1. Field of the Invention
The present invention relates to a backlight module for providing light to a display panel and a display device therewith, and more particularly, to a backlight module with an optical material layer disposed between a frame and a display panel, and a display device therewith.
2. Description of the Prior Art
With development of technology, a portable electronic device with thin design, less power consumption and portability has been more and more popular in daily life, and a display panel plays an important role therein. Since a liquid crystal display device has advantages of thin shape, less power consumption and non-radiation, it has been widely implemented in the portable electronic device, such as a notebook computer, a personal digital assistant, a cell phone and so on, it has possessed a great market share in the consumer electronic product market. Accordingly, it has been a trend to replace a CRT of a desktop PC and a traditional television. Generally speaking, the backlight modules can be divided into an edge-type backlight module and a direct-type backlight module. Since the edge-type backlight module has a design on lateral light emission and has advantages of light weight, thin shape and low power consumption, it has become a critical component of a screen implemented in the cell phone, the personal digital assistant and the notebook computer.
In design of a conventional backlight module, a distance of two adjacent light emitting diodes is represented as P, and a distance between an illuminating surface of the light emitting diode and an active area AA of the display panel projecting to a light guide plate is represented as A. The ratio of A/P plays a critical role in image quality. In general, the larger the ratio of A/P is, the better the image quality will be. Conversely, the smaller the ratio of A/P is, the worse the image quality will be. In other words, in the situation of the high ratio of A/P, the light guide plate can provide more uniform light to the active area AA, while in the situation of the low ratio of A/P, non-uniform light on the active area AA provided by the light guide plate may occur, so as to result in hot spots. Accordingly, the image quality is reduced. In consideration of cost, power consumption, heat dissipation, environmental protection and so on, an amount of the light emitting diodes is required to decrease. As a result, in presupposition of not changing dimensions of the panel, the distance of two adjacent light emitting diodes P increases correspondingly. However, the distance A, which is between the illuminating surface of the light emitting diode and the active area AA of the display panel projecting to the light guide plate, can not increase due to structural limitation. As a result, the ratio of A/P can not be enhanced resulting in decrease of the image quality. On the other hand, the increased distance A can not meet requirement of thin rim design.
Furthermore, in assembly of the conventional liquid crystal display device, an optical material layer for misting and focusing the light is installed on a top surface of the light guide plate, and a plastic frame is used for pressing the optical material layer onto the light guide plate. Since the optical material layer contacts the light guide plate directly, scratches often occur on the optical material layer and/or the light guide plate. Furthermore, since the optical material layer is directly covered with the light guide plate, the light emitted from the light emitting unit focuses inwardly by prism effect, so as to make hot spot stand out. In order to cover the hot spot, a covering area of the plastic frame needs to overlap with the active area AA of the display panel. As a result, it can not meet the requirement of thin rim design. Furthermore, the conventional design utilizes the plastic frame to press and fix the assembly of the optical material layer and the light guide plate. Accordingly, it is necessary to detach the plastic frame as replacing the optical material layer, so as to increase labor hours and result in inconvenience of assembly. Therefore, how to provide a liquid crystal display device with a high assembly yield and convenience of assembly to meet the requirement of a thin size, such as the thin rim design, has become an issue of mechanical design for the consumer products in the market.