How Does Rear Projection Television Work?

What is a Rear Projection TV?

A rear projection TV is a type of television designed to have a particularly large screen. These large screen TVs are very popular. They are part of people's attempts to obtain the big screen movie experience without going to the cinema. The rear projection TV is, as a result, being used as the centerpiece for people's home theater systems. The reference to the theater is where this large screen television gets its name. Where traditional video and films are projected onto a blank screen like in a theater, the image presented on a rear screen television is being projected onto the back of the screen. Though large screen digital televisions are becoming available to the general public, their extremely high price tag means that the reliable rear projection TV is still very much in demand. There are three types of rear projection TVs on the market: CRTs, LCDs and DLPs.

A CRT or Cathode Ray Tube rear projection television is the most common and cheapest of the three types of rear projection TVs. It uses technology that's been around for decades and is relatively cheap to repair. The downside to such a TV is that the large casing required to hold all the delicate electronics and machinery takes up a lot of room in the home. When a CRT television is turned on, three small cathode ray tubes begin to produce beams of light. Each tube produces one of the primary colors which can be combined at different intensities to portray any color in the spectrum. They light up according to the signal they receive, be it through cable, antennae or satellite. These beams are passed through a light magnifying lens. The image produced is bounced off of a carefully angled mirror at the back of the TV to project the image onto the inside of the TV screen. The reason the image we see is the right way around is that the light is inverted when it is reflected off the mirror.

An LCD, or liquid crystal display rear projection TV is generally considered to have a better picture than a CRT TV. It uses more advanced technology which is more costly to produce, hence the greater price for the consumer. A rear-projection LCD television basically works by passing a powerful light source through a transparent LCD chip made up of individual pixels (which displays the moving video image) and projecting that image through a magnifying lens to a mirror, which then reflects that image onto a screen.

The highest quality and best of the three types of TV available is the DLP or Digital Light Processing rear-projection television. Like LCD, the actual image is displayed on a chip, however, the chip used in a DLP projection television is different. The chip in a DLP projection television is referred to as a DMD (Digital Micromirror Device). In essence, every pixel on a DMD chip is a reflective mirror. The image is presented on the DMD chip. Each micromirror tilts as the image changes to create the image's foundation. Color is added by means of a high speed color wheel, which reflects lights striking it onto the micromirrors as they tilt. As the amplified light bounces off the micromirrors, it is sent through the lens, reflected off a large single mirror, and onto the screen. Because of this intense and highly technical mechanical process, DLPs are more prone to breaking than the other two types of rear projection TVs.