Projection HDTV

Introduction

Projection is the display of light onto a surface. There are 2 types of projection used in TV sets; front projection and rear projection.

One drawback of many projection TVs (with the exception of prjection CRTs) is that they use high power lamps. These lamps require replacement, and are often expensive. You should always consider the running costs when looking into a projection based TV.

Front Projectors

Front projection is where the light from the projector shines on the front surface of the screen. Front projectors are usually a small box situated 10's of feet from the screen.

Rear Projectors

Rear projection is where the light from the projector shines onto the rear surface of the viewing screen. Rear projection TVs have the projector built into the TV unit. They are usually bulkier than front projection systems, but do not have the image shining across the room.

Projection Technologies

There are several projection technologies that are readily available today:

• CRT - Cathode ray tubes (as in a traditional TV) are used to project an image onto a screen. These were one of the first commercially available projection systems, but are considered large and bulky. The projection units are fixed to the screen and require regular realignment to ensure good convergence.
• LCD - Liquid crystal display projectors work in a similar way to LCD TVs, except that the liquid crystal area is much smaller. A bright light is shone through it and onto the projection screen. They can suffer from poor black levels, and use high power lamps that will require replacement.
• DLP - Digital Light Processing (DLP) is a trademark of Texas Instruments. DLP projectors use a surface of micromirrors that can be rapidly repositioned. Light is shone onto the mirrors then either via the lens onto the screen or into a light dump. They use high power lamps that will require replacement.

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