What is the TFT display's backlight?

Views: 232     Author: Reshine Display     Publish Time: 2023-11-30      Origin: Site

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What is the TFT display's backlight?

BackLight is a light source located behind the liquid crystal display (LCD), and the luminous effect of the light source has a direct impact on the visual effect of the liquid crystal display module (LCM). Liquid crystal displays do not emit light; instead, they display graphics or are the result of light modulation.


1. Backlight composition:

The backlight source is primarily composed of a light source, a light guide plate, an optical module, and structural components.

Light sources include EL, CCFL, and LED, as well as three types of backlight.

Printing, chemical etching (etching), precision mechanical etching method (V-cut), light micro-shading (stammer), internal diffusion, and hot pressing are the different types of light guide plates.

Lightening film/sheet, diffusion film/sheet, reflective sheet, and black/white adhesive are all molded sheets for optics.

Structural components include the back plate (iron backplate, aluminum backplate, plastic back plate), rubber frame, lamp holder, aluminum profile, and aluminum base strip, of which the back plate and rubber frame are required, while the other structural components are optional.


2. Operating Principle

A liquid crystal display is a passive light-emitting element; the display itself does not emit light, but it is illuminated by the backlight system beneath it. A liquid crystal display module was created by combining a backlight and an LCD. The LCD backlight is a flat, uniform illumination device, with cold cathode fluorescent tubes or LED strips arranged on both or one side of the entire backlight (which can be the long or short side). Line light sources are cold cathode fluorescent tubes, while point light sources are LEDs. Converting this light source to a surface light source requires the use of light guides. Light guides are typically made of high-transmittance acrylic plastic with a surface that is so smooth and flat that the majority of the internal light is fully reflected on its flat surface and is not emitted to the outside of the light guide. A white dot is printed on the bottom of an LCD's light guide. The light will no longer be reflected regularly at the position where the dot is printed on the light guide but will instead be emitted to the top of the light guide. The amount of light emitted from the light guide plate at each position is controlled by adjusting the density of the dots at that position. Precisely designed light guide dots distribute incident light evenly across the entire plane. On top of the optical film will be a light guide plate; these films provide uniform light and large-angle light convergence for the front view. Click here for TFT LCD Display.


The light source, light guide plate, reflective sheet, and optical film are mechanisms for changing the polarization direction of the light. The light then passes through the color filter to produce color before reaching the upper polarizer. Some light can be emitted, and some can be absorbed after being polarized by the liquid crystal. The intensity of the outgoing light can be determined by each pixel on the entire LCD panel. This generates an image.


3. Use of Backlighting

One of the most important components of an LCD panel is the backlight module. The function is to provide enough brightness and a uniform distribution of light sources so that images can be displayed normally.


With the continuous development of liquid crystal display technology, liquid crystal displays, especially color liquid crystal display applications, are also constantly broadening. Pulled by the market for liquid crystal displays and the backlight industry, this shows a prosperous scene. The LCD for a non-luminous display device must be supported by the backlight to achieve the function of the display. In addition to the performance of the backlight having a direct impact on the LCD image quality, the cost of the backlight accounted for 30–50% of the LCD module, and the power consumed by the module accounted for 75%, which can be said to be quite an important a highly component of the LCD module. Highly detailed, large-size LCD, there must be a high-performance backlight technology, so when the LCD industry makes efforts to develop new applications at the same time, the high performance of the backlight technology (such as high brightness, low cost, low power consumption, thin and light, etc.) also plays a role in the backstage hero.


4. Classification of Backlight

4.1 Classification according to the light source

At present, there are three main types of backlight sources: EL, CCFL, and LED.

EL Backlight

Electroluminescent (EL) backlighting is thin and lightweight, providing uniform light. Its power consumption is very low; the required operating voltage is 80 ~ 100 Vac, and the operating voltage inverter can be 5/12/24Vdc input into the AC output. However, EL backlighting has a limited service life (the average service life under 50% brightness conditions is 3,000 to 5,000 hours, and the service life will be much shorter at higher brightness levels). Therefore, an ideal inverter for EL backlighting allows the output voltage and frequency to increase with the aging of the EL bulb, thereby extending the effective life of displays employing EL backlighting sources.


EL backside illumination is suitable for small reflective LCD applications such as watches, digital desktop clocks, and monochrome PDAs that require extremely weak illumination for use in hazy or dim lighting conditions. However, their low efficiency, low brightness, and short lifetime make them unsuitable for use in transmissive backlighting applications such as the large LCDs required for laptop computers and flat-panel desktop monitors.


ccfl Backlighting

ccfl is a cold cathode fluorescent lamp, a gas discharge light-emitting device, its structure is similar to the commonly used fluorescent lamps, through the connection plug and high voltage board connected. ccfl has a small tube, simple structure, the surface temperature rise is small, the surface brightness is high, easy to be processed into a variety of shapes (straight tube, L-shaped, U-shaped, ring, etc.), long service life, color rendering, uniformity of light-emitting and so on. LCD screen is the most ideal backlight.


LED backlight

LED backlighting refers to the use of LED (light-emitting diode) as the backlight of the liquid crystal display. Compared with the traditional CCFL (cold cathode tube) backlight, LED has low power consumption, low heat, high brightness, long life, and other characteristics, and is expected to completely replace the traditional backlight system in recent years.


4.2 Classification according to the light source distribution

Depending on the location of the light source distribution is divided into side light type, straight down type (bottom backlight type), and hollow type. As LCD modules continue to develop in the direction of brighter, lighter, and thinner, side-lit CCFL backlighting has become the mainstream of backlighting development.

Side-illuminated

Edge lighting is a single light source placed on the side, and the light guide plate adopts the injection molding non-printing design, which is generally used in small and medium-sized backlight modules below 30 inches, and its side-incidence light source design has the features of light weight, thinness, narrow frame, and low power consumption, and it is also the light source for cell phones, tablet PCs, and notebooks, and there are also large-sized TV backlight modules adopting the Edge Lighting structure. ②Direct down type


Straight down type

Straight down type (Bottom lighting) oversized backlight module, side light structure has been unable to take advantage of the weight, consumption of electricity and brightness, so does not contain a light guide plate and the light source is placed directly under the straight down type structure will be developed. The light source is released through the reflector from the spontaneous light source (such as a lamp, LED, etc.), and is subsequently uniformly distributed upward through the diffusion plate before being released from the front. The lamp has the advantage of high luminance, good viewing angle, high efficiency of light utilization, and simplicity of structure, so it can be used with two or more lamps depending on the size of the TFT panel due to the larger placement space. However, at the same time, it also increases the thickness of the module, weight, and power consumption. High luminance, a good viewing angle, high light utilization efficiency, a simple structure, etc. are some of the benefits. Therefore, it is suitable for LCD monitors and LCD TVs which are not picky about portability and space requirements, but its high consumption of power (using cold cathode tube), poor uniformity, and heat generation of LCD still need to be improved.


Hollow type

With the increase in the size of the image requirements, LCD is also towards the direction of the development of larger sizes, this type of ultra-large LCD is used as a monitor and wall-mounted TV, not only requires a large picture, high brightness and lightweight, electrical requirements of high power under the low thermal effect, the development of the hollow-type structure of the backlight module, the use of hot cathode tube as a light source. The light source in this structure is transmitted through air; it is reflected and adjusted in the opposite direction by the prism sheet and reflector plate. A portion of the light source travels through the light guide plate and is released onto the surface, while the remaining portion enters the hollow cavity and is re-emitted through the refracting effect. The upward light source either enters the light guide plate directly and is released, or it is released through a sequence of refracting and reflecting effects. The light guide plate is shaped like a wedge. The shape of the light guide plate is a wedge-shaped structure, the purpose is to seek the effect of homogenization.

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