Which topic would you like to jump to?

Whichever type of TV you desire, we have something for you.  The biggest question for customers is what type of TV should you get?  CRT, flatpanel, DLP, LCD, plasma, or projection; and will this be HDTV?  What's the difference between a plasma screen and an LCD screen?  These are great questions to ask. Having a better understanding of the products in which you wish to buy will enable you to make the right choice for you!

CRT (Cathode Ray Tube):
CRT TVs have been around for over 60 years!  While the CRT screens of today may have different and better qualities than their past counterparts, the technology still stays relatively the same.

The Cathode in these tubes is a heated filament, which is not unlike the filament in a regular light bulb.  The cathode is heated in a vacuum created inside the glass tube. The ray comes from the stream of electrons, which naturally pour off the heated cathode and into the vacuum.

Electrons are then focused via anodes (positively charged terminals) into tight beams that are further accelerated by accelerating anodes.  After this is done the beam of electrons hits a flat screen at the other end of the tube made of phosphor.  This phosphor glows when struck by the negatively charged particles.

This is a diagram of the basic setup of a CRT.
1. Cathode
2. Conductive coating
3. Anode
4. Phosphor-coated screen
5. Electron beams
6. Shadow mask
 

Steering coils are used to maneuver the beam inside the tube.  These coils create a magnetic field, which the electrons respond to.  Typically, one set of coils moves the electron beam horizontally, while another set moves the beam vertically.

Phosphor:
The phosphorus colors in a color TV are Red, Green, and Blue.  Requiring three separate electron beams to illuminate the three different colors together, whereas only one beam is needed to illuminate the white phosphor in a black and white television.  Phosphor is excited when it comes in contact with radiation.  This radiation can either be in the form of ultra violet light, or a high concentration of negatively charged particles (electrons). This same phosphor technology is also used in Projection TVs and in Plasma screens.

DLP (Digital Light Processing):
DLP technology is based on an optical semiconductor called a digital micro-mirror device (DMD).  The DMD was developed in 1987.  It works by modulating light digitally.  The DMD is a rectangular array of very small mirrors (16 microns across) that reflect light to form an image.  Each individual mirror in the array can be switched toward or away from the light source reflecting light towards the projection screen or away from it.  This in effect gives the mirrors an on and off position which can be triggered thousands of times a second.  When light is reflected, a single pixel is illuminated with white light. The amount of time the mirror spends reflecting light dynamically affects the color of the pixel seen.  Each pixel can produce 1024 different shades of gray, producing an unmatched grayscale image.

To add color to a DLP, a color wheel is inserted between the light source and the DMD.  This color wheel has three colors on it, blue, green, red.  The wheel rotates at a high rate of speed, exposing the DMD to the three types of colors that comprise visible light; these colors are red, green, and blue.  Coordinating when the micro-mirrors reflect light will change the shade and color that is to be displayed.  For example, to make a shade of purple, the DMD will reflect light only when the red and blue colors of the wheel are filtering light.

Typical DLP projectors can produce up to 16 million colors (computers at 16-bit colors can only display 65,536 colors).  However, there are some DLP projection systems being used in theaters that can produce upwards of 35 trillion colors!  These projects do not use a color wheel; rather, light passes through a prism that splits the white light into red, green, and blue wavelengths.  These colors then reflect off of three separate DMDs.  Because each DMD is dedicated to a single color, more shades of that color can be produced and meshed with the other DMDs to create the richest color ever seen on screen!

Projection TVs:
CRT screens usually top out at 40".  This is because the tube is made of glass, making it extremely heavy and expensive!  Projection units on the other hand, can produce a large image at a reasonable price. 

These televisions work by forming a small image from a device inside the unit itself.  The device may be LCD, DLP, or CRT, which in turn projects an image onto a large screen located elsewhere.  With reflective (rear) projection screens, light is reflected off the projection display panel (a mirror), where it is then projected to the viewing screen.  With transmissive projection screens, the screen is located on the other side of the room.  The image passes through the image-forming panel, and is then projected onto the screen.

LCD (Liquid Crystal Display):
Thinner, lighter, and requiring much less power than CRTs are LCDs.  These displays are similar to that of a slide viewer.  The liquid crystal panel sits in front of a backlight.  Between the liquid crystals and the backlight lays an electronic grid with gates that can be opened or closed to allow light to pass to the pixel. 
 
LCDs are usually fairly small; the reason being is that large displays require more pixels on a grid to fill the screen, thus increasing the rate that a display grid will have one or more defective transistors.  It isn't cost effective to produce big screen LCD screens for this reason, which is why LCD viewing is mostly found on computer or small display devices.

The big advantage with LCD screens is that they make great displays for stationary images, such as a computer screen, videogames, or a home automation display.  There's no tube to put strain on.  CRT screens need to have a constant flow of images otherwise there is strain placed on certain parts of the tube, greatly reducing it's life.

Plasma:
What is plasma?  Well, plasma is a gas, used as the central elements in fluorescent lights.  This plasma gas is made up of ions (ions are positively charged atoms, having more protons than electrons).  In order to cause these atoms to light up, electrons need to be introduced to excite the plasma, creating ultraviolet light, and thus lighting up the phosphor material coating the wall of the plasma cells. To do this, the TV's computer charges the electrodes that interact with the plasma cell (red, green, or blue cells).  The change in voltage causes the electric current to flow through the gas in the cell.

The biggest advantage gained by using plasma is the ability to produce a very wide screen using thin materials.  The picture looks very bright, and has a higher field of view because the pixels are lit individually.   You can even hang them on your wall!

HDTV:
Gaining more popularity in the television display industry, HDTV looks more like a movie screen than a TV set.  The images are lifelike, almost more real than life itself, increasing the clarity of your viewing experience with its high-resolution picture!

With analog TV signals in the United States, there are 525 scan lines for the image (only 480 are visible), each image is refreshed every 30th of a second.  This resolution was amazing 50 years ago, but it now seems rather unimpressive.  On average, computer resolutions usually run at 1024x768 (768 scan lines).  With great clarity increasing in computer displays, the TV pales in comparison.

Digital signals, however, can have 720 to 1080 lines of resolution.  In the latter case, over twice the resolution as a standard TV can produce! Here are the formats used in HDTV:
720p - 1280x720 pixels progressive
1080i - 1920x1080 pixels interlaced
1080p - 1920x1080 pixels progressive

The terms interlaced and progressive explain how the picture is formed.  In an interlaced screen, every odd line is drawn followed up by every even line with a second scan.  Since there are 30 frames shown per second, the screen shows each scan every 60th of a second.  This method works very well for smaller screens, but with a larger screen there could be problem with a noticeable flicker caused by this interlacing.

Progressive scanning paints every single screen every 60th of a second.  This will provide a much smoother image, but it also will use slightly more bandwidth.

To combat with bandwidth issues, HDTV is encoded with the MPEG-2 codec.  This is a method used to compress the signal at a ratio around 55:1.  MPEG-2 is already the leading compression of choice for DVD videos and some satellite TV signals.  This compression does reduce image quality, but it's such that the image that is thrown away is one that the human eye is incapable of seeing.

MPEG-2 also allows the HDTV receiver to interact with multimedia applications on a computer.  It's even possible to record your HTDVs onto a writeable media source such as a recordable CD or DVD.

The image size is also different.  Aspect ratios for standard TVs are 1.37:1. Sometimes this is referred to as a 4x3 screen.  HDTV's have a 1.78:1 ratio (16x9), much closer to the picture size used in theatrical movies.  As it stands right now, movie broadcasters have to use a technique of pan and scan to get the image to fit onto a 4x3 screen.  The problem with this is that it eliminates part of every scene in the movie.  Another way to get the full picture on the screen is to letterbox the image, inserting the viewable image in the middle of the screen with black bars at the top and bottom.  With a 16x9 screen, the pan and scan method doesn't cut out much of the picture, and the letter box doesn't black out as much of the screen.

This image shows the difference between standard and HDTV pictures. There is a significant amount of image lost in the standard 4:3 view, whereas the full picture is shown in 16x9 ratios.

This can be explored in more depth by learning about anamorphic signals. (off site linking)

Image quality is also dramatic.  The NTSC (National Television Standards Committee) gives a picture with 525 scan lines of resolution (only 480 of these lines are visible on the set).  The largest amount of pixels you can get on a 525 resolution TV is around 210,000 pixels.  HDTVs, however, can have upwards of 2 million pixels, resulting in an image that is 10 times clearer!

The two above images are simulated pictures of the difference between high definition and standard resolutions. Also incorporated are the aspect ratios. The image on the left shows HDTV. Crater lake is very crisp and a vast landscape is presented to the viewer. On the right is a standard picture. It's not as clear, nor does it display as much scenery as HDTV does.