Buyers guide: Rear projection TVs
By John Archer
Source: Buyers guide: Rear projection TVs - AVReview Buyers guides
Rear projection still seems to have something of an image problem. This is presumably because many people's only experience of rear projection TVs was in a local pub in the 1990s - and these TVs tended to be extremely poorly set up, and affected by the smoke and general mess associated with the pub environment.
The reality is that when correctly set up, today's rear projection TVs are capable of producing exceptionally good pictures. What's more, they can do so at prodigious screen sizes for a fraction of the cost you'd pay for similar-sized flat panel telly.
There is one problem that might put potential punters off though - confusion over the different technologies available. There are already three different rear projection types to choose from, and a fourth is coming soon.
So here we've tried to explain the key differences between the various technologies as simply as possible in the hope that you at least consider rear projection for your next TV. If you don't, you could be missing out on the best value/screen size ratio in town.
How rear projection TVs work
All rear projection TVs work in essentially the same way. Which is to say that a projector in the TV's base projects a picture onto mirrors in the rear which then bounce the (now enlarged) image onto the back of the TV's translucent screen, so that it becomes visible to anyone sat in front of it. The only key way that rear projection TVs differ is in the type of projector sat in the TV's base.
CRT rear projection
It will be one of these rear projection types that you likely saw in your local pub a few years back. They're the oldest rear projection technology around, and use the same analogue cathode ray tube principles found in the chunky 'direct view' TVs we all lived with for decades.
CRT rear projection pros
1. Superior contrast
2. Cheapness versus rival technologies
3. No technology-based artefacts in the picture
4. Extremely natural colour tones
5. No fan noise
CRT rear projection cons:
1. Pictures aren't usually as bright as with rival technologies
2. Screenburn, where phosphors in the CRT mechanism can become 'tired' by the sort of over-stimulation caused by extended exposure to a permanently positioned and bright channel logo like that on Sky News. This can result eventually in a permanent shadow of that logo being left behind on the screen
3. Their analogue nature means they're not well suited to PC and high definition sources
4. The projectors' red, green and blue components have to be converged at the screen, which often proves very difficult to achieve perfectly, resulting in stray bits of red and blue
5. Bulk - CRT models tend to be a bit deeper round the back than the other two technologies
DLP rear projection
The projectors in DLP TVs are comprised of two key elements. First, there's a tiny microchip with tens of thousands of tiny mirrors on its back, each of which can be controlled individually. Second, there's a spinning colour wheel made up of red, green and blue segments (or sometimes more in more sophisticated designs) that spins around extremely fast to add colour to the light passing through it. It actually adds the RGB colour components sequentially, but does it so fast that your eye puts the separate 'frames' together.
DLP rear projection TV pros
1. Contrast - at least compared to LCD
2. Minimal screenburn potential
3. Usually ready for and adept with PC and high definition pictures
4. Pictures brightness vs CRT
5. None of CRT's convergence issues
DLP rear projection TV cons
1. The so-called 'rainbow effect', where the colour wheel can cause flashing bands of pure colour visible over especially bright points of a DLP picture, or if you flit your eye around it
2. The potential for fizzing dot noise to appear over movement
3. Although it differs from projector to projector, DLP projector bulbs can have limited a lifespan (although they can be replaced at a cost rather than you having to just chuck the TV away!)
4. The colour wheel and the fans used to cool the projection lamp can both make DLP TV's run slightly noisily
5. In some cases, you can see low-level green dot crawl over dark picture areas
LCD rear projection
LCD projectors divide their bulb's light into red, green and blue beams for delivery through three separate LCD panels made up of thousands of individual cells, or pixels. Each panel then adjusts the tone of light that should be allowed through each cell. Then the three 'toned' beams are put back together in one beam for firing at your screen.
LCD rear projector pros
1. They're fairly free of the sort of picture artefacts mentioned with DLP
2. They're immune to screenburn
3. They're potentially adept with PC and HD pictures
4. They don't suffer CRT's convergence problems
LCD rear projector cons
1. They tend not to give such deep black levels as the other two technologies
2. They can suffer from the so-called 'chicken wire effect', in which the physical construction of the LCD panel becomes visible in the picture, appearing as a fine layer of mesh
3. The colour of people's skin can sometimes look a bit odd
4. Some models use fans to cool their lamps, which can make noise
5. LCD projectors may need their lamps changing after anywhere between 1,500-3,000 hours of use
By John Archer
Source: Buyers guide: Rear projection TVs - AVReview Buyers guides
Rear projection still seems to have something of an image problem. This is presumably because many people's only experience of rear projection TVs was in a local pub in the 1990s - and these TVs tended to be extremely poorly set up, and affected by the smoke and general mess associated with the pub environment.
The reality is that when correctly set up, today's rear projection TVs are capable of producing exceptionally good pictures. What's more, they can do so at prodigious screen sizes for a fraction of the cost you'd pay for similar-sized flat panel telly.
There is one problem that might put potential punters off though - confusion over the different technologies available. There are already three different rear projection types to choose from, and a fourth is coming soon.
So here we've tried to explain the key differences between the various technologies as simply as possible in the hope that you at least consider rear projection for your next TV. If you don't, you could be missing out on the best value/screen size ratio in town.
How rear projection TVs work
All rear projection TVs work in essentially the same way. Which is to say that a projector in the TV's base projects a picture onto mirrors in the rear which then bounce the (now enlarged) image onto the back of the TV's translucent screen, so that it becomes visible to anyone sat in front of it. The only key way that rear projection TVs differ is in the type of projector sat in the TV's base.
CRT rear projection
It will be one of these rear projection types that you likely saw in your local pub a few years back. They're the oldest rear projection technology around, and use the same analogue cathode ray tube principles found in the chunky 'direct view' TVs we all lived with for decades.
CRT rear projection pros
1. Superior contrast
2. Cheapness versus rival technologies
3. No technology-based artefacts in the picture
4. Extremely natural colour tones
5. No fan noise
CRT rear projection cons:
1. Pictures aren't usually as bright as with rival technologies
2. Screenburn, where phosphors in the CRT mechanism can become 'tired' by the sort of over-stimulation caused by extended exposure to a permanently positioned and bright channel logo like that on Sky News. This can result eventually in a permanent shadow of that logo being left behind on the screen
3. Their analogue nature means they're not well suited to PC and high definition sources
4. The projectors' red, green and blue components have to be converged at the screen, which often proves very difficult to achieve perfectly, resulting in stray bits of red and blue
5. Bulk - CRT models tend to be a bit deeper round the back than the other two technologies
DLP rear projection
The projectors in DLP TVs are comprised of two key elements. First, there's a tiny microchip with tens of thousands of tiny mirrors on its back, each of which can be controlled individually. Second, there's a spinning colour wheel made up of red, green and blue segments (or sometimes more in more sophisticated designs) that spins around extremely fast to add colour to the light passing through it. It actually adds the RGB colour components sequentially, but does it so fast that your eye puts the separate 'frames' together.
DLP rear projection TV pros
1. Contrast - at least compared to LCD
2. Minimal screenburn potential
3. Usually ready for and adept with PC and high definition pictures
4. Pictures brightness vs CRT
5. None of CRT's convergence issues
DLP rear projection TV cons
1. The so-called 'rainbow effect', where the colour wheel can cause flashing bands of pure colour visible over especially bright points of a DLP picture, or if you flit your eye around it
2. The potential for fizzing dot noise to appear over movement
3. Although it differs from projector to projector, DLP projector bulbs can have limited a lifespan (although they can be replaced at a cost rather than you having to just chuck the TV away!)
4. The colour wheel and the fans used to cool the projection lamp can both make DLP TV's run slightly noisily
5. In some cases, you can see low-level green dot crawl over dark picture areas
LCD rear projection
LCD projectors divide their bulb's light into red, green and blue beams for delivery through three separate LCD panels made up of thousands of individual cells, or pixels. Each panel then adjusts the tone of light that should be allowed through each cell. Then the three 'toned' beams are put back together in one beam for firing at your screen.
LCD rear projector pros
1. They're fairly free of the sort of picture artefacts mentioned with DLP
2. They're immune to screenburn
3. They're potentially adept with PC and HD pictures
4. They don't suffer CRT's convergence problems
LCD rear projector cons
1. They tend not to give such deep black levels as the other two technologies
2. They can suffer from the so-called 'chicken wire effect', in which the physical construction of the LCD panel becomes visible in the picture, appearing as a fine layer of mesh
3. The colour of people's skin can sometimes look a bit odd
4. Some models use fans to cool their lamps, which can make noise
5. LCD projectors may need their lamps changing after anywhere between 1,500-3,000 hours of use
