KR100301666B1 - Subsidiary Light Source for Liquid Crystal Display of Reflective Type - Google Patents

Abstract

The present invention relates to an auxiliary light source for a reflective liquid crystal display device having a uniform light distribution and configured to increase the incident efficiency to the liquid crystal panel.

An auxiliary light source for a reflective liquid crystal display device of the present invention includes a light source for generating a light beam, a light guide plate for emitting the light beam toward the display surface of the reflective liquid crystal panel, a light source reflector for reflecting the light beam generated from the light source toward the light guide plate, and a light guide plate. In a reflective liquid crystal display auxiliary light source having a reflecting plate for preventing light beams from leaking, the light guide plate includes; A light incident part to which the light beam from the light source is incident; A first light emitting portion having a fine protrusion having a stepped structure to emit a light beam incident in the light guide plate toward the liquid crystal panel; A total reflection part for totally reflecting the light beam incident into the light guide plate facing the first light output part; It is characterized by including the 2nd light output part facing the reflecting plate.

By such a configuration, the auxiliary light source for the reflective liquid crystal display device of the present invention increases the uniformity of the light beam and the incident efficiency to the liquid crystal panel, and minimizes the adverse effect on external light to improve the image quality.

Description

Subsidiary Light Source for Liquid Crystal Display of Reflective Type

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an auxiliary light source of a reflective liquid crystal display device, and more particularly to an auxiliary light source for a reflective liquid crystal display device configured to have a uniform light distribution and to increase incident efficiency to a liquid crystal panel.

In general, a backlight in a liquid crystal display (hereinafter referred to as 'LCD') occupies a lot of volume and weight and consumes high power, which is a significant obstacle to the trend of light weight, thinness, and low power consumption. It is pointed out. In response to this trend, research and development on a reflective LCD that does not use a backlight have been recently conducted. Since the reflective LCD does not have its own light source, it displays an image depending on natural light (or ambient light). In this case, the reflective LCD has a problem in that when the natural light does not have a sufficient amount of light (for example, when the surroundings are dark), the luminance level of the display image is lowered and the displayed information cannot be read. In order to solve this problem, a subsidiary light source that is separately installed in the reflective LCD and supplies a light beam to the reflective LCD when ambient light is dark is used. Hereinafter, a conventional reflective LCD and an auxiliary light source will be described.

1 and 2, the reflective LCD includes a reflective liquid crystal panel 10 and an auxiliary light source 20 positioned above the reflective liquid crystal panel 10 to supply a light beam to the reflective liquid crystal panel 10. ). A mirror (not shown) is formed below the reflective liquid crystal panel 10 to reflect natural light (or auxiliary light) incident on the display surface 36 of the liquid crystal panel. The auxiliary light source 20 is generated from a light source 22 that generates a light beam, a light guide plate 26 that uniformly emits the light beam toward the display surface 36 of the liquid crystal panel, and a light source 22. The light reflector 24 reflects the light beam toward the light guide plate 26, and the reflector 28 prevents the light beam from leaking from the light guide plate 26. The reflector 28 prevents light beams from leaking on the remaining surfaces except for the incident surface 32, the upper surface 38, and the lower surface 34 of the light guide plate. Looking at the path of the light beam according to the operation of the auxiliary light source 20 as follows. The light beam generated by the light source 22 travels to the incident surface 32 of the light guide plate 26 by the light source reflector 24. In this case, the light beam propagated into the light guide plate 26 is emitted toward the display surface 36 of the reflective liquid crystal panel. In addition, the emitted light beam displays a desired image by the reflective liquid crystal panel 10 and proceeds toward the user.

On the other hand, some of the characteristics required to be considered in the design of the reflective LCD will be described in conjunction with FIG. First, the light beam from the auxiliary light source 20 is directed toward the user (I ₁ ) should be minimized. At this time, if it is difficult to minimize the I ₁ I ₁ preferably advanced angle of the adjusting causing a departure from the user's field of view. Second, the amount of emitted light I ₂ toward the display surface 36 of the liquid crystal panel over the entire surface of the light guide plate 26 should be substantially uniform. For this purpose, a fine pattern is formed on the lower surface 34 of the light guide plate 26. Third, the light beam emitted from the light guide plate 26 to the reflective liquid crystal panel 10 should be close to the vertical direction. This is because the light efficiency is maximized when the angle of the light beam emitted to the reflective liquid crystal panel 10 is vertical. That is, as the light beam incident toward the display surface 36 of the liquid crystal panel approaches the vertical direction, the incident efficiency of the reflective liquid crystal panel 10 increases. Fourth, when using the external light it should be minimized the adverse effect of the auxiliary light source (20). This is because the auxiliary light source 20 operates only when the ambient light is dark, and otherwise displays the image using the ambient light. Accordingly, it is preferable to design in consideration of this so that the phenomenon that the ambient light is distorted by surface light, incident angle, etc. by the auxiliary light source 20 does not occur.

The second and third requirements of the characteristics of the auxiliary light source for the reflective LCD are important requirements for the design of the reflective LCD. The relationship between the required characteristics and the conventional auxiliary light source for the reflective LCD will be described.

First, the relationship between the second requirement and the conventional auxiliary light source for the reflective LCD will be described. 3, the conditions under which the light beam is totally reflected in the light guide plate 26 will be described. When the light incident on the interface between the medium having a high refractive index and the medium having a low refractive index is incident at an angle greater than a specific angle, total reflection occurs without the amount of light transmitted outside the interface. In this case, when the refractive index of the medium 1 is n1 and the refractive index of the medium 2 is n2, the minimum incident angle ?? of total internal reflection of the internal traveling light in the medium 1 and proceeding only to the medium 1 is represented by Equation 1 Defined in

For example, when the refractive index n1 of the light guide plate is 1.49 and the refractive index n2 of air is 1.0, total reflection is performed as shown in FIG. 3A for an incident angle of about 42 ° or more. At this time, the incident angle (± θ) of the light beam proceeding to the incident surface 32 of the light guide plate 26 is shown in FIG. 3 (b), and the angle distribution characteristic of the incident light is shown in FIG. 3 (c). have.

Meanwhile, the distribution characteristics of the light beams totally reflected inside the light guide plate 26 will be described with reference to FIG. 4. Since the distribution of the incidence angle of the internal traveling light totally reflected by the total reflection condition has an angle distribution larger than the internal total reflection angle, it is totally reflected at the interface between the light guide plate 26 and the air and proceeds as shown in FIG. The light beam proceeding by total internal reflection is emitted to a surface opposite to the incident surface 32 and then reflected by the reflecting plate 28 and re-entered into the light guide plate again. In this case, the incident angle (± θ) of the incident light with respect to the lower surface 34 of the light guide plate is illustrated in FIG. 4B in consideration of the absorption rate of the light guide plate 26, the reflectance of the reflecting plate 28, and other light losses. And the distribution of the incident light is shown in Fig. 4C. It means that the amount of the light beam 35 incident on the light guide plate 26 is larger than the amount of the light beam 37 reflected and propagated by the reflecting plate 28.

On the other hand, when the incident angle θ is smaller than 42 ° at the interface between the medium 1 and the medium 2, there is a light beam emitted to the medium 2. In this case, the size and direction of the emitted light beam will vary depending on the angle at which light is incident. In this case, the interface is a predetermined angle (for example, as shown in Fig. 6A) If it is inclined to), the incident angle of light is changed. This will be described with reference to FIG. 6. As shown in (a) of FIG. 6, when the interface a is inclined to the interface b, the incident angle is changed from θ _a to θ _b . In addition, as shown in FIG. 6B, when the interface a is inclined to the interface c, the incident angle is changed from θ _a to θ _c . In addition, when the changed angle of incidence becomes smaller than the total reflection angle, light is emitted to the outside, and the emission angle can be calculated. Table 1 shows the external emission characteristics according to the interface tilt for the light beam incident at 55 ° from the interface.

External emission characteristics according to the interface tilt (when n1 = 1.49 and n2 = 1.0) θ _a α θ _o 55 ° -30 ° Total reflection -20 ° Total reflection -10 ° Total reflection 0 ° Total reflection 10 ° Total reflection 20 ° 75 ° 30 ° 68 ° 40 ° 62 ° 50 ° 57 ° 60 ° 53 °

On the other hand, when the protrusion 30 is composed of two planes A and B having an arbitrary angle with respect to the plane C, all of the internal traveling lights are emitted to the outside. In particular, in the case where the light incident on the light source 22 and propagates through the plane C is totally reflected to the plane C, the light is totally reflected to the plane A and may be emitted to the outside of the light guide plate. In addition, the light beam reflected by the reflector 28 and traveling toward the light source 22 may be totally reflected in plane B and may exit to the outside of the light guide plate in plane A. FIG. The protrusion 30 may have a semicircular shape as shown in FIG. 5 (b) and may be manufactured in various shapes such as conical, pyramidal, parabolic and sadi-shaped according to the designer's intention. will be. However, as shown in FIG. 4, the distribution of the light beams in the light guide plate is larger than the amount of the light beams 37 reflected and propagated by the light beams 35 incident on the light guide plate 26 without forming the protrusions 30. If the protrusions 30 are formed on the lower surface 34 of the light guide plate, the difference will be greater. As a result, most of the traveling light in the light guide plate 26 is emitted near the light source 22. For this reason, in the conventional reflective LCD, the distribution of the light beams emitted from the auxiliary light source 20 to the reflective liquid crystal panel 10 is nonuniform, leading to deterioration of the uniformity of the screen.

Next, the relationship between the third requirement and the conventional auxiliary light source for the reflective LCD will be described.

As shown in FIG. 5, the angle formed by the planes A and B of the protrusions during the shape machining of the protrusions 30 is limited to a predetermined angle. Also, FIG. 7 shows the incidence and the exit angle of the light beam on one of the surfaces A and B of the projection. When the plane C of the light guide plate is parallel to the display surface 36 of the liquid crystal panel, when the shape of the protrusion 30 is an isosceles triangle, when the angle of incidence formed by planes A and B is β, the incident angle is 55 ° The angle incident on the panel 10 is shown in Table 2.

Angle incident on the reflective liquid crystal panel (when n1 = 1.49 and n2 = 1.0) θ _i β θ _o 55 ° 120 ° 68 ° 110 ° 66 ° 100 ° 62 ° 90 ° 60 ° 80 ° 57 ° 70 ° 55 ° 60 ° 53 ° 50 ° 50 °

The larger the angle θ _o of the light beam incident on the reflective liquid crystal panel is, the more components are reflected on the surface of the liquid crystal panel, resulting in a decrease in incident efficiency. Therefore, in order to reduce the angle θ _o of the light beam incident on the reflective liquid crystal panel, the right angle β formed by planes A and B should be small, but there are many difficulties in manufacturing and there are limitations. Accordingly, there is a need for a new auxiliary light source for a reflective liquid crystal display device for improving the uniformity and incident efficiency of the light beam emitted to the reflective liquid crystal panel.

Accordingly, an object of the present invention is to provide an auxiliary light source for a reflective liquid crystal display device having a uniform light distribution and configured to increase incident efficiency.

1 is a view showing a reflective liquid crystal display device equipped with a conventional auxiliary light source.

FIG. 2 is a cross-sectional view of the LCD shown in FIG. 1 taken along the line AA ′. FIG.

FIG. 3 is a view illustrating a light beam total reflection condition in the light guide plate illustrated in FIG. 2.

4 is a diagram showing a distribution of light beams in an auxiliary light source having no micro-shaped protrusions on the lower surface of the light guide plate.

FIG. 5 is a view illustrating a shape of a protrusion applied to a light guide plate and a path of a light beam. FIG.

FIG. 6 is a view for explaining an emission angle of a light beam according to an inclination of an interface in the light guide plate; FIG.

FIG. 7 is a view illustrating an exit angle of a light beam incident on a protrusion of a light guide plate; FIG.

8 is a view showing an auxiliary light source according to an embodiment of the present invention.

FIG. 9 is a view for explaining a light beam propagation path in the auxiliary light source shown in FIG. 8; FIG.

<Description of Symbols for Main Parts of Drawings>

10,40: reflective liquid crystal panel 20,50: auxiliary light source

22,52: light source 24,54: light source reflector

26,56: LGP 28,58: Reflector

30,60: protrusion 32: incident surface

34: When 38: When

In order to achieve the above object, an auxiliary light source for a reflective liquid crystal display device according to the present invention includes a light source for generating a light beam, a light guide plate for emitting the light beam toward the display surface of the reflective liquid crystal panel, and reflecting the light beam generated from the light source toward the light guide plate. A light guide plate comprising: a light guide plate comprising: a light source reflecting mirror; and a light reflection plate having a light source reflecting mirror; A light incident part to which the light beam from the light source is incident; A first light emitting portion having a fine protrusion having a stepped structure to emit a light beam incident in the light guide plate toward the liquid crystal panel; A total reflection part for totally reflecting the light beam incident into the light guide plate facing the first light output part; It is characterized by including the 2nd light output part facing the reflecting plate.

Other objects and features of the present invention other than the above object will become apparent from the description of the embodiments with reference to the accompanying drawings.

8 to 9, a preferred embodiment of the present invention will be described.

Referring to FIG. 8, in the auxiliary LCD light source for reflective LCDs of the present invention, minute projections having a stepped structure are formed on the lower surface of the light guide plate so that light beams are uniformly distributed. As shown in FIG. 9, the reflective LCD auxiliary light source 50 of the present invention is formed substantially perpendicular to the total reflection boundary E of the lower surface of the first slope D of the protrusion 60. This is the same as the structure in which the surface A in the conventional protrusion 30 is almost perpendicular to the surface C and the angle of the surface B with the surface C is made very small or completely parallel. In this case, when the light beam 61 incident on the light guide plate 56 and the light beam 63 reflected by the reflecting plate 58 are the light which is totally reflected on the upper surface of the light guide plate 56, the light beams 61 are formed of the protrusions 60. When the first slope D is almost vertical, the probability that the reflected light beam 63 is incident on the first slope D is greater than the probability that the light beam 61 incident on the light guide plate 56 is incident on the first slope D. This becomes large. That is, the reflected light beam 63 is incident on the first slope D and is emitted to the outside of the light guide plate 56. In addition, the second slope F is formed to be symmetrical to the first slope D so that the light beam 61 incident on the light guide plate 56 is emitted and the reflected light beam 63 is totally reflected. In addition, when the total reflection boundary surface E is parallel to the upper surface of the light guide plate 56 and the first slope D is formed at a predetermined angle (for example, 95 °) with respect to the total reflection boundary surface E, various incident angles The emission angles are shown in Table 3.

Output angle of the light beam according to the incident angle (when n1 = 1.49 and n2 = 1.0) ?? _i ?? _o 45 ?? 11.71 ?? 55 ?? 36.84 ?? 65 ?? 54.36 ?? 75 ?? 70 ??

Here, the incident angle and the exit angle are set to '0' when it is perpendicular to the total reflection boundary plane E. FIG. As shown in Table 3, it can be seen that the angle of the light beam incident on the reflective liquid crystal panel 40 is incident more vertically than the conventional reflective LCD. Accordingly, the incident efficiency of the light beam incident on the reflective liquid crystal panel 40 is improved.

In addition, a protrusion 60 having a stepped microstructure is formed on the bottom surface so that the light beam incident on the light guide plate 56 travels to the end of the light guide plate 56 far away from the light source 52. By adjusting the first and second slopes D and F, the incident light beam and the reflected light beam can be selectively emitted. Thus, the uniformity of the light beam emitted from the light guide plate 56 can be increased. On the other hand, the auxiliary LCD light source for the reflective LCD of the present invention improves the optical characteristics by varying or continuously changing the area according to the designer's intention throughout the entire area including the height (h) and the length (L) of the protrusion (60). You can do it. For example, in FIG. 8, the stepped protrusion formed on the bottom surface is generally formed in the form of 'V', but the stepped protrusion is formed in the form of 'W' as a whole to reduce the thickness of the light guide plate according to the designer's intention. You can do it.

In addition, when the ambient light is used, the outer surface of the total reflection interface E of the upper surface and the lower surface of the light guide plate 56 forms a parallel or very small angle to minimize the adverse effect of the light guide plate 56, and the first and second slopes ( Since the height h of D and F is much smaller than the length L of the total reflection boundaries E and G, there is little influence on the external light, so that the outer surface of the total reflection boundaries E of the upper and lower surfaces of the light guide plate 56 is little. If the same medium is used, there is no change in the angle at which the ambient light is incident on the reflective liquid crystal panel 40. Accordingly, the adverse effect of the light guide plate 56 is minimized.

As described above, the auxiliary light source for the reflective LCD according to the present invention includes a light guide plate having a stepped interface in which the light beam is emitted toward the liquid crystal panel, thereby increasing uniformity and incident efficiency of the light beam and minimizing adverse effects on external light. The picture quality can be improved.

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.

Claims (7)

A light source for generating a light beam, a light guide plate for emitting the light beam toward the display surface of the reflective liquid crystal panel, a light source reflector for reflecting the light beam generated from the light source toward the light guide plate, and a reflector for preventing the light beam from leaking from the light guide plate. A reflective liquid crystal display auxiliary light source comprising: The light guide plate, A light incident part to which the light beam from the light source is incident; A first light emitting part having a fine protrusion having a stepped structure to emit a light beam incident in the light guide plate toward the liquid crystal panel; A total reflection part for totally reflecting the light beam incident into the light guide plate facing the first light output part; And a second light emitting part facing the reflecting plate. The method of claim 1, The first light output unit A plurality of first protrusions including a first total reflection surface for total reflection of the light beam incident into the light guide plate and a first emission surface for exiting the light beam incident in the light guide plate and totally reflected from the reflection plate toward the reflective liquid crystal panel; A plurality of second protrusions including a second total reflection surface for total reflection of the light beam incident to the light guide plate and a second emission surface for exiting the light beam totally reflected into the light guide plate toward the reflective liquid crystal panel; And the first and second protrusions are symmetrically formed. The method of claim 2, And the first protrusion is formed to be close to the light incident part of the light guide plate, and the second protrusion is formed to be close to the second light exit part. The method of claim 2, And each of the first and second emission surfaces is formed to have an angle of about 90 degrees to about 95 degrees with each of the first and second total reflection surfaces. The method of claim 2, The height of the first and second exit surface is set relatively small compared to the length of the first and second total reflection surface, And the height of the first and second inclined surfaces and the length of the first and second total reflection surfaces are different for each of the first and second protrusions. The method of claim 2, The auxiliary light source of the reflective liquid crystal display device, characterized in that the symmetrical structure of the first and second protrusions is formed to be repeated at least twice. The method of claim 2, The auxiliary light source of the reflective liquid crystal display device, characterized in that the first and second protrusions are formed in a step shape that protrudes toward the liquid crystal panel.