Do you have one of those sleek, sexy, thin-as-a-cracker televisions, or is the TV in your household one of the old-school, big ones that take up more space than necessary?

Without a doubt, television has evolved a great deal since it was invented. The first televisions were black and white (can you imagine!!!), and had very poor resolution and picture quality by today's standards. The next generation of TVs was based on the cathode ray tube (more on that later). But today, the current state of the art TV technology is either Liquid Crystal Display (LCD) or Plasma.

LCD and Plasma television sets are very flat because they use a small amount of charged liquid (in the case of LCD) or gas (in the case of Plasma) to regulate how coloured light passes through to the screen. The advantages of these new technologies are:

The screen is very flat with no distortion at the edges. The units have low power consumption.

However, both LCD and Plasma TVs suffer from a number of different problems, which include:

Black isn't truly black: Instead, it appears like a very dark shade of gray or blue. Poor angular range of view: Meaning that it is hard to see a good image when viewed from the side. Slow video response: In other words, the liquid used in LCD and the gas in Plasma screens change their colours more slowly compared to a conventional cathode ray tube (CRT) television.

Did you know? LCD and Plasma screens are thin because they use charged liquid and gas, respectively, to regulate how coloured light passes through to the screen

While it is possible to deal with these problems, they are to some degree, a fundamental part of the technology. The ideal television would be something that has the benefits of LCD or Plasma without the above-mentioned drawbacks.

The people at Canon believe that they have designed this ideal television. Canon is developing a technology known as Surface-conduction Electron-emitter Display, or SED. This technology uses many of the positive features of CRT technology; along with some novel ways to solve other problems to create a screen that Canon says will be of similar size to an LCD screen, with all of the benefits of a CRT.

To understand why SED is able to produce high quality images like a CRT while also remaining flat and compact like an LCD, we'll start with how a CRT works...which may seem like a review of your Physics class, if you have already learned about electromagnets and magnetic and electrical fields.

At the back of a CRT is an electron gun. This gun fires a beam of electrons in a straight line, in rapid sequence. These electrons can be influenced by magnetic and electrical fields. So, it is possible to change the direction of the beam of electrons. In front of the electron gun are four electromagnets. By changing the current in these electromagnets, the strength of the magnetic field is changed, and so the direction of the electron beam is also changed. Two of the electromagnets are arranged so that they will change the direction of the electron beam up or down, and the other two are arranged to move the electron beam from side-to-side.

Did you know? A magnetic field exerts a force on moving electrons, which causes the electrons to change direction.

Did you know? Electromagnets use electrical current to generate a magnetic force.

Through the correct sequence of changes in the magnetic field, the beam of electrons is moved across the screen from side-to-side, and from top-to-bottom. This might make you wonder why we can't see this movement in the TV image. Because the phosphors glow for a period of time, and the electron beam moves across the screen at very high speed, our brain and eye are unable to tell that this is happening. Instead, we see what appears to be a continuous image.

The electrons are aimed at the back-side of the glass at the front of the TV. The back of the glass has a very fine grid of phosphor, or a substance that glows when struck by an electron. In the case of a modern colour television, the phosphors will either glow red, green, or blue. These three colours are the additive primary colours, and by combining varying amounts of these three colours, all of the colours that our eyes see can be created.

Did you know? When struck by an electron, phosphors can glow red, green or blue. These additive primary colours combine with each other to create all of the colours that we see.

The back-side of a television's glass screen has the phosphors arranged in vertical strips. All of the phosphors in each strip are the same colour (red, green, or blue). A very fine grid is placed over the strips of phosphors so that small sections of three strips (one red, one green, and one blue) are combined together in what is called a picture element, or pixel. Each pixel is a very small dot on the screen, and by combining large numbers of pixels together, shapes are created. The electron gun has three beams to hit all three phosphors in a pixel at the same time. As more electrons hit each phosphor, it glows more brightly and, therefore, adds more red, green or blue to the final colour result. Each phosphor can represent about 256 different brightness levels, so each pixel can have 256-cubed colours, or about16.8 million colours.

Did you know? "Pixel" refers to the term "picture element". Each pixel on a TV screen has a red, green or blue component.

Because there is only one electron gun at the back of the television, it has to be far enough away from the front screen to be able to hit every point on the front screen, from the upper-left to the lower-right corners. As a result, a CRT television is, by necessity, a deep, heavy, and space-consuming piece of equipment.

Canon's SED technology still uses the glowing phosphors and something similar to the electron gun that is used in a CRT. However, instead of using one electron gun for the entire screen, SED technology uses one electron emitter for each pixel. This eliminates the need for the powerful electromagnets to aim the electron beam; the emitter is either on or off, depending on whether the particular pixel needs to be turned on or off. These emitters are also placed very close to the screen of the television, meaning that the package is very flat, allowing for a fancy, thin TV.

Although the SED TV is still in development, this new technology may be the next step in the evolution of the television. It combines the flat screen and thin package of the LCD and Plasma with the picture quality of a CRT. It almost sounds too good to be true!

References:

http://www.canon.com/technology/display/

http://electronics.howstuffworks.com/tv.htm

Andrew grew up in southwestern Ontario, and graduated with a Masters degree in Systems Design Engineering from the University of Waterloo. He is currently working as a computer programmer for GE Healthcare working on CT scanner images. In his spare time he enjoys running and triathlon.

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