What is Liquid Crystal Display (LCD)?

Definition of LCD and How it's Different Than LED Screens

Picture of an Acer S220HQL Abd 21.5-Inch Widescreen LCD Monitor
Acer S220HQL 21.5" Widescreen LCD Monitor. © Acer

Abbreviated LCD, liquid crystal display is a flat, thin display device that has replaced the older CRT display. LCD provides better picture quality and support for large resolutions.

Generally, LCD refers to a type of monitor utilizing the LCD technology but also flat screen displays like those in laptops, calculators, digital cameras, digital watches, and other similar devices.

Note: There's also an FTP command that uses the letters "LCD." If that's what you're after, you can read more about it here but it doesn't have anything to do with computers or TV displays.

How Do LCD Screens Work?

As "liquid crystal display" would indicate, LCD screens use liquid crystals to switch pixels on and off to reveal a specific color. Liquid crystals are like a mixture between a solid and a liquid, where an electric current can be applied to change their state in order for a specific reaction to occur.

These liquid crystals can be thought of like a window shutter. When the shutter is open, light can easily pass through into the room. With LCD screens, when the crystals are aligned in a special way, they no longer allow that light through.

It's the back of an LCD screen that's responsible for shining light through the screen. In front of the light is a screen made up of pixels that are colored red, blue, or green. The liquid crystals are responsible for electronically turning a filter on or off in order to reveal a certain color to or keep that pixel black.

This means that LCD screens work by blocking light emanating from the back of the screen instead of creating the light themselves like with CRT screens.

This allows LCD monitors and TVs to use much less power than CRT ones.

LCD vs LED: What's the Difference?

LED stands for light emitting diode. Although it has a different name than liquid crystal display, it's not something entirely different, but really just a different type of LCD screen.

The major difference between LCD and LED screens is how they provide backlighting.

Backlighting refers to how the screen turns light on or off, something that's crucial for providing a great picture, especially between black and colored portions of the screen.

A regular LCD screen uses a cold cathode fluorescent lamp (CCFL) for backlighting purposes, while LED screens use more efficient and smaller light emitting diodes (LED's). The difference in the two is that CCFL-backlit LCD's can't always block out all the black colors, in which case something like a black on white scene in a movie may not appear so black after all, while LED-backlit LCD's can localize the blackness for a much deeper contrast.

If you're having a hard time understanding this, just consider a dark movie scene as an example. In the scene is a really dark, black room with a closed door that's allowing some light through the bottom crack. An LCD screen with LED backlighting can pull it off better than CCFL backlighting screens because the former can turn on color for just the portion around the door, allowing all the rest of the screen to remain truly black.

Note: Not each and every LED display is capable of dimming the screen locally like I just described. It's usually full-array TV's (versus edge-lit ones) that support local dimming.

Additional Information on LCD

It's important to take special care when cleaning LCD screens, whether they be TVs, smartphones, computer monitors, etc. See How To Clean A Flat Screen TV or Computer Monitor for details.

Unlike CRT monitors and TVs, LCD screens don't have a refresh rate.

Most LCD computer monitors have a connection for HDMI and DVI cables. Some still support VGA cables but that's much less common. If your computer's video card only supports the older VGA connection, be sure to double-check that the LCD monitor has a connection for it.

If there isn't anything showing up on your computer monitor, you can run through the steps in my How To Test a Computer Monitor That Isn't Working troubleshooting guide to find out why.

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