LCD (Liquid Crystal Display) screens are composed of multiple layers because liquid crystals themselves do not emit light and cannot perform the "display" function alone. They require multiple materials to work together to convert electrical signals into the image we see.
The following is an explanation based on "functional logic":
I. The Core Idea of LCD
Using liquid crystals to control light, precisely "modulating light and coloring" through a multi-layered structure.
Each layer is responsible for a specific task; the absence of any layer will cause problems with the image, or even render it completely unreadable.
II. Main Layers of a Typical LCD Screen (from bottom to top)
1️⃣ Backlight Layer
Function: Provides white light
Reason: Liquid crystals do not emit light
Early versions used CCFL lamps, now most use LED backlights
Without this layer, the screen is black.
2️⃣ Light Guide Plate + Diffuser Film
Function:
Transforms point-like LED light into a uniform surface light source
Eliminates bright spots and dark areas
Why multiple layers? Different films are responsible for different optical effects (diffuse, brighten, uniform light)
3️⃣ Lower Polarizer
Function: Transforms stray light into unidirectional polarized light
Reason: Liquid crystals can only "manipulate polarized light"
The polarizer is crucial for LCDs to display images.
4️⃣ Liquid Crystal Layer
Function:
Rotates or remains stationary under voltage control
Changes the polarization direction of light
Essence: A "controllable light valve"
5️⃣ TFT Glass Substrate (Driver Layer)
Function:
Each pixel has a transistor
Precisely controls the brightness of each pixel
Significance: Enables the screen to display complex, dynamic images
6️⃣ Color Filter (RGB)
Function: Separates white light into red/green/blue
Forms all colors through brightness combinations
Each pixel is actually composed of three sub-pixels: R, G, and B
7️⃣ Upper Polarizer
Function:
Works with the lower polarizer
Determines whether light "can pass through"
Result: Creates contrast between light and dark → Image appears
8️⃣ Protective Glass / Touch Layer
Function:
Protects the internal precision structure
Supports touch operation (capacitive screen)
III. Why can't it be simplified to one or two layers?
Because LCD displays require simultaneous completion of the following:
Emitting light
Using uniform light
Controlling light
Coloring
Precise driving
Structural protection
Each of these requires different materials
Different materials cannot be combined
This inherently makes LCDs a highly specialized, multi-layered system.
IV. A comparison makes it clearer:
LCD Screens
LCDs have a distinctly multi-layered structure. Because liquid crystals themselves do not emit light, they rely on multiple optical and control layers, such as backlighting, polarizers, liquid crystal layers, and color filters, to work together to achieve the display effect, resulting in a naturally complex structure.
OLED Screens
OLEDs have relatively fewer layers. Each pixel can emit its own light, eliminating the need for a backlight layer and complex uniform light structures. They mainly consist of an emitting layer, an electrode layer, and an encapsulation layer, making them thinner and simpler overall.
Electronic Ink Screens (E-ink)
Electronic ink screens have one of the simplest structures. They primarily rely on ambient light reflection for display, eliminating the need for a backlight system. Their internal structure is mainly composed of microcapsules or microparticles, consuming almost no power when displaying static content.
In summary,
LCD is a display solution that trades "complex structure" for "stability, maturity, and low cost".