Backlight assembly and liquid crystal display having the same

The present invention claims the benefit of Korean Patent Application No. 72076/2005, filed in Korea on Aug. 8, 2005, which is hereby incorporated by reference.

The present disclosure relates to a backlight assembly for a liquid crystal display, and specifically, to a backlight assembly with high efficiency and brightness.

A liquid crystal display (“LCD”) device displays an image using a dielectric anisotropy of liquid crystal, a twist angle of which varies with an applied voltage. Because the LCD is slim and lightweight and can be driven at a low voltage, it is widely used as a display device for portable electronic equipment and for large-sized display devices such as a monitor.

The LCD includes two substrates where transparent conductive layers are formed, a liquid crystal layer where liquid crystals are injected between the two substrates, polarizers, compensation films, and color filters. The LCD has a plurality of liquid crystal cells. The liquid crystal cells do not emit light themselves. Therefore, since the liquid crystal cells are not self-luminous, the LCD requires a backlight assembly.

The backlight assemblies are classified into edge type backlight assemblies where a light source is located at the front or side of the screen and direct type backlight assemblies where a light source is located at the rear of the screen. As the screen becomes larger and high image quality is increasingly demanded, the direct type backlight assemblies are more widely used. Examples of the light source for the backlight assembly include electro luminescence (“EL”), cold cathode fluorescent lamp (“CCFL”), and hot cathode fluorescent lamp (“HCFL”). Among them, the CCFL is widely used for an LCD with the larger-sized screen because it can be formed without substantial thickness and allows for a thinner LCD device.

In the CCFL type backlight assembly, mercury sealed inside the fluorescent lamp is combined with metal and thus amalgam is easily formed. Consequently, the lifespan of the lamp is reduced, and brightness varies greatly according to temperature change. Also, the use of toxic mercury causes a problem for waste disposal of the toxic chemical.

In light of these problems, a backlight assembly using a light emitting diode (LED) may be desirable. The use of red, green and blue LEDs makes it possible to implement a high-brightness backlight assembly because they can provide the miniaturization of the backlight assembly and uniformity of light.

Hereinafter, a related art LCD will be described with reference to FIGS. 1 , 2 A and 2 B.

FIG. 1 is an exploded perspective view of a related art LCD using LEDs. Referring to FIG. 1 , the related art LCD includes a liquid crystal panel 15 , a top case 16 for protecting the liquid crystal panel 15 , a plurality of LEDs 12 used as a light source, a plurality of printed circuit boards (“PCB”) 14 for supplying a voltage to the LEDs 12 , optical sheets 10 for diffusing and condensing the light generated from the LEDs 12 , an intermediate light guide plate 11 used as a light scattering unit, a lower case 17 provided below the LEDs 12 , and a reflection plate (not shown) for reflecting the light from the LEDs 12 toward the liquid crystal panel 15 .

For the LEDs 12 of the LCD, side emitting type LEDs are used because they can mix the light uniformly and have brightness stabilization. The LEDs 12 include red (R), green (G) and blue (B) LEDs and are connected to electrode patterns of the PCBs 14 to generate light when a voltage is supplied thereto. The light from the R, G and B LEDs 12 is mixed together to emit a white (W) light.

FIG. 2A is a sectional view of the LED of the related art LCD and FIG. 2B is a graph of brightness with respect to angles of the LED in the related art LCD. Referring to FIG. 2A , the LED 12 of the related art LCD includes a light emitting chip 22 , a lens 21 , a body 23 , and a PCB 14 . A side emitting type LED that emits light from its sides is used as the LED 12 . The light from the light emitting chip 22 is diverged from the sides of the LED 12 through the lens 21 .

Referring to FIG. 2B , the side emitting type LED 12 exhibits high brightness at angles ranging from −10° to 30° and angles ranging from 150° to 190° with respect to the light emitting chip 22 . Accordingly, many side emitting type LEDs 12 are required to provide uniform brightness.

The number of the LEDs 12 may be changed according to the size of the liquid crystal panel 15 . In the LCD, the side emitting type LEDs 12 that can mix the light uniformly are used for the brightness stabilization. However, because the related art backlight assembly has to include the intermediate light guide plate 11 so as to provide sufficient brightness to the liquid crystal panel 15 , its structure is complicated and its thickness increases. In addition, a plurality of side emitting type LEDs must be used, resulting in increases of power consumption.

Accordingly, the present disclosure is directed to a backlight assembly for an LCD, where front emitting type LEDs and side emitting type LEDs are arranged in combination with one another.

In a first aspect, a backlight assembly includes a light source including a first light emitting diode (LED) and a second LED. A main emission direction of the first LED is different from a main emission direction of the second LED. The light source is disposed on the board. At least one optical sheet is arranged in front of the light source.

In a second aspect, a liquid crystal display device includes a liquid crystal panel for displaying an image. A backlight assembly for emitting light to the liquid crystal panel includes a light source in which a first light emitting diode (LED) and a second light emitting diode (LED) are adjacent to one another. The first LED is a different type than the second LED.

In a third aspect, a backlight assembly includes one or more front-emitting light emitting diodes (LEDs) and one or more side-emitting LEDs. The one or more side-emitting LEDs are located adjacent to at least one of the front-emitting LEDs. The assembly further includes at least one board housing the front-emitting LEDs and the side-emitting LEDs.

High efficiency and high brightness may be obtained by alternately arranging the front emitting type LED and the side emitting type LED. In addition, since the liquid crystal display device provides high efficiency and stabilized brightness, an intermediate light guide plate can be omitted, thereby reducing the manufacturing cost of the liquid crystal display device.

It is to be understood that both the foregoing general description and the following detailed description of the present disclosure are exemplary and explanatory and are intended to provide further explanation of the embodiments as claimed.

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention. In the drawings:

FIG. 1 is an exploded perspective view of a related art LCD using LEDs;

FIG. 2A is a sectional view of the LED of the related art LCD;

FIG. 2B is a graph of brightness with respect to angles of the LED in the related art LCD;

FIG. 3 is an exploded perspective view of an LCD using LEDs according to one embodiment;

FIG. 4 is a sectional view of the LED according to one embodiment;

FIG. 5 is a graph of brightness with respect to angles of the LED according to one embodiment;

FIG. 6 is a view illustrating a structure of an LED according to one embodiment;

FIG. 7A is an enlarged view of a portion I of FIG. 6A and is an illustration of an embodiment of a cluster of LEDs;

FIG. 7B is an illustration of an alternate embodiment of a cluster of LEDs;

FIG. 7C is an illustration of an alternate embodiment of a cluster of LEDs;

FIG. 7D is an illustration of an alternate embodiment of a cluster of LEDs;

FIG. 7E is an illustration of an alternate embodiment of a cluster of LEDs;

FIG. 7F is an illustration of an alternate embodiment of a cluster of LEDs;

FIG. 7G is an illustration of an alternate embodiment of a cluster of LEDs;

FIG. 7H is an illustration of an alternate embodiment of a cluster of LEDs;

FIG. 7I is an illustration of an alternate embodiment of a cluster of LEDs;

FIG. 8 is a view illustrating a set of clusters of an LED according to an embodiment;

FIG. 9 is a view illustrating a set of clusters of an LED according to an alternate embodiment;

FIG. 10 is a view illustrating a set of clusters of an LED according to an alternate embodiment;

FIG. 11 is a view illustrating a set of clusters of an LED according to an alternate embodiment;

FIG. 12 is a view illustrating a set of clusters of an LED according to an alternate embodiment; and

FIG. 13 is a view illustrating a structure of an LED according to one embodiment with a combination of sets of clusters.

Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

FIG. 3 is an exploded perspective view of an LCD using LEDs according to the present invention. Referring to FIG. 3 , the LCD according to the present disclosure includes a liquid crystal panel 115 for displaying an image, a top case 116 for protecting the liquid crystal panel 115 , a plurality of LEDs 112 used as a light source, a PCB 114 for supplying a voltage to the LEDs 112 , optical sheets 110 for diffusing and condensing the light generated from the LEDs 112 and irradiating the diffused and condensed light onto the liquid crystal panel 115 , a bottom case 117 provided under the LEDs 112 , and a reflection plate (not shown) provided on the bottom case 117 and the PCB 114 to reflect the light from the LEDs 112 toward the liquid crystal panel 115 . The PCB 114 is connected to the LEDs 112 to supply a voltage thereto. The LEDs 112 are provided with the combination of front emitting type LEDs and side emitting type LEDs.

The surfaces of lenses provided on the front emitting type LEDs are formed as a dome shape such that the light from the LEDs may be emitted upwards, thereby increasing the luminous efficiency. Also, the side emitting type LEDs emit light laterally, thereby providing uniform and stabilized brightness. In this manner, high efficiency and high brightness may be simultaneously obtained by utilizing a combination of the front emitting type LEDs and the side emitting type LEDs.

The LCD with high efficiency and stabilized brightness may be implemented by the combination of the front emitting type LEDs and the side emitting type LEDs. Therefore, the related art intermediate light guide plate ( 11 in FIG. 1 ) provided for high efficiency and brightness stabilization may be omitted.

FIG. 4 is a sectional view of an LED according to the present invention. Specifically, a front emitting type LED 212 and a side emitting type LED 212 ′ are illustrated in FIG. 4 . The front emitting type LED 212 and the side emitting type LED 212 ′ are mounted on a PCB 114 and arranged spaced apart from each other by a predetermined distance.

The front emitting type LED 212 and the side emitting type LED 212 ′ include lenses 221 and 221 ′, respectively, for determining light emitting positions. They also include light emitting chips 222 and 222 ′, and bodies 223 and 223 ′ connected to the PCB 114 , respectively.

The front emitting type LED 212 and the side emitting type LED 212 ′ are alternately arranged. When a voltage is supplied through patterns of the PCB 114 , the light emitting chips 222 and 222 ′ generate light. Then, the front emitting type LED 212 emits light upward through the dome-shaped lens 221 , while the side emitting type LED 212 ′ emits light laterally with the side type lens 221 ′.

Accordingly, the light source having the LEDs of the present embodiments mixes the upward emitted light and the laterally emitted light, thereby generating light with improved efficiency and uniform brightness.

FIG. 5A is a graph of brightness with respect to angles of the LED according to one embodiment. Specifically, FIG. 5A is a graph of brightness for the angles for the light emitting chip 222 of the front emitting type LED 212 with respect to the light emitting chip 222 . The front emitting type LED 212 exhibits high brightness at angles ranging from 30° to 150° with respect to the light emitting chip 222 . Therefore, the front emitting type LED 212 has high efficiency because most of light is emitted from the upper surface of the lens 221 .

FIG. 5B is a graph of brightness with respect to angles for the light emitting chip 222 ′ of the side emitting type LED 212 ′. Specifically, FIG. 5B is a graph of brightness for the angles for the light emitting chip 222 ′ of the side emitting type LED 212 ′ with respect to the light emitting chip 222 ′. The side emitting type LED 212 ′ exhibits high brightness at angles ranging from −10° to 30° and angles ranging from 150° to 190° with respect to the light emitting chip 222 ′. Therefore, the brightness is stabilized because most of light is emitted from the sides of the lens 221 ′.

FIG. 5C is a graph of brightness with respect to angles when the front emitting type LED 212 and the side emitting type LED 212 ′ are alternately arranged. In this embodiment, the LCD may obtain high efficiency and stabilized brightness at angles ranging from −10° to 190°.

Therefore, compared with an LCD having only the side emitting type LED, the LCD having a combination of the front emitting type LED 212 and the side emitting type LED 212 ′ can reduce the number of LEDs and stabilize brightness. Also, since the intermediate light guide plate ( 11 in FIG. 1 ) is not required, the cost and thickness of the LCD may be reduced. Due to the high efficiency and the stabilized brightness, the power consumption of the LCD may be reduced for the same brightness of the related art LCD having only the side emitting type LED. In alternate embodiments, various types of LEDs may be combined to improve the brightness of a display.

FIG. 6 is a view illustrating a structure of an LED according to one embodiment, and FIG. 7A is an enlarged view of a portion I of FIG. 6 .

Referring to FIGS. 6 and 7A , the LED of one embodiment includes a front emitting type LED 212 having a dome-shaped lens such that light can be emitted upward, a side emitting type LED 212 ′ emitting light laterally, an electrode terminal 223 , and a board having an electrode pattern 224 connected to the electrode terminal 223 . Also, a reflection plate (not shown) may be provided on the board to reflect light toward a liquid crystal panel.

FIG. 7A shows an embodiment in which a plurality of LEDs are arranged in a cluster. The cluster of LEDs may be formed in a variety of ways. Specifically, as shown in the embodiment of FIG. 7A , the cluster includes eight LEDs arranged in two rows. The top row includes a green, blue, red, and green LED and the bottom row includes a green, blue, red, and green LED. Also, in the top row, the blue and second green LEDs are side-emitting LEDs and in the bottom row, the first green and the red LEDs are side-emitting LEDs. The remaining LEDs are front-emitting LEDs.

The embodiment shown in FIG. 7A , may be modified such that the arrangement of the colors of LEDs may be modified, or the arrangement of front-emitting or side-emitting LEDs may be modified. In other words, in alternate embodiments, the colors may be in a different arrangement than as shown in FIG. 7A . Likewise, the LEDs that are front-emitting versus side-emitting may be different in alternate embodiments.

The embodiment shown in FIG. 7A is merely one embodiment of a cluster of LEDs. A cluster of LEDs may be formed in numerous arrangements. FIGS. 7B-7I show alternate embodiments of a cluster of LEDs. These embodiments are merely exemplary. For each alternate embodiment, it should be understood that the specific arrangement of the colors and whether the LED is side-emitting or another type of LED may be modified in additional embodiments.

The front emitting type LED 212 and the side emitting type LED 212 ′ are alternately arranged. They may be arranged in an “H” structure as shown in FIG. 6 . The “H” structure has six clusters of LEDs are arranged. The six clusters are arranged in sets of two. The first set of two is arranged horizontally in the middle of the PCB 114 , and the remaining two sets are arranged vertically on either side of the horizontal middle set. Four of the clusters of LEDs are located in each of the four corners of the PCB 114 and the remaining two clusters are side-by-side in the middle of the PCB 114 .

The combined structure of the front emitting type LED 212 and the side emitting type LED 212 ′ may make it possible to implement an LED having high efficiency and stabilized brightness only using a small number of LEDs 212 and 212 ′.

FIG. 7A is merely one embodiment for arranging a cluster of LEDs. FIGS. 7B-7I show additional exemplary embodiments. As discussed above, the color of the LED and the type of LED may be modified from the specific embodiments.

FIG. 7B shows a cluster embodiment similar to the embodiment shown in FIG. 7A except for the arrangement of colors is modified. Specifically, the bottom row of LEDs is arranged with green, red, blue and green LEDs. The first green and the blue LED are side-emitting LEDs 212 ; and the red and second green LEDs are front-emitting LEDs 212 . FIG. 7C is another cluster embodiment similar to FIGS. 7A and 7B , except the arrangement of LEDs is modified. Specifically, the cluster of FIG. 7C shows the top row includes front-emitting LEDs and the bottom row includes side-emitting LEDs.

As shown in FIGS. 7A-7C , the specific arrangement of LEDs within a cluster may be variable in alternate embodiments. Specifically, the arrangement of colors may be modified in alternate embodiments. In addition, the type of LED may be alternated in various cluster embodiments.

FIG. 7D is an alternate embodiment of a cluster. The cluster of FIG. 7D is similar to the clusters of FIG. 7A-7C in that the cluster has eight LEDs arranged in pairs. However, the cluster in FIG. 7D shows the pairs of LEDs arranged vertically rather than horizontally. The LEDs that are front-emitting LEDs 212 , and the LEDs that are side-emitting LEDs 212 ′ may be varied from the specific embodiment shown in FIG. 7D , as well as the arrangement of the colors of the LEDs.

FIG. 7E is an alternate embodiment of a cluster including four LEDs arranged in a diamond shape. FIG. 7F is an alternate embodiment of a cluster including five LEDs arranged in a row. FIG. 7G is an alternate embodiment of a cluster including three LEDs arranged in a row. FIG. 7H is an alternate embodiment of a cluster including three LEDs arranged in a triangle. FIG. 7I is an alternate embodiment of a cluster including four LEDs arranged in a row. As discussed above, these embodiments are merely exemplary. Additionally, the color of the LEDs and the type of LED may be modified from the specific embodiments shown in the Figures.

FIGS. 8-12 are views illustrating a set of clusters of LEDs according to various embodiments. FIGS. 8-12 are each an exemplary embodiment of a set of clusters. The embodiments shown in FIGS. 8-12 may include clusters from any of the cluster embodiments shown in FIGS. 7A-7I . Alternatively, the sets in FIGS. 8-12 may include cluster embodiments that are not shown in the exemplary embodiments of FIGS. 7A-7I . Additionally, it should be understood that the embodiments of a set of clusters as shown in FIGS. 8-12 are merely exemplary. Various embodiments of sets of clusters are contemplated according to the various embodiments.

Referring to FIG. 8 , the LED of one embodiment includes a front emitting type LED 212 emitting light upward, a side emitting type LED 212 ′ emitting light laterally, an electrode terminal 223 , and a PCB 114 connected to the electrode terminal 223 . Also, a reflection plate (not shown) may be provided on the PCB 114 to reflect light toward a liquid crystal panel.

The front emitting type LED 212 and the side emitting type LED 212 ′ are alternately arranged. They may be arranged in a combination of a “ ” structure and a “ ” structure. That is, the “ ” structure is provided at a position adjacent to the “ ” structure. According to this embodiment, there may be six clusters of LEDs. Each cluster comprises 4 front emitting type LEDs 212 , and 4 side emitting type LEDs 212 ′. Four of the six clusters of LEDs are located in the four corners of the PCB 114 . The remaining two clusters are arranged on the top and the bottom of the PCB 114 , but are offset from the middle. Each one of the two middle clusters are directly adjacent to corner clusters that are diagonal from each other. As shown in FIG. 6C , the upper middle cluster is to the right of the middle and the lower middle cluster is to the left of the middle. Alternatively, the two clusters could be offset in the opposite direction.

The combination of the “ ” structure and the “ ” structure may make it possible to implement the LED having high efficiency and stabilized brightness only using the small number of the LEDs 212 and 212 ′.

Referring to FIG. 9 , the LED of one embodiment includes a front emitting type LED 212 emitting light upward, a side emitting type LED 212 ′ emitting light laterally, an electrode terminal 223 , and a PCB 114 connected to the electrode terminal 223 . Also, a reflection plate (not shown) may be provided on the PCB 114 to reflect light toward a liquid crystal panel.

The front emitting type LED 212 and the side emitting type LED 212 ′ are alternately arranged. They may be arranged in a combination of a “ ” structure and a “ ” structure. That is, the “ ” structure is provided at a position adjacent to the “ ” structure. In this embodiment, four clusters of LEDs are provided in the four corners of the PCB 114 . Each of four other clusters of LEDs are located directly adjacent to each of the clusters that is located in the corners of the PCB 114 .

The combination of the “ ” structure and the “ ” structure may make it possible to implement the LED having high efficiency and stabilized brightness only using the small number of the LEDs 212 and 212 ′.

FIGS. 10-12 are additional alternate embodiments of a set of clusters. FIG. 10 is an alternate embodiment of a set of clusters. The clusters shown in FIG. 10 are not shown in the cluster embodiments of FIGS. 7A-7I . The clusters shown in this set are arranged in a row of eight LEDs. There are five of these clusters arranged such that four are in each of the corners and one is in the center of the PCB 114 . Additionally, two smaller clusters are shown on either side of the PCB 114 . The smaller clusters are similar to the cluster embodiment shown in FIG. 7I .

FIG. 11 is an alternate embodiment of a set of clusters. The clusters shown in FIG. 11 are similar to the cluster embodiment shown in FIG. 7E . The set of clusters shown in FIG. 11 has ten clusters arranged in a “XX” pattern.

FIG. 12 is an alternate embodiment of a set of clusters. The clusters shown in FIG. 12 are similar to the cluster embodiment shown in FIG. 7E . The set shown in FIG. 12 includes an arrangement of clusters in adjacent diamond shapes.

FIGS. 8-12 are merely exemplary embodiments of a set of clusters. Additional arrangements of clusters in a set is contemplated according to alternative embodiments. Alternate clusters may be used for the embodiments of a set of clusters than those clusters shown in FIGS. 7A-12 .

FIG. 13 is an illustration of a combination of sets of clusters. Specifically, the embodiment of FIG. 13 is a combination of the set embodiment shown in FIG. 6 . FIG. 13 shows that sets of clusters can be combined or arranged together to create a backlight assembly producing improved brightness. In alternate embodiments of combinations of sets, the clusters and the sets may be arranged or combined differently than the exemplary embodiment shown in FIG. 13 .

The LCD display may include any combination of sets as shown in FIG. 13 . In alternate embodiments, the display may only include a single set of any number of clusters as described above. In an additional alternate embodiment, the display may include only a single cluster.

The structures of the LEDs 212 and 212 ′ are not limited to the structures or sets of clusters shown in FIGS. 8-12 . The structures of the LEDs 212 and 212 ′ may be modified in various arrangements without departing from the scope of the present disclosure. In other words, the arrangement of the LEDs within the clusters, the arrangement of the clusters within a set, and the arrangement of the sets for a combination of sets may all be modified in alternate embodiments.

Because the clusters include different types of LEDs, the present embodiments may implement a backlight assembly and the LCD having the same, capable of obtaining high efficiency and high brightness using the small number of LEDs. In addition, since the LCD may provide high efficiency and stabilized brightness, an intermediate light guide plate can be omitted, thereby reducing the cost of materials and the number of manufacturing processes and implement low power consumption.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.