KR20080037249A - Back-light unit and liquid crystal display having it - Google Patents

Abstract

A backlight unit and a liquid crystal display with the same are provided to have a light emitting source having at least one first light source emitting light with at least two wavelengths and at least one second light source emitting light with at least three wavelengths, thereby solving a color reproducibility problem of red, green and blue and a luminance lowering problem at the same time. A backlight unit(200) includes a light emitting source(210) to emit light. The light emitting source has at least one first light source to emit light of at least two wavelength areas in a visible light area, and at least one second light source to emit light of at least three wavelength areas in the visible light area. The first light source emits light of blue and orange wavelength areas. The second light source emits light of red, green and blue wavelength areas. The first and second light sources are arranged in a line.

Description

Back-light unit and liquid crystal display having the same

1A and 1B are graphs showing light emission characteristics of light emitting diodes emitting light in two and three wavelength bands, respectively;

2 is a graph showing the luminance of light emitting sources and Comparative Examples 1 and 2 according to an embodiment of the present invention;

3 is a graph showing color reproducibility of light emitting sources and Comparative Examples 1 and 2 according to an embodiment of the present invention;

4A to 4C are plan views showing respective aspects of light emitting sources according to embodiments of the present invention;

5 is an exploded perspective view showing the structure of a liquid crystal display device with a light emitting source according to an embodiment of the present invention.

<Explanation of symbols for main parts of the drawings>

100 ... display unit, 200 ... backlight unit,

210 ... light emitting source, 211 ... 2 wavelength light emitting diode,

213 ... 3-wavelength light-emitting diode, 220 ... light guide plate.

The present invention relates to a backlight unit and a liquid crystal display device having the same, and more particularly, to a backlight unit and a liquid crystal display device having the structure to improve the decrease in brightness and color reproducibility.

Generally, a liquid crystal display device used in a notebook computer, a desktop computer, an LCD-TV, a mobile communication terminal, etc. is itself a light-receiving element type display device that emits light from outside and displays an image. In addition to the panel, a backlight unit which is installed on the rear of the liquid crystal display and irradiates light is required.

The backlight unit has a direct light type for irradiating light to the liquid crystal panel from a plurality of light sources provided directly below the liquid crystal display device and a sidewall of a light guide panel (LGP) according to the arrangement of the light source. It can be broadly classified into an edge light type for transmitting light from the installed light source to the liquid crystal panel.

In general, a cold cathode fluorescent lamp (CCFL) is used as the light source, and the cold cathode fluorescent lamp has a low color reproducibility, which is unsuitable for high-definition and high-definition TVs or monitors.

Recently, a light emitting diode (LED) is spotlighted as a light source to replace a cold cathode fluorescent lamp.

A light emitting diode as a light source is generally used a product having a yellow phosphor structure on a blue chip, which shows a stable luminance in the structure having a yellow phosphor on the blue chip, but red, green and blue color reproducibility It is difficult to raise.

In addition, when using the red, green, and blue light emitting diodes, the red, green, and blue color reproducibility is relatively improved, but there is a problem in that visibility is lowered due to relatively low luminance.

Accordingly, the present invention has been made to solve the above-mentioned problems, and provides a backlight unit and a liquid crystal display device having the same, which simultaneously solve the problems of red, green, and blue color reproducibility and luminance deterioration. There is this.

In order to achieve the above object, a backlight unit according to the present invention includes at least one first light source for emitting light in at least two wavelength ranges in a visible light region and at least one for emitting light in at least three wavelength ranges in a visible light region. The above second light source is included and includes a light emitting source for emitting light.

Here, the first light source may be a light source for emitting light in the blue and yellow wavelength range, the second light source may be a light source for emitting light in the red, green and blue wavelength range.

Further, the first light source and the second light source are preferably alternately arranged to be linearly arranged, and more preferably, the first light source is provided at at least both ends of the linear array.

In this case, the first light source and the second light source may be light emitting diodes (LEDs).

Furthermore, the light guide plate may further include a light guide plate provided at one side of the light emitting source to adjust the path of the emitted light.

The liquid crystal display according to the present invention includes at least one first light source that emits light in at least two wavelength ranges in the visible region and at least one second light source that emits light in at least three wavelength ranges in the visible region. And a backlight unit having a light emitting source through which light is emitted and a light guide plate that is provided at one side of the light emitting source and controls a path of the emitted light, and a liquid crystal panel that receives the light adjusted by the backlight unit and displays an image.

Hereinafter, exemplary embodiments of a light emitting source according to the present invention will be described in detail with reference to the accompanying drawings.

The light emitting source according to the embodiment of the present invention includes at least one first light source emitting light in two wavelength ranges in the visible region and at least one second light source emitting light in three wavelength ranges in the visible region. do.

1A and 1B are graphs showing light emission characteristics of light emitting diodes emitting light in two and three wavelength bands, respectively.

The first light source that emits light in the two wavelength ranges emits light in the blue (B) wavelength range and the yellow (Y) wavelength range, as shown in FIG. 1A, and the blue (B) and yellow ( Y) Emits white light as a combination of wavelength bands.

The first light source that emits light in the two wavelength bands may be a light emitting diode having a yellow phosphor structure on a blue chip.

In addition, the second light source that emits light in three wavelength ranges emits light in the blue (B) wavelength region, the green (G) wavelength region, and the red (R) wavelength region, as shown in FIG. 1B. In addition, since the white light is emitted by combining the light of the three wavelength ranges, the color reproducibility is excellent.

The second light source that emits light in these three wavelength ranges may be a light emitting diode having blue, green, and red chips.

In the case of Figs. 1A and 1B, the brightness of the light in Fig. 1A is shown in Fig. 1B because it emits light in the vicinity of 550 nm (near yellow) having the best visibility, although shown in the relative intensity. Better than the brightness of the light

That is, the first light source that emits light in the two wavelength ranges of FIG. 1A has better brightness than the second light source that emits light in the three wavelength ranges of FIG. 1B, and the light in the three wavelength ranges of FIG. 1B. The second light source that emits light has better color reproducibility than the first light source that emits light in the two wavelength ranges of FIG. 1A.

An embodiment of the present invention proposes a light emitting source having a compromise between luminance and color reproducibility by combining the characteristics of the first and second light sources in FIGS. 1A and 1B.

2 is a graph showing the luminance of the light emitting source according to an embodiment of the present invention and Comparative Examples 1, 2, Figure 3 is a graph showing the color reproducibility of the light emitting source and Comparative Examples 1, 2 according to the embodiment of the present invention Drawing.

In addition, the luminance in FIG. 2 and the color reproducibility in FIG. 3 are quantitatively shown in Table 1 below.

brightness Color reproducibility [%] Luminance [nit]  Luminance Ratio [%] Comparative Example 1 492 153 53.4 Comparative Example 2 290 100 68.8 Inventive Example 324 121 59.4

Referring to FIG. 2, Comparative Example 1 shows the brightness when only the first light source is used alone, and Comparative Example 2 shows the brightness when only the second light source is used alone, and the invention example shows the first light source and the first light source. It shows the luminance when two light sources are mixed.

In Comparative Example 1 using only the first light source alone, as described above, since the first light source emits light in the vicinity of yellow (550 nm) having excellent visibility, the luminance ratio (153%) is the luminance ratio of Comparative Example 2. (100%) and the brightness ratio (121%) of the invention example were shown to be superior, and the comparative example 2 using only the 2nd light source alone shows the low brightness ratio (100%), compared with the 1st light source and 2nd In the invention example in which the light source is mixed, it has a compromised luminance ratio (121%) in Comparative Example 1 and Comparative Example 2.

In addition, referring to FIG. 3, in the second light source that emits light in three wavelength ranges of blue, green, and red of Comparative Example 2, due to the color of each emitted light, the widest area in the color coordinate system is selected. This means that the color reproducibility (68.8%) of Comparative Example 2 is superior to the color reproducibility of Comparative Example 1 (53.4%) and the color reproducibility of the invention example (59.4%).

In contrast, Comparative Example 1 has the narrowest band in the color coordinate system, and the color reproducibility of Inventive Example (59.4%) is lower than that of Comparative Example 2 (68.8%), but the color reproducibility of Comparative Example 1 (53.4%). Better color reproducibility than

Thus, it can be seen that in the invention example in which the first light source and the second light source are mixed, the color reproducibility is superior to that of Comparative Example 1, and the luminance is superior to that of Comparative Example 2.

The use as an actual light emitting source of this invention example is shown in Figs.

4A to 4C are plan views showing respective aspects of light emitting sources according to embodiments of the present invention.

4A to 4C, a light emitting diode 210 is used as a side light source, and a two-wavelength light emitting diode 211 emitting light of a blue and yellow wavelength range and a blue, green and red wavelength range And a three wavelength light emitting diode 213 for emitting light.

The two-wavelength and three-wavelength light emitting diodes 211 and 213 are linearly arranged on the side with respect to the light guide plate 220, and emit light toward the light guide plate 220. At this time, the aspect of the emitted light, that is, the brightness and color reproducibility are as described above.

In FIG. 4A, after the three-wavelength light emitting diode 213 having excellent color reproducibility is linearly arranged, the two-wavelength light emitting diode 211 having excellent brightness is disposed at both ends of the linearly arranged three-wavelength light emitting diode 213.

The reason why the two-wavelength light emitting diode 211 is arranged at both ends of the three-wavelength light emitting diode 213 is that the three-wavelength light emitting diode 213 is used on the central portion of the display area to provide excellent color reproducibility and to emit adjacent light. At both ends of the relatively weak circle, a two-wavelength light emitting diode 211 having excellent brightness is disposed to compensate for the light emission brightness.

In such an aspect as in FIG. 4A, more precisely in the three wavelength light emitting diode 213 which is not adjacent to the two wavelength light emitting diode 211 in FIG. have.

That is, by using only the three wavelength light emitting diode 213 at the center of the display area, the center may not reach the required luminance.

In order to compensate for this, a two-wavelength light emitting diode 211 may be arranged at the center of the linearly arranged light emitting source 210 in FIG. 4A described above, as in FIG. 4B.

In FIG. 4B, the two-wavelength light emitting diode 211 is arranged at the center of the linear array, and the two-wavelength light emitting diode 211 is disposed at both ends of the linear array and alternately formed with the three-wavelength light emitting diode 213.

The alternate formation of the two-wavelength light emitting diode 211 and the three-wavelength light emitting diode 213 is such that, as shown in FIG. 4C, the three-wavelength light emitting diode 213 is disposed at both ends of the linear array, and thus the two-wavelength light emitting diode 211 is It may also appear as the sun, alternating with each other.

In FIG. 4C, since the number of three wavelength light emitting diodes 213 is disposed more than the two wavelength light emitting diodes 211 than in FIG. 4B, color reproducibility in the entire display area may be better than in the cases of FIGS. 4A and 4B. .

Hereinafter, a backlight unit having a light emitting source and a liquid crystal display according to an exemplary embodiment of the present invention will be described with reference to the accompanying drawings.

As shown in FIG. 5, the liquid crystal display according to the exemplary embodiment of the present invention includes a display unit 100 for displaying an image, a backlight unit 200 for providing light to the display unit 100 for displaying an image, and And a top chassis 300 for fixing the display unit 100 to the backlight unit 200.

The display unit 100 is mounted on the backlight unit 200 and displays an image using light supplied from the backlight unit 200. In detail, the display unit 100 includes a liquid crystal display panel 110, a driving chip 120, and a flexible circuit unit 130.

The liquid crystal display panel 110 is interposed between the first substrate 112, the second substrate 114 coupled to the first substrate 112, and between the first substrate 112 and the second substrate 114. It consists of a liquid crystal layer (not shown).

The first substrate 112 includes a plurality of pixels (not shown) in a matrix form, and each of the plurality of pixels extends in a second direction perpendicular to the first direction and a gate line extending in the first direction. And a data line (not shown) and a pixel electrode to cross the gate line to be insulated from the gate line. In addition, a thin film transistor (hereinafter, referred to as TFT) (not shown) is formed in each pixel and connected to the gate line, the data line, and the pixel electrode.

An RGB pixel (not shown), which is a color pixel, may be formed on the second substrate 114 by a thin film process, and a common electrode facing the pixel electrode is formed. Therefore, the liquid crystal layer is arranged by voltages applied to the pixel electrode and the common electrode, thereby adjusting the transmittance of light provided from the backlight unit 200.

On at least one side of the first substrate 112, a driving chip 120 for applying a driving signal to the data line and the gate line is mounted. The driving chip 120 may be composed of two or more chips separated into a data line chip and a gate line chip, or may be composed of one chip integrating them. In addition, the driving chip 120 is mounted on one side of the first substrate 112 by a chip on glass (COG) process.

In addition, a flexible circuit unit 130 for applying a control signal for controlling the driving chip 120 is attached to one side of the first substrate 112 on which the driving chip 120 is mounted, and the flexible circuit unit 130 is driven. A timing controller for adjusting the timing of the signal, a memory for storing the data signal, and the like may be mounted, and may be electrically connected to the first substrate 112 through the anisotropic conductive film.

Meanwhile, the backlight unit 200 may include a light source 210 generating light and a light guide plate 220 and a light source 210 and a light guide plate 220 to guide light incident from the light source 210 to be emitted in a specific direction. It may include a storage container 230 for receiving the.

Here, the light emitting source 210 includes a plurality of two-wavelength light emitting diodes 211 (see FIG. 4) and a three-wavelength light emitting diode 213 (see FIG. 4) in the form of a point light source, and one side of the light guide plate 220. Disposed on to generate light. In this case, the plurality of light emitting diodes 211 and 213 are arranged to have a predetermined separation distance on the flexible printed circuit board 215 disposed on one side of the light guide plate 220.

The light guide plate 220 includes an incident surface to which light generated from the light emitting source 210 is incident, an exit surface extending from one end of the incident surface to emit light, and a reflecting surface extending from the other end of the incident surface.

The storage container 230 includes a bottom chassis 232 and a mold frame 234. The bottom chassis 232 includes a bottom surface and four sidewalls extending from the bottom surface, and may include a reflector (not shown). In addition, the mold frame 234 is formed of four sidewalls to guide the storage positions of the light emitting source 210 and the light guide plate 220, and the bottom surface has an open shape. In this case, the bottom chassis 232 and the mold frame 234 are coupled to each other by hook fastening or the like.

In addition, the backlight unit 200 further includes a plurality of optical sheets 250 on the emission surface side of the light guide plate 220.

The plurality of optical sheets 250 improves optical characteristics of light emitted through the exit surface of the light guide plate 220. In this case, the plurality of optical sheets 250 includes a diffusion sheet 252, a prism sheet 254, a protective sheet 256, and a reflective polarization sheet 258.

Here, the diffusion sheet 252 is disposed above the emission surface of the light guide plate 220 and diffuses the light emitted through the emission surface. The prism sheet 254 is disposed above the diffusion sheet 252 and condenses the light diffused by the diffusion sheet 252 to improve front luminance.

In addition, the reflective polarization sheet 258 is disposed on the protective sheet 256, and reflects and polarizes the light collected by the prism sheet 254 to convert the polarization axis to be transmitted through the liquid crystal display panel 110. At this time, the prism sheet 254 is connected to each other on the upper surface, and includes a plurality of prisms extending in a predetermined direction.

The protective sheet 256 is disposed between the prism sheet 254 and the reflective polarizing sheet 258 to prevent stain defects displayed in white by the prism sheet 254.

Although the technical spirit of the present invention has been described in detail according to the above-described preferred embodiment, it should be noted that the above-described embodiment is for the purpose of description and not of limitation. In addition, those skilled in the art will understand that various embodiments are possible within the scope of the technical idea of the present invention.

Particularly, in the embodiment described with reference to the accompanying drawings of the present invention, a side emitting type backlight unit is disclosed, but it may be used in a direct type backlight unit as the same technical idea.

In addition, although the embodiment of the present invention has been described with the light emitting diode as an example, other light emitting sources within the scope of the same technical idea in addition to the light emitting diode may be used.

As described above, the backlight unit and the liquid crystal display having the same according to the present invention can simultaneously solve the problems of red, green, and blue color reproducibility and luminance deterioration.

Claims (9)

At least one first light source for emitting light in at least two wavelength ranges in the visible region and at least one second light source for emitting light in at least three wavelength ranges in the visible region includes a light emitting source for emitting light Backlight unit. The backlight unit of claim 1, wherein the first light source is a light source that emits light in a blue and yellow wavelength range. The light emitting source of claim 1, wherein the second light source is a light source that emits light in a red, green, and blue wavelength range. The backlight unit of claim 1, wherein the first light source and the second light source are arranged in a straight line. The backlight unit of claim 4, wherein the first light source and the second light source are alternately arranged. The backlight unit of claim 4 or 5, wherein the first light source is provided at at least both ends of the linear array. The backlight unit of claim 1, wherein the first light source and the second light source are light emitting diodes (LEDs). The backlight unit of claim 1, further comprising a light guide plate provided on one side of the light emitting source to adjust a path of the emitted light. At least one first light source for emitting light in at least two wavelength ranges in the visible region and at least one second light source for emitting light in at least three wavelength ranges in the visible region; A backlight unit having a light guide plate provided on one side of a light emitting source to adjust a path of the emitted light; And A liquid crystal panel for receiving light adjusted by the backlight unit and displaying an image; Liquid crystal display comprising a.

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