Planar led light source and backlight unit

<img file="NL2000416C2_D0001.tif" />

Patent Center

Netherlands © 2000416 © C PATENT²⁰ © Patent application: 2000416 © Filed: 05.01.2007

Int.CI .:

G02F1 / 13357 (2006.01)

<td>© Priority:</td><td>© Patent holder (s):</td>

<td>10.01.2006 KR 10-2006-0002842</td><td>Samsung Electro-Mechanics Co., Ltd. to</td>

<td></td><td>Suwon, Republic of Korea (KR).</td>

<td>© Registered:</td><td></td>

<td>26.07.2007 IE 2007/10</td><td>© Inventors):</td>

<td></td><td>Hyun Ho Lee in Suwon (KR).</td>

<td>© Date:</td><td>jae Wook Kwon in Seoul (KR).</td>

<td> 22.07.2008</td><td>Myoung Bo Park in Seocheon (KR).</td>

<td></td><td>Hyeong Won Yun in Yongin (KR).</td>

<td>© Published:</td><td>Yoon Tak Yang in Hwasung (KR).</td>

<td>01.10.2008 IE 2008/10</td><td></td>

<td></td><td>© Authorized representative:</td>

<td></td><td>Ir. A. van Westenbrugge et al. 2502 LS</td>

<td></td><td>The Hague.</td>

© Surface light source using a light-emitting diode and backlight unit for a liquid crystal display using it.

© Surface light source, capable of reducing color deviations with a reduced number of light-emitting diodes and manufactured at low cost, and a backlight unit for a liquid crystal display using it. The surface light source comprises a plurality of light source clusters arranged in a first and a second direction, the clusters each comprising three light-emitting diodes located in a triangular arrangement, the three light-emitting diodes comprising green, red and blue light-emitting diodes. The surface light source also includes a first array of the clusters arranged in, and alternately inverted from, the first direction; and a second array of the clusters arranged in, and alternately inverted from, the second direction, the first array being perpendicular to the second array. The invention reduces color deviations in order to realize uniform white light and reduces the number of light-emitting diodes in order to be able to manufacture a product at low cost.

NL C 2000416

The contents of this patent correspond to the original filed description with claim (s) and any drawing (s).

The Netherlands Patent Center is an agency of the Ministry of Economic Affairs.

Surface light source using a light-emitting diode and backlight unit for a liquid crystal display using it.

Claim of Priority This application claims the priority of Korean Patent Application No. 2006-0002842, filed January 10, 2006, with the Korean Intellectual Property Office, the disclosure of which is hereby incorporated by reference.

Background of the invention

Field of the Invention The present invention relates to a surface light source using a light-emitting diode (referred to below as LED) for reducing color deviations in a backlight unit for a liquid crystal display (indicated below). as LCD) which it uses. More particularly, the invention relates to a surface light source in which LEDs are housed in clusters of triangular devices which are alternately inverted, thereby significantly reducing color deviations and allowing the use of a smaller number of LEDs to reduce manufacturing costs, and LCD backlight unit which uses it.

Description of the Related Art Cold cathode fluorescent lamps (CCFLs) may contribute to environmental pollution from the use of mercury gas, have a slow response rate, have low color reproducibility, and are unsuitable for miniaturizing LCD panels.

[0004] LEDs, on the other hand, are environmentally friendly, have a high response speed on the order of nanoseconds, can be used effectively for video fast currents, are suitable for impulse driving, and have a color reproducibility of 100%. In addition, the light amounts of red, green and blue LEDs can be adjusted to control luminance, color temperature and the like. The LEDs are also suitable for miniaturizing LCD panels. Therefore, the LEDs are actively used as a light source for backlighting members of LCD panels and the like.

The LCD backlight using the LED can be classified into a side edge type and a direct type depending on the location of the light source. In the side edge type backlight member, a beam-shaped light source is located on one side to emit light through a light guide panel. In the direct type backlight member, a surface light source having an area almost the same as that of the LCD panel is placed below the LCD panel to emit light to the plane of the LCD panel.

As shown in Figure 1 (a), in order to be able to mix red, green and blue light to generate white light, a surface light source 200 used in an LCD panel of the prior art state is included. technique, a plurality of 2x2 LED matrices 205 arranged in lines and rows, each composed of red and blue LEDs located in one diagonal direction and two green LEDs located in the other diagonal direction. In the drawings, the reference character "R" represents a red LED which emits red light, the reference character "G" represents a green LED which emits green light and the reference character "B" represents a blue LED which emits blue light. In general, two green LEDs, one red LED and a blue LED are used to generate white light.

Figure 1 (b) illustrates the LED arrangement of the conventional surface light source 200 comprising a plurality of LED arrays 205 arranged in lines and rows. In the LED device shown in Figure 1 (b), red, green and blue light are relatively well mixed to generate uniform white light in a central portion of the light source 200. Nevertheless, the blue or red LEDs are not appropriately located at corners 211 and 212 of the surface light source, thereby emitting reddish or bluish light.

That is, as shown in Figure 1 (b), in the corner indicated by the reference mark 211, only the red LED R and the green LED G are alternately arranged without a blue LED B, and therefore reddish light is emitted . In the corner indicated by reference numeral 212, only the blue LED B and the green LED G are alternately arranged without a red LED R, and therefore bluish light is emitted.

Thus, the surface light source 200 with the above-mentioned prior art LED device has the problem of non-uniform white light emission at corners 211 and 212 thereof.

As an approach to overcoming this problem, another LED arrangement of a prior art surface light source 300 is shown in Figure 2. In the surface light source 300 shown in Figure 2, a plurality of LEDs are repeatedly arranged in a first row 310 in the order of blue, green, green and red. In a second row 320 which is adjacent to the first row, a plurality of LEDs are repeatedly arranged in a row in the order of green, red, blue and green. In a third row 330, the LEDs are arranged in the order of green, blue, red, and green, and in a fourth row, 340, the LEDs are arranged in the order of red, green, green, and blue. These rows are arranged repeatedly.

In this surface light source 300, green, red, blue, and green LEDs are located at angles 311 and 312 to generate relatively uniform white light, however, portions 315 where four green LEDs are clustered in the central portion of the surface light source exist. 300. Therefore, the green light is dominant in these portions 315, causing color deviations.

Light simulation performed with the surface light source 300 with the above LED device has shown that green light, for which man has a sensitive perception, dominates, causing color deviations on the surface light source.

As a result, the conventional surface light source 30 and the LCD backlight unit using it will have a non-uniform distribution of white light with the color deviations.

In order to overcome the drawback of the color deviations, a different approach has been suggested by the holder of the present invention in Korean Patent Application No. 2005-0062297.

This conventional technology of container of the present invention includes a first LED array 410 repeating two consecutive green LEDs, one red LED and one blue LED, and a second array 420 repeating two consecutive green LEDs, one blue LED and one red LED. The first and second LED arrays are arranged in lines and rows such that two green LEDs are surrounded by red or blue LEDs.

Thus, as shown in Figure 3, the conventional surface light source 400 described above has red, green and blue LEDs in such a way that two green LEDs are surrounded by red or blue LEDs. This allows uniform light without the color deviations in the corners of the surface light source 400 and also in the central portion of the surface light source 400. In addition, this conventional technology allows the surface light source 400 to emit white light similar to human color perception, thereby reducing color deviations to obtain uniform white light.

However, in this conventional technology, a cluster is composed of two adjacent green LEDs, a red LED and a blue LED, that is, a unit of B, G, G and R LEDs, whereby a large number of LEDs per surface unit per surface light source 400 is required. Therefore, the conventional technology still leaves room for realizing a surface light source at a lower cost.

Summary of the Invention The present invention has been made to solve the aforementioned problems of the prior art and, therefore, it is an aspect of the present invention to provide a surface light source using a light-emitting diode which is suitably is for reducing color deviations to generate uniform white light, and a backlight unit for a liquid crystal display using it.

Another aspect of the invention is to provide a surface light source that uses light-emitting diodes, which uses a smaller number of light-emitting diodes per unit area and reduces color deviations in order to obtain excellent white light.

According to an aspect of the invention, the invention provides a surface light source for reducing color deviations. The surface light source comprises: a plurality of light source clusters arranged in an array in a first and a second direction, the clusters each comprising three light-emitting diodes arranged in a triangular arrangement, the three light-emitting diodes being green, red and blue light-emitting diodes; a first array of the clusters arranged in and alternately inverted from the first direction; and a second array of the clusters arranged in and alternately inverted from the second direction, the first array being perpendicular to the second array.

According to an embodiment of the present invention, the triangular device has equal internal angles.

According to an embodiment of the present invention, the triangular device has different inner angles.

According to an embodiment of the present invention, the triangular device has two equal internal angles.

Preferably, the triangular device has inner corners which are respectively equal to that of the triangular device of an adjacent one of the clusters.

Preferably, the clusters of the same type have a pitch in the region represented by D &lt;2H with respect to a height from a reflective sheet to a diffusion sheet in a backlight unit for a liquid crystal display.

According to another aspect of the invention, the invention provides a backlight unit for a liquid crystal display attached to a liquid crystal display panel. The liquid crystal display backlight unit includes: a plurality of light source clusters arranged as an array in a first and a second direction, each of the clusters comprising three light-emitting diodes located in a triangular arrangement, the three light-emitting diodes comprising green, red and blue light-emitting diodes , a first array of the clusters arranged in and alternately inverted from the first direction, and a second array of the clusters arranged in, and alternately inverted from the second direction, the first array being perpendicular to the second array; a diffusion blade for uniformly diffusing the light incident thereon from the surface light source; and a light collecting sheet for collecting the light diffused by the diffusion sheet.

Brief Description of the Drawings The above and other aspects, features and other advantages of the present invention will be more clearly understood from the detailed description given below, read in conjunction with the accompanying drawings, in which:

Figure 1 (a) is a schematic illustrating an LED matrix used in a conventional surface light source, and Figure 1 (b) is a schematic illustrating an arrangement of the LED matrixes shown in Figure 1 (a) );

Figure 2 is a view illustrating an arrangement of LEDs from another conventional surface light source;

Figure 3 is a view illustrating an R, G, G, and B arrangement of LEDs from a further yet conventional surface light source;

Figure 4 is an image showing the white light with color deviations in an LCD backlight unit using the surface light source having the R, G, G and B device;

Figure 5 is a view illustrating the surface light source having triangular clusters of LEDs according to a first embodiment of the present invention;

Figure 6 is an image showing white light with color deviations in the

LCD backlight unit using the surface light source according to the first embodiment of the present invention;

Figure 7 is a view illustrating a surface light source with triangular clusters of LEDs according to a second embodiment of the present invention;

Figure 8 is an image showing white light with color deviations in the LCD backlight unit using the surface light source according to the second embodiment of the present invention;

Fig. 9 is a view illustrating the correlation between a pitch between the clusters in the surface light source of the present invention and a height of a diffusion sheet from a reflective sheet; and Figure 10 is an exploded view illustrating an LCD backlight unit using the surface light source of the present invention.

Detailed description of the preferred embodiment.

Exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

As shown in Figure 5, a surface light source 5 that uses LEDs and is suitable for reducing color deviations comprises a plurality of light source clusters 10 arranged as an array in a first and a second direction. Each of the light source clusters 10 consists of a green G LED, a red R LED and a blue B LED located in a triangular arrangement. The surface light source 5 also includes a first array 20 of the clusters 10 arranged in, and alternately inverted from, the first direction.

As shown in Figure 5, it is assumed that the x axis is the first direction and the y axis is the second direction.

Therefore, the plurality of light source clusters 10 located in the first array 20 are arranged in, and alternately inverted from, the first direction of the x axis.

Therefore, given that a first cluster has 10 at the top and R and B has at the bottom, a second cluster will have R and B at the top and G at the bottom. And a third cluster will have 10 G at the top and R and B at the bottom, and a fourth cluster will have 10 R and B at the top and G at the bottom.

On the other hand, the surface light source 5 also includes a second array 30 of the clusters 10, perpendicular to the first array 20. Each of the clusters 10 of the second array 30 also consists of a green G LED, a red R LED and a blue B LED located in a triangular arrangement. The clusters 10 in the second array 30 are arranged in, and alternately inverted from, the second direction.

That is, as shown in Figure 5, assuming that the y-axis is the second direction, the plurality of clusters 10 arranged in the second array 30 are arranged in, and alternately inverted from , the second direction.

As shown in Figure 5, a first cluster 10 in the second array has 30 G on the top and R on the bottom left and B on the bottom right while a second cluster 10 G on the top and B on the bottom left and R on the bottom right.

A third cluster 10 in the second array 30 has G on the top and R on the bottom left and B on the bottom right in the same manner as on the first cluster 10, while a fourth cluster 10 G on the top and B on the bottom left and R on the bottom right, in the same way as for the second cluster 10.

In addition, in the surface light source 1 to reduce color deviations, the triangular arrangement of each of the clusters 10 has equal inner angles 01, 02 and 03. In this case, the G, R and B LEDs of each of the clusters 10, which is a base unit, are arranged in an equilateral triangle.

In addition, the triangular arrangement of each of the clusters 10 can have different inner angles 01, Θ2 and 03. In this case, the G, R and B LEDs of each of the clusters 10, which is a base unit, can be arranged in a general triangle which has different inner angles.

Furthermore, according to the present invention, the triangular arrangement of each of the clusters 10 may have two equal inner angles from the inner corners 01, 02 and 03. In this case, the G, R and B LEDs of each of the clusters 10, which is a base unit, can be arranged in an isosceles triangle.

In addition, in the triangular arrangement of each of the clusters 10, the inner angles 01, 02 and 03 may respectively be 01, 02 and 03 of the triangular arrangement of an adjacent one of the clusters 10. That is, that an identical shape of triangles is formed by the G, R and B LEDs of each unit cluster 10 arranged in the first array 20 and the second array 30. The surface light source 1 of the present invention with the above-described configuration, when forming an LCD backlight unit 100 as shown in Figure 6, can reduce color deviations to obtain uniform white light. The surface light source 1 using an LED according to the present invention has a reduced level of color deviations similar to the level of the surface light source 400 according to the teachings of the Korean oc9 patent application number 2005-0062297, filed by the holder of the present invention, whereby equally a uniform light source is obtained.

Figure 7 illustrates another structure of a surface light source 1 'which uses LEDs to reduce color aberrations according to a second embodiment of the present invention.

Such a structure has the first array 20 'and the second array 30' as shown in Figure 5, but the G, R and B LEDs are arranged with greater density relative to each other in each unit cluster 10 '. In addition, each of the clusters 10 'is located farther from another one of the adjacent clusters 10' compared to the embodiment shown in Figure 5.

In this configuration, a pitch D between the clusters 10 'has the range represented by D &lt;2H relative to a height H from a reflective sheet 156 to a diffusion sheet 116 in the case where the surface light source forms an LCD backlight unit 100 . Preferably, a pitch D between the clusters 10 is not greater than 2H because then the distance between the clusters will be too great, so that there will be too little light between the clusters to cause color deviations.

In the case where the LCD backlight unit 100 is formed as shown in Figure 8, the surface light source 1 'of the present invention can reduce the color deviations to obtain uniform white light. The surface light source 1 'realizes a reduced level of color deviations similar to the level realized by the surface light source 400 according to the teachings of Korean Patent Application No. 2005-0062297 filed by the holder of the present invention, thereby providing uniform white light in equal measure is acquired. The LCD backlight unit 100 which uses the surface light source 1, 1 'to reduce color aberrations according to the present invention has a structure as shown in Figure 10.

The LCD backlight unit 100 according to an embodiment of the present invention includes a surface light source 1 according to the present invention and a diffusion blade 116 for uniformly diffusing the light incident thereon from surface light source 1.

In addition, the backlight unit 100 also includes at least one light collecting sheet 114 provided above the diffusion sheet 116 on the side of an LCD panel 110 to collect the light diffused by the diffusion sheet 116 in a direction that is perpendicular to the plane of the liquid crystal display panel 110.

A pitch D between the clusters 10 provided in the surface light source 1 has the area represented by D &lt;2A with respect to a height H from the reflective sheet to the diffusion sheet as mentioned above. In addition, the LCD backlight unit 100 of the present invention may further comprise a protective sheet 112 provided above the light collecting sheet 114 to protect optical structures located below. In addition, the surface light source 1 includes a substrate 151 and the plurality of LEDs 152 located in each of the light source clusters 110 on the substrate 151. In addition, the LCD backlight unit 100 may also include a side wall 154 surrounding the LEDs located in clusters 10 and having an inclined surface facing the LEDs and a reflective sheet 156 provided on the substrate 151 to reflect light emitted from the LEDs 152 upwards.

In addition, it is preferable that a reflective material 154a is applied to the oblique surface of the sidewall 154 to reflect the sidewardly emitted light upwards.

In addition, the diffusion blade 116 located above the surface light source 1 diffuses the light incident thereon from the surface light source 1 to prevent local concentration of the light. In addition, the diffusion blade 116 adjusts the direction of the light propagating to the first collecting blade, thereby reducing the inclination angle to the first light collecting blade 114a.

Each of the first light collecting blade 114a and the second light collecting blade 114b has a predetermined arrangement of prisms each having the shape of a triangular pillar. In addition, the prism arrangement of the first light collecting blade 114a crosses that of the second light collecting blade 114b at a predetermined angle (e.g., 90 °). The first and second light collecting blades 114a and 114b serve to collect the light diffused by the diffusion blade 116 in a direction perpendicular to the plane of the liquid crystal display panel. This allows an almost perfect perpendicular incidence of light that has passed through the first and second light collecting blades 114a and 114b to the protective blade 112.

Thus, most of the light passed through the first and second light collecting blades 114a and 114b propagates perpendicularly, allowing uniform luminance distribution.

Although the present invention has been shown by way of example as using two light collecting blades as shown in Figure 10, in other cases it may be that only one light collecting blade is used.

The protective sheet 112 provided above the second light collecting sheet 114b functions not only to protect the surface of the second light collecting sheet 114b, but also to diffuse light to achieve uniform distribution of light. Also, the LCD panel 110 is installed above the protective sheet 112.

As shown here, the LCD backlight unit 100 of the present invention uses the surface light source 1 of the present invention to reduce color deviations and thereby obtain uniform white light. This allows the LCD backlight unit 100 to have a simplified structure without a light guide panel, etc. resulting in low weight and miniaturization and providing a brighter image compared to the conventional LCD backlight unit.

The present invention as shown above allows a surface light source and an LCD backlight unit to use them to have reduced color deviations and achieve uniform white light while the number of LEDs used therein is 25% smaller compared to the conventional R arrangement , G, G and B LEDs.

Thus, according to the present invention, the surface light source and the LCD backlight unit using it have a smaller number of LEDs per unit area thereof, allowing them to be manufactured at low cost while obtaining excellent white light.

While the present invention has been shown and described in connection with the exemplary embodiments, it will be readily apparent to those skilled in the art that modifications and variations can be made thereto without departing from this view of the spirit and scope of the invention as defined by the appended claims.