Backlight Types and Applications (LED, CCFL, and EL)

Backlight

Backlights are primarily divided into three types based on light source: LED, CCFL, and EL. Depending on their distribution location, they are further categorized into edge-lit and direct-lit backlight panels. The following is a brief introduction. In the LED backlighting field, we have been providing customized LED backlight solutions to our clients for a long time, optimizing the layout of light guide plate(LGP) and light sources to enhance display performance and reduce energy consumption.

1. LED Backlight

LED lights, also known as light-emitting diodes, have the lowest power consumption per unit compared to other light sources. LED lights come in various colors from blue to red. There is also a special color called white. Among the various colors, they can be broadly categorized into high-brightness and low-brightness types.

Since white is a mixed color with no identifiable wavelength value, it is represented by its coordinates on the chromaticity diagram. We have defined it as “cool white” and “warm white.” Color deviation issues exist across all colors, with blue and white being particularly noticeable, especially white, which even LED suppliers cannot effectively control.

Edge-lit led backlight:

This involves placing linear or point light sources along the sides of a specially designed light guide plate to create a backlight. Depending on actual usage requirements, it can also be made into a dual-sided or even triple-sided design. Edge-lit backlights can generally be made very thin, but the light utilization rate of the light source is relatively low, and the thinner it is, the lower the utilization rate, with a maximum of approximately 50%. The core technology lies in the design and manufacturing of the light guide plate.

Direct-lit led backlight:

LEDs are uniformly arranged below the display panel. Advantages include good brightness and uniformity. Disadvantages include greater thickness (over 4.0mm), higher LED usage, and noticeable heat generation. Designs typically use low-brightness colors, while high-brightness colors are rarely considered due to cost constraints.

An electric light source refers to a device or apparatus that converts electrical energy into light energy. It is widely used in daily lighting, industrial and agricultural production, national defense, and scientific research.

2. EL backlight

Electroluminescence (EL) is a cold light source that emits light through the intrinsic luminescence of phosphors excited by an alternating electric field. Its primary advantage is its thinness, with a thickness ranging from 0.2 to 0.6 mm. The drawbacks include low brightness, short lifespan (typically 3,000 to 5,000 hours), the need for inverter-driven power supply, and susceptibility to circuit interference, which can cause flickering and noise. EL backlighting can be driven by inverters or Driver ICs. However, since the frequency and load output voltage of Driver ICs do not meet the typical requirements for EL (400 Hz, AC 100 V), their brightness is lower than that of inverter-driven systems. White light (full-color) EL and LCD backlights have also emerged.

Application:however, due to their low brightness, they are primarily used in small-sized LCD displays under 4 inches, such as mobile phones, PDAs, and game consoles. For full-color (white light) and large-sized high-brightness backlights, the mainstream solution remains the use of CCFL as the light source.

3. CCFL Backlight

Early displays mostly used CCFL (cold cathode fluorescent lamps) as backlight sources. These lamps have issues such as high power consumption, high heat generation, limited lifespan, and susceptibility to aging. Additionally, achieving uniform brightness requires stacking multiple lamps, increasing costs and thickness. Differences in the number and layout of lamps across different displays directly affect the uniformity of backlight brightness. The primary advantage of this backlighting is its high brightness, so it is widely used in larger-sized black-and-white negative-phase, blue-mode negative-phase, and color liquid crystal display devices. Theoretically, it can produce various colors based on the principle of color mixing using the three primary colors. However, its drawbacks include high power consumption, the need for an inverter circuit for drive, and a narrow operating temperature range of 0–60°C, whereas other backlighting sources like LEDs can operate between -20°C and 70°C.

Applications: CCFL is mainly used in medium- and large-sized LCD displays and industrial display equipment, and is particularly suitable for graphic display and high-brightness applications.

Summary

The selection of a light guide plate backlight requires comprehensive consideration of display size, brightness requirements, power consumption, lifespan, and cost:

Small, lightweight LCDs: EL backlight or edge-lit LED

Medium to large displays: CCFL backlight or direct-lit LED

Color displays: white light or RGB LED backlight