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How Does a Television Work?

Older televisions use cathode-ray tubes to produce images.
HDTV.
Traditional tube television sets use negative, hot cathodes to produce a picture.
Article Details
  • Originally Written By: Michael Anissimov
  • Revised By: John Allen
  • Edited By: L. S. Wynn
  • Last Modified Date: 13 July 2014
  • Copyright Protected:
    2003-2014
    Conjecture Corporation
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A television produces a series of tiny dots on a screen that, when seen as a whole, appear as an image. Older televisions rely on a cathode-ray tube to produce images, and operate with an analog signal. As technology has advanced and broadcast signals transitioned from analog to digital, plasma and LCD (liquid crystal display) televisions were created. These TVs are more compact and have crisper pictures than their cathode-ray counterparts because they use a thin grid of pixels to create images rather than a vacuum tube.

The Eyes and the Brain

Most kinds of television work from the same basic principle. The tiny dots of light produced on the TV screen, called pixels, flash according to a specific pattern provided by the video signal. A person's eyes transmit this pattern to the brain, where it is interpreted as a recognizable image. The television set refreshes these patterns hundreds of times per second — faster than the human eye can see — which gives the illusion of movement.

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The Cathode-Ray Tube

The cathode-ray tube (CRT), the oldest version of the television, consists of a vacuum tube with a narrow end and a wide end. The narrow end contains an ion gun, which shoots out a series of charged particles of electricity. A series of electromagnets guide the particles to specific points on the wide end of the tube, the screen that viewers look at. Phosphors, substances that light up when a charged electrical particle hits them, coat the screen's inner surface. The ion gun essentially sprays the image at the screen, much like a paint gun sprays paint onto a surface.

Different kinds of phosphors produce different colors, but for color television, only red, blue, and green are needed. Using these colors in various combinations and intensities can create all the colors the human eye can see. As energy travels from the ion gun to the phosphors, it is filtered to strike the exact point on the screen needed to produce a specific hue. In combination, all of these colored pixels create a color image.

Cathode-ray tubes are quite heavy due to the large amount of glass they contain, and relatively inefficient, especially when used in large-screen televisions. For this reason, new technologies were developed to make lighter sets with crisper images. In addition, the development of high definition (HD) digital broadcast signals made bigger screens more popular since the images were of higher quality. Plasma and LCD televisions were created in response.

The Plasma Screen

A plasma screen television consists of a number of tiny cells filled with neon and xenon gases. Each cell is linked to an electrode, which, when fired, excites the gases contained in the cell. The gases emit charge particles, much like the ion gun, that interact with phosphors coating the glass inside each cell. The phosphors light up, creating the image seen on the television screen. The large number of cells in a plasma screen makes for a great number of pixels, rendering a clearer and brighter image.

Compared to other technologies, plasma TVs produce some of deepest blacks, which means that the contrast ratio is very high. They also have very high refresh rates, so images with a lot of motion don't blur as they can on other televisions. If the image remains static, however, it can burn into the screen, creating a permanent discoloration; this is more common in older plasma TVs, and can also occur with CRT screens. Plasma screens can be set to be very bright, which requires a lot of electricity. They also tend to be thicker than LCD televisions, although much thinner than CRTs.

The LCD Screen

LCD televisions also use cells to create images. Rather than exciting gases as plasma TVs do, however, the cells contain a set of red, blue, and green filters covered by a layer of liquid crystals sandwiched between two pieces of glass. Depending on the display type, each cell is linked to either electrodes or thin film transistors (TFT), which trigger the necessary cells to create the image. A backlight — most often cold-cathode fluorescent lamp — lights up the screen so the image can be seen.

While LCDs are very light and thin, they are subject to "dead" pixels, where one or more cells on the screen do not change. Viewing LCD screens from an angle can also lower the picture quality. They have slower response times than plasma or CRT televisions as well, so images can "ghost" or blur in movement.

More recent versions of the LCD television use light-emitting diodes (LEDs) as the light source rather than cold-cathode fluorescent lamps. LED televisions require less electricity than regular LCD screens, and take up even less space. Also, LEDs generally emit a brighter white light, making these screens especially vivid.

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Discuss this Article

anon330840
Post 54

Just wondering, when you say "As energy travels from the ion gun to the phosphors, it is filtered to strike the exact point on the screen needed to produce a specific hue," how exactly is this hue made? What signal is sent? How does the television create a the specific hue?

anon306882
Post 48

How does the remote operate all the signals needed?

anon285087
Post 45

What year was the first analog television invented? I need this information!

pollick
Post 44

This is not meant to be a scientific explanation, but one reason LED and LCD television screens are thinner than CRT screens is the nature of the mechanism. A CRT monitor is essentially a very large vacuum tube; we just watch one end of it. The glass screen holding in all of those gases and electronic parts has to be thick and sturdy. If a CRT monitor is dropped, there's a good chance the glass will shatter and the vacuum will be breached. It's not pretty. The electron gun which shoots the individual flashes of pixels also needs some distance from the screen to work correctly.

LCD and LED television screens, on the other hand, work on a different principle. All of the liquid crystals or light emitting diodes are sandwiched between two thinner layers of glass, so there is no vacuum to maintain. The crystals or the LEDs receive electronic signals in order to turn certain ones on or off.

This all happens so fast that our brains see all of these still pictures as moving images. LED and LCD screens can be flat because they don't require an electron gun to provide the same electronic information.

anon272042
Post 43

Please explain why LED OR LCD tvs are thinner than a CRT.

anon263784
Post 40

How does a TV store the image and how does it send or transmit it to something else?

anon260751
Post 38

How do DVD players turn bumps into sound and pictures? TVs are complicated but DVD players are downright genius.

anon202957
Post 36

Good help, but needs more info about the charge.

anon147590
Post 33

I get what it's saying, but how does the energy "magically" turn into light and sound? And how does the sound change, and the pics move?

anon132350
Post 30

How does a TV use light?

anon103522
Post 26

how did they convert electromagnetism into acoustic light energy again?

anon93125
Post 23

good. but not very clear info.

anon90840
Post 21

Okay. Thanks. That helps a lot with my science thing. it gives a lot of information but i guess it's not the kind I'm looking for.

anon89576
Post 20

It gave a lot of information about how the television was made, when it was made and who made it.

anon85617
Post 18

I wanted to know in detail how a television works. This provides a history TV development, but nearly no information on how a television works.

anon83996
Post 17

well i think it was pretty good and gave good information. They just need to tell what made the person make the television. --Dabaddest

sas
Post 15

Please explain why tv's are square and not round. thanks

anon65310
Post 14

Well, i believe television works like this. Pixels fly through the air an get sucked in by your antenna. Then some magic takes it from your antenna and put it on your screen for your eyes to see.

anon64162
Post 12

I liked your description, but can you tell me when television was first introduced to the market?

-Critic

anon54101
Post 9

Just as a radio and a telephone are devices for converting acoustic energy into electrical and vice versa, the television receives wirelessly transmitted electromagnetic waves and converts them into acoustic and light energy for viewing.

Although the initial inspiration for the television existed as early as the 1830s, when inventor Michael Faraday demonstrated the relationship between light and electricity, the television did not become practical for mass-production until more than a century later - in the 1940s.

The history of the television is marked by a series of devices that were progressively more effective at sending or receiving wireless electronic patterns containing light and sound information.

anon47591
Post 5

good. but you should write how it works the process.

bigmetal
Post 4

i guess we are ushering in another age of televisions with the new DTV transition that will happen in 2009. were the original tvs analog?

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