What is CRT?

A CRT is the technology, stands for cathode-ray tube and is used in television sets and computer monitors. It consists of a vacuum tube with electrostatic deflection plates, one or more electron guns, and a phosphor target behind a glass screen. The word CRT comes from the cathode, which is a positive terminal where electrons can enter. The CRT inside the display may be seen in the image below.

In a computer monitor or in a television set, three types of electron guns are available that are red, green, and blue, often called RGB, which play an important role in the monitor to project pictures on the screen. For each line of the monitor, these guns stream the flow of electrons on the screen in the left to the right direction. The electron beams light up and are projected on the screen once they hit the phosphors. On the screen, the color you see is produced with the combination of three electron guns: red, green, and blue. The gun again starts at the left and continues right when the new line begins. Unless the screen is completely drawn line by line, these guns repeat this process continuously.

The electron beams light up for a while, when they hit the phosphors on the CRT. Due to this fact, the CRT must be refreshed. You may see a noticeable steady line or flickers on the screen if the refresh rate of the video card is not set up high enough. To bend the electron beams, magnetic deflection is used by modern CRT monitors that are done with the help of varying the magnetic field. The magnetic field, which is generated by coils driven through electronic circuits.

The CRT, commonly known as the picture tube, was the sole option for display devices until the less bulky and power-hungry LCD was introduced. Magnetic deflection is commonly used to change the orientation of electron beams. Furthermore, the type of phosphor utilised can impact the brightness, colour, and duration of the light. Especially, different types of phosphor play an important role in making CRTs for different applications.

Features of CRT

Using different kinds of phosphor can impact the brightness, color, and persistence of the illumination. Especially, different types of phosphor play an important role in making CRTs for different applications:

1. Size
   The large size is one of the best features of the CRT, which describes the screen diameter. This is an inherent feature of CRT monitors because to the limits of the technology they employ. And CRTs are available for oscilloscopes in sizes of 1, 2, 3, 5, and 7 inches. For instance, a CRT containing the number 5GP1, which indicates that it is a 5-inch tube.
2. Contrast
   The CRT technology provided a contrast that is better as compared to LCD. CRTs have the ability to produce high dep black levels and have much better contrast ratios. That means, in dark pictures, there are much more visible details on CRT monitors or televisions. However, the brightness level of CRT monitors is falling short than LCD technology.
3. Cost
   Since the LCDs were introduced, CRT technology has almost obsolete. For example, if you want to purchase a CRT monitor, you may be unable to buy a new one and likely have to buy it secondhand; because the production of CRT monitors has ceased by manufacturers. But the cost of CRT monitors is quite cheap. However, it may be inexpensive to go with an LCD (Liquid Crystal Display) for a long time.
4. User Friendliness
   Another considerable feature of CRT when it was more common in use. Most of the media data were in more square-shaped, 4:3 letterbox format, whereas today is widescreen. On top and bottom of the screen, you will have black bars if you are viewing widescreen content on a 4:3 monitor. That means you will be unable to use all the space of the screen. In modern times, all LCD monitors come with a widescreen that allows you to use all the space of the screen or show either smaller bars or no bars at all.

History of CRT (Cathode Ray Tube)

The development of the CRT (Cathode Ray Tube) started after 1854. Cathode rays were discovered by Julius Pl�cker and Johann Hittorf; however, it was not until 1897 that Ferdinand Braun invented the first CRT. Unknown rays were released from the cathode, and Hittorf noticed that the rays were able to throw shadows on the tube's luminous wall. It also indicated that rays were passing in straight lines. In other countries like France and England, Geissler's tubes were sent. They went to researchers like Hittorf, Faraday, and Crookes. They then conducted numerous experiments, which resulted in numerous new discoveries.

Later the Geissler vacuum pump was improved by German chemist Hermann Sprengel in 1865. A solid substance put in front of the cathode blocks the light and demonstrates that rays from the cathode move in straight lines; this was found in 1869 by Johann Wilhelm Hittorf, a German scientist.

Cromwell Fleetwood Varley, an English engineer, proposed that cathode rays are made up of particles in a paper published in 1871. When an electric current is forced with the help of the tube, then the radiation in a vacuum tube is produced, it was shown by the German physicist Eugen Goldstein in 1876. In addition to the cathode ray, later it was founded by Goldstein observed in 1876 that a cathode-ray tube is produced, and the radiation travels in the opposite direction. Because of holes (canals) bored in the cathode, these rays are known as canal rays.

The electrically charged metal plates do not deflect the cathode rays, which was shown by Heinrich Hertz in 1883. It implies that cathode rays are not charged particles. Heinrich Hertz determined (incorrectly) in 1892 that cathode rays must be some type of wave. The conclusion suggests that the photons can pass through thin metal foils.

In 1897, J. J. Thomson measured the charge-mass ratio of cathode rays. He demonstrated that the first "subatomic particles," negatively charged particles smaller than atoms, produced cathode rays.

The Braun tube was the first version of the CRT, and it was invented by German physicist Ferdinand Braun in 1897. It was a modification of the Crookes tube with a phosphor-coated screen (a cold-cathode diode). Braun was the first to think of using a CRT as a display device.

Western Electric's John Bertrand Johnson and Harry Weiner Weinhart were the first to build a cathode-ray tube with a heated cathode; Johnson noise is named after him. In 1922, it was turned into a commercial product.

Later over time, a CRT television with receiving images with a 40-line resolution was demonstrated by Kenjiro Takayanagi in 1926. The resolution of the television was improved by Kenjiro Takayanagi from 40 to 100 lines by 1927, which was unrivaled until 1931. Also, on a CRT display, a human face was first transmitted by him by 1928. By 1935, an early all-electronic CRT television was invented by him; its name was given by Vladimir K. Zworykin in 1929. He was an innovator who was influenced by Takayanagi's previous work. RCA was given a trademark for the word cathode-ray tube in 1932, and it surrendered the term to the public domain in 1950.

The first CRTs for 1,000 hours of use were introduced by Allen B. DuMont in the 1930s, which led to a major revolution in the adoption of television.

Telefunken produced the first commercially electronic television sets with cathode-ray tubes in Germany in 1934.

Although Telefunken introduced the first rectangle CRT in 1938, the size of CRTs changed dramatically between 1949 and the early 1960s, with a transition from circular to rectangular CRTs. In 1954, RCA produced some of the first colour CRTs; the CT-100, the first colour TV set to be mass-produced, used the 15GP22 CRTs. The first rectangular colour CRTs were produced in the same year, 1954. But the color rectangular CRTs that were provided to the public for the first time were manufactured in 1963.

Convergence at the corners of the CRT was one of the difficulties encountered during the production of the rectangular colour CRT. Blue phosphors were eventually phased out in 1965 when dimmer and cadmium-containing red and green phosphors were phased out in favour of brighter rare earth phosphors.

With time, the size of CRTs was increased from 19 inches (1938) to 21 inches (1955). By 1985, the size had expanded to 35 inches, and by 1989, it had increased to 43 inches. In 1960, the Aiken tube, a CRT with a flat panel display format, was introduced. It was a display format with a single electron gun. Due to patent problems, the deflection was never put into production, which was electrostatic and magnetic.

Zenith developed the flat-screen CRTs for computer monitors in 1987; they helped to enhance image contrast and brightness and reduce reflections. These CRT monitors limited the use of computer users as they were costly. By using cheaper and widely available float glass, there were tried to produce the flat-screen CRTs when Sony introduced the first CRTs with HD resolution in the market in 1990.

In the 2000s, flat-panel displays began significantly displacing cathode-ray tubes, and their price was also decreased. In 2003-2004, the sales of the CRTs dramatically decreased, and LCD monitor sales started to over CRTs. In the US in 2005, as compared to CRTs, the sale of LCD TV was more. Consequently, the sales of LCD increased rapidly, and by 2007-2008, it spread out globally and in India in 2013.

In the mid-2000s, Sony and Canon introduced the Surface-conduction electron-emitter display and the Field-emission display, both of which were flat-panel displays. In the place of electron guns, they both contained one (SED) or numerous (FED) electron emitters per subpixel.

Videocon was the last manufacturer of CRTs, stopped in 2015. The production of CRT TVs also ceased around 2015. Furthermore, in the US, various CRT manufacturers were convicted for price-fixing in 2015. In Canada in 2018, the same problem occurred.

Types of CRT

The display tube and picture tube were two major categories of CRT. Display tubes were produced to use in computer monitors, whereas picture tubes were used in televisions, which were also known as CPTs. Display tubes were designed with higher resolution and had no overscan. In contrast to display tube, the actual edges of the image do not show in the picture tube CRTs as they have overscan. But this is done knowingly with the picture tube CRTs to allow for adjustment variations between CRT televisions, through which the ragged edges of the pictures can be shown on the screen. Due to overscan, in order to away the electrons, the shadow mask may have special structures that do not hit the screen.

• Monochrome CRTs: In the neck of the B&W or monochrome CRT is a single electron gun. And on the interior of the CRT, its funnel is coated with aluminium, which is allowed to concentrate and evaporate in a vacuum. Aluminum is important for some tasks such as it helps to prevention burn on the phosphor, eliminating the need for ion traps, reflecting light, managing heat and absorbing electrons, etc.
  Aluminum (coated the inside of the CRT, including the phosphors) began to be used to CRTs in the 1950s, which helped to improve picture brightness. On the outside, Aquadag is used in the aluminized monochrome CRTs. Monochrome CRTs may use magnets around the deflection yoke and ring magnets to alter the centering of the electron beam to adjust the image geometry.
  
• Color CRTs: Color CRTs produce red, green, and blue light, respectively, as they use three different phosphors. They are packed together in clusters known as triads or packed in stripes like in aperture grille designs. There are three kinds of electron guns included in the color CRTs, which are responsible for three colors red, green, and blue. These guns are generally constructed as a single unit arranged either in an equilateral triangular configuration or in a straight line. The triangular arrangement is known as "delta-gun" because of the form of the Greek letter delta."
  In color CRTs, the phosphors are arranged in the same way as the electron guns. A shadow mask tube blocks all other electrons and helps the electron beam to illuminate the correct phosphors on the face of the tube as it uses a metal plate with tiny holes. And, if the shadow mask uses slots rather than holes, it is called slot mask. When electrons strike the inside of a hole, they are reflected back; as a result, the slots or holes through which they may do this are tapered. If the electrons are not absorbed, they are reflected back.
  CRT (Trinitron) is a form of colour CRT that achieves the same objective by using an aperture grille of tensioned vertical wires. The shadow mask is usually 1/2 inch behind the screen, with one hole for each triad. Trinitron CRTs were unique in comparison to other colour CRTs. They had an aperture grille, a single electron gun with three cathodes, and a single electron gun with three cathodes that let more electrons to flow through, which helped enhance image brightness. Except in Trinitron CRTs, the red, green, and blue (three electron guns) are in the neck, and these phosphors may be separated by a black grid or matrix on the screen.

Advantages of CRT

Although CRT technology was not more popular, it still offers many advantages over its main competitors as it is mainly used with television sets and computer monitors. Many people feel the advantages of CRT monitors are more useful than the LCD displays; however, CRT monitors are bigger in size and heavier in weight. Below, there are some advantages of monitors that use CRT technology.

Cost

The price is one of the main benefits of CRT monitors, which was much affordable as compared to LCD monitors with comparable components. On the basis of the quality, the cost of CRT monitors is from $50 to upwards of $300 as of June 2010. Usually, the cost of a common LCD monitor would probably be from $100 to $200, while a common CRT monitor can be expected to purchase by paying half cost of an LCD display.

Viewing angles

Depending on the angle to the picture, you may need attention with some television sets and monitor type; that picture quality changes drastically. For example, if you watch your television or monitor display from some left or right side instead of the front of the screen, you will notice that the picture quality is not clear. In CRT monitors, this problem is virtually non-existent, but this problem is mainly widespread in LCD displays. A CRT monitor provides more flexibility in terms of distance, placement, and view angle, meaning the picture quality will be the same in the CRT monitor no matter what angle you look at it from.

Color Quality

CRT monitors have the ability to display all of the 16.7 million colors used in 24-bit displays, whereas common LCD monitors are unable to display all of these colors as they use TN technology. Hence, compared to some of the competition, CRT monitors can display more detailed and vibrant colors. Thus, CRT monitors are more useful for media-lovers who are unable to go with high-quality HD displays. Also, it is better for gamers and graphic designers.

Image Quality

One of the other advantages of CRT monitors is picture quality as they provide actual colors and have high resolution, which leads to offering more detailed and finer images. CRT technology makes computer monitors used in diverse lighting situations as it includes dark blacks and high contrast levels features. Due to the good image quality, there is no chance of motion blur. And, when pictures change quickly on the screen, the motion blur problem occurs in some monitors. For example, on other monitors, a fast-paced and action-packed video game can be blurry at the time of faster parts. But CRT monitors are able to show these kinds of the game without the added blur.

A Brief Word on LCD

Although CRT picture quality is generally high as compared to an LCD display, LCD technology is rapidly changing and growing much faster than CRT technology. That means it is very close to the image quality of CRT technology. However, these types of high-quality LCD monitors are rare and much expensive that may not be afforded by normal people. But they would become more readily available and inexpensive, too, as the technology advances progressively.

Disadvantages of CRT

Although there are various benefits of CRT technology, it also offers many disadvantages. Below, some disadvantages are given of computer monitors that use CRT technology.

Heavy and Cumbersome

When compared to flat-panel displays based on LCD and OLED, one of the most significant disadvantages of CRT monitors is their size. The CRT devices, like monitors and television sets, acquire much space on the floor, whereas devices that are based on LCD and OLED consume significant amounts of floor space. CRT display technology needs bigger tubes for a wider and bigger screen. CRT monitors require a large configuration that limits their use of them and makes them inappropriate to spaces with limited floor areas. Due to heavier size, mobility and transportation with CRT monitors are also an issue. Furthermore, manufacturing CRTs larger than 40 inches is essentially impractical.

Costly and Energy Inefficient

While comparing to flat-panel displays, CRT monitors are now more affordable as they are obsolete now. However, because of the high manufacturing cost, they were more costly in an earlier time as compared to LCDs. This is the main reason for the obsolete of CRTs and the growing LCD displays.

Another downside of CRT monitors is that they consume more electricity than LCD and OLED panels. For example, a 32-inch CRT TV consumes about 125 watts of energy, whereas a similar-sized LED TV consumes 18 watts. A 42-inch CRT TV consumes 210 watts of energy, while 40-inch LED TV consumes 31 watts.

Safety and Environmental Concerns

A CRT is a vacuum tube that contains a high vacuum inside the tube. Without colliding into molecules of air or gasses, it uses this vacuum to allow electron beams to fly freely. The tube can collapse into numerous fragments if the glass or any surface of a CRT gets any damage. Consequently, even if the power supply is turned off, the CRT and some associated capacitors can also keep an electric charge. Thus, there is a possibility of electric shock.

In the case of recycling and disposing of properly, CRT monitors come under the category of hardest consumer electronic products. The lead and phosphors are included in high concentrations in CRT monitors. Also, even discarded CRTs have been considered hazardous household waste by the United States Environmental Protection Agency.

Some other key points of disadvantages of CRT technology:

• The Gaussian beam profile of CRT emits pictures with softer edges, meaning images' resolution is not clear as an LCD technology.
• Some monitors include Moir� reduction because of producing annoying Moir� patterns by color CRTs. Thus, they may be unable to eliminate the Moir� interference patterns completely.
• They are not ideal for very brilliantly lit areas and offer less brightness than LCDs (Relatively bright but not as LCDs display).