Presentation Technology

A fierce battle is taking place in the projection technology industry between LCD and DLP technologies — and the outcome could determine what kind of projector you'll be using in the 21st century.

Most multimedia projectors sold today are based on transmissive liquid crystal display (LCD) technology. LCD projectors form images by shining (or transmitting) light through one or three LCD panels. Tiny electronic pixel units in each panel correspond to the pixels in the source image — for example, the image on your notebook computer screen. If one LCD panel is used, small color filters are added to each pixel to produce color images. If three panels are used (making the projector larger and heavier, but also increasing image quality), the image is split with a dichroic mirror and colorized with red, green and blue filters. LCD is a proven projection technology that produces bright, high-resolution images. However, when it comes to making the most of the light that the lamp puts out, LCD technology isn't 100 percent efficient; a portion of the light is blocked by the LCD panel structure.

It is precisely this inefficiency that Texas Instruments set out to fix when it developed its reflective Digital Light Processing (DLP) technology. Instead of transmitting light through LCD panels, DLP projectors form their images by bouncing light off small chips called Digital Micromirror Devices (DMDs). Each DMD chip contains nearly half a million microscopic mirrors, which are attached to electrical nodes on a wafer of silicon; each mirror corresponds to a pixel in an image. Light is reflected off the DMD's tiny mirrors to form an image — and because it doesn't have to pass through an LCD, more light makes its way from the lamp to the screen. Unlike one-panel LCDs, one-chip DLP projectors use rotating color filters called flywheels to colorize their images, and three-chip DLPs rely on color filters.

DLP continues to gain ground on LCD technology

When DLP technology was first introduced, it couldn't compete with the image quality of LCD projectors. But the technology has matured, and DLP promises to give LCD technology a serious run for its money. More than a dozen manufacturers now offer DLP-based projectors, and the most recent DLP light engine — found in 7- to 9-pound projectors from In Focus, Davis and Plus — are revolutionary in their light weights and high brightness.

In addition to brightness, one of the main benefits DLPs hold over LCDs is that DLP chips are based on silicon semiconductors rather than glass. This means they can be made in regular semiconductor plants known as "fabs" rather than in highly specialized (and therefore expensive) LCD factories. In the long run, this could mean dramatically lower prices for DLP projectors.

The concept and promise behind reflective projection is so attractive that several companies are trying to develop a successful competitor to Texas Instruments' DLP technology. One approach is to combine reflective silicon-based technology with existing LCD technology. Startups, including s-Vision and Silicon Light Machines, are working on these new alternatives alongside high-tech powerhouses such as IBM and JVC. IBM and Electrohome recently announced a projector prototype based on IBM's reflective LCD technology. This unit is rumored to combine SXGA (1,280 x 1,024) resolution with 500 ANSI lumens of brightness. Meanwhile, JVC has already launched a new projector (featured in our comparison chart) based on reflective technology; the DLA-G10 offers 1,365 x 1,024 pixels of resolution and more than 1,000 lumens of brightness.