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How LCDs Work – Everything You Need To Know

Understanding the working of LCDs is paramount, especially now that almost every screen you see is an LCD. However, it is difficult to differentiate between these screens at face value if you lack prior knowledge of them. Here we shall be looking at LCD screens, their structure, essential components, and how you can improve your display’s lifespan.

A Liquid Crystal Display (LCD) screen is a flat panel display that utilizes liquid crystals to create a visible image. 

What is an LCD Display?

Cross-Section Of An LCD

Fig 1: Cross-Section Of An LCD

A Liquid Crystal Display (LCD) screen is a flat panel display that utilizes liquid crystals to create a visible image. 

The Basic Structure Of An LCD Screen

Backlight

Light Emitting Diode (LED)

An LED Stripe

Fig 2: An LED Stripe

LED-backlit LCD screens utilize LEDs to provide the backlight of the pixels. They have a better dimming range, better contrast ratios, wider color gamut, and are more reliable than CCFL-backlit screens. 

Electroluminescence Panel (ELP)

This technology uses excited colored phosphors to produce light, and they require an electric voltage of 100 volts AC at 400 Hertz frequency to emit light. ELP technology is applicable in monochrome, segment, and character LCDs.

Hot Cathode Fluorescent Lamps (HCFL)

HCFL uses a coiled tungsten filament connected to two cathodes at both ends. When the cathodes are electrically excited at 900 degrees Fahrenheit, they emit electrons that react with mercury in the tube. The effect is that ultraviolet radiation generated reacts with the phosphor to produce light.

Cold Cathode Fluorescent Lamps (CCFL)

Unlike the HCFL, the CCFL doesn’t have a tungsten filament. Instead, the voltage within the tube excites the mercury causing a current flow. The UV radiation from mercury reacts with phosphor to produce light.

Liquid crystal for LCD

How LCDs Work--A Woman Watching On LCD Tv

Fig 3: A Woman Watching On LCD Tv

Nematic Phase LCD

The nematic thermotropic phase takes place at a higher temperature as compared to a smectic degree. Liquid crystals are orientations with their long axes pointing in one direction. 

Their center of mass positions is random within the liquid. However, you can align them with an external magnetic or electric field to create a transparent or opaque view. 

It is due to this alignment property that nematic molecules are applicable in LCDs.

Smectic of Liquid Crystals 

A smectic phase is a thermotropic phase of liquid crystals that exists at low temperatures. Here, liquid crystal molecules align in layers that are perpendicular to the plane of the molecules. 

The crystal arrangement is in a liquid state and slides over each other in the direction of the layer plane.

Cholesteric Of Liquid Crystals 

Here, liquid crystals align in layers that are one molecule thick. Also, the molecules align with their long axes parallel to each other. 

Color Filters Of Liquid Crystals 

Color filters in LCD panels allow specific wavelengths of light to pass through while blocking others. Therefore, it’s possible to enhance and contract colors that are visible to create variations of the same color.

Polarizing Filters Of Liquid Crystals

Polarizing filters allow polarized light of a particular orientation through an LCD setup while blocking all light exposures. 

How LCDs Work– Thin-Film Transistors (TFT)

Thin-film transistor LCDs use TFTs as individual pixel switches to improve image characteristics such as contrast and addressability. 

TFTs are special field-effect transistors (FETs) that are thinner relative to the plane of the device.

How Do LCD Screens Work?

The working of an LCD is primarily based on the properties of polarized light. Polarized light is light whose vibrations face restriction to one plane. In an LCD, white light undergoes polarization with the help of two polarizing films.

An LCD screen has millions of pixels, each with a polarizing film on either side of a linked liquid crystal. Each pixel undergoes further categorization into three distinctive red, green, and blue sub-pixels. 

When you power on your LCD, a backlight shines white unpolarized light towards pixels. The white light travels in various planes, including the horizontal and vertical planes. 

The first polarizing glass allows only the horizontal light waves to pass through, while the second glass filter allows only the vertical light waves. The two polarizing glasses are liquid crystals with electrodes surrounding them, and each subpixel has its electrode and polarizing glass pair.

The liquid crystal is in an electronically nematic form in its natural state. 

The polarizing glass filters rotate the horizontal light to a vertical position in an off state, allowing light to reach the pixels. 

When the polarizing electrodes are on, the nematic liquid crystals orients in a horizontal alignment. The light from the backlight no longer undergoes twisting through a 90-degree angle and passes horizontally. The vertical polarizing glass then blocks the flat light waves. 

By varying the electrical current through each set of electrodes, we can alter the number of liquid crystals that align horizontally. As such, it results in different amounts of light reaching the pixels to create an image. 

Colors on individual sub-pixels are on a scale of 0 to 255. If all three are zero, you’ll see black on the entire screen, and if all three are at 255, you will see the backlight (white). A variation in liquid crystal electrode potential varies the colored light display on an LCD.

Six Factors That Determine The Life Of An LCD Screens

How LCDs Work--Futuristic EKG Medical LCD

Fig 4: Futuristic EKG Medical LCD

Listed below are the six factors that determine an LCD’s lifespan.

Operating Environment Of The Screen

LCDs work best when the liquid crystals are in the nematic phase. A temperature drop below freezing point or higher temperatures hinders an LCD’s, thus reducing its lifespan.

Quality Of Accompanying Electronic Components

LCDs fail primarily due to the bulging of capacitors that result from the drying up of electrolytes within. Poor quality materials lower the lifespan of an LCD.

How LCDs Work– The State Of The External Components

External components such as the stability and frequency of power affect the lifespan of LCD screens. Dust also settles on important circuit components, causing short circuits and heating problems for the device.

Backlight Failure

LCD backlight failure can occur due to a short circuit or a defective internal component. You can quickly sort out this problem by replacing the backlight.

Electromagnetic Radiations

An external magnetic field interferes with the alignment of the liquid crystals between the two glass polarizers. Therefore, a high electric field lowers the image quality and causes a screen to deteriorate with time.

How LCDs Work– Frequency Of Use

LCDs have between 30,000 and 60,000 hours of use. Therefore its lifespan greatly depends on how long it is on during the day. 

Difference between LCD and Plasma Screens

How LCDs Work--Plasma TV On The Wall Of A Room

Fig 5: Plasma TV On The Wall Of A Room

It isn’t easy to differentiate between plasma and LCD screens from face value, and the two are strikingly similar but use very different technologies to display information. 

Listed below are the significant differences between Plasma and LCD screens.

Refresh Rates

A plasma screen has a faster refresh rate when compared to an LCD screen of the same classification. The slow response time in LCD screens is evident when images are displayed at a quicker pace. 

You’ll often see some ghosting effect whereby images tend to drag along the screen. Present-day LCDs don’t experience ghosting effects because their frame rates are closer to those of plasma TVs.

Technology

Another difference between LCD and Plasma screens is their principles of operation. How you light up pixels and sub-pixels to produce an image varies, and LCDs require a backlight to provide the necessary excitement to the pixels to make an accurate depiction of an image. 

Plasma screens use the properties of inert gases to light up pixels. Each pixel can undergo excitation by a grid of electrodes within its structure in a horizontal and vertical arrangement.

When you show UV light into the phosphor coating of the pixel, it undergoes conversion into your color of choice. A light shown on a red phosphor turns the pixel visibly red, and so on.

Weight 

LCDs weigh less than their plasma counterparts of the same size. Also, they consume less electricity and produce less heat. 

However, the weight and power consumption difference doesn’t hold much power since it is relative. Plasma displays are still very lightweight as compared to other display technologies.

Display

Plasma screens display what we regard as more authentic images. Because of the backlight absence, you get detailed photos of the physical object on display using Plasma screens. 

LCD screens are somehow relatively saturated and not as sharp as some plasma displays.

Altitude

Altitude affects plasma screens, and they don’t work well above heights of 6500 feet. 

As you go further up towards space, the air pressure naturally drops. A drop in pressure means that the air expands naturally, creating a massive problem for plasma displays. A variation in the distance between the inert gas molecules results in electrodes working harder to fire up the pixels. In a silent room or displaying white images, you will hear some noise from the screen.

Conclusion

We have discussed the most critical factors that affect the working of LCDs. 

As such, you have sufficient information on its working, components, weaknesses, and how to prolong its lifespan. 

LCD screens are still among the best currently in the market. If you ever feel like buying a new LCD TV, consider the information provided in this article.

For further questions, comments, or interactions, feel free to contact us

Hommer
Hi, I am Hommer, the founder of WellPCB. So far we have more than 4,000 customers worldwide. Any questions you can feel free to contact me. Thanks in advance.

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