Thin Film Transistor (TFT) LCDs are primarily composed of the following components:

1. Backlight: Provides the initial light source necessary for the display. The backlight system typically includes several layers to enhance light uniformity and efficiency, such as diffusers and light guide plates.

2. Liquid Crystal Panel: The core of the display, which modulates light to create images. The panel itself is made up of several layers:

   - Glass Substrates: Two glass substrates sandwich the liquid crystal layer. The substrates provide structural support and house the electrodes necessary for controlling the liquid crystals.

   - Thin Film Transistors (TFTs): Deposited on one of the glass substrates, these transistors act as individual switches for each pixel, controlling the orientation of the liquid crystals.

   - Color Filters: Located on the opposite glass substrate from the TFTs, these filters enable the display of colors by selectively filtering the white light from the backlight into red, green, and blue components.

3. Liquid Crystal Layer: Positioned between the two glass substrates, this layer contains the liquid crystal molecules. The orientation of these molecules is manipulated by the TFTs to control light transmission through each pixel.

4. Polarizers: Two polarizers are placed on either side of the liquid crystal panel. They convert unpolarized light from the backlight into polarized light, which can then be modulated by the liquid crystal layer:

   - Lower Polarizer: Attached to the bottom glass substrate (closest to the backlight).

   - Upper Polarizer: Attached to the top glass substrate (closest to the viewer). This polarizer often includes surface treatments like anti-reflective (AR), anti-glare (AG), and hard coating (HC) for improved viewing and durability.

5. Driving Circuits: These circuits provide the electrical signals required to control the TFTs and, consequently, the orientation of the liquid crystal molecules. This includes the row and column drivers that select which pixels are activated and the controller that processes the input signal and converts it to the appropriate signals for the row and column drivers.

Light Modulation Process

The light modulation process in an LCD involves several steps, leveraging the optical and electrical properties of the components:

1. Polarization by the Lower Polarizer: The unpolarized light from the backlight passes through the lower polarizer, becoming polarized.

2. Light Modulation by Liquid Crystals: As the polarized light enters the liquid crystal layer, the orientation of the liquid crystal molecules, controlled by the TFTs, determines how the light is rotated or not. The amount of rotation affects how much light can pass through the upper polarizer.

3. Color Filtering: After passing through the liquid crystal layer, the light reaches the color filters, which separate the light into red, green, and blue components, depending on the subpixel being addressed.

4. Final Polarization and Emission: The modulated and color-filtered light then passes through the upper polarizer (which may have additional surface treatments), and the resulting light is emitted from the display as part of the image seen by the viewer.

Light Efficiency

Despite the sophisticated design, various factors contribute to the significant loss of light within the LCD system:

- Absorption by Backlight Components: Various layers within the backlight system, such as the light guide plate and diffusers, absorb some portion of the light.

- Absorption by Polarizers: Polarizers inherently absorb about 50% of the light as they only allow light waves aligned in a particular direction to pass through.

- Absorption by Liquid Crystals: The liquid crystal molecules themselves absorb some light as they modulate its passage.

- Absorption by Color Filters: Color filters block unwanted wavelengths, allowing only the desired colors to pass through, which results in additional light loss.

- Pixel Aperture Ratio: The pixel design includes opaque areas for the TFTs and wiring, reducing the overall area through which light can pass.

As a result, the final light output from the LCD panel is only about 5.6% of the initial light emitted by the backlight. Despite this, advancements in backlight technology and panel design continue to improve the efficiency and brightness of LCDs.