Seeing the Digital Light

Television is something we all know and love -- sometimes without good reason. Critics routinely argue that shows like Temptation Island and WWF Smackdown! have pushed us several steps down the evolutionary ladder, but people still watch them. One thing that has evolved is the technology for displaying video images. We're all familiar with the classic cathode-ray tube (CRT), an analog technology that's been around since TV's earliest days. The CRT served us well for over 50 years, but in this digital era, when video can be broken down into ones and zeros and routed through countless conduits, it's become something of a dinosaur.

Enter Digital Light Processing (DLP), a video display technology based on the proprietary Digital Micromirror Device (DMD) from Texas Instruments. Though DLP has been around for a few years, it's only recently started to gain recognition as movie theaters contemplate a move away from traditional film projection. A handful of theaters installed DLP systems to project the much-hyped Star Wars: Episode I - The Phantom Menace when it was released in 1999, and it continues to gain momentum. Worldwide, 30 theaters had made the switch at this writing in late March.

DLP is now starting to show up on the home front in the form of front and rear projectors. The advantage of a DLP-based display is that the video signal remains in the digital domain from the moment it enters the set until it's reflected as light onto the screen. DLP's fully digital signal path not only holds the promise of higher-quality images than CRTs currently deliver but also makes it the ideal display technology for folks who want to mix up their TV viewing with videogames and Web surfing.

Compared with CRT displays, which generate images using high-voltage electron guns and bulky glass tubes, the technology behind DLP is elegantly refined. At the heart of a DLP display is the DMD, an integrated circuit covered with an array of tiny mirrors. A lamp inside the set throws light at the DMD chip, and the mirrors pivot up to 50,000 times a second, switching between on and off states in which light is either reflected toward a projection lens or deflected toward light-absorbing material. The amount of time that each mirror, or pixel, reflects light at the lens determines the pixel's brightness -- that is, where it falls in the scale between black and white.

DLP displays handle color in two ways. In three-chip DLP projectors, which are found in movie theaters and a few ultra-expensive home installations, a prism splits the light from the lamp into red, green, and blue components. Each color is directed to a separate DMD chip, and the reflections are optically recombined before the image hits the projection lens. In less expensive one-chip models -- the kind intended for home use -- a rotating color wheel filters the light into red, green, and blue. Although the three separate beams are reflected off the DMD sequentially, the rate at which they flash onscreen is so fast that the eye perceives a full-color image.

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