Generally speaking, the backlight module can be divided into front light and backlight, and the backlight module can develop the following three structures according to the size requirements and the position of the lamp tube. [6]

Side light type

The edge lighting is a single light source placed on the side. The light guide plate has a non printing design. It is commonly used for small and medium size backlight modules under 30 inches. The light source design of side incidence has the characteristics of light weight, thin type, narrow frame and low power consumption. It is also used for mobile phones and tablet computers The light source of notebook computer and large size TV backlight module adopt side light structure.

Straight down type

(bottom lighting) for the super large size backlight module, the side light structure has been unable to occupy the advantages in weight, power consumption and brightness, so the straight down structure without light guide plate and the light source placed directly below has been developed. The light source is emitted from the spontaneous light source (such as lamp tube, led, etc.), which is reflected by the reflector plate, and then evenly dispersed upward through the diffuser plate and then emitted from the front. Due to the larger space for placement, the lamp tube can be used according to the size of the TFT panel At the same time, it also increases the thickness, weight and power consumption of the module. It has the advantages of high brightness, good light output angle, high light utilization efficiency and simple structure. Therefore, it is suitable for LCD displays and LCD TVs that have less requirements on portability and space The problems of high power consumption (using cold cathode tube), poor uniformity and LCD heating still need to be improved.