In the past, we explained that LCD display screens are composed of multiple layers, with a focus on the liquid crystal layer. In this article, we will introduce the LED backlight layers of different structures such as CCFL, WLED, mini LED, DLED, ELED, and FALED.
1. Comparison of LCD backlight structure
| Backlight Type | Advantages | Disadvantages | Best For |
|---|---|---|---|
| CCFL | High brightness, good color rendering | Bulky, power-hungry, contains mercury | Older displays, largely phased out |
| WLED | Thin, energy-efficient, versatile | Lower contrast without advanced local dimming | Standard monitors, general use |
| DLED | High brightness, local dimming | Thicker design, potential halo effect | Mid-range TVs, displays needing better contrast |
| ELED | Slim, lightweight, cost-effective | Limited contrast, prone to light leakage | Budget TVs, space-saving monitors |
| FALED | Superior local dimming, best picture quality | Higher power consumption, more expensive | High-end TVs, professional monitors |
2. What is the CCFL Backlight Structure?
CCFL stands for Cold Cathode Fluorescent Lamp, which served as the backlight layer in early LCD display screens. CCFL consists of fluorescent tubes laid flat across the back of the display. It has the following features:
High Brightness and Color Temperature: CCFLs offer high color temperature and good color rendering, providing vivid images with rich colors.
Disadvantages:
- High Design Complexity: The backlight layer must be carefully designed to ensure uniform light distribution to the liquid crystal layer, requiring precise flatness.
- Thickness Issues: As screen sizes increase, more CCFL tubes are required, making it difficult to keep the backlight thin. This results in a more complex structure.
- Limited Color Gamut: CCFLs can only achieve about 72% NTSC color gamut coverage, limiting their ability to reproduce colors accurately.
- High Power Consumption: CCFLs consume a lot of power, have low luminous efficiency, and contain toxic mercury, posing environmental risks.
Due to these significant drawbacks, CCFL backlights have largely been replaced and are rarely used in modern LCD displays.
3. What is the WLED Backlight Structure?
WLED stands for White Light Emitting Diode, which is the standard backlight in most LCD displays today. WLED backlighting has replaced CCFL in nearly all LCD screens due to its superior features:
Advantages:
- Simpler Structure: WLED backlighting only requires the LED lamp beads to be evenly distributed on a backlight board, ensuring consistent brightness across the liquid crystal layer.
- Thinner and Lighter: WLED lamp beads are typically only 2mm thick, making them much slimmer than CCFL tubes. This enables the development of thinner and lighter displays like TFT LCDs.
- Lower Power Consumption: WLEDs use less power and have higher luminous efficiency, making them more energy-efficient.
Disadvantages:
- High Design Complexity: The backlight layer must be carefully designed to ensure uniform light distribution to the liquid crystal layer, requiring precise flatness.
- Thickness Issues: As screen sizes increase, more CCFL tubes are required, making it difficult to keep the backlight thin. This results in a more complex structure.
- Limited Color Gamut: CCFLs can only achieve about 72% NTSC color gamut coverage, limiting their ability to reproduce colors accurately.
- High Power Consumption: CCFLs consume a lot of power, have low luminous efficiency, and contain toxic mercury, posing environmental risks.
The advancement of WLED technology has led to more specialized structures like DLED, ELED, and FALED, which are detailed below.
3.1. DLED Backlight Structure
DLED structure backlight is to place the LED backlight under the liquid crystal layer, and the light emitted by the LED backlight is directly projected to the liquid crystal layer. The DLED structure has a high light utilization rate, which ensures higher brightness and contrast of the LCD display, and can be used with local dimming technology to improve the blackness of the image and produce first-class picture quality, with a contrast ratio of up to 10,000,000:1.
Advantages:
- High Light Utilization: Direct placement of the LEDs ensures that most of the light reaches the screen, resulting in higher brightness and contrast levels.
- Local Dimming Capability: DLED backlighting can be paired with local dimming technology, enhancing black levels and creating a contrast ratio of up to 10,000,000:1.
Disadvantages:
- Increased Thickness: Since the DLED structure places LEDs directly behind the screen, it adds thickness to the display.
- Halo Effect: DLED structure does not completely use addressing to control LED backlight, so when displaying a bright image with a dark background, a halo will appear around the bright image, which is called the halo effect..
3.2. ELED Backlight Structure
ELED structure backlight is the most economical and lowest power backlight structure. It distributes LED light sources on the border of the display screen and then uses a light guide plate to evenly distribute the light to the entire display screen. Compared with the DLED structure, the ELED structure backlight uses fewer LED lamp beads and has no LED backlight layer at the back. Therefore, the LCD display of the ELED structure will be thinner and lighter, and the power consumption will be lower. However, the ELED structure is difficult to adapt to the local dimming method. In order to optimize the halo effect, the ELED structure optimizes the lighting method on both sides and controls the upper and lower light separately, but due to the shortcomings of the ELED structure, the halo effect cannot be completely solved.
Advantages:
- Thin and Lightweight: ELED backlighting places LEDs on the display’s edges, making it possible to create very slim and lightweight screens.
- Lower Power Consumption: Fewer LEDs are needed compared to DLED, resulting in lower power use, making ELED a cost-effective solution.
Disadvantages:
- Lower Contrast Efficiency:ELED structure is the backlight structure with the lowest efficiency in achieving high contrast.
- Prone to Light Leakage: Due to structural defects, ELED structure is difficult or even impossible to apply local dimming.
- Halo Reduction Challenges: ELED structure has high dimming requirements for manufacturers and is very likely to cause light leakage.
3.3. FALED Backlight Structure
FALED structure backlight is a full array LED structure backlight, which evenly covers the entire backlight layer with LED lamp beads. Unlike the DLED structure, the FALED structure has more LED lamp beads, and the entire screen is evenly covered by the backlight, providing better contrast and picture quality, and the effect achieved with optical bonding technology is better. FALED structure provides the most effective local dimming because the addressing method can be used to control the dimming of individual LED lamp beads, which helps to achieve a perfect black background and avoid the halo effect.
Advantages:
- Even Light Distribution: FALED’s full-array design ensures consistent lighting across the entire screen, reducing issues like uneven brightness or light bleeding.
- Superior Local Dimming: Each LED can be individually controlled, allowing for precise local dimming. This makes it possible to achieve deep blacks and high contrast without the halo effect.
- Excellent Picture Quality: The even backlight coverage and advanced dimming capabilities result in superior image clarity and contrast, making FALED ideal for high-end displays.
Disadvantages:
- Higher Power Consumption: The larger number of LEDs in FALED increases energy usage.
- Increased Thickness and Weight: More LED components make FALED backlit displays thicker and heavier.
- High Cost: The cost of manufacturing FALED displays is significantly higher than DLED or ELED, which is reflected in the price of the final product.
FALED is often used in premium displays where superior image quality and accurate color reproduction are critical.
4. FQA
1. What is the difference between ELED and DLED?
ELED places LED lights along the edges of the display, making it thinner, while DLED uses LEDs directly behind the screen for better contrast but a thicker profile.
2. Why is FALED preferred for high-end displays?
FALED offers precise local dimming, better light uniformity, and superior picture quality, making it ideal for displays where color accuracy and contrast are critical.
3. Is CCFL still in use today?
CCFL backlighting has been mostly phased out due to its lower energy efficiency and environmental concerns, replaced by LED-based technologies.
4. Which backlight type is the most energy-efficient?
ELED is typically the most energy-efficient option as it uses fewer LEDs. WLED is also a good choice for low power consumption.
5. Does DLED have better picture quality than ELED?
Yes, DLED generally offers better contrast and brightness levels due to its ability to utilize local dimming more effectively.
6. What is a major drawback of FALED?
The main drawback of FALED is its higher cost and increased power consumption, making it less accessible for budget-friendly options.
