Backlight for TFT LCD
The backlight of TFT-LCD is mainly composed of light source, optical films, light guide plate and other materials.
1、 Light source
The light source used by the backlight determines the photoelectric parameters such as energy consumption, brightness and color of the backlight, as well as its service conditions and service life. Light sources are divided into linear light sources, point light sources and area light sources according to the luminous shape. The specific light sources and their characteristics are shown in the table. In TFT-LCD, CCFL linear light source or LED point light source is mainly used.
Specific light sources and their characteristics:
| Light source shape | Light source | Features |
| Linear light source | CCFL(cold cathode fluorescent tube) | High brightness, long life Inverter drive voltage is high |
| HCFL (hot cathode fluorescent tube) | Serious heat generation | |
| Point light source | LED (light-emitting diode) | Long life, low heat generation, slightly lower brightness |
| Faceted light source | VFD (flat fluorescent lamp) | Thin, good uniformity, short life, low brightness |
| ELD (electroluminescent sheet) | Ultra-thin and flat, uniform brightness, long life, bendable | |
| OELD (organic electroluminescent film) | Thin, good uniformity, high brightness, short life span | |
| FED (flat field emission) | High brightness |
2、 Optical Films
The backlight should provide TFT-LCD with a high brightness and high uniformity area light source as much as possible. Optical diaphragms used in backlight sources are mainly divided into two categories:
One is diffusion film and reflector film, whose main function is to enhance the luminous uniformity of area light source; The other is the brightening film, whose main function is to improve the brightness of the backlight.
The diffusion film is divided into upper diffusion film and lower diffusion film. The basic composition of the diffusion sheet is diffusion layer + substrate + protective layer. The diffuser is placed above the straight down backlight source to diffuse the light emitted by the light source and maintain the uniformity of brightness in the surface, so as to prevent the shadow of CCFL or led from being seen on the surface. Another function of the diffuser is to support various optical diaphragms on it to prevent the optical diaphragm from sagging and affecting the optical effect.
Brightening films include BEF(brightness enhanced film) and DBEF (double brightness enhanced film). Through the focusing principle, bef gathers the divergent light in a smaller range to improve the light in this range. Dbef improves the brightness of the light source as a whole through reflection and reuse.
3> Light guide plate
The light guide plate applied to the side light backlight can change the linear light emitted by CCFL, led and other light sources into surface light with good luminous efficiency. The light emitted from the light guide plate has large brightness from the side. By configuring an optical diaphragm on the light guide plate, the brightness of the front viewing angle can be maximized.
With the rapid development of LCD industry, the related LCD industry continues to push through the old and bring forth the new, and the size of LCD products is developing towards diversification and portability. As one of the core components of LCD products, backlight is bound to cooperate with this development trend and devote itself to product diversification and portability.
The above is a brief introduction to the basic material composition of the backlight of TFT-LCD, hoping to help you understand the knowledge and principle of LCD. For any problems and needs of industrial LCD, welcome to consult Deruxi technicial sales, and we will provide you with the best LCD solution.