Backlight Module; BLM

The backlight module (Backlight Module; BLM), also known as the backlight board, is one of the important components of the thin film transistor liquid crystal display (TFT-LCD). Since TFT-LCD is a non-self-luminous display, light must be projected through the backlight, which sequentially penetrates the polarizing plate, glass substrate, liquid crystal layer, color filter, glass substrate, polarizing plate, etc. in the TFT-LCD panel The parts and components finally enter the human eye for imaging to achieve the function of display.

The key components of the backlight module are composed of reflector, light source (cold cathode tube, LED), light guide, Difusser and Prism sheet.

Among the cost proportions of components required for TFT-LCD panels, color filters, driver ICs and backlight modules are the items with higher cost proportions. Traditional backlight module structure: it is composed of reflective sheet, light source, light guide plate, lower diffuser, prism sheet (condensing sheet), and upper diffuser film.

The light guide plate is made by pressing propylene into a wedge-shaped plate with a smooth surface by injection molding, and then a material with high reflectivity and non-light absorption is used. The bottom surface of the light guide plate is printed with circular or square diffusion points by screen printing. The light guide plate is mainly The function is to guide the light direction, improve the brightness of the panel and control the brightness uniformity. The cold cathode tube is located on the end face of the thick side of the light guide plate. The light emitted by the cold cathode tube enters the light guide plate in the form of edge light. Most of the light is transmitted to the thin end by total reflection. 

When the light hits the bottom surface When it reaches the diffusion point, the reflected light will diffuse to all angles, destroying the condition of total reflection and exiting from the front of the light guide plate. The design of dense and different diffusion point patterns can make the surface of the light guide plate emit light evenly. The function of the diffuser is to make the emitted light more evenly distributed, but a prism / lenticular sheet can be added to the diffuser to increase the directionality of the emitted light and achieve the purpose of improving the front brightness. The reflector plate reflects the light leaking from the bottom surface back into the light guide plate to prevent the light source from leaking out, so as to increase the efficiency of light use.

◎The backlight module is divided into two structures according to the position of the light source:

─Edge Type: The light source is around the panel, and the light emitted from the edge of the screen by the light guide plate is transmitted to the center of the screen through the light guide plate

─Direct Type: The light source is behind the panel, and the diffuser is used to uniform the light source.