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Page last updated at 14:00 GMT, Friday, 13 April 2007 15:00 UK

Video projectors embrace HD

By Marc Cieslak
Reporter, BBC Click

Any technology show worth its salt is not complete without screens so big they could double as the scoreboard at a football match.

Projectors are an alternative way of getting HDTV into the living room

But while LCD and plasma screens have been garnering all the press coverage, the humble video projector has been enjoying a renaissance thanks to one little chip.

Domestic video projectors come in two different flavours: LCD or DLP.

The brainchild of Texas Instruments, Digital Light Processing (DLP) first appeared 20 years ago. The key to DLP in a video projector are optical semiconductors covered in millions of tiny mirrors.

These mirrors reflect light which is projected onto them, and each mirror represents an individual pixel. Higher resolutions require more mirrors.

Bob Johnson from DLP manufacturer Optoma explained: "It's a digital device whereas the majority of the other technologies are all analogue devices.

"So if you're using an HD DVD player or your normal home DVD player, that's a digital device, you get a digital image on your screen."

It is possible to use projectors in rooms that are not as dark as your local multiplex - and with HD support, movies, TV and video games now look pin sharp

There is one drawback to DLP. For a chip to produce colour images, a spinning wheel fitted with coloured filters is placed in front of it.

When this wheel spins it can create an effect which looks like rainbow patterns appearing around the pixels. This can be a bit irritating.

LCD projectors do not enjoy the same level of contrast or dark blacks that DLP projectors produce and, up close, some individual pixels can be visible as squares.

There is however a price difference - LCD projectors tend to be cheaper than their DLP counterparts.

Improvements in lamp technology mean that many of the bulbs fitted to the current generation of video projectors are so bright they can viewed in near daylight conditions.

And as LCD screens have embraced HD 1080 pixel resolution so too have video projectors. So it is possible to use projectors in rooms that are not as dark as your local multiplex - and with HD support, movies, TV and video games now look pin sharp.

Key features

But if you are planning to ditch the TV in favour of a projector, what sort of features should you be looking out for?

A 42 inch LCD TV? That is nothing. Some projectors can easily project an image up to 100, 150 or even 200 inches.

Fan noise can be a problem

Picture size is altered by the distance the projector is away from the screen, known as throw. As a rule of thumb a projector about 10ft (3m) away from a wall or a screen will produce an image 100 inches across.

It is also important to select a projector and bulb which can produce a sufficient amount of light to work in a domestic setting.

Known as the lumen value, this allows you to know how bright a bulb is. For a room which has ambient lighting, a bulb which produces in excess of 1200 lumens will be required.

And look out for HDMI ports for plugging in high-definition kit.

Projectors used to make more noise than a normal TV thanks to the fans needed to cool the unit. Although modern projectors are considerably quieter than their forebears, fan noise is still evident.

The biggest drawback is the cost of replacement lamps. Lamps usually last around 2000 to 3000 hours, but after that, it is time for a new one and this can be expensive, in some cases up to £400 ($800).

But overall, prices of domestic projectors have dropped. It is possible to get a DLP HD-ready projector for around £705 ($1,400), which compares favourably with large LCD or Plasma screens.

Great big video projectors are fine if you have got a great big home to put them in, but if there is a shortage of space a tiny little DLP projector can provide a solution.

And as laser technology becomes introduced to projectors they are going to get even smaller. A company in the United States is developing a projector which is so small it will fit inside a mobile phone.

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