Internal Structure of an LCD Panel and Its Functional Analysis

Internal Structure of an LCD Panel and Its Functional Analysis

Understanding how an LCD (Liquid Crystal Display) panel works requires examining the internal layers that control light passage and image formation. Below is a breakdown of each key component and its function within an LCD.

1. Backlight Unit (BLU): The Light Source of the LCD

What Is the Function of the Backlight in an LCD?

The backlight is the essential light source in any LCD panel. Unlike OLED displays, LCD do not emit light on their own. Instead, the backlight provides illumination for the entire screen.

• Modern LCD use LED backlights—either full-array LEDs positioned behind the screen or edge-lit LEDs placed on the sides of a light guide plate.

• Older LCD used CCFL (Cold Cathode Fluorescent Lamp) tubes, which required high voltage and were bulkier.

Since liquid crystals cannot emit light, the backlight shines through the liquid crystal layer and is modulated to form visible images on screens used in TV, monitors, laptops, and mobile phones.

2. Vertical Polarizer: Controlling Light Orientation

What Does a Vertical Polarizer Do in an LCD?

A polarizer is a film made of polyvinyl alcohol (PVA) that filters light waves based on their orientation.

• Function: As light from the backlight travels through the LCD, it first encounters the vertical polarizer. This film only allows vertically oscillating light waves to pass through, blocking all other directions of light.

• Importance: This polarization is critical because the behavior of the liquid crystal molecules depends on the direction of light. The vertical polarizer works with the horizontal polarizer (on the opposite side) to control how much light gets through.

Together with the liquid crystal layer, polarizers determine how much light is transmitted or blocked, directly affecting brightness and image clarity.

3. TFT Substrate: The Pixel Control Matrix

What Is TFT and Its Role in LCD Panels?

TFT (Thin-Film Transistor) technology is a type of active matrix used in modern LCDs for precise control of individual pixels.

• Structure: The TFT substrate is a glass base with an array of microscopic transistors and capacitors.

• Function: Each pixel is linked to its own TFT switch. These switches control the voltage applied to the liquid crystal cell, determining its optical state—whether it lets light pass through or not.

Thanks to the TFT layer, LCDs offer high-speed switching, sharp images, and stable color output. It’s a major improvement over passive matrix displays, offering superior performance in applications like HD TVs, smartphones, and monitors.

4. Liquid Crystal Layer: Light Modulation Core

What Is the Function of Liquid Crystals in an LCD?

The liquid crystal layer is the heart of the LCD panel. It consists of millions of tiny liquid crystal cells, each representing one pixel or subpixel.

• How It Works:

  • Each cell has two transparent electrodes (AVDD and VCOM).

  • When a voltage is applied, the liquid crystal molecules twist or untwist.

  • Their orientation changes the amount of light passing through.

• Function: Liquid crystals do not emit light but control its passage by adjusting their alignment. They rotate polarized light when no voltage is applied and allow it to pass through the second polarizer. When voltage is applied, they change alignment, blocking or modifying the light.

This precise modulation of light at each pixel level enables the formation of detailed images and a wide range of colors.

Conclusion: Harmonized Layers for Clear Display

An LCD panel is a sophisticated system made of multiple layers working in harmony:

1. Backlight provides illumination.

2. Polarizers regulate the light's direction.

3. TFT substrate controls pixel activity.

4. Liquid crystal layer modulates light transmission.