How Does a Computer Monitor Work?

You probably use a computer monitor all day long, but not many of us consider how it works. We tap keys and letters appear on the monitor. But what makes it light up in just the right places?

Current computer monitors work by using liquid crystal display (LCD) technology. The screen is made of two thin sheets of polarized glass with liquid crystal suspended between them. Electric currents pass through the screen to cause specific locations to display the desired colors.

Of course, there’s a lot more to it than that. To really understand how modern computer monitors work, we can dive into the different kinds of technology that light up your screen so you can read your email and post those food selfies on Facebook. We’ll also include information to help take the mystery out of monitor selection.

How the LCD Display in a Computer Monitor Works

LCD displays work by altering the light that passes through to the viewer. These combine red, green and blue light to create a vibrant range of possible colors. Turn off all the lights, and you get black. Turn them all on, you get white. Mix them in different ratios and you get a rainbow of possibilities.

Changing the color of a given pixel is done by sending that pixel a variable amount of electricity. The liquid crystals react to different voltages by displaying different colors. How each pixel gets the signal to change color depends on what kind of LCD display you’re using.

There are two kinds of displays used in LCD computer monitors. These are active matrix displays and passive matrix displays.

Active Matrix Display

Active Matrix Display Circuit Diagram.

Most LCD monitors use an active matrix, where capacitors and transistors are arrayed in a grid that allows them to turn specific pixels on or off. A row is turned on, a charge is sent down that row, and when the right column is turned on, the activated pixel changes state.

Passive Matrix Display

Passive Matrix Display Circuit Diagram.

An older computer monitor technology uses passive matrix technology. For passive matrix, the LCD uses a grid of conductive metal to charge each pixel. While passive matrix displays are less expensive to make than active matrix, we still don’t see many on the market because they just don’t work as well.

Display Technology in Yesterday’s Computer Monitors

LCD monitors are a relatively recent phenomenon. For many years, computer monitors were cathode ray tubes, or CRTs. These were similar to televisions of the time and involved electron guns that tracked back and forth to activate photosensitive glass on the back of the screen.

Color CRT displays use three electron guns. One emits red light, one green, and one blue. When they overlap in a given space (read: a pixel), that spot changes color. These three electron emitters move much faster than your eye can track and continuously update the screen.

CRT Display Structure With Electron Gun.

Fun note: Because the electron guns are fixed in place, the distance from the guns to the center of the screen is shorter than the distance to the edges, which is why CRT monitors and old televisions were curved. Keeping the distance as uniform as possible was important to prevent image and color distortion.

Why Are LCD Computer Monitors Better?

CRT computer monitors are all but dinosaurs now. LCD monitors just have too many advantages:

  • They use less power
  • They don’t get as hot
  • They are a heck of a lot easier to put in a backpack

You may find an old CRT monitor in a second-hand store somewhere, but you’ll never find one attached to a laptop.

Why the Aspect Ratio of a Computer Monitor Matters

The words ‘aspect ratio’ sound like eleventh-grade geometry, but it’s really just tech language that means how wide your screen is compared to how tall. The first number indicates the width and the second indicates height. This does not tell you the actual size of the display, though – it’s just describing how squat a rectangle you have.

Older CRT monitors typically used a squarer aspect ratio of 4:3. This means that the monitor was a little wider than it was tall. This was about the same aspect ratio as old televisions. And when you watched Bladerunner on an old TV, it had the letterboxing at the top and bottom because movies were shot much wider.

The more recent LCD computer monitors typically use an aspect ratio of 16:9. This is a much wider screen, and it matches movie screen sizes enough that you typically only see letterboxing on the sides of the display area if you’re watching reruns of I Love Lucy.

What Resolution Means to a Computer Monitor

No, not New Years. When we’re talking monitors, the resolution indicates how many pixels – tiny individual dots – can be found on your screen. This affects how crisp an image you see.

Strictly speaking, resolution refers to how many pixels are in a given unit of space. Practically speaking, however, it is more important to understand what it means when the box says your new monitor is 1080p versus that expensive one that says 4k.

Progressive and Interlaced Technology

The letter at the end indicates whether your monitor is using progressive (p) or interlaced (i) technology. Don’t be thrown if you see a ‘k’ – that just means 1,000. Those monitors are also using progressive displays. Just about any monitor you can buy today uses progressive display technology, as opposed to interlaced: 

  • Interlaced technology (i): This is the tech used in CRT monitors; pixels were displayed in alternating lines. This method caused the flickering you see in old hacker movies.
  • Progressive technology (p): In this display, on the other hand, lines are painted in sequence. This is faster and cleaner, and less likely to send you into a seizure or give you a screaming migraine.

Deciphering the Numbers and Letters of Monitor Resolution

The number indicates how many pixels are present. If your monitor says 720p, for instance, it means it is 1280 x 720 pixels and uses progressive display. If it says 4k, that’s another term for 2160p, or 3840 x 2160 pixels with progressive display. This additional size means additional visual clarity. It also means that monitor is going to cost you more money.

What Resolution Monitor Do You Need?

Obviously, a larger screen should have higher resolution. If your monitor is only eight inches tall, 720 pixels is okay, but if you have an enormous monitor, those 720 pixels are going to get blurry. Of course, acceptable resolution also depends on what you’re doing with your monitor. If you’re scrolling Twitter, lower resolution is fine, but if you edit photos, you probably want your resolution higher.

Understanding Color Depth of a Monitor

To truly grasp the color depth, you would need to have an understanding of bits, which means you have to understand the underlying language your computer uses to translate your fleshy brain to electrical current. It’s all 0’s and 1’s, and it’s rather complicated.

How Bit Depth Impacts Computer Monitor Colors

Bit depth is simply a measure of how many ‘characters’ are used to describe the color. For instance, if the bit depth is 1, that means it is either 0 (off) or 1 (on). This results in two color options – think black and white, although many old monitors were black and green or black and orange.

More bit depth means longer descriptions for each color. At each increasing bit depth, the range of color combinations increases exponentially. At a bit depth of 2, you have four colors, while at bit-depth 24, you have 16,777,216 potential colors. That’s a lot of visual nuance.

These terms also translate to more human-readable terms. You might see these terms when describing monitors, especially older displays. Most standard monitors boast 16-bit and up, though it is really only a graphic designer’s eye that might actually use a bit-depth higher than 8. 

Bit-depth 12 colors, also known as monochrome
Bit-depth 24 colors, or CGA
Bit-depth 416 colors – EGA
Bit-depth 8256 colors – VGA 
Bit-depth 1665,000+ colors – XGA
Bit-depth 2416,000,000+ colors – SVGA or True Color
Bit-depth 3216,000,000+ colors – True Color + Alpha Channel
Bit Depth Comparison.

Final Words

Perhaps now the magical processes behind your colorful computer display are a little less mysterious to you and you’ll have a better understanding of what to look for when it’s time to purchase your next monitor.

This article was last updated on May 25, 2021 .

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Categorized as Monitors

By Adam

The Display Blog staff account. We know display.