Patent Application
20060077692
This application claims the benefit of priority under U.S.C. § 119 from Korean Patent Application No. 2004-77596, filed on Sep. 25, 2004, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present general inventive concept relates to a backlight unit and a liquid crystal display apparatus employing the same.
2. Description of the Related Art
A liquid crystal display (LCD) is a non-emissive flat panel display that needs external light to display an image since the LCD itself does not emit light. A backlight unit is located behind the LCD to illuminate it.
Backlight units are classified into a direct light type backlight unit and an edge light type backlight unit according to a position of a light source. In the case of the direct light type backlight unit, a plurality of light sources disposed beneath the LCD emits light directly toward the LCD panel. In the case of the edge light type backlight unit, a light source located along an edge of a light guide panel (LGP) emits light toward the LCD panel via the LGP.
The direct light type backlight unit may use light emitting diodes (LEDs) that emit Lambertian radiation as a point light source.
Conventionally, a backlight unit with a transmissive diffusion plate and a reflective diffusion plate and disposed above and below LEDs, respectively, include reflecting mirrors disposed above the LEDs to prevent light emitted from the LED from being directly visible above the transmissive diffusion plate. Light emitted from the LEDs and then reflected by the reflecting mirror tends not to spread out widely and uniformly. Thus, to spread out the light over a broader area, the distance between the LEDs and the transmissive diffusion plate is increased, which results in a thicker backlight unit, and, nevertheless, poor uniformity of light distribution.
The present invention provides a thin backlight unit with improved uniformity of light distribution, and a liquid crystal display (LCD) apparatus employing the same.
Additional aspects and advantages of the present general inventive concept will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the general inventive concept.
The foregoing and/or other aspects of the present general inventive concept may be achieved by providing a backlight unit including: a plurality of light-emitting device units disposed on a base plate in an array, each light-emitting device unit including a collimator to collimate light emitted by a light-emitting device so that light propagates in a principal propagation direction, a plurality of side reflectors disposed in the principal propagation direction opposite to the corresponding light-emitting device units to reflect in lateral directions light incident from the corresponding light-emitting device units, a reflective diffusion plate to reflect and diffuse the light reflected by the side reflectors, and a transmissive diffusion plate that is disposed behind the light-emitting device units in the principal propagation direction, to transmit and diffuse the incident and reflected light.
The collimator may include a transparent body, a reflecting surface formed on an outside surface of the transparent body, to reflect light emitted from the light-emitting device, and a lens portion formed in a center of the transparent body, to refract the incident light.
The reflecting surface may have a parabolic shape or a conical shape. The lens portion may have a curved surface to serve as a convex lens.
The side reflector may be conical or curved cone shaped to uniformly reflect light in the lateral directions. The side reflectors may be disposed on one surface of the transmissive diffusion plate.
Each of the light-emitting device units may emit one of red, green, and blue color beams or white light. The backlight unit may further include at least one of a brightness enhancement film (BEF) to improve directivity of the light traveling in the principal propagation direction. The backlight unit may also include polarization enhancement film to increase an efficiency of polarization of the light traveling in the principal propagation direction.
The foregoing and other aspects of the present general inventive concept may also be achieved by providing a LCD apparatus including: a liquid crystal panel and the backlight unit having a plurality of light-emitting device units disposed on a base plate in an array, each light-emitting device unit including a collimator to collimate light emitted by a light-emitting device so that the light propagates in a principal propagation direction, a plurality of side reflectors disposed in an array above the array of corresponding light-emitting device units, to reflect in lateral directions the light incident from the corresponding light-emitting device units, a reflective diffusion plate to reflect and diffuse light reflected by the side reflectors, and a transmissive diffusion plate that is disposed above the light-emitting device units, to transmit and diffuse the incident and reflected light toward the liquid crystal panel.
The foregoing and other aspects of the present general inventive concept may also be achieved by a method of providing a backlight to a panel, the method including emitting light by an array of light-emitting device units disposed on a base plate in an array, each light-emitting device unit including a collimator to collimate light emitted by a light-emitting device so that the light propagates in a principal propagation direction, reflecting in lateral directions the light incident from the light-emitting units, by a plurality of side reflectors disposed above each light-emitting device unit, reflecting and diffusing the lateral reflected light, and transmitting and diffusing the light in the principal propagation direction.
The foregoing and other aspects of the present general inventive concept may also be achieved by providing a backlight unit including a base plate, a reflective diffusing plate formed on the base plate, a plurality of light-emitting device units disposed on the reflective diffusing plate and spaced apart from each other to emit light in a principal propagation direction, a transmission diffusion plate spaced apart from the reflecting diffusing plate, and a plurality of side reflectors formed on the transmissive diffusion plate to reflect the light from each of corresponding light-emitting device units, in lateral directions.
The foregoing and other aspects of the present general inventive concept may also be achieved by providing a method to form a backlight unit including forming a base plate, forming a reflective diffusing plate formed on the base plate, placing a plurality of light-emitting device units on the reflective diffusing plate, spaced apart from each other, the light-emitting device units emitting light in a principal propagation direction, forming a transmission diffusion plate spaced apart from the reflecting diffusing plate, and forming a plurality of side reflectors formed on the transmissive diffusion plate to reflect the light from each of corresponding light-emitting device units, in lateral directions.
These and/or other aspects and advantages of the present general inventive concept will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:
Reference will now be made in detail to the embodiments of the present general inventive concept, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present general inventive concept while referring to the figures.
Referring to
Here, the term ‘above’ refers to the principal propagation direction of the light emitted from a light-emitting device 30 in each of the light-emitting device units 10a, 10b, and 10c, while the term ‘below’ refers to a reverse direction of the principal propagation direction. The principal propagation direction of the light substantially corresponds to a central axis of each of the light-emitting device units 10a, 10b, and 10c, i.e., the direction in which the light emitted from the light-emitting device unit 10a, 10b, or 10c propagate along a line parallel to the central axis thereof.
The base plate 101 serves as a substrate on which the plurality of light-emitting device units 10a, 10b, and 10c are arranged in a two-dimensional array. The base plate 101 may be a printed circuit board (PCB) to drive a light-emitting diode (LED) chip 31 in each of the light-emitting device units 10a, 10b, and 10c. Alternatively, the base plate 101. may be spaced apart from a PCB to drive the light-emitting device units 10a, 10b, and 10c separately.
Each of the light-emitting device units 10a, 10b, and 10c includes the light-emitting device 30 to emit light and a collimator 50 to collimate the Lambertian light from the light-emitting device 30 so that the light propagates upwardly. The light-emitting device 30 includes the LED chip 31 to generate light and the corresponding collimator 50. The LED chip 31 is mounted on a base 35. The LED chip 31 may adhere closely to the collimator 50 to maximize the amount of light that is emitted by the LED chip 31 into the collimator 50.
The light-emitting device units 10a, 10b, and 10c may emit red (R), green (G), and blue (B) color beams. In this case, the light-emitting device units 10a, 10b, and 10c include the LED chips 31 to generate R, G, and B color beams, respectively. Alternatively, the light-emitting device units 10a, 10b, and 10c may all emit white light. In this case, each of the light emitting device units 10a, 10b, and 10c includes the LED chip 31 to generate white light.
An LCD apparatus employing the backlight unit 100 can display a color image if the light-emitting device units 10a, 10b, and 10c use LED chips generating R, G, and B color beams.
Although the light-emitting device units 10a, 10b, and 10c are separate from each other as shown in
The collimator 50 includes a transparent body 51, a reflecting surface 53 to form on an outside of the transparent body 51 to reflect light emitted from the LED chip 31 upwards, and a lens portion 55 that is formed in a center of an upper portion the body 51 and converges and refracts incident light upward, as shown in
The reflecting surface 53 may have a parabolic shape or a conical shape. The reflecting surface 53 may be a mirror. When the reflecting surface has the parabolic shape, the divergent light emitted by the point-like light source (LED chip 31) and then reflected from the reflecting surface 53 is collimated into a substantially parallel light. When the reflecting surface 53 is conical, the light reflected by the reflecting surface 53 is also a substantially parallel beam. When the reflecting surface 53 has a parabolic shape or conical shape, the incident light is reflected upward from the reflecting surface 53, the reflected light being substantially parallel.
The lens portion 55 may have a curved surface 55a to serve as a convex lens. Since light emitted from the LED chip 31 spreads out, the curved surface 55a of the lens portion 55 causes the incident diverging light to converge and be collimated into substantially parallel light. A major output surface of the collimator may include a curved portion 55a and a flat portion 55b. The light emerging from the flat portion 55b is incident on a first area of the side reflector 130, and the light emerging from the curved surface 55a is incident on a second area of the side reflector 130. A groove 55c between the flat collimator surface and the curved collimator surface prevents light emitted by the LED 30 to exit the collimator directly through the flat surface, unless the light was reflected by the collimator's reflecting surface 53.
The collimator 50 converts the diverging light generated from the LED chip 31 into substantially parallel light that is then incident on the side reflector 130.
The side reflectors 130 corresponding to the light-emitting device units 10a, 10b, and 10c are arranged in a two-dimensional array. The side reflectors 130 spread the light incident from the collimator 50 of the light-emitting device units 10a, 10b, and 10c in lateral directions. The side reflectors 130 may be conical or curved cone shaped to uniformly reflect light incident from the collimator 50 in the lateral directions. In
As described above, the backlight unit 100 including the light-emitting device units 10a, 10b, and 10c, each having the collimator 50, and the side reflectors 130 allows most of light emitted from the light-emitting device units 10a, 10b, and 10c to spread out over a wide area before entering the reflective diffusion plate 110, thereby providing uniform brightness distribution.
The side reflectors 130 prevent transmission of a light spot located at the position of the LED chip 31 or the color of the LED chip 31 emitting a color beam, above the backlight unit 100.
Meanwhile, the reflective diffusion plate 110 reflects and diffuses light reflected by the side reflector 130 so that the reflected light propagates upward.
The reflective diffusion plate 110 is disposed on the base plate 101 at the bottom of the light-emitting device units 10a, 10b, and 10c. The reflective diffusion plate 110 has a plurality of holes in which the light-emitting devices 30 of the plurality of light-emitting device units 10a, 10b, and 10c are respectively disposed. The reflective diffusion plate 110 is disposed on the base plate 101 with the light-emitting devices 30 being inserted into the plurality of holes.
The transmissive diffusion plate 140 reflects and diffuses incident light. As shown in
In the backlight unit 100, the collimated beams are emitted from the light-emitting device units 10a, 10b, and 10c and reflected in the lateral directions by the side reflectors 130 disposed above the light-emitting device units 10a, 10b, and 10c, which causes the beams to spread out widely before entering the reflective diffusion plate 110. Thus, the backlight unit 100 has a reduced thickness over a conventional backlight unit because light can be distributed uniformly although a distance between the light-emitting device units 10a, 10b, and 10c and the transmissive diffusion plate 140 is small.
Meanwhile, the backlight unit 100 further includes a brightness enhancement film (BEF) 150 to improve the directivity of light beams escaping from the transmissive diffusion plate 140, and a polarization enhancement film 170 to increase polarization efficiency.
The BEF 150 is used to refract and condense light beams that escape from the transmissive diffusion plate 140, thereby increasing the directivity and thereby brightness of the light beams. The polarization enhancement film 170 transmits one polarized light beam, e.g., a p-polarized light beam while reflecting the other polarized beam, e.g., an s-polarized light beam. Thereby, after passing through the polarization enhancement film 170, most of incident light beams are linearly polarized, with one polarization direction, e.g., the p-polarized light.
A liquid crystal display (LCD) apparatus employing the backlight unit 100 may include a liquid crystal panel disposed above the backlight unit 100. When a linearly polarized beam is incident on a liquid crystal layer in a liquid crystal panel, the polarization of the light passing through the liquid crystal layer is rotated if an electric field is applied to the liquid crystal layer, thereby enabling image information to be displayed on the liquid crystal panel. Although this embodiment describes the liquid crystal layer through which a polarized light beam passes, the present general inventive concept is not limited thereto.
The efficiency of light utilization may be improved when light incident on a liquid crystal panel has single polarization. Therefore, using the polarization enhancement film 170 for the backlight unit 100 may increase optical efficiency.
As described above, the backlight unit 100 includes light-emitting device units 10a, 10b, and 10c to collimate light emitted from an array of point light sources so that the collimated light propagates upward; the side reflectors 130 reflect incident light in such a manner that they spread out more widely before reaching the reflective diffusion plate 110. The backlight unit 100 having the above configuration is thin while providing uniform light distribution across the entire surface.
Thus, a LCD apparatus employing the backlight unit 100 enables the display of high quality image with uniform brightness across the entire screen.
The present invention provides a thin backlight unit capable of providing uniform light distribution. The present invention also provides a LCD apparatus employing the backlight unit producing a high quality image with uniform brightness across the entire screen.
Although a few embodiments of the present general inventive concept have been shown and described, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the general inventive concept, the scope of which is defined in the appended claims and their equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-77596 | Sep 2004 | KR | national |
