The Working Principle And Types Of LCD Backlight Panel

Backlights are optical components that provide a backside light source in LCD display products. Since the liquid crystal glass itself does not have light-emitting properties, a light-emitting source, that is, a backlight panel, will be added behind the liquid crystal glass as required. Applications cover communications, medical, beauty, instrumentation, industrial equipment, bank terminals, vehicle-mounted equipment, office automation, electronic toys and consumer products.

Types of Backlights

1. There are three types of backlight panels for LCD screens, which are backlight panels using CCFL lamps, namely cold cathode lamps, backlight panels using EEFL lamps without cold cathode lamps, and backlight panels using LED light-emitting diodes.

2. CCFL (Cold Cathode Fluorescent Lamp) backlight is currently the most important backlight product for LCD screens. Cold Cathode Fluorescent Lamp, namely CCFL (Cold Cathode Fluorescent Lamp), or CCFT (Cold Cathode Fluorescent Tube). Its working principle is that when a high voltage is applied to both ends of the lamp tube, a small number of electrons in the lamp tube hit the electrodes at high speed to generate secondary electron emission and begin to discharge. The ultraviolet light generated excites the phosphor coated on the inner wall of the tube to generate visible light.

3. LED backlight uses light-emitting diodes as the backlight source, which is the most promising technology to replace traditional cold cathode fluorescent tubes in the future. Light-emitting diodes are made of several thin layers of doped semiconductor materials. One layer has excess electrons, and the other layer lacks electrons to form a positively charged void. When working, current flows through, and electrons and voids combine with each other, resulting in excess energy. is released in the form of optical radiation. Light-emitting diodes with different light-emitting properties can be obtained by using different semiconductor materials.

Backlight panel details

1. LED light backlight: LED light is also called light-emitting diode. Compared with other light sources, the power consumption of a single LED light is very small. From blue to red, LED lights have many colors, commonly used such as "Table 1" and "Table 2"; another special color is white, and "Table 3" gives its commonly used chromaticity range. In various colors, they can be roughly divided into two types: high light and low light: Basically, "Table 1" belongs to low light (although amber, orange and red also have slightly brighter ones), " Table 2" and "Table 3" are highlighted.

Since white is a mixed color and has no identifiable wavelength value, it is represented by its coordinate value on the chromaticity diagram. We customize it as "Cool White" and "Warm White". In all kinds of colors, there is a problem of color deviation, among which blue and white are more obvious, especially white, and now LED suppliers cannot effectively control it.

2. CCFL backlight: The great advantage of this kind of backlight is high brightness, so it is basically used in black and white negative phase, blue mode negative phase and color liquid crystal display devices with large area. In theory, it can make various colors according to the color matching principle of three primary colors. The disadvantage is that the power consumption is large, it needs to be driven by an inverter circuit, and the operating temperature is narrow, which is between 0 and 60 degrees, while other backlight boards such as LED can reach between -20 and 70 degrees.

Backlight use

1. LCD backlight

The principle of LCD backlight is that the reflector, light guide plate, upper and lower BEF, LED light bar and plastic frame iron frame are assembled together. When the LED light bar is powered on, the component emits side view light, which becomes flat light after passing through the light guide plate, providing backlight for LCD display. source.

During the processing of the mobile phone backlight, when assembling the FPC assembly on the light guide plate, it is necessary to tear off the lamp glue release paper, and then paste the FPC assembly on the corresponding position on the light guide plate (generally provided with grooves), in order to ensure The sticking is firm, and generally needs to be pressed at the sticking position. If the gripper robot in the prior art is used for operation, at least two units are required for each work position, one of which is to tear off the light glue release paper, and the other is used for Grab FPC components.

The backlight is the source of light behind the glass of the phone. But not only refers to LED, because the current stage of the backlight is generally composed of plastic frame, reflective film, light guide plate, diffusion, lower light, upper light, shading glue, LED light bar.

Because the liquid crystal display device itself is transparent and does not emit light, a backlight panel is needed to assist. Some indicators such as the brightness and uniformity of the backlight have a direct impact on the relative performance of the LCD screen.

Backlight (back light) is actually a high-brightness illuminator that combines fluorescent lamps and reflectors on the back of the LCD during the manufacture of the LCD. Because the liquid crystal panel of the LCD liquid crystal display does not emit light, it can only transmit light, so To add a bright light on the back.

Although the optical mechanism of the backlight panel seems simple, the optical characteristics, dimensions and relative positions of each component form an interlocking and closely integrated interactive relationship for the overall optical performance of the backlight panel. At the same time, how to improve the optical efficiency while simplifying the mechanism and process is an important technical key for the future development of the backlight panel.

The role of the backlight

1. Because the liquid crystal display device itself is transparent and does not emit light, a backlight plate is needed to assist the light emission.

Some indicators such as the brightness and uniformity of the backlight have a direct impact on the relative performance of the LCD screen.

1. The basic structure of the product: refers to the shape structure, which affects the assembly of the customer's module.

Since the basic structure of the product is related to the customer module, it cannot be changed at will. Except that the customer module has not been designed yet, it will only be designed after the backlight board is released.

2. Performance includes: brightness, uniformity, storage temperature, operating temperature, input current and voltage and other test conditions and optical requirements.

The input current and voltage are determined by the guest module, so it is necessary to clearly understand the IF and Vf values in the design in order to deal with the brightness.

Brightness refers to the intensity of light per unit of light-emitting area. The storage temperature ranges from -30 degree to plus 80 degree ; the operating temperature ranges from -20 degree to plus 70 degree .