TV Light Guide Plate-LCD Backlight Module Introduction

The LCD itself does not emit light, and it needs a backlight module to provide it with a light source to achieve the purpose of display. Therefore, the performance of the light source of the backlight module determines the visual perception of the display. The backlight module is mainly to provide a uniform and high-brightness light source for the liquid crystal panel. The basic principle is to transform the commonly used point or line light source into a high-brightness and uniform brightness surface light source product through a simple and effective mechanism. In terms of quality, the higher the brightness of the light, the better, and the average brightness generally requires more than 70%. Generally, the backlight module is composed of a light source, a light guide plate, a reflective plate, a diffuser plate and a light-enhancing sheet. The following will introduce the basic components of the backlight module. Figure 1 shows the common structure of the LCD backlight module.

light source

The light source of the backlight module must have the characteristics of high brightness and long life. Generally, cold cathode fluorescent lamps (CCFL: Cold cathode fluorescent lamp) and light emitting diodes (LED: Light emitting diode) are commonly used. Cold cathode fluorescent lamps have high brightness. , High efficiency, long life, high color rendering and other characteristics, coupled with the cylindrical shape, it is easy to combine with the light reflecting element to form a thin-plate lighting device, so it is the most commonly used. However, with the development of LED technology, LED brightness is getting higher and higher, the life span is getting longer, and the color rendering is getting better and better, and there is a trend to gradually replace cold cathode fluorescent tubes.

In the backlight module, according to the distribution position of the light source, it can be divided into a direct type backlight source and an edge type backlight source. Direct-lit backlights are mainly used in relatively large-size screens and high-brightness occasions. The disadvantage is that the product size is relatively thick and the power consumption is high. Side-type backlights are mainly used in small-size display screens, and their structure is relatively light and thin. According to the brightness requirements, the side-type backlight can be made into single-side light or double-side light.

The light guide plate is used in the side-type backlight module, which is an important component that affects the light efficiency. The propylene is pressed into a wedge-shaped plate with a smooth surface by injection molding, and then a high-reflectivity and non-light-absorbing material is used on the bottom surface of the light guide plate. Screen printing is printed with circular or square diffusion dots. The main function of the light guide plate is to guide the direction of the light to improve the brightness of the panel and control the brightness uniformity. The light source is located on the end face of the light guide plate on the thick side. The light emitted by the light source enters the light guide plate by way of end face illumination. Most of the light is transmitted to the thin end by total reflection. , Different sizes of microstructure pattern design can make the surface of the light guide plate emit light evenly.

The light guide plate is divided into wedge plate and flat plate in appearance. Generally, notebook computers use wedge-shaped boards due to the consideration of spatial relationships, while LCD Monitors and LCD TVs use flat panels.

The light guide plate has low surface roughness and good optical properties. The diffusion point types include printing type (printing diffusion dots by screen printing) and non-printing type (made with molds with set dots or lines). Non-printing methods include machining, etching, and thin plate replacement.

Generally, the reflective plate of the edge-lit backlight module is placed at the bottom of the light guide plate to reflect the light leaking from the bottom surface back into the light guide plate to prevent the light source from leaking out to increase the efficiency of light use: while the direct-lit backlight module is placed The bottom surface of the light box may be pasted on it, and the light beam reflected by the diffuser plate is reflected from the bottom of the light box back to the diffuser plate for use. Production material: PET and PC substrate, with a reflectivity of 90%.

The function of the diffuser and the diffuser is to provide a uniform surface light source for the liquid crystal display. Generally, the traditional diffuser is mainly in the diffuser base material, adding one by one chemical particles as scattering particles, while the existing diffuser The particles of the board are dispersed between the resin layers, so the light will continue to pass through two media with different refractive indexes when passing through the diffusion layer. At the same time, the light will undergo a lot of refraction, reflection and scattering. This results in the effect of optical diffusion. Or using holographic technology, through chemical procedures such as exposure and development, the phase of the ground glass is recorded on the surface of the roughened diffusion film substrate to scatter and blur the ink dots or lines on the light guide plate. But under such a light path structure, due to the nature of the material itself and chemical particles, it will cause unavoidable light absorption and its scattering of light will be scattered. For a fixed distance observer, there will be some The light intensity is wasted, and the light source cannot be used effectively. In addition, his chemical process is relatively time-consuming, and the required production cost is relatively high.

The diffusion sheet is made of PET or PC substrate, with smooth front side and rough back side. The production method is to coat the diffusion layer (made of transparent resin mixed with light diffusion material) on the PET substrate or use PC as the base material, using roller hot pressing to form the uneven surface. The difference between the two methods: PET material will be slightly yellow when light passes through; PC material will be slightly blue when light passes through.

Brightening film

The brightness enhancement film is also called a prism film. After the light is emitted from the diffuser, the directivity of the light is poor, so the light-enhancing film must be used to correct the direction of the light. The principle uses the refraction and reflection of the light to achieve the purpose of condensing the light and improving the front brightness, so as to increase the self-direction of the light. The use efficiency of the diffuser after injection can increase the volatility of the overall backlight module by more than 60%-100%. Polyester or polycarbonate is mainly used as the material, and its surface structure is generally a prismatic column or semi-cylinder. At present, the multinational company 3M is the world's exclusive supplier and has a number of related patents. Usually a backlight module uses two brightness enhancement films, which are perpendicular to each other to concentrate the light and increase the brightness.

The brightness enhancement sheet is coated with a serrated or wavy PMMA microstructure on the PET substrate

Types of prism sheet:

BEFⅡ---(Regular Prism) The increment in a single direction is about 60%, and the overlap of two vertical directions can be increased by 120%

BEFⅢ---(irregular prism, avoid interference phenomenon) The increment in a single direction is about 59%, and the overlap of two vertical directions can increase by 111%

RBEF---The microstructure is not right-angled but arc-shaped, brightness comparison: BEFⅡ>RBEF viewing angle comparison: RBEF>BEFⅡ

DBEF--- 3M patent, the structure is made up of multiple reflective polarizers attached to each other, which can change the direction of light, and then use it after reflection.