LCD monitors require a backlight to display images, and the mainstream backlight technologies currently include CCFL (Cold Cathode Fluorescent Lamp) and LED. CCFL is the traditional backlight technology. So, what is CCFL backlighting? What are its advantages, disadvantages, and limitations? This will be explained in detail below.
The biggest difference between LCDs and plasma displays is that LCDs must rely on a passive light source, while plasma TVs are active light-emitting display devices. Currently, the mainstream LCD backlight technologies on the market include LED (Light Emitting Diode) and CCFL (Cold Cathode Fluorescent Lamp).
1. Cold Cathode Fluorescent Lamp (CCFL) Traditional LCD monitors all use CCFL (Cold Cathode Fluorescent Lamp) backlighting. CCFL backlight designs primarily come in two types: edge-lit and direct-lit. However, edge-lit backlights suffer from higher light refraction due to their light guide design, limiting backlight brightness. The brightness decreases with larger panel sizes, making them suitable only for 8-inch to 15-inch TFT LCD panels, ideal for personal viewing in laptops and desktops. For large-screen LCD TVs used in home viewing, edge-lit backlights are insufficient, necessitating the use of direct-lit backlights.
However, the larger the LCD size, the higher the cost of the backlight module. This specifically refers to direct-lit CCFL backlight modules. Statistics show that for 15-inch LCDs using direct-lit CCFL backlight modules, the backlight module accounts for only 23% of the overall cost, but this increases to 37% for 30-inch models, and is estimated to reach 50% for 57-inch models. Therefore, direct-lit CCFL backlights are only suitable for mid-sized LCD TVs around 30 inches and not for larger designs. Meanwhile, CCFLs use mercury gas discharge to generate light. Although the current EU RoHS regulations are acceptable as long as the mercury dosage is below the standard, there is no guarantee that the standard may be raised to zero content (completely prohibiting its use) in the future. At that time, CCFLs will be unusable, or a mercury-free CCFL will have to be adopted.
Even if mercury-free CCFLs are technically feasible, CCFLs are still sealed tube-type gas discharge electronic lighting. The tube has limited resistance to external forces; a large impact will cause the tube to break, resulting in lighting failure. Other solid-state electronic lighting (such as LEDs) does not have this concern. Furthermore, since direct-fall lighting does not require a light guide plate and has less light refraction, it also eliminates the need for a brightness enhancement film. In particular, brightness enhancement films are patented technologies of a few manufacturers and are expensive. Direct-fall lighting eliminates the need for a light guide plate and brightness enhancement film, which helps reduce costs.
However, direct-flush CCFLs also have their drawbacks. To improve screen brightness, the number of LEDs must be increased. However, overly dense arrangement of LEDs hinders heat dissipation. Since the space between the LEDs is reduced, the only solution is to increase the thickness to improve heat dissipation. However, this increased thickness partially negates the advantage of LCD TVs: their slimness.
Incidentally, when using CCFL LEDs in large-screen LCD TVs, the length of the LEDs must also increase accordingly. However, longer CCFL LEDs are prone to brightness and color variability issues in the middle and at both ends, affecting backlight uniformity. To maintain uniformity, a diffuser film must be used, but this also reduces light transmittance, lowering brightness. This brightness reduction is compensated for by increasing the number of LEDs. However, as mentioned earlier, increasing the number of LEDs makes heat dissipation design more difficult, increases the thickness of the backlight module, and even increases power consumption. It is understood that CCFL backlight modules account for as much as 90% of the total power consumption of an LCD TV. Therefore, changing the backlight technology is one of the current directions for improving LCD image quality.
