KR20090021912A - Backlight unit and liquid crystal display device having the same - Google Patents

Abstract

A backlight unit and a liquid crystal display device having the same are provided to place a color converting unit converting blue light, which is emitted from a blue light source, into orange light in one side of a light guide plate facing the blue light source. A backlight unit(120) comprises the follow units. One or more blue LED(Light Emitting Diode)s(150) are in a bottom cover(190). A light guide plate(140) is arranged along with the blue LED. A housing(151) surrounds the blue LED. The housing guides light emitted from the blue LED to the light guide plate. Optical sheets(130) are arranged on the light guide plate. The optical sheets condense or disperse light. A reflective sheet(180) is arranged in a rear side of the light guide plate. The reflective sheet reflects light irradiated to the rear side of the light guide plate in a direction of the LCD panel.

Description

BACKLIGHT UNIT AND LIQUID CRYSTAL DISPLAY DEVICE HAVING THE SAME}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight unit, and more particularly, to a backlight unit having a uniform luminance and a liquid crystal display device having the same, as well as improving color reproducibility.

Cathode ray tube (CRT), one of the widely used display devices, is mainly used for monitors such as TVs, measuring devices, and information terminal devices, but the size and weight of electronic products are reduced due to the weight and size of the CRT itself. Could not actively respond to the response.

As a solution to this problem, the liquid crystal display device has a tendency that its application range is gradually widening due to the features such as light weight, thinning, low power consumption driving. Accordingly, in order to meet the needs of users, liquid crystal display devices are progressing in the direction of large area, thinning, and low power consumption.

BACKGROUND ART A liquid crystal display device is a display device that displays an image by controlling an amount of light passing through a liquid crystal, and is widely used for advantages such as thinning and low power consumption.

Unlike the CRT, the liquid crystal display is not a display device that emits light by itself, and thus, a back light unit including a separate light source is provided on the rear surface of the liquid crystal display panel to provide light for visually representing an image. .

The backlight unit uses a plasma light source such as a cold cathode fluorescent lamp (CCFL), a hot cathode fluorescent tube (HCFL), an external electrode fluorescent tube (EEFL), and an external & internal electrode fluorescent tube (EIFL). Or white light emitting diodes (LEDs).

Among them, white light emitting diodes (LEDs) emitting white light are widely used for advantages of long life, low power, small size, and high durability.

However, the conventional white light emitting diode (LED) has a problem that the color reproduction rate is lowered. Here, the color reproducibility refers to a color reproducibility of a color to be displayed by combining red, green, and blue wavelengths.

In more detail, the white light emitting diode is not designed in consideration of the implementation of color as a light source for emitting white light. That is, a white light emitting diode supplies light of three wavelengths (red, green, and blue) to a liquid crystal display panel, and development has been conducted only in terms of color temperature, high brightness, and the like. The light emitted from the white light emitting diode, which does not consider the implementation of color, is mixed with the color filter of the liquid crystal display panel to implement various colors, and has a limit of about 70% in color reproducibility.

The white light emitting diode is a point light source and has a constant emission angle (emission angle) from which light is structurally emitted. Accordingly, in the backlight unit having the white light emitting diode as a light source, a luminance difference occurs in an area where the white light emitting diode is disposed and an area where the white light emitting diode is not disposed. That is, the luminance difference means that light and dark portions occur in regions where white light emitting diodes are disposed and regions where white light emitting diodes are disposed.

As described above, in a liquid crystal display device using a white light emitting diode as a light source, a method for improving the luminance imbalance caused by the emission angle of the white light emitting diode is urgently needed.

It is an object of the present invention to provide a backlight unit capable of improving color reproducibility.

Another object of the present invention is to provide a backlight unit capable of realizing uniform luminance and a liquid crystal display device having the same.

The backlight unit according to an embodiment of the present invention,

At least one light source emitting blue light;

A diffusion unit provided in parallel with the light source to diffuse the blue light incident from the light source;

A color conversion unit arranged in parallel with the diffusion unit to convert a part of the diffused blue light into yellow light and converting the converted yellow light and the blue light into white light; And

And a light guide plate provided in parallel with the color conversion unit to convert the white light converted from the color conversion unit into surface light.

In addition, the liquid crystal display device of the present invention,

A liquid crystal display panel;

At least one light source emitting blue light to provide light to the liquid crystal display panel;

A diffusion unit provided in parallel with the light source to diffuse the blue light incident from the light source;

A color conversion unit arranged in parallel with the diffusion unit to convert a part of the diffused blue light into yellow light and converting the converted yellow light and the blue light into white light; And

And a light guide plate provided in parallel with the color conversion unit to convert the white light converted from the color conversion unit into surface light.

According to the present invention, a color conversion unit for converting blue light emitted from a blue light source into yellow light is provided on one side of the light guide plate facing the blue light source, thereby improving color reproduction.

In addition, the present invention has the effect that the light emitted from the blue light source is first diffused by the diffuser and secondly diffused by the color converter to improve the luminance difference in the peripheral region of the light source.

In addition, the present invention has the effect of reducing the manufacturing cost of the backlight unit by having a blue light emitting diode cheaper than the conventional white light emitting diode.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is an exploded perspective view illustrating a liquid crystal display according to an exemplary embodiment of the present invention, and FIG. 2 is a cross-sectional view of the light guide plate taken along the line II ′ of FIG. 1.

1 and 2, the liquid crystal display according to the exemplary embodiment of the present invention is provided with a liquid crystal display panel 110 for displaying an image and a rear surface of the liquid crystal display panel 110 to provide light. It includes a backlight unit 120 to.

The liquid crystal display panel 110 includes a thin film transistor (TFT) array substrate and a color filter substrate which are bonded to face each other to maintain a uniform cell gap, and a liquid crystal interposed between the thin film transistor array substrate and the color filter substrate. Layer.

Although not shown in the drawing, a driving unit (not shown) mounted with a driving circuit for supplying a driving signal to the liquid crystal display panel 110 is electrically connected to one side of the liquid crystal display panel 110 by a tape carrier package (TCP). do.

The driving unit is electrically connected to the liquid crystal display panel 110 to supply a control signal and a data signal to a plurality of gate lines (not shown) and data lines (not shown) formed in the liquid crystal display panel 110, thereby providing the liquid crystal display. The pixels of the panel 110 are driven.

The backlight unit 120 includes a bottom cover 190 having a rectangular box shape having an upper surface, a blue light emitting diode 150 provided as at least one light source on an inner side surface of the bottom cover 190, and the blue light emitting diode. The light guide plate 140 disposed in parallel with the 150 and the housing 151 provided to surround the blue light emitting diode 150 to guide the light emitted from the blue light emitting diode 150 to the light guide plate 140. And optical sheets 130 disposed on the light guide plate 140 to focus light diffused on the light guide plate 140, and light disposed on a rear surface of the light guide plate 140 and irradiated to a rear surface of the light guide plate 140. The reflective sheet 180 reflects toward the panel 110.

Although not shown in the drawing, the backlight unit 120 surrounds the edges of the blue light emitting diode 150, the light guide plate 140, the optical sheets 130, and the reflective sheet 180, and the bottom cover 190. It further includes a support frame (not shown) of the rectangular frame shape coupled with.

The blue light emitting diode 150 emits high luminance blue light of a surface mounted type (SMT) or a chip on board (COB) and has a wavelength of about 400 to 500 nm.

The light guide plate 140 converts point light emitted from the blue light emitting diode 150 into surface light.

A diffusion unit 160 is provided on a side surface of the light guide plate 140 facing the blue light emitting diode 150 to diffuse blue light emitted from the blue light emitting diode 150.

The diffusion unit 160 has a diagonal pattern for diffusing light. Here, in one embodiment of the present invention, the diffusion unit 160 including the diagonal pattern is limited, but the present invention is not limited thereto and may include all the patterns for diffusing light.

The color converter 170 is provided at one side of the diffusion unit 160. That is, the diffuser 160 and the color converter 170 are located side by side on one side of the light guide plate 140 facing the light emitting diode 150. The diffusion unit 160 and the color converter 170 may be integrally formed on the side surface of the light guide plate 140.

The color converter 170 diffuses the phosphor 171 converting a part of the blue light incident from the blue light emitting diode 150 into yellow light, and diffuses the yellow light and the blue light converted from the phosphor 171. Diffusion material 173 to be mixed. That is, the color converter 170 is formed of a mixture of the phosphor 171 and the diffusion material 173.

The color converter 170 converts the light incident from the blue light emitting diode 150 into yellow light and simultaneously mixes the blue light and the yellow light.

The blue light emitted from the blue light emitting diode 150 is first diffused by the diffusion unit 160 and is incident on the color conversion unit 170.

A part of the blue light incident on the color converter 170 is converted into yellow light by the phosphor 171 formed of a plurality of particles.

The blue light and the converted yellow light are mixed and secondary diffused by the diffusion material 173 of the color conversion unit 170 and are incident to the light guide plate 140. In this case, the light emitted from the color converter 170 is white light in which yellow and blue light are mixed.

As described above, the blue light emitted from the blue light emitting diode 150 is first diffused by the diffusion unit 160 and secondly diffused by the color conversion unit 170 at the periphery of the conventionally generated light source. The difference in luminance generated can be improved.

In addition, the liquid crystal display according to the exemplary embodiment of the present invention may convert a part of the blue light into yellow light and a mixture of blue light and the converted yellow light at the same time by converting a part of the blue light into yellow light. The color converter 170 may be provided to convert the white light into a white light, thereby reducing the color reproducibility of the white light emitting diode.

In addition, the blue light emitting diode 150 of the present invention may be cheaper than the conventional white light emitting diode to reduce the manufacturing cost of the entire backlight unit 120.

The improved color reproducibility according to the embodiment of the present invention will be described in detail with reference to FIGS. 3 and 4.

3 is a view comparing the color spectrum (b) and the conventional color spectrum (a) of the backlight unit according to an embodiment of the present invention, Figure 4 is a color coordinate of the backlight unit according to an embodiment of the present invention It is a figure which shows the color coordinate of the conventional backlight unit.

As shown in FIG. 3, the spectrum b of light emitted from the backlight unit of the present invention has a red spectral region (dotted line) of about 620 to 650 nm having a higher peak in the red spectral region of the conventional spectrum (a). . Here, the increase in the maximum peak in the red spectral region means that the luminance and color reproducibility are improved.

Referring to FIG. 4, it can be seen that the white light emitted from the blue light emitting diode of the present invention through the diffusion part, the color conversion part, and the light guide plate has a red area extending in the x direction in a horseshoe-shaped color coordinate, so that the entire area becomes wider than before. Can be.

Here, the color of light emitted from the backlight unit of the present invention is determined by chromaticity coordinates defined by the Commission International d'Eclairage (CIE). That is, after calculating tristimulus values X, Y, and Z of the light emitted from the backlight unit of the present invention, color coordinates x, y of red, green, and blue are obtained from the matrix converted from the tristimulus values. Subsequently, when the x, y values of red, green, and blue are expressed in Cartesian coordinates, a horn-shaped spectral trajectory is drawn, which is called a CIE color coordinate.

According to the present invention, a triangular region formed by each color coordinate of red, green, and blue becomes a color reproduction region, and as the triangle region becomes larger, color reproducibility is increased. The color reproducibility depends on color purity and luminance, and as the color purity and luminance increases, color reproducibility increases.

Therefore, in the present invention, the triangular region of the color coordinates is widened, and thus, not only the color reproducibility can be improved but also the luminance can be improved as compared with the related art.

5 is a cross-sectional view of a liquid crystal display according to another exemplary embodiment of the present invention.

As shown in FIG. 5, the liquid crystal display according to another exemplary embodiment of the present invention has the same reference numeral as other components except for the blue lamp 250 among the components of the liquid crystal display according to the exemplary embodiment of the present invention. The description will be omitted and detailed description will be omitted.

The blue lamp 250 emits blue light having a wavelength of about 400 to 500 nm.

The blue lamp 250 may be a high color rendering fluorescent lamp. Here, the high color rendering fluorescent lamp is coated with a high color electrode fluotescent lamp on the inner wall surface of the glass tube in order to improve color reproducibility.

The blue light emitted from the blue lamp 250 is first diffused by the diffuser 160 to be incident on the color converter 170.

A part of the blue light incident on the color converter 170 is converted into yellow light by the phosphor 171, and the yellow light and the unconverted blue light converted by the phosphor 171 are transferred to the diffusion material 173. By the second diffusion and mixing is incident on the light guide plate (140).

As described above, the blue light emitted from the blue lamp 250 is first diffused by the diffusion unit 160 and secondly diffused by the color conversion unit 170 in the conventional light source peripheral region. The luminance difference can be improved.

In addition, the liquid crystal display according to another embodiment of the present invention, the blue lamp 250 for emitting blue light, and not only converts a part of the blue light to yellow light, but also a mixture of blue light and the converted yellow light to white The color converter 170 may be provided to convert the light into a light, thereby reducing the color reproducibility of the white light emitting diode or the white lamp.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the technical spirit of the present invention. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification but should be defined by the claims.

1 is an exploded perspective view illustrating a liquid crystal display according to an exemplary embodiment of the present invention.

FIG. 2 is a cross-sectional view of the light guide plate taken along the line II ′ of FIG. 1.

3 is a view comparing the color spectrum of the backlight unit according to an embodiment of the present invention and the conventional color spectrum.

4 is a diagram illustrating color coordinates of a backlight unit and color coordinates of a conventional backlight unit according to an exemplary embodiment of the present invention.

5 is a cross-sectional view of a liquid crystal display according to another exemplary embodiment of the present invention.

<Explanation of symbols for the main parts of the drawings>

140: light guide plate 150: blue light emitting diode

160: diffusion unit 170: color conversion unit

171: phosphor 173: diffusion material

250: blue lamp

Claims (8)

At least one light source emitting blue light; A diffusion unit provided in parallel with the light source to diffuse the blue light incident from the light source; A color conversion unit arranged in parallel with the diffusion unit to convert a part of the diffused blue light into yellow light and converting the converted yellow light and the blue light into white light; And And a light guide plate provided in parallel with the color conversion unit to convert the white light converted from the color conversion unit into surface light. The method of claim 1, And the color converter comprises a phosphor for converting the blue light into the yellow light, and a diffusion material for diffusing and mixing the converted yellow light and the unconverted blue light. The method of claim 1, The light emitted from the light source is first diffused by the diffuser and secondly diffused by the color converter. The method of claim 1, The light source is a backlight unit, characterized in that any one of a light emitting diode and a lamp for emitting blue light. A liquid crystal display panel; At least one light source emitting blue light to provide light to the liquid crystal display panel; A diffusion unit provided in parallel with the light source to diffuse the blue light incident from the light source; A color conversion unit arranged in parallel with the diffusion unit to convert a part of the diffused blue light into yellow light and converting the converted yellow light and the blue light into white light; And And a light guide plate provided in parallel with the color conversion unit to convert the white light converted from the color conversion unit into surface light. The method of claim 5, wherein And the color converter comprises a phosphor for converting the blue light into the yellow light, and a diffusion material for diffusing and mixing the converted yellow light and the unconverted blue light. The method of claim 5, wherein The light emitted from the light source is first diffused by the diffusion unit, and secondly diffused by the color conversion unit. The method of claim 5, wherein The light source may be any one of a light emitting diode and a lamp emitting blue light.

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