The Origin of the Cathode Ray Tube: From Scientific Discovery to Television and Computer Displays

In the summer of 1897, Karl Ferdinand Braun, a physicist at the University of Strasbourg, was standing in his laboratory holding a magnet instead of a soldering iron. He had just confirmed that a stream of electrons flying inside a cathode ray tube could be bent by a magnetic field. On the end of the glass tube coated with fluorescent material, a small glowing dot moved in response to the motion of his hand. At that moment, what Braun had created was simply a new device for measuring electric current. What he could not have known was that the glowing dot would fill the living rooms of billions of people around the world half a century later.^[1]

The history of the cathode ray tube (CRT) is a story of unintended invention, entangled credit, and the transformation of fundamental science into mass culture.

Tracing Invisible Light: The Origins of Cathode Ray Research

Decades before Braun conducted his experiment, European physicists were fascinated by a strange phenomenon occurring inside evacuated glass tubes. In 1857, German glassblower Heinrich Geißler inserted two metal electrodes into a high-vacuum glass tube and applied a high voltage. He discovered that the residual gas inside the tube glowed with an orange light. This device, which came to be known as the Geissler tube, immediately became a popular attraction at upper-class social gatherings across Europe.^[2]

However, the cause of the Geissler tube’s luminescence was a mystery. In 1869, German physicist Johann Wilhelm Hittorf, repeating experiments under higher vacuum conditions, discovered that some kind of “ray” was being emitted from the cathode (the negative electrode). In 1876, Eugen Goldstein named it “cathode rays” (Kathodenstrahlen).^[3]

British chemist William Crookes was the most systematic investigator of the properties of cathode rays during the 1870s and 1880s. The Crookes tube he constructed achieved a far higher vacuum than the Geissler tube, making the properties of cathode rays far clearer. Crookes demonstrated that cathode rays travel in straight lines, are deflected by magnets, and can cast shadows of objects placed inside the tube.^[3] These were indications that cathode rays were a stream of particles, though many physicists at the time argued they were waves.

The debate was settled in 1897 by British physicist J.J. Thomson. Using electric and magnetic fields, he precisely measured the ratio of mass to charge of the cathode ray particles. The result showed they were approximately 1,800 times lighter than hydrogen ions. Cathode rays were not waves but a stream of extremely light particles — electrons.^[4] Thomson was awarded the Nobel Prize in Physics in 1906 for this discovery.

Controlling a Single Point of Light: Braun’s Cathode Ray Oscilloscope

In the very year Thomson discovered the electron, Karl Ferdinand Braun was applying the cathode ray tube to an entirely different purpose. What Braun devised was a new method of measuring electric current. He coated one end of the cathode ray tube with fluorescent material so that it glowed when struck by the electron beam, then deflected the beam with a magnetic field to make waveforms visible to the naked eye.^[1]

This device was the Braun tube oscilloscope. For this invention, Braun shared the Nobel Prize in Physics in 1909 with Guglielmo Marconi. The prize was awarded for contributions to the development of wireless telegraphy, but without his cathode ray tube research, there would have been no device to visualize high-frequency currents, and wireless communications research would have been set back significantly.^[1]

Braun’s oscilloscope contained a key structural innovation: controlling the electron beam with two pairs of deflection plates so it could move freely in both horizontal and vertical directions. A single glowing point moving on a fluorescent screen — this was the prototype of the CRT. Later, in television, this point would evolve to scan the entire screen dozens of times per second, “drawing” images.

In 1902, German physicist Arthur Wehnelt invented the “Wehnelt cylinder,” which greatly enhanced electron emission using a heated oxide cathode.^[5] This invention increased the electron beam density and control precision within the CRT, which would become a critical foundation for the later development of television receivers.

Making the Screen Move: The Transition to Television

It would take decades for the CRT to transform from a measuring instrument that traced waveforms into a device that displayed images. Between those two stages lay the detour of mechanical television.

In 1884, German inventor Paul Nipkow patented the “Nipkow disk,” a rotating disk with holes arranged in a spiral that scanned images sequentially.^[6] The person who brought this principle to life was British inventor John Logie Baird. In October 1925, Baird succeeded for the first time in transmitting a clear image of a human face in his laboratory, and on January 26, 1926, he gave a public demonstration to scientists at the Royal Institution in London. People lined up to see the small, blurry, flickering screen.^[6]

However, mechanical television had fundamental limitations: low resolution of around 30 lines, severe flickering, and speed constraints imposed by mechanical rotating parts. For clearer, smoother images, it was necessary for electrons — not machines — to draw the picture.

Two figures were central to this transition. Vladimir Zworykin, a Russian-born American engineer, and Philo T. Farnsworth, an American self-taught inventor.

Zworykin filed a patent in 1929 at RCA (Radio Corporation of America) for a picture tube called the “kinescope.” This device was a CRT display that applied the cathode ray tube principle to display images by scanning a fluorescent screen with an electron beam.^[7] In 1933, he developed the “iconoscope,” the camera-side counterpart, completing the basic structure of an electronic television system.

However, it was Farnsworth who demonstrated the principles of electronic television before Zworykin. On September 7, 1927, Farnsworth, then 21 years old, demonstrated the world’s first fully electronic television system in his San Francisco laboratory. What he transmitted to the screen was a simple straight line, but it was the world’s first image transmitted by electrons alone, without any mechanical parts.^[7]

The patent dispute between Farnsworth and David Sarnoff of RCA — Zworykin’s powerful patron — bounced through the courts throughout the 1930s. Eventually, the U.S. Patent Office granted priority to Farnsworth, and RCA was required to pay him patent royalties. It was one of the first instances in history of a large corporation paying royalties to an individual inventor.^[7]

In 1935, Japan’s Kenjiro Takayanagi demonstrated a fully electronic television system using a self-developed high-vacuum CRT, showing that he had independently achieved the same technology.^[8]

Beyond Black and White: The Birth of the Color CRT

After World War II, television spread rapidly. But the era of monochrome (black and white) television did not last long. From the early 1950s, the race for color television began in earnest.

The central technical challenge of the color CRT was to precisely and separately stimulate phosphors of three colors (red, green, and blue) with a single electron beam. The “shadow mask” technique invented by RCA engineer Harold Law solved this problem.^[9] The shadow mask is a thin metal plate with tiny holes arranged in a grid pattern, placed directly in front of the fluorescent screen. When electron beams fired from three electron guns, each at a slightly different angle, pass through the holes in the mask, the geometry of the arrangement ensures that each beam strikes only the phosphor dots of its corresponding color.

RCA released the first commercial color television receiver, the CT-100, in 1954. With a 12-inch screen, it was priced at $1,000 (approximately $11,000 in 2024 value).^[9] The price of color television fell through the 1960s, and by the early 1970s, color broadcasting had begun to replace black and white.

In 1968, Sony introduced the “Trinitron,” an approach different from the shadow mask method. Instead of a grid of holes in a shadow mask, it used an “aperture grille” with vertical slits, and instead of three separate electron guns, it fired three beams from a single gun. The Trinitron provided a brighter, sharper picture than conventional methods and became Sony’s iconic product.^[10]

The Computer’s Eye: The Era of the CRT Monitor

Around the same time as television, the CRT was also playing a central role in an entirely different field.

During World War II, CRTs were already being used for radar displays. By showing returning radio signals on a CRT screen, operators could track the position of aircraft and ships in real time. It is a well-known historical fact that during the 1940 Battle of Britain, Britain’s Chain Home radar network used CRT displays to track the positions of German bombers.

Early electronic computers also used CRTs as storage devices. The “Williams-Kilburn tube,” developed at the University of Manchester by Freddie Williams and Tom Kilburn in 1946–1947, stored binary data by recording electron dot patterns on the fluorescent surface of a CRT. It was a type of the world’s first electronic random-access memory (RAM).^[11]

The CRT as a computer monitor came into its own in the 1960s. Large computers such as DEC’s (Digital Equipment Corporation) PDP series used CRT terminals to input and output data. With the arrival of the personal computer in the 1970s, CRT monitors made their way onto the desks of ordinary consumers. With the launch of the IBM PC in 1981, the CGA (Color Graphics Adapter) standard was introduced, and as standards evolved to EGA and VGA, the resolution and color reproduction of CRT monitors steadily improved.

A World Dominated by One Screen

Until the mid-1990s, the CRT was virtually the only display technology in both the television and computer monitor markets. The living rooms of homes around the world held massive, heavy CRT televisions, and the desks of offices and homes were occupied by thick CRT monitors.

The technical advantages of the CRT were clear: deep, rich blacks, high contrast ratios, fast response times, and real-time reactivity that refreshed the screen the instant an input signal arrived. It was also able to handle a variety of resolution signals without being locked to a fixed resolution.

The principle of the CRT is both simple and precise. An electron gun at the rear of the tube accelerates electrons and fires them in a beam; deflection coils use magnetic fields to steer the direction of the beam. When the beam strikes the phosphors on the front face of the tube, light is produced. The beam scans the entire screen horizontally and vertically dozens of times per second, varying the beam’s intensity at each position to produce bright and dark pixels. In a color CRT, separate electron guns stimulate phosphor dots of red, green, and blue to create mixed colors.

However, the CRT had a fatal weakness: its depth. Because the electron beam needed sufficient distance to reach the far edges of a wide screen, the larger the display, the thicker the entire device became. A 36-inch television could weigh more than 90 kilograms. CRTs also consumed considerable power, required high voltages, and used glass containing heavy metals such as lead.

The Triumph of the Flat Screen: The Decline of the CRT

Liquid crystal (LCD) technology had been in development since the 1960s, but at first it was used only for displaying small characters on calculators and watches. Its image quality and response speed were insufficient for large displays.

The turning point came in the late 1990s. Around 1997, 15-inch LCD monitors began appearing on the market. Early LCDs were more expensive than CRTs and had slower response times, but they had decisive advantages: they were thin and light, and their prices were falling rapidly.

In the early 2000s, as the price of LCD monitors dropped sharply, CRTs were quickly displaced from the computer monitor market. In the television market, the transition was somewhat slower, due to the cost and technical limitations of manufacturing large LCD panels. But as plasma displays and LCD TVs grew larger and became cheaper, CRT televisions also retreated sharply from the market from the mid-2000s.^[12]

In 2012, LG Electronics completely ceased production of CRT TVs, becoming the last major consumer electronics manufacturer to end CRT television production. With that, the commercial era of the CRT — 115 years long — officially came to a close.

A Screen Reborn: The Legacy of CRT and Retro Gaming

After the CRT disappeared from the market, an unexpected phenomenon emerged: demand for CRTs actually increased among certain communities. The protagonists were retro gamers who enjoyed playing console games from the 1980s and 1990s.

The reason is technical. Old console games from systems such as the Famicom, Super Famicom, Mega Drive, and PlayStation 1 were designed with the CRT’s unique characteristics in mind. “Phosphor blending,” where the afterglow of the phosphors naturally fills the space between pixels; the way scanline patterns lend depth and detail to low-resolution sprites; and the near-zero input lag of the electron beam’s screen-refresh speed.^[13] All of these properties are difficult to replicate on LCD displays.

On internet communities, prices for good-condition CRT monitors and televisions began to rise. Sony Trinitron high-end CRT monitors in particular began selling on the second-hand market for prices well above their original retail value. With new production completely discontinued, stocks of high-quality CRTs are steadily shrinking, and the technicians who can repair them are disappearing.^[13]

This paradoxical situation reveals that the lifespan of a technology is not linear. “Old” does not necessarily mean “inferior.” Some technologies perform at their best only as part of the entire system — the ecosystem of content and hardware — for which they were designed. In this sense, the retro revival of the CRT challenges the view that technology’s lineage can be reduced to a simple binary of progress versus obsolescence.

The Journey of a Single Glowing Point

The small point of light that appeared on the end of a fluorescent glass tube in Braun’s laboratory in 1897 would go on to define how humanity consumed information for more than 125 years. The face of a news anchor, the sight of a spacecraft landing on the Moon, the adventures of an 8-bit hero in a video game — all of it unfolded on that same principle: electrons striking phosphors to produce light.

The place left by the CRT in history has been filled by LCD, OLED, and microLED. Those successor technologies surpass the CRT in thickness, weight, and power efficiency. But the distinctive softness produced by the afterglow of phosphors, and the immediacy with which an electron beam redraws the screen faster than human reaction can follow, have not yet been fully replicated. Perhaps that is not a technological incompleteness but the unique texture left behind by a particular era.