Cathode Ray Tube Explained – Everything You Need To Know

The CRT monitor of PDP-1.

Cathode Ray Tube Explained – Everything You Need To Know

Modern-day display technologies continue to improve with each passing year, but throughout the mid-1900s, they didn’t really move an inch. While liquid crystal displays (LCD), organic light-emitting diodes (OLED), and plasma screens dominate the industry in the 21st century, cathode ray tube (CRT) display technology is what used to be king. While this tech is not as prevalent today as it was years ago, CRT tech still exists today and is well worth discussing. Let’s break down the history of CRT, how it works, and its historical significance below.

Ferdinand Braun, Inventor of the cathode ray tube.

Three Facts about the Cathode Ray Tube 

  • In 1855, Heinrich Geissler was awarded a gold medal by the Exposition Universelle (World Exhibition) in Paris due to his excellent work on fine glass — including what would eventually be known as the cathode ray tube.
  • While we think of CRT as display technology, it can also be used for storage. These storage tubes are CRTs made to hold onto an image as long as there’s power being supplied to the tube.
  • Because CRTs require thick glass to safely and effectively create and maintain a vacuum, cathode ray tubes weigh quite a bit. This puts a serious limit on the size and the shape of a CRT display, which explains why LCD and LED eventually left CRT in the dust.

Cathode Ray Tube History

The history of cathode ray tube can be followed back to at least 1854 when the skilled German glassblower and mechanic Johann Heinrich Wilhelm Geißler — also known as Heinrich Geissler — was asked to design an apparatus for evacuating a glass tube by Julius Plücker, the professor of mathematics and physics at Universität Bonn (University of Bonn). Born in Igelshieb, Thuringen and descended from a long line of craftsmen in the Thüringer Wald and in Böhmen, Geissler had worked as an instrument maker with his brothers throughout Germany and the Netherlands for many years. Eventually, in 1852, Geissler decided to settle down in a workshop of his own. It was here that he worked as an instrument maker for the production of physical and chemical instruments. 

Quick Facts

Julius Plücker, Arthur Schuster, William Crookes, J. J. Thomson, Ferdinand Braun, and countless others
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Displaying images

Julius Plücker, on the other hand, was a famous German mathematician who made fundamental contributions to analytic and projective geometry. In the 1840s, he turned away from mathematics and concentrated his attention on physics. In 1847, he began research on the behavior of crystals in a magnetic field, establishing results central to a deeper knowledge of magnetic phenomena. It was at this time that Plücker asked Geissler to make him an apparatus for evacuating a glass tube. His research made him believe this would allow him to concentrate light for his spectral research.

In 1855, Plücker asked Geissler to construct a hand-crank mercury pump and glass tubes that could contain a superior vacuum. With this pump, he hoped to reach very low-pressure levels inside the tube. Luckily for Plücker, Geissler was already interested in these tubes from the experiments of his brother Friedrich in the Netherlands. Geissler had even made earlier versions of these mercury vapor-filled tubes in Amsterdam for the Dutch chemist Volkert Simon Maarten van der Willigen. This low-pressure gas-discharge glass tube eventually became known as the Geissler Tube. As such, Plücker owed his forthcoming success in the electric discharge experiments in large measure to Geissler. 

In 1858, Plücker inserted metal plates into the Geissler tube and noticed a pale green light at the positive end of the tube. This showed Plücker that cathode rays bend under the influence of a magnet, suggesting that they are connected in some way. The future value of Plücker and Geissler’s discovery, apart from neon lighting, would not be fully realized until some 50 years later. In 1897, Karl Ferdinand Braun introduced a cathode ray tube with a fluorescent screen, known as the cathode ray oscilloscope. In 1905, Lee De Forest invented the Audion vacuum tube, creating the entire basis of long-distance wireless radio communications and electronics. However, there are a few steps that took place in between those 50 years that are well worth mentioning.

In 1865, German chemist Hermann Sprengel made improvements to the Geissler vacuum pump. In 1869, German physicist Johann Wilhelm Hittorf found that a solid body put in front of the cathode cut off the glow from the walls of the tube. With this, he established that rays from the cathode traveled in straight lines. In 1871, English engineer Cromwell Fleetwood Varley published a suggestion that cathode rays were composed of particles. Likewise, English chemist William Crookes proposed that they were molecules that had picked up a negative charge from the cathode and were subsequently repelled by it.

Ferdinand Braun Cathode Ray Tube (thought to be the second of five made).

In 1876, German physicist Eugen Goldstein showed that the radiation produced in a vacuum tube when an electric current is forced through started at the cathode. This introduced the term “cathode ray” to describe the light emitted. Later, in 1876, Goldstein observed that a cathode ray tube produced radiation that traveled in the opposite direction in addition to the cathode ray. These rays were called canal rays because of the holes (or canals) bored in the cathode. Later, these would be found to be ions that have had their electrons stripped in the act of producing the cathode ray.

In 1883, Heinrich Hertz showed that cathode rays were not deflected by electrically charged metal plates, which led Hertz to incorrectly conclude that cathode rays cannot be charged particles. Later, in 1892, he doubled down on his incorrect conclusion by asserting that cathode rays must be some form of wave because they could penetrate thin foils of metal.

All of these discoveries eventually led to famous German physicist Karl Ferdinand Braun’s 1897 invention of the first cathode-ray tube (CRT) and cathode ray tube oscilloscope. At this time, Braun also played an important role in the development of semiconductor devices. For his invention, Karl Ferdinand Braun received the Nobel Prize for Physics in 1909 — an honor he shared with Guglielmo Marconi, who developed wireless telegraphy. 

The development of the cathode ray tube greatly facilitated the development of a practical television system. In 1907, Russian scientist Boris Rosing and student Vladimir Zworykin used a CRT in the receiver of a television system. Remarkably, Rosing effectively transmitted crude geometrical patterns onto the television screen with the CRT. Later, in 1929, Zworykin invented a cathode-ray tube he called the kinescope, an essential part used in televisions from then on.

It seems the first device to use a CRT computer monitor was the U.S. military’s SAGE. Developed in the 1950s, the SAGE had more than 150 display consoles housing a 48-inch-long Vector CRT computer monitor. The first commercial device equipped with a CRT computer monitor was Digital Equipment’s PDP-1 in 1959.

Cathode Ray Tube: How It Works

In essence, a cathode ray tube (CRT) is a vacuum tube that displays visuals when its phosphorescent surface is hit by electron beams and scanned by a scanning device. CRTs can be either monochrome or color and are offered in a wide range of display modes. Here’s how it works: magnetic fields curve a moving charged particle’s path, allowing you to control the beam using magnets. The faster the particle, the larger the magnetic field needs to be to bend it. 

With the cathode ray tube, the cathode ejects electrons that are then accelerated through a charge, increasing their speed with each pass-through. Once they get going fast enough, they begin to bounce off of the gas in the tube, bringing forth a glow. This allows the beam’s path to be seen by the naked eye. In the instance of the CRT television or computer monitor, the display technology relies on electrons hitting phosphors in an exact spot on the rear of the screen. This then displays different light shades when hit. For CRT televisions and computers, the tube’s front is scanned in a fixed pattern by a scanning device called a raster.

The CRT monitor of PDP-1.

Cathode Ray Tube: Historical Significance

At the time of its invention, the cathode ray tube was widely considered to be the most complicated and advanced piece of consumer technology ever made. For this reason, they were implemented in everything from computers to ATMs to arcade games to video cameras to radars and everything in between. While modern-day consumers would far prefer the flat-screen LCDs and LEDs that we’re used to today, it’s hard to overstate just how groundbreaking and historically significant this CRT technology was to the world of display technology for nearly a century between the late 1800s and the late 1900s.

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Frequently Asked Questions

What is the Cathode Ray Tube?

A cathode ray tube is a glass vacuum tube that manipulates electron beams to display images on a screen.

How does a Cathode Ray Tube work?

CRTs create images by changing the intensity of three primary colored electron beams with a video signal used for reference.

Who invented the Cathode Ray Tube?

While countless individuals worked on and experimented with CRTs over the past 125-plus years, German physicist Ferdinand Braun is largely considered to be the inventor of the cathode ray tube.

How was the Cathode Ray Tube invented?

The CRT was invented when Julius Plücker inserted metal plates into a Geissler tube and noticed a pale green light at the positive end of the tube.

When was the Cathode Ray Tube invented?

The CRT as we know it was invented in 1897, though Plücker and his contemporaries’ experiments predate this.

Is the Cathode Ray Tube still used?

While it’s much less popular today compared to 30 years ago, the CRT is still used today.

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