JP2001155524A - Surface light source device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface light source device capable of reducing the color tone and the unevenness of color tone even in using a point light source. SOLUTION: In this surface light source device where the light is entered from plural point light sources 2... mounted on one of side end surfaces of a light guide plate 1, and reflected by a reflecting surface 11 at a rear surface of the light guide plate 1, and the light is emitted from the surface of the light guide plate 1, and the point light sources 2 are formed of white light-emitting diode elements, and two white diode elements among six white diode elements, having chromaticity furthermost from the center of a target chromaticity range in the directions of color phases mutually contradictory, are located at an approximate center of a group of white diode elements.

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 comprising a group of point light sources including light emitting elements such as light emitting diode (LED) elements and mainly used for a backlight of a liquid crystal display panel.

[0002]

2. Description of the Related Art As a surface light source for a backlight of a liquid crystal display panel, an edge light type using a light-transmitting flat plate as a light guide plate is known. In such a surface light source, light is made incident from one of the side end surfaces (edge portions) of a light guide plate made of a transparent parallel flat plate or a wedge-shaped flat plate, and the incident light is propagated uniformly throughout the entire light guide plate. A part of the light is converted into diffusely reflected light by the light reflecting member on the back surface of the light guide plate, and diffused light is emitted from the light guide plate surface.

An edge light type light guide plate used as a light source for a liquid crystal display panel is widely used because the thickness of the light guide plate can be reduced and the structure can be simplified.

In many edge light type surface light sources, a cold-cathode tube lamp is used as a light source, and the cold-cathode tube lamp is attached to an edge portion of the light guide plate.

On the other hand, portable devices have become widespread in recent years, and there is a demand for power saving. Therefore, as a backlight light source of a portable device, a light source using an LED element that consumes less power than a conventional cold-cathode tube lamp has attracted attention and has been put to practical use.

FIG. 1 is a schematic sectional view showing a surface light source using an LED element. As shown in the figure, this surface light source is composed of a light guide plate 1, a point light source 2 composed of LED elements, and the like.

At the edge of the light guide plate 1, a plurality of point light sources 2 composed of white LED elements are arranged.

A light reflecting surface 11 is provided on a side of the light guide plate 1 which is located in a direction perpendicular to the point light source 2.
The light exit surface 12 is provided on the side opposite to. Then, light from the point light source 2 is transmitted to the light reflecting surface 11 and the light guide plate 1 3.
Most of the incident light is finally reflected from the light exit surface 12 as a combined light having a uniform directivity. Further, a diffusion sheet 3 and a lens sheet 4 are disposed on the upper surface of the light exit surface of the light guide plate 1.

The structure around the point light source 2 has a structure in which the reflector 22 surrounds the LED board 21 on which each LED is mounted, and is configured to guide the light from the point light source 2 to the light guide plate 1. ing.

[0010]

Incidentally, one of the performance indexes of the surface light source device is a color tone, which is usually evaluated by xy values in an xy chromaticity diagram. The color tone evaluation includes a color tone at the central portion of the light emitting surface of the surface light source device, and a color tone unevenness comparing the central portion with its peripheral portion.

In the case of a surface light source device using a cold-cathode tube lamp, one lamp is usually used for one device.
The color tone unevenness on the light emission surface is small, and the color tone difference between individual lamps is relatively small.

On the other hand, in the case of a surface light source device using an LED element as a light source, a plurality of L
Since an ED element is used and there is also a color tone difference between LED elements, there is a disadvantage in terms of color tone and color tone unevenness as compared with a surface light source device using a cold cathode tube lamp.

Normally, white LED elements are provided with a plurality of ranks according to luminous intensity and color tone, and are shipped so that each LED element belongs to which luminous intensity and color tone. However, it is difficult for a purchaser to specify a rank for purchase, and only the characteristics of the purchased LED can be confirmed. It may also be possible to specify a rank for purchase, but this is disadvantageous in terms of cost and delivery time.

FIG. 3 shows an example of the color tone rank of the white LED element. In this example, it is classified into three ranks (a rank, b rank, and c rank) on the xy chromaticity diagram.
The rank a is bluish white compared to the center b rank, c
The rank is yellowish white. Here, the color tone ranks are distinguished by the manufacturer in the distribution of each white LED element on the xy color diagram for the sake of convenience, and are classified more finely than the three distinctions of a rank, b rank, and c rank, or other names. In some cases, such as is used.

Here, in the case where an area light source device which is within the color tone range shown in the backlight specification surrounded by the broken line in FIG. It is preferable in terms of color tone unevenness and the like. However, in the case of the configuration using only the b-rank product, there is a problem that the a-rank product and the c-rank product are not required, and the total cost is high.

SUMMARY OF THE INVENTION An object of the present invention is to provide a surface light source device in which color tone and color tone unevenness are suppressed even when a point light source is used, in consideration of the above-mentioned conventional problems. For example, in addition to the configuration in which the white LED element is composed of only the b-rank product, a configuration in which the a-rank product and the c-rank product are added to the b-rank product is also composed of only the b-rank product because of the central chromaticity and color tone unevenness. It is an object of the present invention to configure a surface light source device that is not inferior to the above.

[0017]

According to the present invention, light is incident from a plurality of point light sources disposed on one of the side end surfaces of a light guide plate, reflected by a light reflecting surface on the back surface of the light guide plate, and reflected from the surface of the light guide plate. , Wherein two point light sources having chromaticity most deviated from the center in the opposite hue direction from the center of the target chromaticity range are arranged adjacent to each other.

Further, the present invention includes a plurality of point light sources having four or more point light sources and having two point light sources having the chromaticity most deviated from the center in the hue direction opposite to the center of the target chromaticity range. Is arranged at substantially the center of the.

According to the present invention, a white light emitting diode element can be used as the point light source.

In the surface light source device of the present invention described above, since point light sources of opposite hues are arranged adjacent to each other, these colors are mixed, and the color becomes a color located in the middle.
A surface light source device with little color tone unevenness can be provided as a whole.

[0021]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is a perspective view showing a schematic configuration of a surface light source device utilizing the present invention. In this figure, a diffuser sheet and a lens sheet 4 arranged on the light emitting surface side and a reflector covering around a point light source are omitted. The present invention is applied to the surface light source device shown in FIG. 1, and as shown in FIG. 2, a surface light source device having a configuration in which a plurality of point light sources 2 are arranged in parallel on the light incident surface side of the light guide plate 1. It is.

As shown in FIG. 2, the surface light source device according to the present invention includes a light guide plate 1, a point light source 2 composed of white LED elements, and various control circuits (not shown). The control circuit includes, for example, the light exit surface 12 of the light guide plate 1.
And a circuit for detecting the total amount of light emitted from the light source and adjusting and supplying power to the point light source 2 so that the amount of emitted light is optimized.

Point light sources 2 composed of white LED elements are opposed to each other on a light incident surface 1a provided at an edge portion of the light guide plate 1. In this embodiment, six white LED elements are mounted on a substrate 21 as point light sources 2. The white LED element includes, for example, a structure in which three LEDs of R, G, and B are housed in one package and emits white light, or a single-color LED is converted from an LED using a fluorescent substance. What is necessary is just to use what was comprised so that emitted light may be converted into white light. For example, when a GaN-based blue LED is used as this fluorescent material, YAG
(Yttrium Aluminum Garnet) based fluorescent material may be used.

A light reflecting surface 11 is provided on a side of the light guide plate 1 which is located in a direction perpendicular to the point light sources 2. The light reflecting surface 11 is formed with dot printing or a cone-shaped depression to prevent light from leaking and to increase the reflection efficiency.

A light exit surface 12 is provided on the side of the light guide plate 1 facing the light reflection surface 11. Then, light from each LED of the point light source 2 is reflected on the light reflecting surface 11 and the three side surfaces 13 of the light guide plate 1, and almost all of the incident light is finally reflected on the light emitting surface 1.
2 is emitted as synthesized light having uniform directivity.

The material of the light guide plate 1 described above is selected from light-transmissive materials, and usually, acrylic or polycarbonate resin is used. The shape of the light guide plate 1 is a parallel flat plate or a wedge-shaped flat plate having a cross section of about 1 to 5 mm. The thickness of the light guide plate 1 is further reduced by using an LED compared to the case of using a cold cathode tube lamp. It becomes possible.

Other translucent materials include acrylates or methacrylates such as polymethyl methacrylate and polymethyl acrylate, and homo- or copolymers thereof, and polyesters such as polyethylene terephthalate and polybutylene terephthalate. Thermoplastic resins such as polycarbonate, polystyrene and polymethylpentene, or acrylates such as polyfunctional urethane acrylates and polyester acrylates cross-linked by ultraviolet rays or electron beams, transparent resins such as unsaturated polyesters, transparent glass, transparent ceramics, etc. Is used.

Although not shown in FIG. 2, a diffusion sheet and a lens sheet are arranged on the upper surface of the light emitting surface 11 of the light guide plate 1. The sheet configuration may be one or two, and the order of stacking may be reversed.

Then, an LED board 21 on which each LED element is mounted is fixed to an outer frame (not shown) located outside the light guide plate 1 with screws or an adhesive, and point light sources 2. Is arranged.

Each LED light from the point light source 2 enters the inside of the light guide plate 1 and is reflected by the light reflection pattern provided on the light reflection surface 11 and the three side end surfaces 13 to repeatedly converge.
The light exits from the light exit surface 12 to the diffusion plate 3, is uniformly and isotropically diffused within a desired angle range by the lens sheet, and exits as combined light. A liquid crystal display panel is arranged close to the lens sheet.

In the surface light source device configured as described above, the point light sources 2...
The surface light source device of the first example was formed using six D elements.
FIG. 4 shows the color tone of this surface light source device. In the figure, the mark ○ indicates the chromaticity of each of the six white LED elements, and the mark □ indicates the chromaticity on the surface light source when the surface light source device is configured by these white LED elements. . As shown in FIG. 4, all the white LED elements belong to the color tone rank b, and in this case, the chromaticity on the surface light source also satisfies the specification.

Next, 4 white LED elements having a color b rank were used.
A surface light source device constituted by using a single LED and white LED elements of rank a and rank c will be described.

As shown in Table 1 below, the arrangement of the LED elements on the LED board 21 is from rank b, rank a,
The surface light source device of the second example was formed in the order of b rank, b rank, c rank, and b rank.

[0034]

[Table 1]

Each white LED of the surface light source device of the second example
FIG. 5 shows the chromaticity of the element and the chromaticity on the surface light source. Also in this figure. In the figure, the mark ○ indicates the chromaticity of each of the six white LED elements, and the mark □ indicates the chromaticity on the surface light source when the surface light source device is configured by these white LED elements. . From FIG. 5, it can be seen that the chromaticity on the surface light source satisfies the specifications also in this configuration.

However, the surface light source device of this configuration has
As shown in FIG. 6, color tone unevenness that becomes yellowish is seen on the right side (a portion surrounded by a broken line in the figure) where the white LED elements of rank c are arranged, which is not preferable.

Therefore, the white LE used in the second example is used.
Prepare a white LED element with almost the same chromaticity as the D element,
The order of arrangement on the D substrate 21 was changed as shown in Table 2 below, and the surface light source device in this embodiment was formed.

Also in this embodiment, as in the second example, four LEDs having a color tone b rank, a rank a and a c
One white LED element of each rank was used, and the arrangement was as shown in Table 2 below, from the left end, rank b, rank b, c
Rank, a rank, b rank, b rank, and so on.

[0039]

[Table 2]

FIG. 7 shows the chromaticity of each white LED element and the chromaticity on the surface light source of the surface light source device having the configuration of this embodiment. Also in this figure, the circles in the figure represent six white LEs.
The chromaticity of each D element is shown.
It can be seen that the chromaticity on the surface light source satisfies the specifications also in the present configuration of this embodiment showing the chromaticity on the surface light source when the surface light source device is configured by the ED element.

Further, a good surface light source could be obtained without the color tone unevenness seen in the second example.

The reason for this is that, in the case of the surface light source device of the second example, the ratio of incident light from the white LED elements of ranks b and c is considered to be high at the right end of the light exit surface. The emitted light has a color mixture of colors of the ranks b and c. On the other hand, in the case of the surface light source device according to the present embodiment, the LEDs of rank a and rank c are arranged adjacent to each other at the center of the LED board 21.
These colors are mixed, and the color becomes a b-rank color located in the middle, and it is considered that a surface light source device with little color tone unevenness can be configured as a whole.

In the above-described embodiment, the case where the point light sources 2 composed of six white LED elements are used has been described. However, the number of the point light sources 2 is not limited to six but may be two. When the above-mentioned point light sources 2 are used, the white LED elements having chromaticities farthest from each other in the opposite hue direction from the center of the chromaticity range are selected from the target and the two white LED elements are selected. When they are arranged adjacently on the substrate 21, color unevenness can be reduced. When the number of the point light sources 2 is four or more, the white LED elements having the distant chromaticities in the opposite hue directions are selected, and the selected two white LED elements are placed on the LED board 21. Adjacent to the plurality of point light sources 2...

As described above, when a surface light source device using a plurality of white LED elements is formed, the distribution of each white LED element on the xy chromaticity diagram indicates the center of the target chromaticity range of the surface light source device. In the case of the present embodiment, x = about 0.3
1, y = 0.31), the opposite hue directions (in this embodiment, the lower left (blue) direction and the upper right (yellow) on the chromaticity diagram)
Direction), the white LED elements having the most distant chromaticity are selected, and the two selected white LED elements are
By arranging them adjacently on one, it is possible to reduce color tone unevenness. As a result, a white LED element having a wide chromaticity range can be used, and the cost of the surface light source device can be reduced.

[0045]

As described above, according to the present invention, even when a point light source is used, color tone and color tone unevenness can be suppressed, and the cost of the surface light source device can be reduced. In addition to the configuration in which the white LED element is composed of only the b-rank product, in addition to the configuration in which the a-rank product and the c-rank product are added to the b-rank product, only the b-rank product is formed due to the central chromaticity and color tone unevenness. The present invention can provide a surface light source device that is inferior to the above-described device, can use a white LED element having a wide chromaticity range, and can reduce the cost of the surface light source device.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a schematic configuration of a surface light source device to which the present invention is applied.

FIG. 2 is a perspective view showing a schematic configuration of a surface light source device to which the present invention is applied.

FIG. 3 is an xy diagram showing an example of a color tone rank of a white LED element.
It is a chromaticity diagram.

FIG. 4 is an xy chromaticity diagram showing a color tone of a surface light source device when a white LED element of rank b is used.

FIG. 5 is an xy chromaticity diagram showing a color tone of a surface light source device when white LED elements having ranks a, b, and c are used.

FIG. 6 is a schematic plan view of a surface light source device as a premise of the present invention.

FIG. 7 is an xy chromaticity diagram showing a color tone of the surface light source device in this embodiment using white LED elements of ranks a, b, and c.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 light guide plate 2 point light source 11 light reflection surface 12 light emission surface 21 LED substrate

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Toru Yamamura 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Inventor Nobuto Nishida 2-chome, Keihanhondori, Moriguchi-shi, Osaka No. 5 Sanyo Electric Co., Ltd. (72) Inventor Masashi Ochiiwa 2-5-5 Keihanhondori, Moriguchi-shi, Osaka F-term (reference) 2H038 AA55 BA06 2H091 FA14Z FA23Z FA45Z FD03 LA20

Claims (3)

[Claims] 1. A surface light source device that receives light from a plurality of point light sources disposed on one of the side end surfaces of a light guide plate, reflects the light on a light reflection surface on the back surface of the light guide plate, and emits light from the surface of the light guide plate. A two-point light source having a chromaticity most deviated from the center in the hue direction opposite to the center of the target chromaticity range. 2. A light source comprising four or more point light sources, wherein two point light sources having chromaticity most deviated from the center in a hue direction opposite to the center of the target chromaticity range are substantially at the center of the plurality of point light source groups. The surface light source device according to claim 1, wherein the surface light source device is arranged. 3. The surface light source device according to claim 1, wherein the point light source comprises a white light emitting diode element.