surface 12 is a diffuse reflective surface made of, for example, white synthetic resin.

However, also in this conventional example, when a cold cathode tube is used as the light source, the metallic reflecting surface 1 disposed near the light source 2 is used.
The current escapes to 1 and the brightness decreases.

When a metal layer is formed on the surface of a transparent synthetic resin plate or sheet as the reflecting surface 11 to form a reflecting surface, it is considered that light other than the reflected light is absorbed and hardly penetrates. The reflector described in the publication is
The use efficiency of light cannot be improved by using two reflecting surfaces.

[0016]

SUMMARY OF THE INVENTION The present invention provides a bright surface light source in which the current does not escape and therefore the brightness does not decrease even when a cold cathode tube is used as the light source, and the utilization efficiency of the light emitted from the light source is high. To provide a device.

[0017]

The surface light source device of the present invention comprises:
Light emitted from a cold cathode fluorescent lamp arranged in the lamp holder is made incident on a light guide plate made of a transparent material and emitted from the other surface (emission surface) of the light guide plate. A double structure composed of two reflective surfaces sandwiching a layer, each of these reflective surfaces being a white reflective surface, of which the first reflective surface at least near the cold cathode tube. Is made of a white synthetic resin sheet.

The inner surface of the lamp holder may be made of white synthetic resin, and the white synthetic resin surface may be the second reflecting surface on the side farther from the cold cathode tube.

That is, the surface light source device of the present invention includes, for example, a light guide plate made of a transparent material, a cold cathode tube arranged near the incident end face of the light guide plate, and an emission end face of the light guide plate. Side light diffusion member and a reflection member arranged on the side opposite to the light emitting plate's emission end face. Further, a diffusion function is provided on the light emission plate's emission end face side by means of a pattern of multiple diffusing parts. It has a lamp holder that covers the cold-cathode tube, and constitutes a reflector inside this lamp holder.This reflector consists of two reflecting surfaces with an air layer in between. In the structure, all of these reflecting surfaces are white reflecting surfaces, and at least the reflecting surface on the side close to the cold cathode tube is made of a white synthetic resin sheet. This white synthetic resin sheet has a thickness of about 0.1 mm, considering that the sheet itself absorbs light and that the sheet needs to be rigid enough to maintain the curved shape when the sheet is bent. It is desirable to be before and after.

In the surface light source device of the present invention, the second reflecting surface having the above-mentioned structure and having a double structure is provided on the side farther from the cold cathode tube.
The reflective surface of is made of white synthetic resin formed on the inner surface of the lamp holder. In this case, the lamp holder may be formed of a white synthetic resin material, and the inner surface of the lamp holder may be used as the second reflecting surface.

[0021]

Embodiments of the surface light source device of the present invention will be described below with reference to the drawings.

FIG. 1 is a view of a first embodiment of a surface light source device of the present invention, in which 1 is a light guide plate made of a transparent material, and 2 is a light guide plate.
Is a cold cathode tube arranged near the surface 1a of the light guide plate 3, 3 is a light diffusion plate arranged on the side of the emission surface 1b of the light guide plate 4, and 4 is a surface 1c of the light guide plate opposite to the emission surface 1b. A reflecting member provided on the side, 5 is a lamp holder that covers the cold cathode tube 2, 6 is a reflector that constitutes a first reflecting surface provided around the cold cathode tube 2, and 7 is an inner surface of the lamp holder 5. Second formed on
It is the reflective surface of.

In the surface light source device shown in FIG. 1, the reflector 6
Is a sheet made of a thin white synthetic resin having a thickness of about 0.1 mm, for example, a sheet in which a substance having a high reflectance is mixed with polyethylene terephthalate, which constitutes a white first reflecting surface, Also lamp holder 5
Is made of a white synthetic resin or a molding material whose main component is polycarbonate mixed with titanium oxide or the like so as to have a high reflectance, and its inner surface 5a constitutes a white second reflecting surface.

An air layer 13 is provided between the first reflecting surface and the second reflecting surface.

In this embodiment, as described above, the first reflecting surface is made of a thin white synthetic resin sheet, and the molding material is composed mainly of white synthetic resin or polycarbonate mixed with titanium oxide or the like. The inner surface of the formed lamp holder is the second reflecting surface, and no metal is used for both reflecting surfaces, so that current does not escape and the cold cathode tube 2
Does not cause a decrease in brightness.

The light emitted from the cold cathode tube 2 is reflected by the first reflecting surface of the reflector and efficiently enters the incident end surface 1a of the light guide plate 1. Further, a part of the light transmitted through the first reflecting surface is reflected by the second reflecting surface and is incident on the incident end surface 1a of the light guide plate 1.
Incident on. Therefore, the light emitted from the cold-cathode tube 2 is reflected by the first and second reflecting surfaces and is effectively used. Moreover, of the slight amount of light that has passed through the first reflecting surface, the amount of light that further passes through the second reflecting surface is even smaller, and only this extremely small amount of light is not used as a light source. On the contrary, most of the light except the extremely small amount of light that has passed through the two reflecting surfaces will be used.

As described above, in the surface light source device of this embodiment, the light source current does not escape and the utilization efficiency of the light emitted from the cold cathode tube is extremely high.

Although the light guide 1 shown in FIG. 1 has an inclined surface on the side of the reflecting member 4, it may be a light guide in which this surface and the exit surface are parallel planes. Also, the slope angle of the slope may be smaller than that shown.

FIG. 2 is a view showing another embodiment of the present invention, in which the vicinity of the cold cathode fluorescent lamp is shown, and the light guide plate 1, the light diffusing member 3, the reflecting member 4 and the like are shown in FIG. Is substantially the same as. Further, two white sheets are arranged inside the lamp holder 5 with an air layer interposed therebetween, and these sheets form a first reflecting surface and a second reflecting surface.

Also in this embodiment, since no metal is used for each member constituting the lamp holder and the reflectors (first and second reflecting surfaces), the brightness of the light emitted from the cold cathode tube is high, and the two reflecting lights are used. The surface makes the light use efficiency high, and thus can be a bright surface light source device.

As a molding material containing polycarbonate as a main component, there is Iupilon HR3000NR (trade name) manufactured by Mitsubishi Gas Chemical Co., Inc. A molded article formed of this molding material has a high reflectance of 90% or more.

A white sheet can be formed by using the above-mentioned molding material containing polycarbonate as a main component. Therefore, the sheet constituting the first reflecting surface used in the first embodiment and the white sheet can be formed. Both sheets forming the first and second reflecting surfaces used in the second embodiment may be formed by using this molding material. Also in this case, the reflectance of the white sheet has a high value of 90% or more.

Also, a sheet or a molded product using a molding material in which a member for increasing the reflectance is mixed in polyethylene phthalate has a high reflectance, that is, a reflectance of 90% or more.

In the first and second embodiments described above, a bright surface light source device can be obtained, as is clear from a comparative example with other surface light source devices described below.

(Comparative Example) A. A surface light source device in which only one synthetic resin sheet having a reflectance of 90% or more is provided as a reflecting member that covers the cold cathode tube.

B. A surface light source device in which one synthetic resin sheet having a reflectance of 90% or more is provided as a reflecting member for covering the cold cathode tube, and the outside thereof is covered with a lamp holder, and the inner surface of the lamp holder does not serve as a reflecting surface.

C. A surface light source device in which a cold cathode tube is covered with a lamp holder made of a molding material for a reflecting member having a reflectance of 90% or more.

D. The surface light source device of the 1st Example of this invention.

In each of the surface light source devices A to D described above, except for the reflector, the light guide plate of the same configuration was used under the same conditions such as the conditions for causing the cold cathode tubes to emit light. The average brightness on the emission surface is as follows.

Types of surface light source device Average brightness A 2250 (nt) B 2250 (nt) C 2300 (nt) D 2400 (nt) As described above, the surface light source device according to the first embodiment of the present invention is Brighter than the surface light source device. Also, the second embodiment of the present invention has almost the same average brightness as the first embodiment, and the other A to C
Brighter than other surface light sources.

[0041]

The surface light source device of the present invention uses a cold cathode fluorescent lamp, and the reflector covering the cold cathode fluorescent lamp has a double structure, and both reflecting surfaces of the reflector are white reflecting surfaces having high reflectance. A bright surface light source can be obtained by eliminating leaks and by effectively utilizing the light emitted from the cold cathode fluorescent lamp.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a first exemplary embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a reflector portion of a second embodiment of the present invention.

FIG. 3 is a diagram showing a configuration of a conventional surface light source device.

FIG. 4 is a diagram showing a configuration of another conventional surface light source device.

[Explanation of symbols]

 1 Light guide plate 2 Cold cathode tube 5 Lamp holder 6 First reflective surface 7 Second reflective surface

Claims (2)

[Claims] 1. A device for causing light emitted from a cold cathode tube to enter a light guide plate made of a transparent material and to emit from a light exit surface of the light guide plate, wherein light from the cold cathode tube enters as much as possible into the light guide plate. In a surface light source device having a reflector provided so as to cover the cold cathode tube, the reflector has a double structure having two reflecting surfaces with an air layer interposed between A surface light source device in which a first reflective surface is a thin white synthetic resin sheet or a second reflective surface far from the cold cathode tube is a white reflective surface. 2. A lamp holder for holding the cold-cathode tube is provided, the lamp holder is made of white synthetic resin, and an inner surface thereof is a second reflecting surface on a side farther from the cold-cathode tube. Surface light source device.