Patent Application
20100073599
Embodiments of the present invention relate to a backlight module capable of implementing light reflection circulation and a liquid crystal display having such a backlight module.
A liquid crystal display (LCD) is not a self emitting display device, for illuminating which a backlight module is provided. According to the position of a light source in a backlight module, a backlight module can be an edge light type backlight module or a direct light backlight module. As edge light type backlight modules provide more advantages of slimness, the edge light type backlight modules are widely used for manufacturing LCDs.
Since the light emitting from the light source is limited in amount, the light from the light source has to be fully used to improve the brightness of a LCD, that is, the light utilization efficiency has to be improved.
A polarizing plate is an optical element for changing ordinary light into polarized light whose polarization direction is accurately controlled. The most commonly used polarizing plate is an absorbing type polarizing plate, which allows the light having the same polarizing direction as the polarizing axis of the plate to pass therethrough, while absorbing the other component of the light. Only a portion of the light from the backlight module can pass through the display panel, and the other portion is absorbed. As a result, a large portion, at least 50% percent, of the light from the light source is lost and cannot be used, leading to an extremely low optical efficiency.
Several measures have been proposed with regard to the polarizing plate for improving the light utilization efficiency, and one of them is to use a dual brightness enhancement film (DBEF) film as the polarizing plate. The DBEF film is a multilayer film composed of crystals of different crystallization directions. Depending on the crystallization direction, the topmost layer possesses the property of polarization, and the light not passing the topmost layer is reflected downwardly by the topmost layer and then reflected again by underlying crystal films upwardly, so as to form a circulation to fully use the light. As a result, the optical efficiency is improved, but the cost to obtain such polarizing plate is very high, which makes it unfit and difficult to be used in the commonly used LCD displays.
Besides, there is still the technology of reflecting type polarizing plate. A reflecting type polarizing plate has a metal grating whose pitch is smaller than wavelength of light. A LCD having such a reflecting type polarizing plate is disclosed in the Korea patent application KR2006-0119678.
An aspect of the invention provides a backlight module for a liquid crystal display, comprising: a light guiding plate comprising one or more incident surface and one light emitting surface; a reflecting film provided on a side of the light guiding plate opposite to the light emitting surface; and a reflecting type polarizing plate disposed directly on the light emitting surface of the light guiding plate and comprising a metal grating.
Another aspect of the invention provides a liquid crystal display (LCD), comprising: a backlight module; a liquid crystal panel provided on the backlight; and a polarizing plate provided on the display panel. The backlight module comprises a light guiding plate comprising one or more incident surface and one light emitting surface; a reflecting film provided on a side of the light guiding plate opposite to the light emitting surface; and a reflecting type polarizing plate disposed directly on the light emitting surface of the light guiding plate and comprising a metal grating.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from the following detailed description.
The present invention will become more fully understood from the detailed description given hereinafter and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention and wherein:
The reflecting polarizing plate 16 can be fabricated by using a thin-film process. For example, a metal film is deposited on the light emitting surface of the light guiding plate 15, and then grating patterns with a pitch no larger than a half of the wavelength of light irradiated from the light source, i.e., greater than 0 nm and less than 300 nm, is formed by using a photolithographic process. In another example, a metal film is deposited on a transparent substrate and formed into metal grating patterns by using thin-film process, and then the substrate together with the metal grating patterns formed thereon is adhered to the light emitting surface of the light guiding plate 15. Of course, the metal grating can be fabricated by using other methods.
By providing the reflecting type polarizing plate 16 on the light emitting surface of the light guiding plate 15, all the light reflected by the reflecting type polarizing plate 16 enters the light guiding plate 15 again and reflected back by the reflecting film 14 provided under the light guiding plate 15. Thus, a light reflection circulation is realized inside the light guiding plate 15, which enables full use of the reflected light and improves the light utilization efficiency. As compared with the conventional LCD employing an absorbing type polarizing plate, the novel structure of the first embodiment improves the light utilization efficiency and increases the brightness of the LCD by about 50% by means of the reflecting type polarizing plate for realizing the light reflection circulation, though a loss of about 25% of brightness is caused by removing the optical films (e.g., a diffusing plate, a prism film and the like) from the upper side of the light guiding plate 15. As a result, as a whole, the backlight module of the present embodiment can increase the brightness of the LCD by about 25% compared with the conventional backlight module.
Thus, the light reflected by the reflecting type polarizing plate 16 and the reflecting film 14 is diffused by the diffusing beads 17 to make the light distributed more uniformly, so that the problem caused by the lacking of a diffusing plate in the first embodiment is compensated and the display performance of the LCD can be further improved.
Thus, the light circulating inside the light guiding plate 15 is diffused by the diffusing beads 17 to make the light distributed more uniformly, so that the problem caused by the lacking of a diffusing plate in the first embodiment is compensated largely, and the display performance of the LCD is improved to a large extent.
Thus, the light circulating inside the light guiding plate 15 is diffused by the diffusing beads 17 to make the light distributed more uniformly, so that the problem caused by the lacking of a diffusing plate in the first embodiment is compensated largely, and the display performance of the LCD is improved to a large extent.
Accordingly, the prism film 18 improves the light condensation, the luminance and thus the brightness of the LCD. Of course, the prism film may be further provided on the reflecting type polarizing plate of the backlight module according to the second to the fourth embodiments to improve the brightness.
As shown in
In comparison to the conventional LCD shown in
In addition, the LCD of the present invention can also employ the backlight modules according to the second to the fifth embodiments discussed above. The display performance of the LCD of the present invention can be further improved by employing the backlight modules of the second to the fifth embodiments.
As can be seen from the above mentioned, the LCD of the embodiments of present invention and the backlight module therefor have the following beneficial effects:
1. The reflecting type polarizing plate directly disposed on the light guiding plate makes almost all the light reflected by the reflecting type polarizing plate enter into the light guiding plate again and be reflected back by the reflecting film under the light guiding plate, so that the light reflection circulation is realized inside the light guiding plate to fully circulate and use the reflected light, and accordingly the light utilization efficiency is largely improved. In comparison to the conventional LCD using an absorbing type polarizing plate, for the backlight of the embodiments of the invention, though a loss of about 25% of brightness is caused by the removing of the optical films, the light utilization efficiency is improved by using the reflecting type polarizing plate for realizing light reflection circulation, increasing the brightness of the LCD by about 50%. Consequently, as a whole, the backlight module of the present embodiment increases the brightness of the LCD by about 25%.
2. In the embodiments of the present invention, diffusing beads can be further provided between the light guiding plate and the reflecting film. As a result, the light reflected by the reflecting type polarizing plate and the reflecting film can be diffused by the diffusing beads to make the light distributed more uniformly, thereby improving the display performance of the LCD.
3. The light inside the light guiding plate can be circulated by using a light guiding plate having the function of diffusion. With the diffusion of the diffusing beads, the light can be distributed more uniformly, which largely improves the display performance of the LCD. The brightness of the LCD is also improved to a large extent.
4. A prism film can be further provided on the reflecting type polarizing plate, thereby improving the brightness of the LCD.
The embodiment of the invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to those skilled in the art are intended to be comprised within the scope of the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 200810222549.X | Sep 2008 | CN | national |
