KR20020067232A - Direct type backlight unit for lcd - Google Patents

Abstract

The present invention relates to a direct type backlight for LCDs having a high brightness uniformity, in particular, it has an improved structure of a reflector plate used for a conventional direct backlight and reflecting light emitted from a light source, and a diffuser plate for uniformly dispersing light, The present invention relates to a direct type backlight device for an LCD which can be easily applied to a small, medium, or large LCD by providing a high luminance uniformity regardless of the size of the LCD panel.

Direct type backlight device for an LCD having a high uniformity uniformity according to the present invention, the reflector is located at the bottom and reflects the light to the upper side, a reflector formed by crossing the horizontal plane and the acid, and a lamp positioned on the upper part of the reflector to emit light; In the backlight structure of the LCD device which is located on the upper side of the lamp and comprises a diffuser plate for uniformly diffusing the light emitted from the lamp, the second reflecting plate is further provided at both ends of the reflecting plate, The light source is installed 5mm away from the bottom surface, the reflector is located 2mm away from the bottom of the light source, the thickness of the diffuser plate is 2mm, the thickness of the reflector plate is 1mm, the length of the bottom surface of the mountain formed in the reflector plate is 14 mm, the thickness of the second reflector is 1 mm, and the distance between the centers of the light sources is 25 mm.

Description

Direct type backlight unit for LCD {Direct type backlight unit for LCD}

The present invention relates to a direct type backlight for LCDs having a high brightness uniformity, in particular, it has an improved structure of a reflector plate used for a conventional direct backlight and reflecting light emitted from a light source, and a diffuser plate for uniformly dispersing light, The present invention relates to a direct type backlight device for an LCD which can be easily applied to a small, medium, or large LCD by providing a high luminance uniformity regardless of the size of the LCD panel.

Liquid crystal displays (hereinafter referred to as "LCDs") have the advantage of being able to be driven using low power and having vivid color reproduction, whereas non-luminescent LCD panels that display characters or figures do not emit light directly. Element. Therefore, there is a need for a backlight unit for irradiating light to the LCD panel at the rear or bottom of the LCD panel so that the LCD functions as a display device.

Conventional backlight devices used in LCDs are largely divided into two types. The first is an edge (or side) backlight that provides light at the side of the LCD, and the second is a direct backlight that provides light directly from the bottom of the LCD. This distinction is determined by the position of the lamp providing the light, thus showing structural differences. First, the structure will be briefly described with reference to FIGS. 1 and 2 as follows.

FIG. 1 illustrates a side cross-sectional structure of an edge type backlight, and FIG. 2 is a direct type backlight. An edge type backlight has a light source 10 positioned on a side surface of a backlight device and reflects one surface of the light guide plate 40 to reflect light. The surface light source obtained by multiple reflection of the light is reflected on an LCD panel cell (not shown) to provide light to the LCD. By the light pattern design of the light guide plate 40 and the diffuser plate 50, the luminance uniformity can be improved. However, there is a disadvantage in that the luminance is low overall. Reference numeral 30 changes the direction so that the light emitted from the light source 10 is directed to the diffuser plate 50 as a reflecting plate.

On the other hand, in the direct type backlight, the light source 10 is positioned on the lower side of the LCD panel, and the diffuser plate 50 is disposed between the light source 10 and the LCD panel, and the reflector plate 30 is disposed below the light source 10. It is arranged. Most of the light emitted from the light source 10 is incident directly to the diffuser plate 50, and part of the light is reflected from the reflector plate 30 to be incident on the diffuser plate 50. The number of light sources 10 may be determined according to the size of the LCD panel, and the luminance may be improved by the structural design of the reflector 30 and the diffuser plate 50. The shape of the reflector plate 30 may be a flat plate or a form in which a mountain and a horizontal plane are alternately formed as shown. In addition, although not shown in the drawings, each part is fixed by the mold frame, and the size of the mold frame is determined as the final size of the backlight device.

Among the backlight devices as described above, the direct type backlight device is easier to obtain higher luminance than the edge type backlight device, and is evaluated in a manner suitable for LCDs that are getting larger. However, despite the advantages of high brightness, the direct type backlight device has a low luminance uniformity. In particular, despite the advantages of the direct backlight providing high brightness, the size and thickness of the frame have to be changed according to the respective LCD using devices to which the direct backlight is applied, for example, a mobile phone, a PDA and a TFT LCD. Therefore, there is always a problem that the developer has to design a new frame and lamp optimized for the device employing the LCD. In order to overcome these shortcomings and achieve high brightness uniformity, many studies have been conducted, but it has not been possible to achieve satisfactory high brightness uniformity.

The present invention has been invented to solve the above problems, and its object is to provide a direct type backlight device for an LCD which can exhibit a high luminance uniformity of 90% or more by additionally installing a reflecting plate on the direct type backlight device used as a light source of the LCD. To provide.

Another object of the present invention is to optimize the shape and position of the reflector plate, the light scattering characteristics of the diffuser plate and the distance from the light source to optimize the applicability and expandability of the LCD device, which can be used directly under the LCD. It is to provide a type backlight device.

1 is a side cross-sectional view of an edge-type backlight conventionally used;

Figure 2 is a side cross-sectional view of a direct type backlight used in the prior art,

Figure 3 is a perspective view of the main portion cut of the direct backlight of the present invention,

4 is a side cross-sectional view of another embodiment of a direct type backlight according to the present invention;

5 is a graph showing luminance uniformity caused by a light source;

6 is a graph showing luminance uniformity when using a reflector;

7 is a graph showing scattering characteristics of a diffusion plate;

8 is a graph showing luminance uniformity when using a diffusion plate;

※ Explanation of symbols about main part of drawing ※

10 light source 20 reflecting plate for cover

30: reflector 40: light guide plate

50: diffuser plate 100: diffuser plate

102: light source 104: reflector

106: mountain 108: horizontal plane

The characteristic configuration of the present invention for achieving the above object is as follows.

The present invention is to reflect the light to the upper side is located at the bottom, the reflecting plate formed by staggering the horizontal plane and the mountain, the lamp located on the upper portion of the reflecting plate and emits light, the light located on the upper side of the lamp and emitted from the lamp In the backlight structure of an LCD device including a diffusion plate for uniformly diffusing light, the second reflecting plates are provided at both ends of the reflecting plate at predetermined angles.

According to another feature of the invention, the light source is installed 5mm apart from the bottom of the diffuser plate, the reflector is located 2mm away from the bottom of the light source, the thickness of the diffuser plate is 2mm, the thickness of the reflecting plate is 1mm The bottom surface of the mountain formed in the reflecting plate is 14mm, the thickness of the second reflecting plate is 1mm, and the distance between the centers of the light sources is 25mm.

Referring to the present invention having such characteristics in detail as follows.

3 is a partial perspective view of a backlight according to the present invention. As shown, the diffuser plate 100 (diffuser) is located at the upper side, the light source 102 for generating light is located below, the reflector plate 104 is located at the bottom, and for reflecting light The second reflecting plates 110 are provided on both end sides of the reflecting plate 104, respectively. The second reflecting plates 110 are installed to completely block the diffusion plate 100 and the reflecting plate 104, whereby the light emitted to the outside is reflected and irradiated to both end sides of the diffusion plate 100. By the reflection effect, the edge portion of the LCD panel cell, which is darker than the center of the related art, becomes brighter.

In addition, the diffusion plate 100 is used to uniformly diffuse and radiate the light emitted from the light source 102, and is particularly used to increase luminance uniformity. The material used in the manufacture is PET, polycarbonate, it is used by applying a diffusion material to a sheet (sheet) made of PET, polycarbonate.

In the present invention, it is possible to use a diffusion plate conventionally used without particular change of material, the characteristic is the thickness of the overall diffusion plate 100. This has the effect of cost reduction because the luminance uniformity is increased by the present invention without a significant change of the conventional diffuser plate.

Referring back to the drawings, the total thickness of the diffusion plate 100 is preferably 2mm. This is a numerical value that is optimized by the size of the light source 102 located below and the interaction with the reflecting plate 104 and obtains a luminance uniformity of 90% or more. However, it can be changed within an error range of about ± 10% (1.8 ~ 2.2mm). The total thickness of the diffuser plate 100 means the thickness of the entire diffuser plate 100, and this may also be the case when a plurality of sheets are stacked and used as is conventionally used.

As the light source 102 located at the bottom of the diffusion plate 100, a fluorescent lamp, an EL, an LED, a halogen bulb, and the like are used, and a fluorescent lamp (CCFL) is generally used. Fluorescent lamps are either straight or L-shaped and are added or subtracted according to the size of the LCD panel. In order to fit the size of the panel, the light source 102 preferably uses a straight fluorescent lamp.

In the present invention, the distance between the centers of the light sources 102 adjacent to each other is also set to 25 mm. The light source 102 increases and decreases according to the size of the LCD panel of the device in which the backlight is installed. In this case, the brightness of most display areas of the LCD panel is uniformly maintained by keeping the distance between the centers of each light source 102 constant at 25 mm. Can be maintained.

The reflector 104 is positioned under the light source 102. The reflecting plate 104 has a shape in which the horizontal plane 108 and the mountain 106 are connected to each other. This structure has the effect of improving the reflection efficiency, in the present invention, the thickness of the reflecting plate 104 is set to 1mm, and the distance from the light source 102 is also spaced apart by about 2mm. The reflector plate 104 concentrates the light on the cells of the LCD panel and serves to prevent the loss of light. The reflector 104 is formed using a film such as PE or PET.

The positions of the diffuser plate 100, the light source 102, the reflector plate 104, and the second reflector plate 110 are shown well. This installation position is similar to the conventional position shown in FIG. 2, but the present invention is characterized in that the length d of the bottom side of the peak 106 formed on the reflecting plate 104 is set to 14 mm.

4 shows that the shape of the reflecting plate 104 is a flat plate, and shows that the second reflecting plate 110 is added to the end of the reflecting plate 104. This indicates the general installation form of the second reflector plate 110. In this case, the reflection efficiency is slightly lower than that shown in FIG. 4 due to the shape of the reflecting plate 104. However, by the reflection effect, the edge portion of the LCD panel cell, which is darker than the conventional center, is brightened.

The luminance, luminance uniformity, and light scattering characteristics of the backlight of the present invention as described above will be described using the attached graphs. The luminance measurement conditions were 15.1 "in size of the backlight, the light source was five fluorescent lamps, the backlight was 12 mm thick (based on the backlight structure to which the numerical values shown in FIG. 3 were applied), and the measurement position of the luminance was the diffuser plate 100. This is the virtual location of the location where it is installed.

FIG. 5 shows luminance uniformity (flux / mm ² ) of a fluorescent lamp (CCFL) itself installed in a direct backlight. As shown, in the absence of the diffuser plate 100 and the reflector plate 104, the luminance is high only in the portion where the light sources are located and the luminance in the remaining portion is nearly zero. If the luminance uniformity is calculated (the calculation equation is omitted), the luminance uniformity of only the fluorescent lamp itself is about 1.27%, and there are many problems in using it as a backlight for LCD. The luminance uniformity represents a percentage of (minimum value / maximum value) and is calculated using a numerical value on the graph.

FIG. 6 is a graph showing luminance and luminance uniformity when only the reflecting plate 104 is provided in the same state as in FIG. 5 (without the diffusion plate and the reflecting plate). As shown in the figure, calculating the luminance uniformity as a percentage becomes about 11.07%, and it is apparent that the synergistic effect of luminance can be achieved as a side effect. The reflecting plate 104 was configured using a film such as PE or PET.

FIG. 7 shows the transmission and reflection light scattering characteristics of the diffusion plate 100 and is a measurement of two conventional diffuser samples. One of the diffuser samples is D117TF (sample 1) and the other is DR65C (sample 2). Referring back to the drawings, the light scattering characteristics of Sample 1 have a large slope with respect to the angle 0 (transmission and scattering are the same), whereas the light scattering characteristics of Sample 2 have a nearly flat slope compared to Sample 1. This is due to the difference in haze of each sample. The D117TF (sample 1) is a lower haze sample than the DR65C (sample 2). In the present invention, the intensity was measured using a diffuser plate 100 using a high haze sample 2 (that is, a diffusing material having high reflection and transmission uniformity).

8 is a measurement of luminance uniformity in the backlight device using the diffuser plate 100 and the reflector plate 104 coated with DR65C (sample 2). As shown, it can be seen that it has a uniform luminance uniformity over almost all sections. The maximum size of the luminance uniformity is about 0.12, and the luminance uniformity is about 90.74%.

A graph measuring luminance uniformity before and after using the reflecting plate 104 and the diffusing plate 100 as shown in the drawing, with 1.27% before design (see FIG. 5) and 90.74% (see FIG. 8) after design. It can be seen that the luminance uniformity.

As described above, according to the present invention, a reflection plate is additionally installed in the direct type backlight device used as the light source of the LCD to provide a high brightness uniformity of 90% or more, and the shape and position of the reflection plate, the light scattering characteristics of the diffusion plate, and the light source. By having an optimized structure, the applicability and expandability to the LCD using device are high, so there is an effect that can be used universally.

Furthermore, the backlight structure having a specific value according to the present invention has the effect of providing high luminance and luminance uniformity while minimizing the structural change caused by the change in the size of the LCD.

Claims (2)

It is located at the bottom to reflect the light to the upper side, the reflecting plate formed by crossing the horizontal plane and the mountain, the lamp located at the top of the reflecting plate to emit light, and the light emitted from the lamp located on the upper side of the lamp uniformly In the backlight structure of the LCD device including a diffusion plate for diffusing, A direct backlight for an LCD having a high brightness uniformity, characterized in that the second reflecting plate is installed on both side surfaces of the reflecting plate to guide the light emitted through the side to the diffusion plate. The method of claim 1, The light source is installed 5 mm apart from the bottom of the diffuser plate of the backlight, the reflector is located 2 mm away from the bottom of the light source, the thickness of the diffuser plate is 2mm, the thickness of the reflector plate is 1mm, The bottom surface of the formed acid is 14mm, the thickness of the second reflecting plate is 1mm, the direct backlight for LCD with high brightness uniformity, characterized in that the distance between the center of the light source is 25mm.