What is a CRT and why don’t we use it anymore?

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You may have heard the term “CRT” and know it has something to do with televisions, monitors, video games or computers, but what does “CRT” actually mean? We will explain to you.

What is a CRT?

In the context of electronics, CRT stands for “cathode ray tube”. It’s a technical term for the glass picture tube inside a vintage television or computer monitor, the kind used before flat screens became common. CRTs are electronic image display devices that have the advantage of displaying information dynamically without the need for moving parts.

When someone says “a cathode ray tube” they may also be referring to a television or monitor that uses a cathode ray tube instead of the cathode ray tube itself.

Why “cathode ray?” Before the discovery of the electron, scientists called the streams of electrons “cathode rays”, because these mysterious rays were first seen emitted by a cathode (a negatively charged electrode), casting shadows inside of a vacuum tube. In 1897, a German engineer named Karl Ferdinand Braun added a phosphor screen and magnetic deflection control to create the first cathode ray tube, which he used to display the waveform of alternating current like an oscilloscope.

Karl Ferdinand Braun's 1897 diagram of the original CRT.
Braun’s diagram of his original 1897 cathode ray tube design. Karl-Ferdinand Braun

Over time, other scientists discovered that CRTs could be used to display moving images without the need for mechanical moving parts, providing a key component to the commercialization of television. Later computers also began to use CRT monitors as output devices, making them more interactive and eliminating the need for continuously printed paper output.

How do CRTs work?

CRTs are sealed glass vacuum tubes that contain three main components: an electron source (often called an electron gun), an electromagnetic deflection system (which directs the electron beam), and a phosphor screen that glows when is hit by the electron beam.

In the case of a color CRT display, there are three electron guns: one for red, one for green, and one for blue, and they aim at colored phosphors that glow with those colors when hit by the corresponding beams. The intensity of the beam can also be modulated, which changes the brightness in certain parts of the image.

A simplified cathode ray tube diagram.
A simplified diagram of a cathode ray tube. God of Chemistry / Shutterstock

CRT televisions and most CRT computer monitors draw an image on the screen line by line, top to bottom, in a raster pattern, 30 or 60 times per second. This is called a raster display. Other CRTs, such as those used in oscilloscopes and in some early arcade video games, directly trace an image by drawing lines across the phosphor screen with a single electron gun, more like an Etch-A- Electronic sketch. These are called vector displays.

Obviously, we’re just simplifying things here. CRTs need many additional support circuits, such as power and logic to receive and generate the image signals that will be displayed on the screen. These components vary by screen size, type, and manufacturer.

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Why don’t we use CRTs anymore?

Sure, some people still use CRTs for specialty cases, including legacy electronics (like in some older airplane cockpits) and retro gaming, but otherwise the CRT’s time has come and gone.

CRTs were most popular between the 1950s and the mid-2000s, first on televisions and later on computer monitors. In the United States, commercial CRT television production largely ceased in the mid-2000s, with some persistence continuing into the 2010s. Today, a few specialty companies still manufacture or refurbish CRTs, but largely part for non-consumer markets.

A Vizio 4K TV.

Most people no longer use CRT displays because flat panel display technology (led largely by LCDs) has significant business and physical advantages. In general, flat panel displays are cheaper to manufacture, are lighter and thinner, use less electricity, and produce less heat than CRT displays. They also provide possibilities for digital sharpness, clarity, and resolution far beyond that of a CRT display, and flat panel displays can be manufactured in much larger screen sizes than CRTs.

Are there advantages to CRTs?

In the 2000s and 2010s, CRTs still offered advantages over flat panel technologies in some categories, such as better color richness, better response time, and better support for multi-timing resolution , but recent advances in flat-panel technology have shut down most of these technologies. shortcomings.

Still, there are people who prefer CRTs for vintage computer and video game applications because CRTs were the display technologies intended to be used at the time. There are three main reasons why CRTs are often better than flat screens for retrogaming.

A Packard-Bell PC with a CRT monitor running Commander Keen.
Benj Edwards

The first reason is that CRTs handle the odd, non-standard display resolutions of older game consoles better than modern digital displays. When used with modern HDTVs, graphics from older game consoles can appear stretched, washed out, jagged, or blurry. But viewed on a vintage CRT, everything is crisp and properly proportioned.

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Second, some video game accessories, such as light guns, only work with CRT displays. You can’t play Nintendo duck hunting on an HDTV with a stock light gun, as the technology works in perfect sync with the video signal synchronization of a CRT.

Third, the visual artifacts created when images are displayed on a CRT can be considered part of the original intended art style of some video games. In fact, some games have taken advantage of the properties of an NTSC signal or the CRT itself to mix colors or give the illusion of more depth, shading and transparency than would be the case on a screen at pixel near. (For great examples of this, see this deep thread on twitter.)

A comparison of a Shining Force CD portrait on an emulator versus a CRT TV.
A portrait of Brilliant Force CD (Sega CD) as seen in emulator output (L) versus CRT output (R). Note the aspect ratio difference as well as the color shading. Benj Edwards

Most of these positive graphical artifacts are lost when modern games are presented in pixel-perfect formats through emulators or on modern digital displays. You will lose color blending and aspect ratio might also be off, as not all pixels were meant to be square.

With CRTs on the endangered species list, there are fears that we are losing touch with this important 20th century technology for good. But when it comes to supposedly obsolete technology, count nothing forever. Just look at the vinyl hit and Project Impossible, which brought Polaroid instant film back into production.

One day we may see the rise of CRTs for boutique applications again, but until then it behooves today’s technicians to preserve examples of this culturally significant display technology so that future generations can see how it worked for themselves.

RELATED: Why were old video games so pixelated?

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