How do LCD Panel Displays Work?

Brief History

Back in 1888, Friedrich Reinitzer. an Austrian Chemist discovered the Liquid Crystalline Nature. He found that some crystalline molecules retained their alignment like in solids and yet remained in a liquid form. Starting from then, the development of various technologies related to the complex history of Liquid Crystal Displays went on progressively for several years till the first LCD display was developed in Japan by SEIKO in 1980, almost a century after the first discovery. Modern-day technologies have OLED, AMOLED, Plasma, MicroLED, and MicroOLED.

 In the most simplified form,  such displays have the following essential components as shown in the figure below:-

1. A source of light often with a reflecting surface behind it.
2. Two polarizing filters, one verticle, and another Horizontal.
3. A Liquid Crystal layer along with transparent electrodes.
4. Circuitry for controlling the electrical currents.

The construction and principles of each of these components are explained below.

FIGURE 1

1. Source of Light

The source of Light for the displays is provided by CCFL (Cold Cathode Fluorescent Lamps) lights which are much like the CFL bulbs we use at home. In recent years, the CFLs have been replaced with LED (Light Emitting Diode) lights. We did the same at our homes too, didn’t we? To increase brightness, a reflective film, much like a mirror, is placed behind or to the side of the light source./h

FIGURE 2

2. Polarising Filters

Working

Light travels both as a particle as also like a wave. These light waves radiate in all directions equally and as such are non-polarised. When such light falls on a Polarising Filter, which has very narrow slots in one direction (Verticle or Horizontal), they only let through light waves that travel in the same plane in which the slots are oriented. The waves in other directions are absorbed.

Construction

1. Liquid Crystal Displays use two polarizer layers, one vertical and another horizontal.
2. Polarising Layers are essentially cellulose membranes coated with Polyvinyl Alcohol film, which is stretched in one direction to form long thin parallel chains, like the bars of a prison door. This membrane is dyed with Iodine/dye polarizer. The result is a material that will absorb all light waves except those parallel to the axis of the long chains.

FIGURE 3

Nature of Liquid Crystals

All matter has three forms Solid, Liquid, and Gas. Certain molecules like Gallium Arsenide have an intermediary state where the molecules remain more or less fixed and oriented like in a solid, and do not move about like in a liquid. They adapt the shape of the container like a liquid, which enabled their adaption to display technologies.

Principle of Working

The simple principle of working of LCDs is based on the discovery that by changing the electric charge on liquid crystal molecules we can change the orientation of the light waves passing through the crystals thereby controlling the optical output of each pixel.

Molecules of liquid crystals under the influence of electricity can change their orientation and, as a result, change the properties of the light beam passing through them.

Construction

1. Liquid Crystals are sandwiched between two polished thin sheets of glass or plastic, called substrates. The space between them is about 10 Microns (Human hair 100 microns) which is maintained by placing a few glass beads of (10 microns Dia) between the substrate.
2. The substrate is coated with a thin film of conducting material (eg., Iridium Tin Oxide) which is etched by a chemical process to form a transparent electrical grid of connectors to each pixel comprising of rows and columns.
3. The liquid crystal material is then injected between the substrates to form the Liquid Crystal Layer.
4. Finally, the panel is connected to the Circuit board to control voltages across the electrical connectors.

4. Circuitary

The display is composed of millions of pixels put together to form the image. Also, each pixel has three subsegments each of Red, Green, and Blue to form a colour image. A display with a resolution of 768 x 1024 will have 786,432 pixels and over 2.3 million sub-pixels.

Each pixel needs separate power connectors, which are transparent. This is archived by coating the substrate of the Liquid Crystal layer with a transparent conducting material which is etched chemically with silk threading and a matrix of rows and columns is achieved by a square mesh-like design.

The control of voltages to each pixel is done by Graphics Procesor, which sends necessary power to the respective row and column of each pixel thereby forming an image.

FIGURE 5 REPRESENTING A CIRCUIT FOR EACH PIXEL

Power to each pixel is controlled by sending a charge through the vertical connector (column) and discharging/grounding the same from the corresponding horizontal connector (row). Eg., When a charge is sent to pixel 1214 above, the wire in column 12 sends the charge and the wire in row 14 discharges it. All other rows are disconnected at that time and as such only pixel 1214, gets the charge.

Working of Liquid Crystal Displays

1. The screen is lit up from behind with background lighting.
2. After this background light is a polarizing filter. The polarizing filter allows only Vertically Polarised light waves to pass through it
3. This Vertically polarized light falls on the Liquid Crystal layer comprising many pixels.
4. The light is permitted to pass through or stopped depending on the current supplied to the pixel.
5. When the pixel is powered, the Crystals align linearly,
6. The Vertical waves pass through and fall on the Horizontal Filter which does not permit any of the light waves to pass through it. As it permits only horizontally aligned light waves to pass through it.
7. As a result, the particular pixel remains dark.
8. When the amount of charge applied to the pixel is drained, the crystals rotate into a spiral.
9. The vertical waves of light falling on them are turned by 90 degrees, by the spiral crystal molecules, into Horizontal waves. These waves fall on a Horizontal filter which permits these Horizontal waves to pass through it.
10. These light rays are the ones that become visible to the observer.
11. The intensity of each pixel is controlled by changing the voltages applied/discharged.
12. An image is formed by combining all the pixels.

Colors images are achieved by manipulating the amount of charge in each sub-pixel. We have 3 sub-pixels each of Red, Green, and Blue. By controlling the intensity of each colour segment, we can produce millions of shades of colours as desired.

LED Displays work much in a similar manner as the LCDs except for the fact that the backlighting of the screen is done by a matrix of LED lights in place of a CCFL light.

Conclusion

So that’s how LCD panels work—layers of light, filters, and liquid crystals all doing their job in sync. It’s a pretty clever system, and now you know what’s going on behind the screen every time you open your laptop.

LCD panel displays are a marvel of layered engineering—where physics, electronics, and optics work in tight synchronization. From the polarizing filters that manage light flow, to the liquid crystal molecules that modulate pixel states, and the backlighting systems that illuminate the entire matrix—every component plays a vital role in creating a clear, vibrant image.

Understanding how these elements work together not only deepens your appreciation for modern display technology, but also helps when choosing a laptop or troubleshooting screen issues. Whether you’re a tech enthusiast or a casual user, knowing what’s behind your display can be the key to making smarter decisions about the devices you use every day.