LCD display screens are everywhere. You probably own one or more devices with an LCD display screen at home and at work. This includes your TV, computer monitor, watches, clocks, smartphones, and even calculators.
But have you ever wondered about how your LCD display screen works, its lifespan, components, and how it holds up to other emerging display technologies today?
Knowing all these things about your LCD display lets you appreciate your screen all the more. Caring for your device becomes easier when you’re armed with this knowledge.
Without further ado, here are the basic things you need to know about LCD displays.
How Does LCD Display Screens Work?
LCD display screens make use of Liquid Crystal Display technology. The screen is embedded with liquid crystals, a substance that has properties in between a conventional liquid and a solid crystal. Liquid crystals can flow, but their molecules carry a crystal-like solid orientation.
Liquid crystals are responsible for producing an image flashed onto the LCD screen. They don’t emit light, though. Backlights are used to illuminate these crystals.
A display screen is made up of several tiny color blocks called pixels. The term is a portmanteau of “picture” and “element”, denoting pixels as little elements making up an entire screen picture. A screen is typically made up of millions of pixels.
Every pixel on the display screen is made up of red, blue, and green light. These lights can be quickly turned on or off to create an overall moving picture or image.
Now, in LCD displays, pixels are regulated by using liquid crystals for rotating polarized light. Polarized light denotes light waves with vibrations occurring in a single plane. In LCDs, this is achieved by using polarized layers.
Each pixel has polarizing filters on both its front and back. Tiny nematic (twisted) liquid crystals are placed in between these filters. The liquid crystals can be switched on or off electronically through tiny electronic transistors.
When the liquid crystal is turned off, electricity controlled by the transistor stops flowing. The pixel is then turned on, brightening up due to the 90-degree twisting of the nematic liquid crystal. This allows light to pass through both polarizing filters on the pixel, illuminating the pixel by letting light pass through.
When the liquid crystal is turned on, electricity flows through the nematic liquid crystals. They completely straighten out from their twisted state. The polarizing filter in front of the liquid crystal blocks out the light, resulting in the pixel turning off and becoming dark.
A single LCD contains millions of pixels, nematic liquid crystals, polarizing filters, and transistors. They all work together to create images on the screen.
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LCD Display Lifespan
LCD display lifespan depends on several factors such as:
- Backlight source of the LCD screen
- Display screen size
- Storage conditions
- Status of electrical components accompanying the LCD screen
- Frequency of use
- Operating environment of the screen (is it used indoors or outdoors)
Most LCD monitors have a lifespan ranging from 30,000 to 60,000 hours. That’s equivalent to 5-7 years using the monitor for 24 hours per day. It could also translate to 10-20 years with running the monitor for 8 hours a day, 5 days a week.
The backlight’s life expectancy is the biggest factor in determining the LCD display lifespan. It’s because liquid crystals do not give off light from themselves. The liquid crystals depend on the backlight for illuminating them. Hence, the LCD screen wears off when the backlights dim as it reaches its maximum lifespan.
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LCD Display Components
Several components make up an LCD display screen. We’ll explain each one here:
The backlight serves as the illuminator of the entire LCD display device. Without a backlight, the LCD device remains darkened and hard to use. Backlights are installed directly behind the LCD panel to lighten up the display.
Simple devices such as pocket calculators don’t use a backlight for their LCD screens. Users rely on natural light to see the numbers displayed on such calculators. However, the majority of modern LCD screens such as televisions, computer monitors, smartphones, aviation screen panels, outdoor signages, and medical monitoring devices use backlights as their internal light source.
There are various types of backlights used in LCDs, and here are some of them:
a. Light Emitting Diode (LED)
This type of backlight is the most popular and widely-used light source for LCDs today. Light-emitting diodes are semiconductors that emit light once electric current flows into it. Particles carrying the electric current are called electrons holes. These combine with electrons in the semiconductor, releasing photons (light particles).
Band separations called bandgaps determine the photons’ energy. Furthermore, the photon’s energy dictates which color the LED emits, depending on the emitted light’s wavelength. Various kinds of semiconductors and their corresponding varying bandgaps create different light colors.
LED has many sub-categories, including:
- Edge-Lit White LED (EL-WLED)– One or more LED rows are placed on the screen’s edge. A special light diffuser is used to scatter the light evenly across the entire display screen. Computer monitors, laptops, notebooks, and even HDTVs are now lit in this way.
- White LED (WLED)– The LCD panel’s rear side is lit up with several white-colored LEDs. A diffuser is set in front of the LEDs to help evenly smooth out the light throughout the screen. Some computer monitors and large-screen LCD TVs use this LED technology.
- Red-Green-Blue LED (RGB LED)– This technology works like WLED. The difference is that it uses red, green, and blue LED combination lights instead of white lights. Better picture quality and higher color gamut are its advantages over WLED and EL-WLED.
b. Electroluminescence Panel (ELP)
ELP uses electroluminescent materials such as colored phosphors instead of heat to create light. This material is placed in between two conductor layers. The material emits light as a result of an electric current flowing through it. ELPs are mostly used in small LCD screens.
c. Cold Cathode Fluorescent Lamps (CCFL)
CCFL backlight uses a cold cathode fluorescent lamp as its main light source. This lamp consists of a cathode that isn’t heated electrically by a filament, hence the connotation “cold”. A diffuser is placed in front of the CCFL lamp to evenly distribute light across the entire screen.
The cathodes used in CCFL produce light by creating a non-heated thermionic emission of electrons. This is accomplished by using discharges in mercury vapor to create an ultraviolet light. This light, in turn, creates a fluorescent coating inside the lamp, resulting in visible light.
Neon lamps are also considered a type of CCFL. Such lamps emit light through gas molecule excitation.
Computer monitors and TV screens predominantly used CCFLs for backlights. However, modern manufacturers opt for LED technology instead of CCFL for their devices’ backlights.
d. Hot Cathode Fluorescent Lamps (HCFL)
HCFL backlights have filaments that need to be heated to excite mercury atoms, cause the current to flow, and ultimately emit light. HCFLs are often used in LCD equipment such as medical devices, custom task-oriented lamps, scanners, and outdoor LCD signs.
2. Liquid crystal for LCD display
Liquid crystals are the heart of an LCD display. This unique substance flows like a liquid but retains many characteristics of solid crystals. They have long and cylindrical-shaped molecules that can twist when changes in molecular orientation happen.
Different liquid crystal families are used in LCD displays. One requirement of such liquids is to exhibit mutual attraction. Also, the molecules in the liquid crystal need to be anisotropic. This means that the liquid crystal molecules have that average structural order along a molecular axis.
Liquid crystals are often sandwiched in between the color filters and the polarizers. They twist and straighten in response to electrical currents applied to them. The movement of liquid crystals controls whether polarized light will pass through the filters or not.
Liquid crystals have three basic phases of movement:
a. Nematic of Liquid crystals
The nematic phase is characterized by the crystal molecules freely moving around the liquid. However, these molecules point themselves to one direction only, making it unique from pure liquid molecules. Nematic liquid crystals are the most common liquid used in LCD screens.
b. Smectic of Liquid crystals
In the smectic phase, the liquid crystals keep their similar orientation and direction. But the molecules are now lining themselves into layers. The smectic layers have restricted movement, creating a solid-like state in the liquid crystals.
c. Cholesteric of Liquid crystals
Also known as the chiral nematic phase, the cholesteric phase happens when the liquid crystal molecules align themselves at a slight angle to each other. The molecules become stacked in very thin layers as well. The cholesteric phase also allows molecules to change color from exposure to different temperatures.
Now, molecules in liquid crystals move as a reaction to an electric field. Their arrangement changes as a voltage are applied to them. This allows liquid crystals to control polarized light, which, in turn, defines which pixels on a screen will be illuminated or not.
3. Color Filters of Liquid crystals
Color filters are found in between the liquid crystals. These filters determine whether the pixel shows red, green, or blue colors when activated. The filters work by independently controlling the pixel’s red, green, and blue sub-pixels. With this, the LCD screen can reproduce all possible colors found in the color space.
The color filters aren’t active elements, though. It’s the liquid crystal molecules that control the light passing through the filters. The color filters simply determine the color the pixel shows based on how much light is passing through them, as determined by the applied electric voltage and the movement of the liquid crystal molecules.
4. Polarizing Filters of Liquid crystals
An LCD cell is made up of two polarizing filters. They enclose the LCD display and color filters. One polarizing filter is located in front of the backlight and is horizontal in orientation. The other one is found just beneath the pixel in front and is vertical in orientation. Polarizing filters are typically made of transparent crystals or glass substrates.
The role of polarizing filters is to control which light patterns can pass through the LCD screen. Without these filters, visual images generated by the LCD panel will have a poor contrast ratio and an inferior quality image.
Now, light emitted by your panel’s backlight source enters the first horizontal polarizing filter. It then passes through the liquid crystals. The polarized light vibrates vertically if the liquid crystals are in a twisted state. Hence, these light waves can then pass through the second vertical polarizing filter. The pixel on the screen turns on and is illuminated properly.
Meanwhile, if the LCD display is arranged in a straightened way, the horizontal light waves that came from the first polarizing filter will be blocked from entering the vertical polarizing filter. The pixel is then turned off and no light illuminates it.
The two polarizing filters need to be vertical and horizontal in orientation, respectively. If the filters are oriented in the same way (ie; both horizontal or both vertical) will block all the light passing through, displaying nothing on the screen.
5. Thin-Film Transistors (TFT)
TFTs are tiny electrical components etched on the polarizing glass substrates. Amorphous silicon transistors are often used for LCD panels.
TFTs are responsible for providing electrical voltage to the LCD display. Each screen pixel has a corresponding transistor, enabling the pixels to easily be controlled in unison through changes in electrical current.
Using TFTs requires less charge and less power to operate the LCD display screen successfully. TFT use also leads to sharper images because each pixel has its own transistor controlling it. The charge given to a certain pixel can be actively maintained even if the screen is refreshed to display another image.
That’s all the basic information you need to know about LCD display screens. Now, you know how an LCD screen works, its possible lifespan, its components, and how it compares to other display technologies.
Armed with this information, you can better appreciate and take care of your LCD display devices. And in case you’re planning to add display devices to your business, the information you’ve learned will help you make educated choices regarding the display technologies you’ll utilize.