KR100860730B1 - Backlight unit and liquid crystal display including the same - Google Patents

Abstract

A backlight unit and an LCD display having the same are provided to emit white light by a combination of RGB light passing the absorption polarizing film, thereby extending the life of LED(Light Emitting Diode)s and reducing the power consumption of the LEDs. A backlight unit(100) includes plural RGB(Red, Green, Blue) LED light sources(110), a reflective polarizing film(120), and a phase delay layer(130). The reflective polarizing film reflects selectively at least one of random polarized light at G/B wavelength bands, generated in the RGB LED light sources, and transmits random polarized light at an R wavelength band. The phase delay layer is positioned on the reflective polarizing film, converts the polarized light at the G or B wavelength band into linear polarized light in a direction to transmit the polarized light, converts the polarized light at the R wavelength band into linear polarized light in various directions to transmit the polarized light, and emits the transmitted polarized light to an absorption polarizing film(140). The strength of a current inputted to at least one LED light source is smaller than that of a current inputted to other remaining LED light sources so that white light is emitted by a combination of RGB light passing the absorption polarizing film.

Description

BACKLIGHT UNIT AND LIQUID CRYSTAL DISPLAY INCLUDING THE SAME}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight unit used in a liquid crystal display (LCD), and more particularly, to reduce power consumption of a direct type backlight unit using a light emitting diode (LED) as a light source and to prolong the life of the LED light source. It relates to a backlight unit and a liquid crystal display including the same that can extend.

Recently, liquid crystal displays (LCDs) are widely used in various fields such as computer monitors and TVs of large areas as well as small mobile phones and electronic calculators. Since the liquid crystal display is a light-receiving element that does not generate light in itself, a separate light source device capable of illuminating the entire screen from the back is required. To this end, the liquid crystal display further includes a backlight unit as a light source device in addition to the liquid crystal panel.

In the backlight unit, an edge-lighting method of injecting light generated from a light source installed at the lower side of the liquid crystal panel into the liquid crystal panel by using a light guide plate, a reflecting plate, an optical sheet, a reflective polarizer, and an absorbing polarizer, and does not use a light guide plate. Instead, there is a direct-lighting method in which a plurality of light sources are disposed on a rear surface of the diffusion plate disposed at the bottom of the liquid crystal panel, and the light emitted from the light source is directly incident on the liquid crystal panel.

Conventionally, the backlight unit uses a cold cathode fluorescent lamp (CCFL) or an external electrode fluorescent lamp (EEFL) as a light source for illumination. However, these conventional light sources have a problem in that their lifespan is shortened as the gas pressure of the plasma changes, and an inverter for obtaining a high voltage required for plasma discharge is required. In addition, the conventional light sources have a problem that the power consumption efficiency is not good so that excessive power is consumed.

In order to solve such a conventional problem, a backlight unit using a light emitting diode (LED) is used. LEDs may emit light such as red (R), green (G), blue (B), and the like, depending on the type of semiconductor material and impurities, and may generate white light by combining these R, G, and B LEDs. LEDs have the advantages of small size, long life, high energy efficiency, and low operating voltage compared to conventional light sources.

In the case of a direct type backlight unit using an LED as a light source, the light is emitted to the liquid crystal panel by changing the path of light upward or downward, using a reflector. However, LEDs typically have shorter lifetimes for green (G) and blue (B) LEDs than red (R) LEDs at the same current input (life: R LED> G LED> B LED), so these LEDs can be used for a long time. In this case, the luminous efficiency of green (G) and blue (B) is lower than that of red (R), and thus there is a problem in that the quality of the product is deteriorated. In this case, it is cumbersome to replace the green (G) or blue (B) LED, which has an end of life in the liquid crystal display.

Therefore, the technical field is required to develop a technology that can reduce the power consumption according to the extension of the service life of the LED in the backlight unit using the LED light source.

The present invention has been proposed to solve the above problems of the prior art, to provide a backlight unit that can reduce the power consumption while extending the life of the LED light source in the direct type backlight unit using the LED as a light source. There is this.

In addition, another object of the present invention is to provide a liquid crystal display device including the backlight unit.

The present invention for achieving the above object,

In a direct type backlight unit used in a liquid crystal display device including an absorption polarizing film that transmits linearly polarized light as it is, but partially absorbs circularly polarized light and transmits the remaining light,

Multiple R, G, B LED light sources; A reflective polarizing film for selectively reflecting at least one randomly polarized light of the G and B wavelength bands generated by the LED light source and transmitting the randomly polarized light of the R wavelength band; And circularly polarized light in the G or B wavelength band transmitted through the reflective polarization film is converted into linearly polarized light in one direction, and circularly polarized light in the R wavelength band is converted into linearly polarized light in various directions. A phase delay layer which transmits the light to the absorption polarizing film to pass through the light; Including;

The intensity of the current input to the at least one LED light source is smaller than the intensity of the current input to the other LED light sources so that white light is emitted by the combination of R, G, and B light passing through the absorption polarizing film.

In one embodiment of the present invention, the ratio of the R, G, B light intensity transmitted through the absorption polarizing film is preferably equal to the ratio of the R, G, B light intensity generated by the R, G, B LED light source.

In one embodiment of the present invention, it is preferable that the intensity of the current input to the G and B LED light source is less than the intensity of the current input to the R LED light source.

At this time, more preferably, the intensity of the current input to the B LED light source is smaller than the intensity of the current input to the G LED light source.

In one embodiment of the present invention, it is preferable that the R linearly polarized light in various directions switched by the phase delay layer includes the R linearly polarized light in the same direction as that of the converted G or B linearly polarized light.

In one embodiment of the present invention, the plurality of R, G, B LED light source is preferably composed of one set of R, G, B LED light source and arranged in a plurality of sets.

In one embodiment of the present invention, the backlight unit of the present invention,

A diffuser plate configured to diffuse light emitted from the R, G, and B LED light sources; And an optical sheet layer for condensing the light diffused by the diffusion plate and outputting the light to the reflective polarizing film.

In one embodiment of the present invention, any one of the top and bottom of the optical sheet layer, may further include another optical sheet layer having an optical microstructure intersecting with the optical microstructure of the optical sheet layer. .

At this time, it is preferable that each optical microstructure constituting the optical sheet layer has one cross section of a triangle, an arc shape, and a quadrangle when projecting the cross section.

In one embodiment of the present invention, the reflective polarizing film is a cholesteric liquid crystal layer for selectively reflecting circularly polarized light of the G wavelength band or at least one cholesteric liquid crystal layer for selectively reflecting circularly polarized light of the B wavelength band It is preferable that a liquid crystal layer is comprised.

In one embodiment of the present invention, it is preferable that the reflective polarizing film includes one cholesteric liquid crystal layer having a long wavelength or a short wavelength pitch while going from bottom to top to selectively reflect circularly polarized light in the G and B wavelength bands.

In addition, the present invention provides a liquid crystal table market value including the backlight unit according to the above embodiments.

According to the present invention, the life of the LED light source used in the backlight unit can be extended, and furthermore, it can be used for a long time without replacing the LED light source.

In addition, according to the present invention, the power consumption can be reduced by reducing the intensity of the current input to the LED light source of the backlight unit while maintaining high brightness in the liquid crystal display device.

In addition, according to the present invention, since the reflective polarizing film having selective reflection characteristics of the G and B wavelength bands is used in implementing the backlight unit, all of the reflective polarizing films having selective reflection characteristics of the R, G and B wavelength bands are required. The manufacturing process is simplified and more advantageous in terms of manufacturing cost than the prior art.

Hereinafter, a detailed description of a preferred embodiment of the present invention will be described with reference to the accompanying drawings. In the backlight unit according to the present invention, the spirit of the present invention may be widely applied to any structure commonly used in liquid crystal display devices. Therefore, the backlight unit described below is provided as an example for explaining the present invention as a basic structure of the element used in the liquid crystal display device.

Furthermore, in the following description of the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

1 is a cross-sectional view of a backlight unit according to an exemplary embodiment of the present invention.

Referring to FIG. 1, the backlight unit 100 according to the present invention includes a plurality of R, G, and B LED light sources 110 that generate light of red (R), green (G), and blue (B). It is disposed above the light source 110, and among the light generated by the light source 110, at least one randomly polarized light of the green (G) or blue (B) wavelength band selectively reflects and the red (R) wavelength band The polarized light of the polarized light of the green (G) or blue (B) wavelength band transmitted on the reflective polarization film 120 and transmitted through the reflective polarization film 120, The polarized light of the red (R) wavelength band is transmitted by converting into linearly polarized light in one direction and includes a phase delay layer 130 that transmits by converting into linearly polarized light in various directions. Here, the random polarized light is a light including both the right circular polarization and the left circular polarization, and the random polarization generated by the LED light source 110 is circular polarization in one direction when passing through the reflective polarization film 120, that is, left circular polarization or right circular polarization Only circularly polarized light in either direction is transmitted. Therefore, the light after passing through the reflective polarizing film 120 becomes circularly polarized light in either direction.

According to a preferred embodiment of the present invention, the backlight unit 100 of the present invention configured as described above is applied to a liquid crystal display (LCD) including an absorption polarizing film 140, the light emitted from the backlight unit 100 Incident on the absorption polarizing film 140. The absorption polarizing film 140 is positioned on the phase delay layer 130, and linearly polarized light in any one direction is transmitted as it is, and circularly polarized light is partially (the above-mentioned word) out of the light transmitted through the phase delay layer 130. Linearly polarized light in one direction is transmitted, and linearly polarized light in the other direction is absorbed. For example, the absorption polarizing film 140 used in the liquid crystal display device transmits linearly polarized light as it is, and transmits only 50% of circularly polarized light and absorbs the rest. This light absorption and transmission ratio can be adjusted.

The LED light source 110 generates light in R, G, and B wavelength bands. The LED light source 110 of the present invention is disposed under the backlight unit 100 to emit R, G, B light upward. The wavelength of the light emitted as described above may be set differently according to the type of impurities added to the semiconductor constituting the LED. For example, in the case of gallium phosphide, light emission involving zinc and oxygen atoms is red (R), and light emission involving nitrogen cost is green (G). White light may be realized by the combination of R, G, and B lights. In the embodiment of the present invention, the LED light source 110 is preferably implemented as a set of R, G, B LED light source, a plurality of sets are disposed under the backlight unit 100.

In order to optimally express colors in the liquid crystal display, it is important to optimally express white light by a combination of R, G, and B light incident on the liquid crystal panel (not shown) through the absorption polarizing film 140. For this purpose, theoretically, it is ideal to combine the intensities of R, G, and B light in the same ratio. Therefore, in theory, it is ideal that the intensity of R, G, B light emitted from the backlight unit 100 and passed through the absorption polarizing film 140 is 1: 1: 1. In practice, however, these ratios of R, G and B light intensities are difficult to implement. Therefore, in the exemplary embodiment of the present invention, a combination of R, G, and B light intensities for expressing white light may be sufficient to properly express colors in the liquid crystal display. The degree of the white light may be variously set according to the environment of the liquid crystal display.

To this end, in the embodiment of the present invention, the intensity of the current input to at least one LED light source is input to the other LED light source so that white light is emitted by a combination of R, G, and B light transmitted through the absorption polarizing film 140. It is desirable to be smaller than the strength of the current to be. More preferably, the intensity of the current input to the R LED light source is smaller than the intensity of the current input to the G or B LED light source 110. Furthermore, it is further preferable that the intensity input to the B LED light source is smaller than the intensity of the current input to the G LED light source. This will be described in more detail with reference to FIG. 3.

The reflective polarizer 120 is randomly polarized in the green (G) or blue (B) wavelength band among the red (R), green (G), and blue (B) light generated by the R, G, and B LED light sources 110. Selectively reflects at least one random polarized light among; More specifically, the light generated by the R, G, and B LED light sources 110 is randomly polarized light in the R, G, and B wavelength bands. The random polarized light consists of left circularly polarized light and right circularly polarized light. At this time, the reflective polarization film 120 reflects the random polarization in one direction of the random polarization and transmits the random polarization in the other direction. The randomly polarized light in one direction selectively reflected as described above is reflected back by the reflecting plate 111 disposed under the LED light source 110 and is converted into random polarized light in the other direction to transmit the reflective polarization film 120. do.

Accordingly, the reflective polarization film 120 of the present invention selectively reflects random polarization in one direction and transmits random polarization in the other direction to at least one random polarization of the G or B wavelength band. The reflected random polarized light is converted into random polarized light in the other direction by the reflecting plate 111 and then incident on the reflective polarizing film 120, and the above processes are repeated. Randomly polarized light (including left circularly polarized light and right circularly polarized light) in the R wavelength band is transmitted as it is. As described above, the light of at least one wavelength band of G or B among the R, G, and B light transmitted through the reflective polarization film 120 according to the present invention is either left circularly polarized light or right circularly polarized light having the same direction. Light in the wavelength band is randomly polarized light including left circularly polarized light and right circularly polarized light. In other words, in one embodiment of the present invention, the light of the R wavelength band among the R, G, and B lights may be randomly polarized light, and the light of the G and B wavelength bands may be either right circularly polarized light or left circularly polarized light. In another embodiment of the light of the R and G wavelength bands are randomly polarized light and the light of the B wavelength band may be either right-handed polarization or left circularly polarized light, and in another embodiment of the invention the light of the R and B wavelength band Is randomly polarized light and the light of the G wavelength band may be either right circularly polarized light or left circularly polarized light.

The reflective polarizer 120 of the present invention includes a cholesteric liquid crystal layer for selectively reflecting the visible light wavelength band. The cholesteric liquid crystal layer is composed of a curable nematic liquid crystal material and a curable chiral material, and the selective reflection wavelength band of the cholesteric liquid crystal layer may be adjusted according to the mixing ratio of the two materials. For example, when the mixing ratio of the curable nematic liquid crystal material and the curable chiral material is adjusted such that the selective reflection wavelength band center wavelengths of the cholesteric liquid crystal layer are 460 to 480 nm, 530 to 550 nm, and 590 to 650 nm, respectively, Even if only three cholesteric liquid crystal layers are stacked, all visible light regions can be covered efficiently.

Therefore, the reflective polarizing film 120 according to the present invention is a cholesteric liquid crystal layer selectively reflecting light in the green (G) wavelength band or a cholesteric liquid crystal layer selectively reflecting light in the blue (B) wavelength band. At least one of them may be formed by stacking. Since the stacking order of the at least one cholesteric liquid crystal layer is independent of the selective reflection wavelength band, there is no particular limitation on the stacking order. In general, when the nematic liquid crystal material and the chiral material are mixed to form a cholesteric liquid crystal layer, the higher the content of the chiral liquid crystal material is mixed, the shorter the wavelength band of the selective reflection in the reflective polarization film 120 is. As the content of the chiral liquid crystal material is lower, the wavelength band of the selective reflection is shifted to the longer wavelength band.

In one embodiment of the present invention, both the curable nematic liquid crystal material and the curable chiral material may be used as long as the liquid crystal material includes a mesogenic group representing the nematic liquid crystal. In addition, the chiral material may be any material having chiral carbon in a conventional nematic liquid crystal, and is not limited to a specific material. Here, curable is possible as long as it is a substance having a reactive group capable of thermal curing or photocuring in the molecular structure. For example, in the case of thermosetting, a combination of monomers including vinyl groups such as vinyl group, acryl group and methacryl group or having various reactive groups capable of condensation polymerization may be used. As the photocurable, a reactive group crosslinkable by ultraviolet rays such as a vinyl group, an acryl group, and an aryl group can be used. Furthermore, an initiator etc. can also be used at the time of hardening.

In addition, as another embodiment of the present invention, the reflective polarizing film 120 of the present invention may be formed of one cholesteric liquid crystal layer. That is, one cholesteric liquid crystal layer has a longer wavelength or shorter wavelength pitch from the lower portion to the upper portion so as to selectively reflect at least one or more of the light of the green (G) wavelength band or the light of the blue (B) wavelength band, respectively. By including one cholesteric liquid crystal layer having a different selective reflection wavelength band can be set.

As described above, in the preferred embodiment of the present invention, the curable nematic liquid crystal material and the curable chiral material are mixed at a specific ratio, so that the circle of the wavelength band of at least one of green (G) or blue (B) in the reflective polarization film 120 is formed. Allows for selective reflection of polarization.

The phase delay layer 130 is stacked on the reflective polarization film 120 and is configured to convert circularly polarized light in one direction transmitted through the reflective polarization film 120 into linearly polarized light and emit the light. In particular, the phase delay layer 130 according to the present invention, the circularly polarized light of at least one wavelength band of G or B transmitted through the reflective polarization film 120 is converted to linearly polarized light in any one direction and transmitted, Polarization is made to transmit by converting into linearly polarized light having various directions. Therefore, light in the G or B wavelength band transmitted through the phase delay layer 130 is linearly polarized light in one direction, and light in the R wavelength band is linearly polarized light in various directions. In this case, the linearly polarized light in various directions includes any one of the above directions and at the same time includes other directions. As a result, the absorption polarizer 140 may transmit only R, G, and B linearly polarized light in any one of R, G, and B light, and absorb R linearly polarized light in the other various directions. The phase retardation layer 130 serves to change the circularly polarized light transmitted through the reflective polarization film 120 into linearly polarized light by performing the same role as the conventional retardation plate. For example, the phase delay layer 130 of the present invention converts circularly polarized light transmitted through the reflective polarization film 120 into lambda / 4 phase delay and converts the linearly polarized light into linearly polarized light.

In the embodiment of the present invention, the phase delay layer 130 may use various materials for λ / 4 phase delay. For example, a stretched polymer film can be used. In the present invention, the stretched polymer film is not particularly limited in its component or structure, but preferably includes a thermoplastic polymer. The thermoplastic polymer may be used alone or in combination of two or more kinds thereof. As the thermoplastic polymer, for example, polyolefin (polyethylene, polypropylene, etc.), polynorbornene-based polymer, polyester, polyvinyl chloride, polystyrene, riacrylonitrile, polysulfone, polyallylate, polyvinyl alcohol, polymethacryl Acid ester, polyacrylic acid ester, cellulose ester, these copolymers, etc. can be used. Alternatively, in the present invention, the nematic liquid crystal layer may be used as the phase delay layer 130.

When the linearly polarized light emitted from the backlight unit 100 according to the present invention is incident on the upper absorbing polarizing film 140, the absorbing polarizing film 140 is one of G or B transmitted through the phase delay layer 130. The linearly polarized light in at least one wavelength band is transmitted, and in the case of circularly polarized light in the R wavelength band, only linearly polarized light in any specific direction is transmitted, and linearly polarized light in the other direction is absorbed. For example, 50% of circularly polarized light in the R wavelength band absorbs and the other is transmitted. Therefore, after passing through the absorbing polarizing film 140, the linearly polarized light of the G or B wavelength band is maintained as the light intensity, but the circularly polarized light of the R wavelength band is light intensity than when incident on the absorbing polarizing film 140 Decreases (50% decreases in the above example). As described above, in the light of the R, G, and B wavelength bands transmitted through the absorption polarizing film 140, when the intensity of the light in the R wavelength band is relatively decreased, the white light may not be optimally expressed in the liquid crystal display device. The present invention is to optimize the combination of R, G, B light by appropriately adjusting the intensity of the R, G, B light for the optimal expression of such white light.

2 is a cross-sectional view of a backlight unit according to another exemplary embodiment of the present invention.

2, the backlight unit 200 according to another embodiment of the present invention is positioned on the LED light source 110 in the backlight unit 100 described with reference to FIG. 1 and receives light generated from the LED light source 110. It further comprises a diffusion plate 150 for diffusing and an optical sheet layer 160 for collecting the light diffused by the diffusion plate 150 to be emitted to the reflective polarizing film (120).

The diffuser plate 150 serves to diffuse the light generated from the plurality of R, G, B LED light source (110). As a result, the light transmitted through the diffusion plate 150 is uniformly diffused and emitted upward. The diffusion plate 150 may be implemented by applying a resin layer containing a plurality of beads (beads) to the lower portion of the base film. In other words, light is emitted in an arbitrary direction by the beads to cause light diffusion.

The optical sheet layer 160 is positioned on the diffuser plate 150 to increase luminance by condensing the light diffused by the diffuser plate 150 and upward. Although not shown in the drawing, two optical sheet layers 160 of the present invention are preferably disposed up and down. At this time, it is preferable that the individual patterns constituting the optical sheet layer 160 made up and down cross each other perpendicularly. This ensures a viewing angle vertically and horizontally. In addition, it is preferable that each optical microstructure constituting the optical sheet layer 160 has one cross section of a triangle, an arc shape, and a quadrangle in projecting the cross section.

3 is a view illustrating a change in light intensity in the backlight unit according to the present invention.

Referring to FIG. 3, in the backlight unit 100 according to the present invention, light of red (R), green (G), and blue (B) wavelength bands is generated by a plurality of R, G, and B LED light sources 110. . These lights are incident on the upper reflective polarizing film 120. At this time, the incident red (R), green (G), and blue (B) light are all randomly polarized and include left circularly polarized light and right circularly polarized light. As such, the R, G, and B light incident on the reflective polarizing film 120 are preferably combined at a ratio suitable to generate white light. In the present invention, as an example, the conditions for generating white light will be described assuming that the ratio of the R, G, and B light intensities is I _R : I _G : I _B. For example, I _R : I _G : I _B may be 1: 1: 1, and of course, white light may be generated at other ratios.

The reflective polarization film 120 transmits the random polarized light of the R wavelength band as it is among the random polarized light of the R, G, and B wavelength bands, and selectively reflects the random polarized light of at least one of the G or B wavelength bands. More specifically, the left circularly polarized light (or right circularly polarized light) is reflected among the randomly polarized light in the G or B wavelength band and the right circularly polarized light (or left circularly polarized light) in the opposite direction is transmitted. In this case, the reflected left circularly polarized light (or right circularly polarized light) is reflected by the lower reflector 111 to be converted back into randomly polarized light (including right circularly polarized light and left circularly polarized light), which is then incident on the reflective polarizing film 120 to be the same as above. In principle, transmission and reflection occur repeatedly. Finally, light in the R wavelength band transmitted through the reflective polarization film 120 is randomly polarized light, and light in the G or B wavelength band is circularly polarized light (either left or right circularly polarized light).

At this time, assuming that the ratio of the R, G, and B light intensities generated by the R, G, and B LED light sources 110 is I _R : I _G : I _B , all of the R, G, and B light are reflected polarization films 120. Therefore, the ratio of the R, G, B light intensity after passing through the reflective polarizing film 120 is also I _R : I _G : I _B. However, circularly polarized light in the R wavelength band transmitted through the reflective polarization film 120 includes both left circularly and rightly polarized light, whereas circularly polarized light in the G or B wavelength band includes only one of the left and right circularly polarized light.

The phase delay layer 130 transmits the circularly polarized light of at least one wavelength band of G or B by converting it into linearly polarized light in one direction, and the linearly polarized light of the R wavelength band is linearly polarized in various directions including the above one direction. Switch to and transmit. More specifically, since the circularly polarized light in the R wavelength band includes both the left and right circularly polarized light, the polarized light in the G or B wavelength band is transmitted by converting it into linearly polarized light in various directions. Since only polarized light is included, it is converted into linearly polarized light in one direction and transmitted. In the phase delay layer 130, all of the light in the R, G, and B wavelength bands are transmitted, and the ratio of the light intensities thereof is also I _R : I _G : I _B.

However, light in the R wavelength band transmitted through the phase delay layer 130 is linearly polarized light in various directions, and light in the G or B wavelength band is linearly polarized light in any one direction. Therefore, the absorption polarizing film 140 transmits the linearly polarized light of the G or B wavelength band transmitted through the phase delay layer 130 as it is, and the circularly polarized light of the R wavelength band is partially (the direction of the polarized light of the G or B linearly The linearly polarized light is transmitted and the rest (the linearly polarized light different from the G or B linearly polarized light) is absorbed. Therefore, in the embodiment of the present invention, the light of the G or B wavelength band is transmitted as it is to maintain the light intensity, but the light of the R wavelength band is absorbed a part of the light intensity is reduced. For example, when the absorbing polarizing film 140 absorbs 50% of light, only 50% of light in the R wavelength band is transmitted. In this case, the light in the R, G, and B wavelength bands that have passed through the absorption polarizing film 140 has a ratio of light intensity of I _R / 2: I _G : I _B. Such a change in the light intensity ratio may cause a problem in the overall color reproduction.

The inventors of the present invention have repeatedly carried out various experiments in order to make the ratio of light intensity substantially the same by paying attention to the change of light intensity. The inventors of the present invention reduce the light intensity of G or B light relative to the light intensity of R light in order to set the ratio of R, G, B light intensity to I _R : I _G : I _{B which} is a condition for generating white light under the above conditions. Considered. To this end, the present inventors have been able to solve this problem through the relationship between the intensity of light generated from the LED light source and the intensity of current input to the LED light source. That is, as shown in Figure 4, the intensity of the current input to the LED light source and the light intensity has a proportional relationship. That is, as the current input to the LED light source increases (I1-> I2), the light intensity of the LED light source increases (T1-> T2), and the light intensity saturates at a constant current. In general, the voltage for turning on the LED light source is slightly different depending on the LED color, brightness, and the like. Normally, the driving voltage of LED needs 1.8 ~ 5V. The smaller the light intensity, the longer the lifetime of the LED. For example, when comparing the lifespan in A and B in the drawing, the service life of 50,000 hours is shown for A having a relatively high light intensity, while the service life of 80,000 hours is obtained for B having a relatively low light intensity. Increases. This applies to conventional LEDs.

Therefore, the light intensity is reduced by relatively reducing the intensity of the current input from the R, G, B LED light source 110 to the G, B LED light source, but the light intensity ratio of I _R / 2: I _G : I _B is reduced to I _R. / 2: I _G / 2: I _B / 2, that is, I _R : I _G : I _B.

For this purpose, it is preferable that the intensity of the current input to the at least one LED light source of G or B is smaller than the intensity of the current input to the R LED light source. In addition, considering that the B LED light source has a shorter lifetime than the G LED light source, the intensity of the current input to the B LED light source may be relatively smaller than the intensity of the current input to the G LED light source.

As described above, in the present invention, the LED light source having different intensities of the current input to the at least one LED light source 110 so that the predetermined white light is emitted by the combination of the R, G, and B light passing through the absorption polarizing film 140. It is preferable to reduce the intensity of the G or B light by reducing the intensity of the current input to at least one of the G or B LED light source than the intensity of the current input to the R LED light source. The light intensity ratio of the R, G, B light is set to I _R : I _G : I _B which is a ratio for optimal white light generation. As a result, the color and luminance problems of the liquid crystal display device can be solved, and thus the service life of the LED can be increased. In addition, it is possible to reduce the power consumption of the LED light source as a whole by reducing the intensity of the current used.

Furthermore, the reflective polarizing film 120 according to the present invention does not include a cholesteric liquid crystal layer of three R, G, and B sheets for selective reflection of the R, G, and B wavelength bands as in the prior art. By providing only the cholesteric liquid crystal layer of at least one of G or B for selective reflection of the wavelength band there is an advantage in the manufacturing process and production cost.

In addition, in another embodiment of the present invention, as shown in Figure 5 (a), it may further include an optical sheet layer 170 on the reflective polarizing film 120 and the phase delay layer 130. The optical sheet layer 170 has a fine microstructure pattern formed on the upper surface thereof to collect light transmitted through the phase delay layer 130 to emit upward. The optical sheet layer 170 can effectively suppress the scattering phenomenon caused by the passage of light can improve the brightness in the liquid crystal display device. Meanwhile, in another embodiment of the present invention, as shown in FIG. 5B, another optical sheet layer 180 may be further included below the reflective polarizing film 120 and the phase delay layer 130. have. The optical sheet layer 180 has the same function as above. Further, although not shown in the drawing, the optical sheet layer may be further included on the lower portion of the reflective polarizing film 120 and the upper portion of the phase delay layer 130 at the same time.

The individual optical microstructures constituting the optical sheet layers 170 and 180 may have various cross-sectional shapes of triangles, arcs, squares, polygons, and the like. These patterns preferably have a prism shape.

6 is a graph showing the ratio of the R, G, B light intensity generated from the LED light source and the ratio of the R, G, B light intensity transmitted through the absorption polarizing film in the backlight unit according to the present invention.

Referring to Figure 6 (a), the light intensity of the R, G, B random polarization generated in the R, G, B LED light source 110 is I _R : I _G : I _B ( Shown as 1). Figure 6 (b) shows the ratio of the R, G, B light intensity transmitted through the absorption polarizing film in the prior art, Figure 6 (c) shows the ratio of R, G, B light intensity transmitted through the absorption polarizing film according to the present invention The ratio is shown. In Figure 6 (b) it can be seen that the light intensity ratio of the R, G, B light transmitted through the absorption polarizing film is I _R / 2: I _G : I _B. In this case, since the intensity of R light is relatively small compared to the intensity of G and B light, the quality is deteriorated in terms of reproduction of white light.

However, in Figure 6 (c) by reducing the current input to the G, B LED light source, although the intensity of the R, G, B light transmitted through the absorption polarizing film is reduced to 1/2 (X-> Y), R, It can be seen that the ratio of G and B light intensity is a ratio of I _R : I _G : I _B. This is equal to the ratio of I _R : I _G : I _{B, which} is the intensity of R, G, B light emitted to generate white light from the first R, G, B LED light source 110, thereby providing excellent white light representation and color reproduction. It can solve the imbalance of R, G, B color in.

In FIG. 6 (ac), the light intensity ratio of I _R : I _G : I _B is reproduced by reducing the intensity of G and B light to reproduce white light, but in other embodiments of the present invention, at least one of G or B It has been described above that the white light can be reproduced by reducing the light intensity of I _R : I _G : I _B to realize the light intensity ratio of I _R : I _G : I _B.

Although the present invention described above has been described in detail through the preferred embodiments, the present invention is not limited to the content of these embodiments. Those skilled in the art to which the present invention pertains may, although not shown in the examples, imitate or improve various inventions within the scope of the appended claims, all of which fall within the technical scope of the present invention. Belonging will be too self-evident. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

In the display field, the use of LCD is expanding, and high brightness and high definition LCD products are appearing. Since the LCD is a light receiving element, a separate light source is required. LEDs have recently been spotlighted as LCD light sources because they are smaller and have a longer lifespan than conventional light sources (eg, fluorescent lamps) and have low power and efficiency because electrical energy is directly converted into light energy. However, in general, at least one of the G or B LED light source in the R, G, B LED light source has a short lifespan, there is a need to replace the light source when using a long time.

Therefore, according to the present invention, since the power consumption can be reduced while extending the lifespan of the LED light source, it may be usefully used in future LCD devices. Furthermore, in applying the backlight unit according to the present invention to the LCD, since a reflective polarizing film having a selective reflection characteristic of at least one wavelength band of G or B is implemented, reflection having a selective reflection characteristic of a conventional R, G, and B wavelength band Since it is more advantageous in terms of manufacturing cost than the polarizing film, it may be more advantageously applied to LCD devices in the future.

1 is a cross-sectional view of a backlight unit according to an exemplary embodiment of the present invention.

2 is a cross-sectional view of a backlight unit according to another exemplary embodiment of the present invention.

3 is a view illustrating a change in light intensity in the backlight unit according to the present invention.

4 is a graph showing the relationship between the intensity of the current and the intensity of the LED light in the LED light source according to the present invention.

5 is a cross-sectional view of a backlight unit according to another exemplary embodiment of the present invention.

6 is a graph showing the ratio of the R, G, B light intensity generated from the LED light source in the backlight unit according to the present invention and the ratio of the R, G, B light intensity transmitted through the absorption polarizing film.

Claims (12)

In a direct type backlight unit used in a liquid crystal display device including an absorption polarizing film that transmits linearly polarized light in a specific direction and absorbs the remaining light, Multiple R, G, B LED light sources; A reflective polarizing film for selectively reflecting at least one randomly polarized light of the G and B wavelength bands generated by the LED light source and transmitting the randomly polarized light of the R wavelength band; And Located on the reflective polarizing film, the circularly polarized light of the G or B wavelength band transmitted through the reflective polarizing film is converted into linearly polarized light in one direction, and the circularly polarized light of the R wavelength band is converted into linearly polarized light in various directions. A phase delay layer that transmits the light to the absorption polarizing film; Including; The intensity of the current input to the at least one LED light source to emit white light by the combination of R, G, B light passing through the absorption polarizing film is less than the intensity of the current input to the other LED light source. The method of claim 1, And a ratio of the R, G, B light intensity transmitted through the absorption polarizing film is the same as the ratio of the R, G, B light intensity generated by the R, G, B LED light source. The method of claim 1, A backlight unit, characterized in that the intensity of the current input to the G and B LED light source is less than the intensity of the current input to the R LED light source. The method of claim 3, A backlight unit, characterized in that the intensity of the current input to the B LED light source is less than the intensity of the current input to the G LED light source. The method of claim 1, And the R linearly polarized light in various directions switched by the phase delay layer includes R linearly polarized light in the same direction as the converted G or B linearly polarized light. The method of claim 1, The plurality of R, G, B LED light source is a backlight unit, characterized in that each of the R, G, B LED light source is made of one set and arranged in a plurality of sets. The method of claim 1, A diffuser plate configured to diffuse light emitted from the R, G, and B LED light sources; And An optical sheet layer condensing light diffused by the diffusion plate and outputting the light to the reflective polarizing film; Backlight unit, characterized in that it further comprises. The method of claim 7, wherein And at least one of an upper and a lower portion of the optical sheet layer, further comprising another optical sheet layer having an optical microstructure intersecting with the optical microstructure of the optical sheet layer. The method of claim 7, wherein Each optical microstructure constituting the optical sheet layer has a cross section of one of a triangle, an arc, and a quadrangle when projecting the cross section. The method of claim 1, wherein the reflective polarizing film, A backlight unit comprising at least one cholesteric liquid crystal layer of a cholesteric liquid crystal layer for selectively reflecting circularly polarized light in the G wavelength band or a cholesteric liquid crystal layer for selectively reflecting circularly polarized light in the B wavelength band. The method of claim 1, wherein the reflective polarizing film, And a cholesteric liquid crystal layer having a long wavelength or short wavelength pitch while going from bottom to top to selectively reflect circularly polarized light in the G and B wavelength bands. A liquid crystal display device comprising the backlight unit according to any one of claims 1 to 11.

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