Projection Televisions

Learn About Rear Projection Televisions

Learn About Rear Projection Televisions

How do they work? What are the advantages and disadvantages of ownership? Is a rear projection television right for me?

In this section we will demystify the technologies of the rear projection television.

How Does It Work?

The first thing to understand about rear projection televisions is that they use one of four technologies: CRT, LCD, DLP™ or LCoS. The various technologies that can be used inside a rear projection television are covered in depth in the Learn About The Technologiessection.

Regardless of which technology powers a rear projection television, they all operate in much the same manner. All rear projection televisions start with a projector at the base of the television cabinet. This projector is simply a lower powered version of a front projector with a very short throw lens, meaning that its lens can make a very large image without having to be very far away from the screen.

The projector is situated so its projected image is bounced off of one-to-two mirrors, depending on which technology is used. CRT-based rear projection usually uses one mirror, while microdisplay technologies use two. The image is then projected onto a special screen that allows it to be seen through the screen, which is called a rear projection screen. Figure 1. shows a typical set up for a microdisplay (DLP™, LCD, or LCoS) powered rear projection television, and a CRT powered rear projection television.

Learn About Rear Projection Televisions

Pros and Cons

In this section, we will break down each technology to give you a more accurate picture of the advantages and disadvantages that each type of rear projection television presents.

CRT-Based Rear Projection Televisions

Pros:

  1. Least expensive per diagonal screen size of all RPTV technologies.
  2. Color reproduction is excellent.
  3. Best absolute black levels available.
  4. Best contrast ratios available.

Cons:

  1. They are large and heavy. You must have an enormous area available for them.
  2. Because they use three different CRT tubes, one each for red, green and blue, they need to be periodically converged. (See CRT Technology in our Learn About the Technologies section).
  3. They are a phosphor-based technology, which means that burn-in of an image can occur and that the display’s image quality will diminish with time.
  4. Not nearly as bright as microdisplay-powered rear projection televisions.
  5. Usually have very limited viewing angles. You must sit directly in front of the television to get a viewable image.
  6. The technology is being phased out.

LCD (Microdisplay) Based Rear Projection Televisions

Pros:

  1. Good color reproduction.
  2. Can be much slimmer and lighter than CRT-based rear projection televisions, enabling them to be placed where CRT-powered machines cannot.
  3. Although more expensive per viewing area than CRT based machines, they are still much less expensive than similar sized and resolution plasma displays.
  4. Very bright compared to the older CRT-based machines.
  5. All machines are at least at an HDTV resolution.
  6. Microdisplay technologies are easy to repair on-sight.
  7. Microdisplay technologies don’t suffer from burn-in.
  8. Better viewing angles than CRT-based rear projection televisions.

Cons:

  1. Poor fill ratio enables the grid structure to be seen from relatively close up (aka the screen door effect).
  2. Dead pixels can, and usually do, happen.
  3. Improper convergence of three LCD panels can cause color to be off.
  4. Poor absolute black levels and shadow detail.
  5. Poor overall contrast ratios when compared to other microdisplay technologies.
  6. Not as slim as the newest DLP™ powered rear projection televisions.
  7. Lamp-based technology. Lamps must be replaced after 6-8,000 hours. Lamps are costly.

LCoS (Microdisplay) Based Rear Projection Televisions

Pros:

  1. Good color reproduction.
  2. Very high are resolutions available (true 1080p).
  3. Very high fill ratio gives smooth, film-like images
  4. Very bright when compared to the older CRT-based machines.
  5. Can be much slimmer and lighter than CRT-based rear projection televisions, enabling them to be placed where CRT powered machines cannot.
  6. Microdisplay technologies are easy to repair on-site.
  7. Microdisplay technologies don’t suffer from burn-in.
  8. Have better viewing angles than CRT-based rear projection televisions.

Cons:

  1. Dead pixels can, and usually do, happen and because the technology is partially reflective, they can be more noticeable than on other technologies.
  2. Improper convergence of three LCD panels can cause the color to be off.
  3. Absolute black levels and shadow details are not as good as those on DLP™ powered rear projection televisions.
  4. Not as slim as the newest DLP™ powered rear projection televisions.
  5. Very expensive when compared to all other rear projection television technologies
  6. Yield rate is very low for LCoS machines and image quality can vary greatly from machine to machine.
  7. Lamp-based technology. Lamps must be replaced after 6,000-8,000 hours. Lamps are costly.

DLP™ (Microdisplay) Based Rear Projection Televisions

Pros:

  1. Good color reproduction.
  2. Can be very slim. New technologies are being introduced that allow some DLP™ rear projection televisions to rival plasma displays in depth. The new ultra-thin DLP™ displays can even be hung on walls.
  3. Although more expensive per viewing area than CRT-based machines, they are still much less expensive than similar sized and resolution plasma displays.
  4. Very bright when compared to the older CRT-based machines.
  5. All machines are at least of HDTV resolution.
  6. Best contrast ratio, absolute black levels, and shadow detail among the microdisplay technologies.
  7. Microdisplay technologies are easy to repair on-site.
  8. Microdisplay technologies don’t suffer from burn-in.
  9. Better viewing angles than with CRT-based rear projection televisions.
  10. No convergence issues.
  11. The only technology that is not organically-based. Image quality will not fade with time.
  12. Dead pixels are rare.

Cons:

  1. Some people can detect the color separation issues, commonly referred to as the “rainbow” effect.
  2. Still bulkier than plasma or LCD displays.
  3. Lamp-based technology. Lamps must be replaced after 6,000-8,000 hours. Lamps are costly.

Is a Rear Screen Right for Me?

Is a rear projection television (RPTV) right for me? It depends on your needs. Rear projection televisions can be used in a broad range of applications, and it’s actually rare to find specific applications where one cannot be used. Below is a list of common scenarios where a rear projection television performs best, followed by a list of scenarios that might suggest the need to use a different technology.

Best case scenarios:

  1. Applications where a large screen is desired and there is enough available floor area to place the unit.
  2. Installations that have custom cabinets that are designed for rear projection televisions.
  3. Applications that have budget constraints.
  4. Areas that have too much ambient light for front projection displays.
  5. Playrooms, bars, basements and all areas where the sole function of the room is not home theater. (Rooms like this are commonly referred to as media rooms).

Scenarios where another technology might be more effective:

  1. Any in-wall application.
  2. Large rooms with controlled lighting.
Back to top button
Close