How Rear Projection TVs Work

Rear projection TVs are often an economical way to get a big screen and a great picture. They can be thinner than traditional CRT sets, but aren't thin enough to mount on a wall, as you might with a plasma or LCD flat screen.

As the name indicates, a rear projection television contains a projector, which transmits images from behind the screen through a lens that magnifies them to fill the available viewing space.

There are several different projector technologies in use. The most popular are CRT, LCD, DLP and LCoS.

LCD Projection TVs

An LCD rear projection TV sends signals to three small, high-intensity lamps (red, blue and green) then illuminates them from behind to produce pictures of often eye-popping quality.

Still thicker than flat-screen TVs -- a 55-inch display might be 20 inches thick -- LCD rear projection televisions are a less expensive way to get the big, bright pictures you crave. They're also ready for high-definition programming and easily adapt for use as PC screens.

The only downsides are that some LCD models have difficulty displaying true blacks, and others have what is known as a "screen door effect" -- a faintly visible grid on the screen, especially when sitting close to it. As with any TV purchase, you'll want to make a decision based on what looks good to you.

DLP Projection TVs

DLP stands for Digital Light Processing. Essentially, a tiny, very precise chip manipulates light by changing the position of thousands of microscopic mirrors. The mirrors can turn on and off thousands of times per second, and are used to create a black-and-white picture using up to 1,024 shades of gray.

Before that picture reaches the screen, color wheels are used to filter it so that the color is true and bright. Newer-model DLP rear projection TVs can produce more than 35 trillion colors.

The picture quality on a DLP projection TV is usually gorgeous, particularly in more recent models that have three micromirror chips instead of just one. (The older one-chip models are prone to a "rainbow effect" when the picture changes focus.)

LCoS Rear Projection TVs

LCoS is one of the newest technologies for rear projection televisions. It stands for "liquid crystal on silicon" and is an advancement to LCD technology that creates a very high-resolution image.

While these televisions are stunning to look at, only a few makers are using the technology, and it may be hard to find a set you like or a discount that would bring these rear projection televisions into reasonable competition with DLP or LCD sets.

Evaluating a Projection TV

The best projection TV for you isn't necessarily the one that costs the most or takes up the least room. Before you make a purchase, check for these things:

• Be sure your set has at least one and preferably two HDMI inputs This is to make sure your set will work with cable boxes, satellite receivers and HD DVD players.
• Make sure the TV you're looking at displays colors to your liking. If you're looking for great blacks, it's best to consider DLP. Don't like the rainbow effect? Look at a more expensive set with three separate chips or consider LCD.
• Before you make your purchase it's a good idea to walk around the TV, so you can make sure the image quality is pleasing to you from different angles.

Advantages of Rear Projection TVs

You should always evaluate the good and the bad of a product before spending a lot of money. Here are some advantages to rear projection TVs:

• Low cost per-inch compared to other types of large-screen TVs
• 60- to 80-inch models are readily available for those who want very large sizes
• Newer models are approaching plasma and LCD flat-screens in thinness
• Easy to install -- no mounting or drywall work
• Perform well in ambient light

Limitations of Rear Projection TVs

There is always advantages and disadvantages to any product. Here are some of the issues you should consider when purchasing a rear projection TV:

• Limited viewing angles -- the picture becomes dimmer as the viewer moves toward the sides
• Still bulkier than flat-screen TVs
• Some rear project TVs tend to reflect objects in the room
• Rear projection lamps burn out with usage, and will cost $150 to $300 to replace
• Can be unappealing as permanent parts of a room
  

CRT Projection TVs

CRT (cathode-ray tube) projection TVs use the same technology as traditional TVs, but with a projector to magnify the image and achieve larger pictures with the same tubes.

CRTs offer very clear pictures, last a long time and are the best value among rear projection TVs. However, they are also thicker and heavier, and are gradually being phased out in favor of more up-to-date digital technologies that are better suited to high-definition, gaming and PC use.

So when you see an ad for a cheap projection TV, make sure you know what kind of picture technology it has -- the best deal may not be the best picture..