KR20080113562A - Back light unit and display device comprising the same - Google Patents

Abstract

A backlight unit of a display device is provided to minimize the light loss by forming a plurality of reflecting plates in a reflecting plate array. A backlight unit comprises a light source(100), and a reflecting plate array(120). The reflecting plate array has a plurality of reflecting plates(120a~120i) which reflect light from the light source to a light guide plate(110). The backlight units are placed at least two planes of the light guide plate. The backlight unit comprises a light diffusing plate.

Description

Back light unit and display device comprising the same

1 is a view schematically showing a first embodiment of a backlight unit according to the present invention,

2 is a view schematically showing a second embodiment of a backlight unit according to the present invention;

3 is a diagram showing the reflectance of each reflecting plate of the third embodiment of the backlight unit according to the present invention;

4 is a diagram showing the reflectance of each reflecting plate of the fourth embodiment of the backlight unit according to the present invention;

5 is a view showing the refraction of light in the reflector of the backlight unit according to the present invention,

6 is a view showing a step in the reflection plate array of the backlight unit according to the present invention,

7 is a view showing interference of light in the reflector of the backlight unit according to the present invention.

<Explanation of symbols for main parts of the drawings>

100: laser light source 110: light guide plate

120: reflector array 120a: first reflector

500a ~ 500q: Reflector

The present invention relates to a display device, and more particularly to a backlight unit of the display device.

Liquid crystal displays (hereinafter referred to as "LCDs") are electric devices that transmit various electrical information generated by various devices to visual information by using a change in transmittance of the liquid crystal according to an applied voltage. LCD is a kind of flat panel display that is widely used because it does not have self-luminous and needs backlight, but it consumes less power and is convenient to carry.

The Back Light Unit is a surface light source system incident on the LCD, and its purpose is to create a uniform light distribution. Conventionally, a cold cathode fluorescent lamp (CCFL) or a light emitting diode (LED) has a large light distribution, and various technologies have been developed for improvement. In addition, there is an effort to use a laser having good color reproducibility as a light source due to the development of technology for realizing color gamut.

However, when a light source such as a laser having good linearity is used for the backlight unit, it is very difficult to increase the area for the light quantity distribution. In constructing a backlight using a laser as a light source, an attempt has been made to separate light emitted from a laser into a plurality of light sources using a coupler and a plurality of optical fibers. However, using several optical fibers has the advantage of improving uniformity, which is one of the important performances of the backlight unit, with multiple light sources, such as using multiple LEDs. When focusing, there is a disadvantage in that the amount of light is reduced due to the light loss generated in the coupler.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a backlight unit and a display device including the same as having a plurality of light sources as one light source.

Still another object of the present invention is to provide a backlight unit for illuminating light emitted from one light source without light loss and a display device including the same.

In order to achieve the above object, the present invention provides a backlight unit comprising a reflector plate array having a light source and a plurality of reflecting plates reflecting light emitted from the light source to the light guide plate.

Here, the light source and the reflector array may be provided on at least two surfaces of the light guide plate.

The backlight unit may further include a diffuser configured to diffuse light reflected from the reflector plate array.

The reflector may reflect part of the incident light to the light guide plate and transmit the remaining light.

In addition, the reflector may increase in reflectance away from the light source, each reflector may reflect the same amount of light to the light guide plate, the reflector is grouped into at least two groups and each reflector of the group They may have the same reflectance.

Here, the plurality of reflecting plates are composed of the first to the M-th reflecting plate, the N-th reflecting plate (N is an integer greater than or equal to 2, M or less), the light emitted from the light source as much as the path or more changed in the N-1 reflector, It may be provided with a step with the N-1 reflector.

And, the step (d) is d = [t / cos {sin -1 (sin45 ° / n t)}] × sin - may be given by ^{{45 ° (sin -1 (sin45} ° / n t)}. (Where t is the thickness of the reflecting plate and n _t is the refractive index of the reflecting plate).

In addition, the plurality of reflecting plates may include first to Mth reflecting plates, and the Nth reflecting plate (N is an integer greater than or equal to 2 and less than or equal to M) so that light reflected from the Nth reflecting plate is not projected onto the N-1 reflecting plate. It may be provided.

According to another embodiment of the present invention, there is provided a light source; A diffuser for dividing the light projected from the point light source into a plurality of lights to project the light guide plate; A light guide plate for projecting light projected from the diffusion unit; And a panel on which an image signal is displayed.

Here, the diffuser may divide the light projected from the point light source into a plurality of lights and project the light to the light guide plate.

Hereinafter, with reference to the accompanying drawings, preferred embodiments of the present invention that can specifically realize the above object will be described.

The same components as in the prior art are given the same names and the same reference numerals for convenience of description, and detailed description thereof will be omitted.

1 is a view schematically showing a first embodiment of a backlight unit according to the present invention. A first embodiment of a backlight unit according to the present invention will be described with reference to FIG. 1.

The backlight unit according to the present embodiment includes a laser light source 100, a light guide plate 110, and a reflector plate array 120. The laser light source 100 may be another light source that emits light near parallel. In addition, the light guide plate 110 is a component that performs a uniform illumination function and brightness of the backlight unit. The light guide plate 110 uniformly transmits the light emitted from the laser light source 100 to the display panel. In addition, the reflector plate array 120 includes a plurality of reflector plates 120a to 120i. In FIG. 1, eight reflectors are formed, but a larger number of reflectors may be required depending on the size of the display panel or the light guide plate. In addition, when the reflective plate array 120 is provided on two or more surfaces of the light guide plate, the luminance may be further increased.

If the light emitted from the laser light source 100 having strong straightness is directly projected onto the light guide plate, it is not appropriate to serve as a surface light source coming from the front surface of the backlight. In FIG. 1, the light emitted from the laser light source 100 is partially reflected by the first reflecting plate 120a and proceeds to the light guide plate, and the other part passes through the first reflecting plate 120a to the second reflecting plate 120b. . In addition, part of the light is reflected and part of the second reflector 120b is projected. That is, in the embodiment illustrated in FIG. 1, since the light is reflected in the light guide plate direction in total of eight reflecting plates, the same effect as that of light projected from the eight point light sources onto the light guide plate may be obtained. In addition, using a larger number of reflectors can produce an effect similar to projecting light from a surface light source. If a diffuser (not shown) is provided between the reflective plate array 120 and the light guide plate, the light reflected by the reflective plate array 120 may be scattered and diffused to widely project the entire light guide plate.

2 is a view schematically showing a second embodiment of a backlight unit according to the present invention. A second embodiment of a backlight unit according to the present invention will be described with reference to FIG. 2.

In FIG. 2, the reflector array 120 includes 17 reflector plates 120a to 120q. The light 120a 'to 120q' reflected by each of the reflecting plates 120a to 120q is projected onto the light guide plate (not shown). Here, each reflector may be partially reflective or partially transmissive dielectric coating to perform the above-described partial transmission function. In this case, the light reflectance of each reflecting plate is 5.88%, and the light projected by the laser light source 100 is reflected by 5.88% of the first reflecting plate 120a and is projected onto the light guide plate. In addition, 94.12% of the light emitted from the laser light source 100 is projected onto the second reflector. The second reflector reflects 5.88% of the incident light, which corresponds to 5.534256 (94.12 × 5.88)% of the light emitted from the laser light source. As described above, each reflecting plate reflects 5.88% of incident light in the direction of the light guide plate and transmits 94.12% in the direction of the next reflecting plate.

Here, the amount of light reflected and transmitted by the 17 reflectors is shown in FIG. 2. In FIG. 2, about 5.88% of light is reflected by the first reflector and 94.12% of light is transmitted through the second reflector. As the light passes through the reflecting plate, the amount of reflected light decreases gradually. That is, when the amount of light reflected by the first reflector is 100 as shown in the figure, the distance from the light source decreases as the amount of light reflected from each reflector decreases. Specifically, each reflector reflects 94.12% of light than the reflector through which the light passes. That is, the productivity is improved by using a plurality of the same reflector, but the light distribution may not be uniform.

3 is a diagram showing the reflectance of each reflecting plate of the third embodiment of the backlight unit according to the present invention. Referring to FIG. 3, a third embodiment of a backlight unit according to the present invention will be described.

In FIG. 3, the reflector array 120 includes 17 reflector plates 120a to 120q, and the light 120a 'to 120q' reflected from each reflector plate 120a to 120q is projected onto the light guide plate. same. At this time, the reflecting plate becomes larger as the reflecting plate proceeds from the first reflecting plate 120a to the second reflecting plate 120b and the third reflecting plate 120c. Thus, as shown, the total reflectance of the seventeenth reflector 120q reaches 100%. Here, the reflectance of each of the first to seventeenth reflecting plate is as shown, it is natural that the reflectance is different if the number of reflecting plate is different. And, as shown in the graph of Figure 3, the amount of light reflected from each reflecting plate to the light guide plate is the same.

4 is a diagram showing the reflectance of each reflecting plate of the fourth embodiment of the backlight unit according to the present invention. A fourth embodiment of a backlight unit according to the present invention will be described with reference to FIG. 4 as follows.

In FIG. 4, the reflector array 120 includes 17 reflector plates 120a through 120q, and the light 120a ′ through 120q ′ reflected from each reflector 120a through 120q is projected onto the light guide plate as described above. . Here, the reflectivity of the first reflecting plate to the fifth reflecting plate is the same as 7%, the reflectance of the sixth reflecting plate to the ninth reflecting plate is the same as 10%, the reflectance of the tenth reflecting plate to the twelfth reflecting plate is the same as 21%, The reflectances of the thirteenth and fourteenth reflecting plates are the same at 21%. That is, the reflecting plates are grouped into several groups, and the reflectances of the reflecting plates belonging to each group are the same. At this time, the amount of light reflected by the reflecting plate belonging to each of the groups as shown there is some difference, there is no significant difference as in the embodiment shown in FIG. In addition, it is possible to simplify the type of the reflective coating of the reflector to increase the productivity while having a light uniformity of about 70% or more.

5 is a view showing the refraction of light in the reflector of the backlight unit according to the present invention, Figure 6 is a view showing the step of the reflector array of the backlight unit according to the present invention. The steps of the reflector array of the backlight unit according to the present invention will be described with reference to FIGS. 5 and 6 as follows.

In one embodiment of the backlight unit according to the present invention, the reflecting plate may be made by a method such as dielectric coating. Here, FIG. 5 illustrates the refraction of light in one reflective plate 500 constituting the reflective plate array. That is, if the refractive index of the reflecting plate is n _t , the light is refracted twice when it is incident on the reflecting plate 500 and when it is projected outward as shown by the arrow. Here, when the angle at which light enters the reflecting plate 500 (the angle between the normal line of the boundary plane and the incident light) φ is 45 °, the propagation angle of the light within the reflecting plate 500 (the angle between the normal line of the boundary plane and the refracted light) Is φ '. At this time, if the thickness of the reflecting plate 500 is t, the distance the light travels in the reflecting plate 500 is L. Here, after passing through the reflecting plate 500 as shown, the light is moved in the vertical direction by the step d can be obtained as follows.

From Snell's law, φ '= sin ⁻¹ (sin45 ° / n _t ) and L = t / cosφ'. Here, the step d may be represented as follows.

d = Lsin (45 ° -φ ')

= [t / cos {sin ^-1 (sin45 ° / n _t )}] × sin {45 °-(sin ^-1 (sin45 ° / n _t )}

In addition, as shown in FIG. 6, a total of 17 reflecting plates 500a to 500q are provided, and a step is formed by d when passing through one reflecting plate. Here, if it is assumed that the refractive index and the arrangement of each reflecting plate are the same, the total step D after passing from 500a to 500q may be expressed as 16 times d. That is, the reflector array must be provided in consideration of the size and the step of each reflector 500a to 500q. Accordingly, the size and position of the reflector can be adjusted to achieve low cost and miniaturization. That is, it is preferable that each reflecting plate 500a-500q is arrange | positioned with the step of more than d mentioned above.

7 is a view showing interference of light in the reflector of the backlight unit according to the present invention. Referring to Figure 7, the interference of the light in the reflector of the backlight unit according to the present invention will be described.

As shown, the light reflected by the second reflector 500b is projected in the direction of the light guide plate (not shown). Here, in the drawing, the light A 'reflected from the upper portion A of the reflecting plate 500b passes near the lower portion A ″ of the first reflecting plate 500a. Thus, the first reflecting plate 500a When the distance of the second reflecting plate 500b is close, the light A 'reflected from the upper portion A of the first reflecting plate 500b may pass through the lower portion A ″ of the first reflecting plate 500a. In this case, the light reflected from the first reflector 500a and the A ″ may cause interference, and when the extinction interference occurs depending on the path difference, the brightness of the display device may be reduced. Thus, the interference described above may not be generated. It is desirable to sufficiently space the distance between each reflecting plate.

The present invention is not limited to the above-described embodiments, and such modifications are included in the scope of the present invention even if modifications are possible by those skilled in the art to which the present invention pertains.

Referring to the effects of the backlight unit and the display device having the same according to the present invention described above are as follows.

First, the same effect as having a plurality of light sources with one light source can project uniform light similar to the surface light source onto the light guide plate.

Second, the brightness of the display device may be increased by illuminating the light emitted from the light source without light loss.

Third, while using a plurality of reflecting plates can eliminate the interference of the light reflected from each reflecting plate, it is possible to realize the miniaturization of the reflecting plate array.

Claims (13)

Light source; And And a reflector plate array including a plurality of reflector plates for reflecting light emitted from the light source to the light guide plate. The method of claim 1, wherein the light source, A backlight unit, characterized in that the laser light source. The method of claim 1, wherein the light source and the reflector array, And at least two surfaces of the light guide plate. The method of claim 1, And a diffuser configured to diffuse light reflected from the reflector plate array. The method of claim 1, wherein the reflector is A backlight unit reflecting a part of light incident from the light source to the light guide plate and transmitting the remaining light The method of claim 1, The reflector is a backlight unit, characterized in that the reflectance increases as the distance from the light source. The method of claim 1, wherein each of the reflecting plate, A backlight unit, characterized in that for reflecting the same amount of light to the light guide plate. The method of claim 1, The reflectors are grouped into at least two groups, And the reflectors of each group have the same reflectance. The method of claim 1, The plurality of reflecting plates are made of first to Mth reflecting plate, The Nth reflector (N is an integer greater than or equal to 2 and less than or equal to M) is provided with a step with the N-1 reflector at least as long as the light emitted from the light source is changed from the N-1 reflector. Backlight unit. The method of claim 9, The step (d) is a backlight unit, characterized in that as follows. d = [t / cos {sin ^-1 (sin45 ° / n _t )}] × sin {45 °-(sin ^-1 (sin45 ° / n _t )} (Where t is the thickness of the reflecting plate and n _t is the refractive index of the reflecting plate). The method of claim 1, The plurality of reflecting plates are made of first to Mth reflecting plate, The Nth reflector (N is an integer greater than or equal to 2 and M or less) is provided so that light reflected by the Nth reflector is not projected onto the N-1th reflector. Point light source; A diffuser for dividing the light projected from the point light source into a plurality of lights to project the light guide plate; A light guide plate for projecting light projected from the diffusion unit; And And a panel for displaying an image signal. A panel on which image information is displayed; And A display device comprising the backlight unit according to any one of claims 1 to 11.

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