- I want to buy a television
- What are the types of televisions?
- Plasma or LCD which one is better?
- Why do televisions have different shapes?
- What size of television set is best for my room?
- What should be the viewing distance for a 26" wide screen?
- What is the difference between HDTV, Analog and Digital?
You walk into an electronics store to buy a television and are greeted by what appear to be a lot of options, many of which look similar. But of course, each has different features, which make it appealing to different kinds of customers.
Before you understand the working and the types of televisions available in the market, it is important you get familiar with some common television terminology.
Common television terminology
Term |
Definition |
Aspect ratio |
Aspect ratio is a term used to describe the proportional relationship between the width and height of a screen. There are two primary aspect ratios used in display. Movie theatres, DVDS, and HDTV signals use the 16.9 (16 units wide by 9 unit high) aspect ratio, also known as wide screen“ or cinematic“ display. Standard CRT television, satellite and cable television signals, and VHS use a 4.3 (4 units wide by 3 units high) or “full screen” aspect ratio. |
Brightness / contrast ratio |
Technically, brightness in television is often discussed using the term “contrast ratio“. The contrast ratio is a measure of a television’s ability to display very bright objects and very dark objects simultaneously. The greater the contrast ratio, the greater the ability to show subtle colour details. Plasma screen televisions are able to display very high contrast ratios at uniform amounts of brightest, creating a very detailed picture that is not overly garish. Normal CRT televisions often loose brightness with age, or produce images with varying levels of brightness, with darkening at the edges, and overly bright “hot spots” near the centre. |
HDTV |
High Definition Television is a digital television format, which combines high-resolution video and theatre like sound to create a movie theatre quality TV viewing experience. It has approximately twice the vertical and horizontal picture resolution of today’s standard TV, which essentially makes the picture twice as sharp. HDTV also has a screen ratio of 16:9. HDTV offers reduced motion artifacts (i.e. ghosting), and offers 5.1 Independent channels of CD-quality stereo surround sound. |
Pixels |
Individual dots used to create an image. The greater the number of pixels in an image, the higher the resolution and better the quality. |
Resolution |
The number of pixels in an image. The more pixels, the higher the resolution. The higher the resolution, the better the picture. |
Burn In |
This term describes the appearance of a static video image that remains on the screen even after the TV is turned off. It is usually caused by the TV’s brightness controls being set too high, with the result that network logos or other text are permanently burned into the TV’s colour phosphors. This problem only affects TVs that use CRT and plasma technology |
SDTV |
Standard definition television. These 480i or 480p signals have no more lines of detail than analog TV or DVDs, but can be presented in a wide screen format. |
Basically, there are three types of televisions –CRT, Plasma and the LCD.
Each uses a different form of technology in order to generate the picture on the screen. But then, each also has its own advantages and disadvantages.
Cathode Ray Tube (CRT)
This is the oldest kind of TV technology which has been refined over the years. The cathode ray tube works on a simple principal – a stream of electrons is fired at the back of the screen, which is coated with phosphors that emit red, blue and green light when the electrons hit them. By moving the electron beam over the screen (extremely quickly) a combination of light and dark pixels is created, forming a picture.
Standard TVs use an interlacing technique when painting the screen. In this technique, the screen is painted 60 times per second but only half of the lines are painted per frame. The beam paints every other line as it moves down the screen for example, every odd-numbered line. Then, the next time it moves down the screen it paints the even-numbered lines, alternating back and forth between even-numbered and odd-numbered lines on each pass. The entire screen, in two passes, is painted 30 times every second. The alternative to interlacing is called progressive scanning, which paints every line on the screen 60 times per second.
Most computer monitors use progressive scanning because it significantly reduces flicker. The process is repeated to produce the frames of a TV picture and the human brain does the rest, interpreting the series of still images as a moving picture.
Pros
- CRT sets deliver excellent images. Many people still prefer the picture on a CRT set to that of an LCD or plasma screen, especially for regular TV broadcasts
- The viewing angle on CRT sets (how far to the side you can sit and still see a clear picture) is excellent
- The technology has been refined over decades of use and prices can be low even for large-screen sets
- CRT sets have long lives and do not need professional installation like some alternatives
Cons
- CRT sets will not feature in the high-definition revolution. This arena will be left to other technologies that are better suited to handling the extra image resolution of high-definition broadcasts
- They are very bulky when compared with plasma and LCD sets. The CRT itself is the villain here – it has to be big to do its job, and that means it takes up a lot of space in your living room
- They can be very heavy indeed, especially flat-screen sets, and this means you can’t easily move them from one spot to another
- Screen size is limited – a CRT screen can be no bigger than 36 inches (measured diagonally), while plasma sets have reached 60 inches and are still growing
- The picture can be distorted if home cinema speakers are placed too close (the magnetic field from the speakers can influence the electron beams in the CRT)
When a plasma TV isn't displaying an image, the stuff behind the name is just an inert gas — usually a mixture of neon and xenon — but it's a big part of what allows these TVs to measure just 3 to 6 inches thick.
Unlike a CRT TV, a plasma display uses a combination of thousands or even millions of discrete pixels to form a picture. A plasma with a resolution of 1,024 x 768, for example, has 786,432 (1,024 x 768) pixels. If that sounds like a lot of dots, it's really just a third of the story. Each pixel is actually made up of three separate sub-pixels: one each for red, green, and blue.
The sub-pixels, also known as cells, are basically tiny pockets filled with gas.
The inside of each cell is coated with red, green, or blue phosphors. Using phosphors allows plasma TVs to closely mimic the color palette of CRT TV's As you can see from the illustration, each cell has a pair of electrodes associated with it — one in the bottom of the cell and one above — arranged in two layers of glass. The top electrode layer is transparent — you actually look through it to see the picture.
When current is run through the electrode layers, the gas inside each cell is excited into an ionized plasma state that releases ultraviolet photons. Those photons react with the phosphors, producing reds, greens, or blues of various intensities. The combination of colors in each complete pixel can produce millions of real-world colors, from white to black and everything in between.
Pros
- The largest screens available are available in this type, generally in 37" to 60" diagonal.
- Thin depth, usually 3" to 5"
- Long life span of approximately 20 years (6 hours per day) for name brand manufactured units.
- Wider viewing angle compared to most LCDs in the market at this time.
- Accurate and wide range of color.
- Good colour contrast.
- Generally less expensive than an LCD TV of the same size.
- Displays well in darker lighting conditions.
- Small "foot print." It can be hung on wall, mounted on an arm, stand or cabinet.
- Some name brand models include video cards so your plasma may be "future proofed" for some upgrades.
- Available in HDTV (high definition).
Cons
- Burn in (a.k.a., image retention) may occur if the same still image stays on screen for a long time.
- Images not displayed well in brighter light conditions.
- Pixel failure can be a problem with models built by "no name" manufacturers."
- No tuners in most models. (Not a problem for those using satellite, digital cable, or external HD boxes).
- Presently expensive though prices are coming down.
There are five layers within an LCD display: a backlight, polarized glass sheet, a layering of colored pixels, a coating of liquid crystal solution, another sheet of glass. Each pixel contains cells filled with liquid crystals (red, green, and blue cells). Voltage off thin film transistors (TFTs) power the red, green, and blue cells to untwist and allow measured amounts of light to shine through them and form images.
Because light always has to pass through an LCD chip to create an image and because LCDs, unlike plasma screens, do not create their own light source, it is impossible for LCD monitors to produce a true black; instead, it will show up as dark shades of gray. Straight viewing is the best angle for viewing LCD images, because as you move to either side, image quality diminishes and, as the angle increases, the image disappears.
Pros
- Thin depth, usually 1" to 3"
- Long life span of approximately 30 to 50,000 hours bulb life for name brand.
- Sharp picture.
- More vibrant, accurate color.
- Images display well in brighter light conditions.
- Compact and lighter weight than plasmas or traditional CRTs of equal size.
- More user-friendly image if contemplating a home entertainment center including a PC for text as well as graphics.
- Good for still images, such as computer usage.
- Small "footprint." Can be hung on a wall, mounted on an arm, stand, or cabinet.
- Low operating cost per hour
Cons
- Screen sizes not available in large sizes that plasma units are, though larger sizes are being developed.
- Susceptible to a video image delay making objects or figures seem jagged or "digital", particularly with fast action. Most noticeable on screens over 30".
- Black levels are not fully black, but they're darker grey.
- Poor side viewing angles; the 170° field of vision often promoted is sometimes less than accurate.
- Pixel failure possibility, particularly on "no name" brands.
- Presently extremely expensive for units over 35".
A little more about Plasma versus LCD
Feature |
Plasma |
LCD |
Size |
Generally larger than LCD, with screen sizes of 60” or larger |
Wide range of sizes, but topping out around 45” |
Thickness and weight |
4 inches deep, Heavier, so may need additional support for wall mounting |
3 inches deep. Overall lighter, easily mounted on wall |
Viewing angle |
Typically has a wider viewing angle than LCD |
Newer LCD displays with wider viewing angles are making this less of an issue |
Brightness and contrast |
Superior brightness & contrast (in darkened room) |
Superior brightness & contrast (in bright room) |
Usage |
Mostly used for TV display |
Excellent for use as TV and PC display |
Product Life Span |
30,000 to 60,000; hours; however, once light source in cells is gone, not easily repairable. Susceptible to burning |
50,000 to 60,000 hours; when bulb burns out, can be repaired but is expensive to do so |
Pricing |
Lower cost per square inch |
More expensive but also more durable |
Why do they have different shapes?
Televisions today come in two shapes. The most familiar one is called 4:3, which means 4 inches of width for every 3 inches of height. You can also buy wide screen or 16:9. This is the same shape as many movies. Wide screen sets cost more per square inch of screen than standard TVs.
Widescreen is now used in producing DVDs and a limited number of TV programs. But as Digital TV takes off you will start to see more and more people looking for a wide screen experience.
People wonder how much picture they will miss out on by differently shaped programs on different TVs, that is a widescreen program on a 4:3 TV or vice versa.
If you view a widescreen program on a 4:3 TV, then the TV will place black bars at the top and the bottom of the TV to accommodate for the different size. This is also called letterboxing.
If you play 4:3 pictures on a widescreen TV, it will have black bars on the side. This is called window box bars. But it doesn't end there.
When you pay a lot of money for a wide screen TV you want to have a picture on the full screen. Manufacturers have come up with ways of making the 4:3 images fit the screen. They use a variety of techniques to do this including Zoom or enlarge, Wide or Full or Panorama, Theater-wide or Natural. Each has its advantages and disadvantages. The following gives you an example of how each of these technologies work:
Picture |
Explanation |
|
Normal or 4:3: Places windowbox bars on either side of the 4:3 screen |
|
Zoom or Enlarge: Magnifies the entire image, eliminating the windowbox bars but cropping the top and bottom of the image. Often, more than one level of zoom is provided. |
|
Wide or Full: used for native 16:9 content such as that found on DVD. With 4:3 content, such as regular TV, it stretches the image horizontally, making people look shorter and fatter |
|
Panorama, TheaterWide, or Natural: TV makers have many names for modes that compromise between stretching and zooming to fill the screen. Some stretch the sides of the image more than the middle, so people in the centre of the screen look correct. Some crop a little so that they don’t have to stretch as much. |
By now you have an idea of how each TV works the next thing to look at is the size. Of course the bigger the TV the bigger the price so budget will not only determine the type of TV that a customer buys but will also determines the size of the TV. TV sizes are measured diagonally across Another important factoring determining size is the viewing distance. This is how far away from the TV should you sit to get optimum picture quality. This will ultimately be limited by the size of the room in which the TV will be placed (and also there budget!).
Generally a 30-inch and smaller sets are great for bedrooms but too small for the main living room. The opposite is also true. A few points to remember -
- A CRT TV is fairly deep and bulky so make sure there is enough depth in the space where the customer wishes to place the TV
- If placing the TV in an entertainment unit make sure the unit is big enough to hold the TV and allows for an inch or two around the TV for ventilation
- If buying a bigger TV a stand may be appropriate to hold the TV. Many TV's either come with a stand or have an option to buy one
Most CRTs are a 4:3 ratio. The general rule for size with this ration TV is to sit between three and six times the width of the screen. The following distances are recommended viewing
Size (in) |
Min Viewing (m) |
Max Viewing (m) |
13 |
.8 |
1.6 |
19 |
1.15 |
2.31 |
20 |
1.21 |
2.43 |
24 |
1.46 |
2.29 |
27 |
1.64 |
3.29 |
32 |
1.95 |
3.9 |
36 |
2.19 |
4.5 |
40 |
2.43 |
4.87 |
16:9 Widescreen – viewing distance
Size (in) |
Min Viewing (m) |
Max Viewing (m) |
26 |
1 |
1.98 |
30 |
1.15 |
2.31 |
34 |
1.31 |
2.59 |
42 |
1.61 |
3.2 |
47 |
1.8 |
3.59 |
50 |
1.92 |
3.81 |
55 |
2.10 |
3.96 |
60 |
2.28 |
4.57 |
65 |
2.46 |
4.93 |
Currently there are three types of TV technology available Analog, Digital and HDTV. Since the first HDTVs appeared in 1998, high-definition television has been on the mind of every TV buyer. The big question is whether now is the time to pay more and take the plunge on an HDTV set. We can't answer that question for our customers but we can provide basic information that may help them decide.
Analog
An analog TV cannot display progressive-scan DVD or HDTV. It can show only standard-definition programs such as those found on regular TV, cable, or satellite.
Digital
A digital television, sometimes called a DTV, can also display progressive-scan DVD and almost always HDTV.
EDTV
This stands for Enhanced-Definition TV, and usually it describes a television that can display HDTV signals but doesn't have enough resolution to really do them justice. Most often it applies to plasma TVs and denotes 852x480 pixels
HDTV
High-definition televisions, or HDTVs, can display standard TV, progressivescan DVD, and HDTV signals. They're by far the most common type of digital television.
HDTV tuners
Not all HDTVs actually come with a built-in tuner (called HDTV, digital, or ATSC tuners) that can receive high-definition programs over the air by simply connecting an antenna. Sets that have them built in are called integrated
HDTVs, and those that don't are sometimes called HDTV ready or HDTV compatible; mostly they're all lumped together under the name HDTV. If a customer buys a HDTV-ready set, they will also need to connect a separate tuner (or cable or satellite box) to watch high-definition programming.
HDTV resolutions
Resolution, or picture detail, is the main reason why HDTV programs look so good. The standard-definition programming most of us watch today has at most 480 visible lines of detail, whereas HDTV has as many as 1,080. HDTV looks sharper and clearer than regular TV by a wide margin, especially on big screen televisions. It actually comes in two different resolutions, called 1080i and 720p. One is not necessarily better than the other; 1080i has more lines and pixels, but 720p is a progressive-scan format that should deliver a smoother image that stays sharper during.
