1. Field of the Invention
The invention relates in general to a backlight module, and more particularly, to a backlight module that effectively compensates brightness at two corners of a light guide plate near two sides of a light source.
2. Related Art of the Invention
The advancement of multi-media has benefited from the forward looking progress of semiconductor technique or human-machine interface display. For the .display, cathode ray tube (CRT) has dominated the markets for years due to its outstanding display quality and economics. However, the environment of operating desktop terminal/monitors and the trend of power saving with environment protection in mind have manifested the problems of cathode ray tube in terms of space utilization and power consumption. Therefore, the liquid crystal display (LCD) having the characteristics of being light, thin, short, small, and low power consuming has become main stream in the market. However, as the liquid crystal molecules are not luminescent materials, a backlight is required to provide the light source of the liquid crystal panel, so as to achieve the display effect with sufficient brightness and contrast.
FIG. 1 shows a top view of a conventional backlight module, and FIG. 2 shows a side view of the backlight module as shown in FIG. 1. Referring to FIGS. 1 and 2, the backlight module 100 includes a light guide plate 110, a light source 120, a reflection mask 130 and a frame 140. The light guide plate 110 includes a wedge light guide plate with a top surface 112, a bottom surface 114 and a side surface 116. The top surface 112 is designed as the projecting plane, the bottom surface 114 is used as the reflecting plane, while the side surface 116 is designed as the incident plane. The light source 120 such as a cold cathode fluorescent lamp (CCFL) is disposed next to the side surface 116 with two ends fixed on a lamp source holder 150. The light beam provided by the light source 120 is incident onto the side surface 116 of the light guide plate 116. Through the bottom surface 114, the light beam is transmitted to the top surface 112 of the light guide plate 110 and projects therefrom. Therefore, the light projecting from the top surface 112 is a plane light source. The reflection mask 130 is disposed next to the side surface 116 of the light guide plate 110 to cover the light source 120. The light beam provided by the light source 120 is thereby concentrated and incident on the side surface 116 of the light guide plate 110. The frame 140 is used to carry the light guide plate 110, the light source 120 and the reflection mask 140, such that the light guide plate 110, the light source 120 and the reflection mask 130 can be integrated into a single device.
As the cold cathode fluorescent lamp (CCFL) is currently typically used as the light source 120, the brightness of the high- and low-voltage regions at the two ends of the cold cathode fluorescent lamp is normally smaller than that of the middle thereof. Therefore, the brightness at the two comers of the light guide plate 110 near the two sides of the lamp 120 (regions A and B as illustrated in FIGS. 1) is insufficient. To overcome the problem, prior art increases the length of the lamp, such that the regions with insufficient brightness extend externally to the light guide plate. The brightness at the two comers of the light guide plate is thereby increased. However, the width of the liquid crystal display is consequently increased resulting in an enlarged size. This contradicts the trends for being light, thin, short and small.