Classification Knowledge Of Backlight

The backlight is an optical component that provides a back light source in LCD display products. Since the liquid crystal panel itself does not have light-emitting characteristics, a light-emitting source, that is, a backlight source, is added behind the liquid crystal panel as needed. The application range covers industrial equipment, bank terminals, office automation, communications, electronic toys and consumer products.

Working principle of backlight:

The working principle of the LED backlight is to turn a point light source (LED) into a surface light source (backlight).

Backlight classification:

Backlights are currently divided into three types of backlights: EL, CCFL, and LED according to the type of light source. According to the different light source distribution positions, they are divided into side-light type and direct-light type (backlight type).

The following is a brief introduction of them:

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Side light

: The backlight is made by setting the linear or point light source on the side of a specially designed light guide plate. According to the needs of actual use, it can be made into two-sided or even three-sided. Edge-light type backlights can generally be made very thin, but the light utilization rate of the light source is relatively small, and the thinner the light source, the smaller the utilization rate, the maximum is about 50%. The core of its technology is the design and production of light guide plates. The most commonly used side-light type are LED backlight and CCFL backlight.

(1)

LED backlight: LED lights are also known as light-emitting diodes. Compared with other light sources, the power consumption of a single LED light is the smallest. From blue to red, LED lights come in many colors; another special color is white. In various colors, it can be roughly divided into two types: high-brightness and low-brightness. Compared with the traditional cold cathode tube backlight, LED has the characteristics of low power consumption, low heat generation, high brightness and long life. The brightness of the LED backlight is high, and the brightness will not decrease after long-term use. The body of the LED backlight is thinner, the appearance is also beautiful, and the color is softer. The color of the hard screen panel can make the eyes more comfortable. All LED backlights have Yes, power saving and environmental protection have low radiation.

Since white is a mixed color, there is no identifiable wavelength value, so it is represented by its coordinate value on the chromaticity diagram. We customize it as "cool white" and "warm white". In various colors, there is a problem of color deviation. Among them, blue and white are more obvious, especially white. Now LED suppliers can't effectively control it.

(2)

CCFL backlight: The biggest advantage of this kind of backlight is high brightness, so the large area black and white negative phase, blue mode negative phase and color liquid crystal display devices basically use it. In theory, it can make a variety of colors based on the color matching principle of the three primary colors. The disadvantage is that it consumes a lot of power, it also needs inverter circuit drive, and the operating temperature is narrow, between 0 and 60 degrees, while other backlight sources such as LEDs can reach between -20 and 70 degrees.

The inner wall of the CCFL glass tube is coated with fluorescent powder, and the hall is filled with inert gases and mercury elements; electrons showing high voltage ionize the inert gases into positively charged ones, and then during the movement of this charged gas, when it collides with mercury, the mercury emits ultraviolet rays , The ultraviolet rays will excite the phosphor on the inner wall to emit visible light.

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Backlit

: It is a flat surface light source with a certain structure, which can be a continuous and uniform surface light source, such as EL or flat fluorescent lamp; it can also be composed of more point light sources, such as dot matrix LED or incandescent backlight. Commonly used are LED dot matrix and EL backlight.

(1)

EL backlight: electroluminescence, a cold light source that relies on the intrinsic luminescence of phosphors excited by an alternating electric field. Its biggest advantage is its thinness, which can achieve a thickness of 0.2~0.6mm. Disadvantages are low brightness, short life span (usually 3000~5000 hours), inverter drive is required, and flicker, noise and other defects may occur due to circuit interference. There are two types of EL drivers: inverter and Driver IC.

EL backlight is an electroluminescent backlight, which has the advantages of thin thickness, light weight, low power consumption, and uniform light emission. It has different colors, but the most commonly used is white light. Compared with CCFL, EL only needs 80-110V AC voltage to work. At present, EL is mainly used for small-size LCD displays below 4 inches, such as mobile phones, pDA, game consoles, etc., but has not yet been used in LCD color TVs.

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Because the frequency and load output voltage of the current Driver IC cannot reach the typical conditions of EL (400Hz, AC100V), the brightness is lower than that of the inverter drive. Recently, white light (full-color) EL and LCD backlights have emerged. However, due to the low brightness, it is basically used for small size LCD displays below 4 inches. Such as: mobile phones, PDAs, game consoles, etc. Full-color (white light), large-size brightness backlight, and now the mainstream is still using CCFL as the light source.

(2) LED bottom backlight

: The advantages are good brightness and good uniformity. The disadvantage is that the thickness is large (greater than 4.0mm), the number of LEDs used is large, and the heating phenomenon is obvious. Generally use low-bright colors for design, while high-bright colors are basically not considered due to the high cost