What you need to know about backlight unit in lcd
The backlight unit in tft screen is a very important part. The CCFL backlight used at the beginning has been eliminated, and the backlight unit used now is almost all white led backlight unit. What are their advantages and disadvantages? Please read the following article.
Led-backlight lcd module is now the most widely used tft display module, whether it is a smart watch, smart phone, monitor and TV. This also shows that led backlit has great advantages, so what is led backlit, and what is the difference between it and CCFL?
what is CCFL?
CCFL (Cold Cathode Fluorescent Lamp) technology is a backlight technology for LCD (Liquid Crystal Display) screens. Before the maturity of led backlit technology, tft screens used CCFL backlights.
The structure of CCFL backlit
The principle of CCFL is that the light-emitting principle of cold cathode fluorescent lamps is the same as that of general fluorescent lamps. Mercury and rare gases are contained inside the fluorescent tube. Generally, the gas enclosed in the high-efficiency cold cathode fluorescent tube is mainly a mixed gas of Ne+Ar (95%+5%). When the lamp tube applies voltage to both ends of the electrode, electrons are released at the tip of the electrode, and the released electrons collide with the mercury inside, and the excited mercury atoms are in an unstable state and then quickly return to a stable state, the remaining energy is released in the form of ultraviolet rays (main wavelengths are 253.7nm and 185nm). Phosphor powder absorbs ultraviolet rays of this wavelength and converts the energy of ultraviolet rays into visible light to cause luminescence.
Disadvantages of CCFL backlight
The uniformity and thickness of the fluorescent powder on the inner wall of the lamp tube will affect the uniformity of light emission, so the color consistency of CCFL is poor, and with the use of CCFL lamp tubes, the color changes and the brightness will decrease, and the power consumption will increase.
what is led backlight unit?
The structure of the white LED backlight unit is similar to the backlight structure using CCFL, but because the LED backlight unit uses LED beads to improve the light, and the lamp beads are point light sources one after another, an additional layer of diffusion sheet is needed to make the light uniform. The lamp bead has a light-condensing structure and does not need a reflector.
led backlight unit is a backlight technology that uses LED lamp beads as a light source. LED is a PN junction that releases photons through the recombination of holes in the P region and electrons in the N region. It is the direct conversion of electrical energy to light energy, so LED is also called It is a cold light source, so the LED has high luminous efficiency. The white light LED currently used is actually realized by the way that the blue light LED excites the phosphor. Ordinary LED lamp beads use silicate phosphor powder, which absorbs light of a specific wavelength, resulting in a narrow LED spectrum. The effect of LED beads using YAG phosphor will be much better. 85% NTSC, and even 105% NTSC tft displays use led backlight unit made of this kind of LED lamp beads.
How to control led backlight unit color coordinates?
It is also difficult to control and control the waves of light produced by LED lamp beads in a consistent manner. In addition, the uniformity of phosphor powder is different, so the color coordinates of LED lamp beads vary greatly among individuals. During the production process of LED lamp beads, voltage and color sorting will be carried out.
The led beads will screen out several kinds of led lamp beads, which are called LED lamp beads of different color blocks. Usually led backlight lcd module will use two kinds of color blocks of lamp beads, which can mix the required white. Use the combination of lamp beads of different color blocks to adjust the white to blue, white to yellow and other effects.
The white LED lamp bead is the white light emitted by the blue LED light-emitting chip to excite the yellow phosphor, and different colors and different spectrums of light can be obtained by using different phosphors. The uniformity of mixing and the thickness of the phosphor will affect the color.
The relationship between led current and brightness
There is a positive correlation between brightness and current. When the current increases, the brightness will also increase, but there is a current limit. As long as the current exceeds the maximum forward current, it will be damaged. The led-backlight unit uses a patch type LED lamp, and the general current is selected at 2-30mA. Now there is a design that integrates two LED chips into one LED lamp. This is to increase the brightness of the LED backlight unit, but the same current will also increase exponentially.
Common chroma ranges for led backlight unit
|cold white area
|warm white area
The colors in this area are all white but look different.
In the color coordinate system, we can find that the white area is actually larger than the area we set.
How to measure led backlight unit color coordinates
The white color coordinates recognized in the industry are (X=0.31, y=0.32), but it should be noted that although there are sophisticated equipment that can accurately test the excellent coordinates, such as Konica Minolta’s CA-310/CA-410 , or Topcon’s BM-7, etc., although the values tested by the instrument are the same, the resolution of the human eye far exceeds that of the equipment, so when you have a new project, you need to see the product in person to confirm the display effect and color.
what are the advantages of led backlight unit in lcd ?
1. led backlight lcd module has high luminous efficiency and energy saving
the power consumption of led backlight unit is 10%-20% of incandescent lamp with the same brightness, and 1/2 of fluorescent lamp.
2.led backlight lcd module is more environmentally friendly
led backlight unit is a cold light source, not easy to break, and there is no electromagnetic interference when working. And mercury-free lamps have metal.
3. led backlight unit long life
the life of led backlight unit can reach 100,000 hours, and the light decay is small, and the stability is high.
4.the led backlight lcd module is a solid-state light source, small in size and light in weight
led backlight lcd module uses LED lamp beads, the size of a single unit is 3~5mm, and the direction of light emission can be set, making the light more concentrated and efficient.
5.led backlight lcd module fast response time
led backlight lcd module has a very fast response speed and operates in harsh environments.
6. Brightness and color accuracy of led backlight lcd module are easily adjusted
led backlight lcd module can easily achieve a brightness of 350~420cd/㎡ and can achieve a brightness of 1000~3000 cd/㎡ by increasing the number of LED lamp beads and can adjust the color coordinates and the displayed color.
7. relatively low drive voltage and current for led backlight unit
Each LED lamp bead requires a driving voltage of 3V~3.2V and a driving current of 20mA~30mA. Even if many lamp beads are connected in series, the voltage is safe.
8. led backlight lcd module accurate and continuous brightness adjustment
led backlight lcd module can achieve DC continuous dimming, no flicker in the dimming process, and high accuracy.
9.led backlight lcd module better color gamut
The color gamut can be improved by replacing the phosphor used in the led backlight lcd module. The color gamut displayed by the led backlightt lcd module is the result of the superposition of the led backlight unit and lcd display. When using YAG phosphor, the spectral range of light emitted by LED lamp beads will become wider, thereby obtaining a higher color gamut.
10.led backlight lcd module has greater potential
Among the new technologies of led backlight unit, the mini-led technology is available to everyone. By changing the traditional side-entry led backlight unit to tens of thousands or even hundreds of thousands led direct led backlight to obtain performance comparable to OLED. Due to the problem of yield rate, this technology is not popular enough, but with the improvement of technology, I believe that led backlit lcd will become better and better in the future.
The development of led backlight
LED backlight LCD displays are one of the most common display technologies today, and their future potential remains high. Mini led and thinner, more efficient and low energy consumption are the two main directions:
- mini-led: Although the performance of OLED displays is excellent, it is unavoidable that its high cost and relatively low service life limit the further development of OLED. The lcd display has been developed for nearly 20 years. Every lcd screen has a large production capacity, and the price of lcd display is moderate. If the yield rate of mini-led can be improved, then with the ultra-high contrast and high refresh rate of mini-led, It is sure to be well developed in the fields of monitors, car displays and TVs.
- The power consumption of the current led backlit is still very high. If you have read Harmony Optoelectronics’ article on LCD display power consumption
you will find that the main power consumption of the led backlit lcd comes from the led backlit, and the power consumption of the lcd screen is only 0.1~0.3mW.
If it is a sunlight readable display, the power consumption of the led baklit will reach several watts! If the power consumption and size of the led backlight unit can be better, it will undoubtedly be a great boon for devices that need battery power.
China’s lcd screen manufacturer has never stopped the research and development of led backlit. Harmony Optoelectronics is an expert in this field. We have done a lot of research on sunlight readable display, high color gamut, and ultra-low power consumption LCD display. If you are looking for this products, please contact us, our professional team will quickly give design plans and samples!