JP3530442B2 - Chromaticity adjustment method for surface light source device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chromaticity adjusting method for a surface light source device which is composed of a point light source including a light emitting element such as a light emitting diode (LED) element and is 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 back light of a liquid crystal display panel, an edge light system using a transparent 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 faces (edge portions) of the light guide plate made of a transparent parallel plate or a wedge-shaped plate in cross section, and the incident light is evenly propagated to the entire area of the light guide plate and propagated. Part of the light is diffused and reflected by the light reflecting member provided in the propagation path on the back surface of the light guide plate,
Diffuse light is emitted from the surface of the light guide plate.

An edge light type light guide plate used as a light source of 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 the edge portion of the light guide plate.

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

FIG. 1 is a schematic sectional view showing a surface light source using an LED element. As shown in the figure, the surface light source includes a light guide plate 1, a point light source 2 including 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 reflection surface 11 is provided on the side (rear surface) of the light guide plate 1 which is positioned in the vertical direction with respect to the point light source 2, and a white reflection sheet 5 is further provided facing the light reflection surface 11. The light transmitted through the light reflection surface 11 is reflected and returned to the light guide plate 1.

On the other hand, a light emitting surface 12 is provided on the side (front surface) facing (facing) the light reflecting surface 11. And
The light from the point light source 2 is reflected by the light reflection surface 11, the three side surfaces 13 of the light guide plate 1, and the reflection sheet 5, and most of the incident light is finally emitted from the light emission surface 12.

Further, a diffusion sheet 3 and a lens sheet 4 are arranged on the upper surface of the light emitting surface of the light guide plate 1, so that surface emission having a uniform directivity can be obtained.

The structure around the point light source 2 is such that the reflector 22 wraps the LED substrate 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.

[0011]

By the way, a color tone is one of the performance indexes of the surface light source device, and is usually evaluated by the xy value in the xy chromaticity diagram. Further, the color tone evaluation includes color tone of the central portion of the light emitting surface of the surface light source device, and further unevenness of color tone in which the central portion is compared with the 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,
Color tone unevenness on the light emitting surface is small, and color 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's are usually provided in one device.
Since the ED element is used and there is a color tone difference between the LED elements, there is a disadvantage in comparison with the surface light source device using the cold cathode fluorescent lamp in terms of color tone and uneven color tone.

Usually, a white LED element is provided with a plurality of ranks according to luminous intensity and color tone, and shipped so that it can be known which rank each luminous intensity belongs to. However, it is difficult for the purchaser to specify the rank and purchase, and it is only possible to confirm the characteristics of the purchased LED. Also, it may be possible to purchase by specifying the rank, but it 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, they are classified into three ranks (a rank, b rank, and c rank) on the xy chromaticity diagram.
Compared to b rank in the center, a rank is bluish white, c
The rank is yellowish white. Here, the color tone rank is a maker's distinction in the distribution of each white LED element on the xy color diagram for the sake of convenience, and a finer distinction or another name other than the three distinction of a rank, b rank, and c rank. In some cases, etc. are used.

Here, in the case of constructing a surface light source device that falls within the color tone range shown in the backlight specification enclosed by the broken line in the same figure, it is necessary to use only the b-rank LED elements to construct the central color tone, It is preferable in terms of uneven color tone. However, in the case of using only the b-ranked product, there is a problem that the a-ranked product and the c-ranked product are unnecessary and the total cost becomes high.

The present invention has been made in view of the above-mentioned conventional problems, and provides a chromaticity adjusting method for obtaining a surface light source device in which color tone and uneven color tone are suppressed even when a point light source is used. The purpose is to provide. For example, white LED
In addition to configuring the element with b-rank products only, b-rank products with a-rank products and c-rank products added, or configurations with only a-rank products and c-rank products, and without further strictly managing such ranks Another object of the present invention is to provide a chromaticity adjusting method capable of obtaining a surface light source device that is comparable in quality to the one formed only by the b-rank products in terms of central chromaticity and color tone unevenness.

[0018]

According to a first aspect of the present invention, there is provided a color of a surface light source device in which light is incident from a plurality of point light sources arranged on one of the side end surfaces of a light guide plate and light is emitted from the surface of the light guide plate. A method of adjusting the degree of chromaticity, the step of arranging a plurality of point light sources having chromaticities deviated from each other in the opposite hue directions from the center of the target chromaticity range adjacent to each other, The step of measuring the emitted light and inspecting whether or not it falls within the target chromaticity range, and, as a result of the inspection, if it does not fall within the target chromaticity range, a chromaticity correction means corresponding to the emitted light is introduced. Arranging in association with the light propagation path of the light plate.

Further, the invention of claim 2 is a reflecting member which receives light from a plurality of point light sources arranged on one of the side end surfaces of the light guide plate and is arranged in proximity to the back surface facing the front surface of the light guide plate. A method of adjusting the chromaticity of a surface light source device that reflects and emits planar light from the surface of the light guide plate, wherein the point light source is caused to emit light and the light emitted from the light guide plate is measured. And a colored reflection member that corrects the emitted light to a target chromaticity range as a reflection member that is arranged close to the back surface of the light guide plate, based on the chromaticity difference of the measurement result. The method for adjusting chromaticity of a surface light source device, comprising:

According to a third aspect of the invention, the point light source is
It is a point light source group consisting of four or more white light emitting diode elements, and two white light emitting diode elements having chromaticity most deviated from the center in the opposite hue direction from the center of the target chromaticity range are included in the point light source group. It is characterized in that it is arranged substantially at the center. Further, the invention according to claim 4 is characterized in that the chromaticity correction means is a colored reflection member provided on a back surface of the light guide plate facing the front surface of the light guide plate.

According to the first aspect of the present invention, since the point light sources of opposite hues are arranged adjacent to each other, these colors are mixed and the color is located in the middle of the colors, so that there is little unevenness in color tone as a whole. It becomes a surface light source device, and many surface light source devices can satisfy the target chromaticity range, and even those which are not included in the target chromaticity range, chromaticity correction means should be arranged in relation to the light propagation path of the light guide plate. Thus, a surface light source device having a target chromaticity range can be obtained.

According to the invention of claim 2, the chromaticity difference from the target chromaticity range is measured, and based on the chromaticity difference of the measurement result,
By disposing the colored reflection member that corrects the emitted light in the target chromaticity range in close proximity to the back surface of the light guide plate, a surface light source device having the target chromaticity range can be obtained.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION 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 using the present invention. In this figure, the diffuser sheet and the lens sheet 4 arranged on the side of the light emitting surface, and the reflector that covers around the 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 plurality of point light sources 2 are arranged in parallel on the light incident surface side of the light guide plate 1 in a surface light source device. Is.

As shown in FIG. 2, the surface light source device according to the present invention comprises a light guide plate 1, a point light source 2 including white LED elements and various control circuits (not shown). This control circuit includes, for example, the light emitting surface 12 of the light guide plate 1.
It also includes a circuit that detects the total amount of light emitted from the point light source and adjusts and supplies electric power to the point light source 2 so that the amount of emitted light becomes optimum.

On the light incident surface 1a provided on the edge portion of the light guide plate 1, point light sources 2 ... In this embodiment, six white LED elements are mounted as the point light sources 2 on the substrate 21. This white LED element includes, for example, three R, G, and B LEDs housed in one package to emit white light, or a single-color LED using a fluorescent substance. A device configured to convert the emitted light into white light may be used. For example, when a GaN-based blue LED is used as the fluorescent substance, YAG
A (yttrium / aluminum / garnet) -based fluorescent substance may be used.

A reflecting sheet 5 functioning as a light reflecting member is arranged in close proximity to the back surface which is one of the main surfaces of the light guide plate 1 which is located in the direction perpendicular to the point light sources 2 ... The light reflecting surface 11 is configured in cooperation with each other.

A light emitting surface 12 is provided on the surface which is the main surface of the light guide plate 1 facing the light reflecting surface 11. Then, the light from each LED of the point light source 2 is reflected by the light reflection surface 11 including the reflection sheet 5 and the three side surfaces 13 of the light guide plate 1, and most of the incident light is finally emitted from the light emission surface 12. To be done.

The material of the above-mentioned light guide plate 1 is selected from the light-transmitting 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 thickness of about 1 to 5 mm, and it is possible to further reduce the thickness by using LEDs as compared with the case of using a cold cathode tube lamp. It will be possible.

As other translucent materials, homo- or copolymers of acrylic acid esters or methacrylic acid esters such as methyl polymethacrylate and polymethyl acrylate, polyesters such as polyethylene terephthalate and polybutylene terephthalate. , Polycarbonate, polystyrene, polymethylpentene or other thermoplastic resin, or UV or electron beam crosslinked polyfunctional urethane acrylate, polyester acrylate or other acrylate, unsaturated polyester or other transparent resin, transparent glass, transparent ceramic, 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 so that the light emitted from the light emitting surface 11 can be emitted. It has a uniform directivity. Seat structure is 1
One sheet or two sheets may be used, and the order of stacking may be reversed.

Then, the LED substrate 21 on which each LED element is mounted is fixed to the outer frame (not shown) outside the light guide plate 1 with screws or an adhesive, and the point light sources 2 are fixed at predetermined positions on the light guide plate 1. Are placed.

Each LED light from the point light source 2 enters the inside of the light guide plate 1, is reflected by the light reflection pattern provided on the light reflection surface 11 and the three side end faces 13 and repeats focusing, and the light guide plate 1
The light is emitted from the light emitting surface 12 to the diffusing plate 3, and is uniformly and isotropically diffused within a desired angular range by the lens sheet and emitted as combined light. A liquid crystal display panel is arranged close to this lens sheet.

In the surface light source device constructed as described above, as the point light sources 2, ...
The surface light source device of the first example was formed using six D elements.
The color tone of this surface light source device is shown in FIG. 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, it can be seen that the chromaticity on the surface light source also satisfies the specifications.

Next, the white LED element of color b rank
A surface light source device configured by using one LED element and one white LED element of rank a and one white LED element of rank c will be described.

The arrangement of the LED elements on the LED substrate 21 is, as shown in Table 1 below, from the left end, b rank, a rank,
The surface light source device of the second example is formed by forming the b rank, the b rank, the c rank, and the b rank in this order.

[0036]

[Table 1] FIG. 5 shows the chromaticity of each white LED element of the surface light source device of the second example and the chromaticity on the surface light source. In this figure as well, the circles in the figure indicate the chromaticity of each of the six white LED elements, and the squares show the colors on the surface light source when the surface light source device is composed of these white LED elements. Shows the degree. From FIG. 5, it can be seen that even in this configuration, the chromaticity on the surface light source satisfies the specifications.

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

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

Also in this embodiment, as in the second example, four LEDs of color b rank, a rank c and LED c.
One white LED element of each rank is used, and the arrangement is, as shown in Table 2 below, from the left end, b rank, b rank, c rank.
The order is rank, a rank, b rank, b rank.

[0040]

[Table 2] Each white L of the surface light source device having the configuration of this embodiment
FIG. 7 shows the chromaticity of the ED element and the chromaticity on the surface light source. In this figure as well, the circles in the figure indicate the chromaticity of each of the six white LED elements, and the squares show the colors on the surface light source when the surface light source device is composed of these white LED elements. It can be seen that the chromaticity on the surface light source also satisfies the specifications in this configuration of this embodiment showing the degree.

Further, it was possible to obtain a good surface light source 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 proportion of the incident light from the white LED elements of ranks b and c is high at the right end of the light emitting surface, and it is considered that The emitted light is a mixture of b-rank and c-rank colors. On the other hand, in the case of the surface light source device according to the present embodiment, since the LEDs of the a rank and the c rank are arranged adjacent to each other in the central portion of the LED substrate 21,
It is considered that these colors are mixed and the color becomes a b rank color located in the middle of the colors, and thus a surface light source device with less unevenness in color tone can be configured as a whole.

In the above-described embodiment, the case where the point light sources 2 ... Each consisting of six white LED elements are used has been described, but the number of the point light sources 2 ... Is not limited to six, but two. When the above point light sources 2 are used, the white LED elements having the chromaticities that are farthest from the target and the center of the chromaticity range in the opposite hue directions are selected, and the two selected white LED elements are used as LEDs. If they are arranged adjacent to each other on the substrate 21, color unevenness can be reduced. Further, when the number of the point light sources 2 is 4 or more, the white LED elements having the chromaticities that are farthest apart from each other are selected in the opposite hue directions, and the two selected white LED elements are arranged on the LED substrate 21. It is advisable to arrange them adjacent to each other at approximately the center of the plurality of point light sources 2.

When a surface light source device using a plurality of white LED elements is constructed in this way, in the distribution of each white LED element on the xy chromaticity diagram, the center of the target chromaticity range of the surface light source device ( In the case of this embodiment, x = about 0.3
1, y = 0.31), the opposite hue directions (in the case of this embodiment, the lower left (blue) direction and the upper right (yellow) on the chromaticity diagram)
Direction), the white LED elements having the most chromaticity are selected, and the two selected white LED elements are connected to the LED substrate 2.
It is possible to reduce uneven color tone by arranging them adjacent to each other. As a result, it becomes possible to use a white LED element having a wide chromaticity range, and the cost of the surface light source device can be suppressed.

Thus, by devising the arrangement of the plurality of white LED elements as described above, it is possible to reduce unevenness in color tone and obtain a surface emitting device satisfying the chromaticity range.
In some surface light source devices, those slightly deviating from the specifications of the chromaticity range also appear. The reason is that the chromaticity variations of the white LED elements in the same rank used are not constant. Therefore, in the present embodiment, in a surface light source device that is outside the chromaticity range while using a white LED element having a wide chromaticity range, a chromaticity correction unit according to emitted light is associated with the light propagation path of the light guide plate. By arranging them, the chromaticity within the specifications is adjusted.

Specifically, after assembling the point light source of the white LED element having each rank based on the above rule as the LED substrate 21, the standard chromaticity, that is, the white reflective sheet 5 having the target chromaticity is The LE is attached to the light guide plate 1 arranged in advance.
The D substrate 21 is mounted, all the point light sources 2 are turned on, and the chromaticity on the surface light source is measured.

As a result of the measurement, the chromaticity on the surface light source is
A non-defective product is determined whether it is within the target chromaticity range, and if it is determined to be good, the assembly as a surface light source device is continued.

On the other hand, the LED substrate 21 determined to be defective
Is separated from the light guide plate 1, and based on the chromaticity difference from the target chromaticity range, the light guide plate 1 including the colored reflection sheet 5 for correcting the chromaticity difference is newly prepared and assembled. Such a colored reflection sheet 5 is prepared in advance with a chromaticity difference so that a chromaticity having a chromaticity that corrects the chromaticity difference is automatically selected from the chromaticity differences obtained during the chromaticity measurement. This is executed by storing the relationship between the plurality of coloring sheets 5 in the table.

By selecting the colored reflection sheet 5 having a desired chromaticity in this way, a product outside the specification range can be regarded as a non-defective product within the specification range.

Since the chromaticity correcting means may be provided in association with the propagation path of the light guide plate 1, it is not limited to the reflection sheet 5 and may be provided between the point light source 2 and the light guide plate 1. Even if the reflection sheet 5 is a surface light source device that does not require correction, since the standard reflection sheet 5 is required by itself, it is possible to increase the number of components by providing the reflection sheet 5 with a correction function. I'm done.

FIG. 8 is an xy chromaticity diagram for explaining a chromaticity adjusting method according to another embodiment. This embodiment provides a method of performing adjustment without devising the positional relationship of the white LED elements of the LED substrate 21 as in the previous embodiments. That is, in this embodiment, the ranks (a, b, c) of the white LED elements are substantially unrelated.

Even in the surface light source device of FIG. 8, the number of white LED elements is six (however, it is not necessary to be particular about the number, one may be one in this embodiment), and the individual xy chromaticities. Is almost a rank as plotted with a circle in the figure, and the chromaticity on the surface light source is out of the target chromaticity range as a result of the measurement, as plotted with a rhombus (conventional specification is displayed). .

From the result of the measurement, the colored reflection sheet 5 according to the chromaticity difference is selected by the method described above, that is, the table prepared according to the chromaticity difference, and is put in the target chromaticity range. In this embodiment, the color temperature conversion filter part number A1 (denoted as y (A1)) manufactured by Tokyo Stage Lighting can be used to convert the color temperature of 3400 ° k to 3200 ° k. As plotted, a surface light source device having a target chromaticity range was obtained.

For comparison, 5500 ° k is changed to 3200 ° k
When the color temperature conversion filter product number A5 (denoted as y (A5)) manufactured by Tokyo Stage Lighting Co., Inc. was used, the target chromaticity range was exceeded as plotted by the + symbol.

As described above, in this embodiment, the presence of the conventional reflection sheet 5 is particularly noted, and the reflection sheet 5 is provided with the function of chromaticity correction, so that color components can be added without adding components. This enables the use of the LED substrate 21 that is out of the range.

[0056]

As described above, according to the adjusting method of the present invention, color tone and uneven color tone can be suppressed even when a point light source is used, and the cost of the surface light source device can be reduced.

Further, in addition to the white LED element being constituted by only the b-ranked product, the b-ranked product may be added with the a-ranked product and the c-ranked product, or only the a-ranked product and the c-ranked product may be constructed. It is possible to provide a surface light source device that is comparable to the one composed of only b-rank products in terms of central chromaticity, color tone unevenness, etc. without strictly managing the above, and as a result, use a white LED element with a wide chromaticity range. Therefore, the cost of the surface light source device can be suppressed.

Further, a colored reflecting member for measuring the chromaticity difference from the target chromaticity range and correcting the emitted light to the target chromaticity range based on the chromaticity difference of the measurement result is placed close to the back surface of the light guide plate. Since the surface light source device having the target chromaticity range can be obtained by arranging in such a manner, it is possible to use a light source having a wide chromaticity range, and the cost of the surface light source device can be suppressed.

[Brief description of drawings]

FIG. 1 is a 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 shows an example of a color tone rank of a white LED element x
It is a y 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 White LEDs of a rank, b rank, and c rank
It is an xy chromaticity diagram which shows the color tone of a surface light source device when an element is used.

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

FIG. 7 White LEDs of a rank, b rank, and c rank
It is an xy chromaticity diagram which shows the color tone of the surface light source device which is the premise of this embodiment using an element.

FIG. 8 is an xy chromaticity diagram showing a color tone of the surface light source device according to the embodiment using the white LED element of approximately a rank.

[Explanation of symbols]

1 Light guide plate 2 point light source 5 Reflective sheet 11 Light reflection surface 12 Light exit surface 21 LED board

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI H01L 33/00 F21Y 101: 02 // F21Y 101: 02 G02F 1/1335 530 (72) Inventor Nobuto Nishida Osaka Prefecture Moriguchi Keisakamoto 2-5-5 Tsudori Sanyo Electric Co., Ltd. (72) Inventor Masashi Ochiiwa 2-5-5 Keihan Hondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (56) Reference JP-A-11-223805 ( JP, A) JP 9-292614 (JP, A) JP 11-295731 (JP, A) JP 10-307212 (JP, A) JP 7-140567 (JP, A) JP Flat 8-146228 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) F21V 8/00 601 G02B 6/00 G02F 1/00 G09F 9/00 H01L 33/00 F21Y 101: 02

Claims (4)

(57) [Claims] 1. A chromaticity adjusting method for a surface light source device, wherein light is incident from a plurality of point light sources disposed on one of the side end surfaces of a light guide plate and is emitted from the surface of the light guide plate, wherein a target chromaticity is provided. A step of arranging a plurality of point light sources having chromaticities deviating from the center of the range in opposite hue directions in a contiguous manner, and measuring the light emitted from the light guide plate by causing the point light sources to emit light, and the target chromaticity range And a step of inspecting whether or not it is included, and if the result of the inspection is that it is not included in the target chromaticity range, a chromaticity correcting means corresponding to the emitted light is arranged in association with the light propagation path of the light guide plate. A method for adjusting chromaticity of a surface light source device, comprising: 2. Light from a plurality of point light sources arranged on one of the side end surfaces of the light guide plate is reflected by a reflecting member arranged close to the back surface facing the front surface of the light guide plate. A chromaticity adjusting method for a surface light source device that emits planar light from the surface of the light guide plate, wherein the point light source is caused to emit light, and the light emitted from the light guide plate is measured, and the chromaticity from the target chromaticity range is measured. A step of measuring a difference, and a step of selecting a colored reflecting member that corrects the emitted light into a target chromaticity range as a reflecting member that is arranged in proximity to the back surface of the light guide plate, based on the chromaticity difference of the measurement result, A method for adjusting chromaticity of a surface light source device, comprising: 3. The point light source is a point light source group composed of four or more white light emitting diode elements, and two point light sources having chromaticity most deviated from the center in a hue direction opposite to the center of the target chromaticity range. The chromaticity adjusting method for a surface light source device according to claim 1 or 2, wherein the white light emitting diode element of (1) is arranged substantially at the center of the point light source group. 4. The surface light source device according to claim 1, wherein the chromaticity correction means is a colored reflection member provided on a back surface of the light guide plate facing the front surface of the light guide plate. Chromaticity adjustment method.