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What are the two main types of backlights for TFT-LCD?
The backlight source of TFT-LCD is mainly composed of materials such as light source, optical film and light guide plate.
The light source used by the backlight determines the optoelectronic parameters such as power consumption, brightness, and color of the backlight. Light sources are divided into three categories: linear light sources, point light sources, and surface light sources according to their luminous shapes. In TFT-LCD, mainly use CCFL linear backlight source or LED point backlight source.
1. CCFL backlight source
CCFL is a closed gas discharge tube with cold electrodes at both ends of the tube, made of nickel, tantalum, zirconium and other metals, which can emit electrons without heating.
As the light source of the photometric backlight, CCFL needs to install a lamp reflector on the opposite side of the light guide plate to reflect the light of the CCFL lamp tube, so that it can enter the light guide plate for use, thereby improving the utilization rate of light.
2. LED backlight sources
Led is a semiconductor solid-state light-emitting device, which is mainly composed of led crystal grains, phosphors, emitters, prisms, and substrates.
Compared with CCFL, Led backlit has the advantages of energy saving, environmental protection, lightness and high quality. The internal driving voltage of Led is much lower than that of CCFL, and its luminous efficiency is more than twice that of CCFL. It does not contain mercury, which is costly and harmful to the environment.
also. In addition, the Led is small in size and the exit direction is fortunate, which can greatly reduce the thickness of the light guide plate in the traditional backlight source, and at the same time omit the light reflector.
Comparison of LED light source and CCFL light source
| ITEM | LED light source | CCFL light source |
| Backlight uniformity | Good | Ordinary |
| Luminous efficiency | Good | Ordinary |
| NTSC | >105% | About 72% |
| Contrast | High | Ordinary |
| Driver | Conventional DC voltage | High voltage |
| Heat dissipation | Not good | Good |
| Light up and down time | Nanosecond | 1-2s |
| Working life (hours) | 100 000 | 20 000-50 000 |
| Appearance | Light and Thin | Thick and heavy |
| Environmental friendly | No radiation, no heavy metals, recyclable | Radiation, mercury, non-recyclable |
| Application Environment | No limit | Poor low temperature starting ability |
