KR100742125B1 - Back light unit - Google Patents

Abstract

The backlight unit according to the present invention provides a backlight unit that increases brightness by using optical resonance, and makes light mixing more efficient.

The present invention provides a printed circuit board, a plurality of light emitting diodes spaced apart from each other on the printed circuit board, a total reflection layer for reflecting light emitted from the light emitting diodes in an upward direction of the light emitting diodes, and formed and irradiated on top of the light emitting diodes. It includes an optical layer that transmits a part of the light and reflects a part of the irradiated light in a downward direction of the printed circuit board, thereby inducing optical resonance of light emitted from the light emitting diode.

As a result, the power consumption of the backlight unit requiring high luminance white light is reduced, and the lifetime of the backlight unit is increased, and the half width of the spectral histogram for each color on the emission spectrum is reduced by using optical resonance. Thus, color purity is improved, and desired spectral peaks can be realized by adjusting thicknesses of the optical layer and the total reflection layer.

Back light unit, light emitting diode, optical resonance

Description

Back light unit {BACK LIGHT UNIT}

       1 is a front view of an LCD module according to the prior art,

       2 is a perspective view showing the shape of a backlight unit according to an embodiment of the present invention;

3 is a plan view of a part of the backlight unit according to the present invention;

4 is a plan view of a part of a backlight unit having side reflections according to an embodiment of the present invention;

5 is a plan view of a part of a backlight unit having side reflections according to an embodiment of the present invention;

6 is a graph showing the light absorption rate according to the light wavelength of the optical layer according to an experimental example of the present invention,

7 is a graph showing the light absorption rate according to the light wavelength of the optical layer according to an experimental example of the present invention,

8 is a graph showing the luminance according to the light absorption rate according to the experimental example of the present invention;

<Explanation of symbols on main parts of the drawings>

30: printed circuit board 40: light emitting diode

50: total reflection layer 60: optical layer

70: side reflector

The present invention relates to a backlight unit, and more particularly to a backlight unit for increasing the brightness by using optical resonance.

CRT (Cathode Ray Tube), which is one of the commonly used display devices, is widely used in televisions and computer monitors, but the weight and volume of the CRT itself do not meet the recent trend of miniaturization and light weight of electronic products.

Various technologies have been developed to replace existing CRT displays. Liquid crystal displays (LCD) using electro-optic effects, plasma display panels (PDP) using gas discharge, and electroluminescent effects The EL display device (ELD, Electro Luminescence Display) using the is.

Among them, LCDs are rapidly expanding their range of application due to improvements in liquid crystal materials and development of micropixel processing technology along with features such as light weight, thinness, and low power consumption. Widely used in large flat-panel televisions and the like.

However, most liquid crystal display devices require a separate backlight unit as a matting element for displaying an image by controlling an amount of a light source coming from the outside.

As shown in FIG. 1, the LCD module 1 used in a general LCD includes a liquid crystal display panel 2 into which liquid crystal is injected, and a polarizing plate 4a for polarizing light on upper and lower surfaces of the liquid crystal display panel 2. 4b), a backlight unit 6 for supplying a constant light to the liquid crystal display panel 2, a support main 8a and a top case 8b for maintaining the external appearance of the LCD module 1. FIG.

Unlike the CRT or PDP, the liquid crystal display panel 2 mounted on the LCD only changes the arrangement of liquid crystals by applying power, and the liquid crystal display panel 2 itself does not emit light, thereby uniformly irradiating the information display surface. The backlight unit 6 is provided behind the liquid crystal display panel 2.

Here, the backlight unit is divided into an edge type and a direct type according to the position of the light source.

As shown in Figure 2 (a), the light source 12 is provided at the edge of the light guide plate 14 for irradiating light, the direct type is a point light source as shown in Figure 2 (b) Is mounted on a printed circuit board, or a line light source is mounted on a printed circuit board as shown in FIG. 2 (c). As a result, the light source is distributed over the entire surface.

Here, EL (Electro Luminescence), CCFL (Cold Cathode Fluorescent Lamp), or HCFL (Hot Cathode Fluorescent Lamp), etc. are used as light sources. Light emitting diodes (LEDs) are widely used.

As a method of using a light emitting diode as a light source in a backlight unit, first, a method using a blue light emitting diode and a YAG (Yttrium Aluminum Garnet (YAG) phosphor), and second, a red, green, and blue light emitting diode emitting UV light. Third, a method of using phosphors and a method of mixing light emitted from each light emitting diode using a red light emitting diode, a green light emitting diode, and a blue light emitting diode have been studied.

Here, the method of using a blue light emitting diode and a YAG phosphor has a poor red expression ability and a low luminous efficiency, and the method of using red, green, and blue phosphors in a light emitting diode emitting ultraviolet light is difficult to develop a phosphor and is thermal. The property is not good.

In addition, the method using the red light emitting diode, the green light emitting diode, and the blue light emitting diode has a high intensity of the red light, the green light, and the blue light emitted from each light emitting diode, so that a wide color reproduction range can be designed, but the white surface light source is constituted. There is a problem that a combination of light emitting diodes must be achieved.

In addition, in accordance with the recent trend toward larger size and higher image quality of display devices, in order to meet the high luminous flux output demand of the backlight, lenses, chips, and materials for manufacturing light emitting diodes for concentrating light emitted from each light emitting diode are provided. The light emitting diode is a solid element that converts electrical energy into light energy, and generally includes a doping layer and an active layer.

When a bias is applied across two opposing doped layers, holes and electrons are injected into the active layer and then recombined to generate light.

Light generated in the active region is emitted in all directions and escapes out of the semiconductor chip through all exposed surfaces.

The backlight unit including the light emitting diode directs the light escaping from the light emitting diode in the direction of output of the desired light.

However, the light emitting diodes developed to date have not been able to obtain sufficient luminous efficiency due to the light loss due to the degree of transmission in the current diffusion layer and the light loss due to total reflection at the interface where light is emitted.

Therefore, in order to use a light emitting diode in a backlight requiring high luminous flux output, a method of applying a high current to the light emitting diode or increasing the number of light emitting diodes is used.

However, when a high current is applied to the light emitting diode, a large amount of heat is generated in the light emitting diode, so that the light emitting efficiency is reduced, so that a separate heat dissipation design is required on the printed circuit board on which the light emitting diode is mounted. In this case, there is a problem in that the design of the backlight unit becomes difficult and the production cost of the backlight unit increases.

In addition, although a light emitting diode using a nitride semiconductor series or InGaAIP has been developed to increase the light emitting efficiency of the light emitting diode, there is a problem that it is difficult to use the backlight unit because the luminous flux is lower than that of the CCFL.

The present invention has been made to solve the above problems, and an object thereof is to provide a backlight unit for improving light efficiency and color purity of a backlight by using optical resonance.

The backlight unit of the present invention for achieving the above object is a printed circuit board, a plurality of light emitting diodes arranged spaced apart from each other on the printed circuit board, the light formed on the lower side of the printed circuit board and irradiated with the upper side of the printed circuit board A total reflection layer reflecting in a direction and an optical layer formed on an upper side of the printed circuit board to transmit a portion of the irradiated light and reflecting a portion of the irradiated light in a downward direction of the printed circuit board. Induces optical resonance of emitted light.

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

3 is a plan view of a part of the backlight unit according to the present invention, Figures 4 to 5 is a plan view of a part of the backlight unit is formed with a side reflection portion according to the present invention, Figures 6 to 7 is an experiment of the present invention FIG. 8 is a graph showing light absorption according to light wavelength of an optical layer according to an example, and FIG. 8 is a graph showing luminance according to light absorption according to an experimental example of the present invention.

As shown in FIG. 3, the backlight unit 200 according to the present invention includes a printed circuit board 30, a plurality of light emitting diodes 40, which are spaced apart from each other on the printed circuit board 30, and a light emitting diode ( The total reflection layer 50 reflects the light irradiated from the upper side of the light emitting diode 40 to the upper side of the light emitting diode 40 and a portion of the irradiated light formed on the upper side of the light emitting diode 40 to transmit the light. It includes an optical layer 60 for reflecting in the downward direction of the printed circuit board 30.

The printed circuit board 30 having the pattern supports the light emitting diode 40 and simultaneously emits heat generated from the light emitting diode 40.

A plurality of spaced apart light emitting diodes 40 is mounted on the printed circuit board 30, and a total reflection layer 50 is formed under the light emitting portion 41 of the light emitting diode 40.

The total reflection layer 50 may be bonded to the upper side of the printed circuit board 30 on which the light emitting diode 40 is mounted. The total reflection layer 50 may be formed by bonding a reflector film having a high reflectance to an aluminum plate. The film has a high reflectance such that the reflectance is at least 80% or more, and it is preferable that the film has a low water absorption and a low transmittance.

On the upper side of the light emitting diode 40 and the total reflection layer 50 is formed an optical layer 60 that transmits a portion of the light irradiated at a predetermined optical distance d and reflects a portion of the light. The distance d between the 50 and the optical layer 60 is determined by the following equation so that light passing through the optical layer 60 can achieve constructive interference.

Where n is the refractive index of the total reflection layer 50 or the optical layer 60, t is the geometric thickness of the total reflection layer 50 or the optical layer 60, λ is the peak wavelength of the light emitted from the light emitting diode 40, m is an integer of 0 or more.

In the case where the light emitted from the light emitting diode 40 is red light, green light, or blue light, an integral multiple of the half wavelength of the peak wavelength of each color light is a total reflection layer 50 and an optical layer in order for the red light, green light, or blue light to construct constructive interference. When the sum of the products of the refractive indices and the geometric thicknesses is equal to 60, the light passing through the optical layer 60 is subjected to constructive interference, thereby causing optical resonance.

Accordingly, the luminance of light emitted from the backlight unit 200 is increased, and the half width of the spectral histogram for each color on the emission spectrum is reduced, thereby improving color purity.

Here, of course, the desired spectral peak can be obtained on the emission spectrum by adjusting the thickness of the total reflection layer 50 or the optical layer 60.

The maximum transmission amount Tmax according to the resonance effect generated by adjusting the optical distance d between the total reflection layer 50 and the optical layer 60 is confirmed by the following equation.

Here, T ₁ and R ₁ are the transmittance and reflectance of the optical layer 60, T ₂ and R ₂ are the transmittance and reflectance of the total reflection layer 50, k is the extinction coefficient, t is the geometric thickness, θ is the optical layer (60) ) And the angle of light propagating from the inside to the outside between the total reflection layer 50 and λ are wavelengths of light emitted from the light emitting diode 40.

Therefore, when the maximum transmittance is calculated, it is possible to design an optical layer capable of obtaining a corresponding reflectance.

Light emitted from one light emitting diode 40 mounted on the printed circuit board 30 is partially transmitted through the optical layer 60 in the optical layer 60 to be emitted to the outside of the optical layer 60, and the rest is Reflected by the optical layer 60 and proceeds back to the total reflection layer 50, at this time, the light that is advanced to the total reflection layer 50 is reflected by the total reflection layer 50 to proceed to the optical layer 60 again.

Such transmission and reflection are repeated, and the light emitted from the light emitting diode 40 is amplified by the light emitted through the optical layer 60 and emitted to the outside of the optical layer 60, thereby amplifying the optical layer 60. ) Is dimmed to the outside.

In addition, the light path becomes longer, so that the light mixing is more efficient in the case of irradiating white light by using a red light emitting diode, a green light emitting diode, and a blue light emitting diode and mixing the light emitted from each light emitting diode. Will be done.

Therefore, the higher the reflectance of the light propagated to the total reflection layer 50, the higher the transmittance and the lower the absorbance, the better.

In addition, the optical layer 60 may be a method using a metal layer to perform both transmission and reflection.

When the optical layer 60 is designed, it is preferable to minimize light absorption of the optical layer 60 in order to prevent light loss from occurring. In the case of forming the optical layer 60 using the metal layer, the metal layer may be formed. It is preferable to form in the form of a metal thin film.

In addition, as shown in FIG. 4, in order to prevent light emitted from the light emitting diode 40 from leaking out to the side surface between the front reflection layer 50 and the optical layer 60, the total reflection layer 50 and the optical layer ( 60 may be further connected to the side reflection part 70 included in the side of the backlight unit 200.

Like the total reflection layer 50, the side reflector 70 preferably has a higher reflectance, a lower transmittance and an absorptance, and back light emitted from the light emitting diode 40 and irradiated to the side reflector 70. Reflecting the inside of the unit 200 increases the amount of light emitted through the optical layer 60.

As shown in FIG. 5, the side reflection part 70 is preferably formed to face the outside of the backlight unit 200 when viewed from the total reflection layer 50 toward the optical layer 60.

Since light is emitted through the optical layer 60, the light irradiated to the side reflection part 70 is preferably reflected in the direction of the optical layer 60.

As shown in FIG. 5 (a), the side reflection part 70 may be in the form of a flat plate or a film, but may be formed in a bow shape as shown in FIG. 5 (b).

Referring to the specific experimental example for the formation of the optical layer 60 of the backlight unit 200 according to the present invention.

A light emitting diode with a 1W output power is used, with a red light emitting diode having a center wavelength of 627 nm, a green light emitting diode with a center wavelength of 530 nm, and a blue light emitting diode with a wavelength of 455 nm. According to the change in the center wavelength using a light emitting diode within 5%, the drive current is 200 mA.

The light emitting diode is mounted on a printed circuit board, and the mounted light emitting diode maintains an equal interval of 5 to 6 cm, and one light emitting diode set is used by using one red light emitting diode, one green light emitting diode, and one blue light emitting diode. Use

The optical layer 60 was formed by inserting a metal thin film. A metal layer made of silver (Ag) was formed at 21 nm, and an indium tin oxide (ITO) layer was formed at 160 nm.

In this case, as shown in FIG. 6, the maximum light absorption rate of the optical layer 60 was measured at 20%, and the light absorption rate was 11% in the silver metal layer, 5% in the ITO layer, and 4% in other interfaces. Was measured.

Here, as illustrated in FIG. 7, the TiO ₂ layer was further formed and the thickness of the TiO ₂ layer was changed. As a result, the thicker the TiO ₂ layer was, the lower the light absorption was, but the thickness of the TiO ₂ layer was increased. The light absorption rate decreased until 300 nm, but the light absorption rate increased again above 300 nm.

The decrease in the light absorption rate is directly related to the brightness of the light. As shown in FIG. 8, the light absorption rate is analyzed as a result of analyzing the result of increasing the brightness of the transmitted light according to the light absorption rate of the optical layer 60. It is understood that the lower the luminance is, the higher the luminance is.

Although described above with reference to preferred embodiments of the present invention, those skilled in the art will be modified and changed within the scope without departing from the spirit of the invention described in the claims below It should be understood that this can be done.

The backlight unit according to the present invention provides a backlight unit that increases brightness by using optical resonance, and makes light mixing more efficient.

As a result, the power consumption of the backlight unit requiring high luminance white light is reduced, and the lifetime of the backlight unit is increased, and the half width of the spectral histogram for each color on the emission spectrum is reduced by using optical resonance. Thus, color purity is improved, and desired spectral peaks can be realized by adjusting thicknesses of the optical layer and the total reflection layer.

Claims (5)

Printed circuit boards, A plurality of light emitting diodes spaced apart from each other on the printed circuit board; A total reflection layer reflecting light emitted from the light emitting diode in an upward direction of the light emitting diode; An optical layer formed on an upper side of the light emitting diode to transmit a part of the irradiated light, and reflecting a part of the irradiated light in a downward direction of the printed circuit board, The sum of the products of the refractive index and the thickness of each of the total reflection layer and the optical layer is an integer multiple of half the wavelength of the light emitted from the light emitting diode. The light emitted through the optical layer causes constructive interference Back light unit. delete The method of claim 1, The optical layer includes a metal layer for absorbing a portion of light irradiated to the optical layer. Back light unit. The method of claim 1, In order to prevent the light emitted from the light emitting diode from leaking out to the side surface between the total reflection layer and the optical layer, the side reflection portion is connected to the total reflection layer and the optical layer, and included in the side of the backlight unit doing Back light unit. The method of claim 4, wherein The side reflection part is formed to face the outside of the backlight unit when viewed in the direction of the optical layer from the total reflection layer Back light unit.

Images